The Last Propeller-Pulled Corsairs: F4U-5/AU-1/F4U-7

17 February 2024: Bill Spidle, my go-to subject-expert for Vought aircraft, has provided me with a scan of the Vought dimensioned F4U-7 general arrangement drawing that states its overall length was the same as that of the F4U-5/-6 (AU-1)/-7. There has been some confusion about that because the Vought Heritage website (https://www.vought.org/index.html) lists different lengths in feet for the F4U-5/-6( AU-1)/-7

F4U-5 33.5
AU-1  34.1
F4U-7 34.5

The -5 length is clearly incorrect because that would make it shorter than the F4U-4. On the Vought-produced SAC along the waterline, it is 414.15 inches or 34.5 feet (the 33.5 may simply be a typo).

According to the AU-1 SAC, the length listed is correct when taken parallel to the ground with the airplane parked.

Along the waterline, it is exactly the same length as the F4U-5.

Bill Spidle came up with a scan of Vought's dimensioned drawing of the F4U-7. It's overall length, 414.15 inches (not including the tail light that makes it 0.906 inches longer) is identical to that of the F4U-5 and AU-1.

Aft of the firewall, the F4U-5/6 (AU-1)/7 were essentially identical in size and shape to the late production F4U'4 with the raised canopy. They were also very similar to each other forward of the firewall except for changes to the cowl ring, cowl flaps, exhausts, and wing-root inlets dictated by their different R-2800 engine installations. As noted above, all had the same overall length, 9.9 inches longer than the F4U-4 (for modeler's notes on the F4U-4, see http://tailspintopics.blogspot.com/2014/03/f4u-4-modelers-notes.html).

A free downloadable copy of the 1948 Chance Vought F4U-5 brochure is available here: https://aviationarchives.blogspot.com/2018/05/chance-vought-f4u-5-brochure.html

For additional information, see the books recommended in this post: http://tailspintopics.blogspot.com/2011/06/brief-f4u-corsair-oriented-history-of.html

As a hedge against the failure of its transition to carrier-based jets or delays in their availability, the U.S. Navy contracted with Vought for yet another variant of the Corsair, the F4U-5.

The major change was the engine, the Pratt & Whitney R-2800-32W with dual side-mounted, automatically controlled auxiliary stage superchargers. It developed 2,300 horsepower at sea level for takeoff. The combat rating with water injection (from a 28-gallon tank) was 2,700 horsepower at sea level.

The following illustrations are is an overlay of the F4U-5 SAC drawing on the F4U-4 SAC drawing. The installation of the -32W resulted in the most notable changes. First, because of the added length of the auxiliary superchargers and the horsepower increase it was located about 10 inches farther forward and mounted at a nose-down angle of 2.75 degrees. The upper side of the cowling was refaired to take advantage of the downward tilt of the thrust line and therefore provide the same over-the-nose visibility.

Second, the F4U-4's chin inlet was deleted in favor of two cheek inlets at four and eight o'clock (not depicted on this front view) that provided air to the auxiliary stage superchargers aft of the engine. That resulted in the bottom of the cowling curving upward. The ducts between the inlet and the supercharger required a widening of the lower corners of the cowling so it had an pear-shape and flatter bottom when viewed from the front.

 The basic shape of the fuselage from the firewall aft was unchanged.

 Forward of the firewall, the cowling was wider, with a slight but perceptible outward kink in the fuselage at the side of the firewall.

The configuration of the cowl flaps and exhaust collector was also different due to the presence of the ducts between the cheek inlets and the auxiliary air superchargers. The exhaust indentation on the side of the fuselage was located higher than on the F4U-4 (note that there were variations in the exhaust stack configuration). The cowl flaps no longer extended down the entire side of the fuselage. Instead they ended about halfway down and the bottom cowl flaps were reinstated that had been eliminated on the F4U-4. There were fewer turning vanes in the wing root inlet.

Note the structure supporting the lower cowl flaps.

The propeller was slightly different, primarily thinner (not narrower) tips.

The arresting hook was no longer hydraulically raised and lowered. It simply dropped when released. After landing, a hook man had to manually raise it to a park position for taxi, which was somewhat lower than its latched-up position. When the pilot raised the landing gear after the next takeoff, it was raised to a latched-up position by the retracting tail wheel.

Other changes were the replacement of the fabric on the outboard wing panel with sheet metal and the addition of an avionics compartment access door on the right side of the fuselage aft of the pilot's seat.

A 2,000-lb capacity center-line pylon was added between the two center wing section pylons. The armament was basically the same as the F4U-4B: four 20 mm cannon and eight rocket pylons (Mark 9 Mod 3). Spring tabs were provided on the elevator and rudder controls for lower stick and rudder forces. The catapult hooks were relocated slightly forward and the arresting hook shank was beefed up for the higher gross weight.

Pilot access to the cockpit was improved over the -4's by adding a telescoping step below the folding step in the side of the fuselage (it is extended in the photo above). These were actuated by a cable connected to the tail wheel but could also be closed and opened by deck personnel. The seat was a bucket type with folding arm rests. The center console was eliminated below the instrument panel to allow the pilot to stretch his legs on long flight. The manual hydraulic pump was deleted in favor of an electrically driven auxiliary hydraulic pump. There were some detail changes from the -4, e.g. the arresting-hook and wing-fold controls were moved to the right side of the cockpit. The top of the canopy was raised similar to the late production -4s, with a fairing added to the top of the turtle deck aft of the cockpit. The gun sight was one of the first lead-computing designs, the Mark 6 Mod 0 gunfire control system (with a Mark 8 gun sight) that also incorporated rocket aiming capability.

