Bell YFM-1 Airacuda

 The Bell YFM-1 Airacuda was an American heavy fighter aircraft, developed by the Bell Aircraft Corporation during the mid-1930s. It was the first military aircraft produced by Bell. Originally designated the Bell Model 1, the Airacuda first flew on 1 September 1937. The Airacuda was marked by bold design advances and considerable flaws that eventually grounded the aircraft.

The Airacuda was Bell Aircraft's answer for a "bomber destroyer" aircraft. Although it did see limited production, and one fully operational squadron was eventually formed, only one prototype and 12 production models were ultimately built, in three slightly different versions.

Design and development

Bell FM-1 mockup at Langley wind tunnel

In an effort to break into the aviation business, Bell Aircraft created a unique fighter concept touted to be "a mobile anti-aircraft platform. as well as a "convoy fighter. Created to intercept enemy bombers at distances beyond the range of single-seat fighter interceptors, the YFM-1 (Y, service test; F, fighter; M, multiple) was an innovative design incorporating many features never before seen in a military aircraft, as well as several never seen again. Using a streamlined, "futuristic" design, the Bell Airacuda appeared to be "unlike any other fighters up to that time.

According to Major Alexander De Seversky's 1942 book, Victory Through Air Power, the Bell Airacuda "represents a great engineering achievement. But its designation as ′convoy fighter′ is erroneous, since that requires different disposition of armament. With its maximum firepower directed forward, it really offers a preview of an effective long-range interceptor fighter.

A forward-firing 37 mm (1.46 in) M4 cannon with an accompanying gunner was mounted in a forward compartment of each of the two engine nacelles.^[5] Although capable of aiming the cannons, the gunners' primary purpose was simply to load them with the 110 rounds of ammunition stored in each nacelle.

The crew of five included the pilot and gunners; a copilot/navigator who doubled as a fire-control officer, using a Sperry Instruments "Thermionic" fire control system (originally developed for anti-aircraft cannon) combined with a gyro-stabilized and an optical sight to aim the weapons;^[5] and a radio operator/gunner armed with a pair of machine guns stationed at mid-fuselage waist blisters for defense against attack from the rear.^[5]

An unusual feature of the Airacuda was the main door for entry. The door was opened and pulled down and hinges folded in on three steps for the crew to climb into the aircraft.^[6]

Design flaws

Bell YFM-1 during testing

The Airacuda was plagued with problems from the start. The lofty performance estimates were unobtainable as, despite its sleek looks, the Airacuda was heavy and was slower than most bombers. In the event of interception by enemy fighters, the Airacuda was not maneuverable enough to dogfight, while the meager 600 lb (270 kg) bombload was of little use in the intended fighter-bomber role. Even the 37 mm cannons were of less value than predicted. The cannons had a tendency to fill the gun nacelles with smoke whenever fired and, additionally, fears persisted as to how the gunners would escape in an emergency, with the propellers directly behind them. An emergency bailout would have required both propellers to be feathered,^[2] though additional provision was made with the use of explosive bolts on the propellers to jettison them in the event of a bailout. As with other types armed with the 37 mm M4, the low muzzle velocity of the weapon made it difficult to use as an aerial weapon, limiting the useful range.

The Allison V-1710-41 engines, though relatively trouble-free in other types, had insufficient cooling.^[2] Like many pusher designs, they were prone to overheating while on the ground, since there was no propwash blowing over the engines to cool them. On the ground, the aircraft had to be towed to and from the runway and could only be started when the Airacuda was able to take off immediately. Even in the air overheating was not uncommon. Although designed for turbo-supercharging, the first flights were made with V-1710-9 single-stage supercharged engines that only delivered 1,000 hp (750 kW) each. Despite the 5 ft (1.5 m)-long shaft extensions, there were no problems with this feature. When the turbos were fitted to the later YFM-1, they were plagued by cranky turbo regulators that backfired continuously. An explosion during a September 1939 test flight made it apparent that the teething engine troubles would not be solved easily.

