Corsair Information | Airframe | Engine Section
Engine Section Description
Nose Cowl | Cowl Panels | Cowl Support Frame | Cowl Flaps | Diaphragms | Engine Mount Ring | Engine Mount Support Lugs | Engine Mount Structure | Engine Mount Spigots | Exhaust Collector | Air Induction System | Oil Tank
The engine section extends from the nose of the airplane to the firewall at Station 91 3/4 (Fig 126). For the purpose of repair the following items will be considered: the engine mount, cowling, wing gap covers, circumferential channel, diaphragms, exhaust collectors, the ducts of the air induction system, and the oil tank. The materials used in the engine section include welded steel tubing for the engine mount, alclad sheet for the cowling, portions of the wing gap covers and the circumferential channel, stainless steel for the diaphragms, the exhaust collectors and the remainder of the wing gap covers 52SO aluminum alloy sheet for the air induction system ducts and oil tank. There are two major sections of circumferential cowling, the engine cowling enclosing the engine and the accessory compartment cowling enclosing the engine mount and air induction system.
The engine section is accessible by removal of the cowl panels.
Nose Cowl - Engine Section
A distinguishing feature of the F4U-4, the intake scoop for engine auxiliary air, is located in the lower half of the nose cowl (Fig 127). The nose cowl consists in general of an outer and inner formed sheet metal skin, longitudinal former ribs, and a circumferential trailing edge channel. The outer formed skin of alclad material is constructed in several sections and is riveted and spotwelded together. Reinforcing strips are riveted to the lip of the cowl for stiffening purposes. Other reinforcing strips are riveted to the cowl skin and form a base for the longitudinal ribs. The complete nose cowl assembly is attached to brackets on the engine rocker housing by bolts and forged links through the attachment plates on the ribs.
Skin - Nose Cowl: (Fig 127) The nose cowl skin is fabricated of 24ST and 52SO alclad sheet. Eleven sections of formed sheet are spliced together to form the outer skin assembly. The skin sections are butted together and riveted through splice pieces. Four sections of liner constructed of .032 alclad sheet rest against the inner rib flanges. Two stiffeners reinforce the outer skin below the air inlet.
Ribs - Nose Cowl: The nose cowl is reinforced longitudinally by eighteen former ribs. The ribs are stiffened with flanged lightening holes and beads. They extend from the leading edge of the nose cowl to the circumferential channel and from inner to outer skins. The structure below the air inlet is reinforced with stiffeners only which are spotwelded to the skin.
Circumferential Channel: The circumferential channel is constructed in three parts which are riveted together, an upper section and two lower sections, one above and one below the air inlet opening. The channel located under the air inlet is reinforced by an inner channel. (Fig 127)
Dzus spring fasteners, installed on the aft portion of the circumferential channel, secure cowl panels. The forward portion of the circumferential channel is riveted to the nose cowl skin.
Cowl Panels - Engine Section
The engine section cowling is divided into two general sections: the engine cowl panels which are located between the nose cowl and the cowl flaps, and the accessory compartment cowl panels which extend from the diaphragm at Station 58.031 to the firewall. (Fig 126) and (Fig 131)
The engine cowl panels are attached to the nose cowl channel and to the cowl flap support frame with Dzus fasteners. There are five alclad panels: a right hand and a left hand upper panel, two intermediate or side panels, and a bottom panel, of which the auxiliary stage air duct is an integral part. The bottom panel skin is reinforced with stiffeners; the other engine cowl panels are reinforced with an inner pan skin. A neoprene seal attaches to an alclad support which extends laterally across the inside of each panel. The aft edges of the engine cowling are scalloped at each cowl flap division. The cowl panels are attached to each other by means of key and fastener assembles.
The accessory compartment cowling consists of seven separate cured panels; a right and left upper panel, a right and left upper win gap panel, a right and left lower wing gap panel and the hinge intercooler flap. These panels are fabricated of alclad sheet and stainless steel. In addition to the reinforced pan construction, channels stiffen the edges of the upper and lower wing gap covers. With the exception of the splice between the two top panels, Camloc fasteners are used throughout for attachment.
