Arsenal VB 10-02 under construction

Arsenal VB 10 Heavy Interceptor Fighter

By William Pearce

In January 1937, the Ministère de l’Air (French Air Ministry) gave Arsenal de l’Aéronautique a contract to develop a twin-engine heavy interceptor fighter built from wood and powered by two 690 hp (515 kW) Hispano-Suiza 12X engines. The engines were to be mounted in tandem inside the fuselage driving coaxial propellers in the nose. Through the course of several changes, the aircraft’s design was developed into the all-aluminum VB 10 fighter. The VB 10 was designed in 1938 by Michel Vernisse and Robert Badie; the initials of their last names formed the ‘VB’ of the aircraft’s designation.

Arsenal VB 10-01 rear

The Arsenal VB 10-01 prototype powered by two 860 hp (641 kW) Hispano-Suiza 12Y-31 V-12 engines. Note the obstructed rear view from the flush canopy.

The VB 10 was a low-wing monoplane in a standard taildragger configuration with retractable undercarriage and a single-seat. It was a large aircraft with a span of 50 ft 10 in (15.49 m), length of 42 ft 7 in (12.98 m), height of 17 ft 3/4 in (5.2 m), and an empty weight of 15,190 lb (6,890 kg).

While the aircraft was of a standard configuration, the engine arrangement was not. One engine occupied the standard position in the nose of the aircraft and a second engine was included behind the cockpit. Each engine drove a set of propeller blades that, together, made up a coaxial contra-rotating unit in the nose. The front engine drove the rear propeller, and the rear engine drove the front propeller. The drive shaft from the rear engine ran through the Vee of the front engine and to the front propeller. A Vernisse or homocinetic coupling was used in which flexibly-mounted ball joints join sections of the rear engine’s propeller shaft to accommodate deflection and vibration of the shaft.

Latecoere 299A runup

The Latécoère 299A that served as an engine testbed for the Arsenal VB 10. The 229A was powered by two 860 hp (641 kW) Hispano-Suiza 12Y V-12 engines, same as the VB 10-01 prototype. Note the front propeller is not turning and the German markings.

Before the prototype was built, a contract for 40 aircraft was placed in May 1940. However, construction was suspended with the capitulation of France in June 1940. In April 1942, the Vichy government was able to persuade the RLM (Reichsluftfahrtministerium or German Ministry of Air) to allow construction to resume on the twin-engine propulsion system. To thoroughly evaluate the unusual engine arrangement, a Latécoère 299 was made into a flying testbed and renamed 299A. Completed in July 1943, the Latécoère 299A was destroyed in an Allied bombing raid on 30 April 1944.

With the tide of the war changing, the French restarted construction of the first prototype, VB 10-01, in July 1944. The unarmed prototype was powered by two 860 hp (641 kW) Hispano-Suiza 12Y-31 12-cylinder, liquid-cooled engines and had a flush, sliding canopy with an obstructed rear view. This aircraft was first flown on 7 July 1945 by Modeste Vonner. During initial flight tests, the VB 10-01 achieved a sea-level speed of 304 mph (490 km/h). An order for 200 aircraft was placed on 22 December 1945.

Arsenal VB 10-02 under construction

The second prototype VB 10-02 under construction. Note the two 20 mm cannons and three .50-cal machine guns in each wing.

The second prototype, VB 10-02, had a bubble canopy for improved visibility and was powered by two 1,150 hp (858 kW) Hispano-Suiza 12Z engines. The aircraft was also armed with four 20 mm Hispano-Suiza cannons (with 600 rounds total) and six .50-cal Browning machine guns (with 2,400 rounds total), all mounted in the wings. The VB 10-02 first flew on 21 September 1946. Mechanical issues and engine overheating plagued both prototypes; these challenges, combined with the availability of cheap surplus allied aircraft and the jet age on the horizon, led to a revised order of just 50 aircraft.

Arsenal VB 10-02 side open

Another image of the Arsenal VB 10-02 with the side panels removed. Note the bubble canopy.

The first production VB 10 made its maiden flight on 3 November 1947. The aircraft was powered by two Hispano-Suiza 12Z-15/16 engines that were rated at 1,300 hp (969 kW) max and 1,150 hp (858 kW) continuous. It was armored with only four 20mm cannons but had provisions to carry one 1,100 lb (500 kg) bomb under each wing. Additional fuel took the place of the removed machine guns. The production aircraft went on to achieve a max speed of 323 mph (517 km/h) at sea-level and 435 mph (700 km/h) at 24,600 ft (7,500 m).

For the VB 10, the beginning of the end occurred on 10 January 1948 when the second prototype, VB 10-02, caught fire while over southern Paris. An uncommanded propeller pitch change over-reved the rear engine, destroying it and starting the fire. The pilot, Pierre Decroo, was forced to bail out. He survived but suffered burns. On 15 September 1948, the third (some say first) production machine crashed in much the same fashion, killing the pilot, Henri Koechlin. Six days later on 21 September 1948, the Arsenal VB 10 contract was cancelled. At the time of cancellation, four production VB 10 aircraft (including the one that crashed) had flown, six additional airframes had been completed, and a number of airframes were under construction. All remaining VB 10s (including the first prototype) were scrapped.

Arsenal VB 10 C-1 production

The size of the VB 10 is illustrated here by the crowd in front of the first production VB 10. The aircraft was powered by two Hispano-Suiza 12Z-15/16 engines. Note the 20 mm cannons and no machine guns.

The Complete Book of Fighters by Green and Swanborough (1994)
Hispano Suiza in Aeronautics by Manuel Lage (2004)
Jane’s All the World’s Aircraft 1948 by Leonard Bridgman (1948)
– “Behind the Lines: French Development” Flight (3 February 1944)
L’ Arsenal de l’Aéronautique by Gérard Hartmann (pdf in French)

PKZ 2 engines 3

Petróczy-Kármán-Žurovec PKZ 2 Helicopter

By William Pearce

In 1916, Major Stephan Petróczy von Petrócz of the Austro-Hungarian Army envisioned replacing hydrogen-filled observation balloons with tethered helicopters. These helicopters would have been used as static observation platforms. Compared to hydrogen balloons, the helicopters’ were much less likely to catch fire, presented a smaller target for the enemy, increased operational readiness, required fewer ground and support crew, and eliminated the need for hydrogen generating equipment.

