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XF-85 Goblin “Parasite” Fighter

The XF-85 Goblin was an unconventional American fighter prototype built by the McDonnell Aircraft Corporation during World War II. 

Intended to be carried in and dropped from the internal bomb bays of massive customized aircraft flying alongside traditional bombers, the US Army Air Forces (USAAF) had high hopes that their groundbreaking new parasite fighters would revolutionize the way heavy bombers were escorted to and from their targets. 

Theoretically the parasite-host – or parasite-mothership – setup would eliminate the time associated with scrambling fighters from distant airfields, after which they wasted precious fuel climbing to altitude and covering huge distances at high speeds to engage enemy interceptors. 

Then, flying on vapors and possibly arriving too late to make any difference, they’d have but a few short minutes to tangle with their adversaries before returning to friendly airfields. 

In short, it was an expensive, time consuming and ineffective exercise in futility, and it had been a huge problem for years. 

Eventually long-distance fighter escorts like P-51 Mustangs and P-47 Thunderbolts were able to escort B-17 Flying Fortresses and B-24 Liberators to and from their targets in Germany, thanks largely to drop tanks and more efficient engines.

That said, these fighters weren’t parasites, and the long trips were hard on both men and machines. 

A few nations dabbled with parasites during World War II with limited success, but the concept itself had been around since the First World War. 

Evolution & History

In mid-1918 as World War I drew to a close, the Royal Air Force tinkered with the idea of suspending Sopwith Camel biplanes from airships. 

The scheme never got past the experimental phase, but the idea wouldn’t die, and more than a decade later in 1931 the US Navy developed another operational but ultimately unsuccessful parasite, the Curtis F9C Sparrowhawk 

The radial engine powered biplane had some success launching from and docking back onto Navy airships like the USS Akron and Macon, and at the same time the Soviets were conducting similar experiments of their own.

Taking a bolder approach however, they opted for multi-engine fixed wing motherships like Polikarpov TB-2s and Tupolev TB-3 bombers instead of lumbering blimps.

But it wouldn’t be until mid-1941 when these Soviet aircraft combinations set out on what would be the first combat missions ever recorded by parasite fighters, when TB-3s carrying I-16 dive bombers successfully attacked strategic Romanian bridges and ports. 

Later in the war the Luftwaffe experimented with the Messerschmitt Me 328 as a parasite fighter as well. 

A short but rather conventional looking aircraft, the Me 328 was particularly promising, but though its pulse jet engines were relatively powerful, inexpensive and easy to produce, the project was ultimately canceled not because of launching and docking issues, but persistent power plant problems that couldn’t be overcome. 

Enter the Goblin

Characterized by an egg-like fuselage, an ungainly arresting hook sticking up in front of the canopy, an awkward trisurface rudder jutting up and out behind the cockpit, and sweeping wings protruding from the body in front of the pilot’s seat, the Goblin wasn’t as aesthetically pleasing as other aircraft of the day.

An old aviation adage goes something like this – 

If it looks right, it’ll fly right. 

The Goblin didn’t exactly “look right,” but the verdict was still out on its performance.  

Featuring a large bubble canopy and gaping engine intake where the nose cone should’ve been, at least from the cockpit forward it resembled an F-86 Sabre of later Korean War fame. 

The odd XF-85 was McDonnell’s response to a 1942 request for proposals from the USAAF for a pint-size piston-engined parasite fighter.

Of the aerospace companies that considered the RfP however, only McDonnell ended up submitting a preliminary design proposal. 

After successfully producing two wooden mock-ups years later, McDonnell’s engineers and manufacturers got to work making the actual prototypes, but not before the RfP was officially amended.  

Now the new fighter would need a jet engine. 

The USAAF still needed a small, maneuverable and capable fighter that could be carried inside the Northrop XB-35 and B-36 bombers that were then under development, but it needed more power than a piston-engine could provide.  

Though much faster than bombers, the jet fighters of the day had very limited ranges, and development times and costs for true interceptors were prohibitively high.

And like it was in World War II, pilot fatigue was a huge problem, and would be even more taxing when piloting supersonic aircraft. 

