Category Archives: Between the Wars

vought-v-173-in-flight

Vought V-173 Flying Pancake (Zimmer’s Skimmer)

By William Pearce

In the early 1930s, Charles H. Zimmerman became determined to design a low-aspect ratio, flying wing aircraft with a discoidal planform. The wing would have a short span and make up the aircraft’s fuselage. Zimmerman believed that large, slow-rotating propellers placed at the tips of the aircraft’s wings would cancel out wingtip vortices, provide uniform airflow over the entire aircraft, and effectively increase the aircraft’s span. In addition, the propellers would provide continuous airflow over the aircraft’s control surfaces even at very low forward velocities. The propellers were counter-rotating; viewed from the rear, the left propeller turned counterclockwise and the right propeller turned clockwise. The envisioned aircraft would be able to execute short takeoffs and landings, maintain control at very low speeds, and have a high top speed. Zimmerman’s ultimate goal was a high-speed aircraft that could ascend and descend vertically and could hover.

zimmerman-three-place-aircraft

Drawings from Charles Zimmerman’s 1935 patent showing his low-aspect ratio, flying wing aircraft. Note the three occupants lying in a prone position. The aircraft’s layout was very similar to the Vought V-173. The power transfer shaft (22) can been seen connecting the two propeller shafts.

While working at the National Advisory Committee for Aeronautics (NACA), Zimmerman won a design competition in 1933 for a light, general aviation aircraft. However, his low-aspect ratio design was deemed too radical to be built. Undeterred, Zimmerman designed a three-place aircraft in which the occupants lay in a prone position. Zimmerman called this aircraft the Aeromobile. The aircraft’s propellers were forced to rotate at the same speed via a power cross shaft that linked the engine’s propeller shafts together. Each engine could be disconnected from its respective propeller shaft in the event of an engine failure. The power cross shaft would distribute power from the functioning engine to both propellers.

To test his theories, Zimmerman and some friends built a small proof-of-concept aircraft based on the three-place design. The aircraft had a short 7 ft (2.1 m) wingspan and was powered by two 25 hp (19 kW), horizontal, two-cylinder Cleone engines. Despite several attempts, the aircraft was unable to takeoff. The difficulties were caused by an inability to synchronize the propellers, as the power cross shaft was omitted due to the aircraft’s small size.

zimmerman-test-aircraft

The proof-of-concept aircraft built to test Zimmerman’s theories. This image illustrates the aircraft’s 7 ft (2.1 m) wingspan. Due to trouble with synchronizing the engines/propellers, the aircraft was not flown. Charles Zimmerman is on the right side of the image.

Following the unsuccessful trials of small aircraft, Zimmerman took a step back and turned to models. By 1936, he had a rubber band-powered scale model with a 20 in (508 mm) wingspan routinely making successful flights. Others at NACA reviewed Zimmerman’s work and encouraged him to seek financial backing from the aviation industry to further develop his designs—as an individual, his efforts to interest the US Armed Forces had not been successful. Zimmerman found support from Vought Aircraft and was hired on to continue his work in 1937.

Again, the radical nature of Zimmerman’s designs made the establishment question their worth. The US Army Air Corps turned down various proposals, but the US Navy could not overlook the fact that a short wingspan fighter with a short takeoff distance, a very low landing speed, and a high top speed would be ideal for carrier operations. In fact, such an aircraft could operate from just about any large ship. In 1938, the Navy funded the Vought V-162, which was a large model to further test Zimmerman’s ideas. The model was powered by electric motors and took two people to operate. The model sufficiently demonstrated Zimmerman’s design, and the Navy contracted Vought to build a full-size test aircraft on 4 May 1940. The aircraft was designated V-173 by Vought and was given Bureau Number (BuNo) 02978 by the Navy.

vought-v-173-wind-tunnel-side

The Vought V-173 in the Langley wind tunnel. Note the forward rake on the two-blade propellers. The rake (or cone angle) was adjustable, and three-blade propellers of the same type were soon fitted to the aircraft. (Langley Memorial Aeronautical Laboratory / NASA image)

The airframe of the Vought V-173 was made mostly of wood, but the forward cockpit structure and propeller nacelles were made of aluminum. The front part of the fuselage back to the middle of the cockpit was covered with wood, and the rest of the aircraft was fabric-covered. Originally, the pilot was to lie in a prone position, but this was changed to a more conventional, upright seat. The lower leading edge of the aircraft had glazed panels to improve visibility from the cockpit while the V-173 was on the ground. Cockpit entry was via a hatch under the aircraft, but the canopy also slid back. Housed in the aircraft’s fuselage were two 80 hp (60 kW) Continental C-75 engines. Most sources list the engines as Continental A-80s, but C-75s were actually installed in the aircraft. The 80 hp (60 kW) rating was achieved through the use of fuel injection. The C-75 was a flat, four-cylinder, air-cooled engine that displaced 188 cu in (3.1 L). One engine was on each side of the cockpit. The engines were started by pulling a handle through an access panel under the aircraft. Each engine had a cooling fan attached to its output shaft, and engine cooling air was brought in through inlets in the aircraft’s leading edge. The air exited via flaps in the upper fuselage.

Via shafts and right angle drives, the engines powered two 16 ft 6 in (5.06 m), three-blade, wooden propellers at around .167 times engine speed. The variable-pitch propellers turned around 450 rpm at maximum power (2,700 engine rpm) and around 415 rpm at cruise power (2,500 engine rpm). The individual blades could articulate (flap) automatically to compensate for side gusts and uneven loading. The blades were hinged inside the propeller hub in which hydraulic dampers limited their articulation. The rake (or coning) angle of the blades could be adjusted on the ground. This moved the tips of the blades either forward or aft relative to the propeller hub.

vought-v-173-wind-tunnel-front

Underside view of the V-173 shows the windows in the aircraft’s leading edge. The hinge line for the control surfaces between the tails can just be seen near the aircraft’s trailing edge. The surfaces were omitted when the aircraft first flew, but stabilizing flaps were later installed in their place. (Langley Memorial Aeronautical Laboratory / NASA image)

A power cross shaft that ran just behind the cockpit connected the engine gear boxes. The cross shaft ensured that power was delivered equally between the two propellers, and it also synchronized propeller rpm. A failed engine would automatically declutch from the propeller drive system, and the remaining engine would power both propellers. The left engine was started first and then clutched to the propeller drive system. The right engine was then started and automatically clutched to the propeller drive system after it came up to speed.

Under the V-173 were two very long fixed main gear legs that supported the aircraft at a 22.25 degree angle while it sat on the ground. At the rear of the aircraft were two vertical stabilizers. Attached to each side of the V-173 was a horizontal stabilizer with a surface that acted as both an aileron and an elevator (ailavator or ailevator). The ailavators were not part of the initial V-173 design (and were not on the V-162 model), but early model tests indicated that the flight controls were needed.

vought-v-173-in-flight

View of the V-173 on an early test flight that shows no stabilizing flaps between the tails. Note the deflection angle of the ailavator; the V-173 always flew at a nose-high angle because it was underpowered.

The V-173 had a wingspan of 23 ft 4 in (7.1 m) but was about 34 ft 9 in (10.6 m) wide from ailavator to ailavator. The aircraft was 26 ft 8 in (8.1 m) long and 12 ft 11 (3.9 m) in tall. The V-173 could take off in 200 ft (61 m) with no headwind, and it could lift right off the ground with virtually no roll in a 30 mph (48 km/h) headwind. The aircraft’s top speed was 138 mph (222 mph), and cruising speed was 75 mph (121 km/h). With normal prevailing winds, the V-173 would routinely take off in 20 ft (6 m) and land at 15 mph (24 km/h). The aircraft had an empty weight of 2,670 lb (1,211 kg) and a normal weight of 3,050 lb (1,383 kg). The V-173 only carried 20 gallons (76 L) of fuel in two 10 gallon (38 L) tanks.

In November and December 1941, the V-173 was tested in NACA’s Langley wind tunnel in Hampton, Virginia. The aircraft had its original two-blade propellers, but these were found to be insufficient and were replaced by three-blade units shortly after the tests. Two small control surfaces that made up the trailing edge of the aircraft were present between the tails. However, these were removed before the V-173’s first flight. The Navy was encouraged enough by the wind tunnel tests that they asked Vought to prepare a proposal for a fighter version of the aircraft, which eventually became the Vought XF5U-1.

vought-v-173-rear

The V-173 is shown with redesigned ailavators and the stabilizing flaps installed. The cooling air exit flaps can be seen near the cockpit. The two ports forward of each cooling air exit flap were for engine exhaust.

