The turbosupercharger system, wings, firewall forward section of the fuselage including the cowl, and the control surfaces were all part of the restoration work this month.
The turbosupercharger system continues to be a focus of the restoration work. The system gave the Thunderbolt remarkable tactical flexibility. Both high altitude bomber escort and low altitude fighter bomber missions were possible for the P-47 because of the power of the turbosupercharged R-2800.
Most of the work on the fuselage this month was firewall forward, encompassing the engine accessory area, cowling, and the QEC or quick engine change.
The induction vibrator is necessary to provide a strong spark before the magneto has reached the rotational speed that is required for normal operation. It is an aid in starting the engine that operates by bypassing the magnet portion of the magneto, instead supplying the primary coil of one of the magnetos with a pulsating stream of DC taken from the battery.
As the engine is cranked during start up, these pulses of very high voltage travel to the distributor as a “shower of sparks” and from the distributor to the spark plugs to fire the engine.
One of the engineering techniques that enabled rapid maintenance turnaround during WWII was the assembly of the engine mounts and many of the linkages and accessories into a unit called a QEC, an acronym for Quick Engine Change. On the early B model Thunderbolts, maintenance crews found engine changes to be very time consuming. Republic responded by a design change first incorporated in the P-47C-1RE. The fuselage was extended 8 inches to allow for the QEC. This change was the first major change to the P-47 airframe and as a by product of the extension, aircraft handling qualities improved.
The QEC assembly meant that the engine and mounts could all be removed as a unit and replaced with a new QEC assembly, saving as much as 60% of the time required for an engine change.
The main structures of the wings are complete, so work on internal systems, access doors and control surfaces occupied the restorers this month.
With the primary structures of the fuselage, wings and empennage complete, the last large assemblies to be finished will be the control surfaces. The rudder is done and has been test mounted as the cover photo shows. One of the flaps has also been completed and function tested. Work on the other flap and the elevators continues.
One sign of progress is that a flap has been installed and operated this month. P-47 flaps are large, comprising about 13% of the projected wing area. Their design is the NACA slotted trailing edge type. Slotted flaps like these open a slot between the flap and the wing; allowing high-pressure air from the bottom of the wing to flow through the slot to the top of the wing. The design delays airflow separation by energizing the boundary layer on top of the wing and adds lift without excessive drag. Hydraulic fluid pressure operates the flaps, through three trapezoidal linkages that are synchronized by a torque tube connecting them. This system pushes them aft first, and then down.¹
¹ Pratten, Garth (2016). “’Calling the Tune’: Australian and Allied Operations at Balikpapan”. In Dean, Peter J. (ed.). Australia 1944–45: Victory in the Pacific. Port Melbourne, Victoria: Cambridge University Press. pp. 320–340.
The cowl project continues with the cowl flaps.
When the P-47 first arrived in the SW Pacific theater, it was met with a great deal of skepticism. General Kenney had requested more P-38s because, compared to other USAAF fighters, the P-38 had superior range, speed, and its two engines provided a safety margin in the long overwater flights that missions in the SW Pacific required.
US war planning in 1942-43 held that the war in Europe should take first priority. That meant that aircraft shipments to the Fifth Air Force would be based on what was available after the demands of the ETO had been satisfied. Operation Torch in North Africa also had priority for P-38 shipments, and even the 8th Air Force in Europe was stripped of its P-38s for that effort.
No P-38s were available to General Kenney, so he was offered more P-40s. P-40 performance was marginal in combat with the Japanese fighters in the area and its range was limited. The P-47’s range was even more limited without drop tanks, but it had a speed and altitude performance advantage over the P-40 and P-39s still being flown by the 5th AF.
The first P-47 unit, the 348th Fighter Group arrived in Australia on June 30, 1943. Experimentation began immediately on increasing the combat radius of the P-47D-2REs.
