Subject: Number Sixty in the Series--Curtiss P-60

From: [email-masked]
Date: 10 Mar 93 17:21:43 GMT

>From [email-masked]

The story of the Curtiss P-60 is a rather sad one.  This aircraft was 
a desperate attempt on the part of Curtiss to design a replacement for 
the venerable P-40.  It went through a dizzying series of changes in 
engines, changes in requirements, and changes in designations, the 
gyrations of which are difficult to keep straight.  Its ultimate 
failure was a reflection of changing USAAF requirements, but was also 
a reflection of a company which was beginning to run out of fresh new 
ideas.  

The story of the Curtiss P-60 is quite convoluted and rather difficult 
to follow.  Nevertheless, pour yourself a cup of coffee and follow 
along :-).  

The convoluted history of the P-60 actually begins back with the 
Curtiss XP-46.  Following the failure of the XP-46 to win any Army 
production orders, the Curtiss company proposed yet another design in 
their search for the eventual replacement for the P-40.  This was the 
Curtiss Model 88, which was basically an improved XP-46 powered by the 
yet-to-be-built 1600-hp Continental XIV-1430-3 twelve-cylinder 
liquid-cooled inverted Vee engine.  The Model 88 was to use the 
fuselage and tail assembly of the P-40D combined with a NACA laminar 
flow wing.  Armament was to have consisted of eight wing-mounted 
0.50-inch machine guns.  The mainwheel retraction scheme reverted to 
the sequence used by the original P-40, with the mainwheels rotating 
90 degrees before they retracted rearwards into wing wells.  Maximum 
speed was projected to be 430 mph.  

On October 1, 1940, the USAAC ordered two examples of the Model 88 
under the designation XP-53.  Serials were 41-140 and 41-19508.  
However, in a conference held six weeks later, the USAAC informed 
Curtiss-Wright of its need for a fighter combining laminar flow wing 
technology with the British Rolls-Royce Merlin engine.  Since the 
XP-53 was already being designed for laminar-flow wings, Curtiss 
proposed to convert the second XP-53 airframe (41-19508) to the Merlin 
engine while it was undergoing construction.  This airframe was 
redesignated Model 90 by the company.  The USAAC accepted this idea, 
and assigned the designation XP-60 to the new aircraft.  The XP-60 was 
to take the 1300-hp Packard-built Rolls Royce Merlin V-1650-1 engine 
as used in the XP-40F then under development.  The other XP-53 
airframe was to retain the Continental engine.  

However, while the XP-53 and XP-60 were both undergoing construction, 
the Army cancelled the XP-53 order because of the excessive delays in 
the temperamental Continental XIV-1430 engine.  The XP-53 never flew.  
As it turned out, the Continental engine never did enter production, 
and all of those aircraft projects which had planned for it ultimately 
failed.  

In November 1941, the XP-53 airframe was converted into a static test 
airframe in support of the P-60 project, and its bullet-proof 
windshield, self-sealing fuel tanks, and armament were scavenged and 
transferred to the XP-60.  

During construction of the XP-60 aircraft, it was decided to replace 
the rearward- retracting P-40 style landing gear with a new 
inward-retracting gear similar to that which had been fitted to the 
abortive XP-46.  Initially, the XP-60 was fitted with a British-built 
Merlin 28 engine.  The Model 90 (XP-60) flew for the first time on 
September 18, 1941, only eleven days before the first flight of the 
disappointing XP-46.  The performance of the XP-60 was disappointing 
as well, with a top speed of only 387 mph at 22,000 feet.  It took 7.3 
minutes to reach an altitude of 15,000 feet, and service ceiling of 
29,000 feet.  Some of the reason for the disappointing performance was 
due to the wing surface not being finished to the degree of smoothness 
required for the laminar flow wing.  Another factor was the fact that 
the Merlin engine did not deliver the guaranteed output.  Empty weight 
was 7008 pounds, gross weight was 9277 pounds, and maximum takeoff 
weight was 9700 pounds.  Dimensions were wingspan 45 feet 5 1/4 
inches, length 33 feet 7 1/2 inches, height 12 feet 4 inches, and wing 
area 275 square feet.  

