Subject: Number 105 in the series--Republic F-105 Thunderchief (1 of 9)

From: [email-masked]
Date: 31 Jan 94 17:18:11 GMT

>From [email-masked]

The F-105 Thunderchief was the first supersonic tactical fighter-bomber 
that was developed from scratch.  All others before it were 
adaptations of aircraft that had originally been developed as pure 
fighters.  The Thunderchief has the distinction of being the largest 
single-seat, single-engined fighter ever built.  Although designed for 
the nuclear strike role, the Thunderchief gained its distinction for 
the role it played in the Vietnam War in delivering conventional 
ordinance on targets in the North.  Although a large, heavy, and 
relatively sluggish-maneuvering aircraft, the Thunderchief 
nevertheless managed to shoot down 27 enemy fighters during that 
conflict.  

The F-105 had its origin back as far as 1950.  The F-84F Thunderstreak 
swept-wing fighter bomber had yet to make its first flight when, in 
June 1950, the Air Force was already asking Alexander Kartveli of the 
Republic Aircraft Corporation to initiate design studies for its 
successor.  Kartveli and his staff looked at 108 different 
configurations under the company designation AP-63 (where AP stood for 
*Advanced Project*) before settling on a single-seat, single engined, 
swept-winged aircraft.  The role was to be primarily that of nuclear 
strike, but a secondary air-to-air capability was envisaged.  A Mach 
1.5 maximum speed was anticipated.  The airframe was to be matched to 
the extremely exacting requirements of high-speed, low-level 
operation.  

The initial contractor proposal to the Air Force was issued by 
Republic in April of 1952.  It contained most of the features that the 
Air Force would have liked to have had provided on the F-84F had they 
been technically feasible at the time.  The aircraft was to be powered 
by an Allison J-71 turbojet.  In May of 1952, the Air Staff endorsed 
the development of this project in lieu of trying to create an 
improved supersonic version of the F-84F.  The designation F-105 was 
assigned.  

A letter contract was issued in September of 1952 for 199 F-105 
aircraft, the first of which was to be ready for service by 1955.  In 
October of 1952, the Air Force awarded Republic a contract for 
pre-production engineering, tooling, and material procurement for the 
aircraft.  However, in March 1953, the program was reduced to 37 
F-105As and nine RF-105As.  The F-105A was the pure fighter-bomber 
version, whereas the RF-105A was to be a photographic reconnaissance 
variant.  The RF-105A was expected to bear much the same relationship 
to the F-105A as did the RF-84F Thunderflash to the F-84F 
Thunderstreak.  

The Republic design team came up with a large single-seat aircraft 
with a mid-mounted sweptback wing.  The engine was fed by a pair of 
intakes mounted in the wing roots a la RF-84F Thunderflash.  The main 
landing gear retraced inwards into the wings.  Since the undercarriage 
was so stalky, much of the internal volume in the wing was taken up 
with the stowed landing gear, leaving no space for internal fuel 
inside the wing.  All the fuel was to be carried in fuselage tanks or 
inside externally-mounted droptanks.  A low-mounted all-flying 
horizontal tail was fitted.  From the outset, the aircraft was planned 
on massive lines with an internal bomb bay able to accommodate up to 
8000 pounds of nuclear or other weapons.  In addition, as much as 4000 
pounds could be carried externally on four underwing pylons or on an 
under-the-fuselage hardpoint.  

The F-105 mockup was inspected on October 27, 1953.  By that month, it 
was apparent that design had become so large and heavy that the J-71 
engine originally earmarked for the F-105 would not meet the thrust 
requirements.  The extremely advanced Pratt and Whitney J75 turbojet 
was selected in its place.  The J75 was rated at 16,000 lb.s.t. dry 
and at nearly 25,000 lb.s.t. with afterburning.  However, it seemed 
likely that this engine would not be available for several years, so 
it was decided that the Pratt & Whitney J57 would be used in the 
initial machines for tests, with the J75 being introduced on the 
production line when it was finally available.  The J57-powered 
machines were designated F-105A, with the J75-powered version being 
designated F-105B.  

In December of 1953, the Air Force suspended procurement of the F-105 
because of excessive delays at Republic.  Procurement was reinstated 
in February 1954 but reduced to 15 aircraft.  

