Bits and Pieces
How to Extend the Flying Season - An RV-8 on Penetration Skis!
By Patrick Gilligan,COPA Vice President of Operations
I started putting skis on my first Canadian kit plane back in the 1980s - a twin-engine 5.5 hp Lazair aircraft - before the word ultra-light existed and before Transport Canada required an ultra-light airplane registration or a pilot permit to fly them. I would ask a former instructor colleague from Richel’Air flying school, now working as inspector for Transport Canada, what was required to fly my Lazairs. I purchased two kits - s/n 10 & 11. My colleagues would respond “Get away from me, you’re crazy flying that Saran Wrap airplane!” I was often referred to as the ‘‘Saran Wrap’ pilot,” I put letters on the inverted V tail plane of my Lazairs “PAT1 & PAT2”.
The first winter I mounted an old pair of downhill skis to the wheels of my Lazair and had the best winter flying ever, just awesome! Transport Canada was about to implement new requirements for registrations and pilot permits so I opened my ultra-light flight school and was given the first ultra-light instructor pilot permit after I submitted my experience as a Class 2 instructor on certified aircraft and trained 42 students to fly on my Lazairs. The Quicksilver MXII was the next choice for my flight school, winter was approaching, and I needed skis to continue flight training. No manufacturer existed so I designed my own and this opened up a new market. I had the knowledge of what type of ultra-lights were flying in Canada because every ultra-light owner that ordered my registration letters, then my stainless steel identification plate, had sent a purchase order form. I sent out letters introducing my skis for ultra-lights and designed skis for over a dozen types of ultra-lights.
Twenty years later, in early winter, I broke a poorly designed fiberglass ski while taxiing through a small snow covered ditch. It cost me a bent landing gear, a cracked wing tip, a nicked prop blade and the fiberglass ski. This grounded me for the rest of the season. I was very disappointed with the quality of those skis and started researching how I could resolve the sturdiness and usefulness, the issue being that I could not fly when snow was insufficient or land on hard-surface, snow-cleared runways, and all the difficulties I encountered when hangaring the Kitfox with those fiberglass skis. After two years of research and sketching inspired by an old DC-3 on wheel-skis photo, I started on my new design; a combination of UHMW 3/8 inch thick sole, 3/4 inch Douglas Fir 7-ply plywood, and 4130 steel axle fittings.
I opted for penetration skis because flying time is reduced substantially during the dark winter months and I only needed them for safety reasons, and from time to time when conditions were appropriate for landing on snow covered fields, etc. The combination of a light Kitfox with 912 80-hp tailwheel configuration with my wheel-skis proved to be an ideal combination. As I gained confidence, I discovered that I could land in very deep snow and - to my surprise - the trade-off wheels/skis and cutouts did not produce too much drag. I kept this basic design on this latest pair for my RV-8.
My wheel-skis are made up of five parts and 22 stainless steel ¼-inch fasteners. The axle mount is ¼-inch wall rectangle tube aluminum extrusion. The ski shape is retained by two ¾-inch plywood formers and the sole is made of ½-inch UHMW sheet. I used an L-shaped design wheel cutout instead of my usual H shape used on my Kitfox because I could attach the skis on an additional axle installed opposite the wheel axles. Installation takes about five minutes, including attaching the limiting cables. I was not comfortable during test flights because I could not see my skis when sitting in the RV8, so I designed two mirrors attached to the leading edge of the wing to complete my flight test program.
My main concern was flutter. If a ski started fluttering at 140+ kts it could become catastrophic, so I doubled up all the limiting cables and bungee cords. A second benefit of having redundant bungees is that since I used 3/8-inch bungees, it was easy for me to detach the bungees when hangaring the aircraft.
Immediately after take-off: check the ski position. If not correctly positioned, keep airspeed at maximum of 80 kts and land as soon as possible.
Pre-landing: Check ski position. If improper, plan landing tail first on a hard packed surface, the front limiting cables are adjusted for bungee failure three point landing.
I install wheel-skis as additional safety in the event of engine or any other problems or weather. If caught in a snow squall, I can land safely. In an emergency, you should try to select the best snow conditions. In a precautionary landing, take your time to select an appropriate landing area like a straight away on a snowmobile trail. I have been flying on skis for more than 30 years and have learned a lot. Watch out for snow drifts - they may seem small, but touching down at 40 to 50 mph can flip the aircraft, or if they are hard they can cause much damage to the landing gear or even the fuselage.
Tailwheel ski or no tailwheel ski? If your aircraft is a lightweight on the tail you can probably go without, depending on the type of tailwheel gear. If heavy, I suggest a tailwheel ski; however, the tail wheel ski does not need to be a pivoting type. It can be steerable in a fixed positive position.
Wear pucks or wheels for gravel or asphalt runways? I opted for UHMW wear pucks because small wheels need to swivel or else they will skid, wear, or break while executing turns. Small wheels also make the skis heavier and more complex, plus they require more maintenance. Just change these wear pucks every 20 to 50 hours, pucks are made from the UHMW remnants. To see photos and videos and follow flight test progress, click here.