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.

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.

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.

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.

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.

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).

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.

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

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 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 Takeoff” Enterprise (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

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.

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.

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.

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.

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.

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.

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.

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/

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).

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.

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.

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.

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.

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.

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.

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.

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