On two occasions, the XP-60 had suffered damage as the result of 
undercarriage failures.  During the test flights, it was found 
necessary to enlarge the vertical and make some minor modifications.  
These resulted in a change in company designation to Model 90A.  

The XP-60 (41-19508) was modified in August of 1942 with the 
installation of a Packard Merlin V-1650-3 (license-built Merlin 61) of 
1350 hp with a two stage supercharger.  A four-bladed propeller was 
fitted.  The aircraft was redesignated XP-60D by the Army and Model 
90B by the factory.  By the time that the changes were made, the 
intervening Army designations B and C had been assigned to other 
improved versions of the XP-60.  The XP-60D (41-19508) was destroyed 
in a crash on May 6, 1943.  

In late 1941, concern was expressed that the license-built Merlin 
engine would be in such great demand for other aircraft that there 
would likely be engine shortages which would delay the P-60 program.  
Consequently, consideration was given to alternative powerplants for 
the P-60.  The liquid-cooled Allison V-1710 engine was selected on the 
basis of reliability and availability.  On October 21, 1941, a 
contract for 1950 P-60As was approved.  The turbosupercharged Allison 
V-1710-75 liquid-cooled engine offering 1425 hp at 25,000 feet was 
specified as the powerplant.  

However, on November 17, 1941, it was concluded that the P-60A would 
be underpowered if the Allison engine were used, and that either a 
more powerful engine should be found or else another fighter be built 
instead of the P-60A.  

Following Pearl Harbor, officials had second thoughts about the 
desirability of interrupting P-40 production at such a critical point 
by the introduction of a completely new type.  On December 20, 1941, 
work on the P-60A project was ordered halted, and on January 2, 1942, 
the production order for the 1950 P-60A fighters was officially 
cancelled in favor of more P-40Ks and Ls plus some Curtiss-built P-47G 
Thunderbolts.  

However, the P-60 program was not to be scrubbed completely.  The Army 
decided that three experimental P-60s should be built--one XP-60A, one 
XP-60B, and one XP-60C.  The XP-60A (serial number 42-79423) was to 
have the Allison V-1701-75 engine and a General Electric B-14 turbo- 
supercharger.  The XP-60B (serial number 42-79425) was to be similarly 
powered, but was to use the Wright SU-504-2 turbosupercharger.  The 
XP-60C (serial number 42-79424) was to use the experimental Chrysler 
XIV-2220 sixteen-cylinder engine.  Normally, a switch in engines was 
considered by the Army as calling for change of model number as well, 
but such was not the case here.  

The first of these new experimental P-60 aircraft was the XP-60A.  The 
Allison-powered XP-60A could be considered as an adaptation of the 
XP-60 wing to a new fuselage and a new powerplant, in much the same 
spirit as the XP-60 could be regarded as a P-40D with a new wing.  The 
XP-60A was given the company designation of Model 95A (Model 95 having 
been a design study which had been discontinued).  Nose and fuselage 
contours of the XP-60A (serial no 42-79423) were extensively revised 
to accommodate the Allison engine, and armament was reduced to six 
0.50-inch guns in the wings.  A four-bladed propeller was fitted.  

The XP-60A made its initial ground taxiing tests in late October of 
1942.  However, during one of these tests, a minor fire occurred in 
the engine due to the lack of cooling air in the shrouds surrounding 
the exhaust manifold.  The turbosupercharger and long exhaust manifold 
were therefore removed from the aircraft, and short exhaust stacks 
were substituted.  The XP-60A (42-79423) flew for the first time in 
this form on November 11, 1942.  Empty weight was 7806 pounds, gross 
weight was 9616 pounds, and maximum takeoff weight was 10,160 pounds.  
Dimensions were wingspan 41 feet 3 3/4 inches, length 33 feet 7 1/2 
inches, height 12 feet 4 inches, and wing area 275 square feet.  
Estimated maximum speed (never achieved in tests) was 420 mph at 
29,000 feet and 324 mph at sea level.  It was estimated that an 
altitude of 15,000 feet could be attained in 6.5 minutes.  Service 
ceiling was 35,200 feet.  The maximum speed (especially at low 
altitudes) and the initial climb rate were rather disappointing.  The 
XP-60A aircraft was soon dismantled and some of its parts were used in 
the later XP-60C and XP-60E.  

