Category Archives: Aircraft

SNCAC-NC-3021-front-no-cowling

SNCAC NC 3021 Belphégor High-Altitude Research Aircraft

By William Pearce

In the early 1930s, Avions Farman (Farman) built the F.1000-series of aircraft to break altitude records. On 5 August 1935, the F.1001 reportedly achieved stable flight at around 10,400 m (34,120 ft). However, one of the small windows in the aircraft’s pressure vessel soon failed. The sudden decompression incapacitated the pilot, Marcel Cognot, and the aircraft crashed.

SNCAC-NC-160-model

Model of the pre-war NC 160 dive bomber displays the basic layout that would be scaled-up for the NC 3020.

In late 1936, France began a program of nationalizing its arms industry, which many aviation manufacturers fell under. In early, 1937 Farman was combined with Aéroplanes Hanriot to create the state-run Société Nationale des Constructions Aéronautiques du Center (SNCAC or Aérocentre, the National Company of Aeronautical Constructions of the Center).

SNCAC initiated development of some advanced aircraft and designed other aircraft to serve as technological testbeds. One of these aircraft was the NC 130 (NC standing for Nationale Center), a twin-engine monoplane built around a cabin pressure vessel. The NC 130 was designed by Marcel Roca, the former head of the Farman design office, and it had an anticipated service ceiling of 34,777 ft (10,600 m). The NC 130 made its first flight in 1939 but was destroyed in the early part of World War II. Roca and his team also designed the NC 160, a monoplane dive bomber with contra-rotating propellers. The NC 160 did not progress beyond the design stage.

After the German invasion of France on 10 May 1940, SNCAC personnel and offices were relocated south from Boulogne-Billancourt, near Paris, and untimely to Cannes on the Mediterranean Sea. SNCAC, along with SNCASE (Société nationale des constructions aéronautiques du Sud-Est, National Company of Aeronautical Constructions of the South East), SNCAO (Société nationale des constructions aéronautiques de l’ouest, National Company of Aeronautical Constructions of the West), and CAMS (Chantiers Aéro-Maritimes de la Seine, Aero-Maritimes construction sites of the Seine) were combined with and operated under SNCASO (Société nationale des constructions aéronautiques du sud-ouest, National Company of Aeronautical Constructions of the South-West). At the time, southern (Vichy) France operated as an independent and unoccupied ally of Germany, but the state’s “independence” from Germany was certainly not absolute. The German overseers allowed the continued development of commercial and civil aircraft in Southern France.

SNCAC-NC-3021-right-side

The NC 3021 before the dorsal fairing was added forward of the vertical stabilizer. Note the glazing on the lower fuselage. Between the panels was the lower pressure cabin bulge with observation ports.

Roca and the SNCAC team were put in charge of the special aircraft division, which would use the SO 3000-series to designate their designs, SO standing for Sud-Ouest (South West). The SO 3020 was an experimental high-altitude research aircraft designed to observe stratospheric and meteorological conditions, and the basic layout of the aircraft was based on a scaled-up version of the pre-war NC 160 dive bomber design.

The fuselage of the large, taildragger aircraft consisted of three sections. The forward fuselage housed two 1,400 hp (1,030 kW) Hispano-Suiza 12Z engines placed side-by-side and mounted on a tubular frame. Each engine powered half of a six-blade, coaxial, contra-rotating propeller via a SNCAC-designed combining gearbox designated NC T1.

The central fuselage was built around a welded pressure vessel that was 17 ft 1 in (5.20 m) long and 5 ft 7 in (1.70 m) in diameter. A bulge atop the pressure vessel was the cockpit that protruded above the fuselage. A bulge in the lower part of the pressure vessel contained two viewing stations for observations and photography of the stratosphere. The lower bulge was contained within the aircraft’s fuselage, but the fuselage was glazed around the bulge. The cabin pressure vessel accommodated five people: the pilot, a radio operator/navigator, a mechanic, and two scientists/observers. Pressurization of the cabin was achieved by two SNCAC-designed NC 41 positive displacement compressors that were driven directly from the engines. The cabin was accessed via a door in the rear fuselage that led to a hatch at the back of the pressure vessel.

SNCAC-NC-3021-right-rear

Rear view of the NC 3021 illustrates the upper pressure cabin bulge for the cockpit. Note the observation ports on the side of the fuselage.

While the forward and center fuselage sections were all-metal monocoque designs, the rear fuselage had a spruce frame that was covered in plywood. The vertical and horizontal stabilizers were also made of wood, but the rudder and elevators had metal frames that were covered with fabric.

The SO 3020’s three-spar wing was of mixed construction, and the main spar attached to a bulkhead that was mounted to the pressure vessel in the central fuselage. The structure of the wing was made mostly of metal, but spruce was used for the front and rear spars of the outer wing sections. The wing was covered with metal. The ailerons had metal frames and were covered in fabric. When retracted, the landing gear was fully enclosed with the main gear in the wing and the tailwheel in the fuselage. The main gear had a wide track of 18 ft 9 in (5.71 m). Tanks within the wings held the aircraft’s 1,836 US gal (6,950 L / 1,529 Imp gal) of fuel.

The SO 3020 had a wingspan of 73 ft 3 in (22.32 m), a length of 65 ft 3 in (17.90 m), and a height of 19 ft 2 in (5.83 m). It was anticipated that the aircraft would cruise at 311 mph (500 km/h) at 33,793 ft (10,300 m) and have a ceiling of 45,932 ft (14,000 m). The SO 3020 had an empty weight of 13,382 lb (6,070 kg) and a gross weight of 26,015 lb (11,800 kg). This would allow the aircraft to carry 11,023 lb (5,000 kg) of fuel, 1,014 lb (460 kg) of freight, and five crew members. Range was 4,169 miles (6,710 km) with an endurance of seven hours.

SNCAC-NC-3021-front-no-cowling

The maintenance crew underneath the uncowled NC 3021 provides reference to just how large the aircraft was. The duct supplying air to the supercharger can be seen along the side of the engine. Note the open access door in the rear fuselage.

Work on the SO 3020 was allowed to move forward in mid-1941, but progress was slow due to the war situation. A full-size wooden mockup was built toward the end of 1942. When Germany invaded Vichy France in early November 1942, progress on the SO 3020 slowed even further. In March 1943, the letter designation ‘B’ was assigned to SNCASO aircraft, and the SO 3020 was given the name “Belphégor,” for the demon who seduces people by suggesting to them ingenious inventions that will make them rich.

Construction of the SO 3020 continued throughout the war. The aircraft, its design team, and other SNCASO operations were moved west to Le Flayosquet in early 1944. This move was a result of a British air raid on Cannes in November 1943 and was finally completed in May 1944. However, after the Allied landings and subsequent liberation of France, everything was moved back to Cannes between November 1944 and January 1945. With the liberation of France, the nationalized aircraft manufacturers were restored, and SNCAC broke off from SNCASO. The SO 3020 and everything else associated with SNCAC was moved back to Boulogne-Billancourt.

By early 1946, the SO 3020 was complete with the exception of its engines. The war had delayed work on the Hispano-Suiza 12Z, and it would be some time before the engines would be available. As a result, the decision was made to switch to a single 2,950 hp (2,170 kW) Daimler-Benz DB 610 engine. The DB 610 consisted of two coupled DB 605 engines and was similar to what was planned with the two 12Z engines and the NC T1 gearbox. DB 605 engines were available to France and SNCAC in the immediate post-war era. With this new configuration, the aircraft was redesignated NC 3021. At the time, a number of experiments were planned for the aircraft to study cosmic rays and their interaction with the atmosphere.

SNCAC-NC-3021-front

Front view of the NC 3021 displays the DB 610’s side and lower exhaust stacks. Note the duct under the engine to supply air for cabin pressurization. The engine and propeller were most likely repurposed from stock intended for a German Heinkel He 177 bomber.

In March 1946, the NC 3021 was transferred from Boulogne-Billancourt to the Toussus-le-Noble airfield for final assembly. With the DB 610 engine, the contra-rotating propellers were discarded, and a single, four-blade propeller was used. This VDM propeller was 14 ft 9 in (4.5 m) in diameter and was most likely the same as that used on the German Heinkel He 177 bomber. The DB 610 engine was mounted on a tubular frame at the front of the aircraft, and an annular radiator was installed around the propeller’s extension shaft. Ducts on each side of the cowling delivered air to the transversely-mounted superchargers at the rear of the engine. Air for the cabin and its pressurization was brought in from a duct under the spinner. This sealed duct passed around the lower exhaust stacks which helped heat the air.

The NC 3021 had a wingspan of 73 ft 3 in (22.32 m), a length of 65 ft 3 in (17.90 m), and a height of 19 ft 2 in (5.83 m). The aircraft’s estimated performance was a maximum speed of 348 mph (560 km/h) at 19,685 ft (6,000 m) and a cruising speed of 280 mph (450 km/h) at 39,370 ft (12,000 m). The aircraft had a landing speed of 87 mph (140 km/h), an initial rate of climb of 1,968 fpm (10 m/s), and a ceiling of 41,995 ft (12,800 m). Compared to the SO 3020, the NC 3021’s empty weight had increased 3,880 lb (1,760 kg) to 17,262 lb (7,830 kg), and its gross weight had decreased 3,073 lb (1,394 kg) to 22,941 lb (10,406 kg).

SNCAC-NC-3021-inflight-top

Although of poor quality, this image of the NC 3021 in flight shows the dorsal fairing that was added to the tail to aid directional stability.

The NC 3021 was completed at the end of May and registered as F-WBBL. Taxi tests were initiated at the beginning of June, and the aircraft made its first flight on 6 June 1946 with Joanny Burtin as the pilot. The aircraft suffered from directional instability, and a dorsal fairing was soon added in front of the tail to increase its lateral surface area. Testing was brought to a halt later that summer when the right main gear collapsed. The landing gear manufacturer was slow to provide a new main gear leg, and SNCAC resumed flight tests as best as it could with a temporarily repaired main gear fixed in the down position.

The landing gear was eventually repaired, but the DB 610 engine proved to be difficult to service and maintain. To make matters worse, SNCAC was having financial issues and did not have the funds to spend on an experimental project that offered little in return. When SNCAC delivered the NC 3021 to the Centre d’essais en vol (CEV, Flight Test Center) at Brétigny-sur-Orge on 12 October 1948, the aircraft had only made 45 flights for a total of 40 hours of flight time.

The CEV worked to maintain and test the NC 3021. By April 1949, the CEV had put in 1,500 hours of work on the NC 3021 but had only flown the aircraft for 2 hours and 45 minutes. The CEV did not want to continue to operate the aircraft, and SNCAC declared bankruptcy in July 1949. There were no other parties interested in funding the expensive and difficult to maintain experimental aircraft, and the NC 3021 was most likely scrapped in late 1950.

SNCAC-NC-3021-inflight-right

Large, complex, and expensive, the NC 3021 was never used to collect scientific data on the stratosphere. It is doubtful that the aircraft was ever tested to its estimated ceiling.

Sources:
– “NC-3021 Belphégor: le monstre de la haute altitude” by Philippe Ricco, Avions #207 (September/October 2015)
– “NC-3021 Belphégor: le monstre de la haute altitude” by Philippe Ricco, Avions #208 (November/December 2015)
Les Avions Farman by Jean Liron (1984)
Jane’s All the World’s Aircraft 1949-50 by Leonard Bridgman (1949)
https://aviation-safety.net/wikibase/194708

Lear-Fan-E001-and-E003-in-flight-side

Lear Fan Limited LF 2100

By William Pearce

William “Bill” Powell Lear was born on 26 June 1902 in Hannibal, Missouri. From a very young age, Lear had an interest in electronics and an aptitude for design. Starting in the 1920s and continuing through his entire life, Lear developed a number of electronics, devices, and aircraft. Lear was responsible for the development of the car radio in the late 1920s; various radio direction finders, autopilots, and automated landing systems for aircraft in the 1930s and 1940s; the Lear Jet in the early 1960s; and the 8-track in the mid-1960s. He was personally awarded 121 patents and co-authored another seven. Throughout his life, Lear sold off his successful developments to fund his next round of invention and experimentation.

Lear-Fan-E001-landing-Stead

Lear Fan prototype E-001 lands at Stead Airport in Reno, Nevada after a test flight. Despite the nose-up attitude, note the ample clearance between the ventral fin and the runway. The Lear Fan certainly had the appearance of a capable, high-performance aircraft.

In the mid-1970s, and through his LearAvia Corporation located at Stead Airport in Reno, Nevada, Lear worked on a long-range business jet called the LearStar 600. Plans to develop and produce the aircraft were purchased by Canadair in April 1976. Lear and his team worked with Canadair to refine the aircraft, but engineers at Canadair did the same and changed many aspects of the original LearStar 600 design. Around March 1977, the team at LearAvia proposed an updated business jet design called the Allegro, which incorporated many composite components to increase the aircraft’s performance. Canadair was not interested in the Allegro, nor was it interested in Lear’s advice and meddling in the LearStar 600 design, which Canadair eventually developed as the Challenger 600.

Since the 1950s, Lear had contemplated the design of an aircraft utilizing two turboprop engines in the fuselage that powered a single pusher propeller. The benefit of this centerline thrust configuration was that it would provide twin-engine reliability without any yaw effect from asymmetrical thrust in an engine-out situation. The basic design layout was similar to the Douglas XB-42 bomber prototype, which first flew on 6 May 1944, and the Planet Satellite light aircraft, which first flew in mid-1949. In early 1976, Lear discussed the pusher design with Richard Tracy, LearAvia’s chief engineer. Lear sought an aircraft that could carry six to eight passengers from Los Angeles to New York (2,465 miles / 3,967 km) at 400 mph (644 km/h) and at 41,000 ft (12,497 km) with two 500 hp (373 kW) engines. Lear and Tracy intermittently discussed the design for several months.

Lear-Fan-E003-in-flight-rear

The second Lear Fan prototype E-003 was the primary aircraft for gathering fight test data. E-003 is seen here with its original N-number and blue paint. The number on the ventral fin signified the flight number. Note the data boom on the nose.

As the lack of progress with the LearStar 600 at Canadair grew frustrating for the LearAvia staff, Tracy reviewed the pusher design with Rodney Schapel, an aerodynamic engineer, and tasked him with making some preliminary drawings. Lear was initially not interested in the project and would chastise Schapel when he saw him working on the pusher design. However, as Canadair took control of the LearStar 600 and rejected the Allegro, Lear became more interested in the pusher aircraft and reviewed the design with Schapel and Tracy. Around April 1977, Lear decided that the pusher aircraft would be the company’s next design. The new aircraft was briefly called the Futura, but it quickly became the Lear Fan 2100.

The Lear Fan 2100 was a twin-engine, low-wing monoplane with tricycle landing gear. Depending on the configuration, the aircraft could accommodate one or two pilots and up to nine passengers in its pressurized cabin. Other configurations were considered, including a cargo version and an air ambulance that could accommodate two stretchers, each with a dedicated attendant. The Lear Fan was a revolutionary design in several regards. In addition to its two engines powering a single pusher propeller, Lear had decided that the entire aircraft would be made of a composite material. When compared to aluminum, the aircraft’s bonded graphite and epoxy composite structure was smoother, stronger, resistant to fatigue, would not corrode, could be molded into complex shapes, and was 40 percent lighter. The airframe was designed for a maximum loading of +6 and -4 Gs.

Lear-Fan-E001-and-E003-in-flight-side

E-001 (right) and E-003 (left) in flight together. Note the fixed cooling air duct on E-003 between the propeller and ventral fin. E-001 had a different setup with a movable door. The “windows” for both aircraft were at least painted on in the photograph.

The aircraft’s fuselage was formed with close-spaced frames and longerons bonded to the outer skin. The skin was mostly four plies thick, but the thickness increased to eight or ten plies around window and door openings. The fuselage was made in six sections: upper and lower nose, upper and lower cabin, and upper and lower rear fuselage. The sections were bonded in an autoclave to form the entire fuselage structure. The fuselage had a slightly oval shape, and its interior had a maximum height of 4 ft 8 in (1.36 m) and a maximum width of 4 ft 10 in (1.47 m). The cabin was 12 ft 10 in (3.91 m) long and had a 50 cu ft (1.42 m3) baggage compartment that was accessible in flight at its rear.

