Re: CAC CA-15 original design
Kim Margosein said:
I would buy several also if it was easier. I know, you have explained why this does not work, and I understand. As one who discovered your work in Antarctic Press, any chance of showing what you have on the P-47 to F-84 evolution?
A Colonel Condorcet fan.
Kim M
From UNKNOWN! N.3
JET THUNDERBOLT
By mid 1943 the US Army Air Force decided to order the design and construction of the first American air superiority jet fighter to Lockheed company.
The new fighter, named XP-80 under the GOR specification of 23rd June 1943, was flying by the beginning of 1944, being the first American airplane to surpass the 500 m.p.h.
The Republic XP-72, designed to succeed the Thunderbolt, flew for the first time one month later. It was an impressive machine able to fly at 490 m.p.h. propelled by the most powerful piston engine developed during the WWII.
However, the US Army Air Force rejected the project as it was considered obsolete compared to the XP-80 of which 4390 units were ordered on 1st July 1944.
The reason behind the technological delay of the Republic was the consequence of its previous success in the manufacturing of the Thundertbolt, the American fighter produced in highest number during the WWII.
The US Army Force did not wish any delay in the delivery program of the P-47. They adviced against any important modification of the basic model that could alter the production rate.
This policy prevented Republic designing a totally new jet fighter. However, some studies were made in 1943 over the possible adaptation of a De Havilland centrifugal turbojet (the only model available at the time) to the airframe of a P-47 or an XP-72.
There are no documents left on that study, although it must be stressed that there are not many different ways to install the engine without a whole redesigning of the airplane.
We propose below three reasonable possibilities:
SOLUTION 1
It required a minimum of modifications in the airframe. This disposition was used by the Soviets for their first generation of jet fighters Yak-15 and Lavochkin-174 and by the Italians for the building of the supersonic airplane Aerfer "Sagittario 2"
The main problems generated by the position of the jet exhaust were the possibility of a fire to the rear fuselage during take-off (the Russians used metallic tailwheels) and certain reduction in the longitudinal rate of roll.
SOLUTION 2
The fuselage and jet exhaust axis were made to coincide with each other, but it required to make extensive modifications in the upper part of the fuselage raising it in the 'Hellcat style'.
SOLUTION 3
It removed this last problem using an "S" shaped jet exhaust which excessive length affected in a negative way the power of the turbojet and the amount of fuel internally transported.
During July 1944 an unprecedented change took place in the war. The British Gloster Meteor Mk.I (410 m.p.h.) went into service just in time to intercept the first V-1 flying bombs which were projected to reach the 559 m.p.h. but with a maximum real speed of just 408 m.p.h. due to the aerodynamic deficiencies caused by the rough German system of mass production.
The first sightings of the Me 262 (540 m.p.h.) and Me 163 (596 m.p.h.) also happened at that time.
On 4th August the XP-47 J, a lighter version of the Thunderbolt, reached the speed record for airplanes with propellers, flying at 504 m.p.h. But it was not enough to face the new swept wing German designs.
The whole production of centrifugal turbojets was reserved for the Lockheed P-80.
The first flight of the P-47 N, the long range version, was made in September, designed to fight in the Pacific Theatre escorting the B-29 bombers.
No jet fighter could perform this task due to the enormous fuel comsumption made by the first centrifugal turbojets engines which great volume used the whole interior of the P-80 fuselage.
A two-engined formula was tried with the Bell XP-83 (an extended version of the P-59) resulting in a huge and heavy airplane unable to manoeuvre to face the Japanese Shusui and Kikka jet and rocket fighters.
The US Army Air Force reached the conclusion that a new technical miracle was needed to achieve the required high speed and range (mutally exclusive conditions) similar to the one obtained in Europe with the P-47 in 1943.
In May 1944 the Alexander Kartveli team of the Republic company was instructed to design an aircraft around the new General Electric TG-180 axial-flow turbojet.
It was expected that the small diameter of the new engine would leave enough room in the fuselage to transport a big fuel load.
The TG-180 was tested for the first time in April 1944 with great success showing a thrust of 3750 lb (1700 kgp) and a lower compsuntion than the centrifugal engines. It had a diameter of 37.5 inch (45 cm), 12 ft (366 cm) of length and 2500 lb (1132 kg) of weight.
The Air Force General Operational Requirement (GOR), officially published on 11 September 1944, required the design of a mid-wing fighter with a top speed of 600 m.p.h. and combat radius of 850 miles.
The armament should be eight .50 (12.7 mm) calibre M2 machine guns or six .60 of the experimental type.
The TG-180 was too long to locate it at the nose of the airplane. It should be installed in the fuselage behind the pilot. The air-intake located in the nose went through under the cockpit. The new disposition created enormous problems of stability in an airframe designed to carry a heavy engine in the forward area.
Between May and September 1944 the Republic project staff studied the possibility of redistributing the weight by installing the fuel, ammunition and armament in the nose and the air duct being forked in two going through both sides of the cockpit and joining behind it once more. The wings also housed fuel in the weapons previous location.
An insoluble problem appeared when the airplane shot its weapons after having wasted half its fuel. It started to be heavier in the tail and difficult to control during the return flight and landing.
On 19th September the idea of reconverting the P-47 was abandoned opting for a new design named AP-23. The position of the wing was taken 72 cm backwards, the cockpit was put 140 cm forward,a new tricycle type landing gear was installed.
The installation of the nosewheel just allowed an armament of four machine guns in the upper nose. The GOR was modified by beginning of November to transport just six weapons, the other two were installed in the wingroots.
The combat radius was also reduced to 705 miles, abandoning the idea of "long range" in favour of the "penetration fighter" concept, adapted to the new strategy used in the war against Japan where air bases nearer the metropoli were at hand.
On 11 November 1944 the US Army Air Force accepted the new design under the denomination XP-84 fitted with a new rectangular thicker wing specially designed to contain fuel. The building of prototypes was then authorised with the first flight of the new airplane taking place on 28th February 1946.
Bibliography
• Aeroplane Monthly December 1976
• "The Thunder Factory" by Joshua Stoff, ARMS & ARMOUR
• "F-84 Thunderjet in action", Squadron Signal No. 61
• "Republic F-84" by David R. McLaren, Schiffer 1998
• "F-84 Thunderjet" by Bert Kinzey (In detail Vol 59) Squadron Signal 1999
• "Le Fanatique de l'Aviation" Hors Série No. 16, December 2001
• Correspondence with Chuck Davis