The Allies’ Frankenplane Monster

The Fisher XP-75 was a so-called WWII “Wonderplane” that has also earned nicknames like “Turkey,” and “Frankenplane,” and is even dubbed as the worst military aircraft. But did it really deserve these titles?

“Wonderplane”

From late 1942 to early 1943, the US Air Force requested for a plane to be built with a top speed of 440 mph, a climb rate of 5,600 fpm, and a max range of 2,500 miles. 

A man named Donovan Berlin working for General Motors submitted an idea that’s mostly made out of parts already in production. Combining it with the most powerful engine they have, GM promised to develop these “Wonderplanes” quickly and cheaply. GM was eventually awarded a contract for two prototypes of the XP-75 aircraft. 

Original Design

The original components were taken from three planes already in production. The wings would be taken from the P-51, the tail and the whole empennage would be pulled from the SBD Dauntless dive bomber, and the landing gear would be taken from the F4U Corsair. As you might have expected by now, the resulting body design looked a bit odd.

What the aircraft stood out (both positively and negatively) from was on the inside – with its powerplants and weaponry. Since they also owned Allison Engine, they used the best engine Allison had to offer, the V-3420.

Apart from that, it was slated to be one of the best well-armed fighters in the US arsenal. There would be six .50-caliber machine guns in the wings, three in each wing. In addition, four more .50-caliber machine guns were in the fuselage towards the nose.

Issues

The initial production order was raised from 2 to 8. There was also a letter of intent for the order of 2,500 XP-75s if it’s successful in the testing process. However, there were problems even before the first model was completed.

There was a delay in the delivery of the prototypes, and compounding design changes. For instance, the P-51 wings would be swapped with the P-40.

With parts being swapped constantly, the design had to be altered in small and significantly time-consuming ways. Initial test results proved to be disappointing. There were also issues in the engine, tail, and wings. Additionally, there were severe instability issues.

In the end, the new and improved XP-75 looked a lot different than its original model. 

Result Of The Experiment

The XP-75 finally flew for the first time on November 17, 1943, and proved to be a dud. During testing, it was discovered that they miscalculated its center of mass. Furthermore, its poor spin characteristics, high aileron forces at high speeds, inadequate engine cooling, and unexpectedly slow engine solidified the US Air Force’s decision to stay away from the project.

By the time the P-38 and P-51 entered into large-scale production, the XP-75’s production runs were already terminated. Ultimately, only 14 XP-75(including “A” variants) were built.