Cabin access was via a door located on the left side of the fuselage and just forward of the wing. The first prototype had a split upper and lower door, but subsequent examples had a single door that folded down to form stairs for cabin entry. The passenger compartment originally had six windows on its right side and five windows on its left side. However, none of the prototype aircraft had their full allotment of windows, and some of the “windows” were painted on. It seems the window on the door was eventually omitted. Pressurization provided a nominal pressure differential of 8.3 psi (.57 bar), enabling an 8,000 ft (2,438 m) cabin altitude while cruising at a 41,000 ft (12,497 km) flight altitude. The steerable nosewheel retracted forward into the nose of the aircraft.

The single-piece, high-aspect wing had three continuous spars and was mated to the fuselage via six attachment points. Each wing spar was formed by two channel sections joined back-to-back on a honeycomb core. The upper and lower wing skins had 52 plies at their roots, with the thickness decreased to eight plies at the tips. The wing had four degrees of dihedral. The main landing gear had an 11 ft 8 in (3.56 m) track and retracted inward to be fully enclosed within the wing. Fuel tanks were integrated into the wing’s structure, and each wing housed up to 125 US gallons (104 Imp gal / 473 L) of fuel. Flaps extended along approximately 75 percent of the wing’s trailing edge, with ailerons extending almost to the wing tips. The landing gear and the flaps were hydraulically operated.

Lear-Fan-E003-in-flight-bottom

The underside of the Lear Fan as perhaps its least photogenic side. Even so, the view of E-003 illustrates the aircraft’s clean aerodynamic form, even with what appears to be a hydraulic leak from the right main gear. This was the aircraft’s 50th flight.

At the rear of the Lear Fan was a Y tail. The ventral fin had two spars, and a rudder was attached to its trailing edge. The structure of the fin was stressed for ground impacts to prevent the propeller from contacting the runway in case of an over-rotation during takeoff or a hard landing and incorporated a strike pad. Each of the two “butterfly” horizontal stabilizers had one spar. They had 35 degrees of dihedral, which increased the aircraft’s directional stability. The control surface on the horizontal stabilizer was a standard elevator for pitch control only. All normal flight controls were mechanically operated using cables and pushrods.

Originally, two Lycoming (probably LTS101) turboprop engines were to be used, but these were replaced with Pratt & Whitney Canada PT6B-35F engines early in the design phase. The PT6B-35F engines produced 850 shp (634 kW) but were flat-rated to 650 shp (485 kW) for the Lear Fan. The engines were positioned in the fuselage behind the wing’s trailing edge. A scoop on each side of the aircraft brought in air to the engine and expelled exhaust to the rear. The scoop was integral with a large service panel, the removal of which enabled access to the engine. A special mount held each engine in such a way that when the engine was disconnected from its drive shaft and other restrictions, the engine could be swung out for servicing and inspection. The pivot point was the mount at the front of the engine, and this action enabled access to the inner side of the engine.

A 6 ft (1.83 m) aluminum drive shaft with a graphite fiber cover extended from each engine to a combining gearbox at the rear of the aircraft. The gearbox was designed and built by Western Gear Corporation and was equipped with sprag overrunning clutches. If an engine failed, the good engine would continue to power the propeller. As originally designed, wax contained in the gearbox would melt to provide continuing lubrication in the event of oil loss. This method did not work as well as expected, and a back-up oil system was devised in 1984. Referred to as the “spin jet,” oil from a reserve tank was intermittently sprayed directly into the meshing gears. The gearbox was successfully run for over three hours with its main oil supply exhausted and its only lubrication provided by the “spin jet” system. An oil cooler was located under the gearbox. The gearbox had a .3125 propeller speed reduction, resulting in the propeller turning at 688 rpm when the engine’s drive shaft was rotating at 2,200 rpm. Originally, a 7 ft 6 in (2.29 m) diameter three-blade propeller built by Hartzell was to be used. However, a switch to a four-blade Hartzell propeller of the same diameter was made during the design phase when tests indicated that the four-blade propeller was less prone to vibration issues. The propeller was reversible and had 3 ft 1 in (.94 m) of ground clearance when the aircraft was on its landing gear.

Lear-Fan-E001-in-flight-rear

E-001 with its updated paint, which it still wears today. The two ducts under the aircraft were the inlet and exhaust for oil coolers. An open cooling air exit door is seen between the propeller and ventral fin. Subsequent prototypes used a fixed duct. Most images of E-001 in flight are without a spinner.

Although a Lear Fan brochure dating from 1979 lists the aircraft’s length as 38 ft 8 in (11.79 m), as originally built, the aircraft had wingspan of 39 ft 4 in (11.99 m), a length of 39 ft 7 in (12.07 m), and a height of 11 ft 6 in (3.51 m). The Lear Fan’s estimated performance was a top speed of 375 mph (604 km/h) at 39,000 ft (11,887 m), 403 mph (649 km/h) at 31,000 ft (9,449 m), and 414 mph (666 km/h) at 19,000 ft (5,791 m). Stalling speed was 90 mph (145 km/h). The aircraft had an initial climb rate of 3,550 fpm (18.0 m/s), and a ceiling of 41,000 ft (12,497 km). The Lear Fan had an empty weight of 3,650 lb (1,656 kg) and a gross weight of 7,200 lb (3,266 kg). At gross weight, the aircraft had a range of 1,630 miles (2,623 km) at 400 mph (644 km/h) and 2,300 miles (3,704 km) at 350 mph (563 km/h). On a single engine, the Lear Fan could takeoff, climb at 1,900 fpm (9.7 m/s), and execute a go-around. The aircraft’s single engine ceiling was 29,000 ft (8,839 m).

Lear was slowed down by health problems for a few years, but he was back to his old self in late 1977 as he tried to sell the Lear Fan concept to anyone who would listen. Lear made the decision to proceed with production prototypes rather than constructing a proof-of-concept vehicle first. While this decision could lead to cost savings and quicken development if everything went well, it would result in the exact opposite if things did not go well. By this time, Tracy had been replaced as chief engineer by Nicholas Anderson, and Schapel had been fired. Schapel had designed the aircraft’s original Y tail, but Lear wanted an inverted V tail. Schapel was let go over the disagreement. Ultimately, wind tunnel tests indicated that the Y tail was superior, and the Lear Fan reverted back to Schapel’s original tail design.

In early 1978, Lear’s health faltered again. He made arrangements for Lear Fan development to procced even if he were to die, but he desperately wanted to live long enough to see the prototype take to the air. In March, Bill Lear was diagnosed with leukemia, and he passed away on 14 May 1978. Some of his last words were urging that the Lear Fan be finished.

Lear-Fan-E003-in-flight-green

E-003 with its revised green paint and new N-number. The green paint was applied in honor of the Zoysia Corporation, the project’s major financial backer at the time. The number on the ventral fin indicates that this is the aircraft’s 298th flight. A spin chute is installed between the V tail. Although spin testing was never conducted, if needed, a shaped charge would have blown off the propeller before the chute was deployed.

Development of the Lear Fan did continue, and construction of a prototype was started in November 1978. Moya Lear, Bill’s wife, took over as the face of LearAvia. Progress on the aircraft’s untried propulsion system and gearbox, unusual layout, and all-composite structure proved slow and expensive. LearAvia’s financial resources were quickly depleted. In mid-1980, the company was restructured as Lear Fan Limited with the financial backing of investment firms and the British government. The agreement with the British government was that $25 million would go to the project, and another $25 million would be provided for Lear Fan production in Newtonabbey, near Belfast in Northern Ireland. British financial support would end if the prototype did not fly by the end of 1980. At the time, 126 aircraft were on order. Production was expected to start in 1982 and would create at least 1,200 jobs in Newtonabbey. Paramount for Lear Fan production was for the FAA (Federal Aviation Administration) to issue the aircraft a Certificate of Airworthiness. However, the Lear Fan’s all-composite construction was a first for a production aircraft, and certification was going to be a long and costly process.

Under the newly restructured company, the aircraft became the Lear Fan Limited LF 2100, and all prototypes were registered with the FAA as such. Lear Fan E-001 was registered as N626BL, for June 26 (his birthday) Bill Lear. On 31 December 1980, E-001 was rolled out of the hangar at Stead Airport to conduct taxi tests before its first flight. During a high-speed taxi test, the brakes were burned up and needed to be replaced. With 15 minutes of daylight left, the aircraft was preparing for takeoff when the sleeve of a pilot’s flight suit caught on the cockpit fire extinguisher handle, inadvertently activating it and forcing the flight to be scrubbed. The next day, 1 January 1981, the Lear Fan took to the air. The first takeoff was made by Hank Beaird in the left seat, with Dennis Newton in the right seat. The first landing was made by Newton in the left seat, with Beaird in the right seat. It was Beaird’s idea to switch seats so that both pilots had “firsts” during the Lear Fan’s initial flight. While the aircraft’s first flight was one day past the deadline, in the spirit of all that had been accomplished and by a Royal Decree signed by Queen Elizabeth, the British government declared that the Lear Fan made its first flight on 32 December 1980 and was still qualified for funding.

The remainder of 1981 was spent refining E-001 and continuing flight testing, building E-002 for use as a static test airframe, and building E-003. E-003 was registered as N327ML, for March 27 (her birthday) Moya Lear, and the aircraft was planned as the true workhorse for flight testing. With Lear Fan orders reaching 203 by June 1981 and 263 by early 1982, the future looked bright. E-001 had made 53 flights and had accumulated 78 flight hours by the start of 1982.

Lear-Fan-E009-Stead

The third Lear Fan prototype, E-009, seen outside the Lear Fan hanger at the Stead Airport. E-009 appears to have had all of its windows from the start. Although not quite apparent from the image, its colors were dark green and yellow on white.

The second prototype, E-003, had a new fuselage that was 12 in (.30 m) longer than that used on E-001, resulting in a length of 40 ft 7 in (12.37 m). The longer fuselage increased the cabin’s length to 13 ft 4 in (4.06 m) and the baggage compartment’s capacity to 53.7 cu ft (1.52 m3). The aircraft also incorporated some other minor modifications, such as a ventral duct at the extreme rear to bring in cooling air to the gearbox. E-003 made its first flight on 19 June 1982, most likely piloted again by Beaird and Newton. However, Lear Fan Limited had run out of money. The company was reorganized on 15 September 1982 as Fan Holdings, Inc, with the British investing $30 million and with the Zoysia Corporation, a consortium from Saudi Arabia, supplying $60 million. A major player in the Zoysia consortium was Prince Sultan bin Salman bin Abdulaziz Al Saud.

In December 1982, cracks in the wing were detected during static tests. Rather than undergoing a major wing redesign, the existing wing structure was reinforced. These modifications added weight and reduced the fuel load by 10 US gallons (8 Imp gal / 38 L), both of which decreased the aircraft’s range. At the start of 1983, 276 Lear Fans were on order. Flight testing of E-001 and E-003 resumed during the summer of 1983. In mid-July, the lower aft pressure bulkhead of the static test airframe E-002 failed during a pressurization test. On 20 July 1983, E-001 suffered an explosive decompression while at 25,000 ft (7,620 m). With the recent failure of E-002 on their minds, test pilots John Penny and Mark Gamache declared an emergency and brought the aircraft quickly and safely back to Stead Airport. The cause of the decompression could not be found, and the event marked the end of E-001’s flight career.

In December 1983, another test fuselage failed during pressure tests, and Fan Holdings Inc was running short on funds. At the time, Lear Fans had accumulated some 521 total flight hours. In March 1984, E-003 flew with its updated wing and fuselage. In April 1984, more fuselage issues were encountered. In June 1984, the Newtonabbey plant, which had been tooled up for production and had made various test parts, was shut down. Also in June 1984, the registration of E-003 was changed from N327ML to N21LF. Bill Lear’s will had focused on continuing Lear Fan development, but it created some potential conflicts of interest with the aircraft’s management team. Some of the Lear children filed suit in 1978 and 1979. Moya Lear became involved, and everything was settled as far as the courts were concerned in 1984. However, not all parties were appeased, and some consider the N-number change was done to spite Moya. Others feel it was to bring focus to the Lear Fan rather than to people behind the project.

Lear-Fan-E001-Museum-of-Flight---Kaiser

E-001 on display in the Museum of Flight in Seattle, Washington. The aircraft is in good company with the likes of a Douglas DC-3, Boeing 80, Gee Bee Z, and Lockheed M-21/D-21 in the background. (Josh Kaiser image via airliners.net)

Airframes E-004 through E-008 were all test articles for certification, but the continuous issues resulted in there being no end in sight for the certification process. In late 1984, Fan Holdings Inc was attempting to get the Lear Fan certified for unpressurised, VFR (Visual Flight Rules), day flight by January 1985. Certification for pressurized flight up to 25,000 ft (7,620 m) would follow in the spring of 1985, and certification up to 41,000 ft (12,467 m) would follow in mid-1985.

On 15 December 1984, airframe E-009 (N98LF) made it first flight with John Penny and Bob Jacobs at the controls. In April 1985, the aircraft was flown to William P. Hobby Airport in Houston, Texas to give Sultan bin Salman an orientation flight. At the time, Sultan bin Salman was undergoing training for his Space Shuttle flight abord Discovery, scheduled for June 1985. Most likely, it was hoped that the Lear Fan orientation flight would also result in additional financing from the Zoysia Saudi Arabian consortium, but it was not to be. On 25 May 1985, development of the Lear Fan was halted; all employees in Reno and Newtonabbey were let go, and all Fan Holdings Inc facilities were closed.

The Lear Fan’s revolutionary design and construction proved too much to overcome. The decision to develop the aircraft without a proof-of-concept proved costly, as numerous changes needed to be made. Problems had also been encountered with the gearbox, and its excessive wear was cited as the final blow to the program. After 200 hours of inspection, the FAA refused to issue a Certificate of Airworthiness for the Lear Fan. Some contend that the FAA set requirements for the Lear Fan that were two to three times more stringent than those for a comparable aluminum aircraft.

Lear-Fan-E009-Frontiers-of-Flight

E-003 hangs on display in Frontiers of Flight Museum at Love Field in Dallas, Texas. Black pneumatic de-icing boots covered the Lear Fan’s leading edges. Hot exhaust from the engines would prevent the buildup of ice on the propeller. (Johnny Comstedt image via http://www.aviationmuseum.eu)

The final disclosed specifications for the Lear Fan were a wingspan of 39 ft 4 in (11.99 m), a length of 40 ft 7 in (12.37 m), and a height of 12 ft 2 in (3.71 m). The aircraft had a maximum speed of 414 mph (666 km/h) at 20,000 ft (6,096 m) and a stalling speed of 88 mph (142 km/h). Best economical cruise speed was 322 mph (518 km/h) at 40,000 ft (12,192 m), which gave a maximum range of 2,003 miles (3,224 km). The Lear Fan had an initial climb rate of 4,000 fpm (20.3 m/s) and a ceiling of 41,000 ft (12,497 km). The aircraft had an empty weight of 4,100 lb (1,860 kg) and a gross weight of 7,350 lb (3,334 kg). At gross weight, the Lear fan had a range of 1,782 miles (2,868 km). Single engine performance was a 1,300 fpm (6.6 m/s) climb rate and a 33,000 ft (10,058 m) ceiling.

Compared to the original flight specifications, the aircraft had become 450 lb (204 kg) heavier. While its maximum speed had increased by 14 mph, its maximum range at gross weight decreased by 670 miles (1,078 km), and its economical cruising speed decreased by 28 mph. After a peak of some 280 aircraft on order, most customers requested a refund as development dragged on. The entire Lear Fan project had consumed over $250 million.

Lear-Fan-E009-FAA-OKC

E-009 on display at the FAA’s Civil Aerospace Medical Institute in Oklahoma City, Oklahoma. The aircraft was previously in outside storage at the FAA facility and underwent a restoration starting in 2012. The new paint scheme was applied during the restoration. A dedication ceremony for the restored E-009 was held on 29 September 2015.

Years after their development was abandoned, Lear Fan airframes continued to be used to understand composites and develop techniques for their inspection. From November 1993 to October 1994, Northrup Grumman inspected the composite wing structure of E-009. The project was sponsored by US Department of Transportation and NASA to develop inspection techniques for composite aircraft. Although minor defects were detected, they were evaluated as not severe enough to impose a threat to the integrity of the wing structure. The final inspection report advised that composite assembly standards should be established to minimize defects and damage. It was noted that E-009 had about 230 flight hours.