Aerial refueling for existing aircraft was an option as well, though at the time it hadn’t been perfected and was dangerous to tankers, fighters, pilots and crews.

The USAAF even briefly considered developing remotely piloted vehicles, but the technology was in its infancy and also inordinately expensive, and estimates suggested it would take a decade or more to perfect. 

Though it was far from a perfect solution, the parasite concept seemed like the only viable option. 

Two prototypes were built and underwent testing and evaluation in 1948. 

The McDonnell design showed promise, but one big drawback was its performance, which wasn’t up to the standards of many of the enemy fighters it’d be expected to tangle with in aerial combat. 

But there were even bigger problems. 

Initially, the XF-85 was to be carried partially exposed underneath modified B-29s, B-35s, or B-36s. 

However this would have increased both drag and fuel consumption significantly, while at the same time decreasing cruising speed and shortening range, so the proposal was rejected. 

In the future, parasites would clearly need to reside in the internal bomb bays of their host planes – yet another epic engineering hurdle to contend with. 

At just 14 ft 10 in (4.52 m) long and with its swept wings measuring just 21 ft (6.4 m) from tip to tip, the XF-85 was still too big to fit inside the fuselage of even the largest potential motherships.

To address this issue, the Goblin prototype had folding wings that pointed upward while inside, that were lowered and locked into place before detaching from the host plane.  

Performance & Weapons

With a maximum takeoff weight of just 5,600 lb (2,540 kg) the XF-85 was light, and it only carried about 110 gallons (410 L) of fuel which was deemed sufficient to give it between 30 minutes and an hour of loiter time depending on weather conditions, altitude and the intensity of the dogfight. 

Powered by a Westinghouse XJ34-WE-22 turbojet engine producing about 3,000 pounds of thrust, it wasn’t a performance standout even by ‘50s jet standards, but due to its light weight it had a respectable thrust to weight ratio.

Rate of climb was estimated to be about 12,500 feet per minute (64 m/s), and with a service ceiling of about 48,000 feet (15,000 m) it would be able to climb to meet its enemies quickly while achieving a top speed of 650 mph (1,050 km/h).

Its offensive punch consisted of four .50 caliber (12.7 mm) machine guns in the nose, but since it was solely a fighter it wouldn’t carry rockets or bombs.  

By comparison, the first operational jet fighter, the Messerschmitt Me 262, had two engines that combined produced about 4,000 pounds of thrust and sported either two or four 30 mm cannons and had a top speed of about 560 miles per hour (901 km/h). 

Takeoff & Tethering 

At least theoretically, had they gone into full scale production, XF-85s could have been refueled, rearmed and relaunched easily, but those assumptions came before actual flight testing. 

Except in emergency situations the plane wouldn’t be landing on runways, so it didn’t have a traditional landing gear which would have increased weight, taken up lots of space in the wings and fuselage and seriously hindered performance and range. 

Instead, a hook installed along the Goblin’s centerline which connected to the mothership’s trapeze was raised during launch and recoupling and retracted to lay flush during actual free flight. 

During testing the prototype was fitted with a steel skid under the fuselage and runners under the wingtips to provide stability and protection if a belly landing on a traditional runway was required, which it was numerous times. 

Though the gauge-filled cockpit was borderline claustrophobic, the plane was equipped with a  cordite ejection seat, oxygen bottle and ribbon parachute capable of opening at high subsonic speeds. 

The Goblin’s jet engine would be air started when lowered from the host craft, after which the pilot would ease back on the stick which would drop the tail and raise the nose.

Then, with a little luck there’d be sufficient lift to disengage the hook from the trapeze and depart without crashing into the larger plane’s belly, wings or engines. 

During an attempted recovery, the aircraft would approach the mother ship from underneath and link up with the trapeze using its retractable hook.

Test Flights

Early wind tunnel testing at Moffett Field in California almost spelled the end of the project when the first XF-85 prototype fell 40 feet from a crane to the concrete below causing major structural damage. 

Aerial photo of Moffett Federal Airfield, with its immense historic hangers— located in Mountain View, California.
Aerial photo of Moffett Federal Airfield, — located in Mountain View, California. By Ikluft, is licensed under CC-BY-SA

The second prototype had to be substituted for the remainder of the wind tunnel tests and the initial flight tests.

