We've tried many materials, designs, and rigging variations over the years, in search of a simple, low drag, RELIABLE method for mounting skis on an RC plane. We long since gave up on the cable / spring / rubber band systems you may read about elswhere, as they would all fail sooner or later when being used in the real world. The Torque Rod mounting system has proven to be consistantly more reliable and results in a cleaner, lower drag installation. These skis incorporate the design refinements from several years of our combined winter flying experience, for NO-COMPROMISE ski performance.
If you are really serious about winter flying, a TAIL DRAGGER setup is by far the best way to go. Many local fliers have converted several trike gear trainers into fine snow fliers by changing the gear, possibly adding additional tail surface area for better ground handling authority, and removing some of the excess down thrust in the engine mount. The SIG LT-40 in particular, among others, can be converted into a fine snow flier when converted to a tail dragger.
Nose skis are also possible, using the same TORQUE ROD alignment/mounting system for the casual winter flier, so you can try snow flying with your trike gear plane without getting into more elaborate modifications. Just be aware that the typical trike gear plane is at a disadvantage on softer / deeper snow, due to being set up with 40% of the plane's weight on the nose ski / wheel, and having to deal with prop clearance issues. Acceptable performance on packed snow is possible. For getting out and having downright irreverent fun in deeper, softer snow, a tail dragger setup is the direction most will want to go!
The key to long term, low maintenance reliability of the ski mounting / alignment system is in having a RIGID AXLE which can not rotate in flight. For those of you who are fond of bent aluminum or molded composite landing gear, carefully drilling and installing a locating pin or screw through the gear leg into the axle assembly is advised; at a minimum, get a good pair of toothed lock washers, and lock the axle in place well, adding thin CyA glue as insurance against axle rotation. Landings get ugly when a ski tip decides to point at the ground - ( not to mention the destabilizing effect on the aircraft in the air! )
The main ski body needs to be formed into shape, a step that is the main touchy detail in building your own. I had made special clamps to keep the skis accurately shaped while drying; immersing just the front 3" in boiling water for several minutes allows them to be formed. The 3 ply "Baltic Birch" plywood which I've been using for the past 3 years has proven to form well and produce strong, resilient skis in all sizes. The spring steel torque wires need to be bent as shown, and silver soldered into the blocks with 2% to 4% silver solder. (We tried drilling wheel colars in the past for this application, but they didn't allow enough deph for a strong joint for long term rough handling; we're currently using 5/16" square brass bar stock (or steel key stock) for the blocks, and 8-32x1/4" Allen Head Cap Screws to firmly lock them onto your axles.)
(Electric fliers, who are always weight conscious, should be able to achieve excellent results with 3/32" birch ply on 05 size planes.
Assembly of the kits is very straight forward once you've shaped and formed the parts, requiring only sanding paper/ blocks, glue, a drill, and a couple of drill bits. You should have your set ready for finishing in under an hour if you use CyA glues; I use Medium and thin in assembling all of mine, and they hold together very well.
A fuelproof paint is recommended after finish sanding the assembled skis. Light or clear finishes are highly recomended, as they do not have nearly as much problems soaking up heat from the sun and resulting icing of the bottoms. (Aluminum skis are especially bad in this respect; tried that, too...) These wood skis look great with a clear gloss Polyurethane varnish, which is comonly available in aerosol cans. I've recently had excellent results with the "Red Devil" brand, purchased at the local WAL-MART. Allow at least 24 hours final drying time after the last coat at 70 degrees F before getting them out in the snow, and they should slide well!
Use the "40 size" ( 3" wide by 14" long) skis on planes from 4# to 7#, you average 25, 40, & light 60 size planes.
Use the "60 size" (4" wide by 15" long) skis on planes from 7# to 12#.
GIANT SCALE? I'm flying 6" wide by 15-1/2" long skis on my 17# Duster, with torque blocks with 1/8" music wire made to lock onto 3/16" axles. Mount Spines are wider / heavier, but the ski body still works well at 1/8" thick, made from Birch plywood.
If you'd like to read the SKI SETUP text file which is included in the ski kits, partially revised 12-4-97SKISETUP.TXT you can click on this link, then print the file, or save the file for later browsing. (It's only 7K, ascii text format; nothing fancy .) I hope this information will help some of you have a more enjoyable winter flying experience! Come fly with us at Lake Dillon if you're in the area!
Go to the WINTER FLYING Photo Essay