The McDonnell XF-88 Voodoo was a proposed long-range strike fighter and bomber escort that was entered into the Penetration Fighter Competition held by the United States Air Force (USAF) in June and July of 1950.
Despite failing to meet any of the necessary requirements and being outrightly dismissed by USAF evaluators, the creators of the XF-88 Voodoo never stopped believing in the potential of their invention, whose development cycle would later be hailed as the foundation upon which their most successful aircraft, the F-101 Voodoo, was conceived.
- Model 36 Penetration Fighter
- The Voodoo
- Penetration Fighter Mission
- F-101 and NASA Testing
Wishing to replace World War Two-era aircraft including the Lockheed P-38 Lightning, the Republic P-47 Thunderbolt, and the North American Mustang P-51, on August 28th 1945 USAF issued new specifications for a strike fighter designed to escort long-range bombers.
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After several revisions, USAF finally announced they needed a craft that had a single-place cockpit, bubble-type cockpit canopy, sweptback flying surfaces, four to six 20 mm cannons, external tanks and ordnance that could be jettisoned, as well as a combat range of 600 miles, the ability to fly up to 600 miles per hour, and which could climb to an altitude ceiling of 50,000 feet in 5 minutes.
In response, the McDonnell Aircraft Corporation drew up blueprints for its Model 36 Penetration Fighter, with McDonnell chief engineer Kendall Perkins assigning E.M ‘Bud’ Flesh as the project lead and Dave Lewis as head of aerodynamics.
Model 36 Penetration Fighter
Basing the schematics on the failed XF2H-1 Banshee rejected previously by the US Navy, on October 13th 1945 McDonnell submitted their earliest prototype, the McAir Model 36C, to USAF command at Wright Army Air Field in Dayton, Ohio.
Most memorable for its V tail or butterfly tail reminiscent of the later Lockheed Martin F-117A Nighthawk stealth fighter, Model 36C was heavier than other single-seated fighters of its ilk mainly because the designers wanted to meet the fuselage and fuel volume requirements set out by USAF, while also ensuring there was adequate space for the Westinghouse J34 turbojet engines that were to be eventually installed in the production model.
After 8 months of assessment, on June 26th 1946 USAF sent a Letter of Contract informing McDonnell that they would be required to assemble two flyable versions, the XP-88 and the afterburner-equipped XP-88A, a decision that was formally recognized with the issuing of a contract on February 14th 1947 and officially designated as Secret Project MX-811.
Following a lengthy developmental period in which McDonnell was forced to invent its own afterburner, the MAC Short afterburner after engine manufacturer Westinghouse proved unwilling to help, the XF-88, inscribed with the name ‘Voodoo’ on its nose and re-branded with the initial ‘F’ for a fighter, commenced flight evaluations on August 11th 1948 at the McDonnell facility at Lambert Field in St. Louis, Missouri.
The McDonnell XF-88 Voodoo, replete with sweptback wings that had a 39.8-foot span and a 350 square-foot area, was a strike fighter that could also act as an escort for bombers, and in its XF-88A configuration was 54.2 feet long, 17.3 feet high, and had an empty weight of 12,140 pounds as well as a gross weight of 18,500 pounds.
With a top speed of 641 miles per hour, the XF-88A was powered by two Westinghouse J34-WE-13 non-afterburning turbojet engines with a thrust of 3,200 pounds or dual J34-WE-15 afterburning turbojet engines with a thrust of 4,200 pounds, while the later XF-88B used two J34-WE-15 afterburning engines in combination with one Allison XT38-A-5 turboprop engine possessing 2,650 horsepower.
The XF-88A had an arsenal of armaments that included 6 nose-mounted M-24 20 mm cannons with 220 rounds of ammunition each, while provision was made for either two 1,000 pounds bombs or eight 5-inch High-Velocity Aircraft Rockets or HVARS.
After the initial run of pre-flight tests had been completed, the non-afterburning XF-88 piloted by McDonnell chief test pilot Robert M. ‘Bob’ Edholm, took to the skies for the first time on October 20th 1948 for Phase I testing.
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Results were disappointing, with Edholm describing how the dual non-afterburning J34-WE 13 engines with a combined 6,400-pound thrust had simply not provided enough power to propel the aircraft satisfactorily.
Edholm’s concerns were confirmed in a string of 17 further assessments conducted by USAF for Phase II testing undertaken between March 15th and March 26th in 1949, which concluded that although the XF-88 was pleasantly manoeuvrable it was seriously underpowered. Painting a somewhat bleak picture, Edholm would go on to express doubts about the XF-88A fitted with an afterburner, predicting that it wouldn’t be able to reach much above Mach 1.
Nevertheless, with the MAC afterburners yet to be added the XF-88A, slightly different to its twin with the inclusion of an all movable horizontal tail known as a stabilator and six 20 mm M-24 cannons, completed its maiden voyage at Lambert Field on April 26th 1949 without incident.