The FAA acquired two Lear Fan test airframes, presumably from the E-004 to E-008 group. The airframes were tested at the Impact Dynamics Research Facility at the NASA Langley Research Center in Hampton, Virginia. The tests involved swinging the airframes into the ground from a 240 ft (73 m) gantry. This produced a 56 mph (90 km/h) forward velocity and an 1,860 fpm (9.4 m/s) descent rate at impact. The first aircraft was unmodified and tested in 1994. The fuselage broke in two above the wing, and the measured impact forces were greater than those recorded with comparable aluminum aircraft. The deformation and crumpling of aluminum absorbed some of the impact energy, while the composite structure of the Lear Fan absorbed less energy. The second airframe was modified with a composite, energy-absorbing subfloor and was tested on 15 October 1999. In addition, a plywood structure was built for the aircraft to collide with after ground impact. The fuselage cracked in a similar manner to the first airframe but the separation was less.

All three completed Lear Fan aircraft survive. E-001 (N626BL) hangs from the ceiling in the Great Gallery at the Museum of Flight on Boeing Field in Seattle, Washington. E-003 (N327ML/N21LF) hangs from the ceiling in the Frontiers of Flight Museum at Love Field in Dallas, Texas. E-009 (N98LF) was purchased by the FAA and is displayed outdoors at the Civil Aerospace Medical Institute, part of the Mike Monroney Aeronautical Center, adjacent to the Will Roger Airport in Oklahoma City, Oklahoma.

Lear-Fan-impact-test-1999

The second of two incomplete Lear Fan airframes owned by the FAA. The aircraft is pictured after its impact test on 15 October 1999. Off frame to the right is the concrete surface where the airframe made initial contact. It then slid onto the grass (note the red marker lines) and through the plywood barrier. A dirt berm was built-up on the left side of the plywood. Cracks in the fuselage can be seen near the plywood. The left engine cover with its integral duct have separated from the airframe. (NASA/Langley Research Center image)

Sources:
– Email correspondence with John Penny
Stormy Genius by Richard Rashke (1985)
Lear Fan (brochure) by LearAvia Corp (1979)
Lear Fan Propulsion System by Daniel E. Cooney (April 1980)
Jane’s All the World’s Aircraft by John WR Taylor (various editions 1979–1985)
– “Lear Fan 2100—first report” by Bill Sweetman, Flight International (10 January 1981)
– “Lear Fan collapses,” Flight International (8 June 1985)
– “Crosswind TakeoffEnterprise (video, 1984)
Structural Integrity Evaluation of the Lear Fan 2100 Aircraft by H. P. Kan and T. A. Dyer (May 1996)
Simulation of an Impact Test of the All-Composite Lear Fan Aircraft by Alan E. Stockwell (October 2002)
https://www.aviastar.org/air/usa/learavia_learfan.php

Planet-Satellite-Farnborough-front

Planet Satellite Light Aircraft

By William Pearce

John Nelson Dundas Heenan was born on 4 October 1892 in Altrincham, England. He became an engineer and worked for the family engineering firm Heenan & Froude in Manchester. Heenan left the family firm in 1935 when its parent company went bankrupt, and it was acquired by outside investors. Heenan worked for the British Air Ministry During World War II and cofounded the engineering consulting firm Heenan, Winn, and Steel (HW&S) in early 1946.

Planet-Satellite-cockpit-mockup

The cockpit mockup of the Planet Satellite on display in 1948. The major difference from the prototype is how the window panels above the door hinged up on the mockup, rather than sliding up as seen on the actual aircraft.

Like many others, Heenan believed that there would be a post-war boom in civil aviation with a huge need for light aircraft for private pilots. Working with others at HW&S, he designed an aircraft capable of carrying four to five passengers. Heenan decided that the aircraft should be built using a magnesium alloy with zirconium. However, due to a lack of experience with the metal, HW&S approached Magnesium Elektron Ltd to build the aircraft. Magnesium Elektron was owned by the Distillers Company Ltd, and its business had experienced a drastic contraction after the war. The Distillers Company was willing to consider options to expand Magnesium Elektron’s business and formed a partnership with HW&S to create Planet Aircraft Ltd. Planet Aircraft operated as a subsidiary of the Distillers Company to construct and produce the new aircraft, which was named Satellite. The aircraft was commonly referred to as the Planet Satellite.

The Satellite was a streamlined, low-wing, pusher monoplane with tricycle landing gear. The pusher configuration was chosen to reduce passenger cabin noise by isolating it from the engine and propeller. The two-piece fuselage was of monocoque construction and consisted of forward and rear sections. The magnesium fuselage was riveted together for the prototype aircraft, but production aircraft were to be welded. The fuselage was split just behind the wings for access to the engine, which was located aft of the passenger cabin and above the center wing section. A firewall separated the passenger cabin from the engine compartment.

Planet-Satellite-cockpit-construction

The Satellite’s forward fuselage section under construction. The firewall around the engine is visible. Baggage compartments that were accessible in flight existed behind the rear bench seat and on each side of the engine. The many rivets of the prototype would have given way to a welded structure on production aircraft.

The forward fuselage section incorporated the passenger cabin and was 4 ft 8 in (1.42 m) in diameter at its widest point. The pilot and copilot/front passenger sat behind an expansive windscreen that extended to the nose of the aircraft. A bench that could accommodate up to three passengers was behind the pilot’s seat. Cabin access was via two doors that folded down, one by the pilot’s seat and one by the copilot’s seat. As the door was opened downward, the armrest folded down to act as a step. The window above each door slid up toward the center of the fuselage.

An inverted, U-shaped magnesium keel reinforcement ran internally along the bottom of the forward fuselage section from the nose of the aircraft to the wing’s leading edge. At the leading edge, the keel became a single plate that extended to the wing’s trailing edge. The wings and main landing gear were attached to the plate. The pneumatically-operated landing gear was fully enclosed, with the nosewheel retracting to the rear into the keel and the main gear legs retracting forward and into the fuselage. A landing light was incorporated into the front of the aircraft, just above the nosewheel.

Planet-Satellite-Farnborough-front

The Satellite on display at the SBAC Farnborough Show in September 1948. The aircraft was not registered at the time, and was painted blue with a red accent. The main landing gear appears spindly and collapsed after the aircraft’s first hop.

To power the Satellite, buyers could choose between the 250 hp (186 kW) de Havilland Gipsy Queen 31 or the 145 hp (108 kW) de Havilland Gipsy Major 10. While both engines were inverted, inline, air-cooled designs, the six-cylinder Gipsy Queen had a 4.65 in (120 mm) bore, a 5.51 in (150 mm) stroke, a displacement of 621 cu in (10.18 L), and a weight of 510 lb (231 kg). The four-cylinder Gipsy Major had a 4.65 in (118 mm) bore, a 5.51 in (140 mm) stroke, a displacement of 374 cu in (6.12 L), and a weight of 312 lb (142 kg). The selected engine was affixed to a rail mount and could be slid out 18 in (.46 m) from the forward fuselage for maintenance once the rear fuselage was disconnected. A fan driven from the rear of the engine brought in cooling air via a duct atop the fuselage and expelled the heated air out the lower fuselage. Engine exhaust was also expelled in the same manner.

The wing had one main spar at its center and a false spar that supported the flaps and ailerons. The flaps ran along half of the wing’s trailing edge, with ailerons extending to the wingtips. Magnesium sheets 28 in (.71 m) wide were wrapped around the wing’s leading edge and extended to both the upper and lower trailing edges to form the wing skin. The wing had two degrees of dihedral, and each wing accommodated a 34 US gal (28 Imp gal / 127 L) fuel tank, for a total of 67 US gal (56 Imp gal / 255 L). With two additional wing tanks, the fuel capacity could be increased to 109 US gal (91 Imp gal / 414 L) for a long-range flight with a single pilot.

Planet-Satellite-Farnborough-cockpit

A good view illustrating access to the passenger cabin. Doors on each side of the aircraft folded down, and the armrest on the door became a step. The window panel above the door slid up. Note the long windscreen, and the landing light in the nose.

The forward and rear fuselage sections were joined via a quick-release locking “ring,” which Heenan had patented (GB 620,462: applied on 20 January 1947 and accepted on 24 March 1949). Control cables were automatically connected or disconnected in conjunction with the locking ring. The rear fuselage section incorporated the extension shaft, propeller, and Y tail.

The hollow extension shaft extended approximately 10 ft (3 m) from the engine to drive a two-blade, adjustable-pitch Aeromatic propeller at the extreme rear of the fuselage. The hollow steel shaft acted as an oil reservoir for the bearings that supported it. The propeller was 6 ft 6 in (1.98 m) in diameter. The ventral fin of the Y tail incorporated a rudder and a spring-loaded bumper to protect the propeller from ground impacts. The two “butterfly” horizontal stabilizers had 30 degrees of dihedral, which increased the aircraft’s directional stability. The Satellite’s control surfaces were of all-metal construction. The Planet Satellite had a wingspan of 33 ft 6 in (10.21 m), a length of 26 ft 3 in (8.00 m), and a height of 9 ft 3 in (2.82 m).

With a Gipsy Queen 31 engine, the aircraft had a top speed of 208 mph (335 km/h) at sea level and a stalling speed of 62 mph (100 km/h) at its maximum load. An economical cruise speed of 191 mph (307 km/h) was achieved at 3,500 ft (1,067 m), which resulted in a range of 1,000 miles (1,609 km) with a normal fuel load at maximum weight and 2,450 miles (3,943 km) with the extra fuel tanks and a single pilot. The Satellite had a 1,450 fpm (7.4 m/s) initial rate of climb and a ceiling of 22,000 ft (6,706 m). The aircraft had an empty weight of 1,600 lb (726 kg) and a maximum gross weight of 2,905 lb (1,318 kg). Fully loaded, the Satellite could take off in 570 ft (174 m). The Gipsy Queen-powered Satellite was offered for £3,500.

Planet-Satellite-Farnborough-rear

Rear view of the Satellite illustrates the aircraft’s Y tail. The line where the front and rear fuselage sections joined is visible just behind the wing’s trailing edge. The inlet for engine cooling air can be seen atop the fuselage.

With the significantly less powerful Gipsy Major 10 engine, the Satellite’s performance was reduced. The aircraft had a top speed of 173 mph (278 km/h) at sea level and a stalling speed of 54 mph (87 km/h) at its maximum load. An economical cruise speed of 161 mph (259 km/h) was achieved at 5,000 ft (1,524 m), which resulted in a range of 500 miles (805 km) with a normal fuel load at maximum weight and 2,150 miles (3,460 km) with the extra fuel tanks and a single pilot. The Satellite had a 950 fpm (4.8 m/s) initial rate of climb and a ceiling of 18,000 ft (5,486 m). The aircraft had an empty weight of 1,408 lb (639 kg) and a maximum gross weight of 2,280 lb (1,034 kg). Fully loaded, the Satellite could take off in 840 ft (256 m). The Gipsy Major-powered Satellite was offered for £2,500.

Detail design work on the Satellite started in April 1946. For Satellite construction, neither Planet Aircraft, Magnesium Elektron, or the Distillers Company had facilities to build the prototype aircraft. Magnesium Elektron contracted Redwing Aircraft Ltd to build two Satellite prototypes at their facility in Thornton Heath, near London. A mockup of the cockpit and forward fuselage section was completed in 1947, and the construction of two prototypes soon followed.

The first, nearly-complete Satellite made its public debut at the SBAC (Society of British Aircraft Constructors) Farnborough Show in September 1948. The aircraft was registered as G-ALOI on 26 April 1949. The Satellite was moved to Blackbushe Aerodrome, near Farnborough, for flight trials. Flight testing was to be conducted by Hugh Joseph “Willie” Wilson, who had resigned from the Royal Air Force as a Group Captain to serve as a director with Planet Aircraft. On 7 November 1945, Wilson had established a new World Air Speed Record at 606.262 mph (975.675 km/h) in a Gloster Meteor.

Planet-Satellite-Redhill-derelict

The Satellite sits derelict in a hangar at Redhill. The aircraft wears its G-ALOI registration, and a scoop to augment the intake of cooling air has been installed. The scoop was probably fitted after the first round of ground tests. Note that the gear doors are closed despite the landing gear being deployed. This did not appear to be possible from the Farnborough images. Perhaps the gear doors seen at Farnborough were mockups or a redesign occurred.

Wilson took the Satellite for high-speed taxi tests and did a tentative hop in the aircraft. Upon settling back on the ground, the landing gear promptly collapsed. The Satellite was repaired, and Wilson restarted the test program. Again at Blackbushe Aerodrome, Wilson took the aircraft to about 20 ft (6 m) above the runway. This time the landing was uneventful. However, a crack in the magnesium keel was discovered when the aircraft was inspected after the flight. Analysis of the crack indicated that the Satellite’s magnesium structure was severely understressed and would need an extensive rebuild to bring it into tolerance of its expected flight regime. The British Air Registration Board required that the aircraft be restressed before any further flights were made.

Although Heenan was an engineer, he was not an aeronautical engineer, and the Satellite was his first aircraft design. He once said that only 400 drawings were made during the Satellite’s design phase, compared to the roughly 3,000 drawings that would be expected for a comparable aircraft. With the design now coming up short, another £40,000 would be needed to resolve the Satellite’s deficiencies. The Distillers Company had already invested over £100,000 and withdrew further funding. The Satellite was moved to Redhill Aerodrome south of London, where it sat and slowly deteriorated until 1958, when it was finally scrapped.

The second Satellite prototype was registered as G-ALXP in 1950, but it was never completed. G-ALXP’s mostly-finished fuselage was later used by Firth Helicopters as the basis for the FH.01/4 Atlantic helicopter, a twin-rotor design which was built in 1952. The FH.01/4 Atlantic was also designed by HW&S, but it never flew and was eventually scrapped in the 1960s. Most likely by coincidence, the basic layout of the Planet Satellite would be resurrected in the late 1970s as the Lear Fan 2100, another unconventional aircraft constructed of unconventional materials in hopes of revolutionizing private air travel.

Planet-Satellite-Firth-FH1

The fuselage of the second Satellite prototype was used for the Firth FH.01/4 helicopter, which never flew. The helicopter was donated to the College of Aeronautics at Cranfield in 1955, which is probably when the image above was taken.

Sources:
The Planet Satellite by Planet Aircraft Ltd (cira 1948)
Jane’s All the World’s Aircraft 1949–50 by Leonard Bridgman (1949)
– “Heavenly Body” by Don Middleton, Aeroplane Monthly (October 1983)
– “Ones That Got Away: Planet Satellite” by Mike Jerram, Wingspan International (March/April 2001)
Aircraft Engines of the World 1948 by Paul H. Wilkinson (1948)
– “Improvements in and relating to Aeroplanes” by John Nelson Dundas Heenan, GB patent 620,462 (applied 20 January 1947)
https://www.secretprojects.co.uk/threads/planet-aircraft-ltd-and-firth-helicopter-prototypes.1170/

Kellner-Bechereau-28VD-top

Kellner-Béchereau 28VD Air Racer

By William Pearce

Société Kellner was a French luxury coachbuilder run by Georges Kellner. During World War I, the company turned to producing SPAD VII, S.XI, and S.XIII fighter aircraft under license. The SPAD (Société Pour L’Aviation et ses Dérivés / Company for Aviation and its Derivatives) aircraft were designed by French aeronautical engineer Louis Béchereau. After World War I, Société Kellner returned to coach making, and SPAD went out of business. Béchereau progressed through a number of companies until 1926, when he founded the Société pour la Réalisation d’Avions Prototypes (SRAP / Prototype Aircraft Company).

Kellner-Bechereau-28VD-construction

The Kellner-Béchereau 28VD under construction. The cowling attached to the very front of the aircraft contained the surface oil cooler. The top of the coolant tank is visible just behind the fairing atop the engine. Note the fuel tanks forward and aft of the cockpit.

Société Kellner was taken over by Jacques Kellner after his father’s passing. Jacques was an aviation enthusiast and wanted to steer the company back to being involved with aviation. In 1931, Jacques Kellner joined forces with Louis Béchereau to form Avions Kellner-Béchereau in Boulogne-Billancourt, France. Kellner-Béchereau immediately began designing aircraft, and one of their first concepts was that of the 28VD (also known as KB-28), an air racer intended for the 1933 Coupe Deutsch de la Meurthe. The Coupe Deutsch de la Meurthe was a race to cover 1,242 miles (2,000 km) with a mandatory 90-minute stop at 621 miles (1,000 km), and aircraft were limited to using a single engine with a displacement no greater than 488 cu in (8.0 L). Additional stops could be made but were not mandatory and would count against the total time to finish the course. Ten laps of the 124-mile (200-km) course would complete the race, and the rhombus-shaped course was laid out with towns of Chartres, Moisy, Orléans, and Étampes at its corners. The Étampes-Mondésir airfield was the start and finish point, and the prize in 1933 was four million Francs.