PKZ 2 with basket 3

Follow-on to the PKZ 1, the Petróczy-Kármán-Žurovec PKZ 2 is shown here with the observation basket attached above the rotors. This image was taken after the PKZ 2 was modified in May 1918 and the 120 hp (89 kW) La Rhône engines are installed.

To achieve his goal, Petróczy, along with Oberleutnant Dr. Theodor von Kármán and Ingenieurleutnant Wilhelm Žurovec, conceived the Schraubenfesselflieger (S.F.F) mit Elektromotor (captive helicopter with electric motor). This machine is now commonly refered to as the Petróczy-Kármán-Žurovec 1 (PKZ 1) helicopter. Built in 1917 and primarily designed by von Kármán and Žurovec, the PKZ 1 consisted of a rectangular frame with an observation basket in the middle. On each side of the basket were two lift rotors. All four rotors were powered by a single 190 hp (142 kW) Austro-Daimler electric motor.

The PKZ 1 was flight tested and was able to lift three men to a tethered height of 20 in (50 cm).  However, the electric motor generated 50 hp (37 kW) less than anticipated, and on the fourth flight, the straining motor gave out. Because of the scarcity of high-grade electrical copper and quality insulation, Daimler was not able to repair the motor. In addition, the PKZ 2, which was originally known as the S.F.F. mit Benzinmotor (captive helicopter with petrol engine), was nearing completion. No further work was done on the PKZ 1.

PKZ 2 engines 3

PKZ 2 rotary engine arrangement with the 100 hp (75 kW) Gnomes installed.

The PKZ 2 helicopter (for which he received German patent 347,578) was designed solely by Wilhelm Žurovec. The PKZ 2 was privately funded by the Hungarian Bank and the iron foundry / steel fabrication firm of Dr. Lipták & Co AG, who built the machine. The PKZ 2 utilized two two-blade contra-rotating rotors to cancel out torque and provide lift. The rotors, made of high-quality mahogany, were 19 ft 8 in (6.0 m) in diameter and were rotated at 600 rpm by three 100 hp (75 kW) Gnome rotary engines. A removable observation basket sat atop the rotors.

The craft had three outrigger legs; each supported one engine. All engines were connected to the rotors via a common gearbox. The PKZ 2 was supported by a central air cushion and three additional air cushions; one on each outrigger leg. These air cushions were filled by an air pump driven from the rotor drive. Attached to each outrigger was a tethering cable that was connected to the ground and controlled by an electric winch. With one hour of fuel, The PKZ 2 weighed 2,645 lb (1,200 kg).

PKZ 2 Takeoff2

PKZ 2 shown just off the ground and without the observation basket on 5 April 1918, powered by the 100 hp (75 kW) Gnome engines.

Tethered and unmanned, the PKZ 2 was test flown on 2 April 1918. After several flights, including one that lasted about an hour, tests were suspended on 5 April because of insufficient power from the Gnome engines. The engines were replaced by 120 hp (89 kW) La Rhône engine (that were captured and rebuilt) and, with a few additional modifications, tethered and unmanned flight tests resumed on May 17th. With the new engines and calm winds, an altitude of 165 ft (50 m) was achieved, and the PKZ 2 could lift 330–440 lb (150–200 kg). The craft would lose lift at higher altitudes, but the PKZ 2 was kept under control as long as tension remained on the tethering cables.

PKZ 2 hover 2

PKZ 2 in a tethered high hover with power provided by the 120 hp (89 kW) La Rhône engines on 10 June 1918.

On 10 June 1918 the PKZ 2 was demonstrated for high ranking members of the military. A flight was made with the observation basket in place, but the engines were not running well and the craft became unstable. The basket was removed and another flight attempted. The wind had picked up, and as the PKZ 2 hovered at 40 ft (12 m) tethered to the ground, the craft began to rock. The overheating engines lost power, and the tether winch crew could no longer maintain control. The PKZ 2 crashed from a height of 6.5 ft (2.0 m), severely damaging the airframe and completely destroying the rotors.

Realizing the technical problems could not be overcome quickly, the government cancelled the project on 21 June 1918. However, Žurovec pressed on and began to design an individual cylinder water jacket to water-cool the rotary engines. The craft was being rebuilt to resume flight tests in November 1918 when the end of the war and revolution caused all development to cease. The PKZ 2 made over 15 tests flights, but it is doubtful any were manned.

PKZ 2 Crash 2

Remains of the PKZ 2 after it crashed on 10 June 1918.

Austro-Hungarian Army Aircraft of World War One by Grosz, Haddow, and Schiemer (2002)
Recent Developments in European Helicopters NACA Technical Note No. 47 by von Kármán (1921) pdf
– Comment by Kees Kort

Argus As 5 Aircraft Engine

By William Pearce

Following World War I, the Treaty of Versailles severely limited aircraft production in Germany; military aircraft could not be built or developed. Germany created the Department of Aviation within the Ministry of Transportation to oversee commercial aircraft. The Department of Aviation initiated development of a large, powerful engine to solely provide power for an equally large aircraft. This led to the Argus As 5—the company’s first post-World War I engine project.

The 24-cylinder Argus As 5. (Polish Aviation Museum Krakow image)

The Argus As 5 was a liquid-cooled, 24-cylinder engine with six banks of four cylinders. The cylinders were arranged in a double-W, or double broad arrow fashion. The top and bottom banks of cylinders had 45-degrees of separation from the bank on either side. The top set of three cylinder banks was separated by 90-degrees from the bottom set of three cylinder banks. All cylinders used a common crankshaft with a master and articulated connecting rod arrangement.

