| XF-92A | |
|---|---|
 A photo of the Convair XF-92A in flight | |
| General information | |
| Type | |
| Manufacturer | Convair |
| Status | Canceled |
| Primary user | United States Air Force |
| Number built | 1 |
| History | |
| First flight | 18 September 1948[1] |
| Variant | Convair F-102 Delta Dagger |
TheConvair XF-92 (re-designated fromXP-92 in 1948) is anAmerican,delta wing,first-generation jet prototype. Originally conceived as apoint-defenceinterceptor, the design was later used purely forexperimental purposes and only one was built. However, it led Convair to use the delta-wing on a number of designs, including theF-102 Delta Dagger,F-106 Delta Dart,B-58 Hustler, theUS Navy'sF2Y Sea Dart as well as theVTOLFY Pogo.
Prior to August 1945, the Vultee Division of Consolidated-Vultee looked at the possibility of a swept-wing aircraft powered by a ducted rocket. Years earlier, the company had performed designs which involved liquid-cooled radiator engines. With this design, fuel would be added to the heat produced by small rocket engines in the duct, creating a "pseudo-ramjet".[2]
In August 1945, theUnited States Army Air Forces (USAAF), soon to be renamed theUnited States Air Force, issued a proposal for a supersonic interceptor capable of 700 mph (1,100 km/h) speeds and reaching an altitude of 50,000 feet (15,000 m) in four minutes.[citation needed] Several companies responded, among which was Consolidated-Vultee, which submitted its design on 13 October 1945.[2] This design featured swept wings andV-tails, as well as a powerful propulsion system. Besides the ducted rocket, four 1,200 pounds-force (5.3 kN) rockets were positioned at the exhaust nozzle, along with the 1,560 pounds-force (6.9 kN) 19XB turbojet produced by Westinghouse.[2]
A proposal byConsolidated Vultee (later Convair) was accepted in May 1946, with a proposal for a ramjet-powered aircraft, with a 45°swept wing under USAAFAir Materiel Command Secret Project MX-813. However,wind tunnel testing demonstrated a number of problems with this design.[3]
Convair found that by straightening the trailing edge and increasing the sweep of the leading edge, the characteristics of their new wing were greatly improved. Thus, contrary to suggestions that German designerAlexander Lippisch influenced it, Convair independently discovered the thin high-speed delta wing.[4] Ralph Shick, chief of aerodynamic research, later met Lippisch atWright-Patterson Air Force Base. This helped to convince him that the thin delta was the way forward, however the influence of Lippisch provided no more than "moral support" and Convair rejected many of his ideas, such as the thick wing of theLippisch P.13a project and theDM-1 test glider which the US had tested.[5][4]
Thrust was to be provided by a 1,560 lbf (6,900 N)Westinghouse J30 jet engine assisted by a battery of six 2,000 lbf (8.9 kN) liquid-fueled rockets. This mixed-propulsion system required a very large intake duct, which not only fed the jet engine but also passed air around the rocket exhaust to providethrust augmentation. Located centrally, the large duct left nowhere to put a traditional cockpit; in its normal location it would have projected deep into the duct. To address this, the team modified the design in a fashion similar to both theLeduc 0.10 andMiles M.52, placing the cockpit in a cylindrical body in the center of the intake. The design was presented to theU.S. Air Force in 1946 and was accepted for development as the XP-92.[6]
In order to gain inflight experience with the delta wing layout, Convair suggested building a smaller prototype, theModel 7002, which the USAAF accepted in November 1946.[7]
In order to save development time and money, many components were taken from other aircraft; the main gear was taken from aNorth American FJ-1 Fury, the nosewheel from aBell P-63 Kingcobra, the engine and hydraulics were taken from aLockheed P-80 Shooting Star, the ejection seat and cockpit canopy were taken from the cancelledConvair XP-81, and the rudder pedals were taken from a BT-13 trainer.
