Aviation History

Did you know the “extreme blending” of the futuristic XP-67 has been used in B-1 and B-2 bombers for their low observability properties? How the World War II prototype interceptor Moonbat influenced frontline types.

The XP-67 Moonbat may not have gone into production, but it did have two lasting effects on future aircraft in general, and McDonnell Aircraft Company’s fighters in particular.


The series of X-planes that sprang from the US Army’s Request for Data R40C, focused on high-altitude, high-speed, long-range bomber interceptors. Among these aircraft was the McDonnell Aircraft Corporation’s (MAC) first ever clean sheet design, the XP-67 Moonbat. Its futuristic lines promised performance that it was ultimately unable to deliver, but development was still underway when disaster struck.

The XP-67 first flight took place on Jan. 6, 1944, with chief test pilot E. E. “Ed” Elliot at the controls. Temperamental engines caused the airplane’s first flight to last only six minutes. Further test-flight delays were caused by several bouts of engine overheating and fires. With only 40 hours on the airframe, the final blow came on Sep. 6, 1944, during a mission out of Lambert Field in St. Louis, Mo.

The experimental U.S. Army Air Forces McDonnell XP-67 Moonbat.

Shortly after takeoff, the right engine caught fire. Elliot quickly returned to base and approached for a crosswind landing, keeping the flames away from the fuselage. However, as the aircraft was coming to a full stop, a brake failure caused the aircraft to turn the burning engine upwind. Elliot escaped uninjured as the No. 1 prototype was fully engulfed in flames. The program was halted, and the No. 2 prototype, only 15 percent complete, was never finished.

As told by Steve Richardson and Peggy Mason in their book McDonnell XP-67 “Moonbat”, the XP-67 may not have gone into production, but it did have two lasting effects on future aircraft in general, and MAC fighters in particular.

First, before the XP-67 there had been no database for designers to draw on concerning its unusual style of inlet ducts carved out of a wing leading edge. In the Model 1 and 2 stages of its development, this caused a good deal of head-scratching at NACA, judging by contemporary citations. Similarly, there was little data on the aerodynamics and control issues inherent in highly blended wing/ nacelle/fuselage airframes. XP-67 data thus became a foundation on which future design teams could build.

McDonnell XP-67 Moonbat

Second, MAC itself benefitted from the XP-67 not solely because of that data, but because of the experience that it gave the company’s fledgling team in understanding how to plan, estimate, and execute a complex Government aircraft program. Even the most seasoned of MAC’s core group of engineers who had come with McDonnell from Glenn L. Martin lacked experience in high-performance fighters; they had been working on medium bombers and large seaplanes. The XP-67 developed MAC expertise in fighter aircraft.

Some of the fighter aircraft produced by McDonnel in the next years would show definite linkages to the unique features of the XP-67. MAC’s first jet fighter, the XFD-1 (later FH-1 Phantom), designed under US Navy contract during the same period that the XP-67 was having its struggles, incorporated smooth blending of its twin jet engines with the wings and fuselage. Its engines were mounted in the fuselage/wing interface rather than in nacelles like the XP-67’s, but with blending the design looked much sleeker than Bell’s contemporary P-59. Despite the fact that the P-59 (a larger, heavier aircraft, but with more powerful engines) had a thrust-to-weight ratio of 0.36, while the FH-1’s was just 0.32, the MAC fighter was 80 knots faster, thanks to its cleaner, lower drag configuration.

The FH-1 saw limited service and was quickly supplanted by the next MAC product, the F2H Banshee. The same proven blending was refined to fit this more advanced fighter, and the result was a machine that gave MAC its first of what would one day become an avalanche of international orders.

The experimental U.S. Army Air Forces McDonnell XP-67 Moonbat (s/n 42-11677) in flight. This aircraft was damaged beyond repair by a midair fire in September 1944.

The XP-67’s features can thus be traced through a whole series of subsequent MAC designs. As usual in such pioneering cases, later developments become more refined and gradually take on their own unique identities, but the influence is always traceable.

Extreme blending turned out to have unforeseen advantages in areas other than aerodynamics. Decades later, the B-1 and B-2 bombers would emerge with highly faired engines and wings as a key part of their low observability or “stealth” properties.

McDonnell XP-67 “Moonbat” is published by Osprey Publishing and is available to order here.

Photo credit: U.S. Air Force

Highly blended techniques pioneered by the XP-67 have made a comeback, and aircraft using them are still flying today.
Dario Leone

Dario Leone is an aviation, defense and military writer. He is the Founder and Editor of “The Aviation Geek Club” one of the world’s most read military aviation blogs. His writing has appeared in The National Interest and other news media. He has reported from Europe and flown Super Puma and Cougar helicopters with the Swiss Air Force.

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