The Kellner-Béchereau 28VD was a low-wing taildragger made almost entirely of metal, and its design was tested in a wind tunnel. The aircraft’s slim monocoque fuselage was of all-aluminum construction with an open cockpit at its center. A sloped fairing led up to the cockpit, and an extended headrest trailed from it. This resulted in the pilot sitting rather low with little forward visibility, but side visibility was quite good. Fuel tanks were housed in front of and behind the cockpit. The aircraft’s vertical and horizontal stabilizers were made of aluminum, but the rudder and elevators were made of wood. The angle of the horizontal stabilizers was adjustable and could be altered to trim the aircraft while in flight. An aerodynamic fairing partially covered the tailskid.

Kellner-Bechereau-28VD-maintenance

The 28VD undergoing final touches. This image gives a good view of how the surface radiators wrapped around the wing’s leading edge. Note the large Ratier metal propeller. Intakes to the engine’s superchargers can just been seen on the cowling’s undersides.

The relatively-short, cantilever wings of the 28VD were attached to the fuselage by a main spar at its center and a rear spar. The wings were further supported by false front and rear spars. A large aileron ran almost the entire length of the wing’s trailing edge and was attached to the false rear spar. Wing construction kept its interior mostly open, and three fuel tanks were positioned in each wing. Each of the wing tanks was equipped with a quick-drain dump valve 3.94 in (10 cm) in diameter. For the valve, carbonic acid gas was fed into a space that blew out a lower seal, allowing an upper plug to fall free followed by the contents of the fuel tank. Although not specifically stated, it is presumed that the pilot would control the flow of the carbonic acid gas to initiate the fuel dump. It is not clear if the fuselage tanks were also equipped with a dump valve.

The upper surface of each wing was covered with radiators in five sections. Each surface radiator section consisted of a forward and rear part. The front radiator for each section curved around the front of the wing to form the leading edge. The inner three radiator sections terminated shortly after making the turn to the wing’s underside. The outer two sections continued around the leading edge to cover the front half of the underwing, and additional radiators covered the rear outer surface under the wing. Water from the coolant tank installed above the engine flowed through pipes in the wing’s leading and trailing edges and then into the surface radiators. After passing through the radiator, the cooled water was collected in a tube running along the center spar and returned to the engine. A large fairing connecting the wing’s trailing edge to the fuselage contained a number of louvers to allow heat, vapors, and moisture to escape from the wing.

Kellner-Bechereau-28VD-right

The newly completed 28VD is rolled out of the hangar for testing. The aircraft’s streamlining and slim fuselage are apparent. This image provides a good view of the landing gear’s arched supports. For retraction, the top of the gear leg slid toward the wingtip, and the lower gear leg pivoted around the arched support.

Mounted under the inboard sections of the wings was the partially-retractable main landing gear, which had a 4 ft 10 in (1.48 m) track. When extended, a fixed ball at the top of each gear leg was locked into place, and the leg itself was supported by an arched member attached to the fuselage. The ball atop the gear leg was mounted in a channel in the wing. To retract the gear, a retraction lever released the downlock and bled pressure in a cylinder, which unlocked a drum and allowed a cable to unwind. As the gear leg pivoted around its arched support, an elastic cable pulled the top of the gear leg toward the wing tip until the gear leg rested against the underside of the wing. An uplock under the inner wing secured the gear leg in the retracted position, and the arched support provided a crude aerodynamic fairing. To extend the gear, an extension lever released the uplock and fed pressurized air into a cylinder. The piston in the cylinder rotated a drum which wound a cable. The cable was attached to the upper gear legs and pulled them inboard against the tension of the elastic cable. Once the cable had pulled the gear to its extended position, the ball atop the gear leg was secured by the downlock.

Housed in a streamlined, close-fitting cowling at the front of the 28VB was the Delage 12 CDirs engine. Built by la Société des Automobiles Delage (the Delage Automobile Company), the engine was specially made for the Coupe Deutsch de la Meurthe race. Its “12 CDirs” designation stood for 12 cylinders, Coupe Deutsch, inverse (inverted), réducteur (gear reduction), and suralimenté (supercharged). The 400 hp (298 kW) engine was a water-cooled V-12 with twin-Roots superchargers. The 12 CDirs had a 3.94 in (100 mm) bore, a 3.31 in (84 mm) stroke, and a displacement of 483 cu in (7.92 L). Intakes in each side of the lower cowling brought in air to the engine’s superchargers. Exhaust was expelled through individual stacks protruding from the cowling. A saddle water tank sat atop the rear part of the engine. A U-shaped oil tank was installed between the engine and the propeller. A surface oil cooler was positioned atop the engine and covered the area between the water tank and the spinner. The engine turned a two-blade, metal, ground-adjustable Ratier propeller that was approximately 7 ft 9 in (2.37 m) in diameter.

Kellner-Bechereau-28VD-top

Elevated view of the 28VD illustrates the surface radiators covering the upper wings. Note the vents in the wing’s trailing edge fairing. The race number “5” has been applied to the fuselage. This image was most likely taken on 14 May 1933, the day of the accident, as the aircraft is prepared for its qualification flight.

The Kellner-Béchereau 28VD had a wingspan of 21 ft 10 in (6.65 m), a length of 23 ft 6 in (7.16 m), and a height of 8 ft 8 in (2.64 m). The aircraft weighed 2,176 lb (987 kg) empty and 3,527 lb (1,600 kg) fully loaded. The 28VD had an anticipated top speed of 249 mph (400 km/h) and a cruising speed of 214 mph (345 km/h). On 5 May 1933, the aircraft was moved to the Étampes-Mondésir airfield where it would be completed for the Coupe Deutsch de la Meurthe, to be held on 28 May. Qualifying for the race was scheduled 8–14 May, which left very little time for flight testing. The 28VD was given race number 5 and made its first flight on 12 May. Armée de l’Air Capitaine Maurice Vernhol conducted the very brief flight tests, which did not reveal any issues, and would fly the 28VD for the race. Refining and preparing the aircraft used up most of the qualifying time. Based on previous tests, Vernhol felt that the engine’s full power was not being utilized and requested that the propeller be adjusted to a finer pitch.

During an afternoon qualification flight on 14 May 1933, Vernhol added full power, and the engine revved to an excess of 4,400 rpm—over 600 rpm more than its maximum limit. At that moment, a coolant hose blew free from its mount, and Vernhol was enveloped in a shower of steam and hot water. It is not clear if the increased coolant pressure from the engine overspeed caused the hose to blow free, or if it was just bad timing. Regardless, Vernhol was blinded by the spray and attempted an emergency landing near Ville Sauvage, north of the Étampes-Mondésir airfield. In his impaired condition, Vernhol misjudged the landing, and the 28VD hit the ground hard. The extended landing gear broke off, and the aircraft flipped upside down, tearing off the engine and breaking the fuselage behind the cockpit. Amazingly, Vernhol escaped with only minor injuries, but the 28VD was completely destroyed. A Potez 53 flown by Georges Détré went on to win the 1933 Coupe Deutsch de la Meurthe at a speed of 200.58 mph (322.81 km/h).

Kellner-Béchereau also designed a fighter along the same lines as the 28VD / KB-28. Known as the KB-29, the fighter was powered by a 550 hp (410 kW), 731 cu in (11.97 L) Delage 12 GVis inverted V-12 engine. The engine was displayed at the 1932 Paris Salon de l’Aéronautique, but the KB-29 fighter never materialized.

Kellner-Bechereau-28VD-crash

The remains of the 28VD after its forced lading. The landing gear and engine have been ripped away, and the fuselage is broken at a right angle behind the wing. The surface radiators under the outer wing are visible. The circular openings seen in the wing’s underside are the dump valves for two of the three fuel tanks.

Sources:
– “Les avions de la Coupe Deutsch de la Meurthe 1933” by Pierre Léglise, L’Aéronautique No 171 (August 1933)
– “L’éphémère Kellner-Bechereau KB 28” by Robert J. Roux, Le Fana de l’Aviation No 253 (December 1990)
– “Le Kellner-Béchereau 28V.D.” by Michel Marrand, L’Album du Fanatique de L’Aviation 23 (June 1971)
– “Le Coupe Deutsch de la Meurthe” by L. Hirschauer, L’Aérophile 14 Annee No 6 (June 1933)
– “The 1933 Contest for the Deutsch de la Meurthe Trophy” by Pierre Léglise, L. Hirschauer, and Raymond Saladin, National Advisory Committee for Aeronautics Technical Memorandum No. 724 (October 1933)
https://www.secretprojects.co.uk/threads/kellner-bechereau-project.32989/
https://www.secretprojects.co.uk/threads/louis-b%C3%A9chereau-designations.26384/
https://en.wikipedia.org/wiki/Kellner-B%C3%A9chereau_28VD
https://www.aviafrance.com/kellner-bechereau-28vd-aviation-france-891.htm

Curtiss-XP-23-rear-left

Curtiss XP-23 / YP-23 Hawk Biplane Fighter

By William Pearce

On 8 July 1931, the United States Army Air Corps (AAC) issued production contract W535-ac-4434 to the Curtiss-Wright Corporation for the production of 46 P-6E Hawk fighter aircraft. The P-6E was one of many variants that had branched from the P-6 line, which originated in 1928. The basic P-6 was a refined P-1 equipped with a Curtiss V-1570 Conqueror engine; however, the 46th aircraft from contract W535-ac-4434 would not be finished as a P-6E. Rather, it would become the Model 63, which carried the AAC designation XP-23. In the early 1930s, the AAC was interested in exploring advancements with turbosuperchargers to create a fighter capable of high speeds at high altitudes, and the XP-23 was an opportunity to create just such an aircraft.

Curtiss-XP-23-front-left

The Curtiss XP-23 Hawk with an unidentified individual (contact us if you can ID). Visible is the large turbosupercharger, its intake, and the two exhaust pipes feeding the turbine. Note the engine coolant radiator between the main gear.

The Curtiss XP-23 was a single engine biplane with conventional fixed taildragger undercarriage. The only components the aircraft had in common with a P-6E were the wings, although some sources state that the wings had a spar and rib frame built of metal rather than wood. Whether it was made of wood or metal, the wing’s frame was covered in fabric. The upper wing had a 1.5-degree dihedral, was mounted 4 in (102 mm) higher than on the P-6E, and was positioned 28.5 in (724 mm) forward of the lower wing. The lower wing had no dihedral and was 5 ft 6 in (1.68 m) shorter in span. Ailerons were located on the upper wing only.

The aircraft’s monocoque fuselage and tail were of all-metal construction. The main and reserve fuel tanks were housed forward of the cockpit and held a total of 78 US gallons (65 Imp gal / 295 L). The oil tank held 11 US gallons (9 Imp gal / 42 L). A .30-cal machine gun was mounted on each side of the aircraft just forward of the cockpit. A long blast tube extended from each gun, through the engine bay under the exhaust, and exited just behind the spinner. Some sources indicate the armament was one .30-cal and one .50-cal machine gun, while other sources state two .30-cal and one .50-cal machine gun. It is not clear where the third gun would have been located, if indeed there was one. Aerodynamic fairings covered the main wheels except for their outer side.

Curtiss-XP-23-left

Side view of the XP-23 illustrated the aircraft’s rather smooth, all-metal finish. Note the machine gun port just under the engine’s exhaust and the left-handed (counterclockwise) propeller. The image was dated 12 April 1932, four days before the aircraft was accepted by the AAC.

The XP-23 was powered by a liquid-cooled Curtiss V-1570 Conqueror V-12 engine, which was equipped with a General Electric F-2C turbosupercharger. The turbosupercharger was externally mounted to the left side of the engine. Exhaust from the left cylinder bank was fed directly into the turbosupercharger, and exhaust from the right cylinder bank was ducted through the cowling just behind the engine and to the turbosupercharger. The intake was just forward of the turbosupercharger. The engine did not have a mechanically-driven supercharger or blower.

The turbosupercharger enabled the V-1570 engine to produced 600 hp (447 kW) at 2,400 rpm from sea level to 15,000 ft (4,572 m). The V-1570 had a 6.1 to 1 compression ratio and consumed 60 US gph (50 Imp gph / 227 L/h) at full throttle and 36 US gph (30 Imp gph / 136 L/h) at 2,100 rpm (cruise power / 88% throttle). At a .500 reduction, the engine turned a metal, three-blade, ground-adjustable Hamilton Standard propeller that was 9 ft 6 in (2.90 m) in diameter. Mounted under the engine and between the main gear was the radiator for the engine’s ethylene glycol cooling system.

Curtiss-XP-23-rear-left

The drag-inducing installation of the side mounted turbosupercharger is illustrated in this rear view of the XP-23. Note the reduced span of the lower wing.

The XP-23’s upper wing had a span of 31 ft 6 in (9.60 m), and its lower wing had a span of 26 ft (7.92 m). The aircraft had a length of 23 ft 9 in (7.24 m) and a height of 8 ft 9 in (2.67 m). The XP-23’s top speed was 223 mph (359 km/h) at 15,000 ft (4,572 m) and 178 mph (286 km/h) at sea level. The aircraft’s cruising speed was 192 mph (309 km/h) at 15,000 ft (4,572 m), and its stalling speed was 69 mph (111 km/h) at sea level. The XP-23 had an initial climb rate of 1,370 fpm (6.96 m/s), and its service ceiling was 32,000 ft (9,754 m). The aircraft’s range was 292 miles (470 km) at full throttle and 435 miles (700 km) at cruise power. The XP-23 had an empty weight of 3,142 lb (1,425 kg) and a gross weight of 4,032 lb (1,829 kg).

The XP-23 was allotted serial number 32-278 and built at the Curtiss Airplane Division Plant 1 on Kenmore Avenue in Buffalo, New York. The aircraft was accepted by the AAC on 16 April 1932 at a cost of $12,279.36. Although the XP-23’s performance met expectations, there is some indication that the turbosupercharger overheated and was unreliable. Regardless, the age of biplane fighters was at an end, and the XP-23 was the last biplane fighter accepted by the AAC. The Boeing P-26 Peashooter prototype was the AAC’s first monoplane fighter to enter service and made its first flight on 20 March 1932. The P-26 out-performed the XP-23 and showed that the monoplane type was the future.

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The YP-23 with the turbosupercharger removed and a two-blade propeller installed. It also appears that either a support was installed between the main wheels or that a fairing was installed over the existing brace wires.

Curtiss had proposed powering the XP-23 with a V-1800 Super Conqueror engine. The V-1800 had a mechanically-driven supercharger that eliminated the bulbous side-mounted turbosupercharger previously used on the XP-23 and resulted in a much cleaner cowling. The engine produced 800 hp (597 kW) at 2,400 rpm and turned a 10 ft (3.05 m) diameter, metal, three-blade, ground-adjustable Hamilton Standard propeller at a .714 reduction. With the V-1800, the XP-23 had an anticipated top speed of 234 mph (377 km/h) at 12,000 ft (3,658 m) and a cruise speed of 199 mph (320 km/h). At 23 ft 11 in (7.29 m) long and 3,227 lb (1,464 kg) empty, the aircraft was 2 in (51 mm) longer and 85 lb (39 kg) heavier than the V-1570-powered variant. Curtiss did note that the wing might need to be moved forward slightly to achieve a proper center of gravity. However, the V-1800 was never installed in the XP-23.

The sole XP-23 was modified by removing the turbosupercharger, but the V-1570 was retained. It is not clear if the modifications were in anticipation of further changes to incorporate the V-1800, or if it was done to compare the turbosupercharger setup to the normally-aspirated V-1570. With the turbosupercharger removed, the aircraft became commonly known as the YP-23. The engine’s air intake was positioned atop the cowling, a two-blade propeller was fitted, and its armament was removed. In this configuration, the YP-23 achieved 200 mph (322 km/h) at 15,000 ft (4,572 m).

Curtiss-YP-23-left-radiator

A new cowling was made for the YP-23 that did not incorporate gun ports below the engine’s exhaust stacks. Note the intake atop the cowling and the Wright “Arrowhead” painted on the fuselage. The aircraft as pictured is similar in appearance to the proposed V-1800-powered XP-23.

