Experimental

The XF-85 Goblin “parasite” Fighter Built to Protect B-36 Bombers


Parasite is not normally a word associated with the aviation industry. That was until the McDonnell Aircraft Corporation introduced the idea for the XF-85 parasite fighter to protect the mammoth B-36 Peacemaker as well as other large next-generation aircraft.

With the U.S. utilizing large heavy bombers with huge ranges, smaller fighter aircraft were unable to fly the same distance to protect them. The idea was that the B-36 would carry its own fighters to be deployed if intercepted by the enemy. Almost like a flying aircraft carrier. Both the UK and Russia had experimented with this idea before in the 40s but never had much success.

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Harebrained Thinking


During World War II a heavily employed tactic by the Allies was mass bombing raids. Huge numbers of aircraft, in some cases over 1,000, would be sent against the Axis powers to overwhelm their defenses. Operation Millennium was one such occasion where the RAF sent 1,047 bombers to Cologne.

The destruction in Cologne due to the thousand bomber raids.
The huge amount of destruction in Cologne was due to the thousand bomber raids.

This tactic was relatively effective and carried out twice more in June 1942 by the RAF. However, filling the entire sky with an armada of aircraft can have its downsides. The most obvious is their position – whilst so many bombers would overwhelm the basic radar, enemy aircraft would be able to spot the formation easily.

Defending these bombers from the Luftwaffe was no easy task and whilst friendly fighters would be employed as escort, it was not possible to protect every Lancaster and Wellington.

They needed to look after themselves and many large bombers from all nations had some form of defensive armament – either machine gun or cannon turrets. The most iconic example is the B-17, with almost 360-degree coverage of .50 cal firepower.

The B-17 had a lot of gun turrets
The B-17 had almost full defensive coverage thanks to the turrets strategically placed on the fuselage.

As fighters got faster, the effectiveness of turrets diminished. Being able to move the guns quickly enough to get lead on an aircraft going 450+ mph is extremely difficult. Bombers were easier to shoot down by making high-speed passes.

Defending these lumbering beasts with friendly aircraft became more difficult too – the range of a typical first-generation jet aircraft was nowhere near that of a comparable bomber and inflight refueling was considered too risky. So they simply couldn’t fly the distance to the target and ensure the bomber had cover, making it a sitting duck.

If only the bombers could carry their payload as well as have an effective way to defend themselves… Cue the XF-85 Goblin.

The XF-85

To overcome the hurdles presented by long-range heavy bombers, in the late 40s the McDonnell Aircraft Corporation decided to test small aircraft that could be carried by said bombers, to be launched and intercept incoming enemy fighters. Once the enemy aircraft had been defeated, they could dock with the bomber ready for deployment again.

Of course, there were no aircraft already in the US’s arsenal that could perform this role and a new design was put forward.

The Goblin had a strange egg-like appearance with an unusual tail design all with the goal of saving space and the ability to fit inside a bomb bay. The overall length was only 14ft 10 in and a wingspan of 21ft. By comparison, the P-51 Mustang had a wingspan of 36 feet.

XF-85 had a strange appearance
The XF-85 looked very unusual for the time.

With such a small size, many other challenges were present and needed to be overcome to make this work. The XF-85 only had a fuel capacity of 93 gallons and thus the ability to fly for 30 minutes before needing to be refuelled.

Weight was kept to a minimum to aid performance and only weighed 4,000 lbs empty. It even lacked proper landing gear and had a fixed skid under the fuselage for an emergency.

A tiny but powerful engine was required to keep weight down but propel the XF-85 to 650 mph. The Westinghouse J-34 was selected and it produced a rather measly 3,000 lbs of thrust. This model of the engine was also used by the F-2H Banshee and the F3D Skyknight.

The armament was typical of America’s early jet aircraft with four M3 Browning .50 cal machine guns mounted in the nose.

Upon each bombing mission, B-36s would fly in formations of four, with three of them being fighter carrier models and one that carried an explosive payload. Each B-36 was intended to house three or four F-85s meaning potentially 12 parasite fighters buzzing around to defend the bombers.

The XF-85 was designed to be carried by the B-36 Peacemaker
The XF-85 was designed to be carried by the B-36 Peacemaker.