The As 5 had bore of 6.30 in (160 mm) and stroke of 7.68 in (195 mm). Total displacement was 5,742 cu in (94.1 L) and the engine had a compression ratio of 5.6 to 1. The As 5 developed 1,500 hp (1,120 kW) at 1,800 rpm and weighed 2,425 lb (1,100 kg). The As 5 used individual cylinders with welded steel water jackets. All the cylinders for a single bank shared a common aluminum head. Valves were actuated by a single overhead camshaft. The aluminum crankcase was separated into a top and bottom half.

Close-up view of the top three cylinder banks of the Argus As 5. (Stanislaw Guzik image)

After a few engine runs, the idea to power a large aircraft with a single large engine progressed no further, and the As 5 never took flight. Three Argus As 5 engines were built between 1924 and 1927. Development was abandoned partly because no aircraft could handle the engine’s immense size and weight. In addition, the German Ministry of Transportation decided that two smaller engines were more practical than a single large engine.

One of the three engines built still exists and is on display at the Polish Aviation Museum Krakow. The Argus As 5 is the largest engine in the museum’s aircraft engine collection.

Left view of the 1,500 hp Argus As 5. (Štepán Obrovský / Zdeněk Kussior image)

Argus – Flugmotoren und Mehr by Wulf Kisselmann (2012)
Flugmotoren und Strahltriebwerke by von Gersdorff, Schubert, and Ebert (2007)
Kolben-Flugmotoren by Hans Giger (1986)

Deschamps V 3050 Diesel Aircraft Engine

By William Pearce

In the late 1920s, Desire Joseph Deschamps moved forward with his vision of an inverted, two-stroke, high-speed, diesel aircraft engine. Deschamps had immigrated to the United States from Belgium, where he had worked for the Minerva Company. Reportedly, Deschamps had a hand in designing Minerva’s first aircraft engine, which was also the first aircraft engine to incorporate Knight sleeve-valves (two sleeves).

Deschamps rotary valve as outlined in U.S. patent 2,064,196. On the left is a transverse sectional view of the cylinder with the rotary valve below (inverted engine) and feeding to the combustion chamber. On the right is a side view of the rotary valve for two cylinders revealing the various ports in the valve.

Working out of St. Louis, Missouri, Deschamps began the design of an inverted, liquid-cooled, straight six-cylinder, diesel aircraft engine. Outlined in U.S. patent 2,064,196, what was unique about this diesel engine was the use of a rotary sleeve valve. This rotary valve was essentially a cylindrical tube that ran the length of the engine below (inverted engine) the combustion chamber. Induction air flowed through the tube that rotated at half crankshaft speed. As the tube rotated, ports in the tube aligned with a port to the cylinder, allowing fresh air to force the exhaust gases out of the cylinder and provide air for the next combustion cycle. The exhaust ports were around the cylinder wall and covered/uncovered by the piston.

From all accounts, the rotary valve engine was never built. A more conventional valve arrangement was adopted, utilizing poppet-valves, rather than the rotary valve, for the intake . A two-cylinder test engine was built and run in the early 1930s. The test engine engine developed 174 hp (130 kW) at 1,600 rpm. This two-cylinder engine was expressly for the development of the Deschamps inverted V-12 diesel, having the same bore, stroke, and general configuration of the larger engine to come.

Deschamps V 3050 inverted V-12 aircraft diesel engine of 1934.

The Deschamps V 3050 was an inverted, 12-cylinder, diesel aircraft engine of all aluminum construction. The engine was built by the Lambert Engine and Machine Company in Moline, Illinois and completed in 1934. The cylinder banks were arranged in a 30-degree Vee to minimize the engine’s frontal area. With a 6.0 in (152 mm) bore and 9.0 in (229 mm) stroke, the engine had a total displacement of 3,053 cu in (50.0 L). The liquid-cooled, direct drive engine produced 1,200 hp (895 kW) at 1,600 rpm for takeoff and 950 hp (708 kW) at 1,500 rpm for cruise. Fuel consumption was 0.41 lb/hp/hr (249 g/kW/h). When built, it was one of the largest and most powerful diesel aircraft engines in the world.

The compression ratio of the V 3050 was 16 to 1, and air was forced into the cylinders by two gear-driven GE superchargers. The centrifugal superchargers were driven at 13.5 times crankshaft speed (21,600 rpm) and provided air at 12 psi (0.83 bar). Cylinder scavenging for the two-stroke cycle required eight psi, leaving four psi for boost. A small portion of the air entering the superchargers was taken from the crankcase to provide ample ventilation and burn away any fuel vapors. Sea-level power could be maintained to an altitude of 10,000 ft (3,048 m).

Each bank of cylinders had an intake manifold on the inside of the Vee to deliver air from the superchargers to the cylinders. The compressed air entered each cylinder via two poppet valves actuated simultaneously by an overhead camshaft driven at crankshaft speed.

Rear view for the Deschamps diesel highlighting the two GE superchargers. The glow plugs are also visible on the right cylinder bank.

A ring of 12 exhaust ports was located in the cylinder wall and exposed by the piston. To prevent excessive oil consumption and exhaust smoke, a small horizontal groove was cut in the cylinder wall just below each of the 12 exhaust ports. The grooves in the cylinder liner aligned with an annular groove in the cylinder casing wall. The annular grooves for all 12 cylinders were connected to a vacuum pump that scavenged oil from the pistons. The amount of oil stripped from the pistons was controlled by the amount of vacuum.

The superchargers and camshafts were driven from the crankshaft via separate vertical shafts with bevel gears. A Lanchester type torsional vibration damper was incorporated on the rear of the crankshaft to protect the gear drives. The damper was combined with a torque limiter clutch that would slip momentarily under sudden changes in torque.

Each bank of cylinders had independent intake delivery, exhaust, liquid-cooling connections, oil connections, oil and fuel pumps, and fuel injectors. In theory, each bank could be operated independently of the other bank, sharing only a common crankshaft. At 1,600 rpm, oil was circulated at 80–100 psi (5.5–6.9 bar) while coolant circulation was at 230 gpm (871 l/m).