The poor performance of the XP-60A had caused official interest in the 
P-60 fighter to sour, the project being in serious danger of being 
cancelled outright.  However, Curtiss-Wright proposed to the Army that 
the XP-60C prototype then under construction be fitted with the Pratt 
& Whitney R-2800 radial air-cooled engine driving a pair of 
three-bladed contrarotating propellers.  The substantial improvement 
in performance that this modification promised to provide aroused 
sufficient interest that in November 1942 the Army issued a letter 
contract for the production of five hundred R-2800-powered production 
P-60A-1-CU fighters.  The first 26 aircraft on this production 
contract, Army serials 43-32762/32787, were to be delivered as service 
test models designated YP-60A.  

The XP-60C (Model 95C, Army serial number 42-79424) was originally to 
have had an airframe similar to that of the XP-60A and XP-60B, but 
fitted with the new and experimental 2300 hp Chrysler XIV-2220 engine.  
Since this engine was experiencing development difficulties, an order 
was given in September 1942 to complete this aircraft with a 2000-hp 
Pratt & Whitney R-2800-53 engine driving a a pair of three-bladed 
contrarotating propellers.  Armament was reduced to four 0.50-inch 
machine guns.  First flight of the XP-60C was on January 27, 1943.  
Apart from somewhat high elevator and rudder forces, the aircraft's 
flight characteristics were generally satisfactory.  

The single XP-60B (Model 95B, Army serial number 42-79425) was to have 
been similar to the XP-60A but with a Wright instead of a General 
Electric supercharger for the V-1710-75 engine.  The aircraft was 
never completed in this configuration.  On December 2, 1942, the Army 
ordered that it be fitted with a Pratt & Whitney R-2800-10 radial 
engine in place of the original V-1710.  Unlike the XP-60C, a 
single-rotation four-bladed propeller was to be used.  In this form, 
the aircraft was redesignated XP-60E.  Owing to the lighter propeller 
installation of the XP-60E as compared to that of the XP-60C, it was 
found necessary to move the R-2800 engine forward by ten inches.  
Owing to a fault experienced during the initial ground running tests 
which necessitated a change of engines, the first flight of the XP-60E 
did not take place until May 26, 1943.  

During the latter part of April 1943, the USAAF decided to undertake a 
series of comparative tests at Patterson Field with various fighter 
types in an attempt to weed out the least desirable types so that it 
could concentrate on the best types.  Curtiss-Wright was notified by 
the Army that the XP-60E would have to be delivered for tests within 
four days.  Since the XP-60E had not yet made its first flight, 
Curtiss-Wright decided to substitute the XP-60C in its place.  The 
XP-60C was hastily reassembled and delivered to Patterson Field.  

During trials with the XP-60C at Patterson Field, it proved impossible 
to obtain full rated power.  In addition, the experimental wing finish 
had peeled off from the leading edge of the wing, destroying the 
smooth laminar-flow characteristics and resulting in a further loss of 
speed.  Consequently, the XP-60C made a very poor impression on the 
Army, being in fact inferior to the Republic P-47D and the North 
American P-51B.  The P-60 series was henceforth eliminated from any 
further consideration for production.  In June 1943 the Army contract 
for the P-60A-1-CU was reduced from 500 to two aircraft.  

The XP-60C was powered by a Pratt & Whitney R-2800-53 engine 
delivering 2000 hp.  Empty weight was 8698 pounds, gross weight was 
10,785 pounds, and maximum takeoff weight was 11,835 pounds.  
Dimensions were wingspan 41 feet 3 3/4 inches, length 34 feet 1 
inches, height 12 feet 4 inches, and wing area 275 square feet.  
Maximum speed was 414 mph at 20,350, 324 mph at sea level.  An 
altitude of 30,000 feet could be attained in 6 minutes, and initial 
climb rate was 3890 feet per minute.  Service ceiling was 37,900 feet.  
Normal range was 315 miles.  Armament consisted of four 0.50-inch 
machine guns with 300 rpg mounted in the wings.  

