The XF-85 was a response to a USAAF requirement for a fighter to be carried within the Northrop XB-35 and B-36, then under development. This was to address the limited range of existing interceptor aircraft compared to the greater range of new bomber designs. The XF-85 was a diminutive jet aircraft featuring a distinctive potato-shaped fuselage and a forked-tail stabilizer design. The prototypes were built and underwent testing and evaluation in 1948. Flight tests showed promise in the design, but the aircraft's performance was inferior to the jet fighters it would have faced in combat, and there were difficulties in docking. The XF-85 was swiftly canceled, and the prototypes were thereafter relegated to museum exhibits. The 1947 successor to the USAAF, the United States Air Force (USAF), continued to examine the concept of parasite aircraft under three related projects following the cancellation: MX-106 "Tip Tow", FICON, and "Tom-Tom."
Design and development
During World War II, American bombers such as the Boeing B-17 Flying Fortress, Consolidated B-24 Liberator, and Boeing B-29 Superfortress were protected by long-range escort fighters such as the Republic P-47 Thunderbolt and North American P-51 Mustang. These fighters could not match the range of the Northrop B-35 or Convair B-36, the next generation of bombers developed by the United States Army Air Forces (USAAF). The development cost for longer-ranged fighters was high, while aerial refueling was still considered risky and technologically difficult.[1] Pilot fatigue had also been a problem during long fighter escort missions in Europe and the Pacific, giving further impetus to innovative approaches.[2]
The USAAF considered a number of different options including the use of remotely piloted vehicles before choosing parasite fighters as the most viable B-36 defense.[3] The concept of a parasite fighter had its origins in 1918, when the Royal Air Force examined the viability of Sopwith Camel parasite fighters operating from their 23-class airships. In the 1930s, the U.S. Navy had a short-lived operational parasite fighter, the Curtiss F9C Sparrowhawk, aboard the airships Akron and Macon.[4] Starting in 1931, aircraft designer Vladimir Vakhmistrov conducted experiments in the Soviet Union as part of the Zveno project during which up to five fighters of various types were carried by Polikarpov TB-2 and Tupolev TB-3 bombers. In August 1941, these combinations flew the only combat missions ever undertaken by parasite fighters – TB-3s carrying Polikarpov I-16SPB dive bombers attacked the Cernavodă bridge and Constantsa docks, in Romania. After that attack, the squadron, based in the Crimea, carried out a tactical attack on a bridge over the river Dnieper at Zaporozhye, which had been captured by advancing German troops.[5] Later in World War II, the Luftwaffe experimented with the Messerschmitt Me 328 as a parasite fighter, but problems with its pulsejet engines could not be overcome.[1] Other late-war rocket-powered parasite fighter projects such as the Arado E.381 and Sombold So 344 were unrealized "paper projects".[6]
On 3 December 1942, the USAAF sent out a Request for Proposals (RfP) for a diminutive piston-engined fighter.[7] By January 1944, the Air Technical Service Command refined the RfP and, in January1945, the specifications were further revised in MX-472 to specify a jet-powered aircraft.[4] Although a number of aerospace companies studied the feasibility of such aircraft, McDonnell was the only company to submit a proposal to the original 1942 request and later revised requirements.[4] The company's Model 27 proposal was completely reworked to meet the new specifications.[7]
Top view of the XF-85, with the hook extended over top of the canopy
The initial concept for the Model 27 was for the fighter to be carried half-exposed under the B-29, B-35, or B-36. The USAAF rejected this proposal, citing increased drag, and hence reduced range for the composite bomber-fighter configuration.[4] On 19March1945, McDonnell's design team led by Herman D. Barkey,[8] submitted a revised proposal, the extensively redesigned Model 27D.[9] The smaller aircraft had a potato-shaped fuselage, three fork-shaped vertical stabilizers, horizontal stabilizers with a significant dihedral, and 37° swept-back folding wings to allow it to fit in the confines of a bomb bay.[10] The diminutive aircraft measured 14ft 10in (4.52m) long; the folding wings spanned 21ft (6.4m). Only a limited fuel supply of 112USgal (93impgal; 420L) was deemed necessary for the specified 30-minute combat endurance.[10] A hook was installed along the aircraft's center of gravity; in flight, it retracted to lie flat in the upper part of the nose.[10] The aircraft had an empty weight just short of 4,000 pounds (1.8t).[11] To save weight, the fighter had no landing gear.[9][N 1] During the testing program, a fixed steel skid under the fuselage and spring-steel "runners" at the underside of the wingtips were installed in case of an emergency landing.[4][13] Despite the cramped quarters, the pilot was provided with a cordite ejection seat, bail-out oxygen bottle, and high-speed ribbon parachute.[14] Four .50in (12.7mm) machine guns in the nose made up the aircraft's armament.[15]