By 1954, the design had crystallized sufficiently for a development 
contract to be placed under the WS-306A weapon system designation.  On 
June 28, 1954, a formal contract was awarded for fifteen F-105As, all 
to be powered by the J57 engine.  Further slippages led the Air Force 
to decide in September 1954 to reduce the program to three aircraft.  
However, next month, the number of aircraft was restored to six 
aircraft.  

In February 1955, the Air Force again authorized acquisition of the 15 
test aircraft.  However, the contract was at that time amended and 
subdivided into 2 YF-105As, 10 F-105Bs, and three 
photographic-reconnaissance RF-105As.  

While the first two YF-105As were under construction, Republic 
engineers learned of the difficulties being encountered by Convair 
with its YF-102 all-weather interceptor.  In particular, engineering 
calculations of the transonic drag on the YF-102 had proven to be way 
off, and the aircraft could not exceed the speed of sound in level 
flight.  Convair had found that the cure for the problem was the 
so-called "Area Rule", in which the cross-sectional area of the 
fuselage is narrowed in the region of the wing roots, so that the 
total effective cross section over the entire length of the airplane 
varies in a smooth and continuous fashion.  Republic engineers decided 
to adopt the same sort of change for their F-105, the new "wasp waist" 
to be first incorporated on the F-105B.  An immediate benefit from the 
reduction in drag produced by the adoption of the area rule was that 
full advantage could be taken of the increased thrust offered by the 
J75 engine, making a Mach 2 high-altitude performance possible.  

Construction on the YF-105A continued unabated while these redesign 
efforts were underway.  The YF-105A retained the straight-sided 
fuselage, without the "wasp-waisting" that was to be introduced on the 
B-version.  The F-105 had a set of "clover-leaf" speed brakes attached 
to the end of the tailpipe.  During braking, these petals unfolded to 
stand at right angles to the airflow.  A ventral fin was added to the 
bottom of the rear fuselage to provide good stability at high speeds.  

The first YF-105A rolled out of the factory in the autumn of 1955.  
The first flight of the YF-105A (54-0098) took place on October 22, 
1955, with Republic test pilot Russell M. Roth at the controls.  It 
easily exceeded the speed of sound on its first flight, although, as 
expected, the transonic drag was quite high.  It was the largest and 
heaviest single-seat fighter ever built up to that time.  The maximum 
speed attained was Mach 1.2, even though it was powered only by a J57 
engine and lacked a fuselage that was area ruled.  After 22 hours of 
flight time, the first YF-105 was returned to the factory because of 
major damage sustained in flight and landing.  

The second YF-105A flew for the first time on January 28, 1956.  It 
was identical to the first YF-105A.  

Only two YF-105As were built.  Following their initial flight trials, 
they were used in support of the F-105B program.  

Serials of the YF-105A:

54-0098/0099		Republic YF-105A-1-RE Thunderchief

Specification of the F-105A Thunderchief: 

One Pratt & Whitney J57-P-25 turbojet, rated at 10,200 lb.s.t. dry 
and 15,000 lb.s.t. with afterburner.  Maximum speed: 857 mph at 
36,000 feet, 778 mph at sea level.  Stalling speed was 185 mph.  An 
altitude of 30,000 feet could be reached in 17.6 minutes.  Combat 
ceiling was 49,950 feet.  Normal range was 1010 miles and maximum 
range with full external fuel was 2720 miles.  Fuel capacity was 850 
US gallons internal fuel.  With full external fuel capacity, a total 
of 2500 US gallons of fuel could be carried.  Dimensions: wingspan 34 
feet 11 inches, length 61 feet 5 inches, height 17 feet 6 inches, wing 
area 385 square feet.  Weights: 21010 pounds empty, 28,966 pounds 
combat, 40,561 pounds maximum takeoff.  Armed with one 20-mm M61 
rotary cannon.  Up to 8000 pounds of ordinance could be carried.  

  The Illustrated Encyclopedia of Aircraft Armament, Bill Gunston,   
  Orion, 1988.

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

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

  Fighters of the United States Air Force, Robert F. Dorr and
  David Donald, Temple Press Aerospace, 1990.

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

  Post-World War II Fighters, 1945-1973, Marcelle Size Knaack,
  Office of Air Force History, 1986. 

  The World Guide to Combat Planes, William Green, MacDonald, London, 1966

  The World's Fighting Planes, William Green, Doubleday, 1964.

  The Aircraft of the World, William Green and Gerald Pollinger, Doubleday,
  1965.

  The Thunder Factory, Joshua Stoff, Motorbooks, 1990.

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