Every aerospace engineer should know about this underpowered failure.
The Vought F7U Cutlass carrier-based jet fighter was one of the most unusual designs ever produced for the United States Navy (USN). Designed as the company’s entry in a 1945 carrier-based jet fighter design competition requiring capability to fly at 600 miles per hour at 40,000 feet, the aircraft featured broad-chord, low aspect ratio, swept wings, with a wing-mounted tail fin on either side of a short fuselage- resulting in a semi-tailless twin-engine jet. The cockpit was located as far forward as possible for pilot visibility.
Experience Should Have Helped
How did Vought arrive at such a novel design? German engineering. That’s right. Although at the time Vought denied any influence or even access to German aerodynamic engineers or their data, Messerschmitt and Arado engineers provided design inputs based on their experience with tailless German aircraft during the waning days of World War II. The F7U Cutlass was the last design overseen by Vought’s Rex Beisel, who designed the first Navy-specific fighter aircraft (the Curtiss/Naval Aircraft Factory TS-1 in 1922) as well as the Vought F4U Corsair.
High-pressure hydraulically actuated elevons (Vought dubbed them “ailevators”) were utilized for pitch and roll control. The wings had full span leading edge slats. The nose landing gear strut, easily the longest ever used on a Navy carrier-based aircraft, was both required for high angle of attack takeoffs and recoveries and sufficiently sturdy to accomplish its job. However, support structures such as down-locks were not up to the task and the high stresses of carrier operations caused nose gear failures- which also often caused spinal injuries to the pilots who were 14 feet up in the air when sitting on the deck.
Early Power Deficiencies
The Navy’s Bureau of Aeronautics (BuAer) ordered three XF7U prototypes in 1946. The first one flew for the first time from Naval Air Station (NAS) Patuxent River in Maryland on September 29th 1948 with Vought’s chief test pilot J. Robert Baker at the controls. The specifications for the production F7U-1s were similar to those of the prototypes. However, further testing and development of the 19 Westinghouse J34-WE-32 turbojet-powered F7U-1s built by Vought resulted in the revised F7U-2 and the F7U-3 variants. Both would be equipped with more powerful engines.
A Better Airframe But Still Lacking Thrust
At least that was the plan. At the end of the day the F7U-2 never got off the drafting board because of engine development problems. But the F7U-3 would incorporate as many improvements identified during F7U-1 flight hours as possible, resulting in a longer and stronger airframe. The first 16 F7U-3s built by Vought had non-afterburning Allison J35-A-29 engines. The remaining -3s, powered by Westinghouse J46-WE-8B afterburning turbojets, became the production standard. But that didn’t necessarily mean thrust the Cutlass pilots could trust.
Wicked Shimmies and Other Challenges
The F7U-3 Cutlass entered operational service with the US Navy with VA-66 Waldos (soon to become VF-81) in April of 1954. Eventually 13 squadrons would be equipped with Cutlasses. But operational problems were many and varied. The F7Us were all underpowered. The high-pressure hydraulic system constantly leaked. Landing gear doors had a tendency to fall off the jet. Takeoff and carrier approach performance were poor, and to make matters worse the J35 engines had a tendency to flame out when flying in rain. There were “wicked shimmies”- unpredictable crash-causing post-stall gyrations. The aircraft quickly picked up unflattering sobriquets such as “Gutless Cutlass”, “Ensign Eliminator”, and “Praying Mantis.”