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#1
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Teflon gap seal tape...
I need to replace the flap/aileron gap seal tape on our LAK-17A. The
control surfaces are bottom hinged, and the gap was factory sealed on the bottom with what is apparently ordinary polyethylene tape. The tape cracks over the hinges, which I would have to patch periodically, plus it shrinks over time, limiting control movement and increasing stick forces. It seems like Teflon tape is the way to go. I poked around and found multiple online sources of 1" x 18 yard Teflon PFTE tape with high temperature silicone adhesive on one side, available in thicknesses from ..0035" (~$25/roll) to .0115" (~$75/roll). There are less readily available variations with acrylic adhesive, along with "High Density" PFTE (100% stretch instead of 300%). Does anyone have any idea what thickness and type of tape would be best for my needs? Thanks, Marc |
#2
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Look for teflon tape on this page
http://www.streifly.de/Price1-00.htm If you ask they will do you a complete kit, I'm on my third kit and haven't been disappointed yet, third glider in 4 years, LS7 Cirrus and Ventus cT |
#3
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Not sure that tape is the way to go, Mark. I have found that properly
installed Mylas is all that is necessary. Proof--------when the seals on my Nimbus 3 needed replacing, I eliminated the internal seals and also got rid of that ridiculous lower mylar that went inside the gap, never did understand the reasoning there. Replaced it with Mylar on top and bottom, nothing else. She climbed and cruised right with another Nimbus 3 with factory seals. Another data point..............The ASW-20 had a terrible reputation for dropping a wing and entering a spin, when they first came out.................then the spin problem seemed to go away, why? Most 20's today have Mylar, top & bottom. Was the external tape triggering separation at low speed? Something to think about, JJ |
#4
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#6
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Udo Rumpf wrote:
The edge of the Mylar tape .010" plus the edge tape .002" it should not effect turbulent flow. A gap, covered by a sealing tape could. The Mylar seal if it wipes it will seal. If you were to have difficulties with this a separate seal would be the way to go, as long as it does not interfere with The Mylar. Sometimes if the hinge is to close to the bottom surface it would be difficult to get a wiping action through all the motion of the flap and aileron. I hope I understood your question. Yes, it does answer my question. I suspect the best solution is that used by Bob Fidler on his LAK, use Teflon tape to act as both a flow seal and a wiping surface, then put a Mylar seal over it. Thanks to all, Marc |
#7
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the Mylar would seem to me to be every bit as likely to trip the airflow as the Teflon tape. Second, the point behind external tape (or internal seals) is to prevent airflow through the gap. Are properly fitted Mylar seals actually going to prevent this flow? Would it make sense to use Teflon tape to seal the gap, then put Mylar over the tape? Thanks, Marc I have seen it done this way (mylar & tape) Just have come to the conclusion it isn't necessary. I fit foam rubber in the flap well to seal any cross-flow at each end of flap and aileron, then the mylar comes over this area and prevents any air from entering. I believe the big bug-aboo with tape only is the leading edge starts to come loose and this = some real drag on that wing. JJ |
#8
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If I recall correctly, Dick Johnson tested Sam Fly's Ventus 2 with oil flow
and found that the mylar alone did not prevent cross flow from bottom to top. He removed the ailerons and installed S-seals and stopped the flow. As I further vaguely recall, this did only a little for the performance! There was considerable data scatter. Does anyone know of any hard data that shows, one way or the other, if the mylars are effective? Hartley Falbaum ASW27B "KF" USA wrote in message oups.com... the Mylar would seem to me to be every bit as likely to trip the airflow as the Teflon tape. Second, the point behind external tape (or internal seals) is to prevent airflow through the gap. Are properly fitted Mylar seals actually going to prevent this flow? Would it make sense to use Teflon tape to seal the gap, then put Mylar over the tape? Thanks, Marc I have seen it done this way (mylar & tape) Just have come to the conclusion it isn't necessary. I fit foam rubber in the flap well to seal any cross-flow at each end of flap and aileron, then the mylar comes over this area and prevents any air from entering. I believe the big bug-aboo with tape only is the leading edge starts to come loose and this = some real drag on that wing. JJ |
#9
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We tend to think that internal seals (and external tape) completely
eliminate any cross flow from the lower surface (hi pressure) to the upper surface (lo pressure), but does it? Look at both ends of your flaps or ailerons; The internal seal stops, so does the external tape. It must or you couldn't get full down flap and full up aileron, at the same time. The other end of these control surfaces are open also. What does this mean? Air can, and will move laterally along the control surface until it reaches the end and then move vertically and get to the upper surface. We have just experienced cross flow. The best we can do is slow it down as much as possible. I use properly fitted mylar on both surfaces and control surface wipers (felt) at both ends of the controls. Works for me. I also fill the flap/aileron well at each end with foam rubber in an attempt to stop this vertical movement of air. JJ |
#10
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I agree with J.J.
Make sure the edge of the tape wipes and makes contact at the bottom of the aileron when deflected. Install samples at discrete points to find out if you have the correct radius and position for the Mylar. Bottom hinged flap/aileron Mylar seal require a slightly different approach versus the top. Regards Udo "Marc Ramsey" wrote in message m... I need to replace the flap/aileron gap seal tape on our LAK-17A. The control surfaces are bottom hinged, and the gap was factory sealed on the bottom with what is apparently ordinary polyethylene tape. The tape cracks over the hinges, which I would have to patch periodically, plus it shrinks over time, limiting control movement and increasing stick forces. It seems like Teflon tape is the way to go. I poked around and found multiple online sources of 1" x 18 yard Teflon PFTE tape with high temperature silicone adhesive on one side, available in thicknesses from .0035" (~$25/roll) to .0115" (~$75/roll). There are less readily available variations with acrylic adhesive, along with "High Density" PFTE (100% stretch instead of 300%). Does anyone have any idea what thickness and type of tape would be best for my needs? Thanks, Marc |
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