The YP-23 underwent one last round of modifications to explore the effects of radiator drag on high-speed aircraft. The coolant radiator was removed, the V-1570 engine was switched to a total-loss water cooling system, and the aircraft’s main fuel tank was used as a water reservoir. Using fuel from the reserve tank, cooling water flowed through the engine at a reduced rate from the main tank and was then vented overboard. The previous deletion of the turbosupercharger and the removal of the radiator gave the YP-23 an exceptionally clean appearance. Unfortunately, test results of these modifications have not been found. It is possible that thorough testing was never conducted since monoplanes offered higher performance. The YP-23 was disassembled, and its wings were reportedly used on the XF11C-1 Goshawk prototype fighter for the United States Navy.

Curtiss-YP-23-left-no-radiator

The YP-23 in its final form with the radiator removed and serving as the AAC’s last biplane fighter design. While the aircraft exhibits an exceptionally clean appearance, its flight endurance was very short with its total-loss cooling system.

Sources:
Curtiss Fighter Aircraft by Francis H. Dean and Dan Hagedorn (2007)
Curtiss Aircraft 1907–1947 by Peter M. Bowers (1987)
U.S. Fighters 1925 to 1980s by Lloyd S. Jones (1975)
American Combat Planes of the 20th Century by Ray Wagner (2004)
http://www.joebaugher.com/usaf_fighters/p23.html

Lockheed-1249-R7V-2-in-flight-no-wing-tanks

Lockheed Model 1249 Turboprop Super Constellation

By William Pearce

In 1938, the Lockheed Corporation in Burbank, California began design work on a large commercial airliner intended to outperform other transports then in service. Initially known as the Model 44 Excalibur, the aircraft’s design changed as feedback provided by Pan American Airways was evaluated. In 1939, Transcontinental and Western Air (TWA) approached Lockheed in search of an aircraft with performance superior to that of the planned Model 44. Lockheed decided to redesign its airliner based on TWA’s requirements, and the new design became the Model 049 Constellation (originally Model 49 and known as Excalibur A).

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The Lockheed Model 1249 was a turboprop-powered Super Constellation originally ordered by the US Navy as the R7V-2. The aircraft was the fastest of the Constellation series by far, but other turboprop and jet aircraft were favored by all parties.

The Model 049 Constellation was an all-metal, low-wing aircraft with tricycle landing gear. The airliner was powered by four 2,200 hp (1,641 kW) Wright R-3350 engines and carried 60 passengers in its pressurized cabin. The Model 049 had a 123 ft (37.5 m) wingspan and was 95 ft 2 in (29.0 m) long and 23 ft 8 in (7.2 m) tall. The aircraft’s tail had three vertical stabilizers with rudders to keep the aircraft’s overall height down so that it would fit in TWA’s existing hangars. The Model 049 had a top speed of 329 mph (529 km/h) at sea level, a cruising speed of 275 mph (443 km/h) at 20,000 ft (6,096 m), an initial climb rate of 1,620 fpm (8.2 m/s), and a range of 2,290 miles (3,685 km) with a maximum payload of 18,400 lb (8,346 kg). The aircraft had an empty weight of 55,345 lb (25,104 kg) and a maximum weight of 86,250 lb (39,122 kg).

In 1940, the design of the Model 049 was mostly finalized, and three airlines had placed orders for a total of 84 aircraft (30 of these were long-range Model 349s). In May 1941, the United States Army Air Corps ordered 180 Model 349s to be used as transports. Lockheed tooled-up for aircraft production, and construction of the first Model 049 was underway when the United States entered World War II after the bombing of Pearl Harbor on 7 December 1941. With the United States at war, production priorities shifted, and all of the aircraft intended for the airlines would be completed as C-69s, the military designation for the Model 049/349.

Lockheed-1249-R7V-2-under-wing

Installation of the Pratt & Whitney T34 turboprop engines onto the Super Constellation airframe was well-executed. The tight-fitting cowling was much smaller than those needed to cover the larger-diameter R-3350 piston engine. The aircraft’s main gear was unchanged, which resulted in an awkward hump under the No. 2 and 3 engines. Note the wide cord of the three-blade propeller.

The C-69 received a low priority compared to Lockheed’s other commitments, and the prototype made its first flight on 9 January 1943. Only 15 C-69s were completed by the end of the war. After the war, Lockheed again focused on the Constellation for airline use, and new orders were received. In May 1945, Lockheed made use of new 2,500 hp (1,864 kW) R-3350 engines and designed the Model 649 and the Model 749, which had increased range. The United States Air Force also used the Model 749 as the C-121A. The Model 749 had a top speed of 358 mph (576 km/h) at 19,200 ft (5,852 m), a cruising speed of 304 mph (489 km/h) at 20,000 ft (6,096 m), an initial climb rate of 1,280 fpm (6.5 m/s), and a range of 1,760 miles (2,834 km) with a payload of 16,300 lb (7,394 kg). The aircraft had an empty weight of 58,970 lb (26,748 kg) and a maximum weight of 107,000 lb (48,534 kg).

In late 1949, Lockheed investigated ways to improve the Constellation’s performance and keep the aircraft on the frontline of airline service. The result was the Model 1049 Super Constellation, which had two new fuselage sections added that increased the aircraft’s length by 18 ft 5 in (5.6 m). In addition, 2,700 hp (2,013 kW) R-3350 engines were installed, and the height of the vertical stabilizers was increased by 1 ft 3 in (.38 m). The aircraft could accommodate up to 92 passengers. The Model 1049 was 113 ft 7 in (34.6 m) long, 24 ft 9 in (7.6 m) tall, had a top speed of 338 mph (544 km/h) at sea level, a cruising speed of 302 mph (485 km/h) at 20,000 ft (6,096 m), an initial climb rate of 1,100 fpm (5.6 m/s), and a range of 2,880 miles (4,635 km) with a payload of 18,800 lb (8,528 kg). The aircraft had an empty weight of 69,210 lb (31,393 kg) and a maximum weight of 120,000 lb (54,431 kg). The Model 1049 made its first flight on 13 October 1950. The Model 1049B was a military transport version of the Super Constellation, designated R7V-1 (originally R7O-1) for the US Navy and C-121C for the US Air Force.

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The first R7V-2 (BuNo 131630) seen on a test flight without the wingtip fuel tanks. The Constellation-series of aircraft is known as one of the more graceful airframes, and the turboprop engines made the aircraft that much more impressive.

From the start of the Model 1049’s design, Lockheed had envisioned using 3,250 hp (2,424 kW) R-3350 Turbo Compound (TC) engines, which used three power recovery turbines to harness energy from the exhaust and feed it back to the crankshaft via fluid couplings. However, Wright’s development of the engine lagged behind that of the aircraft. The R-3350 TC engines were first incorporated into the Model 1049C, which made its first flight on 17 February 1953. The pinnacle of the Super Constellations was the Model 1049G, powered by 3,400 hp (2,535 kW) R-3350 TC engines. The aircraft made its first flight on 7 December 1954. The Model 1049G had a top speed of 370 mph (595 km/h) at 20,000 (6,096 m), a cruising speed of 310 mph (499 km/h) at 20,000 ft (6,096 m), an initial climb rate of 1,165 fpm (5.9 m/s), and a range of 4,165 miles (6,704 km) with a payload of 18,300 lb (8,301 kg). The aircraft had an empty weight of 73,016 lb (33,120 kg) and a maximum weight of 137,500 lb (62,369 kg).

The US Navy had been instrumental in supporting Wright’s development of the turbo compound engine, but in the early 1950s, the turboprop engine was making its way onto the aviation scene. In June 1950, Lockheed considered a turboprop-powered Super Constellation airliner as the Model 1149, but the design did not procced. In November 1951, Lockheed proposed to the Navy a turboprop R7V-1 (Model 1049B) powered by Pratt & Whitney T34 turboprop engines. The Navy was interested, and Lockheed proceeded with design work on the turboprop Super Constellation as the Model 1249. The Navy ultimately amended its R7V-1 order to include two airframes converted to turboprop-power. These aircraft were designated R7V-2 by the Navy and carried the Lockheed serial numbers 4131 and 4132 and the Navy BuNos 131630 and 131631.

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Side view of the R7V-2 shows the reinforcements on the rear fuselage above and below the large cargo door, which hinged up. The turboprop aircraft used standard Super Constellation fuselages, and most were reused on piston-powered aircraft once their days of testing were over.

Two additional airframes were ordered in May 1953. They carried the Lockheed serial numbers 4161 and 4162 and Navy BuNos 131660 and 131661. In October 1953, BuNos 131660 and 131661 were slated to be completed as YC-121Fs for the Air Force and were also assigned Air Force serial numbers 53-8157 and 53-8158. The YC-121F was the Lockheed Model 1249A. Since the order originated with the Navy, all four turboprop Super Constellations carried the Navy designation R7V-2, with the last two also assigned the Air Force designation. All four aircraft were purely intended to test the serviceability of the turboprop engine.

The Model 1249 was based on the Model 1049B, with a modified wing and new engines. The R-3350-powered Constellations had the engine nacelle’s centerline mounted below the wing. The Model 1249 had the engine nacelle’s centerline mounted above the wing, and the nacelle extended back to the wing’s trailing edge. Exhaust from the turboprop engine was expelled from the back of the nacelle and generated thrust. The Model 1249 could also accommodate removable 600 US gallon (500 Imp gal / 2,271 L) wingtip tanks that were first installed on Navy Super Constellations and later used by airlines. Additional fuselage fuel tanks were fitted, and the landing gear was strengthened.

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The first YC-121F, still with Navy BuNo 131660 painted on the tail, seen on a test flight over Pacific Palisades, just north of Santa Monica, California. Note the large, removable wingtip fuel tanks.

The T34 turboprop was an axial-flow engine that consisted of a 13-stage compressor powered by a three-stage turbine. Sources indicate that the R7V-2s for the Navy used T34-P-12 engines, while the YC-121Fs for the Air Force used T34-P-6 engines. The T34-P-12 produced 5,005 shp (3,732 kW) and 1,360 lbf (6.05 kN) of thrust, for a total of 5,550 eshp (4,139 kW) at 11,000 rpm for takeoff power. Continuous power for the T34-P-12 was 4,210 shp (3,139 kW) and 1,165 lbf (5.18 kN) of thrust, for a total of 4,675 eshp (3,486 kW) at 10,500 rpm.

The T34-P-6 produced 5,500 shp (4,101 kW) and 1,250 lbf (5.56 kN) of thrust, for a total of 6,000 eshp (4,474 kW) at 11,000 rpm for takeoff power. Continuous power for the T34-P-6 was 4,750 shp (3,542 kW) and 1,125 lbf (5.57 kN) of thrust, for a total of 5,200 eshp (3,878 kW) at 10,750 rpm. Each engine turned a three-blade Hamilton Standard A-3470 propeller at .0909 engine speed. The propeller was 15 ft in (4.57 m) diameter, and each blade was 24 in (610 mm) wide.

The Model 1249 had a 117 ft (35.7 m) wingspan without wingtip fuel tanks and a 119 ft (36.3 m) wingspan with wingtip fuel tanks. The aircraft was 116 ft 2 in (35.4 m) long and 25 ft 6 in tall (7.8 m). The Model 1249 had a top speed of 444 mph (715 km/h) at 15,000 ft (4,572 m) and could maintain 420 mph (676 km/h) at 25,000 ft (7,620 m). The aircraft had an initial climb rate of 4,600 fpm (23.4 m/s) at maximum power and 2,310 fpm (11.7 m/s) at normal power. The Model 1249’s ceiling was 32,900 ft (10,028 m) at maximum power and 26,400 ft (8,047 m) at normal power. The aircraft’s range was 2,230 miles (3,589 km) with a payload of 24,210 lb (10,981 kg), and it had an empty weight of 72,387 lb (32,834 kg) and a maximum weight of 148,540 lb (67,377 kg). The Model 1249 could accommodate 106 passengers and four crew members for short flights, 87 passengers and 15 crew members for long flights, or 35,500 lb (16,103 kg) of cargo. For medical evacuations, the aircraft could accommodate 73 litters, four attendants, and four crew members.

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The second YC-121F, Air Force serial number 53-8158, seen with flaps and gear extended. Note the exhaust outlet at the rear of the engine nacelles.

The Model 1249 / R7V-2, BuNo 131630, made its first flight on 1 September 1954. The aircraft was not initially fitted with the wingtip tanks, and it was accepted by the Navy on 10 September 1954. The second R7V-2 soon followed and was accepted by the Navy on 30 November 1954. The Navy put the R7V-2 aircraft through various tests. A top speed of 479 mph (771 km/h) was achieved in a slight dive, and the aircraft took off overweight at 166,400 lb (75,478 kg). However, the R7V-2’s career was short. In December 1956, and with just 109 total hours, BuNo 131630 was put into storage at Naval Air Station (NAS) Litchfield Park in Arizona. The aircraft was struck off charge in April 1959 and provided spare parts for other Constellations.

In late 1956, BuNo 131631 was loaned back to Lockheed as an engine testbed for the L-188 Electra airliner and later the P-3 Orion maritime patrol aircraft. At the time, BuNo 131631 had accumulated 120 hours of operation. Rohr Aircraft in Chula Vista, California removed the T34 engines and replaced them with Allison 501-D (T56) engines in new nacelles intended for the Electra. The 501-D produced 3,460 shp (2,580 kW) and 726 lbf (3.23 kN) of thrust, for a total of 3,750 eshp (2,796 kW) for takeoff power. The engines turned four-blade Aeroproducts 606 propellers that were 13 ft 6 in (4.11 m) in diameter. The modified aircraft was nicknamed ‘Elation,’ a combination of Electra and Constellation. Elation made its first flight in July 1957 and was used until July 1959 when it was damaged at Palmdale, California. With 882 hours, BuNo 131631 was delivered to NAS Litchfield Park. In May 1960, the aircraft was sold to California Airmotive. The fuselage and some other parts were used to rebuild 1049G Super Constellation N7121C, and the remainder was scrapped. N7121C went through various air cargo owners until it was scrapped in March 1968.

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Lockheed serial 4132, the second R7V-2 (BuNo 131631), fitted with Allison 501-D engines to test their installation for the L-1888 Electra. Known as the Elation, the aircraft flew more with the Allisons than it did with its original Pratt & Whitney engines. Note the four-blade propellers.

The Model 1249A / YC-121F, serial no 53-8157, made its first flight on 5 April 1955 and was accepted by the Air Force in July. The second aircraft, serial number 53-8158, took to the air in August 1955. Both YC-121Fs were assigned to the 1700th Test Squadron of the Military Air Transport Service, based at Kelly Air Force Base in San Antonio, Texas. In April 1956, a YC-121F set a point-to-point speed record, traveling the 1,445 miles (2,326 km) between Kelly, Texas and Andrews Air Force Base, Maryland in 2 hours 53 minutes, an average of 501.16 mph (806.54 km/h). Between 25 and 26 January 1957, another record was set flying from Long Beach, California to Andrews Air Force Base, Maryland. The 2,340-mile (3,766-km) route was covered in 4 hours 43 minutes at an average speed of 496.11 mph (798.41 km/h). Both record flights were most likely made by 53-8157.

In June 1957, 53-8158 was assigned to McClellan Air Force Base in Sacramento, California; 53-8157 followed a year later. In February 1959, the two YC-121Fs were placed in storage at Davis Montham Air Force Base in Tucson, Arizona. Both aircraft were sold to the Flying Tiger Line 1963. The fuselages of the two YC-121Fs were used with wings, engines, and tails from two 1049Gs and pressed into cargo transport service in 1963. In 1966, both aircraft were sold to North Slope Aviation Company in Alaska. Serial number 53-8158 (N174W) was written off in May 1970. Serial number 53-8157 (N173W) was sold to Aviation Specialties and written off in June 1973.

Along with the military versions, Lockheed had designed a turboprop Super Constellation airliner in 1952 designated as the Model 1249B. The aircraft was planned to have a maximum speed of 451 mph (726 km/h) and a maximum range of 4,125 miles (6,639 km). However, the 1249B was not pursued, and the L-188 Electra eventually took its place.

Lockheed-1249-Super-Constellation-ad

An ad for the turboprop Super Constellation as Lockheed made a light push to interest airlines in the concept. There were no takers, and Lockheed developed the L-188 Electra instead.