Sectional view of the Deschamps V 3050 diesel with the glow plug detailed on the lower left.

Fuel was injected directly into each cylinder via two Deschamps-designed (U.S. patent 2,020,302) fuel injectors operating at 3,500 psi (241.3 bar). The two injectors per cylinder alternated supplying fuel into the cylinder, each firing every-other compression stroke. For slow rpm operation, one injector was shut off, essentially making the engine a four-stroke. This kept the engine running smoothly and the cylinders warm for instant application of more power. One fuel pump for each engine bank was used and supplied fuel at 15 psi (1.0 bar) with a maximum flow of 150 gph (9.4 l/m).

The engine was air-started by a compressor charged to 850 psi (58.6 bar). For staring the engine in cold weather, glow plugs were provided in the right cylinder bank while the left bank’s intake valves were kept open with the fuel shut off. A reversing gear could be fitted for utilizing the engine in airships. The V 3050 was 26.5 in (0.67 m) wide, 49.5 in (1.26 m) tall, and 99 in (2.52 m) long. It weighed 2,400 lb (1,089 kg) with all accessories, giving it 2.0 lb/hp (1.2 kg/kW).

After completing the engine, no funds remained for testing. Deschamps met with the Army Air Corps Power Plant Laboratory in June 1934, but it seems no further testing was done on the engine. Deschamps went on to work for various aviation corporations, patenting a number of fuel injectors and pumps along the way. Amazingly, the Deschamps V 3050 diesel engine survives and is in storage at the National Air and Space Museum’s Garber Facility in Silver Hill, Maryland.

Deschamps Diesel in storage at the National Air and Space Museum’s Garber Facility in Silver Hill, Maryland. (Fred van der Horst image via the Aircraft Engine Historical Society)

Aircraft Diesels by Paul H. Wilkinson (1940)
Aerosphere 1939 by Glenn Angle (1940)
Diesel Aviation Engines by Paul H. Wilkinson (1942)
Jane’s All the World’s Aircraft 1934 by C. G. Grey (1934)
– “A 1,200 H.P. Diesel Engine.” Flight. May 24, 1934
– “Internal Combustion Engine” U.S. Patent 2,064,196 by Desire J. Deschamps (1930) pdf

McDonnell Aircraft Corporation Model 1

By William Pearce

In 1938 James McDonnell found himself diligently at work with the Glenn L. Martin Company in Baltimore, Maryland. While employed with Martin, McDonnell had designed a number of successful aircraft and was now focused on a streamlined design with the engine mounted in the fuselage. McDonnell had worked for the Martin Company since 1933 but was very interested in starting his own aircraft company. Late in 1938, he left Martin.

Artwork of the McDonnell Model 1 with a four-gun nose.

The McDonnell Aircraft Corporation was incorporated on 6 July 1939. The company began work out of St. Louis, Missouri and quickly obtained subcontracted work for other aircraft manufacturers. In addition, McDonnell submitted a few aircraft proposals to the United States Army Air Corps and Navy. Although none of the proposals led to any contracts, they did open the door for McDonnell to be included in the Air Corps Request for Data R40-C, officially issued on 20 February 1940.

R40-C was an informal Request for Data that encouraged aircraft manufacturers to propose unorthodox aircraft. These aircraft would need to be capable of at least 450 mph (724 km/h), but preferably 525 mph (845 km/h), and meet other requirements outlined in Type Specification XC-622. R40-C asked aircraft engine manufacturers to develop new power plants. A total of 26 aircraft designs were submitted by six selected aircraft companies. These designs included a mix of eight different engines from four engine companies. An additional engine from an additional manufacturer was later added.

Three-view general arrangement drawing of McDonnell’s Model 1 from November 1939. The drawing seems to illustrate a five-gun nose: two machine guns housed in the fuselage sides, two more (or cannons) toward the nose, and one cannon (possibly 37 mm) in the center of the nose.

McDonnell’s answer to R40-C was the Model 1 (often called Model I). It was the company’s first design, and McDonnell submitted its proposal to the Air Corps on 11 April 1940. Four Model 1 variations were submitted that differed only by engine type. While the Model 1 design appeared fairly conventional, it was possibly the most radical of the designs submitted. The Model 1’s shape was a direct evolution of concepts James McDonnell was working on during his last days with the Martin Company.

The Model 1 featured unprecedented streamlining and incorporated airfoil-shaped fillets where the wing and fuselage joined. The proposed engines were the 24-cylinder Allison V-3420-B2, 24-cylinder Pratt & Whitney H-3130, 24-cylinder Pratt & Whitney X-1800-A2G, and 42-cylinder Wright R-2160 Tornado; all were liquid-cooled. Regardless of the type selected, the engine was buried in the fuselage aft of the pilot. Engine power was transmitted via extension shafts and right angle gear drives to a pair of two-speed, four-blade, 10 ft 7 in (3.23 m) diameter, pusher propellers mounted on the wings. The aircraft featured gear-driven radiator cooling fans. Originally the aircraft was to be armed with two .30-cal. machine guns and two 20 mm cannons, but armament varied throughout the design process. However, armament always consisted of a combination of two to four machine guns and one to four cannons.

Allison V-3420-powered McDonnell Model 1 cutaway dated April 3, 1940. Armament now includes six guns: two machine guns in the fuselage sides, two more (or 20 mm cannons) toward the nose, and two 20 mm cannons in the nose.

The X-1800 and R-2160-powered designs did not meet the specifications of XC-622 and were dropped from the R40-C competition.  With a two-stage supercharger for the V-3420 engine and a two-stage, two-speed supercharger for the H-3130, both engines provided sufficient power for their respective Model 1 designs to achieve the XC-622 specifications.