After an extended period of taxi tests, the V-173’s first flight took place on 23 November 1942 at Bridgeport Airport (now Sikorsky Memorial Airport) in Stratford, Connecticut, with Vought test pilot Boone T. Guyton at the controls. Guyton found the aircraft’s controls extremely heavy and thought that he might need to make a forced landing. Fortunately, He had enough control to make a large circuit and land the aircraft after 13 minutes of flight. Adjustments to the propellers were made, and the ailavators were redesigned as all-moving control surfaces with servo tabs. These changes improved aircraft control, but landing the V-173 was still difficult. As it approached the ground, air would get trapped under the aircraft and force the tail up. Subsequently, the nose of the aircraft would drop, causing the V-173 to rapidly descend the last few feet. The aircraft would hit the runway harder than intended and bounce back into the air. After about 40 flights, the two stabilizing flaps were added between the aircraft’s tails. The flaps were larger than the control surfaces tested in the wind tunnel, and they were separated by the tailwheel. When the aircraft was near the ground, air loads acted on spring-loaded struts to automatically deflect the stabilizing flaps up and allow air to escape from under the aircraft.

A number of different pilots, including Charles Lindberg, flew the V-173. Over its flight career, the aircraft did experience a few difficult landings that resulted in minor damage. The most serious issue occurred on 3 June 1943 when Vought-pilot Richard Burroughs made an emergency landing on Lordship Beach, Connecticut. Vapor lock had caused fuel starvation and subsequent engine failure. Immediately after touchdown, Burroughs flipped the V-173 onto its back to avoid hitting a sunbather. No one was injured, and the aircraft was not seriously damaged.

vought-v-173-runup

The V-173 undergoing an engine run. The engine cooling air intakes can be seen in the aircraft’s leading edge. The canopy is open, and the cockpit access hatch on the aircraft’s underside is also open. Note that the stabilizing flaps are deflected up and that streamlined fairings have been fitted to cover the wheels.

Overall, the V-173 flew as expected, but it was not entirely like a conventional aircraft. The V-173 was underpowered, and there were unresolved vibration issues caused by the propeller gearboxes and drive shafts. The aircraft made around 190 flights and accumulated 131 hours of flight time.

The V-173 made its last flight on 31 March 1947. The Navy kept the aircraft in storage at Norfolk Naval Air Station, Virginia for a number of years and gave it to the National Air and Space Museum in September 1960. The V-173 was stored at the Paul E. Garber Facility in Suitland, Maryland until 2003, when it was moved to Vought’s Grand Prairie facility near Dallas, Texas for restoration by the Vought Aircraft Heritage Foundation. Restoration was completed in February 2012, and the aircraft was loaned to Frontiers of Flight Museum in Dallas, where it is currently on display.

Zimmerman’s aircraft were given several nicknames during their development: Zimmer’s Skimmer, Flying Flapjack, and Flying Pancake. Test pilot Guyton said that the V-173 could fly under perfect control while maintaining a 45 degree nose-up angle with full power and full aft stick. During the flight test program, the pilots were not able to make the V-173 stall completely or enter a spin. The aircraft rapidly decelerated in sharp turns, and this could prove advantageous in getting on an opponent’s tail during a dogfight. But if the shot were missed, the aircraft could be at a disadvantage because of its decreased speed. The V-173 proved the viability of Zimmerman’s low-aspect ratio, flying wing aircraft concept, provided much information on how to refine the design, and directly contributed to the Vought XF5U-1.

vought-v-173-restored

Painstakingly restored by volunteers, the V-173 is currently on display in the Frontiers of Flight Museum in Dallas, Texas. The aircraft is on loan from the National Air and Space Museum until at least 2022. (Frontiers of Flight Museum image)

Sources:
Chance Vought V-173 and XF5U-1 Flying Pancakes by Art Schoeni and Steve Ginter (1992)
Aeroplanes Vought 1917–1977 by Gerard P. Morgan (1978)
“Aircraft” US patent 2,108,093 by Charles H. Zimmerman (applied 30 April 1935)
“The Flying Flapjack” by Gilbert Paust Mechanix Illustrated (May 1947)
https://www.youtube.com/watch?v=SSkVC9bC_Mg
http://www.vought.org/products/html/v-173.html
http://www.airspacemag.com/history-of-flight/restoration-vought-v-173-7990846/?all
https://crgis.ndc.nasa.gov/historic/Charles_H._Zimmerman
http://www.flightmuseum.com/exhibits/aircraft-3/aircraft-3/
Correspondence with Bruce Bleakley, Director of the Frontiers of Flight Museum

pander-s4-engine-run

Pander S.4 Postjager Trimotor Mailplane

By William Pearce

In the early 1930s, Dutch pilot Dirk Asjes was disappointed with the slow development of Dutch airmail flights and Fokker aircraft. Asjes sketched out an aircraft design and asked the aircraft manufacturer Pander to build a special mailplane to compete with KLM (Koninklijke Luchtvaart Maatschappij or Royal Dutch Airlines) mail and passenger service. Officially, Pander was called the Nederlandse Fabriek van Vliegtuigen H. Pander & Zonen (H. Pander & Son Dutch Aircraft Company). Pander was a furniture company that had expanded to aircraft construction in 1924 when its owner, Harmen Pander, purchased the bankrupt VIH (Vliegtuig Industrie Holland or Holland Aircraft Industry).

pander-s4-engine-run

The Pander S.4 Postjager displays its clean lines. The trimotor aircraft was purpose-built as a mail carrier to fly from Amsterdam to Batavia.

Airmail service to the Dutch East Indies involved using the relatively slow Fokker F.XVIII, which had a top speed of 149 mph (240 km/h). To improve service, KLM ordered the Fokker F.XX Zilvermeeuw, which had a top speed of 190 mph (305 km/h). While the F.XX was being built, Pander took up the challenge to build a faster aircraft solely to transport mail. Pander’s new design was the S.4 Postjager, and financial support came from a few Dutch shipping companies who hoped to break KLM’s monopoly on air transport to the East Indies.

The Pander S.4 Postjager was designed by Theodorus (Theo) Slot, who was originally with VIH. The aircraft was a low-wing trimotor with retractable main gear. The S.4 was made almost entirely of wood. The aircraft was powered by three 420 hp (313 kW) Wright Whirlwind R-975 engines. The aircraft’s interior was divided into three compartments: cockpit, radio room, and mail cargo hold.

pander-s4-takeoff

On paper, the S.4 appeared to be an impressive, purpose-built aircraft that could improve airmail service for the Netherlands. In practice, the aircraft never had an opportunity to fully demonstrate its capabilities without outside difficulties hindering its performance.

The S.4 used external ailerons that mounted above the wings’ trailing edge. Sometimes called “park bench” ailerons because of their appearance, they are often mistaken for Flettner tabs. A Flettner tab is a supplementary control surface that attaches to and assists the primary control surface. By contrast, a “park bench” aileron is the primary control surface, and there is no other control surface integral with the wing. External ailerons operated in the undisturbed airflow apart from the wing and were more responsive during minor control inputs or during slow flight. In addition, external ailerons allowed the use of full-span flaps to give the aircraft a low landing speed. However, external ailerons had a tendency to flutter at higher speeds, potentially causing catastrophic damage to the aircraft (but flutter was not well understood in the 1930s). On the S.4, the flaps extended from the engine nacelles to near the wingtips.

The S.4 had a wingspan of 54 ft 6 in (16.6 m) and was 41 ft (12.5 m) long. The aircraft had a maximum speed of 224 mph (360 km/h), a cruising speed of 186 mph (300 km/h), and a landing speed of 60 mph (97 km/h). The S.4 was designed to carry 1,102 lb (500 kg) of mail. It had an empty weight of around 6,669 lb (3,025 kg) and a loaded weight of around 12,125 lb (5,200 kg). Six fuel tanks, three in each wing, carried a total of 555 gallons (2,100 L). The aircraft had a range of 1,510 miles (2,430 km) and a ceiling of 17,717 ft (5,400 m).

pander-s4-underside

This underside view of the S.4 shows its PH-OST registration. Also visible are the external ailerons attached to the wings’ upper surfaces. The aircraft’s slot flaps (not visible) extended from the engine nacelle to near the wingtip.

