Thursday, August 05, 2021
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Republic P-47 Thunderbolt

 

Known affectionately throughout SEAC as the ‘T-Bolt’, the P-47 was powered by a Pratt and Whitney R-2800 turbo-supercharged eighteen cylinder Double Wasp radial.  The fuselage was constructed in two sections.  The front section was built up as an upper portion, which incorporated the cockpit, and a lower half which contained two large bulkheads for wing attachments.  A single unit formed the rear section of the fuselage.  The wing design had two main spars and metal stressed-skin covering.  Frise-type ailerons were fitted with hydraulically operated slotted flaps being installed in the wing trailing edges between the ailerons and fuselage. 

 

The P-47 had an elliptical engine cowling with the two oil coolers being positioned below the power plant.  The R-2800 radial powered a four bladed propeller of twelve foot diameter.  The turbo/supercharger was fitted beneath the rear fuselage, behind the pilot and fed by air from an intake duct located under the engine.  This produced the distinctive oval shape of the P-47 cowling and as the duct passed below the wing was responsible for the aircraft’s deep fuselage.  The turbo waste gate outlet was located at the rear of the cowling almost underneath the aircraft.  In order to give sufficient ground clearance for the large propeller, specially designed landing gear oleo (air-oil) legs were fitted which shortened as they retracted.  To provide a wide wheel track the landing gear folded inwards.  The tail wheel was fully retractable and could be steered. 

 

The ‘T-Bolts’ used by SEAC had modified turbo-supercharging and engine vents with extra cooling gills being fitted each side at the rear of the cowling.  The early metal-framed sliding canopy was replaced with a ‘bubble’ (Hawker Typhoon type) canopy fitted with the rear fuselage being modified to accept the new type of canopy. 

 

The P-47 commenced operational service with the Royal Air Force in September 1944 being used only with SEAC against the Japanese forces occupying Burma.  830 P-47’s entered service with the RAF, of which 240 were Mk I’s (FL731 to FL850 and HB962 to HD181) and 590 were Mk II’s (HD182 to HD301, KJ128 to KJ367, KL168 to KL347 and KL838 to KL887).  The Mk II’s had the ‘bubble’ hood.  RAF squadrons equipped with the P-47 were 5*, 30*, 34, 42, 60, 79, 113*, 123*, 131, 134*, 135, 146*, 258*, 261* and 615 (* denotes that a squadron used Mk1 and Mk2).  Except for 615 Squadron all the squadrons moved from Hurricane MkIIC’s to P-47 and flew the Thunderbolts until the end of the war with Japan.  615 Squadron moved from Spitfires to Thunderbolts from June 1945 to September 1945 and then transferred back to Spitfires until the end of the war.  The RAF Thunderbolts operated as fighter-bombers giving cover to the RAF Liberators and also created havoc among Japanese bases and supply routes.  Soon after VJ-Day, the P-47 disappeared from RAF service.

 

 

P-47M (article by Roger Freeman):  Fastest propeller driven fighter to see operational service with the Allies during World War Two.  The P-47M attained 473mph for very short periods of maximum engine boost using water injection.

 

The turbo-supercharged radial (R-2800) that powered the Thunderbolt provided an excellent high altitude performance but its fuel consumption was high.  Additional tanks were required which meant a redesigned of the wings.  The additional fuel and enlarged structure increased the weight which in turn required extra power.  The extra power was to be supplied by the Pratt and Whitney R-2800 Double Wasp ‘C’ model which differed from the ‘B’ model, which hitherto had powered the P-47, in having strengthened components to withstand higher supercharger boost pressure.

 

When the Luftwaffe introduced fighters with enhanced performance, notably the Me262, it was decided to manufacture a number of P-47D airframes with ‘C’ series engines.  The last 130 Thunderbolts of the P-47D contract being met at the Farmingdale factory were completed as P-47Ms having been fitted with R-2800 57s (military designation for ‘C’ series), revised propellers and new model turbo-supercharging equipment.  They were delivered in autumn 1944 and all were shipped to the 56th FG who were scheduled to be the only remaining P-47 group in the Eighth Air Force.  

 

The first P-47M arrived at Boxted on the 3rd January 1945.  On the 21st January the engine on 44-21161 suddenly failed.  The pilot managed to ‘belly in’ at Boxted.  Other pilots had previously reported the R-2800 57s cutting out when the P-47Ms were taken to high altitude and power reduced to cruising speed.  On these occasions excessively low cylinder head temperatures had been noticed.  Examination of 44-21161 found that the HT leads from the magneto to distributor were cracked.  MTS (Maintenance and Technical Services) at Bovingdon recommended that neoprene leads be fitted and to improve cylinder head temperatures MTS advised lagging all pushrod covers.  P-47M cylinder head temperatures were still considered too low at reduced power and a metal baffle, which was an extension of the engine pre-heater ring, was introduced.  Col Cass Hough, Deputy Director of MTS suspected that the correlation of throttle to supercharger controls were also contributing to the problem, he was proved to be right.

 

Back at Boxted two other problems had materialized.  One, propeller brakes failing to function due to operating spring breakage and distortion, was rectified at MTS by adding small protective sleeves around each spring.  The other, carburettor poppet valve diaphragms splitting, was corrected at Boxted by modification of the poppet valve.

 

The first squadron, 61st, to be equipped with the P-47M was only able to undertake one mission with the P-47Ms in January.  To continue operations the pilots had to borrow aircraft from the other squadrons as all their P-47Ds had been returned.  When, on the 3rd February,  the 62nd Squadron began to receive its P-47Ms, it retained its P-47Ds as did the 63rd Squadron when their first P-47Ms arrived two weeks later. 

 

Each ground crew in these squadrons were readying the P-47Ms whilst keeping the P-47Ds maintained for combat use. 

 

On the 9th February 44-21178 suffered an engine failure, the pilot managed to crash land the Thunderbolt in a field at Dedham.  A few days later another P-47M suffered engine failure and crashed, this time the pilot was killed.  There were other crash landings.  When, on the 4th March, the 62nd Squadron flew its first all P-47M mission six of the fourteen Thunderbolts turned back with engine trouble.  During a mission on the 14th March 44-21136 suffered engine failure.  The pilot was killed when the aircraft crashed into the North Sea.  On the same day two pilots were killed when their P-47Ms collided, mechanical failure was suspected as a contributory factor.  The next day 44-21222 had an engine failure shortly after take-off, the pilot was killed. 

 

It was suspected that the engine failures were due to the incompatibility of the 150 PEP additive fuel in use.  Comparison tests were running using ‘straight’ 150 and 130 octane fuel, results were inconclusive.  It was noted that nearly all the engine that had failed had only a few hours time on them.  P-47Ms with more than fifty hours appeared to be trouble free.  When seized engines were stripped scale was found in the cylinders which was traced to rust abrasions on liners and pistons.  Salt water moisture had entered the engines during shipment.  Every engine that had run for less than fifty hours was changed.  In all seventy five engines were changed and slow timed in two weeks.

 

In late March the 56th were in a position to fly all P-47M missions.  By this time few enemy aircraft were to be encountered within the P-47Ms range operating out of Boxted.  Nine victories were accredited to 56th pilots flying P-47Ms, four of these were Me262s.  Two P-47Ms were lost to ground fire. 

The long range wing P-47N arrived in the UK in April.  All were flown to Burtonwood, none saw combat.  No P-47Ms exist.  ‘No guts no glory’ features D model wings on a N model fuselage, is powered by a C type R-2800 and has P-47M configurations.   

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