From: jfb@ihlpl.att.com
Newsgroups: sci.military
Subject: Number Forty-Seven in the Series--Republic P-47 Thunderbolt (1 of 9)
Keywords: XP-47, XP-47A, XP-47B, P-47B
Date: 24 Jan 93 16:03:09 GMT
Organization: AT&T Bell Laboratories -  Naperville, Illinois


From jfb@ihlpl.att.com


The Republic P-47 Thunderbolt originated from the drawing board of 
Alexander Kartveli of the Seversky Aircraft Corporation (later 
renamed Republic Aviation).  The Thunderbolt is consistently rated as 
one of the three outstanding USAAF fighters of World War II-- rated 
right up there along with the North American P-51 Mustang and the 
Lockheed P-38 Lightning.  The P-47 was built in larger numbers than 
any other American fighter, 15,683 examples rolling off the assembly 
line before production finally ended.  

At one time during the heady days of 1944, there were no less than 31 
front-line fighter groups flying Thunderbolts.  Thunderbolts fought on 
all fronts in World War 2, including Alaska.  Approximately two-thirds 
of all Thunderbolts built actually reached operational units overseas.  
In two and a half years of combat, from March 1943 to August 1945, 
these Thunderbolts flew over half a million combat missions, 
destroying over 12,000 enemy aircraft both in the air and on the 
ground, as against a total of 5222 Thunderbolts lost, only 824 of them 
in the heat of combat.  This corresponded to 54 percent of the 
Thunderbolts which went overseas being eventually lost either to enemy 
action or to accidents, which was a fairly typical attrition rate for 
a wartime fighter.  Losses of Thunderbolts on operational missions 
were 0.7 percent of those dispatched, an exceptionally low figure.  

By the end of the war, the Thunderbolt had established an overall 
ratio of air-to-air combat victories to losses of 4.6 to 1.  
Thunderbolts dropped 132,482 tons of bombs, fired 59,567 rockets, and 
expended 135 million belts of machine gun ammunition.  

From D-Day to V-E Day in Europe, Thunderbolts destroyed 86,000 railway 
cars, 9000 locomotives, 6000 armored vehicles and tanks, and 68,000 
trucks.  By the end of the war, Thunderbolts had destroyed 2752 enemy 
aircraft in the air and 3315 on the ground.  

The P-47 as originally conceived was quite different from the aircraft 
which was ultimately to emerge from the Republic factories.  On August 
1, 1939, Kartveli, in response to an official requirement, proposed a 
lightweight high-altitude interceptor to the USAAC under the company 
designation of AP-10.  It was to be powered by a 1150 hp Allison 
V-1710-39 liquid-cooled in-line engine.  This was a radical change in 
design philosophy for Kartveli, since he had always preferred radial 
air-cooled engines for fighters because of their greater simplicity 
and their ability to absorb a greater amount of battle damage.  Gross 
weight was to be 4900 pounds and estimated maximum speed was 415 mph.  
Armament was to be a pair of 0.50-in machine guns mounted in the 
engine housing.  

The USAAC looked over the proposal and was favorably impressed.  
However, they deemed that additional armament would be required, even 
if it adversely affected performance.  Kartveli increased the size of 
his AP-10 design somewhat, and added four wing-mounted 0.30-inch 
machine guns.  Gross weight rose to 6570 pounds.  In this guise, in 
November 1939 the USAAC ordered one prototype of the AP-10 design 
under the designation XP-47.  The serial number was 40-3051.  

In addition, on January 17, 1940, the USAAC ordered a stripped, 
unarmed version under the designation XP-47A.  The serial number of 
the XP-47A was 40-3052.  

In the meantime, combat reports coming in from Europe were changing 
everyone's ideas about air combat.  More firepower, more armament, 
more armor protection, and self-sealing fuel tanks were likely to be 
required in future air battles.  Both the XP-47 and XP-47A had 
insufficient engine power to accommodate the additional weight 
required by these features, and the USAAC came to the conclusion that 
these designs were likely to fall far short of future air combat 
requirements.  Kartveli went back to the drawing board.  