The Model 1 had a 45 ft (13.7 m) wingspan and was 45 ft 4 in (13.8 m) long. With the Allison V-3420, the aircraft weighed 13,826 lb (6,271 kg) and had a maximum speed of 383 mph (616 km/h) at 5,000 ft (1,524 m) and 448 mph (721 km/h) at 20,000 ft (6,096 m). With the Pratt & Whitney H-3130, the Model 1 weighed 14,800 lb (6,713 kg) and had a maximum speed of 385 mph (620 km/h) at 5,000 ft (1,524 m) and 454 mph (731 km/h) at 20,000 ft (6,096 m).


This wind tunnel model illustrates the evolution of the Model 1 as it became the XP-67. Seen here is the Model 2, with wing-mounted Continental XI-1430 engines in a tractor configuration. The basic shape of the Model 1’s fuselage and wings remained unchanged. The next version, known as the Model 2A, incorporated significant blending of the fuselage and engine nacelles with the wings. The Model 2A was the final step to the XP-67. (Image is flipped as the model was actually hung inverted in the wind tunnel.)

It would take an estimated 42 months to develop the engine and power drives for the Model 1. In addition, the Model 1 was the heaviest aircraft in the competition. These and other factors resulted in the two remaining Model 1 proposals to be ranked 21st and 22nd out of 26 submissions. Even so, the Model 1 did interest the Air Corps enough for them to purchase engineering data and a wind tunnel model on 6 June 1940 for $3,000. This was the McDonnell Aircraft Corporation’s first sale to the Army Air Corps.

The new engines involved with the R40-C competition became known as the “hyper” engines, an abbreviation of high-performance. The aircraft that won the competition were the Vultee XP-54 Swoose Goose, Curtiss XP-55 Ascender, and Northrop XP-56 Black Bullet. All were built and were pusher designs that failed to meet expectations and were fraught with technical difficulties. None of the hyper engines or R40-C aircraft entered production. The Model 1 was developed into the McDonnell XP-67 Moonbat that, although not successful, was built and did fly.

McDonnell Aircraft Corporation ad featuring the Model 1.

American Secret Pusher Fighters of World War II by Gerald Balzar (2008)
McDonnell Douglas Aircraft Since 1920: Volume II by Rene Francillion (1990)
American Secret Projects 1937–1945 by Tony Buttler and Alan Griffith (2015)
– “Design for a Pursuit Airplane” U.S. Design Patent 134,425 by James McDonnell (1942) pdf

Papin-Rouilly Gyroptere (Gyropter)

By William Pearce

The Papin-Rouilly Gyroptere as depicted on the cover of the September 1922 edition of Popular Science.

The Gyroptere was designed in France from 1911-1914 by Alphonse Papin and Didier Rouilly. Their monocopter was based on the sycamore seed; a single blade extends from the seed to spin the seed and slow its descent as it falls. Though unsuccessful, the machine was the first air-jet helicopter. Papin and Rouilly obtained French patents 440,593 and 440,594 for their invention and later obtained U.S. patent 1,133,660 in 1915 (filed in 1912).

Construction of Papin and Rouilly’s Gyroptere began in February 1914 and was completed in June of the same year. The prototype was named Chrysalis (Chrysalide). Constructed of molded wood, the Gyroptere was well built with compound curves and a smooth sweep of its single, long, airfoil-shaped blade. The fabric-covered blade was hollow and approximately 19.5 ft (5.9 m) long and 4.4 ft (1.33 m) wide, giving it an area of 130 sq ft (12 sq m). The blade was counterbalanced by an 80 hp (60 kW), nine-cylinder Le Rhone rotary engine. The pilot occupied a nacelle between the blade and engine. The bottom of the nacelle included a structure to support the machine while it was on the ground or act as a float when on water.

The Le Rhone engine was started with a pulley system. The engine, turning at 1,200 rpm, drove a fan that produced an output of just over 250 cu ft (7 cu m) of air per second. The air, along with the engine’s hot exhaust for thermal expansion, was directed through the length of the blade and exited the blade’s tip through a nozzle on the trailing edge at 330 ft/s (100 m/s). This jet of air would turn the blade, and the gyroscopic force of the motor would lift the blade into a positive angle of attack. The nacelle that carried the pilot was centered on the axis of rotation. The nacelle was mounted on ball-bearings and was centered against four horizontal rollers. The entire machine weighed 1,100 lb (500 kg), which was 220 lb (100 kg) more than originally planned.

This image offers a good view of the Gyroptere. The blade does not have its covering, the float and directional control tube can clearly be seen in the center nacelle, and the Le Rhone engine in its fan housing is on the right.

The pilot controlled the Gyroptere through the use of two foot pedals: one pedal opened a valve to admit air to the blade; and the second pedal allowed air into an L-shaped tube above the craft that served as a rudder for directional control. The L-shaped tube was directed by the pilot; its discharge provided forward thrust, steering, and stabilized the center drum to prevent it from spinning with the blade. A switch in the nacelle allowed the pilot to engaged or disengaged the engine.

This view highlights the air-jet nozzle on the trailing edge of the blade, which can be seen on the left.

The outbreak of World War I delayed testing until 31 March 1915. During tests on Lake Cercey (Reservoir de Cercey), near Pouilly-en-Auxois, France, the craft achieved a rotor speed of only 47 rpm, well below the 60 rpm calculated as necessary for liftoff. Even so, the machine was wildly out of balance, and the blade repeatedly contacted the water, damaging itself and shaking up the pilot. In addition, the Le Rhone engine used was not powerful enough; the Gyroptere had been designed to use a 100 hp (75 kW) engine which could not be obtained.

A military commission observing the test determined that such a machine could not aid the war effort and halted further evaluation. The Gyroptere remained at Lake Cercey until it was sold for scrap in 1919.

The completed Gyroptere awaiting tests on Lake Cercey on 31 March 1915.