Sources:
The Lockheed Constellation by Peter J. Marson (2007)
Lockheed Constellation by Curtiss K. Stringfellow and Peter M. Bowers (1992)
Lockheed Aircraft since 1913 by René J. Francillon (1987)
Lockheed C-121 Constellation by Steve Ginter (1983)
Characteristics Summary YC-121F by US Air Force (1 April 1957)
Lockheed Constellation by Dominique Breffort (2006)
https://www.thisdayinaviation.com/tag/lockheed-yc-121f/
http://www.conniesurvivors.com/1-QandA.htm

Blackburn-B20-front-water

Blackburn B-20 Experimental Flying Boat

By William Pearce

On 13 February 1935, John Douglas Rennie submitted a patent application for “Improvements in and relating to Seaplanes.” Rennie was the Chief Seaplane Designer for the Blackburn Aeroplane and Motor Company, which was renamed in 1936 as Blackburn Aircraft Ltd. Rennie’s design idea was for the lower portion of the flying boat’s hull to be sealed and extend for takeoff and landing. The extendable hull would essentially act as the aircraft’s main float.

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An excellent view of the Blackburn B-20 highlighting the aircraft’s extended hull, retracted wingtip floats, and well-engineered cowlings for the Vulture engine.

In order to provide clearance for the propellers, traditional flying boats have some combination of a parasol or strut-mounted wing positioned above the fuselage, a gull wing, and a tall hull. In addition, the hull and wing are designed for the essential task of lifting the aircraft from the water, but they are far from optimized for cruise flight. All of these compromises add significant drag to the aircraft. With Rennie’s hydraulically-operated extendable hull, the flying boat’s cross section with the hull retracted was much more like that of a conventional aircraft, and drag was significantly reduced. In addition, when the hull was extended, the aircraft assumed the ideal angle for takeoff and landing, which allowed the aircraft’s wing to have an angle of incidence optimized for cruise flight when the hull was retracted. Rennie’s patent also included retractable wingtip floats.

Rennie was granted Great Britain patent 433,925 on 22 August 1935. In 1936 the British Air Ministry issued Specification R.1/36 for a small, general purpose flying boat capable of cruising at 230 mph (370 km/h). Rennie and Blackburn responded with a twin-engine flying boat that featured a retractable hull. Blackburn’s design carried the company designation B-20. The Air Ministry ordered the Saunders-Roe A.36 Lerwick for Specification R.1/36, but they were sufficiently intrigued by the Blackburn B-20 to order a prototype, which was later assigned serial number V8914.

Technically, the B-20 was more of a floatplane with a retractable center main float than a flying boat. However, when the float was retracted, the aircraft took on the appearance and configuration of a flying boat. The B-20 had a high wing and was of all-metal, stressed-skin construction. All of the control surfaces were fabric covered. With the exception of the extending hull, the aircraft had a conventional layout. The B-20 had a standard crew of six. The fuselage housed a bombardier’s compartment in the nose. The fight deck was located well forward of the wing attachment and provided the pilot and copilot a good view. Behind and slightly below the cockpit was the flight engineer, navigator, and observer’s compartment. Under the wing was a wardroom with sleeping accommodations for two, followed by the crew’s quarters with accommodations for four, a galley, and a lavatory.

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This side view of the B-20 illustrates how the hull moved forward as it was extended. The rear member of each of the four hull mounts was a hydraulic cylinder that actuated the extension and retraction of the hull.

The one-piece wing had three main spars, a straight leading edge, and a tapered trailing edge. Mounted in a nicely streamlined nacelle on each wing was a Rolls-Royce Vulture II X-24 engine capable of 1,800 hp (1,342 kW) for takeoff. The engine had an international rating of 1,780 hp (1,327 kW) at 4,000 ft (1,219 m) and 1,660 hp (1,237 kW) at 13,500 ft (4,115 m). A scoop under the engine nacelle housed the engine’s coolant radiator and oil cooler. Each engine turned a three-blade, constant-speed, de Havilland propeller. Unlike the patent design, which featured wing floats that retracted into the engine nacelles, the wing floats of the B-20 retracted outward to be flush with the wing and form the wingtip.

The extendable hull had five watertight compartments. The center compartment housed four fuel tanks with a total capacity of 1,172 US gallons (976 Imp gal / 4,437 L). The hull also housed most of the mooring equipment. Four hydraulic cylinders mounted in the fuselage controlled the extension and retraction of the 48 ft 9 in (14.86 m) hull. The hydraulic cylinders extended the hull approximately 5 ft 8.25 in (1.73 m) down from the fuselage for operating on the water’s surface. Forward of each hydraulic cylinder was a hinged triangular frame mounted to one point on the fuselage and two points on the hull. As the hull extended down, it also traversed forward. This movement of the hull gave the aircraft the proper angle for landing and taking off. Entry to the fuselage was achieved with the hull extended. Hatches under the fuselage led to the bombardier’s station, the wardroom, and the galley. A ladder that hinged down from the hatch under the bombardier’s station was the main access point.

Although the prototype was unarmed, the B-20’s planned armament consisted of two .303 machine guns in the nose, a dorsal turret with two .303 machine guns, and a tail turret with four .303 machine guns. In each wing, two compartments between the engine nacelle and the fuselage could each house a 500 lb (227 kg) bomb or two 250 lb (113 kg) bombs.

Blackburn-B20-front-water

The B-20 on the water looked a little ungainly with its hull extended. Note the access ladder between the hull and the fuselage.

The Blackburn B-20 had a wingspan of 82 ft 2 in (25.04 m) with the floats retracted and 76 ft (23.16 m) with the floats extended. The aircraft was 69 ft 7.5 in (21.22 m) long, and was 25 ft 2 in (7.67 m) tall on its beaching gear with the hull extended. Without the turrets, the B-20 had a top speed of 322 mph (518 km/h) at 15,000 ft (4,572 m), 302 mph (486 km/h) at 5,750 ft (1,753 m), and 280 mph (451 km/h) at sea level. With the proposed turrets, the aircraft’s performance fell to a maximum speed of 306 mph (492 km/h) at 15,000 ft (4,572 m), 288 mph (464 km/h) at 5,750 ft (1,753 m), and 268 mph (431 km/h) at sea level. Cruising speed was 200 mph (322 km/h), and the B-20’s range was 1,500 miles (2,414 km). The aircraft had a normal weight of 35,000 lb (15,876 kg).

The B-20 was completed at Blackburn’s factory in Dumbarton, Scotland, near the River Clyde. The aircraft made its first flight on 27 March 1940, piloted by Blackburn’s test pilot Harry Bailey. Another four or five flights were made with some aileron trouble, but otherwise there were no issues. The extending hull worked well, although its extension and retraction in flight were not entirely smooth. Once extended, the hull offered an open platform from which to conduct mooring operations, and the aircraft was well-behaved on the water.

Blackburn-B20-right-side-water

The B-20 providing a good view of the wing float design. Note the Short Sunderland and what appears to be a Short Empire framed nicely between the B-20’s hull and fuselage.

On 7 April 1940, Bailey was joined by Blackburn test engineer Fred Weeks, Blackburn aircraft riggers Sam McMillan and Duncan Roberts, and Rolls Royce flight engineer Ivan Waller. The task of the day was to complete high-speed tests in the B-20. During the fight, the aircraft reached an unofficial speed of 345 mph (555 km/h). On the next run, an aileron experienced flutter and failed, sending the B-20 out of control. The aircraft crashed in the Firth of Clyde off Garroch Head. Weeks and Waller were able to successful bail out and were picked up by the HMS Transylvania, a merchant ship converted to an auxiliary cruiser. Bailey also bailed out but was too low for his parachute to fully open. His body was recovered from the sea. However, the bodies of McMillan and Roberts were never found.

Even though its flight career was very short, the B-20 had given every indication that its hull design significantly improved performance. Based on the B-20 design, the Blackburn B-40 and B-44 were proposed. The B-40 was in response to Specification R.13/40. The aircraft was a twin-engine flying boat transport powered by two Bristol Centaurus radial engines and intended as a possible replacement for the Short Sunderland. The B-40 was larger and heavier than the B-20 and had twice the range. Two B-40 prototypes were ordered on 9 September 1941, but the aircraft’s poor single engine performance and other priorities led to its cancellation on 6 January 1942. The B-44 was a single-engine floatplane fighter designed to Specification N.2/43. The aircraft was armed with four 20 mm cannons and powered by a Napier Sabre H-24 engine turning contra-rotating propellers. Two B-44 prototypes were ordered in October 1942, but the project was cancelled shortly after a mockup was built. An analysis of the design indicated that the B-44 would be difficult to handle on the water.

In August 1998, one of the B-20’s Vulture engines was recovered after becoming tangled in the nets of a trawler. The B-20’s crash site was subsequently classified as a war grave. What remains of the Vulture engine is now on display at the Dumfries and Galloway Aviation Museum in Scotland.

Blackburn-B20-rear-water

Rear view of the B-20 helps visualize the defense the four .303 machine guns in the turret would have provided.

Sources:
Aircraft of the Fighting Powers Volume 6 by Owen Theyford (1945/1980)
Blackburn Aircraft since 1909 by A. J. Jackson (1989)
British Experimental Combat Aircraft of World War II by Tony Buttler (2012)
British Prototype Aircraft by Ray Sturtivant (1990)
Jane’s All the World’s Aircraft 1945/46 By Leonard Bridgman (1946)
– “Improvements in and relating to Seaplanes” GB patent 433,925 by John Douglas Rennie (applied 13 February 1935).
https://aviation-safety.net/wikibase/204426
http://helensburgh-heritage.co.uk/index.php/heritage/military/1608-three-died-in-prototype-crash

Hawker-Tornado-P5224-front

Hawker Tornado Fighter

By William Pearce

In early 1937, Hawker Aircraft Limited and the company’s chief designer, Sydney Camm, began to consider the next generation of fighter aircraft for the Royal Air Force. The British Air Ministry was also considering the future of fighter airframes as well as the incorporation of powerful, new engines under development—specifically the Napier Sabre H-24, the Rolls-Royce Vulture X-24, and the Bristol Centaurus 18-cylinder radial.

Hawker-Tornado-P5219-front

The first Hawker Tornado prototype P5219 in its original form with the belly radiator. The Vulture’s two rows of exhaust stacks are evident. The aircraft’s resemblance to the Hurricane is apparent.

In July 1937, Hawker proposed two Camm-designed aircraft—the N-type and the R-type, named for their respective Napier and Rolls-Royce powerplants. The Air Ministry told Hawker to wait until an official request was issued, which came in March 1938 in the form of Specification F.18/37 seeking a fighter capable of 400 mph (644 km/h) at 20,000 ft (6,096 m). Hawker was notified in August 1938 that they had won the design contest for Specification F.18/37, and two prototypes of each N-type and R-type were ordered. However, an official contract was not issued until December 1938. The N-type went on to become the Sabre-powered Hawker Typhoon, while the R-type became the Vulture-powered Hawker Tornado. The two Tornado prototypes were assigned serial numbers P5219 and P5224.

The Tornado was a single-engine fighter of all-metal construction with a conventional taildragger layout. The aircraft somewhat resembled an enlarged Hawker Hurricane. From the engine to just behind the cockpit, the fuselage consisted of a tubular frame covered with aluminum panels. The rear fuselage and tail were of monocoque construction. The pilot sat in an enclosed cockpit that was accessible via side entry doors. A fairing extended behind the cockpit and limited the pilot’s rearward vision.

The Tornado’s wing was mounted to the tubular frame of the center fuselage. Because of the Vulture’s installation, the wing was mounted to the fuselage about 3 in (76 mm) lower than on the Typhoon. The wing had two main spars and consisted of an inner and outer section. The inner section had a 1.0-degree anhedral and housed the inward-retracting main landing gear. The landing gear had a wide track of 13 ft 8 in (4.17 m). A 48 US gal (40 Imp gal / 182 L) fuel tank was located in each wing between the main gear leg well and the rear spar, and a 42 US gal (35 Imp gal / 159 L) fuel tank was located in the leading edge of each inner wing section. The Tornado’s total fuel capacity was 180 US gal (150 Imp gal / 682 L). Each outer wing section had a 5.5-degree dihedral and housed six Browning .303 machine guns with 500 rpg. The thick wing was originally designed for the possible installation of six 20 mm cannons, but this configuration was never tried. Each wing had a two-section, hydraulically actuated split flap and featured a large aileron. Except for the fabric-covered rudder, all control surfaces were covered with metal.

Hawker-Tornado-P5219-rear

Another shot of the newly completed P5219 displays the aircraft’s original short tail. Note the opaque fairing behind the cockpit that blocked the pilot’s vision.

The Tornado’s Rolls-Royce Vulture II engine had 24 cylinders arranged in an X configuration. The engine was mounted to the forward part of the tubular fuselage frame and produced 1,760 hp (1,312 kW). Two rows of exhaust stacks protruded from each side of the engine’s cowling. A belly scoop between the main gear wells housed the engine’s coolant radiator and oil cooler. A door in the aft section of the scoop regulated temperatures. Two intakes between the belly scoop and the underside of the fuselage fed air to the engine’s carburetor. The engine turned a three-blade, constant-speed Rotol propeller that was 14 ft (4.27 m) in diameter.

The Hawker Tornado had a wingspan of 41 ft 11 in (12.78 m), a length of 32 ft 10 in (10.01 m), and a height of 14 ft 8 in (4.47 m). The aircraft had a top speed of 398 mph (641 km/h) at 23,000 ft (7,010 m) and stalling speeds of 82 mph (132 km/h) clean and 61 mph (98 km/h) with flaps and gear extended. The Tornado had an empty weight of 8,377 lb (3,800 kg) and a loaded weight of 10,668 lb (4,839 kg). The aircraft’s initial rate of climb was around 3,500 fpm (17.8 m/s), and its ceiling was 34,900 ft (10,638 m).

Hawker-Tornado-P5224-front

The second Tornado prototype P5224 with the chin radiator and windows behind the pilot to help improve vision. The aircraft now resembles a Typhoon, with which it shared many components.

The Tornado prototype P5219 was built at the experimental shop in Hawker’s Canbury Park Road facility in Kingston, but it was sent to Hawker’s new facility in Langley for final assembly in July 1939. The Vulture II engine was delivered in September 1939, and ground tests were started later that month. Piloted by Philip Lucas, P5219 made its first flight on 6 October 1939. During the preliminary flight tests in October and November, the aircraft achieved a speed of 370 mph (595 km/h) at 15,000 ft (4,572 m). However, the Tornado’s tail was lacking in surface area, and the rudder did not have sufficient authority to hold a straight course during takeoff and proved ineffective at speeds under 150 mph (241 km/h). Engine cooling was a constant issue, especially during ground operations. While in flight at higher speeds, turbulence from the wings disrupted airflow into the radiator, which impaired engine cooling. A new radiator was designed that would relocate the cooling system from its ventral position to a chin location under the engine. Metal was also found in the engine oil, indicating a possible issue with the Vulture’s bearings.

While the Vulture engine was undergoing maintenance, the Tornado airframe was modified with the new chin radiator and oil cooler, which shifted the aircraft’s appearance away from that of the Hurricane. In November 1939, an order for Hawker to produce 1,000 Tornados was placed. The contract was later changed to Typhoons, but then amended for 800 Typhoons and 200 Tornados, with the Tornados to be built by Avro due to Hawker’s production commitments of other aircraft, namely the Hurricane. Other Tornado production contracts were later issued, including 200 aircraft to be built by Cuncliffe-Owen and another 760 aircraft to be built by Avro. The revised Tornado took to the air on 6 December 1939, but Lucas reported that the aircraft was even more directionally unstable with the chin radiator. Performance tests in March 1940 indicated a top speed of 384 mph (618 km/h) at 20,500 ft (6,248 m), but the engine was not making full power. Various modifications were made to improve the aircraft’s stability. The exit of the radiator was extended 3 in (76 mm); the vertical stabilizer and rudder were enlarged in May 1940; and tailwheel doors were added in June 1940.

Hawker-Tornado-P5224-in-flight

P5224 in flight displaying the aircraft’s aggressive appearance and enlarged tail. Note the carburetor intake atop the engine cowling.

With stability improved, P5219 was sent to Rolls-Royce’s flight-testing facility at Hucknall to improve the engine’s performance. The aircraft was returned to Langley in mid-July 1940 with a new engine and a new Rotol propeller that was 13 ft 2.5 in (4.02 m) in diameter. Performance flight testing continued, and on 27 July, the Tornado climbed to 20,000 ft (6,096 m) in 6 minutes and 36 seconds and achieved a speed of 396.5 mph (638.1 km/h) at 20,800 ft (6,340 m). On 31 July, the Vulture engine failed in flight, and the aircraft was damaged in the subsequent forced landing.