Cleverly registered as PH-OST, the completed S.4 mailplane made its public debut on 23 September 1933. The Fokker F.XX also made its debut at the event, which was attended by Prince Henry of the Netherlands. The S.4 flew the following month, when Gerrit Geijsendorffer and Funker van Straaten made the maiden flight on 6 October 1933. Flight testing went well, and on 9 December 1933, the S.4 departed on an 8,700-mile (14,000-km) flight from Amsterdam to Batavia (now Jakarta, Indonesia). Flown by Geijsendorffer, Asjes, and van Straaten, this flight was a special run to demonstrate the aircraft’s speed and range and also to deliver 596 lb (270 kg) of Christmas mail (made up of some 51,000 letters and postcards) to the Dutch colony. At the time, the Fokker F.XX was being prepared for the same flight.

The S.4 had made a scheduled stopover in Rome, Italy and was proceeding to Athens, Greece when the right engine lost oil pressure. The aircraft made an emergency landing in Grottaglie, Italy, and inspection revealed that the right engine needed to be replaced. With no engines available anywhere in Europe, one was shipped from the United States and set to arrive on 22 December. This setback put the Christmas mail service in jeopardy. To make sure the mail was delivered, arrangements were made for the F.XX to pick up the S.4’s mail and continue to Batavia. But, the F.XX had its own engine issues before it even took off. This left the Fokker F.XVIII, the aircraft the S.4 and F.XX were meant to replace, as the only alternative. A F.XVIII picked up the mail and continued to Batavia with enough time for Christmas delivery. The failed Christmas flight was a huge embarrassment for both the S.4 and F.XX programs.

pander-s4-ground-side

This side view of the S.4, now named Panderjager, shows the aircraft as it appeared in the MacRobertson Race. Note the “park bench” aileron extending above the wing.

The repaired S.4 set out for Batavia on 27 December and arrived on 31 December. It made the return flight, leaving Batavia on 5 January 1934 and arriving in Amsterdam on 11 January. Although the S.4 averaged 181 mph (291 km/h) on the flight from Batavia, the aircraft’s mail flight failed to impress, and the S,4 was not put into service. Pander decided to prepare the aircraft for the MacRobertson Trophy Air Race flown from London to Melbourne, Australia.

The MacRobertson Race started on 20 October 1934 and covered some 11,300 miles (18,200 km). For the race, the S.4 was flown by Geijsendorffer, Asjes, and Pieter Pronk and carried race number 6. The aircraft had been renamed Panderjager, but some referred to it as the Pechjager (“pech” meaning “bad luck” and “breakdown”). After leaving Mildenhall airfield in England, the S.4 arrived in Bagdad, Iraq in third place at the end of the first day of the race. The next day, the aircraft proceeded to Allahabad, India, still in third place. Upon touchdown in Allahabad, the left gear collapsed, resulting in bent left and front propellers and a damaged left cowling and main gear.

pander-s4-rear

This rear view of the S.4 shows the external brace on the horizontal stabilizer and the elevators’ trim tabs. The image also provides a good view of the “park bench” ailerons.

Allahabad did not have the facilities to repair the S.4. Geijsendorffer took the propellers and traveled by train to the KLM depot in Calcutta (now Kolkata), India to make the needed repairs. This delay took the S.4 out of competition, but the decision was made to finish the race. Repairs were completed, and the S.4 was ready to fly on the evening of 26 October 1934. A service vehicle towing a light was positioned across the field from the S.4 to illuminate its path. The S.4’s crew found the light distracting and asked for it to be shut off, as the aircraft could provide its own lighting.

Once the service vehicle’s light was shut off, the S.4 prepared for takeoff. Unfortunately, the crew of the service vehicle misunderstood the instructions. They thought they were to proceed to the S.4 and illuminate the aircraft from behind. As they made their way toward the S.4 in darkness, the aircraft began its takeoff run. At about 99 mph (160 km/h), the S.4’s right wing struck the service vehicle. Fuel spilled from the ruptured wing and quickly ignited as the S.4 skidded 427 ft (130 m) to a stop. Pronk was uninjured, and Geijsendorffer and Asjes escaped with minor burns, but the S.4 was completely destroyed by the fire. The two operators of the service vehicle were severely injured.

Pander planned to convert the S.4 to a scout or bomber after the race and sell it to the military. With the loss of the S.4, there was no aircraft to sell, and Pander was not able to recover its expenses. The company went out of business a short time later.

The S.4 sits at Allahabad, India with bent propellers on its front and left engines. The de Havilland DH 88 Comet “Black Magic” suffered engine trouble, and work to repair its engine was underway as it sat next to the S.4. The S.4 never left Allahabad.

The S.4 sits at Allahabad, India with bent propellers on its front and left engines. The de Havilland DH 88 Comet “Black Magic” suffered engine trouble, and work to repair its engine was underway as it sat next to the S.4. The S.4 never left Allahabad.

Sources:
Nederlandse Vliegtuigen Deel 2 by Theo Wesselink (2014)
Jane’s All the World’s Aircraft 1934 by G. G. Grey (1934)
Blue Wings Orange Skies by Ryan K. Noppen (2016)
“High-Speed Mail Machine” Flight (7 September 1933)
“The Aerial Phost” Flight (5 October 1933)
“Opening of Amsterdam Aero Club’s New Clubhouse” Flight (28 September 1933)
“The Pander Postjager Pauses” Flight (14 December 1933)
http://www.aviacrash.nl/paginas/panderjager.htm
https://de.wikipedia.org/wiki/Pander_S4
https://en.wikipedia.org/wiki/Pander_%26_Son

savoia-marchetti-s65-calshot

Savoia-Marchetti S.65 Schneider Racer

By William Pearce

After the Italian team was defeated on its home turf at Venice, Italy in the 1927 Schneider Trophy Race, the Italian Ministero dell’Aeronautica (Air Ministry) sought to ensure victory for the 1929 race. The Ministero dell’Aeronautica instituted programs to enhance aircraft, engines, and pilot training leading up to the 1929 Schneider race. Early in 1929, the Ministero dell’Aeronautica requested racing aircraft designs from major manufacturers and encouraged unorthodox configurations.

savoia-mrachetti-s65-orig-config

The Savoia-Marchetti S.65 in its original configuration. Note the single strut extending from each float to the tail, the short tail and rudder, and the short windscreen.

Alessandro Marchetti was the chief designer for Savoia-Marchetti and was preoccupied with the design of the long-range S.64 aircraft. Originally, he did not submit a Schneider racer design, but the Ministero dell’Aeronautica encouraged him to reconsider. Soon after, Marchetti submitted the rather unorthodox S.65 design. On 24 March 1928, the Ministero dell’Aeronautica ordered two S.65 aircraft and allocated them the serial numbers MM 101 and MM 102.

The Savoia-Marchetti S.65 was a low-wing, tandem-engine, twin-boom monoplane that utilized two long, narrow floats. The aircraft was designed to incorporate the largest amount of power in the smallest package. The S.65’s tension rod and wire-braced wings were made of wood and almost completely covered with copper surface radiators. The floats were made of wood (some say aluminum), had a relatively flat bottom, and housed the S.65’s fuel tanks. The floats were around 28 ft 8 in (8.75 m) long and were mounted on struts. Originally, one strut extended from the rear of each float to the tail, but a second strut was later added.

savoia-marchetti-s65-2nd-config

The S.65 has been modified with an additional strut extending from each float to the tail. The tail and rudder have also been extended below the horizontal stabilizer. Note that the windscreen has not changed, that the rudder has a rather square lower trailing edge, and that there are no handholds in the wingtips.

A narrow boom extended behind each wing to support the tail. The boom was hollow and had flight cables running through its interior. Sources disagree on whether the booms were made of metal or wood. The horizontal stabilizer was mounted between the ends of the booms. The vertical stabilizer was positioned in the center of the horizontal stabilizer. Originally, the rudder and tail extended only above the horizontal stabilizer, and the rudder was notched to clear the elevator. Later, the tail and rudder were enlarged and extended below the horizontal stabilizer, and the elevator was notched to clear the rudder. The tail and all control surfaces were made of wood and were fabric-covered.

