Tailhook Topics Drafts

Wednesday, January 10, 2018

The Grumman XF9F-9, Too Little, Too Soon

After the debacle of the XF10F Jaguar and the hasty conversion of the straight-wing F9F Panther to the swept-wing F9F Cougar, Grumman elected to propose the jet-powered equivalent of their F8F Bearcat to the Navy, encouraged to do so by BuAer's Fighter Class Desk. It was to be light, simple, inexpensive, maneuverable, and capable of near sonic speed in level flight without an afterburner. The engine selected was the Wright J65, a license-built British Armstrong Siddeley Sapphire that had also been selected to power the Navy's FJ-3 Fury and A4D Skyhawk. At the last moment, BuAer decided to add an afterburner in this instance.

Wright experienced difficulty in qualifying the afterburner so the first XF9F-9 made its first flight without one (it was subsequently redesignated F11F Tiger, since it bore no resemblance to its F9F Cougar forebear even in a dim light).

Like the Bearcat, it was relatively small and would have been wrapped snugly around its engine except that it was snugly wrapped with fuel tanks, not enough as it turned out.

Unfortunately, the F11F not only proved to be too small, lacking endurance, it was too soon, since the General Electric J79 then in development subsequently exceeded expectations as the afterburning Wright J65 was falling short of them. When evaluated with the J79, the F11F not only had terrific performance, it had somewhat better endurance. By then however, the Vought F8U Crusader had enough of a head start that the little Tiger became an also-ran.

A model of the first-flight prototype would be a relatively straight-forward conversion of a production F11F since most of the airframe was unchanged.
Note that the nose is even shorter than the original production F11F's but the wings, horizontal tail, and much of the fuselage is the same (the extreme aft fuselage has to be reshaped and shortened). Deletions include the wing fillet on the second production lot airplanes and the splitter plate ahead of the inlet (the inlet was offset from the fuselage, however). The vertical tail is smaller. Some other notable differences are the large pitot on the right side of the forward fuselage (it was subsequently moved to the vertical fin), the nose-landing-gear doors, the size of the wing fence, and the leading edge slat arrangement.

Wednesday, October 25, 2017

FJ-2/3 Nose Landing Gear

Warning: Probably more than you want to know!

First an overview of the nose landing gear from the side.
Note that the shock strut is angled slightly forward and the yoke is mounted in front side of it. The anti-torque scissors on the right side of the strut is angled somewhat aft. The Sword assembly illustration would have you mount the yoke on the bottom of the strut and have the scissors angle forward. Paul Boyer also noted that it would have you put the shimmy damper and the anti-torque scissors on the wrong sides.

This is a closeup of the interface between the strut and the yoke;
Craig Kaston photo

Note that there is a shimmy damper mounted on the left side of cylinder that the yoke is mounted under. It turns out that the yoke is free to rotate within that cylinder since it is basically a sleeve ( there is no nose-gear steering; the pilot steered during taxi and the first part of takeoff and the last part of landing with the brakes).
The shimmy damper does not turn with the nose wheel; it is connected to the yoke where it protrudes at the top of cylinder. What confused me at first looking at pictures of FJs in museums was that lever extending aft on the left side of the yoke. At first I assumed that the museum had left something off but I finally realized that the shiny cylinder at the end of that lever contacted some kind of "ramp" in the nose-wheel well as it was going into the well that turned the wheel 90 degrees so it lay flat under the inlet duct. (On the F-86 that was done with an actuator.) Presumably the shimmy damper provides a centering function when the landing gear is extended.

The line coming down from the wheel well to the bottom of the shock strut pressurizes it to raise the nose for a catapult takeoff. However, the actual routing, at least early on, is along the scissors as shown on this early production (a few were blue) FJ-2:

Here is a comparison of the "normal" strut extension and pressurized for a catapult launch:
However, the strut might be somewhat or fully extended at other times for various reasons.

The Sword nose landing gear strut appears to be too long. I assembled the three big pieces. I drilled an .080 hole in the cylinder in front of the strut and in the yoke to pin them together with a piece of wire since I think simply gluing them won't be sturdy enough.
It looks like I'll need to cut off that thicker section at the top of the strut and "flatten" the tire a bit to get closer to the right "sit". The yoke is also too long but shortening it looks like to much work.

Wednesday, October 18, 2017

Sword FJ-2 Preliminary

The accuracy of the planform of the new Sword 1/72 FJ-2 has come into question. This was my assessment, using a photo of the Sword FJ-2 wing provided by MVW (Martin) compared to my layout of the FJ-2 wing planform using NAA data for root and tip chords, wing span, and wing sweep at 25% chord. I had some difficulty in establishing the exact location of the trailing edge due to shadow.

In summary, the FJ-2 kit's wing appears to have a little too much wing span and about the right wing sweep depending on the exact location of the trailing edge, which needs some cleanup (and maybe thinning) anyway. Both the root and tip chords look a little too big but not as much as the 6-3's wing. All in all, I'd say its well within my tolerance for error.

Unfortunately, a review of the fuselage picture published by Sabrejet on Britmodeller  indicates a more significant problem. It is clearly somewhat long by 6 to 8 mm (1/4 inch). In checking the comment of another modeler who has the FJ-2 kit that the fuselage was actually slightly undersized relative to the published length, I noticed that the FJ-2 overall length including the extension of the stabilators aft of fuselage of 37' 7" is identical to the 1/72nd length of the kit fuselage from the tip of the nose to the tip of the fairing above the tail pipe. That may be the cause of the fuselage length error.

