From: Joseph F Baugher <jfb@ihlpl.att.com>
Subject: Number Forty in the Series--Curtiss P-40 (1 of 11)
Keywords: XP-40, P-40A,B,C
Organization: AT&T Bell Laboratories -  Naperville, Illinois
Date: Tue, 22 Dec 1992 17:28:15 GMT


From Joseph F Baugher <jfb@ihlpl.att.com>


The P-40 was the best known Curtiss-Wright airplane of World War II.  
It was also one of the most controversial fighters of the war.  It was 
vilified by many as being too slow, lacking in maneuverability, having 
too low a climbing rate, and being largely obsolescent by contemporary 
world standards even before it was placed in production .  The 
inadequacies of the P-40 were even the subject of a Congressional 
investigation.  It gets regularly included on lists of the worst 
combat aircraft of World War 2.  

All of these criticisms certainly had some degree of validity, but it 
is also true that the P-40 served its country well during the first 
year of the war in the Pacific when very little else was available.  
Along with the P-39 Airacobra, the P-40 was the only American fighter 
available in quantity to confront the Japanese advance during the 
first year of the Pacific War.  It helped stem the speed of the 
Japanese advance until more modern types could be made available in 
quantity.  The P-40 had no serious vices and was a pleasant aircraft 
to fly, and, when flown by an experienced pilot who was fully aware of 
its strengths and weaknesses, was able to give a good account of 
itself in aerial combat.  The P-40 continued in production long after 
later types were readily available, the numbers manufactured reaching 
the third highest total of American World War II fighters, after the 
Republic P-47 and the North American P-51.  

The P-40 was obsolete by European standards even before the first 
prototype flew, and it never did catch up.  Its Initial inadequacies 
in the form of low firepower and lack of self-sealing fuel tanks or 
armor were a reflection of mid-'thirties USAAC requirements which were 
outmoded.  The P-40 had been developed as basically a low-altitude 
close-support fighter under mid-1930s US tactical concepts which 
envisaged more need for low-level ground support operations than for 
high-altitude interceptions.  The military doctrine of the "ascendancy 
of bombardment over pursuit" was dominant in 1937 when the P-40 first 
appeared.  This doctrine assumed that the prospect of high-altitude 
enemy air attack on the USA was extremely remote, with coastal defense 
and ground attack in the defense of US territory being seen as the the 
main tasks for any future fighter aircraft.  Low-altitude performance 
and rugged construction received priority over high-altitude 
capabilities.  

During the war, the Senate Special Committee to Investigate the 
National Defense Program (usually known as the "Truman Committee", 
after its chairman, Senator Harry Truman of Missouri) criticized the 
P-40 on several accounts, particularly on the original volume purchase 
of an inadequate design and its continued production long after later 
designs were readily available.  However, they finally concluded that 
this was not brought about by any undue favoritism to Curtiss.  

Some indication of the enormous P-40 production program undertaken by 
Curtiss can be assessed by its claim on factory floor space and 
manpower.  During 1941, the Curtiss Airplane Division expanded its 
manufacturing area by 400 percent.  The total work force was 45,000.  
This expansion included two new plants, one at Buffalo, New York and 
the other at Columbus, Ohio, to supplement the original Curtiss plant 
in St.Louis, Missouri.  At the peak of wartime production, the entire 
Curtiss Airplane Division complex of factories was producing sixty 
aircraft A DAY! 

The origin of the P-40 can be traced back to the Curtiss P-36 (Model 
75) fighter, which was powered by a radial, air-cooled engine.  A step 
in the direction toward what was eventually to emerge as the P-40 was 
the XP-37, which was described in an earlier post.  The P-36 design 
was reworked to incorporate the Allison V-1710 liquid-cooled V-type 
engine, resulting in the XP-37.  The XP-37 was equipped with a General 
Electrc turbosupercharger, and featured a cockpit pushed very far to 
the rear.  Thirteen YP-37 service-test aircraft were built, but 
problems with the turbosupercharger caused the development of the P-37 
to be abandoned in favor of a less complex and more straightforward 
conversion of the P-36 for the Allison V-1710 engine.  

Realizing that the radial-engined P-36A was at the limit of its 
development, Curtiss designer Donovan Berlin got USAAC permission in 
July 1937 to install a 1150 hp Allison V-1710-19 liquid-cooled engine 
with integral supercharging in the 10th P-36A (Serial No 38-10).  This 
project was given the company designation of Model 75P, and the USAAC 
gave the project a new fighter designation, XP-40.  