French Aircraft of the First World War by Davilla and Soltan (1997)
– “Helicopter” U.S. Patent 1,133,660 by Papin and Rouilly (1915) pdf
– “Will This ‘Whirling Leaf’ Flying Machine Solve Greatest Problem in Aviation?Popular Science (September 1922)

Sikorsky S-56 (CH-37 Mojave/Deuce) Helicopter

By William Pearce

At the time of its introduction, the Sikorsky S-56 was the largest and fastest military helicopter in the Western world. In 1956, the helicopter set two height-with-payload world records and one world speed record. The S-56 was also Sikorsky’s first multi-engined helicopter and remains the largest piston-engined helicopter ever built.

CH-37B Mojave in flight. The screen on the side of the engine nacelle to maximize engine cooling is visible.

The S-56 was powered by two Pratt & Whitney R-2800 air-cooled radial engines with a takeoff rating of 2,100 hp (1,566 kW) and a cruise rating of 1,900 hp (1,417 kW). R-2800-50 engines were initially used, but late production aircraft used R-2800-54 engines, which had upgraded magnetos and additional mounting studs. The engines were connected to the main rotor’s transmission via a hydro-mechanical clutch. This clutch allowed the engines to run independently from the main rotor for starting or in the event of an engine failure. Power for the tail rotor was taken off the main transmission.

Unlike most heavy lift helicopters, the engines were not located in the upper section of the fuselage. Instead, each engine was housed in a nacelle fixed to the end of a short shoulder-mounted wing on each side of the helicopter. The engine nacelles also accommodated the machine’s fully retractable, twin-wheeled main landing gear.

The S-56’s engine arrangement allowed for an unobstructed cargo bay of nearly 1,500 cubic feet (24.5 cu m)—large enough to carry three Jeeps, 24 stretchers, or up to 26 fully-equipped troops. The cargo bay measured 30 ft 4 in (9.2 m) long, 7 ft 8 in (2.3 m) wide and 6 ft 8 in (2.0 m) high. The S-56’s nose section was equipped with large clam-shell doors which allowed vehicles to be driven straight into the cargo area. The cockpit was placed above and slightly aft of the doors to ensure good visibility. The single main rotor was five-bladed and designed to sustain the aircraft in flight with one blade shot away in combat. For storage, the helicopter’s main rotor blades folded back along the fuselage and the tail rotor mast folded forward.

Head on shot of the CH-37 with the clam-shell doors open and distinctive engine pods visible.

Sikorsky originally developed the Model S-56 in response to a 1950 Marine Corps requirement for a heavy-lift assault transport able to carry 26 fully equipped troops. In 1951 the Navy ordered four XHR2S-1 prototypes for USMC evaluation, and the first of these made its maiden flight on 18 December 1953. In 1954 the Army borrowed one of these pre-production machines. Re-designated YH-37 Mojave, it was subjected to rigorous evaluations before it was returned to the Marines.

Based on the helicopter’s excellent showing during the Marine and Army evaluations, Sikorsky was awarded a contract for 55 HR2S-1 for the Marines, who nicknamed the helicopter Deuce, and 94 H-37A Mojaves for the Army. The H-37A was delivered to the Army during the summer of 1956, at about the same time the HR2S-1 naval variant was entering regular Marine squadron service. The Marines set three world records for helicopters in November 1956 when a HR2S-1 carried an 11,050 lb (5,012 kg) payload to an altitude of 12,000 ft (3,658 m), carried 13,250 lb (6,010 kg) to over 7,000 ft (2,134 m), and set a three kilometer speed record of 162.743 mph (261.910 km/h). All aircraft were delivered to their respective services by May 1960.

In 1961 Sikorsky began converting the Army’s H-37As to B model standards. The upgrade included the installation of automatic flight stabilization systems that gave the H-37B the ability to load and unload while hovering, crash-resistant fuel cells, and modified nose doors. All but four A models were eventually converted. In 1962 military aircraft designations in the United States were unified, and the H-37A were re-designated CH-37A; the modified B machines became CH-37B, and the Marine’s HR2S-1 became CH-37C.

Three CH-37C Deuces on a carrier deck. The hole on the front of the engine nacelles is the air intake for the R-2800 engine.

The S-56 was developed just prior to the widespread adoption of the turbine engine as a helicopter powerplant. As a result, the type was forced to rely on larger, heavier, and less powerful piston engines. Even so, the S-56 ultimately proved to be a more than capable heavy-lifter. In June 1963, four CH-37B Mojaves were temporarily deployed to Vietnam to recover downed U.S. aircraft. By the following December, the Mojaves had recovered an estimated $7.5 million worth of equipment. Most of the recoveries were sling-lifted out of enemy-held territory that was virtually inaccessible by any other means.

In September 1965 a Marine detachment of eight Deuces was sent to Vietnam for general transport duties in support of Marine Air Group 16 at Marble Mountain. Although this detachment had only ten pilots for eight aircraft, they flew about 5,400 hours in 1,500 missions, hauled more than 12.5 million pounds (5.67 million kg) of cargo, and transported some 31,000 passengers without an air accident.

The Mojave did not see more extensive service in Vietnam primarily because of its replacement by the turbine-powered Sikorsky CH-54 Tarhe (S-64 Skycrane), a machine that weighed slightly less than the CH-37 but could carry nearly four times as many troops or five times as much cargo. In addition, the R-2800 engine was very loud, created a lot of vibration, and required much more maintenance than a turbine engine. The last CH-37 was withdrawn from Army service in the late 1960s. The Marine’s Deuces were replaced by CH-53 Sea Stallions in 1967.

When built, no helicopter could surpass the CH-37’s lift capacity.

U.S. Army Aircraft Since 1947 by Stephen Harding (1997)
R-2800: Pratt & Whitney’s Dependable Masterpiece by Graham White (2001)

Douglas XA-26D 41-39543

Douglas XA-26D and XA-26E Invaders

By William Pearce

The Douglas XA-26D and E were improved versions of the Douglas A-26B and C respectively. Both the XA-26D and E were upgraded with a more powerful version of the Pratt & Whitney R-2800 radial engine, the -83, built by Chevrolet and rated at 2,100 hp (1,566 kW). The engine’s output increased to 2,400 hp (1,780 kW) with water injection. The carburetor air scoops in the cowling were revised along with the carburetors, superchargers, engine mounts, and generators. The aircraft were fitted with wide-cord, 12.7 ft (3.87 m), four-blade propellers with spinners, although three-blade propellers were also tested. The top speed of the XA-26D and E was 403 mph (649 km/h) at 15,000 ft (4,572 m)—about 50 mph (80 km/h) faster than the B and C models—and the climb rate doubled to 2,326 fpm (11.8 m/s).

