Throughout the duration of the test flights for the first FM Airacuda, on the date of September 28th, 1939 one of the turbo superchargers exploded.
The Airacuda was Bell Aircraft’s answer to bomber destroyer aircraft. The innovation of placing an aircrew away from the fuselage was not just a German idea. The Bell Aircuda YFM-1 had almost the same wing mounted crew cabins.
Developed during the late 1930’s for use against enemy bomber formations, the YMF-1 featured manned forward facing gun turrets that were on both wings, each was packing a 37mm cannon. This was to make room for the cabins; the plane’s engines would face the aft.
The first military aircraft produced by Bell, it was originally designated the Bell Model 1. The Airacuda was first flown on September 1st, 1937.
It incorporated several features that had never been seen before in the military aircraft. It was also never seen again. By using a streamlined, “futuristic” model, the Bell Aircuda seemed to be unlike any other fighters that were at that time.
As stated by Major Alexander De Seversky’s book, the Victory Through Air Power, the Bell Aircuda “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.”
It had been designed during a time when heavy escort fighters like the BF-170 were in the development stages.
The crew of five included the pilot and gunners, with the co-pilot and navigator doubled as a fire control officer.
The radio operator/gunner was armed with a pair of machine guns that were stationed at mid-fuselage waist blister. The purpose of this was to defend against aerial attacks from behind the plane.
A certain unusual feature of the Aircuda had been the main door to enter the plane. The door was able to be opened and pulled down and the hinges folded in on three steps for the crew to be able to climb inside the aircraft.
Ultimately Bell’s FM Aircuda was slower and less maneuverable than the bombers it was supposed to be protecting. This left it useless as an escort fighter.
The Design flaws
The Aircuda was plagued with problems from the start. Regardless of the sleek look it possessed, the Airacuda was heavy and was much slower than most bombers. With the event of interception by enemy fighters, the Airacuda was not able to be maneuverable enough to fight. Meanwhile, the lack of quality of the 270 kg (600 lb) bomb load was not useful for the intended fighter-bomber role. Even the 37 mm cannons were less valued than predicted. The cannons had the tendency to fill the gun nacelles with smoke when they were fired. Additionally, it was feared the gunners would be unable to escape during an emergency. They had propellers directly behind them. That kind of emergency bailout would have required both of the propellers to be feathered.
The Allison V-1710-41 engines, although they were relatively trouble free, had no additional cooling systems.
Like several pusher designs, they were vulnerable to overheating. When it was on the ground, the aircraft needed to be towed to and from the runway and could only be started when the Airacuda was ready for takeoff immediately.
Even while the plane was in the air, it was not uncommon to experience overheating issues.
Even though it was designed for turbo super charging, the first flights were made with V-1710-9 carbureted engines that would only deliver 1,000 hp each.
Regardless of the 5-foot long shaft extensions, there were no issues with that feature. The turbos were later fitted to the YFM-1; they were being plagued by unpredictable regulators that backfired endlessly. An explosion that occurred during the September 1939 test flight made it obvious that the teething engine problems would not be solved with ease.
The other sources that were noted by Marshall Wainwright indicated the first eight aircraft were originally to have been powered by the Allison V-1710-41 engines that were fitted with GE Type B-r turbo super chargers. These aircraft would eventually be delivered with the improved V-1710-23 engines. Wainwright had further stated that two of the YFM-1 air frames were being changed on the production line to accept the V-171041 engine without having to turbo supercharge, turning it into the YFM-1Bs.
This was noted in a contract change that was dated October 19th, 1939, which shows that the aircraft 34-489 and the 38-490 possessed their turbos, all linked ducting, and controls had been removed. The V-1710-41 “Altitude Rated” engines were installed instead. The D2A had been essentially a -23 with escalated supercharger gear ratios. This allowed the motor to develop about 1,090 horsepower that was up to 13,300 ft ASL. They use the exact ratings and components as the Altitude Rated V-1710-33 Allison that was fitted to the original Curtiss XP-40. Allison had been paid $1,690 to be able to modify each engine.
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