In service, the parasite fighter would be launched and retrieved by a trapeze. With the trapeze fully extended, the engine would be airstarted and the release from the mother ship was accomplished by the pilot pulling the nose back to disengage from the hook.[14] In recovery, the aircraft would approach the mother ship from underneath and link up with the trapeze using the retractable hook in the aircraft's nose.[14] The anticipated production shift would see a mixed B-36 fleet with both "fighter carriers" and bombers[16] employed on missions.[17] There were plans that, from the 24th B-36 onward, provisions would be made to accommodate one XF-85, with a maximum of four per bomber envisioned.[15][N 2] Up to 10 percent of the B-36s on order were to be converted to fighter carriers with three or four F-85s instead of a bomb load.[N 3]
Hangar test of recovery trapeze, with wings folded in stowed configuration
On 9 October 1945, the USAAF signed a letter of intent covering the engineering development for two prototypes (US serial numbers46-523/4), although the contract was not finalized until February 1947.[18] After the successful conclusion of two reviews of a wooden mock-up in 1946 and 1947 by USAAF engineering staff,[3] McDonnell constructed two prototypes in late 1947.[9] The Model 27D was re-designated XP-85, but by June1948, it was changed to XF-85 and given the name "Goblin".[N 4] There were plans to acquire 30 production P-85s, but the USAAF took the cautious approach– if test results from the two prototypes were positive, production orders for more than 100 Goblins would be finalized later.[16][18]
Operational history
During wind tunnel testing at Moffett Field, California, the first prototype XF-85 was accidentally dropped from a crane at a height of 40ft (12m), causing substantial damage to the forward fuselage, air intake, and lower fuselage.[9][20] The second prototype had to be substituted for the remainder of the wind tunnel tests and the initial flight tests.[21]
As a production series B-36 was unavailable, all XF-85 flight tests were carried out using a converted EB-29B Superfortress mother ship that had a modified, "cutaway" bomb bay complete with trapeze, front airflow deflector, and an array of camera equipment and instrumentation.[9] Since the EB-29B, named Monstro, was smaller than the B-36, the XF-85 would be flight tested half-exposed.[21] To load the XF-85 into the host plane, a special "loading pit" was dug into the tarmac at South Base, Muroc Field, where all the flight tests originated.[22][N 5] On 23July 1948, the XF-85 flew the first of five captive flights, designed to test whether the EB-29B and its parasite fighter could fly "mated".[13] The XF-85 was carried in a stowed position, but was sometimes tethered and extended into the airstream with the engine off, for the pilot to gain some feel for the aircraft in flight.[23]
XF-85 suspended from an EB-29 via a trapeze
McDonnell test pilot Edwin Foresman Schoch was assigned to the project, riding in the XF-85 while it was stowed aboard the EB-29B, before attempting a "free" flight on 23 August 1948. After Schoch was released from the bomber at a height of 20,000ft (6,000 m), he completed a 10-minute proving flight at speeds between 180 and 250mph (290–400km/h), testing controls and maneuverability.[24] When he attempted a hook-up, it became obvious the Goblin was extremely sensitive to the bomber's turbulence, as well as being affected by the air cushion created by the two aircraft operating in close proximity.[24] Constant but gentle adjustments of throttle and trim were necessary to overcome the cushioning effect.[22] After three attempts to hook onto the trapeze, Schoch miscalculated his approach and struck the trapeze so violently that the canopy was smashed and ripped free and his helmet and mask were torn off.[25] He saved the prototype by making a belly landing on the reinforced skid at the dry lake bed at Muroc.[N 6] All flight testing was suspended for seven weeks while the XF-85 was repaired and modified. Schoch used the down period to undertake a series of problem-free dummy dockings with a Lockheed P-80 Shooting Star fighter.[22]
After boosting the trim power by 50 percent, adjusting the aerodynamics, and other modifications,[22] two further mated test flights were carried out before Schoch was able to make a successful release and hookup on 14 October 1948.[27] During the fifth free flight on 22 October 1948, Schoch again found it difficult to hook the Goblin to the bomber's trapeze, aborting four attempts before hitting the trapeze bar and breaking the hook on the XF-85's nose. Another forced landing was carried out at Muroc.[23]
