Tuesday, January 7, 2014

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,

No comments:

Post a Comment