Launch and Docking Procedure


Even with all of the design challenges with the Goblin itself, the biggest hurdle was the launch and docking procedures. A trapeze was used and would fully extend keeping the parasite fighter well below the mothership.

It would then be air started and immediately be ready for combat. What looked like a tangled mess of metal tubes was a clever piece of design that allowed the XF-85 to be lowered safely attached via retractable hooks on the Goblin.

After the 30-minute endurance period was up, the hook would be lowered by the crew aboard the mothership and the pilot of the Goblin would reattach to the trapeze and fold in the wings, and be hoisted up into the belly.

XF-85 docked with the EB-29 mothership
XF-85 docked with the EB-29 mothership.

What is the smallest military plane?

The XF-85 Goblin is the smallest military plane. During WWII, McDonnell Aircraft created two XF-85 prototypes to protect the Northrop XB-35 and B-36 planes. Their idea was to launch this fighter jet when enemies attacked these planes. However, the XF-85 was slow compared to its competition, and pilots had difficulty landing the fighter jet back inside the bigger planes. A year after its first flight, McDonnell canceled the XF-85 project.

Operational Use

Theoretically, the idea of a parasite is great, but in practice, it is much more complicated. Two XF-85s were ordered by the US Air Force for testing. The first was mainly used in the wind tunnels, but it was dropped from 40 feet and was badly damaged.

The second aircraft was kept for flight testing. It was accomplished by using a heavily modified B-29 Superfortress aircraft, designated EB-29B Monstro. Although it was smaller than the B-36, there were no production versions available to use for this testing.

Size comparison of B-36 vs B-29
The size difference between the B-36 and B-29 is huge.

A special loading pit was made to join the two aircraft for flight testing. July of 1948 was the first time the Goblin took to the skies. It was still attached to the EB-29B to ensure no issues would be encountered before it was released and a month later it was ready to fly under its own power.

At 20,000 feet the Goblin was released for the first time. The test pilot flew for a total of 10 minutes to get a feel for the handling at relatively low speeds of up to 250 mph. Major issues started to appear when attempting to dock back with the EB-29B.

Due to the large size difference, the Goblin had a rough time with the turbulence from the modified Superfortress. It took three attempts to latch onto the trapeze and due to the turbulence, the coupling was so violent the canopy smashed and broke off the aircraft, as well as taking the pilot’s mask and helmet with it.

Amazingly Edwin Schoch managed to land the wounded XF-85 at the dry lake bed at Muroc that was being used for testing.

A view of
An overhead view of Muroc Dry Lake where lots of experimental aircraft testing was done.

This accident led to the suspension of all flight testing whilst the XF-85 was repaired and modifications made. Seven weeks after this incident Schoch finally managed a successful docking after several attempts in mid-October.

Unfortunately, this was more of a stroke of luck, Several days later another attempt was carried out and the Goblin’s nose hit the trapeze meaning another forced landing had to be made.

To compound these issues, the flight performance itself was underwhelming. The top speed was supposed to be around 650 mph but it fell short.

It would have been very unlikely that a production F-85 would have ever caught up to attacking enemy aircraft that were already traveling at speed due to poor engine response from early jets.

McDonnell made several modifications to the wing and tail of the XF-85 to try and compensate for some of the issues. But this was not enough to save the project.

The Goblin was cancelled. The blame lay with the lacklustre performance and the challenges with docking. With limited fuel and over enemy territory, this was not an acceptable solution as almost certainly the F-85s would end up ditching and the pilots either dying or being captured.

Another Article From Us: When a Victor Bomber Accidentally Took Off

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Specifications

  • Crew: 1
  • Length: 14 ft 10 in (4.52 m)
  • Wingspan: 21 ft 1 in (6.43 m) wings spread
  • Height: 8 ft 3 in (2.51 m)
  • Empty weight: 3,740 lb (1,696 kg)
  • Max takeoff weight: 5,600 lb (2,540 kg)
  • Powerplant: 1 × Westinghouse XJ34-WE-22 engine, 3,000 lbf (13 kN) thrust
  • Maximum speed: 650 mph (1,050 km/h)
  • Service ceiling: 48,000 ft (15,000 m)
  • Rate of climb: 12,500 ft/min (64 m/s)
  • Armament: 4 x .50 cal in (12.7 mm) M3 Browning Machine Guns
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