In 1926, the
United States Army was very interested in the
turbo-supercharger as a way of improving engine performance, and requested that one be added to the last of the
PW-9s, and the engine upgraded to a 510 hp
Packard 1A-1500. This machine was designated XP-4. All these modifications added weight, so the lower wing span was extended by 9.5 feet. The airplane was delivered to
Wright Field for testing on 27 July 1927, but it quickly became apparent that the Packard engine did not have sufficient power to compensate for the 800 lbs of extra weight, the craft performing more poorly than its predecessor, and the project was quickly abandoned. ==Specifications (XP-4) ==