Attached to the wing was a small fuselage nacelle that housed two Isotta Fraschini Asso 1-500 engines. The engines were mounted in a push-pull configuration with one engine in front of the cockpit and the other behind. The nacelle was made of a tubular steel frame and covered with aluminum panels. Oil coolers were mounted on both sides of the cockpit between the engines. Two windows to improve the pilot’s lateral visibility were positioned above each oil cooler. Just behind the front engine was a windscreen for the cockpit. Initially, a short windscreen was installed, but this was later replaced by a longer, more streamlined unit. The fuselage nacelle was around 18 ft (5.48 m) long, including the propeller spinners.

isotta-fraschini-1-500-s65-engine

The 1,050 hp (783 kW) Isotta Fraschini Asso 1-500 engine. It is unclear how much this engine differed internally from a standard Asso 500 engine. The three cantilever mounts and the nearly-flush rear of the engine can clearly be seen. The exhaust ports have been relocated from the outer side of the cylinder head to the Vee side. A water pump and magneto are just visible on the extended gear reduction case. The vertical ribbing on the lower crankcase served to increase its strength.

The S.65’s Asso 1-500 V-12 engines were based on the Asso 500 Ri engine and were heavily modified by Giustino Cattaneo, head engineer at Isotta Fraschini. The engine’s crankcase was ribbed and strengthened to become a structural member of the S.65’s fuselage nacelle. Each engine mounted directly to a steel bulkhead on the end of the cockpit via three cantilever supports. The rear of the engine sat flush with the bulkhead. At the front of the engine was an extended gear reduction case which allowed for a streamlined cowling. Engine accessories, such as the two water pumps and two magnetos, were mounted to the gear case. Each Asso 1-500 engine produced 1,050 hp (783 kW) at 3,000 rpm.

At the bottom of each side of the cowling were two inlets. Air flowed from each inlet into a carburetor and then into three cylinders of the engine. Exhaust ports were located on the Vee side of the engine, and the exhaust gases were expelled up though the top of the cowling. Both engines turned counter-clockwise. Since the rear engine was installed backward, the propellers of each engine turned in opposite directions relative to one another. This installation effectively cancelled out the propeller torque that had been an issue for a number of Schneider racers. The metal, two-blade, fixed pitch propellers had a diameter of approximately 7 ft 5 in (2.26 m). The rear propeller’s spinner was about one-third longer than the front spinner.

savoia-marchetti-s65-calshot

The S.65 as seen at Calshot, England. The long windscreen has now been installed. The lower trailing edge of the rudder is now rounded, and the wingtips now have handholds. This image gives a good view of the surface radiators that cover nearly all of the wings. Also visible is the rectangular cover of the exhaust ports between the cylinder banks.

Italian sources and drawings from Savoia-Marchetti list the S.65 as having a wingspan of 31 ft 2 in (9.5 m) and a length of 35 ft 1 in (10.7 m). However, other sources often cite a wingspan of 33 ft (10.05 m) and a length of 29 ft (8.83 m). It is not entirely clear which figures are correct. The weight of the aircraft was approximately 5,071 lb (2,300 kg) empty and 6,173 lb (2,800 kg) loaded. The top speed of the S.65 was estimated between 375 and 400 mph (600 and 645 km/h).

In mid-1929, Alessandro Passaleva, one of Savoia-Marchetti’s pilots, tested the first S.65 (MM 101) on Lake Maggiore, near the company’s factory in Sesto Calende, Italy. Although the aircraft was not flown, Passaleva recommended a number of changes to stiffen and improve the S.65’s tail. The second S.65 (MM 102) was modified with the additional tail brace and extended rudder and tail. It is doubtful that MM 101 was ever flown or that MM 102 was flown on Lake Maggiore. MM 102 was delivered to the Reparto Alta Velocità (High Speed Unit) at Desenzano on Lake Garda in July 1929.

Initial flight tests of the S.65 were conducted by Tommaso Dal Molin and began in late July 1929. This is most likely the first time an S.65 was flown. Dal Molin was an experienced pilot and also small enough to fit inside the S.65’s very cramped cockpit. Some accounts state that Dal Molin did not bother with a parachute because the cockpit was so small, and the rear propeller made bailing out nearly impossible. A number of issues were encountered with the aircraft’s engines and cooling system. In addition, exhaust fumes constantly entered the cockpit.

savoia-marchetti-s65-calshot-runup

This image shows the S.65’s rear engine being run-up at Calshot. The oil radiator is clearly seen between the two engines, and it gives some perspective as to the small size of the cockpit. Note the various engine accessories mounted to the extended gear reduction case.

It was soon obvious that the S.65 would not be ready in time for the Schneider Trophy Race held on 6–7 September 1929 in Calshot, England. However, the Italians decided to send the aircraft anyway, to give the British team something to consider. Before the S.65 arrived at Calshot, the lower rudder extension was rounded; the longer windscreen was installed, and handholds were added to the wingtips. During the races, the S.65 MM 102 was displayed, and its rear engine was run-up on at least one occasion. Some saw the S.65 as a sign of future high-speed aircraft to come.

Italy had developed four new aircraft for the 1929 Schneider Trophy Race: Macchi M.67, FIAT C.29, Savoia-Marchetti S.65, and Piaggio P.7. The end result was that Italian resources were spread too thin, and none of their aircraft were developed to the point of offering serious competition to the British effort, which was victorious. Once back in Italy, the head of the Reparto Alta Velocità, Mario Bernasconi, decided to recover some pride by making an attempt on the world speed record. Britain had just set a new record on 12 September 1929 at 357.7 mph (575.7 km/h) in its Schneider race-winning Supermarine S6 (N247) piloted by Augustus Orelbar.

savoia-marchetti-s65-dal-molin-calshot

Tommaso Dal Molin poses in front of the S.65. Note the longer windscreen and the side windows just above the oil cooler. Each rectangular port on the cowling leads to a carburetor. Also visible are the louvers that cover the cowling.

The S.65 underwent further refinements in late 1929, and it was believed that the aircraft could exceed the S6’s speed by a reasonable margin. It appears the aircraft was fitted with new aluminum (duralumin), V-bottom floats. In addition, the engine cowling had what appear to be six exhaust ports positioned on each side. Exhaust fumes entering the cockpit was an issue due to the central exhaust location, and relocating the ports to the engine sides (their original location in the Asso 500 engine) would help solve the issue. The carburetor intakes were not changed.

Dal Molin took the S.65 on a test flight from Lake Garda on 17 January 1930 to prepare for his speed record attempt the following day. On 18 January, Dal Molin made three takoff attempts, which were all aborted due to excessive yaw. On the fourth attempt, the S.65 became airborne and then pitched up at an extreme angle. The aircraft stalled some 80 to 165 ft (25 to 50 m) above the water and crashed into the lake. Rescue vessels arrived quickly, but the S.65 with Dal Molin still aboard had quickly sunk 330 ft (100 m) to the bottom of the lake. It was Tommaso Dal Molin’s 28th birthday. A special recovery vessel called the Artigilo retrieved the S.65 on 29 January. Dal Molin’s body was recovered on 30 January. While the exact cause of the crash was never determined, many believe the elevator jammed, resulting in the abrupt pitch up and subsequent stall.

Note: As mentioned above, many sources disagree on various aspects of the S.65. For example, sources (some of which were not used in this article) list the wing spars as being made from four different materials: duralumin, walnut, mahogany, and spruce. While images were closely scrutinized to give an accurate account of the S.65 in this article, only so much can be determined from analyzing a grainy, 85-year-old image. In addition, some sources claim that only one S.65 was built (MM 102). Others say construction of MM 101 was started but never completed, and still others contend that MM 101 was completed and stored at the Reparto Alta Velocità at Lake Garda until 1939.

savoia-mrachetti-s65-recovery

The remains of the S.65 after it was recovered from Lake Garda and placed onboard the Artigilo. The rear engine is in the foreground. Note what appear to be exhaust ports along the sides of the cowling. The aircraft’s fuselage seems to be rather undamaged. Reportedly, the S.65 sank quickly, and some sources claim that Dal Molin could not swim.

