The McDonnell XF-85 Goblin was an experimental jet fighter developed in the late 1940s by McDonnell Aircraft for a unique and ambitious concept—serving as a parasite fighter for the enormous B-36 Peacemaker strategic bomber. Its design was intended to address a specific challenge of the time: how to protect the B-36 during long-range missions and defend it against enemy interceptors. The Goblin was designed to be stored inside the B-36’s bomb bay, then deployed to fight off attackers before returning to the bomber for recovery. However, despite its innovative design, the XF-85 Goblin proved impractical, leading to the cancellation of the project after a brief test period. It stands today as one of aviation history’s most unusual and short-lived experiments.

The Parasite Fighter Concept

The parasite fighter concept originated in the 1940s, during the early years of the Cold War, when the need for long-range bombers capable of reaching the Soviet Union was paramount. At the time, the B-36 Peacemaker was one of the largest and most powerful bombers ever built, with the ability to carry an impressive payload over vast distances. However, one of the challenges facing the B-36 was its vulnerability to enemy fighters, especially in the latter stages of its flight. As the bomber would be flying at high altitudes and cruising over great distances, its ability to defend itself against fast, intercepting fighters would be limited.

The solution proposed by McDonnell Aircraft was to create a small, lightweight jet fighter that could be housed in the B-36’s bomb bay. This fighter, which would be released when needed, was meant to escort the bomber in hostile airspace, fend off enemy interceptors, and then return to the bomber to be “re-docked” in midair using a trapeze system. This concept of a “parasite” aircraft was part of a broader trend in military aviation at the time, where engineers experimented with innovative ways to enhance the capabilities of bombers.

Design and Features

The McDonnell XF-85 Goblin was a remarkable aircraft in terms of design and size. Measuring just 13 feet long with a wingspan of only 22 feet, the Goblin was an extremely compact jet, making it an ideal candidate for storing inside the massive B-36’s bomb bay. Its small size was crucial, as it allowed the bomber to carry several of these aircraft, providing an additional layer of defense without taking up valuable space.

Powered by a single Allison J35 turbojet engine, the XF-85 Goblin was capable of reaching speeds of around 600 mph—a fairly impressive speed for such a small aircraft. Its straight wing design and light weight made it agile and fast, and it could be deployed quickly once released from the B-36.

The Goblin was equipped with basic weaponry, including four .50 caliber machine guns and the potential to carry small bombs or rockets. However, its primary role was to defend the B-36 and provide quick fighter escort capability, not to engage in prolonged dogfights or complex bombing missions.

Trapeze System and Midair Docking

One of the most innovative features of the XF-85 Goblin was its ability to reconnect with the B-36 in midair. The system that was designed for this was called the “trapeze system”. Essentially, the bomber would release the Goblin, and after the fighter completed its mission, it would return to the B-36. The B-36 had a tail-mounted trapeze device, which would be extended to catch the fighter as it approached. The aircraft would then latch onto this device and be safely pulled back into the bomber’s bomb bay.

However, the trapeze system was far more challenging than it appeared. The airspeed and turbulence around the B-36 during flight made it extremely difficult for the small XF-85 to reconnect. The fighters often had difficulty lining up with the trap, and in turbulent conditions, the process was nearly impossible. The midair docking was not only hazardous but also impractical in operational conditions, as it required near-perfect precision to execute successfully. These challenges were a key factor in the eventual cancellation of the project.

Limitations and Cancellation

While the XF-85 Goblin performed reasonably well in test flights—demonstrating its speed, maneuverability, and stability—it had several inherent limitations that ultimately led to the project’s discontinuation.

Limited Range: The XF-85 had an extremely short combat radius, largely due to its small size and lack of internal fuel capacity. It could only operate for short periods of time before it needed to return to the B-36 for refueling or re-docking. This made it an impractical solution for long-range missions, where a bomber would need constant fighter support.

Docking Difficulties: As mentioned earlier, the midair docking process was fraught with difficulty. Turbulence and varying flight conditions made it almost impossible for the small fighter to reconnect with the bomber in any but the calmest of weather conditions. This proved to be a major operational challenge and rendered the concept unfeasible.

Aerial Refueling: As aerial refueling technology advanced during the late 1940s and early 1950s, it became clear that this was a far more viable solution for extending the range and operational effectiveness of fighter escorts for bombers. Aerial refueling allowed fighters to stay in the air for much longer and provide more consistent protection to bombers, without the need for complex midair docking systems.

As a result, the McDonnell XF-85 Goblin was abandoned after only a handful of test flights. The concept of the parasite fighter was ultimately deemed impractical, and with the advent of aerial refueling and improved fighter technologies, the need for such an aircraft faded.

Legacy

Although the XF-85 Goblin was a failure as a practical solution for the B-36, its legacy remains as one of the more unusual and innovative experiments in aviation history. It represented a bold attempt to solve the problem of bomber defense in the early days of the Cold War, using technology and concepts that were ahead of their time.

Today, the XF-85 Goblin is remembered as one of aviation’s strangest aircraft designs. Only two prototypes of the fighter were ever built, and one of them is now on display at the Smithsonian National Air and Space Museum in Washington, D.C. While the Goblin never saw combat or widespread use, it continues to fascinate aviation enthusiasts and historians alike as a curious footnote in the development of military aircraft.

In retrospect, the XF-85 Goblin was a product of its time—a bold, innovative solution to a complex problem. However, with the advancement of technology and the development of more effective solutions like aerial refueling and faster fighter aircraft, the Goblin never had a chance to become more than just a fascinating experiment.