Kelly wing modification

[CRG]

Been a little quiet here, thought I'd start a thread on one of my latest projects. After losing my GR7 at Parker last year, Peter Goldsmith very generously gifted me his Kelly F1D fuselage, whose wing was broken beyond reasonable repair after hitting a runway light. I am planning a new wing for it, and it's underway but will be a while longer than expected so ended up getting a stock wing from Tom at Team Extra for it.

If I had any sense, I'd have just put some servos in it and could have been ready to fly in a weekend or so. But for some reason I can't leave stuff alone and decided to move the gear mounts outboard to a more scale location. At the very least the ground handling might be slightly improved, not sure if there's much aero benefit from having them in cleaner air. Will be using the gear from the GR which is a little more streamlined anyway.

Being a molded wing, moving the gear requires a little work, and a fair amount of hacking. This is the kind of job that I usually regret after starting, but then it's too late. Hopefully the result will be worth it.

[CRG]

First step is to mark out the gear pocket locations. Originally the gear legs are a little less than 9" from center, I moved them to 12.5" along a spanwise line paralleling the leading edge. You might notice from the pictures that the original pockets are not equidistant from the centerline.

I cut out the marked areas and inserted a pocket made from plywood. 1/8" ply base with 1/32" sides. This will give something to locate all the main structure to behind it.

[CRG]

Pictures showing cutout, pocket installed, and gear test fit. No magic to the box angle, it's just tangential to the chord line and the gear will be very close to level.

[CRG]

Now to gain access for new internal structure. There's not really any way to do this other than cut out a chunk of the upper skin. This will also allow removal of the old gear mount plate, saving some weight.

I marked out the upper skin and removed it. This goes quickly except where the skin is tied to the gear plate and lower skin, required some careful work with a carbide cutter and took quite a while.

I had to cut out the old pocket to get to the plate enough to cut it loose. The two square pieces on the spar face are where the original gear plate located. Through the top skin cutout you can see the new pocket in place.

[CRG]

A little more progress, got the gear plates made and installed. They're from 1/4" ply, get glued to the inside of the gear pocket, lower skin and spar face with a mixture of micro/cabo thickened resin.

The gap between the plates and upper skin will get filled with 2lb. blue foam, then closing the wing can be started.

[CRG]

Not part of the mod, but took a few hours this morning to cut the aileron covers loose and mount them. There are a few ways to do this, I didn't do anything too fancy and it turned out ok.

Unlike their GR-7, the Team Extra Kelly wing does not have a flange molded into the wing surface for the hatch to mount. Instead, an outline of the hatch is molded onto the wing. I cut the hatches free using a #15 razor saw blade, this gives maybe a slightly wider kerf than ideal but is acceptable. Using a shallow blade angle when cutting will help prevent delaminating the inner glass layer of the wing.

I then cut out a 1/8" lite ply frame to serve as the mounting flange. This protrudes into the opening 1/4" and has local hardpoints of 1/8" birch ply in the corners to receive the hold down screws. It gets CA'd to the inner skin.

The hatch/wing skin is a rohacell and glass sandwich and needs reinforcement in the corners for the screw hardpoints. For this I cut a slot in each corner and inserted a piece of 1/16" birch ply, glued in with CA.

The hatch and flange are then drilled, and the flange tapped for the 4-40 retaining screws. I use Philips head screws from Aircraft Spruce as they have a 100 deg. countersink. Allen head screws would be cooler looking but the only ones I can seem to find have an 82 deg. countersink, and tend to thin out the material too much, sometimes ending with the screw tearing through the material.

The servo will end up getting mounted to the inside of the hatch, with the arm protruding through the hatch and all the linkage external.

[CRG]

Here the foam has been installed between the upper skin and the gear plate, and the upper skin that was cut out reinstalled. To try and get it pretty close to flush with the surrounding wing I glued some hardwood sticks to the skin and the cut out and weighted them down. The ironing will have to wait a while...

[CRG]

Here's the same patch as shown above after sanding and a little filling. A bar sander was used to try and keep the profile in good shape, then I shot a quick coat of rattle can primer on it to get the color uniform and check for defects. Needs a little more work but turned out ok.

[paffy]

Very clean work !!

[CRG]

Thanks paffy.

[KennyMac]

Very nice work Craig....not many would make the effort. That will pay off in the long-run.

KMac

[CRG]

Here's the last step before the wing is back to it's normal state and it can be prepped for finishing. Patches for the original gear pockets were cut from a damaged wing, and potted in with a cabosil/micro mixture. Some minor filling and they'll be ready to go.