Sources:
Schneider Trophy Seaplanes and Flying Boats by Ralph Pegram (2012)
Aeroplani S.I.A.I. 1915–1945 by Giorgio Bignozzi and Roberto Gentilli (1920)
Schneider Trophy Aircraft 1913–1931 by Derek N. James (1981)
MC 72 & Coppa Schneider by Igino Coggi (1984)
L’epopea del reparto alta velocità by Manlio Bendoni (1971)
http://wwwteamgrs-marco.blogspot.com/2015/04/il-recupero-della-salma-del-pilota.html

Koolhoven FK55 mockup front

Koolhoven FK.55 Fighter

By William Pearce

In November 1936, the Dutch aircraft manufacturer Koolhoven surprised many by bringing a very advanced fighter aircraft mockup to the Paris Salon de l’Aviation (Air Show). Mounted on stands to make it appear suspended in flight, the Koolhoven FK.55 mockup caught everyone’s attention. The impressive mockup was so detailed that anyone who did not study it for a period of time would think that it was a real aircraft. But converting the unique ideas showcased in the mockup into a workable aircraft would pose serious problems for Koolhoven.

Koolhoven FK55 mockup front

The sleek lines of the Koolhoven FK.55 can be seen in this image of the mockup at the 1938 Paris Salon de l’Aviation. Note the machine guns mounted in the wings and the radiators in the aircraft’s nose. The outline of the aircraft’s main gear is just visible under the wings.

The FK.55 was designed by company founder Frederick (Frits) Koolhoven. The mockup was of all wooden construction and featured an aerodynamic fuselage with a somewhat triangular cross section. One corner of the triangle formed the lower part of the fuselage, and the wings extended from the other two (upper) corners. The shoulder-mounted wings were well blended into the fuselage and located just behind the cockpit. The wing center section was built integral with the fuselage.

The FK.55 mockup did not include ailerons. Roll control was to be achieved by slot-spoilers in the outer wing sections. While the “slots” did exist, the “spoilers” were never installed on the mockup, and the slots were covered by aluminum panels. The pivot point of the retractable main landing gear was just off the aircraft’s center line. The legs of the main gear had a bend that allowed them to retract flush into the sides of the fuselage and underside of the wings. At the rear of the aircraft was a non-retractable tail skid.

Koolhoven FK55 mockup gear

The elaborate FK.55 mockup being built at the Koolhoven factory. The very long main gear posed problems when adapted to the prototype.

It is not clear whether or not an engine was actually installed in the mockup. If an engine was installed, it was a Lorraine Pétrel water-cooled V-12 engine installed behind the cockpit and at the aircraft’s center of gravity. A shaft extended from the engine, ran under the pilot’s seat, and connected to a propeller gear reduction unit in the nose of the aircraft. The gear reduction unit enabled the use of contra-rotating propellers. Metal, fixed-pitch propellers were fitted to the prototype.

A cannon could be positioned behind the gear reduction unit and fire through the propeller hub. Each wing had a machine gun installed outside of the propeller arc. Radiators were located on each side of the mockup’s cockpit, between the nose and the wings. Two scoops under the mockup’s fuselage provided air to the engine. The position of the cockpit, forward of the wings and at the very front of the aircraft, provided the pilot an excellent view.

The FK.55 mockup had a 29.5 ft (9.0 m) wingspan and was 27.6 ft (8.4 m) long. The complete aircraft was forecasted to weigh 2,425 lb (1,100 kg) empty and 3,638 lb (1,650 kg) loaded. Estimated performance for the FK.55 included a top speed of 323 mph (520 km/h) at 13,123 ft (4,000 m) and a cruising speed of 280 mph (450 km/h) at the same altitude. The aircraft had an initial rate of climb of 2,983 fpm (15.2 m/s), a service ceiling of 31,496 ft (9,600 m), and a range of 559 mi (900 km).

Koolhoven FK55 mockup

Suspended on stands, the FK.55 mockup was an impressive sight. Note the tail skid and the aluminum covers over the openings for the slot-spoilers.

Back in their factory at Waalhaven Airport in Rotterdam, Netherlands, the Koolhoven team went to work building a flying FK.55 prototype. The aircraft grew wider, longer, heavier, and slower than the original estimates. Each change necessitated another change as the FK.55 prototype came together, and what was once the sleek airframe of the FK.55 mockup eventually resembled a “pregnant duck” (in the words of one Dutch pilot).

The triangular cross section of the mockup’s fuselage had been replaced by a larger, mostly circular form. The wings had lost their blended look and now appeared tacked onto the fuselage. Strength issues with the long and complex landing gear necessitated using fixed gear temporarily attached to the fuselage until the retractable gear issues could be resolved. The front and middle sections of the fuselage were made from welded steel tubing, while the rear section and tail were made from wood. The wings were also made of wood and had split flaps and ailerons. The FK.55 maintained provisions for a 20 mm or 37 mm cannon to fire though the propeller hub, and each wing now housed two machine guns with 500 rpg. However, no armament was installed in the prototype.

Lorraine Petrel and Sterna engine CR props

The Lorraine Pétrel engine (top) and the Sterna (bottom). Note how the front propeller rotates clockwise on the Pétrel but counterclockwise on the Sterna. Roughly translated, the sign under the Sterna reads, “The engine Lorraine Sterna 900 hp; Has offset reducer and double propellers; Dutch Koolhoven FK.55 in flight since 1938.”

There is some disagreement about which engine powered the FK.55 prototype. Most sources state an 860 hp (641 kW) Lorraine Pétrel 12Hars was used, but the 12Hars typically produced around 700 hp (522 kW). Some sources claim a 1,000 hp (746 kW) Lorraine Sterna was used. A 900 hp (671 kW) Sterna with an extension shaft and propeller gear reduction unit was displayed at the Paris Salon de l’Aviation in November 1938. A sign under the engine indicated that it was intended for the FK.55, but it is doubtful that the engine was ever installed in the aircraft, as the FK.55 flew before the 1938 Salon. In images of the FK.55 prototype, the gear reduction unit appears to be the one used with the Pétrel engine. In addition, the front propeller of the Pétrel engine rotated clockwise. The front propeller on both the FK.55 mockup and prototype also rotated clockwise; however, the front propeller of the Sterna engine rotated counterclockwise. Therefore, the Pétrel engine was most likely used, with the Sterna intended to replace it in the near future.

Two two-blade, adjustable-pitch, metal Ratier propellers were installed. The engine’s induction scoops had grown in size and were now positioned on the lower sides of the prototype. The radiators were retained in their original position but had also grown in size, again spoiling the aircraft’s aerodynamics.

The FK.55 prototype had a 31.5 ft (9.60 m) wingspan and was 30.3 ft (9.25 m) long. The complete aircraft weighed 3,527 lb (1,600 kg) empty and 5,027 lb (2,280 kg) loaded. The performance estimates for the FK.55 had been reduced to a top speed of 317 mph (510 km/h) at 11,811 ft (3,600 m) and a cruising speed of 280 mph (450 km/h) at the same altitude. The aircraft had an initial rate of climb of 1,367 fpm (6.9 m/s), a service ceiling of 33,136 ft (10,100 m), and a range of 528 mi (850 km).

Koolhoven FK55 prototype front

The FK.55 prototype was an odd and awkward aircraft, especially when compared to the mockup. Note the fixed landing gear and that the front propeller turned clockwise (when viewed from the rear).

In June 1938, the FK.55 was trucked to Welschap Airfield, a more secluded location for flight testing. The prototype was given the serial number 5501 and had been registered as PH-APB, but the registration was never applied to the aircraft. On the morning of 30 June 1938, Koolhoven pilot Thomas Coppers conducted high-speed taxi tests and hopped the FK.55 into the air on three separate occasions. Later that afternoon, Coppers took the FK.55 into the air for its first flight. Shortly after takeoff, Coppers made a 180 degree turn and quickly landed with the wind. Frits Koolhoven approached the aircraft, where he and Coppers engaged in an animated discussion regarding the FK.55. Some sources state that Coppers had found the cockpit unbearably hot. The taxi test should have given some indication of the heat experienced in the cockpit. Whatever the reason, the FK.55 never flew again.