With the first prototype's repairs completed, it also joined the flight test program, completing captive flights. While in flight, the Goblin was stable, easy to fly, and recoverable from spins, although initial estimates of a 648mph (1,043km/h) top speed proved optimistic.[21] The first test flights revealed that turbulence during approach to the B-29 was significant, leading to the addition of upper and lower fins at the extreme rear fuselage, as well as two wingtip fins to compensate for the increased directional instability in docking.[9] All the initial flights had the hook secured in a fixed position, but when the hook was stowed and later raised, the resulting buffeting added to the difficulty in attempting a hookup. To address the problem, small aerodynamic fairings were added to the hook well that reduced the buffeting when the hook was extended and retracted.[22] When testing resumed, on the 18 March 1949 test flight, Schoch continued to have difficulty in hooking up, striking and damaging the trapeze's nose-stabilizing section, before resorting to another emergency belly landing.[23] After repairs to the trapeze, Schoch flew the first prototype on 8 April 1949, completing a 30-minute free flight test, but after three attempts, abandoned his efforts and resorted to another belly landing at Muroc.[28][N 7]
Aware of the problems revealed in flight tests, McDonnell reviewed the program and proposed a new development based on a more conventional design promising a Mach 0.9 capability, using alternatively a 35° swept wing and delta wing.[29] McDonnell also considered adding a telescoping extension to the docking trapeze that would extend the device below the turbulent air under the mother ship.[28] Before any further work on the trapeze, other modifications to the XF-85, or continued design studies on its follow-up could be carried out, the USAF canceled the XF-85 program on 24 October 1949.[N 8][31]
Two main reasons contributed to the cancellation. The XF-85's deficiencies revealed in flight testing included a lackluster performance in relation to contemporary jet fighters, and the high demands on pilot skill experienced during docking revealed a critical shortcoming that was never fully corrected.[29] The development of practical aerial refueling for conventional fighters used as bomber escort was also a factor in the cancellation.[21][13] The two Goblins flew seven times, with a total flight time of 2 hours and 19 minutes with only three of the free flights ending in a hookup.[21] Schoch was the only pilot who ever flew the aircraft.[32]
Further developments
Despite cancellation of the XF-85, the USAF continued to examine the concept of parasite aircraft as defensive fighters through a series of projects. These included Project MX-106 "Tip Tow", Project FICON, and Project "Tom-Tom"– which involved fighter aircraft attached to bomber aircraft by their wingtips.[33] Project FICON ("fighter conveyor") emerged as an effective Convair GRB-36D and Republic RF-84K Thunderflash combined bomber-reconnaissance-fighter, although the role was changed to that of strategic reconnaissance.[16] Project FICON drew heavily on data from the abortive XF-85 project and closely followed McDonnell's recommendations in designing a more refined trapeze.[34] A total of 10 converted B-36s and 25 reconnaissance fighters saw limited service with the Strategic Air Command in 1955–1956, before they were supplemented by more effective aircraft and satellite systems.[35]
Aircraft on display
McDonnell XF-85 Goblin on display at the National Museum of the United States Air Force at Wright-Patterson AFB in Dayton, Ohio.
After the program's termination, the two XF-85 prototypes were stored, before being surplussed and relegated to museum display in 1950.[29]
46-0523 – National Museum of the United States Air Force at Wright-Patterson Air Force Base near Dayton, Ohio. Following the cancellation of the program, the aircraft was transferred to the museum on 23 August 1950 and was one of the first experimental aircraft to be displayed at the new Air Force Museum. For several decades, the aircraft was displayed alongside the museum's Convair B-36. In 2000, the aircraft was moved to the museum's Experimental Aircraft Hangar.[36]
46-0524 – Strategic Air and Space Museum in Ashland, Nebraska. It was originally transferred to the Norton Air Force Base (near San Bernardino, California) in 1950, still in a damaged state after its last emergency landing. When the base museum was closed and its collection dispersed, the second XF-85 prototype languished in an unrestored condition as part of the Tallmantz private collection in California, until being acquired by Offutt AFB. It is now refurbished and displayed on its ground-handling trestle, nestled under the wing of a B-36J bomber (serial number 52-2217).[37]
Specifications
Three-view image of XF-85 Goblin
Data fromExperimental & Prototype U.S. Air Force Jet Fighters,[38]McDonnell XF-85 Goblin: USAF Museum factsheet,[36]McDonnell XF-85: Boeing.com factsheet[13]
The Lockheed P-80 Shooting Star was the first jet fighter used operationally by the United States Army Air Forces (USAAF) during World War II. Designed and built by Lockheed in 1943 and delivered just 143 days from the start of design, production models were flying, and two pre-production models did see very limited service in Italy just before the end of World War II. Designed with straight wings, the type saw extensive combat in Korea with the United States Air Force (USAF) as the F-80.