In order to accommodate the heavy firepower, armor, and self-sealing 
fuel tanks and still provide a performance capable of meeting enemy 
aircraft on equal terms, a lot of engine horsepower would be needed.  
Kartveli decided to produce a design based around a turbosupercharged 
Pratt and Whitney R-2800 Twin Wasp eighteen-cylinder air-cooled radial 
engine, one of the most powerful aircraft engines available at the 
time.  Armament was to be a set of eight 0.50-in machine guns in the 
wings, following the RAF's trend toward eight-gun fighters and making 
the Republic proposal among the heaviest-armed fighters yet considered 
by the USAAC up to that time.  Total weight was to be a massive 11,500 
pounds, unprecedented for a USAAC single-seat fighter.  On June 12, 
1940, Kartveli submitted his ideas to the USAAC.  The USAAC was 
sufficiently impressed with the proposal that on September 6, 1940 it 
ordered a prototype under the designation XP-47B.  This designation 
was sort of unusual at the time, namely, using the same P-number for 
what was in effect a totally new design.  All work on the XP-47 and 
the XP-47A was cancelled, and the serial number of the abortive XP-47 
was transferred to the XP-47B.  

One week later, on September 13, 1940, 773 production examples of the 
Thunderbolt were ordered by the USAAC, 171 to be delivered as P-47Bs 
and 602 as P-47Cs.  At the same time, the Army contract placed back in 
1939 for 80 P-44 Rockets was cancelled.  The contract was replaced 
with an order for a similar quantity of P-43 Lancers which would keep 
the Farmingdale production lines occupied pending the introduction of 
the new fighter.  

Kartveli decided to design the XP-47B fuselage around the large 
turbosupercharger from the start, rather than to add it onto the 
aircraft later as sort of an afterthought.  In order to preserve a 
streamlined fuselage with a small cross-section, the large 
turbosupercharger was placed in the rear fuselage.  It was fed by an 
air duct located beneath the large R-2800 engine.  Engine exhaust 
gases were directed back to the rear fuselage in separate pipes to the 
turbine and were expelled through an exhaust under the rear tail.  
Ducted air was fed to a centrifugal impeller and was returned to the 
engine under pressure via an intercooler.  

Another problem that had to be solved was that the aircraft required a 
very large twelve-foot diameter four-bladed propeller in order fully 
to take advantage of the R-2800 engine's high power output.  This 
large propeller in turn required a long and stalky undercarriage in 
order that the propeller be given adequate ground clearance during 
takeoff and landing.  If a conventional retractable undercarriage were 
used for the P-47, its suspension would have to have been placed very 
far outboard on the wings, leaving insufficient space for the eight 
wing guns and their ammunition.  In order to solve this problem, the 
landing gear telescoped and was nine inches shorter when retracted 
than when extended.  Somewhat surprisingly, this complex telescoping 
landing gear seems to have caused few problems in the field.  

Like the earlier P-35 and P-43 fighters, the P-47 was a cantilever 
low-wing monoplane, the wing being elliptical in shape with the 
ailerons on the outer trailing edge and flaps on the inner trailing 
edge.  The semimonocoque fuselage was all metal, but initially the 
control surfaces were fabric covered.  The tailwheel was steerable and 
was fully retractable.  All the fuel tanks were inside the fuselage 
and were self-sealing from the start.  The cockpit was protected by 
armor and was unpressurized.  

The XP-47B prototype flew for the first time on May 6, 1941, piloted 
by Lowry L.  Brabham.  This was only eight months after the order was 
placed.  The XP-47B was the largest single-engine fighter built up to 
that time.  On the first flight, the pilot was forced to make an 
unplanned emergency landing because of a leakage of exhaust fumes into 
the cockpit.  At a loaded weight of 12,086 pounds, the XP-47B dwarfed 
all previous fighters, being almost twice as heavy as most of its 
contemporaries.  Its eighteen-cylinder XR-2800-21 radial engine 
offered 1960 hp at 25,800 feet, and gave it a maximum speed of 412 
mph, 12 mph faster than Kartveli had projected.  An altitude of 15,000 
feet could be attained in five minutes.  Empty and normal gross 
weights were 9189 pounds and 12,086 pounds respectively.  The 
prototype was destroyed in an accident on August 8, 1942.  