Following the return of the XP-60C to Curtiss-Wright, some further 
tests were undertaken, but a forced landing terminated all testing 
work with this aircraft.  

By this time, there was essentially no chance for the P-60, since the 
P-47 and P-51 seemed to satisfy all the Army's needs for fighters.  
Nevertheless, the Army agreed to test the delayed XP-60E which had 
missed out on the May 1943 trials at Patterson Field.  In January 
1944, the XP-60E (Model 95D) was flown to Elgin Field for official 
tests.  The engine was a Pratt & Whitney R2800-10 eighteen-cylinder 
radial offering 2000 hp.  Empty weight was 8285 pounds, gross weight 
was 10,320 pounds, and maximum takeoff weight was 11,520 pounds.  
Dimensions were wingspan 41 feet 3 3/4 inches, length 33 feet 11 
inches, height 12 feet 6 inches, and wing area 275 square feet.  
Maximum speed was 410 mph at 20,200, 391 mph at 24,200 feet, and 405 
mph at 15,000 feet.  An altitude of 15,000 feet could be attained in 
4.8 minutes.  Service ceiling was 38,000 feet.  Normal range was 315 
miles.  Armament consisted of four 0.50-inch machine guns with 250 rpg 
mounted in the wings.  USAAF test pilots found that the XP-60E did not 
compare very favorably in level flight performance with later 
fighters, but it did match them in climbing rate.  The aircraft was 
sensitive to slight changes in flight condition and had to be 
constantly retrimmed.  Stability in level flight was poor and the 
climing speed was difficult to maintain.  

In May of 1944, Curtiss-Wright finally recognized that the P-60 was a 
lost cause, and indicated to the Army that they wanted to discontinue 
all further work on the project.  However, the USAAF insisted that the 
company follow through on its agreement and complete at least one of 
the two YP-60A aircraft still under construction under the revised 
P-60A-1-CU contract.  These aircraft had been redesignated YP-60E 
owing to the number of design modifications incorporated that were 
related to the XP-60E.  

One one of the YP-60As was to see the light of day as a YP-60E.  This 
was the second YP-60A, serialled 43-32763.  It flew for the first time 
on July 15, 1944, powered by a 2100 hp Pratt & Whitney R-2800-18 
eighteen-cylinder radial engine driving a single four-bladed 
propeller.  It differed from previous P-60s in having a bubble canopy 
over the cockpit and revised fuselage and vertical tail shapes, so 
that it ended up looking a lot like a P-47D-25 Thunderbolt.  Empty 
weight of the YP-60E was 8225 pounds, gross weight was 10,270 pounds, 
and maximum takeoff weight was 11,520 pounds.  Dimensions were 
wingspan 41 feet 3 3/4 inches, length 33 feet 11 inches, height 12 
feet 6 inches, and wing area 275 square feet.  Estimated maximum speed 
was 405 mph at 24,500.  Initial climb rate was estimated at 4200 feet 
per minute.  Service ceiling was 34,000 feet.  Armament consisted of 
six 0.50-inch machine guns with 267 rpg mounted in the wings.  

Only two test flights of the YP-60E were undertaken by Curtiss-Wright 
before the aircraft was transferred to Wright Field.  By this time, 
the Army had absolutely no need for the P-60, and no further trials 
were undertaken.  The YP-60E was eventually disposed of as surplus 
after the war.  It was purchased by James DeSanto and was entered in 
the 1947 National Air Races with Race No.  80 and civil registration 
NX21979, but crashed on a qualifying flight.  

Here is a brief summary of serial numbers, which may help to make the 
history of the P-60 a bit less confusing :-) 

41-140 		Curtiss XP-53 - cancelled before construction 
41-19508 	Curtiss XP-53 ---> XP-60 ---> XP-60D 
42-79423 	Curtiss XP-60A 
42-79424 	Curtiss XP-60C 
42-79425 	Curtiss XP-60B --> XP-60E 
43-32762/32787  Curtiss YP-60A 32763 to YP-60E, rest cancelled.  
43-32789/33262  Curtiss P-60A-1-CU - all cancelled June 1943.  

Sources: 

  Curtiss Aircraft, 1907-1947, Peter M. Bowers, Naval Institute Press, 
  1979.  

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

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

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

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