1/72 Academy North American F-86F-2 Sabre

Project Gunval

by J.C. Bahr

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During the Korean War, due to increased structural strength being built into the jet fighters of the day, U.S. F-86A/E Sabre pilots were quick to discover that the U.S. standard armament of the .50 calibre machine gun with its fast rate of fire did not pack as much of a "punch" as it had against lighter built aircraft in World War II.  It took more hits in vital areas from a .50 to bring down a Mig-15, which in comparison, had two 23 mm and one 37 mm cannon and had been known to bring down a Sabre with just one round, whereas Sabre pilots fired approximately 1,000 rounds to down one out of every three Migs engaged!  The Mig was not without its own deficiencies though, as it's cannon armament had a slower rate of fire and the gun-sights were not as good as that found on the Sabre.  Other than their gunnery systems, they were basically comparable aircraft.

As pilots returned to the U.S. from Korea and imparted their experiences on higher command, it was decided that an evaluation was needed to improve and upgrade the Sabre both in armament and engine thrust.  In regards to engine thrust, pilots got their wish with the F-86F variant (and late E's), but were still saddled with the .50 cal machine guns.  By 1952 Project Gunval had been initiated to assess the armament situation and the Air Research and Development Command (ARDC) at Eglin AFB, Florida, was given this task.  Modifications were undertaken to fit four German-designed Mauser T-160 (M39) 20 mm cannons in place of the six .50 calibre machine guns.  The weapons bay had to be lengthened and widened to accept the weapons and new larger titanium gun blast panels with two cannon ports were manufactured.  Six F-86F-1's and four F-86E-10's were modified and reclassified as F-86F-2's.  Of these, eight were sent to Korea for combat evaluation and two were kept at Eglin AFB for further testing.

The Korean bound aircraft were attached to the 335th FS of the 4th FW at Kimpo Air Base and started flying combat testing in about February 1953.  A couple of initial problems arose quickly.  The first being that there were no tracer rounds with which the pilots could observe the trajectory of their rounds, which consisted of armor piercing-incendiary (API) and high energy-incendiary (HEI).  This was overcame by dipping the heads of the projectiles in a mixture of beeswax and kerosene that was allowed to harden and would give off a light smoke trail when fired.  The 2nd problem was with gun-gas ingestion causing compressor stalls and flameouts when the guns were fired at higher altitudes.  This lead to the loss of one aircraft during an early combat mission when the pilot could not get the engine to restart and had to eject over the Yellow Sea.  Many different tests and modifications were made trying to sort out the problem, including making holes at the back of the gun-bay panels to help purge gun gases, but this didn't totally fix the problem.  North American Aviation also devised a simple horse-shoe shaped deflector that could be welded into the gun-port troughs that would still allow the rounds to pass by, but deflected the gun gases out away from the aircraft.  This still didn't totally cure the problem though.  The pilots just had to be aware and take measures to try to avoid it by dropping the nose of the aircraft and flying out of it if they sensed a compressor stall coming on.

To conceal their Top-Secret mission, the Gunval aircraft were mixed in with flights of normal F-86's with standard call signs and tactics being used.  No special markings were painted on the aircraft and the cannons were not discussed over the radio.  To make them appear like the normal .50 cal armed birds, a "fake" gun-port was painted below the two 20 mm cannon ports.  Thankfully, of the two aircraft that were lost from the program, they were both ditched in the Yellow Sea... and of the two aircraft that got damaged in combat, they were able to make it back to Kimpo to be repaired... so none ever fell into Communist hands.

The project ended in May of 1953 after 307 combat sorties, in which Migs were sighted and engaged on 139 occasions.  41 Migs were fired on with hits being registered on 22.  6 were destroyed, 4 probably destroyed and 12 damaged, which was a higher percentage in comparison to their machine-gun armed brethren.  Even though the project seemed a success, 5th Air Force concluded that the modification was not suitable to combat due to the compressor stall/flame-out problems and the limited amount of ammunition that could be carried for the cannons.  Thus it was decided not to modify anymore Sabres as the standard F-model was deemed sufficient (due to its improved high-altitude capabilities) against the Migs at this late stage of the war.  The project did pave the way for heavier cannon armament to be introduced into future generations of U.S. fighters though.

One of these aircraft still survives today and is currently displayed at Buckley ANGB in Denver Colorado, in the markings of the Minute Men flight demonstration team:

http://www.airliners.net/photo/USA---Air/North-American-F-86F/0259757/M/

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I can't remember when it was that I first recall hearing about this little-known project, but I have always been fascinated with the concept as it sounded like a pretty good idea that may have had better success if it had been initiated earlier in the war and had more time to be fully developed, as it always seemed odd to me that even in World War II, the U.S. stuck with machine gun armament with the majority of its fighters, even though most of the other Allied and Axis countries had been arming their fighters with cannons.  (Interestingly, several of the U.S.'s top aces from WW II had flown the P-38 which had a 20 mm cannon... coincidence?)

