McDonnell XF-88
| McDonnell XF-88 | |
|---|---|
 The first XF-88 (46-525) after roll-out on August 11, 1948 at the St. Louis factory |
|
| Type: | Escort hunter |
| Design country: | |
| Manufacturer: | |
| First flight: |
October 20, 1948 |
| Number of pieces: |
2 |
The McDonnell XF-88 Voodoo (factory designation Model 36) was a fighter aircraft made by the American manufacturer McDonnell Aircraft Corporation , of which only two prototypes were produced in the late 1940s. The XF-88 formed the basis for the further development of the McDonnell F-101 .
history
development
Decisive for the development of the F-88 were the positive experiences during the war effort of the P-51 Mustang as an escort fighter for the heavy bombers B-17 Flying Fortress and B-29 Super Fortress . In August 1945, the USAAF issued an informal request for a " penetration fighter " with a deployment radius of at least 1440 km (900 ml) and an additional combat capability over the target area of the bombers, in order to be able to repel any enemy fighter aircraft has been. Fulfillment of these conditions appeared to be hopeless for the requested companies. Just like adhering to the target weight limit of 6,810 kg (15,000 lb), which was even less than the weight of a piston engine-driven P-47 from World War II.
The development team around Kendall Perkins and Edward "Bud" Flesh considered the use of two turbo jets in the enlarged wing roots to be the most suitable design, as it had already proven itself with the McDonnell FH Phantom and McDonnell F2H Banshee. With relatively low aerodynamic resistance, a high level of reliability resulted from the use of two engines, which also enabled a long range by allowing one engine to be operated in idle during cruising flight. The Westinghouse J34s used also had a small frontal area and specific fuel consumption. The first drafts for the "Model 36" were still very similar to the Banshee, but had a thinner wing and shorter wings, which only had a sweep of 20 ° at the leading edge, while the trailing edge was not swept.
When German test results on the advantages of the swept wing became available, the design was changed in September 1945 to a laminar wing with a 35 ° sweep in 1/4 of the profile depth and only 7.9% profile thickness . In order to enable this wing configuration and enough space for a large fuel supply, the engines had to be relocated to the lower fuselage area, where they could be easily installed and removed downwards. Because of a favorable center of gravity, they had to be installed relatively far forward, so that long nozzle outlets were actually necessary in the rear. For weight reasons and to avoid thrust losses, it was decided to use short outlets, despite the deformed hull line. Further disadvantages were critical temperatures of the fuselage surface and problems with pressure surges in the outlet area, which apparently could be controlled so well that the same design was used again for the McDonnell F3H Demon and the McDonnell F4H Phantom II.
The configuration of the engine inlets was also problematic, despite the disadvantages of around 8% in fuel consumption and maximum thrust, it was decided to keep the inlets in the wing root that were typical for McDonnell up to that time. After many attempts, the wing could also be made so stiff that in low flight Mach 0.85 was possible with full aileron deflection. The attachment of wing end tanks (tip tanks) was not possible with the thin wings.
On June 20, 1946, McDonnell received the order to build two prototypes (USAAF serial numbers 46-525 and -526) of the aircraft, which was still designated as XP-88 until June 11, 1948. In addition, a full-scale mock-up was also produced. After its inspection from August 21 to 23, 1946, the engine intakes were changed by increasing the sweep there from 35 to 40 ° and providing a splitter plate ( duct splitter ) to prevent the fuselage boundary layer from penetrating into the intake. Wind tunnel tests resulted in further changes to the design, so the originally planned V-tail was replaced by a conventional variant.
testing
The first flight of the XF-88 with Robert M. Edholm at the controls took place on October 20, 1948 at Muroc Army Air Force Base . The subsequent testing only revealed a design flaw: at low speeds and at full power, the air supply to the engine was insufficient, so that automatically actuated spring flaps were provided in the inlet, through which additional air could be sucked in during these flight conditions. On the seventieth flight on May 12, 1949, the maximum power values of the flight envelope could be flown without problems . In the dive, a maximum speed of about Mach 1.17 to 1.19 was achieved with a rate of descent of 20,600 m / min (67,600 ft / min).
Internal performance comparison
In January 1949, McDonnell carried out an internal comparison of the planned production variant of the F-88 with a hypothetical model "McDonnell 58A". The latter was a modified version of the F3H Demon, which was under development at the time, without the additional equipment required for carrier operation, such as catch hooks and wing flap device. A Westinghouse XJ40 with afterburner was provided as the drive . Two F-88s, one with J34 engines, the other with Westinghouse J46 , both equipped with afterburners, served as comparison samples .
The comparison showed that the performance of the three models did not differ very much, only the F-88 with the J46 showed a significantly better climbing performance of 8350 m / min (27,400 ft / min) compared to 7870 m / min (25,800 ft / min). min) of the Model 58A and J34-F-88 at 5190 m / min (17,010 ft / min). The results had no direct impact on Air Force planning, but allowed a comparison of the latest Air Force and Navy fighters.