The F4U-5 was produced in three flavors: basic -5 fighter; -5N night fighter with an autopilot, Mk 20 illuminated sight, and a radar pod on the right wing; and -5P photo-reconnaissance with camera ports on both sides and the belly as well as a small fairing on the fin leading edge for the relocated compass transmitter.

In addition to the radar pod, the F4U-5N external features were a glare shield over the upper engine exhaust stacks, which were all fitted with flame suppressors as well; flash suppressors on the cannon barrels; and additional antennas. A gun-camera light/flash guard was sometimes added.

This F4U-5N has also been equipped with the wing and empennage deicing boots.

The F4U-5P was equipped with three camera ports, one on each side and one on the belly. They were fitted with sliding covers:

A hatch was also added to the turtle deck (with a folding ladder that was stowed in the top of the compartment) for access to the cameras:

The most noticeable external feature, unique to the -5P, was a bulge on the vertical fin that housed the remote-sensing compass.

 One of three different cameras could be loaded in the camera bay. The pilot would select which viewing port it would rotate to and take photographs from.

The AU-1 was a Corsair tailored for Marine Corps close-air support, provided to them as a placeholder in lieu of AD Skyraiders. (Also see http://thanlont.blogspot.com/2009/03/f4u-corsair.html.)

Originally designated the F4U-6, it was a minimal modification of the F4U-5 optimized for low-altitude performance, incorporating increased protection from flak and small arms fire, and providing more stores options. Since it did not need high-altitude capability, the big auxiliary stage superchargers were removed with the installation of a R-2800-83WA with single-stage supercharging. A new cowl ring without cheek inlets was installed but the pear-shaped cowling remained since the F4U-5 tooling was used. The oil coolers were turned 90 degrees and moved inboard.

Armor was added to the underside of the fuselage and the cockpit.

Because the oil coolers had been moved into the fuselage, there were only turning vanes in the air inlet in the wing leading edge and no oil cooler vent flap behind the inlet under the wing. For some reason, possibly to reduce the glare from the exhaust stacks at night that had been a shortcoming of the -5, the exhaust indentation on the side of the fuselage was located lower than the F4U-5's (this was possible because the ducting between the -5's chin inlets and superchargers had been removed). The cowl flap configuration remained the same.

Five multi-purpose pylons were provided on each outboard wing panel in place of the four rocket pylons of the -4/5.

The wing center-section pylons were subsequently increased to carry 2,000 lb stores.

Finally, the French need some new fighters for their aircraft carriers that were too small to operate jets. Since the Corsair was the best candidate, the AU-1 configuration then in production was adapted for the mission and designated the F4U-7. Note that the armament on the outboard wing panel is identical to the AU's.

Note that the tail hook is in the "park" position. See the French AU-1 picture below for the "latch" position. 

The major difference was the need for a high-altitude capability, which was provided by installing a two-stage supercharged R-2800 engine, reportedly from surplus F4U-4 inventory. However, the forward fuselage was the same as the AU-1's with the exception that a new cowl ring was incorporated that had a chin inlet to supply air to an F4U-7-unique oil-cooler installation.

The bottom of the cowling aft of the cowl ring was slightly lower than the F4U-5/AU-1's to provide room under the engine for the duct between the chin inlet and the oil cooler.

 Vought Drawing via Bill Spidle

Note the beginning of the cowling bulge at the firewall that was common to the F4U-5/AU-1/F4U-7.

 Photo via Jim Sullivan

Like the AU-1 wing root inlet, the F4U-7's only contained turning vanes (and no oil cooler vent flap) but in a different configuration because of the different utilization of the air. This is my current guess at its configuration.

Since it was built using F4U-5/AU-1 tooling, and this is an important distinction, the lower forward fuselage remained pear-shaped up to and including the aft side of the cowl ring. The exhaust stack indentation on the side of the fuselage was the same as the AU-1's.

There is understandably some confusion about the detailed differences between the AU-1 and F4U-7 configuration. For one thing, the French were provided with some USMC AU-1s straight from Korea. As a result, there are blue French-marked Corsairs that are not F4U-7s but AU-1s, the main external difference being the lack of a chin inlet.

 AU-1 129391 14 Flotille Cuers NAB 17 March 1964 via Jim Sullivan

Another is that the Corsair marked as a USMC VMA-212 AU-1, including BuNo, at the USS Alabama Battleship Memorial Park in Mobile, Alabama was actually a former French F4U-7;  the -7 cowl was subsequently replaced with an AU-1's, which still left miscellaneous antennas as configuration anomalies. It is now on display at the San Diego Air & Space Museum, again as an AU-1.

And the French F4U-7 war bird featured in a walk-around photo collection here: http://www.arcair.com/awa01/601-700/awa689-Corsair-Salaun/00.shtm is reportedly a converted F4U-5N. Its authentic cowl (note the bulge and chin inlet) reportedly came from the F4U-7 that was on display at Mobile, Alabama.

More later...