Douglas XA-26D 41-39543

The second XA-26D Invader, serial number 41-39543, is seen here with three-blade propellers. Note the spinners and revised engine cowlings compared to a typical A-26.

The D model was a solid nose version primarily intended for ground attack. The aircraft was equipped with 14 forward-firing .50-cal. machine guns: eight in the nose and six more in the wings. The aircraft also had dorsal and ventral barbettes with two machine guns each.

The first XA-26D Invader was modified from an A-26B, serial number 44-34100, starting in January 1945. Serial number 44-34100 was accepted by the USAAF on 31 January 1945 but was not available until 31 October 1945. The individual aircraft record card has a notation indicating the aircraft was to remain at the contractor’s plant for 180 days. The first record entry listing the aircraft as an A-26D was on 11 November 1945. Another XA-26D was created using A-26B serial number 41-39543, and the D modifications were completed by July 1945.

Some sources list another A-26B, serial number 44-34776, as being converted to the XA-26D standard. However, the data card for this aircraft makes no reference to a conversion program.

One B-26C, serial number 44-35563, was modified by the Douglas plant to XA-26E specifications. The E model was the glass nose version with two machine guns in the nose, six in the wings, and two in each dorsal and ventral barbettes.

A contract for 750 production A-26Ds was placed on 13 April 1945, following an order of 1,250 A-26Es placed on 5 April 1945. Both contracts were cancelled at the end of World War II; none of the aircraft were built.

Douglas XA-26D 41-39543 4-blade

The second XA-26D aircraft with four-blade propellers. Note the first Douglas XB-42 Mixmaster prototype at left in the background.

American Bomber Aircraft Development in World War 2 by Bill Norton (2012)

NA-98X Front

North American Aviation NA-98X Super Strafer

By William Pearce

In 1943, North American Aviation (NAA) created an internal design for an improved attack bomber that would provide the firepower of the B-25H but with substantially improved performance. This evolution of the B-25 line was intended as an alternative to the heavily-armed and delayed Douglas A-26B Invader. Power was to be provided by a pair of Pratt & Whitney R-2800 air-cooled radial engines housed inside low-drag cowlings and driving a pair of cuffed, four-blade propellers with spinners. The empennage was changed to a conventional single-tail, altering one of the B-25’s most notable characteristics. The wing tips were square-cut like a P-51’s, rather than rounded, permitting the ailerons to be extended farther outboard to provide better roll control. Armament improvements were to include a computing gun sight and a new low-drag canopy designed by North American for the top turret. A compensating sight was to be used in the tail turret and illuminated reflector optical sights for the waist guns. Otherwise, the aircraft had the same armament as the B-25H, including the 75mm cannon.

NAA B-25 based high performance attack bomber drawn by Eugene Clay.

In early 1944, a low-cost and less ambitious alternative was submitted to the Army Air Forces. This proposal was to take the existing B-25 airframe and apply many of the enhancements from the NAA internal design. A B-25H-5 (serial number 43-4406) was chosen as a testbed for the modifications, which no longer included the single tail and four-blade propellers. It was given the designation NA-98X by NAA and nicknamed Super Strafer. Since it was not designed for any USAAF requirement, it never carried an official USAAF designation.

The new aircraft was powered by a pair of 2,000 hp (1,491 kW) Pratt & Whitney R-2800-51 engines with 15 minutes of water injection, all housed in A-26 cowlings. Large conical spinners were used on the three-blade propellers. The squared wing tips allowed the ailerons to be extended by one foot, and the control system was changed to lighten the stick forces. Except for the removal of the fuselage blister gun packs, the aircraft had the same armament as the B-25H.

The NA-98X: a B-25H, serial number 43-4406, modified with R-2800 engines, spinners, and squared wings.

The first flight of the NA-98X took place at Mines Field in Los Angeles on 31 March 1944. NAA test pilot Joe Barton was at the controls with Jim Talman as the NAA flight engineer. The flight lasted an hour, and Barton reported better speed and acceleration, reduced vibration, and a higher roll rate compared to a standard B-25. The Super Strafer performed well. The aircraft reached 10,000 feet (3,048 m) in 4.9 minutes at war emergency power and in 5.3 minutes at military power. A maximum speed of 328 mph (528 km/h) was achieved at sea level with war emergency power, and Barton eventually achieved 350 mph (563 km/h) at a higher altitude. The performance numbers were a drastic improvement over the standard B-25H’s top speed of 273 mph (439 km/h) and 790 fpm (4.0 m/s) climb rate. There were 16 more NAA test flights before the aircraft was turned over to the USAAF for evaluation.

The increased power of the R-2800 engines, along with the increased aileron area and reduced stick forces, created the possibility to operate the aircraft outside the structural limits of the wings. This could lead to a catastrophic failure, loss of the aircraft, and possible loss of life. Without strengthening the wings for intended dives of 400 mph (644 km/h) and high-g pullouts, the maximum airspeed was restricted to 340 mph (547 km/h), and a g-limit of 2.67g was imposed during flight tests.

NAA NA-98X cowling

A detailed look at the A-26 cowling covering the R-2800 engine installed on the NX-98X.

Major Perry Ritchie was assigned as the evaluator for the USAAF and had made 13 flights in the aircraft before disaster struck on 24 April 1944. Returning from the aircraft’s 29th test flight, Maj. Ritchie and Lt. Winton Wey approached Mines Field at a very high speed, above the 340 mph (547 km/h) redline. As he made a steep pull-up, in excess of the 2.67g restriction, both wings separated outboard the engine nacelles and struck the horizontal stabilizers, causing the tail to break free from the aircraft. The NA-98X crashed, killing both Maj. Ritchie and Lt. Wey.

