McDonnell XF-85 Goblin

Posted: July 27, 2011 in Aircraft, AVIATION, Figther, Weapon

The McDonnell XF-85 Goblin was an American prototype fighter aircraft conceived during World War II by McDonnell Aircraft. It was intended to be carried in the bomb bay of the giant Convair B-36 bomber as a defensive parasite fighter. During World War II, Luftwaffe fighters provided stiff opposition for Allied bombers. The XF-85 was a response to a United States Army Air Forces (USAAF) requirement for a parasite fighter capable of being carried within the Northrop XB-35 and B-36, then under development. Two prototypes were built and underwent testing and evaluation in 1948. Flight tests showed promise in the design, although inherent design flaws associated with parasite fighters were never resolved. The XF-85 was swiftly canceled due to a number of factors, and the prototypes are now museum exhibits.

The U.S. Navy had been testing the viability of such aircraft in the 1930s, constructing the USS Akron and Mason for scouting, as well as launching the Curtiss F9C Sparrowhawk. At the end of World War II, Luftwaffe fighter jets posed a danger to Allied bombers. This emphasized the importance of long-range escort fighters such as the P-47 Thunderbolt and P-51 Mustang. However, the United States Army Air Force (USAAF) was developing bombers, namely the Northrop B-35 flying wing and Convair B-36, which had a much longer endurance than the B-17s, B-24s, and B-29s the fighter escorts were protecting at the time.

There were a number of options to protect the bombers. The first, developing longer-ranged fighters, was very expensive. A second option was the technically-risky aerial refueling. The last option was to develop a parasite or “internally stowed fighter”.[4] In late 1942, the USAAF sent out a Request for Proposals (RfP) based on a parasite concept, originally conceived as a diminutive piston-engined fighter. By January 1944, the Air Technical Service Command (ATSC) refined the RfP and in January 1945, the specifications were further revised to specify a jet-powered aircraft. 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. The company Model 27 proposal was completely reworked to meet the new specifications

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. On 19 March 1945, a revised proposal was submitted. The smaller aircraft had an egg-shaped fuselage, three fork-shaped vertical stabilizers, horizontal stabilizers with significant dihedral, and 37° swept-back wings. The miniature aircraft measured 14 ft 10 in (4.55 m) long; the folding wings spanned 21 ft (6.4 m). The aircraft had an empty weight just short of 4,000 pounds (1.8 t). To save weight, the parasite fighter had no landing gear. During the testing program, steel skids were installed under the fuselage in case of an emergency. Four .50-caliber machine guns made up the aircraft’s armament.

In service, the parasite fighter would be launched and retrieved by a trapeze system. The aircraft would approach the mother ship from underneath and link up with the trapeze using a retractable hook on top of the cockpit. There were plans that, from the 24th B-36 onward, provisions would be made to accommodate one XF-85, with a maximum of three per bomber envisioned.

On 9 October 1945, the USAAF signed a letter of intent covering the engineering development for two prototypes (US serial numbers 46-523/4), although the contract was not finalized until February 1947. The Model 27 was re-designated XP-85, but by June 1948, it was changed to XF-85 and given the name “Goblin”. 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 the Goblins would be finalized later. During wind tunnel testing at Moffett Field, California, the first prototype XF-85 was damaged when dropped from a height of 40 ft (12.19 m) and receiving substantial damage to the forward fuselage, air intake and undersurface. Consequently, the second prototype was substituted for not only the remainder of the wind tunnel tests but also for the initial flight tests.

As the B-36 was unavailable, all XF-85 flight tests were carried out using a converted EB-29 Superfortress parent ship. Since the B-29, named Monstro, was smaller than the B-36, the XF-85 would be flight-tested half-exposed. On 23 July 1948, the XF-85 flew the first of five captive flights, designed to test whether the EB-29 and its parasite fighter could fly “mated”.The XF-85 was variously carried in a stowed position, but was also extended into the airstream for the pilot to gain some feel for the aircraft in flight, although it still remained tethered.

McDonnell test pilot Edwin Schoch, who flew the only proving flights on the type, completed a series of dummy dockings with a Lockheed F-80 without problems, before attempting a “free” flight with the XF-85. On 23 August 1948, Schoch was released and after a 10-minute proving flight, testing controls and maneuverability, attempted a hook-up, but it became obvious that turbulence around the bomber created difficult control problems as the lighter Goblin proved to be more sensitive to turbulence than the F-80. In an aborted effort, Schoch struck the trapeze so violently that the canopy was smashed and ripped free and his helmet and mask were torn off. He saved the prototype by making a belly landing, landing on the reinforced skids.

After a series of modifications to improve handling and two further mated test flights, Schoch was able to make a successful release and hookup on 14 October 1948. 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, breaking the hook on the XF-85’s nose. Again, a forced landing in the desert was successfully carried out.

With the first prototype’s repairs completed, it also joined the flight test program, completing captive flights. Schoch continued to have difficulty in hooking up, again damaging the trapeze on the 19 March 1948 test flight, that resulted in a further emergency belly landing. While in flight, the Goblin was stable, easy to fly, and recovered well from spins, although initial estimates of a 648 mph (1,043 km/h) top speed proved optimistic.

With repairs made to the mothership’s trapeze, Schoch flew the first prototype on 8 April 1949, but after three attempts, abandoned his efforts and resorted to another belly landing. To address some of the problems in connecting to the trapeze, although slight changes were made to aircraft’s hook apparatus, McDonnell considered adding a telescoping extension to the docking trapeze. Before further modifications could be carried out, the USAF canceled the XF-85 program on 24 October 1949.

The program was canceled not only because the XF-85’s performance proved inferior to contemporary foreign jet fighters, but, also as evidenced by the test program flights, the high pilot demands involved in the docking to a mothership and should the XF-85 fail to dock, the necessity to carry out a forced landing. The development of practical aerial refueling was also a factor. The two Goblins flew six times, with a total flight time of 2 hours and 19 minutes; Schoch was the only person who ever flew the aircraft.

Two XF-85 prototypes were built.

The first example, serial number 46-523, is on display at the National Museum of the United States Air Force at Wright-Patterson Air Force Base near Dayton, Ohio. The aircraft was transferred to the museum on 23 August 1950 following the cancellation of the program, 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. Museum staff and visitors objected to this, believing the aircraft should be displayed alongside the B-36 to properly represent its original design intentions.

The other example, serial number 46-524, is on display at the Strategic Air and Space Museum in Ashland, Nebraska.

Comments
  1. so much great info on here, : D.

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