Tim,

I find it helpful to draw centerlines (with a thin sharpie) everywhere on the cores when building - root, tip, LE, TE, top and bottom as well as draw the cutout template directly onto the core. The centerline on the top and bottom in this case is the retract strut centerline or the mid point between the rails (spars). I also draw lines parallel to the root (perpendicular to the stub spars) indicating the wheel center and the gear rotation axis. These lines extend beyond the stub spars (about 4" long in your case) on either side so that I can track the locations once the core has been cutout. The distance between these two lines in a standard configuration is 4". In your case, I believe you've added 1" to this distance to accomodate the larger prop. In making this spacing 5" (rotation axis to wheel center), I would leave the wheel center fixed per plans and move the gear outboard an additional inch.

The stub spars help to encapsule the retract plate structure as well as provide strength to the wing in this area where core material has been removed. Because I'd rather err on the safe side (especially on models this size), I went one step further and bonded CF spars 24" long atop the stub spars and extending toward the tip of the core. The third strip which goes on top of the core between these two acts a bit like a truss to prevent the wing from folding in high G forces when the model is either upright or inverted. I'm probably repeating myself here...

When you say "glue the landing gear onto the rails" I think you might mean "glue the landing gear plate between the rails" - does that make sense? The nice thing about having the stub spars in place is that the inner dimension provides you with the 3" spacing between them (in your case since you're using 2.5" wheels). Your retract plate can be cut to 3" x 4" and the U-shape cutout made to accomodate the width of the gear. Again, I also draw centerlines and so forth on the plate to make sure I'm matching the core lines. Without guides, its easy to misalign something which would make for wonky landings or takeoffs.

I would go about the cutout/install in the following order: spars, plate, wheel well, gear tunnel, strut tunnel. In your case, the gear and strut tunnel is probably the same width so there is only one continuous tunnel. The extra width in the strut tunnel provides space for the strut coil and makes it easier to line. When making the shallow 1/4" cutout for the plate, be careful to not overshoot - if you're using a hotwire, it's very easy to do so. One way to prevent this is to make the hot wire 5/16" deep by bending some flanges into the wire that sit atop your template. The wire then runs along the template (1/16" thick I would imagine) only removing foam to the depth required. If you're dexterous controlling the heat and have a light hold on the gun, you can freehand it. Actually, in order to keep the edges square, I find it helpful to first make incisions in the core with a #11 (or longer blade) to the required depth along the cutout edge. The gun will then actually melt the foam up to this incision even if kept a 1/4" away from it. I find this is the critical part of building foam wings. If your hand drops or the gun slips, you can end up with a nice swath burned out of your core!

Your generous 1/2" around the wheel (when retracted) will allow you to line the well (and tunnel), if desired, first with 1/16" balsa before skinning and then with 1/64" ply after skinning. Lining with ply after skinning flush with the sheeting top has the effect of sealing the 1/16" balsa sheeting edge around the well cutout. Both layers aren't needed but the laminate makes for a more durable well and the ply takes paint a little better. Some modelers actually glass their wells but I'm not as patient.

Attached are a couple of shots of the cores prior to skinning. The offset cutout in the gear plate (and strut tunnel) is due to the off center location of the strut entering the Kraft multicons. Pneumatics typically have the struts centered on the retract body. I also placed the aileron servo "pockets" just outboard of the gear plate - the only reasonable location I could think of. The groove in the wing core top below the forward spar is the servo lead tunnel. My apologies if all these descriptions are overkill.

David.