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Thursday, 10 November 2016 02:29

Vought XF8U-3 Crusader III

XF8U-3 Crusader at Edwards AFB 1958

Conceived as a high speed, all weather interceptor evolution from the already deployed F-8 Crusader II, Vought began studying work barely a year after the first flight of the Crusader II. In early 1957, the Navy awarded a contract for the delivery of three developmental models, to be designated the XF8U-3.

XF8U-3-07The F8U-3, called the ”Super Crusader” or “Big Crusader,” was much larger than the F8U-1 Crusader. Powered by a Pratt & Whitney J75 engine that provided over 26,000 pounds of thrust, it could attain speeds in the Mach 2 range. It had a similar general configuration to the earlier F8U-1 in that it had a variable-incidence wing, but the engine inlet was much different. There was a scoop on the lower lip of the inlet to properly align the shock wave at high speed. There were also manual-control bypass doors to bleed excess air overboard so as to prevent inlet choking at supersonic speeds. A long, sharp nose cone and two large folding ventral fins made the F8U-3 distinctively different from its predecessors

Vought Aircraft built the F8U-3 in competition with the McDonnell F4H Phantom II. The Navy selected the F4H over the F8U-3 as its next fleet fighter. Both aircraft were flown in an extensive evaluation program prior to selection, but the F4H won the “fly-off” because of its multi-engine, two-place configuration. There had been times when a multi-engine fighter landed safely on one engine while single engine aircraft were often lost due to engine failure. The Phantom II’s versatile design made it the choice of all the services. It provided decades of service to the Navy, Marines, and Air Force. The F8U-3 had better speed and turning performance and had less drag, but the F4H had greater ruggedness and survivability and was better suited to carrier operations.

XF8U-3 in flight

In his book "The smell of Kerozene", Test pilot Lt Cdr Donald Mallick wrote:

"The F8U-3 had better performance than any aircraft flown to date. It was a big fighter, almost 40,000 pounds with full fuel, and had a tremendous engine. I was extremely impressed during my first takeoff. I accelerated to “military power,” released the brakes and lit the afterburner. The aircraft lurched forward, rapidly accelerated, and I passed through rotation speed almost before I realized it. After takeoff, I had to pull the nose up quickly to avoid exceeding safe limits for gear-down with the wing in takeoff position.[...]After takeoff, I climbed in military power to about 25,000 feet. I lit the afterburner climbed to an altitude of around 30,000 feet. The F8U-3 had excellent handling qualities. It had light and comfortable control forces, as a fighter should, and there was no tendency to over-control or cause pilot-induced[...]I can remember the response of one GCI controller as he followed my track north, and I quickly accelerated to Mach 2.0. “Sir,” he asked, “what in the hell are you flying?” He was unaccustomed to seeing such performance on his radar screen, and my rapid acceleration and high speed immediately caught his attention.[...]speed control added another task for the pilot


Preliminary Flight Guide for Model F8U-3 Airplane - Download PDF


The F8U-3 also had a problem with compressor stalls. On a high-speed supersonic aircraft, the relationship between engine and inlet is important. A problem that affects one will immediately affect the other. On the F8U-3, engine stall occurred without warning during a supersonic run. I had no method to
restart the inlet or clear the stall until the aircraft had slowed to subsonic speeds. Both Bill (ed: Bill Alford)  and I experienced stalls, and they were startling and dramatic. I can recall one stall I experienced as I accelerated through Mach 1.6. The engine inlet was located right under the floor of the cockpit, and the stall hit with a
loud thump. My feet lifted right off the cockpit floor! This was just the beginning. The inlet started to buzz, shaking and rattling the aircraft as it slowed down. I moved the throttle out of afterburner to the military thrust setting and waited. The F8U-3 had to slow to Mach 0.9 before the engine stall cleared."

The F8U-3 program was canceled with five aircraft built. Three aircraft flew during the test program, and, along with two other airframes, were transferred to NASA for atmospheric testing, as the Crusader III was capable of flying above 95% of the Earth's atmosphere. NASA pilots flying at NAS Patuxent River routinely intercepted and defeated U.S. Navy Phantom IIs in mock dogfights, until complaints from the Navy put an end to the harassment.
All of the Crusader IIIs were later scrapped.

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