The NA-98X was a very powerful and responsive aircraft. Maj. Ritchie was primarily a fighter pilot and had a tendency to fly the maneuverable bomber more like a fighter. Maj Ritchie had made the high-speed pass and abrupt pull-up twice before and was warned not to do it again. Some eyewitnesses estimated that the NX-98X made the last pass at around 400 mph (644 km/h) and hit around 5g in the pull-up. Simply put, the aircraft was flown beyond its known structural limitations by Maj. Ritchie.

Following the crash, all further work on the NA-98X project was abandoned even though the RAF had shown interest after a test flight. Admittedly, the wings would have required a redesign to cope with the power from the R-2800s, negating any cost savings for performance on par with the Douglas A-26. In its short 25-day life, the NA-98X Super Strafer totaled 40:15 hours of flight tests. NAA time totaled 21:25 hours over a period of 22 days, including eight days of down time. Total time for Maj. Ritchie was 18:50 hours over a period of three days.

NA-98X Front

Front view of the NA-98X Super Strafer with the 75mm cannon and squared wingtips clearly visible.

– “North American B-25 Variant BriefingWings of Fame Volume 3  (1996)
American Bomber Aircraft Development in World War 2 by Bill Norton (2012)
North American Aircraft 1934-1998 Volume 1 by Tom Avery (1998)

Monaco-Trossi1935 Wiki

Monaco Trossi 1935 Grand Prix Racer

By William Pearce

One of the oddest Grand Prix race cars ever built was the 1935 Monaco Trossi. Built by Augusto Camillo Pietro Monaco and funded by race driver Count Carlo Felice Trossi, the 1935 Monaco Trossi was a front-wheel drive car powered by an air cooled, 16-cylinder, two-stroke radial engine.

Augusto Monaco had built a successful racing car / hill climber but had aspirations of building a Grand Prix car for the 750 kg (1,653 lb) Grand Prix racing formula. For the Grand Prix car, Monaco joined forces with an engineer/driver named Giulio Aymini. The team also received support from Senator Agnelli at FIAT, who offered FIAT’s Lingotto facilities, in Turin, to build and test the new two-stroke radial engine. However, once the engine was built, tests revealed so many problems that Agnelli and FIAT withdrew their support, leaving Monaco in search of new financial and manufacturing assistance.

A vintage shot of the Monaco Trossi at Monza. With the cowling removed to aid cooling, a good view is provided of the engine and its paired cylinders.

Monaco convinced race driver Count Felice Trossi, who was a successful member of the Alfa Romeo team, to become a partner in the project providing financial and manufacturing support. The car was built in Trossi’s workshop, which was part of the Gaglianico castle outside Biella in northern Italy. A friend of Trossi, Count Revelli, helped design a streamlined body for the car. Many rumors and much speculation surrounded the racer, and it was finally revealed to the public at the Autodromo Nazional Monza in July 1935 for tests and qualifying sessions in preparation for the Italian Gran Prix.

The air cooled, 16-cylinder, two-stroke radial engine was mounted at the very front of the car. With a 65 mm (2.56 in) bore and 75 mm (2.96 in) stroke, the engine displaced 3,982 cc (243 cu in). The cylinders were arranged in two rows of eight with each front row cylinder and rear row cylinder paired together. While having two cylinders and two pistons, each cylinder pair had a common combustion chamber and spark plug. The eight two-cylinder pairs were positioned around the crankcase. Being a two-stroke engine, there were no intake or exhaust valves. The inlet ports were in the rear cylinders and exhaust ports were in the front cylinders. The crankshaft was a three-piece design and the crankcase was made of duralumin. For both cylinder rows, the connecting rods were of the normal radial engine type with one master rod connected to the crankshaft and the seven articulating rods connected to the master rod.

Rare view of the Monaco Trossi under its own power at Monza in 1935.

Behind the engine were two Zoller M 160 superchargers providing a pressure of 0.68 atm (10 psi), each supplied by a Zenith carburetor. Exhaust gases discharged into two four-pipe manifolds on the front of the engine. These manifolds led to two long exhaust pipes that extended under the car and exited behind the rear wheels. The engine produced 250 hp (186 kW) at 6,000 rpm.

Power from the engine was transferred to the four-speed transmission by a shaft that went through the transmission to the clutch, then back into the transmission. The independent suspension for each wheel was provided by double wishbones, horizontal coil springs, and cockpit adjustable oil dampers. The aircraft-type spaceframe chassis was made with 4 cm (1.57 in) diameter manganese-molybdenum steel tubes with larger cross tubes at the front and rear. The lightweight alloy body panels were screw-fastened to the chassis. The car featured large hydraulic drum brakes on each wheel, which was advanced for the time. Front tires were 5.25 x 31 and rear tires were 4.40 x 27. The vehicle weighed about 710 kg (1,565 lb).

Monaco-Trossi1935 Wiki

A clear view of the two four-pipe manifolds taking the exhaust to the rear of the car. Also note the spark plugs extending out of the engine cowl. (Image by Brain Snelson via Flickr/Wikimedia Commons)

Both Aymini and Trossi tested the car at Monza reaching speeds of 240 km/h (150 mph), and the car was on the entry list for the 1935 Italian Grand Prix. However, testing revealed that the car experienced severe overheating and a tendency for the engine to destroy the spark plugs. But the more serious issue was the extreme understeer caused by the 75% front / 25% rear weight distribution. With the problems uncorrectable without a serious redesign, the car proved too dangerous and it was never raced.

After Count Trossi’s death in 1949, the 1935 Monaco Trossi racer was donated by his widow, the Contessa Lisetta, to the Museo dell’Automobile in Turin where it is currently on display.


This view clearly illustrates the Monaco Trossi’s front end complexity. (Image by Brain Snelson via Flickr/Wikimedia Commons)