I had always wanted to model one of these birds and like with many other projects in my back-log, was waiting for the right time for all my skills, technology, references, etc. to come together to allow it to be possible.

I chose to go with the Hobbycraft/Academy kit as the basis for this build (and all my other future Sabre builds) as they seem to be a little more commonly available than the Fujimi kit and have a few less parts that helps speed up the build process.  I would also highly recommend going for the Academy boxings, as I discovered that there's not much out there in the aftermarket in the way of all the stenciled type markings that are found on the Sabre and Academy has most of these included in their boxings.  They have also re-moulded a few places on the kit to help with construction and clarify some problem areas found in the original Hobbycraft boxings.

An area that I would recommend paying close attention to during the build is the intake ring.  The instructions have you attaching this after the fuselage halves and the intake trunking/cockpit have all been glued together, but this risks a bad fit between the intake trunking and the opening in the intake ring.  I found it better to glue the intake ring directly to the trunking BEFORE sandwiching the trunking and the cockpit between the fuselage halves... as it is easier to deal with the seams on the outside of the intake ring, than it is on the inside (where alignment is concerned), and helps with the alignment of the cockpit and trunking inside the fuselage.

In regards to accuracy, the fuel tanks and pylons do not appear to be very accurate for the birds that flew in Korea.  The pylon itself seems to be accurate as a Sabre pylon (seen in photographs), but this type was rarely seen in Korea.  They are moulded with the front of the pylon being angled, when most had this leading edge straight up and down vertically.  I fixed this with sheet styrene and cyano.  I then moved the pylon about 2 (maybe 3) mm's forward on the top of the tanks as they appeared to sit too far back on the tanks.  I also filled in the mounting holes on the underside of the wing and moved them back on the wing about 4 mm's each as the pylons were mounted too far forward on the wing.  The way they are out of the box, they would especially be a problem with the thinner chord wing of the E-models, as the pylon would interfere with the slats on those models, so they definitely do need to be moved back.  Many pictures that I poured over confirmed my suspicions and the finished kit looks much better now in my opinion.

Another small accuracy issue with these kits is the little wing fence on the leading edge of the 6-3 hard-wing as moulded out of the box... they're way too tall and incorrectly shaped.  Careful filing can help this.

For the Gunval modifications, I had to do a lot of careful filling of certain panel lines with cyano and re-scribing of the gun-bay panels and the gun-port panels.  To replicate the larger 20 mm cannon troughs, I used some plastic tubing from Evergreen.  I cut elongated holes in their approximate positions within the nose and got pre-cut sections of the tubing positioned in their approximate locations and then froze them there with cyano.  I went back and ground the tubing down as close to the fuselage surface as possible and then finished fairing them in with files and sand paper.  Once covered in paint they came out pretty good.  I also had to drill a few extra gun-gas purge holes as seen in photos of the Gunval aircraft.

Painting was done with Citadel Mithril Silver, Chainmail and Bolt-gun metal acrylics.  I also used Floquil Platinum Mist enamel and Model Master Chrome Silver enamel.

Marking this aircraft was a lot of fun.  Early on I had decided that I wanted to replicate two different aircraft, so decided to give this kit a split-personality.  The left side is of 51-2836 "Sweet Carol" flown by Capt. Lonnie Moore who scored 1.5 kills in this aircraft and the right side is of 51-2867 in which Lt. Col. George Jones scored a Mig kill in March of 1953 to become an ace and which also made him the 30th jet ace of the war.

I created the name "Sweet Carol" and the numbers and codes to be printed on my laser printer and I also printed the 1.5 star kill marks for Moore's side of the aircraft.  I had reservation about the quality of the red in the name and on the kill marks, but decided that they came out pretty good once I got them applied on the model.  Creating the codes and numbers was fun too, since I could not find any suitable fonts anywhere that matched to the type applied to Korean War Sabres.  Seeing as I have three other future Korean War Sabre projects, I just decided to create them all now, so that they would be ready when I decide to tackle those projects in the future.

The "fake" gun-port was even created on my laser printer and I wasn't sure if it would show up against the natural metal due to questionable opacity, but I think they came out pretty good and look the part.

The yellow/black I.D. bands came from an older Superscale sheet and were touched up with Model Master Blue Angel yellow acrylic as it was the only yellow I could find that came close to matching the yellow that Superscale used.  The rest of the markings are from the Academy kit and worked pretty well when used in hot water.

The last modification I made was to use a nose-wheel from an Airfix F-80C as pics of many of the Gunval Sabres show this kind of wheel instead of the finned wheel that comes in the Hobbycraft/Academy kits.  Since some of my F-80 projects will use the finned Sabre wheel, this was a good swap.

And there you have it, the beginnings of the big-gun Sabres!

J.C.

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Photos and text © by J.C. Bahr