The next major flight trial occurred on June 2nd 1949 with the XF-88A installed with a single MAC Short afterburner placed on the left-hand engine only. Proving Edholm wrong the test turned out to be an unqualified success, and soon enough the prototype was fitted with another afterburner on its right-hand engine, while the other underperforming XF-88, was also retrofitted with the same afterburner configuration and re-designated as the XF-88A.
Shortly afterwards, USAF awarded another contract to McDonnell on July 15th 1949 permitting them to go-ahead with a planned conversion of one of the XF-88As, now to be equipped with a cutting edge Model-501F-1 Allison XT38-A-5 turboprop engine and transformed into the XF-88B.
Before this was to take place however, the XF-88A was entered into the Penetration Fighter fly-off competition, where it was to face off against the Lockheed XF-90A ‘Super Star’ and the North American YF-93A ‘Sabre Cat’ for the prized USAF contract.
Penetration Fighter Mission
The XF-88A did not get off to the most auspicious of starts, for 13 days before the competition commenced on June 16th 1950 it was forced to make a wheels-up landing because of a hydraulic failure. Nevertheless, after being patched up it did enough to win first place following USAF appraisals on August 15th 1950.
The XF-88A though was only the best of a bad bunch, failing alongside its competitors to provide the sufficient range and endurance that USAF envisioned for the Penetration Fighter mission, leading to the program’s cancellation.
Poor performance however, was not the sole reason for the project’s demise, for there were other unanticipated factors at play that were beyond McDonnell’s control. For instance, as a result of President Harry Truman’s May 13th 1948 imposition of a fiscal ceiling on the 1949 and 1950 budgets, General Joseph T. McNarney advised USAF to revise its programs for those years.
Consequently, the B-39 bomber squads of Strategic Air Command were prioritized to the detriment of the XF-88 and its proposed production model the F-88, since the Voodoo had not been designed to work alongside this particular breed of the bomber.
F-101 and NASA Testing
Despite being sidelined by USAF, McDonnell engineers continued to believe in the merits of their aircraft, repurposing it as a test bed for their Model 36W Program, which was to eventually sire the F-101A Voodoo after being declared the winner of a long-range fighter competition in May 1951.
Granted a production contract by USAF in early 1952, more than 800 F-101A Voodoo fighters in many variants were assembled such as the RF-101A, the F-101B, the CF-101B, the TF-101B, the F-101C, the RF-101C, and the TF-101F.
While the first XF-88A, now referred to as the XF-88A-2, was utilized for F-101 development and in particular in-flight refuelling examinations, the second took a different route following its conversion into the XF-88B and was instead employed as a supersonic propellor test bed, making its flight debut at Lambert Field on March 14th 1953.
NASA would also transfer it to their test facility at Langley Research Center, where several supersonic propellor variants were mounted to its Alison turboprop engine in a series of 23 trial flights lasting until January 1958, which resulted in the recording of one of the fastest speeds ever attained for a propellor-driven aircraft at Mach 1.12.
Before both the XF-88A and XF-88B were relegated to the scrapheap in the early 1960s, McDonnell proposed several variants such as a two-seated All Weather Fighter optimized for nighttime operations that were to be three feet longer than the XF-88A, but this was rejected by USAF who chose to explore this arrangement alternatively with the North American F-86D ‘Sabre Dog’, the Northrop F-89J Scorpion, and the Lockheed F-94C Starfire.
- Crew: 1
- Length: 54 ft 1.5 in (16.497 m)
- Wingspan: 39 ft 8 in (12.09 m)
- Height: 17 ft 3 in (5.26 m)
- Empty weight: 12,140 lb (5,507 kg)
- Max takeoff weight: 23,100 lb (10,478 kg)
- Powerplant: 2 × Westinghouse J34-WE-15 afterburning turbojet engines, 3,600 lbf (16 kN) thrust each dry, 4,825 lbf (21.46 kN) with afterburner
- Powerplant: 1 × Allison XT38-A-5 turboprop engine, 2,750 shp (2,050 kW) equivalent – (2,550 shp (1,900 kW) + 415 lbf (1.85 kN)) – XF-88B
- Propellers: 2, 3 and 4-bladed constant-speed supersonic propellers, 4 ft (1.2 m) diameter to 10 ft (3.0 m) diameter, operating at 1,700 rpm, 3,600 rpm or 6,000 rpm XF-88B
- Maximum speed: 706 mph (1,136 km/h, 613 kn) at 20,000 ft (6,100 m) 641 mph (557 kn; 1,032 km/h) at sea level
- Range: 1,737 mi (2,795 km, 1,509 nmi)
- Service ceiling: 39,400 ft (12,000 m)
- Rate of climb: 8,000 ft/min (41 m/s)