The McDonnell F-101 Voodoo is a supersonic jet fighter designed and produced by the American McDonnell Aircraft Corporation.
The McDonnell XF-88 Voodoo was a long-range, twinjet fighter aircraft with swept wings designed for the United States Air Force. Although it never entered production, its design was adapted for the subsequent supersonic F-101 Voodoo.
The Republic F-84 Thunderjet is an American turbojet fighter-bomber aircraft. Originating as a 1944 United States Army Air Forces (USAAF) proposal for a "day fighter", the F-84 first flew in 1946. Although it entered service in 1947, the Thunderjet was plagued by so many structural and engine problems that a 1948 U.S. Air Force review declared it unable to execute any aspect of its intended mission and considered canceling the program. The aircraft was not considered fully operational until the 1949 F-84D model and the design matured only with the definitive F-84G introduced in 1951. In 1954, the straight-wing Thunderjet was joined by the swept-wing F-84F Thunderstreak fighter and RF-84F Thunderflash photo reconnaissance aircraft.
The North American B-45 Tornado is an early American jet bomber designed and manufactured by aircraft company North American Aviation. It has the distinction of being the first operational jet bomber to enter service with the United States Air Force (USAF), as well as the first multiengine jet bomber to be refueled in midair.
The Century Series is a popular name for a group of US fighter aircraft representing models designated between F-100 and F-106 which went into full production. They included the first successful supersonic aircraft designs in the United States Air Force's service, which remained in active service well into the 1970s and 1980s with the Air Force Reserve and Air National Guard. Three later variants, the QF-100, QF-102, and QF-106, also continued in service, primarily as aerial target drones, until the late 1990s. The F-104G stayed in service with the Italian military until 2004. The NASA airborne science program maintains a group of F-104G in airworthy condition for use as test platforms and chase aircraft.
The North American XF-108 Rapier was a proposed long-range, high-speed interceptor aircraft designed by North American Aviation intended to defend the United States from supersonic Soviet strategic bombers. The aircraft would have cruised at speeds around Mach 3 with an unrefueled combat radius over 1,000 nautical miles, and was equipped with radar and missiles offering engagement ranges up to 100 miles (160 km) against bomber-sized targets.
A parasite aircraft is a component of a composite aircraft which is carried aloft and air launched by a larger carrier aircraft or mother ship to support the primary mission of the carrier. The carrier craft may or may not be able to later recover the parasite during flight.
The Convair XF-92 was an American, delta wing, first-generation jet prototype. Originally conceived as a point-defence interceptor, the design was later used purely for experimental purposes and only one was built. However, it led Convair to use the delta-wing on a number of designs, including the F-102 Delta Dagger, F-106 Delta Dart, B-58 Hustler, the US Navy's F2Y Sea Dart as well as the VTOL FY Pogo.
The Lockheed XF-90 was built in response to a United States Air Force requirement for a long-range penetration fighter and bomber escort. The same requirement produced the McDonnell XF-88 Voodoo. Lockheed received a contract for two prototype XP-90s. The design was developed by Willis Hawkins and the Skunk Works team under Kelly Johnson. Two prototypes were built. Developmental and political difficulties delayed the first flight until 3 June 1949, with Chief Test Pilot Tony LeVier at the controls. Embodying the experience gained in developing the P-80 Shooting Star, the XF-90 shared some design traits with the older Lockheed fighter, albeit with swept-wings; however, this latter design choice could not sufficiently make up for the project’s underpowered engines, and the XF-90 never entered production.
The North American F-107 is North American Aviation's entry in a United States Air Force tactical fighter-bomber design competition of the 1950s, based on the F-100 Super Sabre. It incorporated many innovations and radical design features, notably the over-fuselage air intakes. The competition was eventually won by the Republic F-105 Thunderchief, and two of the three F-107 prototypes ended their lives as test aircraft. One is on display at the National Museum of the United States Air Force and a second at Pima Air and Space Museum.
The Air Force Test Center (AFTC) is a development and test organization of the United States Air Force. It conducts research, development, test, and evaluation of aerospace systems from concept to deployment. It has test flown every aircraft in the Army Air Force's and the Air Force's inventory since World War II. The center employs nearly 13,000 people, and controls the second largest base in the Air Force.
