Monday, October 5, 2009

Convair XF-92

A photo of the Convair XF-92 in flight, courtesy of NASA
Designed by
Alexander Lippisch
First flight
1 April 1948
Primary user
United States Air Force
Number built
Unit cost
US$4.3 million for the program
F-102 Delta Dagger
The Convair XF-92 was the first American delta-wing aircraft. Originally conceived as a point-defense interceptor, the design was later made purely experimental. However its design, suitably enlarged, led Convair to use the delta-wing on a number of designs, including the F-102 Delta Dagger, F-106 Delta Dart, and B-58 Hustler as well as the experimental XFY.

Design and development

The XF-92A at Edwards Air Force Base, 1952

The XF-92—nicknamed Dart—traces its ancestry to an August 1945 USAAF proposal for a supersonic interceptor capable of 700 mph speeds and reaching an altitude of 50,000 feet in four minutes. Several companies responded, and in May 1946 Convair (then still Consolidated Vultee) won with their proposal for a ramjet-powered aircraft with a 45-degree swept wing under USAAF Air Materiel Command Secret Project MX-813. However, wind tunnel testing demonstrated a number of problems with this design.

Looking for solutions, Convair came across the work of Dr. Alexander Lippisch, who had come to the United States as part of Operation Paperclip. Before and during the war, Lippisch had worked on a variety of delta-wing aircraft, first as low-speed gliders, and later as high-speed interceptors. Lippisch had concluded that the delta-wing was a natural design for supersonic flight, as the highly swept leading edge remained free of the shock wave off the front of the aircraft. He had plans to develop this as the Lippisch P.13a, but progressed only to a unpowered glider example, the Lippisch DM-1.

The P.13 design consisted of two large triangles joined together. One formed the main structure and wing, the other was the vertical stabilizer and cockpit. The only deviation from the triangular layout was an oval air intake at the nose, and round nozzle at the rear. The engine was powered by coal dust stored in a large rotating disk, the odd power source being a solution to the twin problems of lack of petroleum and manufacturing capability in Germany at the time the design was being proposed.

Convair took up Lippisch's work, redesigning it for jet power using the 1,560 lbf Westinghouse J30 assisted by a battery of six 2,000 lbf liquid-fueled rockets. The engine layout was rather portly and would not fit cleanly into the wing of the original P.13 layout, forcing a redesign. The new layout placed the engine in a seemingly oversized cylindrical fuselage, moving the pilot out of the triangular rudder into a separate cockpit centered in the middle of the fuselage, serving double duty as a shock cone for the engine intake. The basic layout of the fuselage was very similar to the Miles M.52 design, although the M.52 did not use a delta wing. The rudder, no longer serving as the cockpit as well, was reduced in size. The new design was presented to the U.S. Air Force in 1946, and was accepted for development as the XP-92.

In order to gain in-flight experience with the delta wing layout, Convair suggested building a smaller prototype, the Model 7002, which the USAAF accepted in November 1946. The design was similar in general layout as the original, but by placing the pilot in a conventional cockpit at the front, instead of centered in the fuselage, the resulting aircraft looked considerably less odd. In order to save development time and money, many components were taken from other aircraft; the main gear was taken from an FJ Fury, the nosewheel from a P-63 Kingcobra, the engine and hydraulics were taken from a Lockheed P-80 Shooting Star, the ejector seat and cockpit canopy were taken from the cancelled Convair XP-81, and the rudder pedals were taken from a BT-13 trainer.

Construction was well underway at Vultee Field in Downey, California when North American Aviation took over the Vultee plants in summer 1947. The airframe was moved to Convair's plant in San Diego, and completed in the autumn. In December it was shipped without an engine to NACA's Ames Aeronautical Laboratory for wind tunnel testing. After testing was completed, the airframe was returned to San Diego, where it was fitted with a 4,250 lbf. Allison J33-A-21 engine.

By the time the aircraft was ready for testing, the concept of the point-defense interceptor seemed outdated and the (now redesignated) F-92 project was cancelled. They also decided to rename the test aircraft as the XF-92A.

General characteristics
  • Crew: 1
  • Length: 42 ft 6 in (12.99 m)
  • Wingspan: 31 ft 4 in (9.55 m)
  • Height: 17 ft 9 in (5.37 m)
  • Wing area: 425 ft² (39.5 m²)
  • Empty weight: 9,078 lb (4,118 kg)
  • Loaded weight: 14,608 lb (6,626 kg)
  • Powerplant: 1× Allison J33-A-29 turbojet, 7,500 lbf (33.4 kN)
  • Maximum speed: 718 mph (624 knots, 1,160 km/h)
  • Service ceiling: 50,750 ft (15,450 m)
  • Rate of climb: 8,135 ft/min (41.3 m/s)
  • Wing loading: 34 lb/ft² (168 kg/m²)
  • Thrust/weight: 0.51