The FK.55 mockup appeared to be a maneuverable fighter aircraft that afforded the pilot an excellent view, and its contra-rotating propellers eliminated engine torque, making the aircraft manageable for inexperienced pilots. The FK.55 prototype was an odd, ungainly aircraft that was underpowered and incomplete. The Koolhoven team endeavored to rework the FK.55’s design, changing to low wings and a Lorraine Sterna engine of at least 1,100 hp (820 kW), but Frits Koolhoven himself wanted nothing more to do with the aircraft. On 10 May 1940, a German bombing raid struck the Waalhaven Airport. The FK.55 mockup and prototype were destroyed, along with the entire Koolhoven factory, affectively putting an end to the company.

Koolhoven FK55 prototype engine run

When viewed from the side, the FK.55 prototype had a rather “pregnant” appearance. This image illustrates how the pilot was positioned between several heat sources.

Sources:
Jane’s All the World’s Aircraft 1936 by C. G. Grey and Leonard Bridgham (1936)
Jane’s All the World’s Aircraft 1937 by C. G. Grey and Leonard Bridgham (1937)
Jane’s All the World’s Aircraft 1938 by C. G. Grey and Leonard Bridgham (1938)
The Complete Book of Fighters by William Green and Gordon Swanborough (1994)
Koolhoven Vliegtuigen by Theo Wesselink (2012)
Les Moteurs a Pistons Aeronautiques Francais Tome I by Alfred Bodemer and Robert Laugier (1987)

Ford 15P front

Ford 15P Personal Aircraft

By William Pearce

Henry Ford was an absolute titan of industry. His ability to mass-produce the automobile made them affordable to the average citizen in the United States. Owning cars revolutionized the way people lived. On more than one occasion, Ford attempted to do the same thing with the airplane—create a simple, affordable, and easy-to-fly aircraft for the masses. The design of an inexpensive and mass-produced aircraft was referred to as a “flivver” plane. The Ford Motor Company’s last flivver aircraft was the 15P, and like previous attempts, it did not succeed.

Ford 15p mockup

Full-scale mockup of the Ford 15P from January 1935. With the exception of an unfaired tailwheel, the complete aircraft was very similar to the mockup.

Edsel Ford, Henry’s son, had an interested in aviation, and he helped finance William B. Stout’s founding of the Stout Metal Airplane Company in 1922. By 1924, Henry had joined Edsel to help the Stout Metal Airplane Company, and the Ford Motor Company (FMC) built an airport and factory for Stout in Dearborn, Michigan. In 1925, the FMC purchased Stout’s company, which became the Stout Metal Airplane Division of the Ford Motor Company. The Stout Division went on to create the famous Ford Tri-Motor transports.

The Great Depression had a large impact on the FMC and Stout Division. By 1932, Henry Ford had refocused his efforts on automobiles; aircraft production and development at FMC had virtually stopped. In November 1933, the Aeronautics Branch of the Department of Commerce challenged the aviation industry to develop an $800 aircraft that just about anyone could afford, fly, and maintain. This concept—a Model T of the air—mirrored that of Ford’s flivver plane attempts.

In early 1934, FMC had experimented with a flathead V-8 modified for aircraft use. Coinciding with this engine’s development was the design of the 15P aircraft by Harry Karcher and Gar Evans. A model of the 15P was built in September 1934, and a full-scale mockup was completed in January 1935. It is not clear if the main proponent of the 15P was Henry, who had a long-standing quest to make aircraft ownership possible for the average citizen, or Edsel, who had always been interested in aviation. In all likelihood, they probably both had an equal roll. Regardless, construction of the 15P followed the mockup, and the aircraft was completed by early 1936.

Ford 15P rear aerofiles

Rear view of the Ford 15P displays the five air scoops that led into the engine compartment and the three rows of louvers that allowed the cooling air to exit. (image via Aerofiles.com)

The Ford 15P was a tailless, flying wing aircraft with the pilot and single passenger sitting side-by-side in a teardrop-shaped fuselage. The cockpit had dual controls and instrumentation in the center, making the aircraft easy to fly from either seat. Each seat in the cockpit was accessible by a hinged top hatch that opened up toward the center of the aircraft and a hinged side window that opened toward the front of the aircraft.

The fuselage was made of steel tubing and covered with aluminum sheeting. The wings had an aluminum structure, were fabric-covered, and each carried 15 gallons (57 L) of fuel. Along the wing’s trailing edge, flaps were positioned near the fuselage. Outboard of the flaps were drag rudders, and elevons (combination elevator and aileron) were at the wingtips. The 15P was supported on the ground by standard taildragger landing gear. The main gear was positioned under the wings and enclosed in large, streamlined fairings, which also housed a landing light. The castoring tailwheel was positioned at the extreme rear of the aircraft.

Directly aft of the firewall behind the pilot and passenger was the Ford flathead V-8 engine. Although engine specifics have not been found, the engine most likely had a 3.0625 in (77.8 mm) bore, a 3.75 in (95.3 mm) stroke, and displaced 221 cu in (9.62 L). The engine is noted as being virtually standard so that parts would be available from most Ford auto repair shops. Unique to the aircraft engine was its all-aluminum construction and that it produced 115 hp (86 kW) at 4,000 rpm. The engine drove an enclosed propeller shaft that ran between the pilot and passenger. Sources list the 15P as using a 6.5 ft (1.98 m) diameter, wooden Gardner propeller. However, photos appear to show a metal propeller.

Ford 15P engine

The flathead Ford V-8 in the 15P’s engine compartment. Note the fixed radiator or header tank at the rear of the compartment. Also note the hinged top and side panels for cockpit access. (image via The Aviation Legacy of Henry & Edsel Ford)

The engine cowling consisted of two panels that hinged up toward the center of the aircraft. Each panel had two air scoops, and another scoop was positioned between the panels on the aircraft’s spine. The radiator was positioned aft of the engine, and three rows of louvers were behind the radiator. Cooling air would enter the engine compartment via the five scoops and through an additional scoop positioned under the aircraft. Air would pass through the radiator and exit via the louvers at the rear of the aircraft. Some sources state the radiator was retractable and could extend below the aircraft; however, this would have added much complexity to what was supposed to be a simple aircraft. Instead, perhaps the ventral scoop could be extended to allow more airflow during ground running. The engine’s exhaust was expelled under the aircraft.

Very little information regarding the Ford 15P remains. The aircraft’s approximate specifications are a wingspan of 34 ft (10.4 m), a length of 14 ft (4.27 m), and a gross weight of 1,600 lb (726 kg). The 15P had an estimated top speed of 120 mph (193 km/h) and a maximum range of 500 miles (805 km).

The Department of Commerce assigned registration number X999E to the 15P on 29 November 1935. The date of the aircraft’s first flight has not been found. Reportedly, the 15P made several flights, all made by FMC’s head pilot, Harry Russell. Controlling the aircraft was problematic and an issue that was not solved before the plane was damaged in a landing accident. The damaged 15P was placed in storage and not repaired.

FMC ceased aircraft operations, closing the Stout Metal Airplane Division in 1936. Apparently, what remained of the 15P was stored until 1941 when Henry Ford requested that it be used as a basis for an autogyro-type aircraft. Ultimately, the autogyro aircraft never flew, and its design was deemed unworkable. Whatever was left of the 15P disappeared along with the autogyro.

Ford 15P front

This front view of the Ford 15P shows what appears to be a metal propeller. Note the air scoop and engine exhaust under the aircraft. (image via The Aviation Legacy of Henry & Edsel Ford)

Sources:
The Aviation Legacy of Henry & Edsel Ford by Timothy J. O’Callaghan (2000)
“Ford Reviews Test of Flivver Plane,” The Cincinnati Enquirer (14 January 1936)
http://www.aerofiles.com/_ford.html
https://en.wikipedia.org/wiki/Stout_Metal_Airplane

de Havilland DH91 Forbisher front

De Havilland DH.91 Albatross Transport

by William Pearce

In the mid-1930s, the de Havilland Aircraft Company (de Havilland ) sought financial support from the British Air Ministry to develop a new transport aircraft. De Havilland felt that Britain was not developing transport aircraft of the same performance level as those from the United States. On 21 January 1936, the Air Ministry ordered two of the new de Havilland transports as transatlantic mailplanes under Specification 36/35. Five additional aircraft were ordered by Imperial Airways Ltd. and would be completed as passenger transports. The mailplane and airliner versions had only minor differences, and both aircraft were designated DH.91 Albatross.

de Havilland DH91 Forbisher flight

The flagship of Imperial Airways F class: the de Havilland DH.91 Albatross ‘Frobisher.’ Its clean lines can be seen in the image above.

