A3D/A-3 Skywarrior Vertical Fin Fold

I was recently asked for information on the A3D/A-3 Skywarrior vertical fin fold. Since that may be of interest to one or two others, here is a pretty good set of pictures and illustrations. First, an overall depiction.

The forward hinge location:

Crop of Bill Spidle photo

The small circle halfway between the hinge and the leading edge is the retracted end of the unlock indicator.

The aft hinge location:

Crop of Bill Spidle photo

An illustration of the fold joint:

Note that the upper (folding) and lower (fixed) sections of the fin are separated in the illustration; the upper section has to be moved right and down to be in the position relative to the lower section when it is attached. Also note that the lower end of the jury strut is not shown in the installed position in the inset photo.

A photo of the fold joint (the closeout of the upper section is primarily a shear web with two different types of stiffeners; the top of the lower section is mostly lightning holes as shown in the illustration above):

The triangle is also the forward hinge; the fold actuator attaches to the hole on the lower right side of the triangle.

The warning pin extended.

 Crop of Bill Spidle Photo

This pin appears to be extended when only the wings are folded as well.

The jury struts for the fin and wings (the fin strut folded for storage compactness).

The fin jury strut installed:

 Crop of Bill Spidle Photo

The location of the hole for the bottom end of the jury strut on the 20mm tail:

F4U Corsair Wire Antenna Alternatives

Dana Bell, Steve Eisenman, Don Fenton, David Hansen, Allan Peters, and Jim Sullivan have all provided comments and photos to me following the first appearance of this post, which I very much appreciate. However, as Steve noted, I've barely scratched the surface...

The high frequency communication radios in use at the start of World War II required a fairly long wire antenna. The XF4U had a mast forward of the cockpit on the upper right side of the fuselage; the wire antenna ran aft from the top of this mast to the top of the rudder, directly above the rudder hinge line so no slack or tension was introduced when the pilot pushed a rudder pedal. A lead-in wire was connected to the antenna about halfway along. The entry point to the radio was through a ceramic insulator on the right side of the fuselage just aft of the canopy when it was slid fully open. (This mid-run lead-in connection is known as a dipole.)

 In early production F4U-1s, the lead-in wire was attached to the far end of the antenna instead of halfway along it.

 The above is a VF-17 F4U-1 landing on Bunker Hill on 9 July 1943. The mast on the top of the fuselage behind the canopy was added after Corsair production began. I had thought it was for a VHF radio (which only required a short antenna) but I'm beginning to wonder if it was initially added for an alternative lead-in arrangement. (See F4U-2 discussion below.) For one thing, VHF appears to have only become available in 1943 for Navy fighters as the AN/ARC-1.

I had thought that the attachment at the top of rudder included a spring, but according to the 1941 Vought antenna installation drawing provided by Bill Spidel, the tensioner was actually a rubber cylinder, NAF 1086-1 (NAF stood for Naval Aircraft Factory).

This is an example of the antenna from the rudder to the fuselage entry point being connected to an insulated wire attached to the mast aft of the cockpit before going to the fuselage entry point.

Crop from Steve Eisenman Collection photo

I had thought that the Corsair's antenna in the picture above was slack because the forward mast had been removed for maintenance on the fuel cell, but Allan Peters pointed out that on this VMF-211  Corsair, a short mast mounted on the pitot on the left wing leading edge was substituted for the forward mast, which had been removed, either to increase speed or reportedly in the case of the F4U-2, to improve forward visibility.

The antenna was slack because the wing had been folded (by crane). Allan has noted this antenna arrangement on 17735 and 17883 in addition to 17818 shown above and at least a couple of VMF-321 Corsairs.

In the process of looking more closely at a picture of a VF-17 Corsair taken during squadron qualification aboard Bunker Hill in July 1943, I discovered that at least one of their F4U-1s had the pitot-mounted mast (and no forward fuselage mast) arrangement as well at the time (gray arrows added for emphasis).

