This month Aaron worked on finishing the various custom drain and vent lines unique to the Christmas tree tank equipped P-47s. Work also continued on the systems inside the wings. The fitted skins were removed to prepare for permanent riveting.
Finally, we’ll look into a few features of the P-47’s that are pretty unique to the big fighter.
Aaron has finished the main installation of the radio system. He continues work on wiring and hydraulic systems, including some custom routing of tubing for the Christmas tree tank. Another system he is installing is the oil cooling control system.
Whenever aluminum skin sections are made and eventually riveted on, they must be fitted, drilled, removed, holes deburred and sometimes chamfered, and finally refitted and riveted in place permanently. This month the skins are mostly off and are gradually being riveted in place permanently.
One of the problems engineers had to solve for high altitude fighters like the P-47 was a tendency for guns to become inoperative in the cold air at high altitudes. Lubricants became too thick, any moisture present would freeze; and the result was guns that didn’t fire or fired unreliably. To solve cold related problems the answer is, of course, heat.
The turbosupercharger system made heating the guns with hot air tapped from the exhaust a relatively simple engineering solution.
The Erection and Maintenance Instructions for P-47 Aircraft , page 351 describes the system and the changes that were made as later series Thunderbolts evolved:
“1) The gun bay is heated by hot air tapped off the exhaust manifold tail pipe shrouds at a point just forward of spar 2 of the wings. The air is carried through metal ducts to the gun bay. Systems independent, except for the control knob, are used for each side of the airplane.
2) Flow of this hot air is controlled by a damper in each duct, located at the point where air is taken from the exhaust shrouds. These dampers extend into the shrouds when open and act as scoops to aid the pressure differential which prevails during flight in maintaining a flow from the shrouds to the gun bays. These dampers are normally open and held by spring pressure. They can be closed and locked by means of tension cables working in flexible casings which run to a control knob located near the trim tab control at the left side of the cockpit. This knob is pulled and turned clockwise to lock the dampers closed.
3) The gun bay heat control assembly was not included in P-47D-15 through P-47D-30 airplanes. On these airplanes the duct dampers are spring loaded to the open position so a constant supply of heat is provided.
4) P-47D-20 and subsequent P-47 airplanes have an additional duct to supply heat to the outboard gun. On P-47D series airplanes, this consists of a separate duct which picks up heat as it enters the gun bay and directs it to the outboard gun. On P-47N airplanes, a “Y” is included in the heating duct; one branch directing heat to the inboard side of the gun bay and the other branch directing heat to the outboard gun.”
This system is a stark contrast to the P-51 and many other fighters which used electrical gun heat systems as shown in these diagrams from the P-51 Parts manual:
Another difference between the Mustang and Thunderbolt is how the oil temperature was controlled. On a P-47, an oil temperature regulator is controlled manually via electrical switches. From the Pilot Flight Operating Instructions for the P-47:
“Oil COOLERS.—- Two oil coolers are installed , one on each side of the lower part of the engine compartment. Adjustable split doors are located in the exit ducts and are electrically operated and controlled from the cockpit by a switch.”
The oil temperature regulator switch location varied, some P-47s had it on the main switch panel, but our D-23 had it mounted near the shutter indicator on the left side of the cockpit.
In contrast to the manually controlled oil temperature regulating system on the P-47, the P-51 had a more automated system.
Oil temperature on a P-51 was controlled automatically by an electric actuator for the oil radiator air outlet flap. The control is on the radiator control panel and has 4 positions OFF, CLOSE, AUTOMATIC, and OPEN. In normal operation, the switch was left in AUTOMATIC and a thermostat automatically starts and stops the actuator to move the oil radiator air outlet flaps. Only if the automatic feature fails and an abnormal temperature is indicated is it necessary to control the flap manually by changing switch positions between OPEN and CLOSED.