These experiments resulted in the 200-gallon belly tanks that were designed and manufactured in Australia, and the Christmas tree tank behind the pilot that 42-27609 is equipped with as a field modification. The belly and Christmas tree tanks improved range, but not enough. So, in the summer of 1944, as the Japanese pulled back from Papua /New Guinea and bombing attacks on oil installations in Balikpapan increased, the P-47s were loaded with 3 drop tanks.
The addition of the drop tanks widened the combat radius of the P-47 to as much as 750 miles.
This provided an answer to unescorted bomber losses in raids to Balipapan on the island of Borneo, part of the Dutch East Indies. The need for a long range escort in this area was directly related to the enemy’s supply of petroleum. Some estimates state that 35% of the refined petroleum products and as much as half of the aviation fuel used by Japan in WWII came from the Dutch East Indies refineries.
“In late September and early October 1944, the US Thirteenth and Fifth Air Forces began long-range bombing raids from Noemfoor. The first two raids suffered heavy losses due to the lack of escort fighters and inflicted minimal damage; however, after a brief pause and a change of tactics by the US airmen, the final three raids resulted in heavy damage to the refineries and the destruction of most of the Japanese aircraft defending.”²
These and other long range missions demanded specific tactics to achieve success.
² Pratten, Garth (2016). “’Calling the Tune’: Australian and Allied Operations at Balikpapan”. In Dean, Peter J. (ed.). Australia 1944–45: Victory in the Pacific. Port Melbourne, Victoria: Cambridge University Press. pp. 320–340.
Major John R. Young describes maximum range mission tactics in the book Fighter Tactics inThe Southwest Pacific Area, by Ray Merriam.
The mission Young describes was a long range fighter sweep intended to clear the target area ahead of the B-24 bombers. The target was 835 statute miles from his base at Morotai, Netherlands East Indies, which necessitated hanging 3 external drop tanks on the P-47s. Two were 165 gallon wing tanks and the third was a 75 gallon centerline tank.
The Thunderbolts on this extreme range mission would draw fuel from the large wing tanks until they were emptied or combat necessitated dropping them.
Interestingly, in order to get back home on a long range mission like this, the centerline 75 gallon tank was not dropped in combat. This was a practice that was highly unusual because, in almost all other cases during WWII, the drop tanks were immediately jettisoned when combat was imminent. Dropping the tanks had several desirable outcomes; it improved flight performance and maneuverability, and also greatly reduced vulnerability to fire or explosion should the tanks be hit by enemy fire. In fact, if a drop tank failed to detach, the pilot was usually ordered to return to base rather than engage in combat with the tank still attached.
However, on a maximum range mission it would have been impossible to return to base without the remaining fuel in the centerline tank, the P-47s on these maximum range missions couldn’t get home, so the risk was worth taking. It is also likely that the opposition at this late stage in the war was much less fierce than it had been when Japan’s cadre of fighter pilots were experienced veterans. By late 1944 many Japanese pilots were newly trained and inexperienced, and therefore less of a threat.
While it isn’t clear from his account which version of the P-47 Major Young was flying, it was probably a D-25 with slightly increased internal fuel over the D-23 version.
In the same book, Captain Leroy Grosshuesch of the 39th Fighter Squadron describes another mission. He specifically mentions the P-47D-16, D-21, and D-23s as having their range stretched to a 750 mile radius of action, with about 15 minutes of combat time over the area of the fight.
The superior maneuverability and the inferior armament and pilot protection of the Japanese fighters along with the P-47’s superior armament, ability to survive damage, pilot protection, and diving and level flight speed dictated the tactics.
Grosshuesch explained that once the enemy was sighted, he always tried to position himself and his formation above and behind the enemy aircraft. The P-47s would then make a diving pass on the enemy, firing as they went. Capt. Grosshuesch told his men to keep their speed up to 200 miles an hour at all times in combat and to never chop the throttle.
“One good burst will finish him anyway. My advice is if you don’t get him on your first pass, pull off to the side and climb at 200 mph. After you have altitude, come back and do it again.”
He also mentioned that he would never refuse a head-on pass because the superior firepower of the eight .50 caliber guns on the P-47 “would take care of that”.