The pitot-mounted mast is a little hard to see and the wire runs a little confusing (it looks like the lead-in to the fuselage is going back to the pitot mast) but in a high-resolution picture (National Archives 80-G- 78539 via Jim Sullivan), it's clear that it's the same as the one Allan Peters identified.

Allan provided this excellent picture of the pitot-mounted mast on a VMF-321 Corsair. The short thick segment in the antenna wire is probably a ceramic insulator. Note that is well away from the mast, indicative of the desire to have the wire antenna of a specific length to match the radio frequencies of most importance.

 Note that this is an early F4U-1 because it has the landing light and the vent (the little tube inboard of the light) for the fuel tank in the wing. However, it has the upper-cowl flap fix.

Another revelation was that early F4U-1s had an IFF (Identification Friend or Foe) antenna going from the outboard leading edge of the horizontal stabilizer to the fuselage on both sides. This doesn't show up well in any but fairly high resolution or closeup pictures. One side reportedly received the interrogation signal and the other transmitted the response. This particular system was developed by the British and first installed on Spitfires in early 1940.

(A ZB antenna was used with the YA transmitter on the aircraft carrier for homing back to it.)

For a discussion of this IFF antenna on the F4F see http://www.network54.com/Forum/149674/thread/1200071509/F4F-4+antennas+-+how+many-

Another picture of an antenna installed on an operational F4F in September 1942 is here: http://www.history.navy.mil/photos/images/g10000/g11103c.htm

Once you know where to look, it begins to show up more frequently on early F4U-1s.

Both of the pictures above were from the July 1943 VF-17 qualification aboard Bunker Hill and were provided by Jim Sullivan.

The wires from the stabilizer tips to the sides of the fuselage for the IFF were soon replaced by a simple short whip antenna.
 
Another alternative that eliminated the forward antenna mast was to originate the antenna on the tip of the right horizontal stabilizer. It is shown here on Ira Kepford's F4U-1A but it was typical on the F4U-2 night fighter. (Also note that this VF-17 F4U does not have the mast aft of the cockpit; it does, however, have a whip antenna in that location that is presumably for a VHF radio.)

 Crop from Steve Eisenman Collection photo

F4U-2 wire antenna (white arrows added for emphasis

Note the VHF whip antenna immediately behind the cockpit in place of the rigid mast. The fact that the rigid mast that had been added aft of the cockpit was not used leads me to wonder if it was not, at least originally, a VHF antenna per se. However, it is clear based on a NATC FG-1 and FG-1A evaluation test report that the mast aft of the canopy did in fact, at least by early 1944, serve as a VHF antenna.  The F4U-2s were modified at the Naval Aircraft Factory  from early production F4U-1s so it's possible that they got a different VHF antenna from the production standard during the modification process to add the radar installation. Moreover, the early mast appears to be identical in size and shape to the later VHF mast and the timing of its introduction is about right for the VF-17 at-sea qualification aboard Bunker Hill. (I don't know yet what to make of the fact that it was not originally installed on the FG-1 BuNo 13623 that was received by NATC for evaluation in March 1944—it was on FG-1A BuNo 14062 that they got in June 1944; perhaps there was a shortage to the production line.)

A variation on the HF antenna going between the stabilizer, rudder, and fuselage entry point was to route it rudder/stabilizer/fuselage.

Arrows added for emphasis to a crop of a photo provided by Jim Sullivan.

Dana Bell reported that the F4U-1 raised canopy, when opened, might short out the antenna at the lead in to the fuselage so the aft frame of the canopy was cutout to provide more clearance. This is an example on an F4U-1D in February 1945.

Crop from Steve Eisenman Collection photo

At least some of the Bunker Hill Corsairs were using the stabilizer origin with the forward antenna mast removed.

F4U-1D Essex 1945 (cropped from a picture provided by Jim Sullivan)

 The F4U-4 wire antenna lead-in to the fuselage was on the left side instead of the right side, possibly as a result of radio equipment relocation. (White arrows and circle added for emphasis)

Note the shorter forward antenna mast.

