RANS S-7 C-FDQL On SKIIS
(and the ULTIMATE tail ski)
This is a 92 model with 80hp 912.
Not sure who built the original skiis. They have an aluminum bottom riveted to bent aluminum angles down the sides with additional sheet where the pedestal sits and Lexan bottoms. Pedestal is a bit high (about 3” higher than where the 800 6 tires put the axles). I added the steel square tube diagonal to brace the tips. Front shock cords are from Princess auto. These skiis are not light at 30lbs each.
What I’m really excited about is the basin for a tail skii (also from Princess Auto). Some have commented on potential lack of directional control but I believe that is not an issue on skiis and what is more important is a shape that will allow the rudder to easily move the tail sideways. The basin shape will do this.
This particular plane can use an additional 20lbs at the tail to achieve the forward limit when solo. Even when fully loaded the cg with the tail weight is still ahead of the rear limit. The basin with lead weights is 21lbs but it displaces the 7.5lb tail wheel so it adds a net 13.5 lbs.
Before coming up with this solution, I was trying to figure a clean way to attach the extra weight to the tail and looked for awhile at my previous skii made from a shovel. To get lead on the shovel would have required melting and recasting it . I had not really been happy with the shovel skii anyway.
After the inverted U bracket that is bolted into the existing tail spring hole, the basin is held on with a 5/16 stainless pivot bolt and the 3/8 threaded rod at the front. Angles are 1x1 steel. Since the bowl is pretty thin stainless, I added the disc of plywood and a chunk of 2x6 to provide some vertical stiffness. The lip of the bowl has an additional plate of steel between the two angle iron attach bolts where the threaded rod attaches.
The angle of the top of the bowl in level flight is adjusted with the threaded rod. Because I was concerned about the leading edge of the bowl being too high when the tail is on the ground, I adjusted it for a couple of degrees down in level flight. However on the ground the flex of the tail spring lets it sit almost level so I’ll re-adjust it to sit level in flight.
For the first flight, snow conditions were the worst with lots of slush but performance was fine. Some slush did get into the bowl so I will eventually rivet covers on either side of the angles.
I’m fortunate that I can start and return to “dry” land in these conditions. Take off was to left; return from right. Steers fine.
Second run was on glare ice. While take off and landing were fine steering at slow speed was a problem due to ease of “ice-looping”. Needed more control at rear. So I added a 4” sharp runner under the bowl which totally stopped any looping tendancy but made turning at slow speeds an effort: had to lift the tail with full rudder and a burst of power. Next I’ll add a steerable runner.
Below is a picture of the steerable runner. The shaft is 5/8 mild steel rod but could have been much lighter tube. The runner is only a 2 ¼” piece of ¾” by .060 square tube cut in half and shaped. It rides on a plate of 1/8” HMD plastic. Beside this steerable unit is the previous fixed runner and a piece of plastic pipe I’d planned to use as a bearing but didn’t.
Today the lake is still quite icy but has an inch of snow covering. Slow speed steering was just excellent with a measured turning radius of about 32 feet. The final conditions for testing will be deep snow which I expect the Bowlski will handle just fine.
The next version will be made from this WOK giving us a WokSki which is smaller at 12” in diameter.
Here is the way the main skiis the were mounted on another Rans:
For more pictures of this installation see: Skiis
This is a site which has some ski rigging tips: Click