Marshall Wainwright notes that other sources indicate the first eight aircraft were to originally have been powered by Allison V-1710-13 engines fitted with GE Type B-6 turbo-superchargers (turbochargers). These aircraft were eventually delivered with improved V-1710-23(D2) engines. Wainwright further states that two of the YFM-1 airframes were changed on the production line to accept the V-1710-41 without turbo-supercharging, becoming YFM-1Bs. This is noted in a contract change dated 19 October 1939 which shows that aircraft 38-489 and 38-490 had their turbos, all associated ducting, and controls removed and V-1710-41(D2A) "Altitude Rated" engines installed instead. The (D2A) was essentially a -23 with higher supercharger gear ratios (8.77:1 versus 6.23:1), which allowed the motor to develop around 1,090 horsepower (810 kW) up to 13,200 ft (4,000 m) ASL. They used the same ratings and components as the Altitude Rated V-1710-33(C15) Allison fitted to the original Curtiss XP-40. Allison was paid $1,690 to modify each engine.^[7][8]

Initial flight testing by Lt. Ben Kelsey proved the Airacuda virtually impossible to control with only one engine, as the aircraft would go into an immediate spin. Problems with stability in pitch were also encountered and had to be corrected by reducing power.^[5] Test pilot Erik Shilling described his experiences in a later book, Destiny: A Flying Tiger's Rendezvous With Fate as

Flying the Bell Airacuda was a new experience for me, since it was the first pusher aircraft I'd ever flown. Its handling characteristics were foreign to anything I had ever had my hands on. Under power it was unstable in pitch, but stable with power off. While flying straight and level, if a correction in pitch was required, a forward push on the control resulted in the airplane wanting to pitch over even more. Pitch control became a matter of continually jockeying the controls, however slightly, even when the aircraft was in proper trim. The same applied if pulling back on the control. It would tend to continue pitching up, requiring an immediate corrective response. The same happened in a turn with power off, the Bell became stable in pitch. This was fortunate because during approach and landing, it was very stable, and a nice flying airplane.^[3]

The Airacuda was also saddled with a complex and temperamental electrical system and was the only aircraft ever built to rely on an independent auxiliary power unit (APU) to power both engine fuel pumps, as well as all aircraft electrical systems.^[9] Systems usually powered by an aircraft's engines were instead powered by the single generator. The generator, with its own supercharger, was located in the belly of the aircraft. In the event of a failure (and they occurred frequently), the crew was instructed to begin immediate emergency restart procedures as the aircraft basically shut down. When the APU failed, the pilot had "NO fuel pressure, NO vacuum, NO hydraulic pressure, NO gear, NO flaps and NO ENGINES".^[10]

Accidents

Page from Bell YFM-1 and YFM-1B handbook (T.O.-01-110HA-1) showing emergency equipment and exits.

Despite the aircraft's many faults, only two were lost in accidents (although considering that only 12 were ever built, the statistics are not favorable with many other types, at a 16.6% loss ratio; especially when the actual aircraft saw so little operational service that would even expose it to hazard of accidents). The seventh aircraft (38-492) was on its final test flight from the Buffalo factory prior to delivery to the Air Corps when pilot John Strickler, a Bell pilot and engineer/co-pilot Brian Sparks, Bell's chief test pilot, encountered problems recovering from a deliberate spin attempt which was part of the test flight profile. Despite every effort to emerge from the spin, the aircraft would not respond, and it appeared that the rudder had locked. Co-pilot Sparks shut down the engines and waited for the propellers to come to a stop before bailing out. Because of the tandem seating, it was necessary for Sparks to exit the aircraft first, and in doing so he struck the empennage, breaking his legs — and in the process, freeing the rudder.^[5]