While P5219 was being repaired, the second Tornado prototype, P5224, was flown on 7 December 1940. Construction of the second prototype was delayed by other priority war work. P5224 was built from the start with the chin radiator and an enlarged tail. The aircraft also had the carburetor intake atop the engine cowling, inner gear doors to completely enclose the main gear, and side windows behind the cockpit to improve the pilot’s vision (which was still restricted). However, engine cooling was still an issue, as were excessive vibrations with the Vulture engine.

The repaired P5219 returned to active flight testing with a 1,980 hp (1,476 kW) Vulture V engine installed by March 1941, but the future of the Vulture engine was in doubt. P5224 suffered an engine failure on 21 March 1941, and its Vulture II was subsequently replaced by a Vulture V. P5224 first flew with the Vulture V on 11 June 1941. Around June 1941, Avro was instructed to halt work on producing the Tornado fighter, and the Tornado contracts were cancelled. The Vulture engine was stalled by Rolls-Royce so they could focus on the Merlin, and the Vulture was officially cancelled in October 1941. The Sabre-powered Typhoon fighter would be produced and take over resources previously allocated to the Tornado.

Hawker-Tornado-CR-props

The first and only production Tornado, R7936, was used as a propeller testbed after its initial flight testing. The aircraft is seen here with Rotol contra-rotating propellers, which had a smaller diameter than the standard, single-rotation propellers used on the Tornado and Typhoon. Note that the aircraft did not have the windows behind the pilot like the second prototype.

P5219 continued flight testing with Hawker until at least April 1943, and the aircraft was scrapped in August 1943. P5224 was tested by the Aeroplane & Armament Experimental Establishment at Boscombe Down starting in October 1941. The aircraft was then delivered to the Royal Aircraft Establishment at Farnborough in December 1941. P5224 was scrapped in late 1944.

After the Tornado contracts were cancelled, construction of the first production Tornado, serial number R7936, was allowed to continue as well as components for two other examples that were nearing completion. R7936 was powered by a Vulture V engine and made its first flight on 29 August 1941, piloted by Lucas. In general, pilots that flew R7936 were impressed by its handling and performance. The aircraft recorded a speed of 402 mph (647 km) at 21,800 ft (6,645 m) and climbed to 20,000 ft (6,096 m) in 6 minutes and 54 seconds. With the Tornado program dead, R7936 was used as a testbed for Rotol and de Havilland contra-rotating propellers. Little information has been found on these tests, but the aircraft was delivered to Rolls-Royce in March 1942 for the installation of a Vulture engine with a contra-rotating gear reduction. The six-blade Rotol contra-rotating propeller was 11 ft 3 in (3.43 m) in diameter, and the aircraft was first flown with the unit on 11 August 1942. The de Havilland contra-rotating propellers were installed as early as December 1942. It appears R7936 continued with propeller tests until April 1944, when it was scrapped.

Hawker-Tempest-HG641-side-org

Typhoon HG641 was built to serve as a testbed for the Bristol Centaurus engine. Seen here with its original three-blade propeller, cowling, and single large exhaust manifold. The silhouette of the oil cooler can just be seen between the main landing gear.

From the first discussion with the Air Ministry before Specification F.18/37 was issued, Camm and Hawker had given some consideration to a Centaurus-powered Tornado, but little progress was undertaken beyond the preliminary design. With the Vulture and Sabre engines running into development issues by late 1940, more-serious consideration was given to installing a 2,210 hp (1,678 kW) Centaurus engine in a Tornado airframe. In September 1940, Hawker was given permission to proceed with the Centaurus-powered Tornado prototype, but the official contract was not issued until February 1941. Some work was also done on using a Wright R-3350 engine, but this design was dropped in June 1941.

The Centaurus Tornado was assigned serial number HG641. The aircraft was built by Hawker at Langley using components from uncompleted Tornado production airframes and a new center fuselage. The Centaurus engine turned a 12 ft 9 in (3.89 m) diameter, three-blade, Rotol propeller and was covered by a conventional cowling. Exhaust from the engine was expelled via a single manifold protruding from the cowling under the left side of the engine. An oil cooler was mounted between the wells for the main landing gear. The air-cooled radial reduced the aircraft’s weight by about 350 lb (159 kg). Lucas took the Centaurus Tornado up for its first flight on 23 October 1941.

Hawker-Tempest-HG641-side-mod

HG641 with the new four-blade propeller and revised cowling. The oil cooler was located in the large duct under the engine.

Initial flight tests of HG641 indicated that airflow through the oil cooler was not efficient and led to the engine running near its upper temperature limit. Even so, a speed of 378 mph (608 km/h) was recorded at 20,000 ft (6,096 m). The oil cooler was modified, and testing continued until December 1941. At that time, the aircraft was modified to improve the installation of the engine package, including exhaust and oil cooler. The cowling was revised, and a new oil cooler duct was faired into the lower cowling. Two exhaust stacks were incorporated into the left and right sides of the fairing. A four-blade propeller, also 12 ft 9 in (3.89 m) diameter, was installed, and the modified Centaurus Tornado took its first flight on 23 December 1942, piloted by Lucas. Cooling was improved, and the aircraft achieved 403 mph (649 km/h) at 22,000 ft (6,706 m) and had a ceiling of 32,800 ft (9,997 m). In February 1943, the aircraft was transferred to Bristol’s facility in Filton, where a speed of 412 mph (663 km/h) at 18,000 ft (5,486 m) was reportedly recorded. The Centaurus Tornado continued engine testing until August 1944, when the aircraft was scrapped.

The testing of Tornado aircraft provided information for developing the Typhoon fighter, contra-rotating propellers, and the Bristol Centaurus engine, which was particularly helpful when applied to the Centaurus-powered Hawker Tempest II fighter. Although the Tornado has been mostly forgotten, both the Typhoon and the Tempest served with distinction during World War II.

Hawker-Tempest-HG641-rear-mod

Side view of HG641 with the new cowling. The aircraft did not have the windows behind the pilot and used hinged doors on the landing gear to completely conceal the main wheels. This was also tried on the prototypes before switching to a separate inner door.

Sources:
The Hawker Typhoon and Tempest by Francis K. Mason (1988)
Hawker Typhoon, Tempest and Sea Fury by Kev Darling (2003)
British Experimental Combat Aircraft of World War II by Tony Buttler (2012)
Fighters Volume Two by William Green (1964)
Hawker Typhoon and Tempest: A Formidable Pair by Philip Birtles (2018)
Aircraft of the Fighting Powers Volume V by H. J. Cooper and O. G. Thetford (1944)
The Secret Years: Flight Testing at Boscombe Down 1939 – 1945 by Tim Mason (1998)
Hawker Aircraft since 1920 by Francis K. Mason (1991)

Beardmore-Inflexible-nose

Beardmore Inflexible / Rohrbach Ro VI Transport

By William Pearce

In 1914, Adolf Karl Rohrbach started working for Luftschiffbau Zeppelin GmbH as the company began to diversify from airship construction into building heavier-than-air aircraft. Claude Dornier was also employed by Zeppelin and was tasked with designing airframes out of metal, rather than wood. Rohrbach worked with Dornier on the design of several aircraft before Rohrbach was reassigned in 1917 to the Zeppelin plant in Staaken, near Berlin, Germany. At Staaken, Rohrbach worked with Alexander Baumann and was involved in the design of large R-Plane (Riesenflugzeuge, or giant aircraft) bombers.

Beardmore-Inflexible-rear

The duralumin fuselage skin of the Beardmore Inflexible exhibited significant wrinkling. The staining above the wings was caused by engine exhaust and oil. Note the cable running from the wing to the lower fuselage.

Immediately following World War I, Rohrbach designed the Zeppelin-Staaken E.4/20. Like Dornier and Hugo Junkers, Rohrbach was pioneering the construction of aircraft using metal and stressed skin. The E.4/20 was an all-metal, four-engine airliner that made its first flight on 30 September 1920. However, the Treaty of Versailles prevented Germany’s possession of large aircraft, and the E.4/20 was scrapped in 1922. That same year, Rohrbach founded Rohrbach Metall-Flugzeugbau GmbH (Rohrbach Metal Aircraft, Ltd) in Berlin. To work around the Treaty of Versailles, aircraft designed at Rohrbach in Berlin were built at an assembly plant in Copenhagen, Denmark or licensed to be constructed elsewhere.

Following World War I, the British Air Ministry became increasingly interested in all-metal aircraft. In 1923, the Air Ministry issued specification No. 18/23 for a large, all-metal, experimental transport, and order No. 445337/23 was awarded to William Beardmore & Company, Ltd in Dalmuir, Scotland for the construction of such an aircraft. At the time, Beardmore was involved in building ships, locomotives, aircraft engines, and airships. In addition, the company had built aircraft under license during World War I. Beardmore was to collaborate with Rohrbach on the design of the transport aircraft. Beardmore outlined the aircraft’s basic specifications, Rohrbach supplied some of the detailed drawings, and Beardmore built the transport. The aircraft was known as the Beardmore AV 1 Inflexible, or the Rohrbach Ro VI, or the BeRo 1—a combination of Beardmore and Rohrbach. Most commonly, the aircraft is referred to as the Beardmore Inflexible. It was not until 1924 that Beardmore obtained the license from Rohrbach and construction of the aircraft began.

Beardmore-Inflexible-top

The Inflexible at Martlesham Heath. In the lower right of the image are the wheel trollies used to move the aircraft sideways into the hangar.

At Beardmore, the design of the Inflexible was initially laid out and modified by William. S. Shackleton. The project was later taken over by Rollo A. de Haga Haig. The aircraft’s design was tested in the Royal Aircraft Establishment’s wind tunnel at Farnborough. Except for its size, the aircraft possessed a fairly conventional layout. The monoplane trimotor had shoulder-mounted wings and taildragger landing gear. One engine was mounted in the nose, and an engine was mounted on each wing. Each engine was a water-cooled Rolls-Royce Condor II that produced 650 hp (485 kW) and turned a wooden, fixed-pitch, two-blade propeller. The radiator for the nose-mounted engine was directly below the fuselage, and the radiator for each wing-mounted engine was located under the wing between the engine nacelle and the fuselage. The two-place, side-by-side, open cockpit was positioned just forward of where the wings mounted to the fuselage. Below the cockpit on the left side of the fuselage was a small propeller for a wind-driven pump. The pump supplied oil to a servo system that boosted movement of the ailerons and elevator.

Beardmore-Inflexible-nose

The group posing in front of the Inflexible gives scale to the aircraft’s immense size. The radiator for the fuselage-mounted engine can be seen under the nose. Exhaust manifolds carried the gasses from the center engine away from the cockpit. Just under the cockpit is the windmill for the servo system pump.

The Inflexible was made of duralumin, an aluminum alloy that incorporates copper, manganese, and magnesium for increased strength. The fuselage had a rectangular cross section and consisted of front and rear sections that were bolted together. Both sections were made of duralumin sheets riveted to a duralumin frame. Mounted to the rear of the fuselage were the horizontal and vertical stabilizers. The elevator spanned the entire length of the horizontal stabilizer. A Flettner servo tab trailed behind the rudder and controlled its movement.

The wings were formed by a wing box that bolted to the fuselage and made up the center wing section. An outer wing section bolted to each side of the wing box and was supported by two spars. Like the fuselage, the wing was covered with sheets of duralumin. A cable that kept each wing in tension while in flight connected the rear spar, at about two-thirds the span of the wing, to the lower fuselage. This cable was tensioned to about 3,000 lb (1,361 kg). The wings had a six-degree dihedral. Sections of the leading and trailing edges of the wings were hinged for access and inspection of the inner wing. The aircraft’s 656 US gal (546 Imp gal / 2,482 L) of fuel was carried in four wing tanks. The Inflexible did not have any flaps, but its large ailerons spanned the outer half of each wing’s trailing edge. Extending from each of the aircraft’s control surfaces was an aerodynamic balance horn.

The Inflexible was on hand at the Royal Air Force Display at Hendon in late June 1928. The aircraft now has “9” painted on the fuselage. In a size comparison, the Inflexible was displayed with a de Havilland DH.71 Tiger Moth (far left). The Tiger Moth’s 22 ft 6 in (6.59 m) wingspan was about one-eighth that of the Inflexible.

The aircraft’s immense weight was supported by two large main wheels and a steerable tailwheel. During component testing, wire wheels collapsed under the expected weight of the Inflexible. New wheels were designed and made from steel and aluminum. Mounted to the wheels were 90-in (2.29-m) tall tires, specially developed by the Dunlop Rubber Company. The weight of the large tires increased by 70 lb (32 kg) when they were filled with air. Each main wheel was supported by a shock-absorbing strut that extended from just inside the engine nacelle. An A-frame mounted to the lower fuselage secured each main wheel. The main gear had a track of 25 ft 7 in (7.80 m). For landing, the main wheels had a hydraulic braking system that could be automatically applied when the tail wheel connected with the ground. This system was designed by Rohrbach engineer Kurt Tank.

The Beardmore Inflexible had a wingspan of 157 ft 6 in (48.01 m), a length of 75 ft 6 in (23.01 m), and a height of 21 ft 2 in (6.45 m). The aircraft had a top speed of 110 mph (177 km/h) at sea level and 101 mph (163 km/h) at 6,500 ft (1,981 m). Its landing speed was 65 mph (105 km/h). The Inflexible had a climb rate of 359 fpm (1.8 m/s) and took 18 minutes and 06 seconds to reach 6,500 ft (1,981 m). The aircraft’s service ceiling was 9,350 ft (2,850 m). The Inflexible had an empty weight of 24,923 lb (11,305 kg), a gross weight of 31,400 lb (14,243 kg), and a maximum weight of 37,000 lb (16,783 kg). Reportedly, the aircraft could seat 20 passengers, but it does not appear that such accommodations were ever installed.

Beardmore-Inflexible-bottom

Underside of the Inflexible as it overflies the Royal Air Force Display at Hendon. The radiators for the wing-mounted engines are visible by the fuselage. Note the aerodynamic balance horns extending from all of the control surfaces.

Construction of the Inflexible progressed slowly and was often delayed by various material shortages. The aircraft was initially given civil registration G-EBNG on 29 December 1925. This registration was cancelled on 12 July 1927, and military serial number J7557 was assigned. The aircraft was completed at Dalmuir, near Glasgow, Scotland, in mid-1927. It was then broken down into various sections and transported by sea from Glasgow to Ipswich, England. However, the Aeroplane and Armament Experimental Establishment had no way to transport the large components from the Ipswich docks to the nearby Martlesham Heath Airfield. Disassembled, the two fuselage sections were 41 ft (12.50 m) long, and the outer wing sections were 61 ft (18.59 m) long. Moving the large sections of the Inflexible to Martlesham Heath required the construction of a special transport with steerable axles. Once assembled, the Inflexible’s wingspan was larger than any hanger opening at Martlesham Heath. Special trollies were built that supported each of the aircraft’s wheels and enabled movement in all directions. With the trollies, the aircraft could be moved sideways into the hanger.

Initial ground tests were started in January 1928, and the Inflexible was soon ready for flight tests when the weather was clear. The aircraft’s first flight occurred on 5 March 1928 and was flown by Jack Noakes. A Beardmore mechanic was also on the flight. The Inflexible took off in about 1,014 ft (309 m) and flew for 15 minutes; at the time, it was the world’s largest aircraft to fly. The Inflexible was stable in flight and exhibited good controls. Further flight testing revealed the aircraft to be underpowered, and its pitch and roll control was lacking in rough weather and at slow speeds. Wake turbulence from the fuselage-mounted engine also caused vibration issues with the aircraft’s tail.

Beardmore-Inflexible-flight

The Inflexible makes a pass during the Royal Air Force Display. The pilot, Jack Noakes, is just visible in the open cockpit.

The Inflexible was displayed for the public on at least three different occasions. On 27–30 June 1928, the aircraft was flown during the Royal Air Force Display at Hendon, near London. On 18–20 May 1929, it appeared at the Norwich Aero Club Air Display at the Mousehold Aerodrome. On 10 June 1929, the Inflexible was at the Cambridge Aero Club Display in Conington.