The escort fighter was a concept for a fighter aircraft designed to escort bombers to and from their targets. An escort fighter needed range long enough to reach the target, loiter over it for the duration of the raid to defend the bombers, and return.
The Yakovlev Yak-25 was a Soviet military aircraft, an early turbojet-powered fighter aircraft designed by the Yakovlev OKB. The designation was later reused for a different interceptor design. Tasked by the Council of Ministers in a directive issued on 11 March 1947, with producing a straight winged fighter similar to the earlier Yak-19, but powered by a Rolls-Royce Derwent V, OKB-115 swiftly produced the Yak-25, which blazed several trails as the first Soviet fighter with a fully pressurised cockpit, air conditioning, jettisonable canopy, and hydraulic airbrakes on the fuselage amongst other innovations.
The FICON program was conducted by the United States Air Force in the 1950s to test the feasibility of a Convair B-36 Peacemaker bomber carrying a Republic F-84 Thunderflash parasite fighter in its bomb bay. Earlier wingtip coupling experiments included Tip Tow, which were attempts at carrying fighters connected to the wingtips of bombers. Tom-Tom followed the FICON project afterwards.
An airborne aircraft carrier is a type of mother ship aircraft which can carry, launch, retrieve and support other smaller parasite aircraft.
A composite aircraft is made up of multiple component craft. It takes off and flies initially as a single aircraft, with the components able to separate in flight and continue as independent aircraft. Typically the larger aircraft acts as a carrier aircraft or mother ship, with the smaller sometimes called a parasite or jockey craft.
The term penetration fighter has been used to describe a long-range fighter aircraft designed to penetrate enemy air defences and attack defensive interceptors. The concept is similar to the escort fighter, but differs primarily in that the aircraft would not operate in close concert with bombers. Both types are sub-classes of the strategic fighter. The same general mission is also carried out by intruders, but these are generally night fighters or light bombers that do not have the air combat performance of this concept.
Edwin Foresman Schoch was a United States Navy aeronautical engineer, combat pilot and test pilot.
References
Notes
↑ A fixed tricycle landing gear was considered for the flight tests but was discarded as the drag was excessive.[12]
↑ The initial specification called for the B-36 carrier aircraft to be able to carry either one F-85 and one atomic bomb or three F-85s.[9]
↑ The modifications included a structurally reinforced bomb bay that included the trapeze apparatus and an "umbilical" fueling station. In operational use, provisions for repair of oxygen and other mechanical systems, as well as replenishing ammunition were contemplated.[16]
↑ This name does not follow McDonnell practice and is the name that the USAAF gave to the aircraft.[15] McDonnell personnel nicknamed the aircraft "Bumble Bee."[19]
↑ The XF-85 were hooked onto fully extended trapeze and then hoisted into the mother ship.[22]
↑ On the last XF-85 flight, after completing a lengthy flight test, due to the limited fuel on board, Schoch was forced to abandon further attempts to dock.[22]
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Davis, Larry and David Menard. F-84 Thunderjet in Action (Aircraft No. 61). Carrollton, Texas: Squadron/Signal Publications, 1983. ISBN978-0-89747-147-3.
Dorr, Robert F. "Beyond the frontiers: McDonnell XF-85 Goblin: The built-in fighter." Wings Of Fame, Volume 7, 1997.
Fitzsimons, Bernard, ed. The Illustrated Encyclopedia of 20th Century Weapons and Warfare, Volume 5. London: Phoebus, 1978. ISBN978-0-8393-6175-6.
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Jenkins, Dennis R. and Tony R. Landis. Experimental & Prototype U.S. Air Force Jet Fighters. North Branch, Minnesota: Specialty Press, 2008. ISBN978-1-58007-111-6.
Knaack, Marcelle Size. Encyclopedia of US Air Force Aircraft and Missile Systems: Volume 1 Post-World War II Fighters 1945–1973. Washington, DC: Office of Air Force History, 1978. ISBN0-912799-59-5.
Lepage, Jean-Denis G. G. Aircraft of the Luftwaffe, 1935–1945: An Illustrated Guide. Jefferson, North Carolina: McFarland & Company, 2009. ISBN978-0-7864-3937-9.
Lesnitchenko, Vladimir. "Combat Composites: Soviet Use of 'Mother-Ships' to Carry Fighters, 1931–1941." Air Enthusiast, No. 84, November/December 1999.
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