The XP-40 flew for the first time on October 14, 1938, with Edward 
Elliot at the controls.  Armament was two 0.50-inch machine guns 
located in the upper fuselage deck and synchronized to fire through 
the propeller arc, standard armament for US pursuit aircraft at the 
time.  Wing racks could be fitted for six 20-pound bombs.  A small oil 
cooler was located beneath the pointed nose.  The air intake for the 
single-stage supercharger was mounted on top of the engine cowling 
between the two machine guns, but during tests it was replaced by a 
long cowled intake duct which became characteristic of all the early 
P-40 production models.  Initially, the coolant radiator was placed 
under the fuselage aft of the wing, but it was gradually moved forward 
until it finally ended up located underneath the extreme nose.  The 
radiator intake was redesigned to include an oil cooler and two 
coolers for the ethylene/glycol engine coolant.  The initial XP-40 had 
a single exhaust port on each side of the fuselage, but in its final 
form it had six separate exhaust ports on each side.  The initial 
XP-40 had inherited from the P-36 a set of mainwheel fairing plates 
which covered the mainwheels when they retracted into their wing 
wells, but these were eventually deleted and replaced by two small 
doors which closed over the wheel struts upon retraction.  

The maximum speed of the XP-40 was 342 mph at 12,200 feet at a gross 
weight of 6260 pounds.  This was faster than the Hawker Hurricane, but 
slower than the Spitfire or the Bf 109E.  Empty weight was 5417 
pounds, and fully-loaded weight was 6870 pounds.  Range was 460 miles 
at 299 mph with 100 gallons of fuel.  With 159 gallons of fuel at 200 
mph, a range of 1180 miles was claimed, almost twice that of the 
contemporary Hurricane, Spitfire, and Bf 109E.  Wingspan was 37 feet 4 
inches, wing area was 236 square feet, length was 31 feet 1 inch, and 
height was 12 feet 4 inches.  The wingspan and wing area were to 
remain the same throughout the entire history of the P-40 production 
run.  

In the late 1930s, the USAAC was planning to expand its force, and on 
January 25, 1939.  manufacturers were invited to submit proposals for 
pursuit aircraft.  The Army was still thinking in terms of 
low-altitude, short-range fighters.  Among the contenders were the 
Lockheed XP-38, the Bell XP-39, the Seversky/Republic XP-41 (AP-2) and 
XP-43 (AP-4), and no less than three planes from Curtiss, the H75R, 
XP-37, and XP-42.  Although the XP-40 could not match the performance 
(especially at altitude) of the turbosupercharged types, it was less 
expensive and could reach quantity production fully a year ahead of 
the other machines.  In addition, the XP-40 was based on a 
already-proven airframe that had been been in production for some 
years.  Consequently, on April 26, 1939, the Army adopted a 
conservative approach and ordered 524 production versions under the 
designation P-40 (Curtiss Model 81).  At that time, it was the 
largest-ever production order for a US fighter, and dwarfed the 
service test orders placed that same day for YP-38 and YP-39 fighters.  
A couple of weeks later, 13 YP-43s were also ordered.  

The P-40 was similar to the final XP-40 configuration except for 1040 
hp V-1710-33 (C15) engines and provisions for the mounting of one 
0.30-inch machine gun in each wing.  Flush riveting was used to reduce 
drag.  Armor, bulletproof windshields, and leakproof fuel tanks were 
added in service.  The P-40 was a relatively clean design, and was 
unusual for the time in having a fully retractable tailwheel.  

The first flight of a P-40 (Ser No 39-156) was on April 4, 1940.  
Maximum speed was 357 mph at 15,000 feet, service ceiling was 32,750 
feet, and initial climb rate was 3080 feet per minute.  An altitude of 
15,000 feet could reached in 5.2 minutes.  The length of the P-40 was 
31 feet 8 3/4 inches, which became standard for all early models.  
Weights were 5376 pounds empty, 6787 pounds gross, and 7215 pounds 
maximum.  

Deliveries of the P-40 to Army units began in June of 1940.  Three of 
the P-40s were used for service testing, the USAAC contract making no 
provisions for the standard practice of supplying YP models.  

