Subject: Number Eighty-One in the Series--Convair XP-81

From: [email-masked]
Date: 11 Jul 93 01:09:16 GMT

>From [email-masked]

In March of 1943, the Consolidated Aircraft Corporation merged with 
Vultee Aircraft Incorporated, forming the Consolidated Vultee Aircraft 
Corporation.  The name of the new merged corporation was often 
abbreviated to *Convair*, although that name did not get officially 
registered as a trademark until 1954.  One of the first products of 
this new merged corporation was the XP-81 mixed-power escort fighter.  

The primary drawback of most early jet fighters was their high fuel 
consumption, leading to a relatively limited range and a rather short 
endurance as compared to piston-engined fighters.  In 1943, the USAAF 
was interested in figuring out a way to couple the improved 
performance offered by jet propulsion with the long endurance that was 
demanded by the Pacific campaign, and issued a requirement for a long 
range escort fighter to be powered by a combination of turboprop and 
jet engine.  The turboprop engine would be used for cruising flight, 
with the turbojet engine being turned on for takeoff and for high 
speed flight.  The specification called for a 1250-mile operating 
range and a maximum speed of 500 mph.  

Charles R. 'Jack' Irvine, Vultee's chief designer and chief test 
pilot Frank W. Davis collaborated with the USAAF and came up with an 
all-metal cantilever low-winged monoplane powered by an experimental 
General Electric TG-100 (later redesignated XT31) turboprop in the 
nose with a ventral exhaust and an Allison-built J33-GE-5 turbojet in 
the rear fuselage fed by a pair of dorsal intakes.  A retractable 
tricycle undercarriage was fitted.  The pressurized cockpit was housed 
underneath a bubble canopy.  The project bore the company designation 
of Model 102.  

Convair began detailed design work on the Model 102 on January 5, 
1944.  The USAAF ordered two prototypes of the design from Convair on 
February 11, 1944.  The designation XP-81 was applied, and the serials 
were 44-91000 and 44-91001.  The contract was subsequently modified to 
include thirteen service-test YP-81s.  The YP-81 was to have been 
powered by the lighter and more powerful TG-110 turboprop, the wing 
was to have been moved aft ten inches, and an armament of six 0.5-inch 
machine guns or six 20-mm cannon was to have been fitted.  

The TG-100 turboprop engine encountered an extensive series of 
teething troubles and was not yet available when the XP-81 (44-91000) 
was ready for its first flight.  A Packard Merlin V-1560-7 power 
package from a P-51D Mustang was supplied in its place.  A P-38J-style 
beard radiator inlet was mounted below the propeller spinner.  The 
Merlin-powered XP-81 was trucked to Muroc Dry Lake, where it was flown 
for the first time on February 11, 1945.  The handling proved to be 
exceptionally good.  However, the directional stability was marginal 
and a 15-inch fin extension and a short ventral fin were added.  The 
second XP-81 was fitted at the factory with a rounded fin extension 
and a long ventral fin.  

In the meantime, the war against Japan had progressed to the point 
where the capture of such islands as Guam and Saipan had largely 
eliminated the need for long-range, high-speed escort fighters.  The 
13 pre-production YP-81s were cancelled shortly before V-J Day, but 
work continued on the two XP-81s.  

The first XP-81 was flown back to Vultee Field to be fitted with the 
TG-100, but the work was not finished until after V-J Day.  The first 
flight with the TG-100 took place on December 21, 1945.  The TG-100 
was supposed to deliver 2300 e.h.p, but actually delivered only 1400 
e.h.p..  Consequently, the performance of the turboprop-powered XP-81 
was no better than that of the Merlin-powered version.  In addition, 
excess propeller vibration and persistent oil leaks became important 
problems.  

The XP-81 program was officially terminated on May 9, 1947.  Both 
prototypes were redesignated ZXF-81 in 1948, indicating a testbed 
status.  In 1949, they were both stripped of useful parts and placed 
on a photographic and bombing range at Edwards AFB.  The remains of 
both machines are now with the Flight Test Museum.  Can anyone confirm
that they are still there? 

Specification of the XP-81: One 2300 ehp General Electric XT31-GE-1 
(TG-100) turboprop and one 3750 lb.st. Allison J33-GE-5 turbojet.  
Proposed armament (never fitted) was six 0.50-inch machine guns or 6 
20-mm cannon and two 1600-pound bombs.  Weights were 12,755 pounds 
empty, 19,500 pounds loaded, 24,650 pounds maximum overload.  
Dimensions were wingspan 50 feet 6 inches, 44 feet 10 inches, height 
14 feet 0 inches, 425 square feet wing area.  The following estimated 
performance figures were based on an assumption of a full 2300 hp 
output from the turboprop: Maximum speed, 478 mph at sea level, 507 
mph at 30,000 feet.  range 2500 miles at 275 mph at 25,000 feet.  
Initial climb rate was 5300 feet per minute.  Service ceiling was 
35,500 feet.  

Sources: 

  General Dynamics Aircraft and their Predecessors, John Wegg, Naval 
  Institute Press, 1990.  

  War Planes of the Second World War, Fighters, Volume Four, William 
  Green, Doubleday, 1964.  

  American Combat Planes, Third Enlarged Edition, Ray Wagner, Doubleday, 
  1982.  

Joe Baugher		AT&T Bell Laboratories   	
2000 North Naperville Road      Naperville, Illinois 60566-7033