At some point, the attachment on the vertical tail was moved from the top of the rudder to the top of the vertical fin. Note the hook on the end of the rudder-mounted mast of the FG-1 and the much longer spring generally associated with the rudder attach point.

 David Hansen thinks that the wire entry on the left side of the fuselage and the attachment at the tip of the vertical fin began with late Goodyear production of FG-1Ds. For example, this is a postwar FG-1D in that configuration (note, however, that it has the much longer spring of the original rudder attachment and if you click on the picture, you can see that the canopy has the cutout for the original fuselage entry point just aft of the canopy on the right side of the fuselage).

 Crop from Steve Eisenman Collection photo

David notes, however, that it is impossible to distinguish between Goodyear and Vought-built Corsairs if you can't see the BuNo or designation, which was originally very small (see the picture immediately above this one for an example) until the practice began of locating them under the horizontal tail.

To reduce weight and drag, the 2,000th and subsequent F4U-4s were delivered without the forward mast and provisions for the medium high frequency radio installation. The antenna now ran from the fin to the top of that mast aft of the cockpit with the lead-in to the fuselage attached in between (black arrows added for emphasis). The survivors among the previous 1,999 -4s built were to be modified in accordance with Service Bulletin 215 dated 15 March 1945. (Thanks to Dana Bell for a copy of the Service Bulletin.)

On at least some F4U-5s, the wire antenna also originated at the top of the mast aft of the cockpit, went to the tip of the vertical fin, but then went back forward and down to an entry point on the right side of the fuselage (white arrows added for emphasis).

In others, the wire was configured like later -4's mid-run connection, only with the entry point again on the right side of the fuselage.

 Cropped from Steve Eisenman Collection Photo

However, later F4U-5s had a low-aspect-ratio antenna aft of the cockpit (and that ADF "football"). The wire antenna may have originated on one side of the fuselage and entered on the other.

Don Fenton added some detail to the F4U-4 and forward antenna discussion:

The AN/ARR-2 VHF homing antenna installed in the late-war F4U-4 used a retractable rod antenna. It was located on the underside of the fuselage at about station 208 and extended and retracted with a manual control on the right side of the fuselage just under the canopy track. The Pilot's Handbook for these aircraft advised the pilot to extend the antenna during flight only when actually using the function, "since it causes a certain definite, though small, loss in maximum speed (1 mph)". Removal of the much larger forward antenna mast may have led to a significant increase in maximum speed. And moving the antenna wire from a position above the canopy may have resulted in less breakage and hindrance to the pilot and crew when entering and exiting the cockpit.

More later as people send me new information,

Things Under Wings: Skyraider Outboard Wing Pylons

23 November 2025: With the help of Ed Barthelmes, I've retitled and revised with corrections and additions

The AD Skyraider had three different outboard wing pylons. The first was a simple rocket launcher:

The second was a direct substitute for the rocket launcher that allowed for up to 260-lb bombs and other stores to be loaded on it. The Mk 55 Bomb Rack was about 13 inches long and included sway braces.

Note that this AD-4 outboard wing panel has both types:

Note that the Mk 55 utilized the single-lug option to attach the bomb.

The AERO* 14A/B was subsequently developed that could be loaded with either a bomb (up to 500-lbs) or a rocket:

This picture illustrates the difference in the size of the Mk 55 and the AERO 14:

For the spacing of the AD's outboard wing pylons and details of the center line and inboard wing pylons, see https://tailhooktopics.blogspot.com/2015/07/douglas-ad-1-skyraider-pylons.html
 

*Note that strictly speaking, AERO should be all capital letters, since it is an acronym for Aircraft Equipment Reference Ordinal...

SB2C-4 SAC

F7F Tigercat Shell Ejection Ports

A question arose on a modeling web site about the location of the shell/clip ejection ports for the nose-mounted Grumman F7F .50 caliber machine guns. That turned out to be not very well documented. I also determined that because the narrow fuselage required that all four ammunition boxes be staggered, the pair of guns on the right side of the fuselage were located aft of the two on the left side, with the ejection ports positioned accordingly. (There was a longer blast tube on the right side so the ports in the nose were not staggered.)