Foreign air forces were beginning to take notice of the P-40, and in 
May of 1940, the Armee de l'Air of France placed an order for 140 
H-81A (export model of the P-40).  

Only 200 of the initial P-40 order were actually completed as P-40s.  
Serials were 39-156/280 and 40-292/357.  The remaining 324 aircraft of 
the order had their delivery deferred to enable Curtiss to expedite 
the delivery of the 140 H-81As to France.  However, none of these 
actually reached France before the Armistice in June 1940, and the 
contract was taken over by the Royal Air Force as Tomahawk I.  

16 P-40s were sent to the Soviet Union after the German invasion.  

The P-40 lacked such things as armor for the pilot, self-sealing fuel 
tanks, and a bulletproof windshield, so it was not considered as being 
suitable for combat.  On October 22, 1942, the P-40s still in USAAF 
service were ordered restricted from combat duty and were redesignated 
RP-40.  

The P-40A designation was skipped in the initial designation 
assignments.  However, it was applied retroactively to P-40 Ser No 
40-326 when it was converted to a camera-carrying photographic 
reconnaissance model at Bolling Field in March of 1942.  

The P-40B (Model H81B) differed from the P-40 in having an extra 
0.30-inch machine gun in each wing.  The engine was still the 
V-1710-33.  In September 1940, 131 P-40Bs were procured by the Army to 
replace the deferred P-40s.  Serials were 41-5205/5304 and 
41-13297/13327.  The first P-40B flew on March 13, 1941.  The P-40B 
retained the same dimensions of the P-40, but weight was increased to 
5590 pounds empty, 7326 pounds gross, and 7600 pounds maximum loaded.  
Because of the additional weight, the P-40B had an inferior 
performance to the P-40, maximum speed being 352 mph, service ceiling 
being 32,400 feet, and initial climb rate being 2860 feet per minute.  
Normal range was 730 miles, but a maximum range of 1230 miles could be 
attained at the minimum cruise settings.  

The export equivalent of the P-40B was the Tomahawk IIA (Model 
H81-A2).  They differed from the American version by having the wing 
guns replaced by 0.303-inch Brownings.  110 were produced for the RAF.  
RAF serials were AH881/990.  23 of these planes were transferred to 
the USSR, and one (AH938) went to Canada as an instructional airframe.  

The initial P-40 order was finally completed with 193 P-40Cs (company 
designation H81-B).  Serials were 41-13328/13520.  The first flight of 
a P-40C was made on April 10, 1941.  The P-40C retained the 1150 hp 
Allison V-1710-33 engine, but was fitted with a new fuel system with 
134 gallons in new tanks with improved self sealing.  In addition, 
provisions were made for a 52-gallon drop tank below the fuselage.  
The P-40C had a SCR-247N radio instead of the SCR-283.  These 
additions produced yet another upward crawl in the weight--the weights 
for the P-40C were 5812 pounds empty, 7459 pounds gross, and 8058 
pounds maximum loaded.  Consequently, the performance continued to 
degrade.  Maximum speed was 345 mph at 15,000 feet.  Normal and 
maximum ranges were 730 and 945 miles respectively.  Service ceiling 
was 29,500 feet, and initial climb rate was 2650 feet per minute.  
Dimensions were wingspan 27 feet 3 1/2 inches, length 31 feet 8 1/2 
inches, height 10 feet 7 inches, wing area 236 square feet.  

The export equivalent of the P-40C was the Tomahawk IIB (Model 
H81-A2).  A total of 930 were built.  RAF serials were AH991/999 (all 
to USSR), AK100/570 (36 to China), AM370/519 (64 to China), and 
AN218/517.  

100 of these planes, unofficially designated H81-A3, were transferred 
to China where they were used by the American Volunteer Group--the 
famous "Flying Tigers".  23 went to the USSR, and unspecified numbers 
went to Turkey and Egypt.  The rest were used extensively by the RAF 
and South African Air Force in the North African theatre.  

Sources:

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

  The American Fighter, Enzo Anguluci and Peter Bowers, Orion Books, 1987.

  United States Military Aircraft since 1909, Gordon Swanborough and Peter 
  M. Bowers, Smithsonian Institution Press, 1989.

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

  The Curtiss P-40 Tomahawk, Ray Wagner, Aircraft in Profile, Volume 2,
  Doubleday, 1965.

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

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