Construction was well underway at Vultee Field inDowney, California whenNorth American Aviation took over the Vultee plants in summer 1947. The airframe was moved to Convair's plant inSan Diego, and completed in the autumn. In December it was shipped without an engine toNACA'sAmes 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 (18,900 N)Allison J33-A-21 engine.[6]
By the time the aircraft was ready for testing, the concept of thepoint-defense interceptor seemed outdated and the (now redesignated) F-92 project was cancelled; the test aircraft was nevertheless completed as theXF-92A.[7]
In April 1948 the XF-92A was shipped toMuroc Dry Lake (later to becomeEdwards AFB). Early tests were limited to taxiing, although a short hop was made on 9 June 1948. The XF-92A's first flight was on 18 September 1948 with Convair test pilot Ellis D. "Sam" Shannon at the controls. On 21 December 1948 Bill Martin began testing the aircraft for the company. After 47 flights totaling 20 hours and 33 minutes, the aircraft was turned over to the USAAF on 26 August 1949,[8] with the testing being assigned toFrank Everest andChuck Yeager.[3]
On 13 October 1949 Yeager became the first Air Force pilot to fly the XF-92A.[8] On his second flight he dove the aircraft in a 4 gsplit-S dive, reaching Mach 1.05 for a brief time.[9] When approaching for landing on this flight he continued to pull the nose higher and higher in order to slow the forward speed to avoid the problems from his first attempt. Surprisingly, the aircraft simply wouldn't stall; he was able to continue raising the nose until he reached 45 degreespitch, flying under control in that attitude to a landing at 67 mph (108 km/h), 100 mph (160 km/h) slower than Convair had managed.
In 1951, the XF-92A was refitted with an Allison J33-A-29 engine with an afterburner, offering a thrust of 7,500 lbf (33,000 N). The re-engined XF-92A was flown by Yeager for the first time on 20 July 1951. However, there was very little improvement in performance. In addition, there were maintenance problems with this engine and only 21 flights were made during the next 19 months.[3] A final engine change was made to the 5,400 lbf (24,000 N) J33-A-16.
On 9 April 1953,Scott Crossfield began a series of flights on behalf of NACA. These tests revealed a violent pitch-up tendency during high-speed turns, often as much as 6 g, and on one occasion 8 g. The addition ofwing fences partially alleviated this problem. Crossfield flew 25 flights in the XF-92A by 14 October 1953.[10] After the aircraft's last flight the nose gear collapsed as Crossfield taxied off the lake bed; the aircraft was retired.[11]
None of the pilots had much good to say about the design. Yeager commented "It was a tricky plane to fly, but ... I got it out to 1.05 Mach." Crossfield was more direct, saying "Nobody wanted to fly the XF-92. There was no lineup of pilots for that airplane. It was a miserable flying beast. Everyone complained it was underpowered."[12][13]
The delta wing's thin airfoil cross section, low weight and structural strength made it a good candidate for a supersonic airplane. The large surface area of 425 ft2 (39 m2) gave a lowwing loading which in turn led to good low-speed performance. Very slow landing speeds could be achieved, at the cost of extremely nose-high landing angles and the resulting poor visibility. The combination of good high-speed and low-speed characteristics was very difficult to achieve for otherplanforms. Although the XF-92 itself was not liked, the design concept clearly had promise and the delta wing was used on several Convair designs through the 1950s and 1960s.
Of particular interest to aircraft designers was the unexpectedly good low-speed behavior Yeager had noticed on his second flight. The aircraft continued to remain controllable at very highangles of attack (alpha), where a conventional layout would have stalled. The reason for this turned out to be the unexpected creation of a largevortex over the top of the wing, generated by the airflow between the fuselage and leading edge of the wing at high alpha. The vortex became "attached" to the upper surface of the wing, supplying it with air moving at speeds much greater than the aircraft's forward speed. By controlling the flow in this critical area, theperformance envelope of the delta could be greatly expanded, which led to the introduction ofcanards on most delta-wing designs in the 1960s and 1970s. More recentlyleading edge extensions have become common on most fighter aircraft, creating the vortex over a more conventional wing planform.
Data fromFighters of the United States Air Force[15]
General characteristics
Performance
An unusual application of the XF-92A was as a movie model, stepping into the role of the "MiG-23" in the Howard Hughes film,Jet Pilot, starringJohn Wayne andJanet Leigh. Due to the lengthy delay in releasing the film, by the time it appeared in 1957, the XF-92A's role had been left on the cutting room floor.[17] It did appear in the filmToward the Unknown (1956) starring William Holden, again in the guise of another aircraft, this time as its descendant design the F-102 Delta Dagger.[18]
Related development
Aircraft of comparable role, configuration, and era
Related lists
