Cuff , Ice/Frost and stuff.
Hi again. I would like to talk about the X-winds Leading Edge Cuff. First a little story. It was Christmas time and all of the relatives were visiting and the wife was preparing the ham to be cooked for dinner. As her husband was walking through the kitchen she chopped the end off of the ham and threw it in the trash and set the rest of the ham in the pan. Her husband saw the action and asked her why she threw away that good piece of ham. She answered ?because her mother used to do it?. He said, well she is here, lets ask her why. Her answer was ?because her mother used to do it?. So they decided to ask grandmother why she cut the end of the ham off. Her answer was ?because it wouldn?t fit into the pan otherwise?. With this in mind, I?m very sure that Crash?s friend had experienced a situation in which he believed that a frost covered cuff wouldn?t perform as well as a plain frosted wing. My experience and testing of the cuff has been contrary to that belief.
There has been a lot of input on this string that to me is long on book learning and short on logic. I will deal with ice first and then frost. First a definition of terms. Frost as dealt with here is 1/8? to ¼? thick. Sometimes as much ice as frost and spread evenly over the surface. I?m not talking about ½ ? hoar frost. Which can sometimes be roped down to the former. Ice is clear and spread evenly over all of the leading edge surfaces, including windows etc. Rime ice is another matter. I have never picked up rime in VFR conditions. But clear ice is common in VFR.
http://www.supercub.org/upload/burr/104.jpg
This is 1/8? of clear ice on a cuff. Notice that the ice is confined to just the small radius of the cuff and does not extend more than 1 5/8? up on the top contour of the cuff. This ice was picked up at cruise speed. A lower speed would have moved the ice to an area lower on the leading edge in accordance with the increased AOA. Even with the iced leading edge there is still more upper camber available to the relative wind than there would be with a stock leading edge. The flatter stock leading edge tends to build ice farther up the camber. The additional 1 ½? of chord provided by the cuff gives an additional ramp effect to the upper camber. In either case the V.G.?s located in this area tend to energize the relative wind going over the ramp area a great deal better than those mounted back at the spar where dis-attatchment is already taking place.
http://www.supercub.org/upload/burr/103.jpg
You can see the additional ramp area here, and the fact that the V.G.?s and ramp area are completely free of ice. For what it?s worth, getting on the ground before the ice melts and taking pictures of clear ice on a white airplane is a story in itself.
Another story. I stayed over at Teslin Lake on the way to Gulkana one year and the next morning we had major frost everywhere. The runway is on the side of the lake and is situated east and west. I unloaded the heavy junk out of the airplane and mounted the tripod and 35mm in the back seat area looking at the trailing edge of the right wing. Then after a warm up took off to the east and stayed low in the cold air. When over the center of the lake I climbed into warm air and into the rising sun. The effect of the water pouring off the wing into the rainbow was dramatic. And the lake provided a clean backdrop. Now I am not suggesting that ANYONE TAKE OFF WITH ANY FROST ON THEIR WINGS. If preheat is not available I usually go up light and clear the frost and warm the engine, then come back and load up and leave. I have tried to do stall tests with frosted wings, but the frost is usually gone by 200 feet so it has never panned out. On the other hand loading a Cub over gross, with frost on the wings and a short runway, would be non-habit forming in my opinion.
For those of you who feel obligated to preach me a sermon about my ideas, FORGET IT. I have already included a disclaimer, and in case you missed it, here it is again. I DON?T SUGGEST THAT ANYONE TAKE OFF IN A CUB WITH ANY FROST ON THE WINGS. Jerry.