Designed by Arthur E. Hagg, the Albatross was an exceptionally clean, four-engine monoplane constructed almost entirely of wood. The long, circular fuselage had a steady taper toward the tail and was made of balsa wood sandwiched between thin layers of either cedar or birch, depending on location. The wood layers were cemented together and formed under pressure. Cabin construction allowed for pressurization, but such a system was never designed for the aircraft. The wing of the Albatross was constructed as one piece from a spruce structure covered with two layers of diagonal spruce planking. The thin wing was virtually sealed and would provide some level of buoyancy in the event of a water landing. The aircraft’s control surfaces were fabric-covered.

The Albatross had twin tails. Originally, the vertical stabilizers were positioned near the fuselage, about a third of the way along the horizontal stabilizer. Due to control issues, the tails were redesigned and positioned at the ends of the horizontal stabilizer. The aircraft used a conventional taildragger landing gear arrangement. The main wheels retracted inward and were fully enclosed in the wing’s center section. The tailwheel did not retract.

de Havilland DH91 Faraday early

The first Albatross prototype. Note its original tail and how close the vertical stabilizers are to the fuselage. This mailplane version would later be named ‘Faraday.’

Four de Havilland Gipsy Twelve (King I) engines powered the Albatross. The Gipsy Twelve was an air-cooled, supercharged, inverted, V-12 engine. The engine had a 4.65 in (118 mm) bore, a 5.51 in (140 mm) stroke, and a total displacement of 1,121 cu in (18.4 L). The Gipsy Twelve produced 525 hp (391 kW) at 2,600 rpm for takeoff power, 425 hp (317 kW) at 2,400 rpm for maximum climbing power, and 320 hp (239 kW) at 2,200 rpm for maximum economical cruse power. Each engine was housed in a very tight-fitting, streamlined cowling. Cooling air was brought in via pressure-ducts in the wing’s leading edge. The ducts were located in the propeller’s slipstream on both sides of each engine nacelle. The cooling air flowed forward along the outer side of the cylinders, from the back of the engine to the front. The air was forced through the cylinders’ cooling fins and into the Vee of the engine, where an exit flap on the bottom of the cowling allowed the air to escape. The opening of the exit flap controlled the engine temperature. Each engine turned a two-blade, constant-speed, 10 ft 6 in (3.2 m) diameter de Havilland propeller via a .66 gear reduction.

The basic structure of the mailplane and airliner versions of the Albatross were the same, but the aircraft did have their differences. The mailplane was designed to carry 1,000 lb (454 kg) of mail 2,500 mi (4,023 km) against a 40 mph (64 km/h) headwind, while the airliner was designed to carry 22 passengers and four crew 1,000 mi (1,609 km). The mailplane had four cabin windows on each side of its fuselage, compared to six for the airliner version. The mailplane utilized split flaps, while the airliner used slotted flaps. The mailplane Albatross had four 330 gal (1,250 L) fuel tanks mounted in the cabin, while the airliner had one 270 gal (1,022 L) and one 170 gal (644 L) fuel tank mounted under the cabin floor. The mailplane had two 9 gal (7.5 L) oil tanks per engine; the airliner had just one oil tank per engine.

de Havilland DH91 Forbisher front

The cooling-air ducts in the wing’s leading edge can be seen in this view of ‘Frobisher.’ Each duct brought in air to the nearest cylinder bank. Note the landing gear wheel wells and the hinged cover on the main wheels.

The Albatross had a wingspan of 105 ft (32.0 m) and was 71 ft 6 in (21.8 m) long. The mailplane had a top speed of 222 mph (357 km/h) at 8,700 ft (2,652 m) and a maximum economical cruse speed of 204 mph (328 km/h) at 11,000 ft (3,353 m). Its maximum range was 3,300 mi (5,311 km), and its gross weight was 32,500 lb (14,742 kg). The aircraft had a 550 fpm (2.8 m/s) climb rate and a ceiling of 15,100 ft (4,602 m).

The airliner version had a top speed of 225 mph (362 km/h) at 8,700 ft (2,652 m) and a maximum economical cruse speed of 210 mph (378 km/h) at 11,000 ft (3,353 m). Its maximum range was 1,040 mi (1,634 km), and its gross weight was 29,500 lb (13,381 kg). The aircraft had a 710 fpm (3.6 m/s) climb rate and a ceiling of 17,900 ft (5,456 m).

de Havilland DH91 Forbisher rear

This view of ‘Frobisher’ shows the additional windows incorporated into the airliner version of the Albatross. The revised tail is also apparent.

The Albatross mailplanes were built first, and the initial prototype flew for the first time on 20 May 1937. Robert John Waight was the pilot for the first flight. By October, the need to redesign the tails was evident, and the new tail fins were installed on the ends of the horizontal stabilizer. After the modification, the aircraft was registered as G-AEVV on 3 January 1938. On 31 March 1938, the Albatross suffered a belly landing due to a landing gear issue. Once repaired, G-AEVV became part of Imperial Airways in August 1939. All DH.91s were part of Imperial Airways F (Frobisher) class of aircraft and were given names starting with the letter “F.” G-AEVV was named Faraday. When Imperial Airways was merged with British Airways Ltd. in 1940 to form the British Overseas Airways Corporation (BOAC), the ownership of all DH.91s was eventually transferred to BOAC. Faraday was transferred to BOAC on 17 June 1940. On 1 September 1940, Faraday was impressed into service (as AX903) during World War II as a transport shuttle flying between Great Britain and Iceland. While landing at Reykjavik, Iceland on 11 August 1941, the aircraft collided with a Fairey Battle and was damaged beyond repair. Fortunately, the five people onboard the Albatross escaped unharmed. Some records claim the accident occurred on 11 August 1940, but this does not fit the timeline, especially since the date of impressment is recorded as 1 September 1940.

The second mailplane was registered as G-AEVW and named Franklin. On 27 August 1938, the aircraft’s rear fuselage broke in two during overload landing tests, revealing a structural weakness. The aircraft was repaired, and the changes were incorporated into the other Albatross aircraft. G-AEVW was transferred to BOAC on 8 July 1940. Like Faraday, Franklin was impressed into service (as AX904) on 1 September 1940 and was damaged beyond repair in a landing accident at Reykjavik. The mishap occurred on 7 April 1942 when the aircraft’s landing gear collapsed. The four people onboard were not injured.

de Havilland DH91 Forbisher side

The DH.91 was a very graceful and aerodynamic aircraft. Note the sleek engine installation and the cooling-air exit flaps under the engine nacelles.

The first Albatross airliner was registered as G-AFDI and given the name Frobisher. It was delivered in October 1938 and served as the flagship for Imperial Airways. The aircraft started experimental service in December and averaged 219 mph on its first service flight from Croydon, England to Cairo, Egypt. The aircraft was transferred to BOAC on 22 August 1940. Frobisher was destroyed during a German air raid at the Bristol (Whitchurch) Airport on 20 December 1940.

The second airliner was registered as G-AFDJ and named Falcon. It was delivered to Imperial Airways in November 1938 and entered service in January 1939. The aircraft was transferred to BOAC on 27 August 1940. Falcon was scrapped in August 1943 after the loss of Fortuna (see below) and because the spare parts supply for the Albatross aircraft had been depleted.

The third airliner was registered as G-AFDK and named Fortuna. It was in service by mid-1939 and was transferred to BOAC on 27 August 1940. Fortuna crashed on approach to Shannon Airport in Ireland on 16 July 1943. The aircraft’s wing started to break up, and Fortuna crash landed short of the runway. All fourteen people on the aircraft survived the crash. This accident precipitated the last two surviving DH.91s, Falcon and Fiona (see below), to be removed from service.

de Havilland DH91 Franklin

The two Albatross mailplanes served as transports during World War II, and both were lost in separate landing accidents at Reykjavik, Iceland. ‘Franklin,’ the second mailplane  is seen above in its wartime camouflage.