Strickler decided to stay with the aircraft and attempt an emergency landing. By this time, the aircraft had lost sufficient altitude that there was not time to restart the engines. Strickler put the Airacuda down hard in a farmer's field, and walked away unhurt. The Airacuda was so badly damaged it had to be scrapped. All three Airacudas with tricycle landing gear encountered problems and were damaged at one time or another. The most serious accident occurred to YFM-1A (Model 8) 38-497, on a flight between Chanute Field, Illinois, and Keesler Field, Mississippi, when a broken oil line started a fire. The cause of the broken line appeared to be serious airframe vibration encountered during the flight. With no way of extinguishing the fire, both the pilot and crew chief agreed to bail out. The pilot was killed when his parachute failed to deploy (he may have struck the tail while bailing out). This was the only fatality to occur during the flying of Airacudas. The accident investigation report stated "inherent defects in design caused constant maintenance difficulties and the flying of this type has been very limited."

Operational history

Bell XFM-1 Airacuda in flight

Despite these problems, one fully operational Airacuda squadron was eventually assembled, and operated from 1938 until 1940. Funds were appropriated, but never released, for the purchase of two groups of Airacudas.^[5] Continuing problems gave the aircraft a reputation as "hangar queens".^[11] Near the end of the type's operational life, the aircraft were flown primarily for photo opportunities and always accompanied by a chase plane for safety. Eventually the decision was made to disperse the aircraft to various airfields to give pilots an opportunity to add the unusual aircraft to their log books. Airacudas were sent at various times to Langley Field, Virginia; Maxwell Field, Alabama; Hamilton Field, California; and Wright Field, in Dayton, Ohio. YFM-1 38-488 was displayed at the 1940 World's Fair in New York, finished in the markings of the 27th Pursuit Squadron. During this time, the aircraft saw limited flight time, as few pilots were interested in flying the unusual aircraft.

Several plans were made to modify the Airacudas to give them operational status, including modifying the airframe and adding more powerful engines, but all proposals were eventually rejected. In early 1942, despite fears of enemy bomber attacks against which the Airacuda was intended, the aircraft were stricken from inventory.^[5]

Variants

The prototype, known as the XFM-1, incorporated a tailwheel, side "blister" ports, and a smooth, rounded canopy. This is the best known, and most produced version. An updated version called the YFM-1A eliminated the side blisters and added externally mounted radiators and turbo-superchargers. Produced in 1940, the final version designated YFM-1B, was slightly larger, had slightly less powerful Allison engines and incorporated a tricycle landing gear. The canopy was redesigned, with a flat forward windshield. A rearward-facing belly gunner's position was also added. The resulting aircraft was roughly the size of a Douglas B-18 Bolo medium bomber. Three YFM-1Bs were produced in 1939 before production was finally terminated.

XFM-1

(Model 1) Prototype powered by two 1,150 hp V-1710-13 engines, one (38-351) built.^[12][13]

YFM-1

(Model 7) Development aircraft powered by two 1,150 hp V-1710-23 engines and fitted with 37 mm cannons in wing nacelles, eight built, two later converted to YFM-1B.^[12]

YFM-1A

(Model 8) Development aircraft with tricycle landing gear, three built.^[12]

YFM-1B

YFM-1 re-engined with 1,090 hp V-1710-41 engines, two converted from YFM-1.^[12]

YFM-1C

(Model 17) – proposed variant not proceeded with.^{[N 1]}

Scrapping

By 1942, all nine surviving YFM-1 airframes had been flown by ferry crews to a training facility at Chanute Field, Illinois, where the aircraft were assigned to the 10th Air Base Squadron to be used for ground crew instruction. By March 1942, all Airacudas had been scrapped.^{[5][N 2]}

Specifications (XFM-1)

General characteristics

• Crew: five (pilot, copilot/navigator, radio operator/gunner, two gunners)
• Length: 44 ft 10 in (13.67 m)
• Wingspan: 69 ft 10 in (21.29 m)
• Height: 13 ft 7 in (4.14 m)
• Wing area: 684 sq ft (63.5 m²)
• Airfoil: NACA 23018/NACA 23009 ^[15]
• Empty weight: 13,376 lb (6,067 kg)
• Gross weight: 17,333 lb (7,862 kg)
• Max takeoff weight: 21,625 lb (9,809 kg)
• Fuel capacity: 400 US gal (1,500 L)
• Powerplant: 2 × Allison V-1710-9 liquid-cooled turbosupercharged V-12, 1,090 hp (810 kW) each
• Propellers: three-bladed

