Subject: Number Seventy-Five in the Series--Fisher P-75 Eagle

From: [email-masked]
Date: 28 May 93 16:28:37 GMT

>From [email-masked]

In February of 1942, the USAAF issued a Request For Proposals (RFP) 
which called for aircraft companies to submit designs for a 
fighter/interceptor having an exceptional performance.  Maximum speed 
was to be 440 mph at 2000 feet, operational ceiling was to be 38,000 
feet, and range was to be 2500 miles.  A special requirement was added 
for the initial climb rate, which was to be no less than 5600 feet per 
minute.  High speed, high climb rate, high ceiling, and long range, 
all in one package--a tall order for any aircraft company.  

In April of 1942, the famous designer Donovan Berlin (who had been 
responsible for such successful designs as the P-36 and the P-40) left 
the Curtiss company after many years of service to take over the 
directorship of the Aircraft Development Division of the Fisher Body 
Division of the General Motors Corporation.  As one of his first 
assignments, he took it upon himself to work on a design in response 
to the USAAF RFP.  In September of 1942, Fisher submitted their 
proposal to the USAAF.  The Fisher proposal used the most powerful 
liquid-cooled engine then available, the twenty-four cylinder Allison 
V-3420.  This engine was basically a pair of coupled V-1710 engines, 
mounted side-by-side in a W-type configuration.  Significant savings 
in cost and time were to be gained by employing major assemblies from 
existing aircraft already in production in the manufacture of the new 
interceptor.  

On October 10, 1942, a contract for two prototypes was awarded to 
Fisher under the designation XP-75.  In assigning the XP-75 
designation to the Fisher design, the designations XP-73 and XP-74 
were skipped, for reasons which are not altogether clear even today.  
The aviation historian James Fahey claims that the P-73 and P-74 
designations were deliberately omitted as a result of political 
pressure applied to the Army by Fisher.  According to the story, 
Fisher wanted the Army to assign to its new escort fighter a "nice 
symbolic number", a number that would sound nice in advertising copy 
and would make for memorable slogans--something like "The French 75 in 
World War 1, the Fisher P-75 in World War 2" was envisaged.  The Army 
agreed, and skipped the designations P-73 and P-74 and gave Fisher the 
P-75 designation.  

Serial numbers 43-46950 and 43-46951 were assigned to the two XP-75 
prototypes.  The Allison engine was to be located behind the cockpit a 
la P-39 Airacobra, and was to drive a set of contrarotating propellers 
via an extension shaft and a reduction gearbox.  The engine was cooled 
by means of a large duct in the ventral fuselage.  Initially, it was 
planned that the outer wing panels of the P-51 Mustang would be used 
in an inverted-gull configuration, and that the tail assembly of the 
Douglas A-24 (Army version of the SBD Dauntless) and the undercarriage 
of the Vought F4U Corsair would be used.  However, at an early stage 
it was decided to drop the inverted gull-wing configuration and go 
with a straight wing design utilizing outer wing panels from a P-40.  

By the summer of 1943, the USAAF had a more urgent need for long-range 
escort fighters than it did for fast-climbing interceptors.  On July 
6, 1943, the USAAF ordered six more prototypes that would be adapted 
to fulfill the long-range escort role.  They were assigned the 
designation XP-75A, and the serial numbers were 44-32161/32166.  They 
were to be powered by an Allison V-3420-23 engine, and were to be 
armed with six 0.50-inch machine guns in the wings and four 0.50-inch 
guns in the fuselage nose.  At the same time, the USAAF decided to 
order no less than 2500 production P-75As, although they did stipulate 
in the contract that if the production aircraft did not meet 
specifications the order might be cancelled.  Maximum speed was to be 
434 mph at 20,000 feet and 389 mph at sea level.  These production 
P-75As were to be built at the Fisher plant in Cleveland, Ohio.  

The first XP-75 flew on November 17, 1943.  It was powered by an 
Allison V-3420-19 engine rated at 2600 hp for takeoff and driving a 
pair of contrarotating propellers.  As planned, the wing was of a 
straight center section with P-40 outer panels with modified tips.  
The tail assembly was from an A-24, and the main undercarriage members 
were taken from an F4U Corsair.  

All six XP-75A long-range escort versions were in the test program by 
the spring of 1944.  Some problems were encountered with instability, 
since errors had been made in the initial estimate of the aircraft's 
center of mass.  The coupled Allison engine failed to give its full 
rated power.  The engine cooling was inadequate, aileron forces were 
excessively high, and the spinning characteristics were poor.  

The P-75A production aircraft featured a modified tail assembly and 
had a bubble-type canopy replacing the framed and braced cockpit hood 
of the earlier versions.  It featured the V-3420-23 engine of the 
XP-75A.  The first P-75A flew on September 15, 1944.  By that time, 
most of the bugs had been ironed out of the design.  However, at that 
stage in the war, the Republic P-47D Thunderbolt and the North 
American P-51D Mustang were more than adequately fulfilling the 
long-range escort role, and the USAAF decided that there was no longer 
any need for a new escort fighter.  Consequently, the USAAF decided to 
terminate the P-75 development program, and the production contract 
for the P-75A was cancelled on October 27, 1944 after only six 
examples had been built.  The serial numbers of the six P-75As built 
were 44-44549/44553.  

By the time of contract termination, the first and second P-75A had 
been delivered to Elgin Field, Florida for tactical suitability 
trials, the third machine was in the shop being fitted with an 
experimental intercooler, and the fourth and fifth machines were 
almost complete.  Although the USAAF no longer had any need for the 
P-75, it was decided to go ahead and finish these machines and use 
them for development work.  The sixth machine was to be placed in 
storage and scavenged for spare parts to keep the rest flying.  

The five production P-75As never completed official performance 
trials, but enough testing was performed to confirm the fact that the 
maximum speed was at least 30 mph below that guaranteed by the 
manufacturer.  The third machine received an experimental intercooler 
installation which permitted substantial increases in engine power.  
The following specification for the long-range XP-75 are those quoted 
by the manufacturer; One 2885 hp Allison V-3420-23 twenty-four 
cylinder liquid-cooled engine.  433 mph at 20,000 feet, initial climb 
rate 4200 feet per minute st 10,000 feet, 3900 feet per minute at 
20,000 feet.  Service ceiling was 36,400 feet and absolute ceiling was 
29,500 feet.  Range with maximum external fuel was 3500 miles.  
Weights were 11,495 pounds empty, 13,807 pounds normal loaded, and 
18,210 pounds maximum.  Dimensions were wingspan 49 feet 4 inches, 
length 40 feet 5 inches, height 15 feet 6 inches, and wing area 347 
square feet.  Armament consisted of six 0.50-inch machine guns in the 
wings (235 rpg) located outboard of the propeller arc and four 0.50-in 
machine guns (300 rpg) in the fuselage nose synchronized to fire 
through the propeller arc.  In addition, a pair of 500-pound bombs 
could be carried.  

The last production P-75A (serial number 44-44553) is on display in 
the Annex at the Wright-Patterson Air Force Base Museum in Dayton, 
Ohio.  I saw it there in June of 1992.  It was in fairly good shape, 
but needs some restoration work.  This was apparently the aircraft 
that had been scavenged to keep the other P-75s flying, so more than a 
few things may be missing.  

Sources: 

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

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

  Fighters of the United States Air Force, Robert F. Dorr and David 
  Donald, Temple Press Aerospace, 1980.  

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

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