Beardmore struggled financially after World War I, and the aircraft department closed in February 1929. Rohrbach also suffered financial difficulties, and the company merged with a Deschimag subsidiary to form Weser Flugzeugbau GmbH in 1934. Although the Inflexible had demonstrated the feasibility of all-metal, stressed-skin construction, it would be a few years before the technique was fully adopted by the British aircraft industry. In January 1930, the Inflexible was disassembled for static tests at Martlesham Heath. The aircraft had accumulated 47 hours and 55 minutes of flight time. The engines were removed and placed into storage. After the static tests, the wings, fuselage, and other components were left exposed to the elements for corrosion tests. Occasionally, parts of the duralumin skin were removed and repurposed, and the fuselage served as a space for guards to get out of the weather. The remains of the Inflexible were eventually scrapped in 1931. The only surviving component of the aircraft is one main wheel, which is on display in the Science Museum, London.

Beardmore-Inflexible-side

Aerodynamic wheel covers were added to the aircraft sometime in early 1929. The Flettner tab controlling the rudder extended some distance behind the aircraft. The aerodynamic balance horns of the rudder and aileron are clearly visible.

Sources:
Beardmore Aviation 1913-1930 by Charles Mac Kay (2012)
British Prototype Aircraft by Ray Sturtivant (1990)
Jane’s All the World’s Aircraft 1928 by C. G. Grey and Leonard Bridgman (1928)
British Flight Testing: Martlesham Heath 1920-1939 by Tim Mason (1993)
– “Die Monster von Beardmore” by Philip Jarrett, Flugzeug Classic (May 2002)
https://earlyflightera.com/dr-adolf-rohrbach-chronicles-2/
https://en.wikipedia.org/wiki/Beardmore_Inflexible
https://en.wikipedia.org/wiki/Rohrbach_Metall-Flugzeugbau

Martin-XB-51-flight-top

Martin XB-51 Attack Bomber

By William Pearce

In February 1946, the United States Army Air Force (AAF) sought design proposals for an attack aircraft to replace the Douglas A-26 Invader. The Glenn L. Martin Company (Martin) responded with its Model 234, a straight-wing aircraft of a rather conventional layout, except that the engine nacelle on each wing housed a turboprop and a turbojet engine. The Model 234 had a crew of six and was forecasted to carry 8,000 lb (3,629 kg) of ordinance over 800 miles (1,287 km).

Martin-XB-51-flight-top

The Martin XB-51 was a unique attack bomber designed at the dawn of the jet age. The first prototype is seen here with its original tail. Note the inlet for the fuselage-mounted engine. The dark square behind the canopy is a window over the radio operator. (Martin/USAF image)

Martin was awarded a contract to develop the Model 234 on 23 May 1946, and the aircraft was designated XA-45. A few weeks later, the AAF decided to discard the “Attack” category, and the XA-45 was subsequently redesignated XB-51. The AAF then requested new requirements for the XB-51 with an emphasis on speed. The AAF’s new desired specifications for the A-26 replacement was a top speed of 640 mph (1,030 km/h) and the ability to carry 4,000 lb (1,814 kg) of ordinance over 600 miles (966 km). The new requirements necessitated a complete redesign of the XB-51, which Martin completed and submitted to the AAF in February 1947. After slight modifications, the design was somewhat finalized by July 1947. The AAF ordered two prototypes, which were assigned serial numbers 46-685 and 46-686.

The Martin XB-51 was a radical departure from the firm’s previous aircraft designs. The XB-51 was an all-metal aircraft that featured a relatively large fuselage supported by relatively small swept wings. The aircraft had a crew of two and was powered by three General Electric J47-GE-13 engines, each developing 5,200 lbf (23.13 kN) of thrust. Two of the engines were mounted on short pylons attached to the lower sides of the aircraft in front of the wings. The third engine was buried in the extreme rear of the fuselage.

Martin-XB-51-rollout

The XB-51 with its flaps up and its wing at an incidence of three degrees as the aircraft is rolled out on 4 September 1949. The circle on the side of the fuselage just behind the cockpit is a side window for the radio operator. There is no window mirrored on the left side of the aircraft. Note that the intake for the fuselage-mounted engine has its cover rotated closed. (Martin/USAF image)

The pilot sat in the front of the aircraft under what appeared to be a small canopy in contrast to the large fuselage. Behind the pilot and completely within the fuselage was the radio operator, who was also in charge of the short range navigation and bombing (SHORAN) system. The crew compartment was pressurized, and access was provided by a door on the left underside of the fuselage, between the pilot and radio operator’s stations. In case of an emergency, both crew were provided with upward firing ejection seats.

The engine housed in the rear fuselage was fed by an inlet duct located atop the fuselage. A rotating assembly was installed forward of the inlet to either cover the inlet with an aerodynamic fairing when the engine was not in use, or rotate to provide a duct to feed air to the engine. The rear engine could be shut down in flight to extend the aircraft’s range. When not in use, a door in the intake duct prevented the back flow of air through the rear engine. Large doors swung open beneath the fuselage to access the rear engine.

Martin-XB-51-color

The first XB-51 with flaps down and its wing at an incidence of 7.5 degrees. Note that only one of the wingtip outrigger gears is touching the ground. (Martin/USAF image)

Mounted above the rear engine was the vertical stabilizer, with the horizontal stabilizer mounted to its top. Originally, the XB-51’s design had the horizontal stabilizer mounted midway up the vertical stabilizer, but the aircraft was not built with this configuration. The horizontal stabilizer was swept back 35 degrees, and its incidence could be changed for trimming. Two rocket assisted takeoff (RATO) bottles could be fitted to each side of the rear fuselage. The RATO packs would be ignited to shorten the XB-51’s takeoff distance, then discarded once the aircraft was in flight. Each bottle provided 1,000 lbf (4.44 kN) of thrust. Hydraulically operated air brakes were located on each side of the fuselage, under the intake for the rear engine. A braking parachute was housed in the left side of a fairing located below the rudder.

The XB-51 used tandem (bicycle) main gear that consisted of front and aft trucks, and outrigger wheels that deployed from the aircraft’s wingtips for support. Martin had used a similar gear arrangement for the straight-wing XB-48 jet medium bomber and had initially tested the setup using the Martin XB-26H, a B-26 Marauder specially modified for to test the tandem landing gear. The main trucks could swivel to counteract the aircraft’s yaw while taking off or landing with a crosswind.

Martin-XB-51-ordinance

Ordinance for the XB-51 that would fit in the bomb bay. From left to right, four 1,600 lb (726 kg) bombs, eight 5 in (127 mm) High Velocity Aircraft Rockets (HAVR), one 4,000 lb (1,814 kg) bomb, four 2,000 lb (907 kg) bombs, four 1,000 lb (454 kg) bombs, and nine 500 lb (227 kg) bombs. The 4,000 lb (1,814 kg) bomb required an enlarged bomb bay door. (Martin/USAF image)

The aircraft’s bomb bay was located in the fuselage between the main wheels. The bomb bay had a single rotating door to which the bomb load was attached. Opening the rotating door did not create any buffeting or require any speed restriction normally required by two conventional doors. In addition, the rotating door was removable and could be quickly replaced with another door already loaded with ordinance. The standard door could accommodate nine 500 lb (227 kg) bombs, four 1,000 lb (454 kg) bombs; four 1,600 lb (726 kg) bombs; or two 2,000 lb (907 kg) bombs. Two additional 2,000 lb (907 kg) bombs could be accommodated on exterior bomb racks mounted on the bottom of the door. A special enlarged door could be fitted to carry a single 4,000 lb (1,814 kg) bomb or a Mk 5 or Mk 7 nuclear bomb. The XB-51’s maximum bomb load was 10,400 lb (4,717 kg). Eight 5 in (127 mm) High Velocity Aircraft Rockets (HAVR) could be carried in the bomb bay in place of internal bombs.

Three fuel tanks were installed in the aircraft’s fuselage. The forward tank was located above the front main gear and held 640 US gal (2,426 L). The center and aft tanks were both located above the bomb bay and held 745 US gal (2,820 L) and 1,450 US gal (5,489 L) respectively. All the standard fuel tanks could be filled via a single fueling receptacle. A 160.5 US gal (607.6 L) water/alcohol tank to boost engine performance during takeoff was mounted between the front and center fuel tanks. Two 350 US gal (1,325 L) tanks could be carried in the bomb bay for ferrying the aircraft over long distances. The XB-51 had a total normal fuel capacity of 2,835 US gal (10,732 L), and 3,535 US gal (13,381 L) with the bomb bay tanks.

Martin-XB-51-takeoff

The XB-51 executing a high-performance takeoff provides a good view of the aircraft’s leading-edge slats and large flaps. No RATO bottles are fitted. (Martin/USAF image)

In the nose of the XB-51 were eight fixed 20 mm cannons with 160 rpg and a forward strike camera. The nose of the second XB-51 was detachable, and different noses could be fitted depending on the aircraft’s mission. In addition to the standard gun nose, other noses featured equipment for precision bombing and equipment for photo-reconnaissance. As standard, the XB-51 had a reconnaissance camera installed under the cockpit and a strike assessment camera installed in the lower rear fuselage.

With fuel, engines, and the main landing gear all housed in the fuselage, the XB-51’s mid-mounted wings were very thin. The wings were swept back 35 degrees and had six degrees of anhedral. Outrigger wheels deployed from the wingtips to steady the aircraft on the tandem main gear. Slats extended along the outer 70 percent of the wing’s leading edge. Large, slotted flaps covered 75 percent of the wings trailing edge, with small ailerons taking up 15 percent of the trailing edge. While the ailerons contributed to aircraft’s roll control, their main purpose was to provide feedback for the pilot. The majority of roll control was provided by spoilers positioned on the wing’s upper surface, just forward of the flaps. The spoilers extended about 40 percent of the wing’s span. The incidence of the entire wing could vary from 2 to 7.5 degrees and would automatically change with deployment of the flaps. The wing incidence increased at lower speeds to decrease the aircraft’s stall speed and make the aircraft assume the correct attitude for landing, which was with the nose high approximately six degrees. The tandem landing gear required the simultaneous touchdown of both the forward and aft trucks. To prevent the accumulation of ice, hot air was bled off from the engines, directed through a passageway in the wing’s leading edge, and exhausted out the wingtip.

The Martin XB-51 had a 53 ft 1 in (16.18 m) wingspan, was 85 ft 1 in (25.93 m) long, and was 17 ft 4 in (5.28 m) tall. The track between the outrigger landing gear was 49 ft 5 in (15.06 m). The aircraft had a top speed of 645 mph (1,038 km/h) at sea level and 580 mph (933 km/h) at 35,000 ft (10,668 m). Cruising speed was 532 mph (856 mph) at 35,000 ft (10,668 m), and the aircraft’s landing speed was around 140 mph (225 km/h). The XB-51’s initial rate of climb was 6,980 ft (35.5 m/s) at maximum power and 3,600 ft (18.3 m/s) at normal power. The service ceiling was 40,500 ft (12,344 m); normal range was 980 miles (1,577 km), and ferry range was 1,445 miles (2,326 km). The XB-51 had an empty weight of 30,906 lb (14,019 kg), a combat weight of 44,000 (19,958 kg), and a gross weight of 55,930 lb (25,369 kg).

Martin-XB-51-ground

The first XB-51 undergoing an engine run. The bullet fairing has been added to the tail. Note the covered ports in the nose for the 20 mm cannons. (Martin/USAF image)

On 24 February 1948, a mockup of the XB-51 was inspected by the United States Air Force (USAF), which had become a separate branch of the US Armed Forces on 18 September 1947. Construction of the first prototype (46-685) proceeded swiftly at the Martin plant in Middle River, Maryland, and the completed aircraft was rolled out on 4 September 1949. After completing ground tests, aircraft 46-685 made is first flight on 28 October 1949, piloted by Orville Edward ‘Pat’ Tibbs. Initial flight testing went well until the rear main gear collapsed after landing on 28 December. The aircraft was repaired and returned to flight status in early 1950. High-speed testing had revealed some vibrations with the tail and a tendency to Dutch roll. A bullet faring was added at the intersection of the horizontal and vertical stabilizers in March 1950 to mitigate the issues.

The second prototype (46-686) made its first flight on 17 April 1950, piloted by Frank Earl ‘Chris’ Christofferson. Although 46-686 was initially flown with the original tail, bullet fairings were soon added. Both aircraft were involved in numerous landing accidents, mostly attributed to the tandem landing gear and the pilot’s lack of familiarity with its nuances. Nose high landings resulted in tail strikes that damaged the aft fuselage. Nose low and hard landings resulted in the collapse or shearing of the front main gear. Despite the landing difficulties, pilots seemed to like the aircraft and its performance. While the XB-51 could perform rolls and outpace some fighters, the aircraft was not stressed for aggressive maneuvers.

Martin-XB-51-flight

Another image of the first XB-51 with its bullet tail fairing. Note the RATO bottles attached to the rear fuselage. The shield painted under the cockpit says “Air Force Flight Test Center.” (Martin/USAF image)

The USAF considered putting the XB-51 into production, but the role for which the aircraft was intended had changed again with the outbreak of the Korean War. Speed was no longer the main focus, and the USAF now desired an aircraft that could loiter in an area until needed by ground forces. The USAF compared the XB-51 against the North American AJ-1 Savage and B-45 Tornado, the Avro Canada CF-100 Canuck, and the English Electric Canberra. Under the new criteria, the USAF selected the Canberra as the winner in February 1951, and the XB-51 program was essentially cancelled. The Canberra had more than twice the range and loiter time of the XB-51. The following month, Martin was awarded a contract to build the Canberra as the B-57, and the rotary-style bomb bay pioneered on the XB-51 was installed on the B-57. Ultimately, 403 B-57 aircraft would be produced. Both XB-51 aircraft continued to be evaluated and tested. The two XB-51s underwent performance and armament tests at Edwards Air Force Base (AFB) in California and Elgin AFB in Florida.

On 9 May 1952, the second prototype XB-51 was destroyed at Edwards AFB when Major Neal Lathrop executed a roll at low altitude and collided with the ground. Lathrop was the sole occupant on board. At the time of the accident, 46-686 had accumulated 151 hours of flight time and had made 193 flights.

Martin-XB-51-two-ship-plant

The second (left) and first (right) XB-51 aircraft at the Martin plant in Middle River. Both aircraft have the bullet tail fairings, and the second prototype (left) has RATO bottles attached. The Martin plant in the background still has the camouflage paint scheme applied during World War II. Compare the different flap and wing positions between the two aircraft. (Martin/USAF image)

The first prototype played the role of the “Gilbert XF-120” fighter in the 1956 movie “Toward the Unknown.” The movie was shot mostly at Edwards AFB in 1955. On 25 March 1956 the 46-685 was destroyed while taking off from El Paso Municipal (now International) Airport in Texas. The stop in El Paso was to refuel as the aircraft traveled from Edwards AFB to Eglin AFB. The accident occurred due to a premature rotation and subsequent stall. The radio operator, Staff Sergeant Wilbur R. Savage, was killed in the crash, and the pilot, Major James O. Rudolph, died of his injuries on 16 April 1956. The first XB-51 prototype had accumulated 432 hours and made 453 flights.

Performance of the Martin XB-51 had exceeded the manufacturer’s guarantees. However, the aircraft was designed and built at a time when USAF’s desires and priorities were rapidly shifting, and it turned out that the service did not really want the aircraft they had originally asked for. Pilots held the XB-51 in a high regard despite its demanding landing characteristics. Ultimately, the XB-51 faded into history as a short-lived experimental aircraft investigating a new direction at the dawn of the jet age.

Martin-XB-51-two-ship-pass

The second (right) and first (left) XB-51 aircraft make a low pass over Martin Field on 11 October 1950. Note the shadows of the aircraft on the runway. (Martin/USAF image)

Sources:
The Martin XB-51 by Scott Libis (1998)
“Martin XB-51” by Clive Richards, Wings of Fame Volume 14 (1999)
Martin Aircraft 1909–1950 by John R. Breihan, Stan Piet, and Roger S. Mason (1995)
Standard Aircraft Characteristics XB-51 by U.S. Air Force (11 July 1952)
Jane’s All the World’s Aircraft 1951-1952 by Leonard Bridgman (1951)
U.S. Bombers 1928 to 1980s by Lloyd S. Jones (1980)
https://www.avgeekery.com/the-xb-51-martins-movie-star-bomber-smashed-the-bomber-mold/
https://www.thisdayinaviation.com/tag/martin-xb-51/