The fourth airliner was registered as G-AFDL and named Fingal. It entered service for Imperial Airways in 1939 and was transferred to BOAC on 29 August 1940. The aircraft was lost on 6 October 1940 while making an emergency landing near Pucklechurch, England because of a fractured fuel line. Fingal hit a farmhouse during the forced landing and was damaged beyond repair, but none of the three people onboard were injured.

The last airliner was registered as G-AFDM and named Fiona. The aircraft entered service with Imperial Airways in 1939. The aircraft was transferred to BOAC on 22 August 1940 and continued in service until being withdrawn after the Fortuna crash. Fiona was scrapped along with Falcon in August 1943.

The de Havilland DH.91 Albatross was a beautiful aircraft that performed well in service. Part of its downfall can be attributed to its production right before World War II. It is rather remarkable to consider that four of the aircraft crashed during the landing phase of flight but that no one was killed in any of the accidents. While the Albatross cannot be considered a success, the techniques used in the Albatross’ wooden construction were applied directly to the incredibly successful World War II-era DH.98 Mosquito. Hagg went on to design the Napier-Heston Racer, and some of the Albatross’ streamlining traits can be seen in that aircraft.

de Havilland DH91 Fortuna

While landing in Shannon, Ireland, the wing of ‘Fortuna’ (seen above) began to break apart. The aircraft crashed short of the runway, but no lives were lost. Due to the crash and lack of spare parts, the two remaining DH.91s were withdrawn from service. Note the Bristol Beaufighter in the distance.

Sources:
“The Albatross in Detail” Flight (17 November 1938)
De Havilland Aircraft since 1909 by A. J. Jackson (1987)
Shannon Airport: A Unique Story of Survival by Valerie Sweeney (2004/2015)
“Cooling the Gipsy Twelve” Flight (31 March 1938)
http://aviation-safety.net/database/record.php?id=19400811-0
http://aviation-safety.net/database/record.php?id=19420407-0
http://aviation-safety.net/database/record.php?id=19401220-0
http://aviation-safety.net/database/record.php?id=19401006-0

Piaggio P16

Piaggio P.16 Bomber

By William Pearce

Rinaldo Piaggio founded the Rinaldo Piaggio SpA in Genoa, Italy in 1884. The company was renamed Piaggio & C. SpA (Piaggio) in 1887. Piaggio originally furnished ship interiors and manufactured railroad equipment but turned to the licensed construction of aircraft during World War I. Piaggio decided to manufacture aircraft of its own design in 1923. That same year, Piaggio purchased the Pegna-Bonmartini company and acquired the services of aeronautical engineer Giovanni Pegna. By the early 1930s, Piaggio looked to create military and commercial aircraft that incorporated modern advancements in design and manufacture. By 1932, Pegna had designed the Piaggio P.16 bomber.

Piaggio P16 1932

A circa 1932 drawing of the Piaggio P.16. Note the very unique wing shape that was not used on the actual aircraft prototype.

The P.16 possessed many features used for the first time on a Piaggio aircraft: tri-motor design, variable-pitch propellers, all metal construction, and retractable main landing gear. The P.16 was powered by three Piaggio P.IX RC engines—one in the nose of the aircraft and one on each wing. The P.IX RC engine was a nine-cylinder radial developed from the French Gnome-Rhône Mistral 9K. The engine displaced 1,517 cu in (24.9 L) and produced 610 hp (455 kW). The metal, two-blade propellers were developed by Corradino D’ Ascanio and built by Piaggio.

The wings of the P.16 were of all duralumin construction, while the fuselage and tail had a steel tube frame. The front and upper sections of the fuselage were covered in duralumin. The aircraft’s control surfaces and the rear sides and lower sections of the fuselage were fabric-covered. The P.16’s original inverted gull wing design consisted of a very long wing root that ran from just behind the cockpit back to the tail. The wing continuously tapered toward its tip, which had a very narrow cord. The wing used on the actual aircraft maintained the same basic shape of the earlier design but extended back only to the middle of the aircraft’s fuselage and did not have such a narrow tip. The thickest part of the wing was by the engine nacelles, after which it narrowed toward the tip and toward the fuselage. The relatively thin wing roots helped reduce buffeting of the aircraft’s tail.

Piaggio P16

The completed P.16 with its revised wing. Just below the cockpit side window is the circular window in the cockpit access door.

On each side of the aircraft, two braces extended from the lower engine nacelle to the lower fuselage. Hydraulically operated flaps extended out from the engine nacelles to about mid-span, and ailerons occupied the rest of the wing’s trailing edge. The leading edge of the outer wing sections had retractable slats to improve the aircraft’s control at low-speed. The main landing gear retracted aft and was fully enclosed in the engine nacelles. The steerable tailwheel did not retract but was enclosed in an aerodynamic fairing.

The P.16 had a five-man crew. The pilot and copilot sat side-by-side in the cockpit. Behind the cockpit was a bomb bay that accommodated 2,200 lb (1,000 kg) of bombs. Some sources indicate the bombardier was in the lower forward fuselage just below the cockpit. Other sources state the bombardier was behind the bomb bay in the middle of the aircraft. Given the aircraft’s layout, the mid-position seems more likely. Along the upper mid-fuselage was a retractable turret that housed one 7.7 mm machine gun. In the rear of the fuselage and just below the vertical stabilizer was another 7.7 mm machine gun position. Two additional 7.7 mm machine guns were forward firing. Most sources state the guns were located in the wing roots, but that would require the guns to be located right next to the cockpit and to fire through the propeller arc. It is possible that the forward firing machine guns were housed in the outer wing sections, but there is no obvious indication of their location.

Piaggio P16 side

The unique position of the rear gunner is illustrated in this side view of the P.16. The retracted dorsal turret can be seen just behind the wing root on the top of the fuselage.

The cockpit was accessible by a door on each side of the aircraft, just under the cockpit side windows and in front of the wing. Another door just under the trailing edge of the left wing provided access to the rear fuselage.

The P.16 had a wingspan of 72.2 ft (22.0 m) and was 44.0 ft (13.4 m) long. The aircraft’s empty weight was 12,346 lb (5,600 kg), and its loaded weight was 18,629 lb (8,450 kg). Its maximum speed was 224 mph (362 km/h) at sea level and 249 mph (400 km/h) at 16,404 ft (5,000 m). The aircraft had a cruising speed of 201 mph (324 km/h) and a landing speed of 65 mph (105 km/h). The P.16 could climb to 19,685 ft (6,000 m) in 17 minutes. The aircraft’s range was 932 miles (1,500 km) with a maximum bomb load and 1,243 miles (2,000 km) with a 1,100 lb (500 kg) bombload.

Piaggio P16 rear

This rear view of the P.16 shows the inverted gull wing and the struts running from the engine nacelles to the fuselage. Note the aircraft’s flaps and ailerons.

The P.16 was officially ordered on 4 July 1933, but construction of the aircraft had already begun. The P.16 was given the serial number MM 226 and first flown in November 1934 at Villanova d’Albenga Airport with Mario Gamna at the controls. Starting in February 1935, the aircraft was evaluated by the Regia Aeronautica (Italian Royal Air Force). In October 1935, the P.16 made its public debut at the first Salone Internazionale Aeronautica (International Aviation Display) in Milan, where it attracted a lot of attention and interest.

The Regia Aeronautica ordered 12 Piaggio P.16 aircraft, but this order was later cancelled in favor of the more promising (and conventional) Piaggio P.32, which was designed in 1935. While just one P.16 was built, the aircraft did help Piaggio learn the skills required to construct large, all-metal aircraft, which culminated with the Piaggio P.108 heavy bomber of World War II.

Piaggio P16 rear gunner

A detailed view of the rear gunner position indicates firing above and directly behind the P.16 would be problematic. However, the gunner does have a good field of fire to the sides and below the aircraft. The P.16’s MM 226 serial number can be seen painted on the side of the aircraft. Note the tailwheel’s aerodynamic housing.

Sources:
Italian Civil and Military Aircraft 1930-1945 by Jonathan W. Thompson (1963)
Volare Avanti by Paolo Gavazzi (2000)
Jane’s All the World’s Aircraft 1936 by C.G. Grey and Leonard Bridgman (1936)
http://www.secretprojects.co.uk/forum/index.php?topic=12311.0
http://www.giemmesesto.org/Documentazione/Aerei/PIAGGIO_P-16.html