Cowl Support Frame - Engine Section
The cowl support frame is located at Station 40.094, and consists in general of an upper channel, riveted on each side and through a short splice channel to two lower channels. one lower channel is located against the skin and stops at the bottom panel air duct, and the other lower channel passes over the air duct. (Fig 133) The lower channels are reinforced by eight diagonal channel pieces. The cowl support frame is further reinforced at the top by two angles to which the uppermost "dead" cowl flap attaches and at the bottom panel air duct by additional channels, angle pieces and gussets The frame is attached to the aft rocker boxes on the engine.
Cowl Flaps - Engine Section
The cowl flaps are constructed of .040 gauge, 24ST alclad outer skin, reinforced by a spot welded inner pan of the same material. (Fig 134) There are ten movable cowl flaps extending around the engine section just forward of the diaphragm and actuated through a cable assembly by a single hydraulic strut. They are supported by the cowl support frame. An eleventh, battened-own or "dead" cowl flap is located at the top center of the cowl flap ring. The aft portion of the "dead" cowl flap is reinforced by a stiffener; longitudinal edge stiffening is provided by angle pieces on which the adjacent movable flaps rest.
The inner and outer diaphragms are made of stainless steel and are bolted to the engine mount ring. (Fig 135). Camloc collars and Dzus fastener springs are installed in the channel on the outside perimeter of the outer diaphragm for the attachment of the accessory compartment cowling.
Diaphragms - Engine Section
The inner and outer diaphragms are made of stainless steel sheet and are bolted to the engine mount ring. (Fig 135) Camloc collars and Dzus fastener springs are installed in the channel on the outside perimeter of the outer diaphragm for the attachment of the accessory compartment cowling.
Skins-Diaphragms: The outer diaphragm is fabricated of 18-8 stainless steel sheet AN-QQ-S-757, with a tensile strength of 80,000 psi. It consists of five separate skin sections which butt together, one upper section, a right and a left intermediate section, and a right and left lower section. The upper and intermediate sections are attached through splice plates which are bolted to the upper section and spotwelded to the intermediate sections. The two lower sections are spotwelded to a splicing channel. Stiffening from inner to outer edge is provided by ten bead plates. The two rectangular air duct cutouts located in the lower sections are reinforced by channels on the left side.
The inner diaphragm is constructed of three, irregularly shaped, 18-8, AN-QQ-772 stainless steel sections having a tensile strength of 80,000 psi. These sections are attached to splicing channels with rivets and screws. A stainless steel stiffener is spotwelded to the aft side of the lower portion of the diaphragm.
Channels-Diaphragm: The outer diaphragm is reinforced by channels at its inner and outer perimeter. Six sections of ring channel are spotwelded to the inner edge. Eight sections of spotwelded and riveted channel form the outer circumferential reinforcement. The two cutouts located in the lower portion of the diaphragm are reinforced by channel pieces.
A slender spotwelded channel piece stiffens the upper right hand portion of the inner diaphragm where a number of cutouts occur in a limited area. The three skin sections of the inner diaphragm are spliced with channel pieces, which are attached with screws and rivets.
Engine Mount Ring - Engine Section
The engine mount ring which is 33 ¾ inches in diameter, consists of a steel tube to which six mount fittings are welded to provide engine attachment points. It is fabricated of 2 ¼ inch diameter, .095 gage, SAE 4130, AN-WW-T-850 steel tube, having a tensile strength of 95,000 psi. It is permissible to use N.E. 8630 steel tubing, Specification AN-T-15, as an alternate for SAE 4130. At the top center of the
engine mount ring a steel bushing is inserted through the tube and welded into place. The bushing acts as a hoisting point.