At one time, it had been hoped that it would be possible for the RAF 
to test the Thunderbolt in combat in the Middle East, but production 
difficulties caused the British Air Ministry to be informed in 
September 1941 that it was probably not a good idea to do this until 
all the bugs had been wrung out of the design.  

The first production P-47B was delivered on December 21, 1941, and 
five more were delivered in March 1942, only eight months after the 
XP-47B had first flown.  Numerous problems soon presented themselves 
as the test program advanced.  At altitudes above 30,000 feet, 
ailerons snatched and froze, the cockpit canopy could not be opened, 
and control forces became excessive.  These problems caused further 
P-47B acceptances to be delayed until May.  The problem of the 
freezing ailerons was solved by having all control surfaces being 
fully metal-covered on all subsequent P-47Bs.  The ailerons were 
revised in shape and fitted with blunt noses, which alleviated the 
excessive control force problem.  Balanced trim tabs were adopted to 
reduce rudder pedal loads.  The stuck cockpit canopy problem was 
solved by replacing the original hinged canopy by a rearward sliding 
hood.  This meant that the dorsal radio antenna had to be redesigned 
and moved aft to accommodate the rearward-sliding hood.  

The production P-47B was fitted with a a production R-2800-21 engine 
of 2000 hp.  An increase in the amount of internal equipment raised 
the empty, normal loaded, and maximum loaded weights to 9346, 12,245 
pounds, and 13,360 pounds respectively.  However, the increased power 
of the production-ready engine provided an increase in level speed to 
429 mph at 27,000 feet.  The maximum speed was 349 mph at 5000 feet.  
Initial climb rate was 2560 feet per minute and an altitude of 15,000 
feet could be attained in 6.7 minutes.  Service ceiling was 42,000 
feet.  Range (clean) at maximum cruising power was 550 miles at 335 
mph at 10,000 feet.  Wingspan was 40 feet 9 3/4 inches, length was 35 
feet 3 1/4 inches, height was 14 feet 1 3/4 inches, and wing area was 
300 square feet.  

P-47Bs were first issued in mid-1942 to the 56th Fighter Group.  This 
group was chosen to be the first recipient of the P-47B because it 
was based near New York City and hence located near the Farmingdale 
plant where Republic engineers could be easily called upon to help in 
ironing out problems as they arose.  The P-47Bs of the 56th Fighter 
Group were used largely for stateside testing and operational 
training, and very few ever went overseas.  The 56th Fighter Group 
found the process of working up to its new mounts rather difficult--13 
pilots and 41 aircraft were lost in accidents.  

The last P-47B was delivered in September 1942.  Serial numbers of the 
170 P-47Bs constructed were 41-5895/6065.  

The last example of the P-47B series (41-6065) was converted during 
manufacture in September 1942 as the XP-47E with a pressurized cockpit 
and a hinged canopy.  However, increased emphasis on low-level 
operations over Europe lead to the cancellation of plans to introduce 
this pressurized Thunderbolt into production.  

XP-47F was the designation given to another P-47B airframe (serial 
number 41-5938) which was used to test a new larger-area wing with a 
laminar-flow aerofoil.  It flew for the first time on September 17, 
1942.  No production was undertaken.  

Sources:

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

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

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

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

  The Republic P-47D Thunderbolt, Aircraft in Profile, Edward Shacklady, 
  Doubleday, 1969.  

  Famous Fighters of the Second World War, Volume I, William Green, 
  1967.  

  Thunderbolt!, Robert S.  Johnson and Martin Caidin, Ballantine Books, 
  1958.  

  British Military Aircraft Serials, 1912-1969, Bruce Robertson, Ian 
  Allen, 1969.  

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