Afterburner version XF-88A
During the dummy inspection in the summer of 1946, McDonnell received the order to test the possibility of installing an afterburner in the second prototype. However, an official contract was not signed until December 15, 1947. One problem was the short possible installation length of only 1.32 m (52 in.), Half the afterburner length provided by the manufacturer. Since McDonnell already had some experience with the use of Ramjets and Pulsejets on small helicopters, the company received im December 1947 an additional order for the installation of afterburner engines in the second prototype, which was then designated as the XF-88A. For this, McDonnell developed its own J34 variant with adjustable nozzle outlets, which provided a standstill increase of 34%. The XF-88A made its maiden flight on April 26, 1949 with two J34-WE-13 engines without afterburner, then one of them was replaced by a J34-WE-15 afterburner engine for test flights. With two WE-15s, the XF-88 reached exactly Mach 1 on June 9th.
The first prototype was shut down on August 26, 1949 due to a lack of financial resources and first parked in Muroc, but then transported by truck to St. Louis towards the end of the year. By then the XF-88 had completed 93 flights with a flight time of 82 hours. On November 9, 1949, the XF-88A made an emergency landing, after which it had to be transported back to the factory in St. Louis for repairs. Test operations with the repaired second machine could only be resumed on March 27, 1950. After more funds were available, the first machine could also be equipped with a J34 afterburner engine, but kept the XF-88 designation, without the A suffix. The first flight of the modified machine took place on May 1 and the transfer to Muroc on May 22, 1950.
The testing of the XF-88A in phase II took place from May 5 to June 14, 1950 and comprised 18 flights over 12½ hours. The increase in power through the afterburner resulted in an increase in speed from 1008 (630) to 1110 km / h (693 mph) at 4580 m (15,000 ft), the maximum Mach number increased from 0.91 to 0.945 at 10,680 m (35,000 ft). Mach 1.18 could easily be achieved in flat orbit flight without the buffeting effects becoming too noticeable. After an emergency landing on June 16, 1950, due to an engine compressor failure, the machine was not made airworthy again.
Comparison flies
Between June 29 and July 10, 1950, a comparison flight between the competitors XF-88, Lockheed XF-90 and North American YF-93 A took place in Muroc. Since the originally planned XF-88A was badly damaged and not available, the XF-88, which was now also equipped with an afterburner, could be used instead. The machine was tested by eight Air Force pilots in 26 flights. On September 11th, McDonnell received notification that their design had been declared the winner. McDonnell submitted information about the planned series version, which was to receive a front fuselage that was 1.43 m longer, but an order for the start of production was not placed.
Propeller test vehicle XF-88B
After the first XF-88 returned to St. Louis on August 3, 1950, it was converted into a test aircraft for propeller testing . By the time it was converted, the machine had completed 160 flights. The XF-88B was the last propeller plane in the F-designation sequence of the US Air Force. It was planned to examine 27 different propellers, powered by a 2750 hp Allison XT38 -A-5 turboprop engine. The XT38 was essentially one half of the XT40 used in the similarly designed Republic XF-84H . The engine was installed slightly to the left and the nose landing gear to the right. The fuel capacity had to be reduced to 2050 liters (543 US gallons) to make room for the gauges and to compensate for the engine weight, 109 kg (240 lb) of ballast was placed in the stern.
The conversion to a "three-engine" aircraft took place from August to November 1952, after which a 42-minute first flight followed on April 14, 1953. Initially, a four-blade Curtiss propeller with a diameter of 3.05 m (10 ft) was used; in the further trial operation, propellers with a smaller diameter of 1.2 and 2.1 m were also used. When taking off, the propellers were always in the sail position to prevent damage to the blades. The propeller gearbox allowed three ratios with propeller speeds of 1700, 3600 and 6000 min −1 . Mach 0.97 could be flown as the maximum speed in the tests. Only at low speeds and with high engine power was the rudder effect insufficient to compensate for the gyroscopic forces of the propeller. After the flight tests were completed in 1956 with 43 flights, the XF-88B was parked in a scrap yard at Langley AFB for a few years before the machine was scrapped together with the XF-88A.
Technical specifications
| Parameter | Data |
|---|---|
| crew | 1 |
| length | 16.51 m |
| span | 12.10 m |
| height | 5.26 m |
| Wing area | 9.94 m² |
| Empty mass | 5512 kg |
| Takeoff mass | 10,487 kg |
| Marching speed | 843 km / h |
| Top speed | 1026 km / h at sea level |
| Climb performance | 14.5 min at 10,675 m |
| Service ceiling | 10,980 m |
| Range | 2800 km |
| Engines | two Westinghouse J34-WE-13s with 13.35 kN (3000 lb) each or WE-22 with 18.25 kN (4100 lb) each with afterburner |
| Armament | six 20 mm cannons |
See also
literature
- Bill Gunston: The Experimental Voodoos. In: Airplane Monthly. July 1982, pp. 354-357.
- Dennis R. Jenkins & Tony R. Landis: Experimental & Prototype - US Air Force Jet Fighters. Specialty Press, 2008, ISBN 978-1-58007-111-6 , pp. 131-137.
- Hans-Jürgen Becker: XF-88 and F-101 Voodoo - the witchers from St. Louis. In: Jet & Prop. Issue 4, 2002, pp. 32–37.
- René J. Francillon: McDonnell Douglas Aircraft since 1920. Putnam & Company, 1979, ISBN 0-370-00050-1 , pp. 460-463.
- Robert F. Dorr: McDonnell F-88 / F-101 Voodoo Variant Briefing. In: Wings of Fame. Vol. 1, pp. 166-187.
