Model Airplane News: How to Install landing gear in a foam wing

Model Airplane News, Aug 1998 by Morrow, Les

There are many ways to install landing gear in foam wings, and most work pretty well. If you aren't careful, though, overzealous bracing can add a lot of weight. It also seems that if something is easy to install, it just doesn't last very long.

Over the years, my son and I have built and flown warbird racers and have sometimes had trouble keeping gear mounts in the wing, especially with the finished weights of the aircraft we race. We tried all the methods we had read or heard about and have had limited success installing conventional landing gear in WW II single-engine fighters, but occasionally, a landing-gear mount would loosen or fail on a lessthan-perfect landing. We tried various ways to securely mount the gear and still keep the weight reasonable, and we figured out a foolproof installation that's secure, light and compact, easy to install and will take all the abuse we hand it (short of an all-out crash). If you're interested in a landing-gear mount that will take lots of abuse, will still function correctly landing after landing and doesn't weigh as much as the engine, keep reading.

The first thing to do is make 1/4-inchthick birch aircraft plywood landinggear plates to fit your retracts. The plates need to be bigger than the gear assembly by about 3/4 to 1 inch all around. After you make the plates, temporarily mount the gear to each plate so you can fit the plate into the foam wing-core (before sheeting) and align the rake, castor, retraction angle and position of the gear on the wing.

Mark the wing-core and carefully remove foam as needed to clear the wheel, strut, gear retract mechanism and mounting plate.

After the proper amount of foam has been removed and you are satisfied with the position, rake, castor, etc., take the core to your saw and cut two 1/8-inchwide slots from the leading edge of the wing, chordwise, to approximately 1/2 inch past the hole you made for the mount. Make a cut on each end of the mount. I know; it looks as if the wing is going to fall apart, but trust me; it will all work out. Now take a sheet of 1/s-inch birch aircraft ply (three-ply minimum; five-ply is better) and slide it as far as you can into the slot you just cut. Next, draw around the core on the plywood (you're marking a landing-gear rib that will fit the wing profile exactly). After you've drawn around one plywood rib, slide the gear mount (minus the retract unit) in place tightly against the 1/8-inch ply, then draw a line on the plywood rib to mark where to cut a slot to insert the mount into the rib. Remove the new rib and gear mount, then repeat for the other end of the mount. When you've finished, do the same thing for the other wing.

Cut out your plywood ribs, check the fit of all parts and epoxy the entire landing-gear mount assembly into the wing with 5-minute epoxy. Tape it into place and set it aside until it has dried.

When the glue has dried, check the position of the plywood ribs and sand them flush with the foam wing surface, if needed. You probably won't need much sanding, if any, assuming you did a good job of test-fitting the assembly on the bench before inserting it into the wing.

After you place the other controls, e.g., the pushrods and aileron/flap bellcranks, in the wing, prepare the wing for sheeting as per your favorite method. Sheet the bottom surface of the wing-core first so you can see where to make the wheel well and strut cutouts. If you're a purist, prepare a wheel-well liner of thin balsa, 1/64-inch ply, or something similar. Because we race our warbirds around pylons with other aircraft on the same course, and the potential for a midair is always present, we just sand the foam wheel well carefully, coat it with epoxy, then prime and paint. This method works well and is quick and light. Once you've finished the cutouts for the wheels, struts and retracts, finish sheeting the wing as usual, attach your leading and trailing edges, and sand to finish. After the wing is finished and the gear has been installed, build and paint gear doors and retract covers to match your documentation and color scheme and attach them using your favorite method.

This may sound somewhat complicated, but study the photos carefully. You will find this method is quicker than reading this article, and the mount assembly will be strong enough to outlast the airplane. You'll never go back to your old way of mounting retracts once you find how light, easy and strong this method is; we sure haven't!

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