Performance

• Maximum speed: 277 mph (446 km/h, 241 kn)
• Cruise speed: 244 mph (393 km/h, 212 kn)
• Range: 2,600 mi (4,200 km, 2,300 nmi)
• Service ceiling: 30,500 ft (9,300 m)
• Rate of climb: 1,480 ft/min (7.5 m/s)

Armament

• Guns: ** 2 × 37 mm (1.46 in) M4 cannons (110 rpg)
  • 2 × .30 in (7.62 mm) M1919 Browning machine guns in front of nacelles
  • 2 × .50 in (12.7 mm) M2 Browning machine guns (600 rpg) in side blisters
• Bombs: 20 × 30 lb (14 kg) fragmentation bombs in wing bay

Bell XFL Airabonita

  The Bell XFL Airabonita was an American experimental carrier-based interceptor aircraft developed  by Bell Aircraft Corporation of Buffalo, New York for the United States NavyUnited States Navy by Bell Aircraft Corporation of Buffalo, New York. It was similar to and a parallel development of the U.S. Army Air Corps’ land-based P-39 Airacobra, differing mainly in the use of a tailwheel undercarriage in place of the P-39's tricycle gear. Only one prototype was built.

Design and development

The XFL-1 (Bell Model 5) was powered by a single 1,150 hp (858 kW) Allison XV-1710-6 liquid-cooled V12 engine installed amidships behind the pilot and driving a three-bladed Curtiss Electric propeller in the nose through a 10.38 ft (3.16 m) extension shaft. The aircraft had provisions for a single 37 mm (1.46 in) Oldsmobile T9 cannon which could be replaced by a .50 in (12.7 mm) Browning M2/AN machine gun firing through the propeller shaft and two .30 in (7.62 mm) machine guns in the fuselage nose. It first flew on 13 May 1940.^[1]

Although based on the P-39, the XFL-1 utilized a conventional tail-wheel undercarriage and the coolant radiators were housed externally in fairings under the wings instead of within the wing center section. The Allison engine was the first of its type to be tried out by the Navy, and lacked the turbosupercharger fitted to the XP-39.^{[N 1][1]}

Operational history

The XFL-1 in flight

In January 1938, the U.S. Navy issued a specification for a light carrier-based fighter to replace the obsolete biplanes then in use. On 11 April 1938, Bell, Brewster, Curtiss, Grumman, and Vought-Sikorksy submitted proposals but only three received contracts. Two of them were awarded contracts for one prototype each on 30 June 1938; these were for the Grumman XF5F-1 Skyrocket and the Vought XF4U-1 Corsair. The third contract, which was signed on 8 November, went to Bell Aircraft for one XFL-1 Airabonita. All three aircraft made their first flight in 1940: the XF5F-1 on 1 April, the XFL-1 on 13 May, and the XF4U-1 on 29 May.

Subsequent tests were prolonged because of difficulties with the Allison engine and problems with the balance of the aircraft. Official evaluation began in July 1940 but the XFL-1 failed to be certified for carrier operations because of main landing gear problems. The prototype was returned to Bell for modifications in December 1940 and returned to the Navy on 27 February 1941 at Naval Air Station Anacostia, District of Columbia. Based on the test results, the Navy decided not to order production of the aircraft.

