McDonnell F-88 Voodoo

Introduction

While the B-36 had evaded enemy defenses during The Big One by overflying them, it was regarded as inevitable that the aircraft would become vulnerable as fighter and guided missile technology improved. Thus, the development of a fighter escort for the B-36 became a high priority. One approach to this was the development of the F-85 Goblin parasite fighter. Another was the development of long-range, jet-engined fighters. As it turned out, neither was a viable proposition and both turned out to be technology dead-ends. However, the F-88 turned out to be a useful aircraft in the mid-1950s and formed the basis for the F-101 long-range interceptor.

Early Development

In early 1946, spurred by the disastrous losses suffered by B-29 formations, the USAF informally requested proposals for a "penetration fighter" with a combat radius of at least 900 miles and a performance capable of meeting all opposing fighters on more than equal terms. In addition, the USAF wanted to keep the gross weight of the aircraft below 15,000 pounds. Spurred on by the USAF request, the McDonnell Aircraft Corporation of St. Louis, Missouri initiated work on the Model 36 on April 1, 1946. The Model 36 project called for a large twin-jet aircraft powered by a pair of 3000 lb. st. Westinghouse J34 engines. Originally, McDonnell had considered installing the engines in the wing roots, but this proved infeasible and the engines were moved to a side-by-side location in the lower central fuselage where they could be more easily reached for maintenance. The engines were fed by straight-through air intakes mounted in the wing roots. The jet exhausts were underneath the rear fuselage. This configuration, it was hoped, would leave enough space in the fuselage for the fuel needed for the long-range penetration mission. A 35-degree sweptback wing was fitted, and a V-tail was to be used. The V-tail arrangement was selected because of the desire to reduce compressibility effects, which was thought would be helped by cutting the number of tail intersections from three to two. A set of perforated dive brakes was mounted on the rear fuselage, hinged at the rear. The pilot's cockpit was situated well forward of the wing. The armament was to be six 20-mm cannon. The name Voodoo was assigned, consistent with McDonnell's tradition of choosing the names of spirit-like apparitions for its aircraft.

Some minor problems were encountered during the test flight program. Some loss of thrust was encountered during takeoff due to choking in the S-shaped air ducts. This was solved by fitting spring-loaded blow-in doors in the wheel well section of the ducts. The rolling rate was found to be insufficient. It was improved to a certain extent by increasing the aileron chord by 26 percent, but the full cure for this problem required an increase in the torsional rigidity of the wing. Performance was disappointing, due primarily to the demanding range requirements and to the weight increases which had taken place since the initial design phase. Maximum speed at sea level was only 641 mph. It took approximately six minutes for the XF-88 to reach an altitude of 30,000 feet. It would appear that the XF-88 needed more power. McDonnell proposed to fit afterburners to the J34 engines that powered the second prototype, and the production F-88s were to be powered by 6000 lb.st. Westinghouse J46 afterburning turbojets. The USAF did not choose to fund the J46 installation, but they did approve the adaptation of the second prototype to the afterburning J34 engines.

The second prototype was designated the XF-88A, and was fitted with the afterburning XJ34-WE-15 engines. It was also fitted with bladder fuel cells in the wings to increase internal fuel capacity to 834 gallons. The XF-88A made its first flight on April 26, 1949. The performance improvement was apparent —- maximum speed at sea level was almost 700 mph, time to climb to 30,000 feet was cut to 4 minutes, and takeoff run was reduced by 20 percent. The XF-88A was faced with some stiff competition for the USAF penetration fighter order. The Lockheed XF-90 and the North American XF-93A had also been entered as contenders for the USAF penetration fighter order. The XF-90 was a twin-jet design which first flew in June of 1949. The XF-93A was a beefed-up derivative of the F-86D Sabredog, initially ordered under the designation of F-86E. The flyoff between the Lockheed XF-90, the McDonnell XF-88, and the North American YF-93A took place between June 30 and July 8 of 1950. On August 15, 1950, the Evaluation Board declared the McDonnell XF-88A to be the winner of the contest.

Variants

McDonnell F-88A Voodoo

The F-88A was a production version of the XF-88A and was similar to that aircraft in most respects. The only significant change was the provision for aerial refueling that substantially extended the aircraft’s range. A total of 50 F-88A aircraft were built, partially equipping one strategic fighter group (previously the 555th Tactical Fighter Wing that was converted to strategic status rather than being stood down like most tactical aviation units in the 1950s.)

Specification of the F-88A:

Two Westinghouse J34-WE-15 turbojets, 3600 lb.st. dry, 4825 lb.st with afterburning. Dimensions: wingspan 39 feet 8 inches, length 54 feet 1 1/2 inches, height 17 feet 3 inches, wing area 350 square feet. Weights: 12,140 pounds empty, 18,500 pounds loaded, 23,100 pounds maximum. Maximum speed: 641 mph at sea level. 706 mph at 20,000 feet. Initial climb rate 8000 feet per minute. climb to 35,000 feet in 14.5 minutes, service ceiling 39,400 feet, tactical radius 700 miles, max range 1737 miles. Armament consisted of six 20-mm cannon in the nose.