Right side (XF7F-1 wind tunnel test)

Here is a better view of the location of the 20 mm cannon ports in the wing:

They appear to be pretty much in line with the barrels, maybe slightly outboard.

Left side (early F7F-1)

Note how much farther forward they are relative to the wing leading edge than those on the right side.

F2H-2 External Stores

F2H-2 Ordnance Options

1,540-lb maximum; some examples on the SAC:

Eight 100-lb bombs or five-inch rockets

Four 250-lb bombs

Two 500-lb bombs

Four 250-lb bombs and four five-inch rockets

Some bombs were darkish green olive drab. The bands were generally yellow. The fuse in the nose was unpainted metal.

Note that tail fins, which were stored separately from the bomb body, were generally pristine since any distortion from rough handling affected accuracy.

Rockets also varied in the shade of olive drab. Again, the fins were generally pristine.

  

Half-baked 1/72nd Grumman WF-2/E-1B Conversion

Hasegawa produced an excellent kit of the S2F-1 (S-2A Stoof) with the later aft engine nacelles. Unfortunately, all the modification kits to produce the rest of the family, the Trader (TF-1/C-1 COD) and the Tracer (WF-2/E-1B Fudd), relied on the same inaccurate three-view drawings. The major error was the planform view of the radome for the Tracer. As it turns out, the Fudd also had a greater wingspan and more dihedral in the outboard wing panels although most of the outer wing panel structure of the Stoof was retained.

For more, see http://tailspintopics.blogspot.com/2010/11/trader-and-tracer.html

Having bought a few Mach II kits and only finished one (the F2Y Seadart, which wasn't too bad actually), I decided to use the Falcon conversion that is still available as of this date.

It's probably best to ignore the wingspan and dihedral differences and simply sand of the external hinges, fill the old fold line, and redo it with the Grumman sto-wing panel. However, I decided to model the kit with the wings folded: then Fudd tended to ride on the tail wheel, which was changed from the Stuff to be free swiveling. That eliminated the need to put weight in the nose, always hard to find enough places to do so in a twin prop, and the increase in chord of the wing center section. Nevertheless, it still requires extension of the outboard wings to get the right interface with the vertical fins when the wings are folded.

 

I did the wingspan increase two different ways: one with a plug, to utilize the inboard end of the outboard wing that resulted from very carefully cutting the wing along the fold line; and the other by creating an extension of the inboard end of the outboard wing that matched the outboard end of the center wing section. The decision to do it two different ways was deliberate: I wanted to see which was a better choice from a modification standpoint. Unfortunately, if there is an advantage of one over the other, I've forgotten.

The stub fin needs to be cut down as shown.

 

I've forgotten exactly how I produced a new trailing edge for the radome but it wasn't a big deal. I correct things that are obviously wrong and easy to fix and don't bother correcting errors that are not obvious and hard to eliminate. The radome planform is the former. Basically I added a piece of sheet plastic with the right shape of the aft part of the radome between the upper and lower halves of the Falcon radome. Then I completed the shape with putty.

 

 

I think the depth of the belly needs to be fixed as well, another legacy of those inaccurate drawings, but I stalled out before I got there. All I was going to do was build a "egg crate" with two longitudinal beams and three or four transverse ones cut from sheet plastic with the right added depth and curvature and fill in the pockets with putty or Apoxie Sculpt. I subsequently discovered that the fuselage cross section was more different than I thought (see the blog post referenced above) but I'd still ignore that except for the size of the cockpit side windows.

I felt the need to add a small extension on the horizontal tail with a bit of sheet plastic. I can't remember why but it may have been needed to get the correct span for the stabilizer or the right mounting angle for the vertical fin. The vertical fins must have been pretty close because I don't see any notable modification.

 

If I remember correctly, the kit instructions would have you cut the kit nacelle off too far forward.

(Note that the front strut of the landing gear hasn't been glued in so the gear could be "retracted" to prevent damage during construction and painting.)

The bulkhead between the cockpit and the cabin also had to be corrected.

And then I got distracted or something...