In February 1942, the XFL-1 was transferred to the Aircraft Armament Unit at Naval Air Station Patuxent River, Maryland. It was later grounded, used for armament tests, and later destroyed. For many years its remains were visible at the dump at NAS Patuxent River.^[2][3]

As a possible further reason for the rejection, it is often stated that the Navy's position during that era was that all its aircraft should use air-cooled engines (while the Allison was liquid-cooled). This appears unfounded speculation. The U.S. Navy "would consider a liquid-cooled engine installation provided a material increase in performance over air-cooled engine can be shown."^[4]

In addition, the Allison engine had only a single-speed supercharger. Consequently, its altitude performance was much inferior to other naval fighters of the period, such as the Grumman F4F Wildcat. ^{[N 2]}

Lastly, the Airabonita had to compete against the faster though not "light" Vought F4U Corsair, which in the initial F4U-1 version was capable of 390 mph at 24,000 ft.^[5]

Operators

 United States

• United States Navy

Specifications (XFL-1 Airabonita

XFL-1

Data from^{[citation needed]}

General characteristics

• Crew: One
• Length: 29 ft 9 in (9.07 m)
• Wingspan: 35 ft 0 in (10.67 m)
• Height: 12 ft 9 in (3.89 m)
• Wing area: 232 sq ft (21.6 m²)
• Empty weight: 5,161 lb (2,341 kg)
• Gross weight: 6,651 lb (3,017 kg)
• Max takeoff weight: 7,212 lb (3,271 kg)
• Powerplant: 1 × Allison XV-1710-6 V-12 piston engine, 1,150 hp (858 kW)

Performance

• Maximum speed: 336 mph (541 km/h, 292 kn)
• Range: 1,072 mi (1,725 km, 932 nmi)
• Service ceiling: 30,900 ft (9,421 m)
• Rate of climb: 2,630 ft/min (13.4 m/s)
• Wing loading: 29 lb/sq ft (140 kg/m²)
• Power/mass: 0.17 hp/lb (280 W/kg)

Armament

• Guns:
  
  • 2 × 0.30 cal (7.62 mm) machine guns
  • 1 × 0.50 cal (12.7 mm) machine gun or 37 mm cannon

ACAZ C.2

 

ACAZ C.2
Role	Training Fighter
National origin	Belgium
Manufacturer	(Ateliers de Construction Aeronautique de Zeebrugge)
First flight	1926
Number built	1

The ACAZ C.2, Ateliers de Construction Aeronautique de Zeebrugge, was a prototype Belgian biplane fighter aircraft built in the 1920s.

Design and development

Built entirely of Duralumin metal, it was an advanced design at the time of its first flight in 1926, but although evaluated by the Belgian air force, no orders were placed. Of conventional biplane construction, the C.2, registered as O-BAFX, later OO-AFX, incorporated one unique feature - all four of its wings were identical and interchangeable. The aircraft also included space for cameras, allowing it to be used for photo reconnaissance.

Operational history

The C.2 was used in a failed aerial expedition by Edmond Thieffry, who with two companions (Joseph Lang and Philippe Quersin), attempted to fly it to Belgian Congo, departing Belgium on 9 March 1928, but only getting as far as Philippeville (Belgium).

The sole prototype was written off in a crash on 25 January 1933.^[1]

Modified ACAZ C.2

Specifications (ACAZ C.2)[edit]

ACAZ C.2 3-view drawing from Les Ailes September 30, 1926

Data from The Complete Book of Fighters^[1]

General characteristics

·       Crew: 2

·       Length: 8.25 m (27 ft 1 in)

·       Wingspan: 12.5 m (41 ft 0 in)

·       Height: 3.4 m (11 ft 2 in)

·       Wing area: 40.56 m² (436.6 sq ft)

·       Empty weight: 1,260 kg (2,778 lb)

·       Gross weight: 2,070 kg (4,564 lb)

·       Powerplant: 1 × Hispano-Suiza 12Ha V-12 water-cooled piston engine, 340 kW (450 hp)

Performance

·       Maximum speed: 250 km/h (160 mph, 130 kn)

·       Endurance: 3.5 hours at full power

·       Time to altitude: 6,000 m (20,000 ft) in 35 minutes

Armament

·       One .303 in (7.7 mm) Vickers machine gun firing through the propeller hub

·       Two .303 in (7.7 mm) Lewis machine guns on a flexible mount for the observer