Subject: Number Fifty in the Series--Grumman XP-50

From: [email-masked]
Date: 7 Feb 93 18:42:12 GMT

>From [email-masked]

The Grumman Aircraft Engineering Corporation of Bethpage, Long Island 
is best known for its line of superb carrier-based fighters such as 
the F4F Wildcat and the F6F Hellcat.  One of its less well-known 
products was the XP-50, which was an Army-financed development of the 
Navy's Grumman XF5F-1 Skyrocket experimental twin-engined shipboard 
fighter.  

The XF5F-1 traces its origin back to 1935, when the US Navy's Bureau 
of Aeronautics (BuAer) first contemplated the development of a 
single-seat, twin-engined carrier-based fighter.  In early 1937, the 
BuAer sent out a request for proposals for twin-engined, carrier-based 
fighter designs capable of exceeding 300 mph.  Brewster, Curtiss, 
Lockheed, Seversky, and Vought all submitted proposals in response to 
the request.  Grumman's submission was its Design 25--a high-altitude 
fighter powered by a pair of turbosupercharged Allison V-1710 liquid- 
cooled engines.  However, the Navy deemed that none of these proposals 
promised sufficient performance improvements over new single-engined 
fighters to justify issuing a development contract.  

The Bureau of Aeronautics revised its fighter requirements in early 
1938.  They concluded that the best performance could be obtained by 
using either a pair of turbosupercharged R-1535 or R-1830 radials, or 
a single turbosupercharged V-1710 liquid-cooled engine.  On February 
1, 1938, the BuAer issued a new request for proposals, calling for 
either a single-engined fighter powered by a mechanically-supercharged 
Allison engine or for a twin-engined fighter powered by a pair of 
radial engines.  Armament was to be 2 20-mm cannon and two 0.30-in 
machine guns.  The top speed was not specified, but it was to be the 
highest possible that could be attained.  

Bell, Brewster, Curtiss, Grumman, and Vought all submitted designs in 
response to the request for proposals.  Vought also took a chance and 
submitted a design powered by the Pratt and Whitney R-2800 radial 
engine, although this particular engine was not specified in the RFP.  
On April 11, 1938, the Navy issued contracts to Vought for the XF4U-1 
with an 1850 hp Pratt and Whitney XR-2800-4 radial (this was to evolve 
into the famous Corsair), and to Grumman for the XF5F-1 powered by a 
pair of 750 hp.  Pratt and Whitney R-1535-96 radials driven by 
two-speed superchargers.  On November 8, 1938, a third contract was 
issued to Bell for the XFL-1 (a navalized version of the P-39 
Airacobra) powered by the 1150 hp Allison V-1710-6 liquid-cooled 
engine.  

Grumman's XF5F-1 design was given the company designation of Design 
34.  Very early on, Grumman was forced to substitute Wright R-1820 
radials for the much smaller R-1535 engines, since Pratt and Whitney 
was no longer offering the two-speed supercharger as an option.  
Although the greater diameter of the Wright engines offered the gloomy 
prospects of considerably poorer forward and downward visibility 
(particularly serious defects for a carrier-based aircraft), the Navy 
reluctantly agreed to the change.  Since Grumman was at that time 
forced to give priority to the development of the F4F-3 Wildcat, work 
on the XF5F-1 proceeded only slowly.  

The prototype XF5F-1 (BuNo 1442) finally took to the air for the first 
time on April 1, 1940.  An unusual feature of the aircraft was the 
extremely short nose--the forward extremity of the nose did not go 
past the leading edge of the wing.  A large and high cockpit canopy 
was fitted.  Like Navy carrier-based planes of the period, the XF5F-1 
was a taildragger.  The wings folded just outboard of the engine 
nacelles, and the main undercarriage members retracted into the engine 
nacelles.  Provision was made for four 23-mm Madsen cannon in the 
abbreviated nose, but no armament was ever actually fitted.  The 
XF5F-1 was powered by two 1200 hp Wright XR-1820-40 and -42 engines 
driving 3-bladed propellers rotating in opposite directions.  

There were problems with the XF5F-1 almost from the very beginning-- 
engine oil cooling was inadequate, aerodynamic drag was excessive, and 
there were problems with the closing of the undercarriage doors.  
Sideward and downward visibility were both atrocious, owing to the 
forward location of the wings and the position and large diameter of 
the radial engines.  

