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...