McDonnell F-88B Voodoo

The F-88B was a development of the F-88A that featured under-fuselage launch rails for two GAR-1 Falcon missiles. These were never actually carried by the F-88B and the non-availability of the GAR-1 restricted production of the F-88B to 25 aircraft that were issued to the 555th Strategic Fighter Group to bring it up to full strength.

McDonnell F-88C Voodoo

The Air Force had assumed that the high performance of the B-52 and B-60 bombers would make escort fighters unnecessary in any future conflict. For a while this had been true but the continuing Red Sun exercises showed that defensive technology had caught up with the B-36, was very close to doing so with the B-60 and threatened the B-52. However, the F-88 was too slow and short-ranged to provide an adequate escort for the jet-engined bombers. To fill this gap, McDonnell proposed a larger and more powerful version of its F-88B penetration fighter prototype. Although virtually a new aircraft, this was designated the F-88C. A Letter of Intent for the development of the McDonnell proposal was issued on January 3, 1952.

In December of 1951, the McDonnell team lead by Edward M. Flesh recommended that the F-88C be powered by a pair of afterburning Allison J71 turbojets. This nearly tripled the thrust of the pair of Westinghouse J34s that had powered the F-88B. However, the Air Force thought that even this additional power was still not enough, and was in favor of using a pair of even more powerful Pratt & Whitney J57 afterburning engines. Unfortunately, the use of the more powerful J57 engines required some major design changes. Although the engines were to be placed in the same location as they were in the F-88B, the air intakes in the wing roots had to be redesigned and considerably enlarged to accommodate the increased air flow requirements. Since considerably more fuel had to be carried, the fuselage had to be lengthened and widened, increasing the internal fuel capacity more than threefold (2341 versus 734 US gallons). Provisions were made for the fitting of a pair of 450-gallon external tanks. The F-88C was to be equipped with APS-54 radar and was to be armed with four 20-mm cannon as well as three Falcon air-to-air missiles and 12 unguided rockets.

The first F-88C was delivered in August of 1954. After completing some ground trials in St. Louis, it was shipped out to Edwards AFB. It took off on its maiden flight on September 29, 1954, McDonnell test pilot Robert C. Little being at the controls. He reached Mach 0.9 at 35,000 feet. Less than a month later, maximum speed had progressively been pushed to Mach 1.4. Despite the dramatically improved performance of the F-88C, SAC had begun to doubt the viability of the concept. They now concluded that the range of the F-88C, impressive as it was, was not nearly large enough to be able to escort SAC's bombers all the way to the target. There was a mismatch in aircraft speeds, without using afterburners, the F-88C could not keep up with the B-52; if it did use afterburners to keep up, the F-88Cs range was drastically reduced. Also, the F-88C was purely an air-to-air dogfighter and could not protect the B-52 fleet from surface-to-air missiles. Behind all of this, of course, was the growth of the “Strategic Reconnaissance” aircraft and the development of the RB-58 Hustler.

Nevertheless, it was decided that a strategic fighter force should be maintained. The new role was to protect bombers while they waited at their fail-safe point. At this time, SAC had a total of eight strategic fighter groups, four equipped with F-84F Thunderstreaks, one with F-88A/Bs and three composite groups with GB-36/F-85s. It was decided to equip the five groups with F-84s and F-88s with the new F-88C. Production was thus authorized and 400 F-88Cs were built.

Specification of the F-88C:

Engine: Two Pratt & Whitney J57-P-13 turbojets, 10,200 lb.s.t. dry and 15,000 lb.s.t. with afterburner. Dimensions: wingspan 39 feet 8 inches, length 67 feet 5 inches, height 18 feet 0 inches, wing area 368 square feet. Performance: Maximum speed 1009 mph at 35,000 feet. Initial climb rate 44,100 feet/min. Service ceiling 55,800 feet, combat ceiling 49,450 feet. Combat radius 1,200 miles, maximum range 2925 miles. Weights: 24,970 pounds empty, 48,120 pounds gross, 39,495 pounds combat weight, 50,000 pounds maximum takeoff. Fuel: Maximum internal fuel load was 2341 US gallons. A total of three under-fuselage drop tanks could be carried, bringing maximum fuel load to 3467 US gallons. Armament: Four 20-mm Pontiac M-39 cannon in the nose with 200 rpg.

McDonnell XF-88D Voodoo

It had not gone unnoticed that the F-88C had the altitude and speed characteristics to form the basis of a good long-range interceptor, capable of handling B-52 type targets. Accordingly, McDonnell offered a two-seat interceptor version of the F-88C designated the F-88D. This was approved but because of the very different role of the aircraft, it was redesignated the F-101A Voodoo.


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