Engine Mount Support Lugs - Engine Section
Each of the six engine mount support lugs consists of a front and a rear portion welded to the engine support ring. The rear lug is drilled through to provide one attachment point to the adapter fitting. The front lug has two tapped bosses into which bolts are screwed through the adapter fitting to complete the three-point attachment to the engine. The lugs are machined forgings, fabricated of SAE 4130,
AN-QQ-S-684 steel with a tensile strength of 90,000 psi.
Engine Mount Structure - Engine Section
The tubular steel framework and the reinforcing gussets of the engine mount structure are welded together and to the engine mount ring. (Fig 136) Fabricated of SAE 4130 steel tube, AN-WW-T-850 and having a tensile strength of 90,000 psi, the engine mount structure attaches to the fuselage through four heavy welded fittings. It is permissible to use N.E. 8630 steel tubing, Specification AN-T-15 as an
alternate for SAE 4130. The two upper fittings are bolted to the ends of the upper longerons through fittings on the firewall, and the lower engine mount fittings are bolted to fittings located on the center section main beam at the end of the lower longerons.
Four spigots are press-fitted into the upper and lower engine mount sockets. The spigots are made from heat treated 4130 steel bar material and have a minimum tensile strength of 150,000 psi.
Exhaust Collector - Engine Section
The exhaust collector consists of two upper sections, two intermediate sections and two lower sections. (Fig 137) The upper and intermediate right and left hand sections are attached through two spot welded brackets. The exhaust collector assembly is fabricate of formed an welded 18-8 stainless steel sheet, AN-QQ-S-757, of varying gauges. Each of the eighteen cylinders has its own exhaust port to which the exhaust collector tubes are fastened through nipple assemblies by three Boots nuts. The front cylinder, however, have short stacks fastened to their exhaust ports which extend back between the rear cylinders an telescope into the exhaust collector tubes.
Air Induction System - Engine Section
The air induction system provides air to the engine through the two wing leading edge air intakes, and through the nose cowl inlet. It consists of the nose cowl inlet, bottom panel duct, supercharger entrance duct, intercooler exit ducts, intermediate ducts, carburetor air box, carburetor, supercharger exit ducts and intercooler entrances.
The ducts are fabricated generally of 52SO aluminum alloy material Specification 47-A-11, having a tensile strength of 31,000 psi.
The supercharger entrance ducts are constructed in two halves, butt-welded together. They connect the bottom panel duct with the supercharger. The forward ends of the ducts fit against cutouts in the outer diaphragm.
The intermediate ducts attach to the carburetor air box and to the intercooler exit ducts. Each intermediate duct consists of two welded aluminum alloy sheets and is attached to adjacent ducts by clamp and rubber hose connections.
Each intercooler exit duct attaches to the intermediate duct and to the bottom of the intercooler, and consists of four shell sections which are welded together. The flange through which each is bolted to the intercooler is welded to the rest of the duct.
The carburetor air box is a forked duct which attaches to the intermediate ducts and is bolted to the carburetor. It consists of three sections of heavy aluminum alloy sheet welded together. The carburetor air ox has one sheet metal vane welded to each leg.
The supercharger exit ducts are short sections which connect the intercooler entrance ducts with the supercharger. They consist of a duct welded to a flange. The flange is bolted to a matching flange on the supercharger and the duct connects through rubber hose and clamp to the intercooler entrance duct.
The intercooler air entrance ducts connect the intercoolers with the supercharger exit ducts. The left intercooler duct is distinguished from the right by the splice in its middle. The upper and lower sections consist of several burr-welded sections of aluminum sheet, and a flange which bolts to the top of the intercooler. Vane assemblies are riveted to both upper and lower sections of the left hand duct. The right hand intercooler entrance duct consists of a mounting flange which bolts to the intercooler, and an inner and an outer shell, burr-welded together. Both intercooler entrance ducts have welded handles.
Oil Tank - Engine Section
The oil tank is located in the top of the accessory compartment just forward of the firewall. The tank consists of three shell sections of welded 52SO aluminum alloy, Specification 47-A-11. (Fig 140)
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