Actual flight tests were carried out with a modified EB-29B, because the B-36 mothership wasn’t yet available. 

The B-29 Superfortress had a cutaway bomb bay, trapeze, airflow deflector, and a number of cameras and instruments installed to monitor and record launches and recouplings for analyzing later on. 

To load the XF-85 into the B-29, a pit was dug into the tarmac at South Base, Muroc Field, where all the flight tests originated.

In late July of 1948 the XF-85 flew the first of five captive flights to determine whether the two craft could fly safely coupled together. 

During the first few flights the XF-85 remained stowed and tethered, but was lowered into the atmosphere with its engine off to acclimatize McDonnell test pilot Edwin Foresman Schoch to the feeling of flying in such close proximity to a much larger host aircraft. 

Schoch apparently felt comfortable enough to take things to the next level in late August, because he lit the jeg engine, detached the little Goblin from the B-29 and roared upward to nearly 20,000 ft (6,000 m).

The flight lasted just 10 minutes, during which he reached a maximum speed of just 250 miles per hour (400 km/h) to get a feel for the plane’s flight characteristics. 

Though the flight was uneventful, his attempted hook-up was anything but routine. 

As the tiny Goblin bobbed and swayed in the big bomber’s turbulence, Schoch made multiple attempts to reattach to the Superfortress, but all were unsuccessful.

The final try was so violent that a last minute lurch forward smashed the canopy and tore off his helmet, after which he managed to descend and make a belly landing on the dry lake bed at Muroc.

All flight testing was suspended for seven weeks while the XF-85 was repaired and modified. 

After extensive changes, two additional test flights were made before Schoch eventually made a successful hookup on October 14, 1948. 

Just a week later however, he had major difficulty pulling it off again, and after four attempts, one of which broke the trapeze bar and the XF-85’s nose hook, he again belly landed at Muroc. 

Schoch reported that while in free flight the Goblin was a pleasure to fly, though he thought the estimated top speed of 648 mph (1,043 km/h) was glaringly optimistic, and that reattaching was positively hair raising, and would probably always be so. 

Nonetheless, to combat the turbulence issues when the two planes were uncoupling and tethering, fins were added along the rear fuselage and at the wingtips for stability. 

In addition, small aerodynamic surfaces were added to the goblin’s retractable hook which reduced buffeting and kept it more stable while it was in its upright position. 

Despite these improvements however, when tests resumed in early 1949 Schoch – the only pilot who ever flew the aircraft – found that he still had the same difficulties retethering, and at least once more he had to resort to a belly landing. 

Ever optimistic, McDonnell engineers proposed a new wing design that they hoped would improve stability and high-speed performance, but by October of 1949 the USAF had seen enough.

Funds were withdrawn, the project was cancelled, and the shiny little jet fighter was relegated to the dustbin of aircraft that might have been. 

The main reasons given for the cancellation were the XF-85’s flight deficiencies compared to traditional fighters of the day, and the precarious nature of redocking after free flight. 

Also, while the XF-85 was being developed there had been huge advances in aerial refueling, and by late 1949 refueling traditional aircraft in-flight seemed like a much better option than launching parasite fighters from modified bombers. 

At one time the Air Force had tentatively planned for nearly 100 production XF-85s that would have been paired with a fleet of B-36 motherships, each of which may have been able to carry four Goblins.  

In the end though, the two Goblin prototypes flew just seven times, managed three successful hookups, and accumulated just over 2 hours of flight time.

Further developments

Despite cancellation of the XF-85, the USAF continued to develop the parasite fighter concept. 

One notable attempt was Project MX-106 “Tip Tow,” in which F-84D fighters referred to as “children” were affixed to the outer edge of each of a B-29 “mother’s” wings. 

Though easily launched, the F-84s were never meant to recouple with the B-29s after free flight. 

Instead, they carried out their reconnaissance missions, and with excess fuel reserves returned to their home base where they made traditional landings on good old-fashioned runways. 

Now the McDonnell XF-85 Goblin is on display at the USAF Museum at Wright-Patterson AFB in Dayton, OH.

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