The XF5F-1 was delivered to the Navy at NAS Anacostia on February 22, 
1941.  By that time, it was painfully obvious to just about everyone 
that the Skyrocket would never make a useful carrier-based fighter.  
The XF4U-1 Corsair was already exceeding 400 mph in its test flights, 
and the Navy had requested that Vought adapt its design for 
production.  Nevertheless, the Navy returned the XF5F-1 to Grumman for 
major modifications in an attempt to alleviate some of its more 
obvious shortcomings.  The engine nacelles were lengthened and 
extended further aft, spinners were fitted to the propellers, the 
height of the canopy was reduced, wing fillets were added, and the 
fuselage nose was extended forward of the wing leading edge.  However, 
when the plane was returned to Anacostia on July 24, 1941, it was 
found that the changes had not provided any significant improvements 
in the aerodynamic drag or in the engine cooling problems.  

The strongest point of the XF5F-1 was its rate of climb--4000 feet per 
minute as compared to 2660 ft/min for the XF4U-1 and 2630 ft/min for 
the XFL-1.  However, maximum speed was only 383 mph at sea level.  
Empty weight was 8107 lbs and normal loaded weight was 10,138 lbs.  
Service ceiling was 33,000 feet and maximum range was 1170 miles.  The 
XF5F-1 was used off and on for tests in support of the XF7F-1 project 
for the next couple of years, until it was finally stricken off record 
on December 11, 1944 after suffering an undercarriage failure.  

As detailed in the previous article on the XP-49, in early 1939, the 
Army issued a Circular Proposal calling for a new generation of 
fighters which would match existing airframes with new and more 
powerful engines.  Four companies submitted designs in response to the 
proposal.  Lockheed submitted its Model 522, which was an adaptation 
of the P-38 powered by either Pratt and Whitney XH-2600 or Wright 
R-2160 turbosupercharged engines.  Grumman submitted a proposal known 
under the company designation of Design 41.  Design 41 was an aircraft 
quite similar to Design 34 (XF5F-1) but was powered by a pair of 
Wright R-1820 radials fitted with turbosuperchargers.  

The Lockheed design came in first in the competition, and was ordered 
by the Army as the XP-49.  However, the Army saw sufficient merit in 
Grumman's Design 41 that they encouraged the company to submit a 
revised design, just for insurance in case the XP-49 ran into 
problems.  The revised proposal, Design 45, encorporated a nosewheel 
undercarriage and a longer nose.  Provision was to be made for 
self-sealing fuel tanks and for armor protection for the pilot.  On 
November 25, 1939, the Army issued a contract for one prototype of 
Grumman's Design 45 under the designation XP-50.  The XP-50 was to be 
powered by two 1200 hp Wright R-1820-67/69 radials fitted with 
turbosuperchargers.  Armament was to be two 20-mm cannon and two 
0.50-in machine guns, all mounted in the nose.  

The XP-50 (Ser No. 40-3057) flew for the first time on February 18, 
1941, with Grumman test pilot Robert L. Hall at the controls.  Early 
tests were encouraging, and the XP-50 handled much better than did the 
XF5F-1.  Furthermore, the supercharged engines of the XP-50 gave it a 
much better performance at medium and high altitudes.  However, on May 
14, 1941 the XP-50 experienced an inflight turbosupercharger explosion 
while on a flight over Long Island Sound, and pilot Robert Hall was 
forced to parachute to safety.  The loss of the aircraft brought an 
abrupt end to the XP-50 program.  

Estimated maximum speed of the XP-50 (never achieved in tests) was 424 
mph at 25,000 feet.  Estimated service ceiling was 40,000 feet.  An 
altitude of 20,000 feet could supposedly be reached in 5 minutes.  
Maximum range was estimated to be 1250 miles.  Empty weight was 8307 
lbs, and loaded weight was 10,558 lbs.  Maximum weight was 13,060 lbs.  
Wingspan was 42 feet, length was 21 feet 11 inches, height was 12 
feet, and wing area was 304 square feet.  

Sources: 

  Grumman Aircraft Since 1929, Rene J.  Francillon, Naval Institute 
  Press, 1989.  

  The American Fighter, Enzo Angelucci and Peter Bowers, Orion, 1987.  

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

Joe Baugher       AT&T Bell Laboratories    2000 North Naperville Road 
		  Naperville, Illinois 60566-7033.   (708) 713-4548