21 October Update: I now have all three kits in hand and they are lovely to behold.

The surfaces and panel lines are engraved and petite. All the detail parts such as the pitot look as close to scale as you can probably do in 1/72. I haven't checked the fit except for fuselage halves and the wings but so far, so good. The canopy is injection molded in two pieces and clear.

The FJ-2 fuselage and wing are not the same, correctly, as the FJ-3's. The FJ-3s have a slightly deeper inlet and forward lower fuselage and a different air scoop on the upper fuselage aft of the break. The FJ-3s have a cambered leading-edge wing that has a representation of the 6-3 planform change that differentiates it from the -2 and blue FJ-3s slatted wing, which were similar to the F-86E's and early F's. (Remarkably, the FJ-3 wings have three of the four barricade snaggers—these are teeny things in 1/72—on the leading edge of each wing, missing only the most outboard one.) They also have alternative rudders and horizontal stabilizers with the external ribbing on the trailing edge whereas the FJ-2 kit does not.

Both the FJ-2 and FJ-3 fuselages are a little less 1/4" too long. Theoretically you could take 1/8" out of the aft fuselage (but you can't do it at the break as I had hoped) and about 1/8" off the inlet. I'm for certain going to forget sectioning the aft fuselage. However, in my opinion, the downward curve in the top of the fuselage forward of the windscreen is incorrect (it needs to curve down more) and the bottom of the intake curves a bit forward and shouldn't.
There appears to be enough plastic in both places to get closer to what I think is correct. See http://tailspintopics.blogspot.com/2017/10/sword-172-north-american-fj-23-furies.html for one approach.

The only difference besides decals between the -3 and the -3M kits is that the latter has two Sidewinders and the requisite pylons. Both have the inflight refueling probe.

Getting enough weight in the nose to keep it from tail sitting might be interesting. A little scraping of the upper fuselage at the forward end of the windscreen appears to be required for a good fit. My guess is that putting the nose gear together (seven pieces!) might need to be altered from the instructions with respect to the location of the nose-wheel yoke, which may be too deep otherwise by a teeny bit. I'm pretty sure that the top of the nose gear door should be inside the forward end of the wheel well when it was extended.
More later...

Tuesday, October 17, 2017

VA-72 A4D-2

In response to a request...

Saturday, September 30, 2017

F8F-2P Propeller Hub

Note: The answer didn't take long - see comment below.

I recently took a close look at the propeller on this F8F-2P:

It appears to have an extension on the propeller hub. Moreover, the extension looks like a censored detail.

This same hub and appearance of censorship is on other -2P photos.

I did find one that showed the feature, uncensored or at least not painted white.
I didn't see this extension on hubs of F8F fighters in a quick survey of other photos.

The pod under the wing of the F8F-2P in the top photo is not a mystery. It contains a trimetrogon camera capability:

Wednesday, September 27, 2017

F8U Two-Position Wing

The F8U was one of the few production airplanes with a variable-incidence wing, with the wing raised for takeoff and landing to reduce the nose-highness of the fuselage for those flight conditions while still providing a wing angle-of-attack that maximized lift and therefore minimized takeoff and landing speed to meet carrier-basing limitations.

It was in part the result of Vought's experience with the F7U Cutlass and the Navy's dislike of its nose-high attitude on takeoff and landing. The F7U-3's radome, cockpit, and canopy had to be redesigned to provide adequate visibility over the nose before at-sea carrier landing qualification trials were authorized.
When Vought proposed what was to become the F8U, the need for low drag for maximum speed restricted the height of the canopy. The height of the landing gear, particularly the nose gear, was also to be minimized for various reasons, including weight reduction and to avoid problems experienced with the F7U's long nose landing gear. However, these two design stipulations were difficult to accommodate with the longer aft fuselage of a conventional tailed airplane with an afterburner.

The two side views in the following illustration are to the same scale with the main landing gear wheels and static ground line (approximately the landing attitude relative to the deck) coinciding. Note that the aft fuselage of the F8U would strike the deck with the nose raised only a little over five degrees.
The result was the incorporation of a two-position wing to allow for both adequate visibility over the nose for carrier landings and aft-fuselage clearance on touchdown.

Thursday, September 14, 2017

F4U-4 Lancer II Reno Air Races

Once upon a time, I was the pit crew on F4U-4 BuNo 97259 at the 1967 Reno Air Races. When I say "the" pit crew, I was it. The rest of the team were the co-owners, Gene Akers and Mac Mendoza. Gene was the pilot and Mac was the head (and only) mechanic.

When I met them, N6667 was parked behind a hangar at Fox Field, Lancaster, California and I was working as a McDonnell flight test engineer at Edwards AFB.

It had come a long way from its disposal by the Navy, circa 1960.

June 1957

I volunteered to be their pit crew at Reno for room and board that year. It was a shoestring operation, including the first paint job.

If you look closely at this picture, you'll see that the right tire is missing.  Another Corsair arrived with a failing engine and the pilot blew a tire when he landed. We loaned it to his crew to get him off the runway.

 Basically, all we did was fill the oil and check the gas between races. Gene and Mac were there with their wives and went to bed early. I went into Reno with some of the other crews.
A couple of mornings I made a functional check of the oxygen system in a vain attempt to accelerate the end of a hangover.

This picture was taken 22 September 1967. I'm at the left wheel, ready to pull the chocks.

For the 1968 race (I wasn't there; I had gone back east to graduate school), Gene and Mac found a sponsor to give it a real paint job.
Several years ago, I looked up Mac and asked him what color it was. He didn't remember, other than it was a "bright green" that was picked from color chips at the aircraft paint shop they took it to.

More later...