Experimental swept wing/canard interceptor. Stability and control problems were never fully resolved.
After a number of abortive design efforts for follow-on to P-40, C-W responded to Army Air Corps Request for Data (R-40C) for radical new departure in fighter design. Up to this time, C-W proposed a number of "improvements" over the P-40, but they could not come up with a winner. Competition in response to proposal won by Vultee with twin-boom pusher, XP-54 "Swoose Goose." C-W second with XP-55, and Northrop third with XP-56. Although Air Corps turned down XP-55 design because of poor stability and probability of bad stall characteristics, C-W proceeded to build full-scale flying mockup, Model 24-B. Was plywood, steel-tube, and fabric test airframe powered by 275 hp Menasco engine and intended only to prove feasibility of configuration--which, with its pusher propeller, lack of empennage, and forward elevator surface--was wildly radical for the time. Flown initially by J. Harvey Gray 2 Dec 42 on first of 169 flights, tests showed configuration was feasible and, although had some problems, worthy of development. Money available and 3 prototypes ordered, not with the P&W X- 1800 engine (about 2000 hp) for which it was designed, but by semi-obsolescent Allison V-1710 used in P-40. Thus, at best, XP-55 was condemned to level of performance of dated 1300 hp engine. Gray first flew XP-55 Jul 43. Nov, he began exploring effect of wing spoilers on pitching characteristics in stall. After 2 tries to obtain full stall, during third, XP-55 pitched forward 180 degrees onto its back and fell into same inverted descent predicted in original Air Corps wind tunnel tests. Engine quit and nothing Gray did could break stall. After perfectly stable fall of 16,000 feet, Gray bailed out safely. Aircraft continued straight down and was totally destroyed on impact. Rash of fixes followed including 2-ft wing tip extension, elevator travel limits increased, and inverted fuel system added. No matter, performance mediocre with Allison engine--377 mph instead of the hoped-for 500 mph. Test pilots spooked about aircraft and one, Ben Kelsey, talked about indescribably wild gyrations it went through time and again as he tried to determine what went wrong when engine stalled. Another pilot, Russ Schleeh, added it was terribly unstable, and that if you took your eyes off horizon for a moment, even in landing pattern, plane would drift wildly off course. Third prototype lost in accident at Wright Field when pilot came low over field, attempted a barrel roll at low altitude, and crashed.