Aileron Gap Seals
Posted: Fri Dec 17, 2021 8:52 am
by GraemeSmith
Anyone tried these? A search in the forum reveals discussion about a rudder gap seal - but I can’t see that anyone has tried them on ailerons. Or I can’t find the thread.
Seems to me that the underside gap of an aileron is a hunk of drag hanging out there under the wingtips.
In another thread Jeff Schultz makes an interesting point that the increased drag caused by the bigger gap under an up aileron will help counter adverse yaw. But didn’t indicate that this has been tested.
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Some measurements suggest the worst gap under a standard aileron deflected full up is in the order of 2 1/8".
Probably try it with stiff card duct taped in place to start with and if I think there is any benefit - move on to 3" Mylar gap seal sold for gliders if there seems to be any benefit.
I don’t think the “seals” will help with pressure differential. Like the doped fabric seal used on WWII Mustang ailerons where there was a true gap between the aileron and wing. The Sonex full length hinge seals the aileron fairly well. More likely the benefit would be better streamlining and less drag.
A concern is that if there IS an improvement in the load carrying characteristic of the wingTIP - this could have an effect on the spar - especially near the root where the leverage of the tip has most effect. To get a sense of this - I was thinking of fitting the wing with stick on foil strain gauges along the length of the spar to measure a before and after effect and see if this is significant.
Hoped for Benefits:
- Slight speed increase
- Improved roll rate
Potential Downsides:
- Higher loading on spar root.
- More adverse yaw
- If I was painted (which I am not) loss of paint.
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That would be back to Phase 1 as it involves a flight control surface modification.
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Anyone want to throw some popcorn at this before I try it?
Re: Aileron Gap Seals
Posted: Fri Dec 17, 2021 9:49 am
by bvolcko38
I’ve been thinking of doing the same thing. You’ll never see a glider with a big chunk unfaired like we have on all our control surfaces.
Re: Aileron Gap Seals
Posted: Fri Dec 17, 2021 9:53 pm
by Skippydiesel
Haven’t done it on a Sonex, however did on my previous aircraft ATEC Zephyr. (& will on Sonex) Cant quantify improvements but I like to think they were there.
Seal (very thin Teflon, if memory serves) consists of at least two parts.
Wider strip stuck (good quality exterior double sided tape) along trailing edge/under side side of wing. Between hinges
Narrow piece, as a wear strip/preventer, stuck under aileron upper skin where forward seal rubs
Previse aircraft - only practical to seal under side of hing line, which is on upper skin.
Always intended to do elevator & flaps - never got round to it. Rudder a nice tight fit, so little point.
My intention was to do elevator similar to ailerons. Flap was going to be an “internal” felt or brush seal.
I doubt that there was much speed advantage (may be some) main advantage low speed handling when wing at high angle of attack.
Re: Aileron Gap Seals
Posted: Sat Dec 18, 2021 11:30 am
by Bryan Cotton
Don’t forget this thread. It was tailfeathers, but the construction is the same.
viewtopic.php?f=5&t=4959
Re: Aileron Gap Seals
Posted: Sat Dec 18, 2021 3:42 pm
by karmarepair
I’ve been thinking along these lines, and just reviewed the Van’s Air Force forums. It doesn’t seem to be worth the effort on those airframes, but details on what was actually tried are lacking. Victor Bravo on the HBA forum notes that sailplanes ALWAYS have “wiper” seals on the gaps on the underside of the wings. Wheel pants (pressure recovery, and/or tightening up the gap between the tire and the pant) and cooling drag were the best bang for the buck/hour for drag reduction it seems.
I HATE the way my nosewheel fairing was installed by the original builder, it’s WAY too high up on the tire/wheel, and it’s going to get fixed once I get the airplane flying.
Eventually I’m going to switch to a top-mounted oil cooler as well and close the lower inlet completely.
Re: Aileron Gap Seals
Posted: Sun Dec 19, 2021 5:05 pm
by Skippydiesel
karmarepair wrote:I’ve been thinking along these lines, …
Eventually I’m going to switch to a top-mounted oil cooler as well and close the lower inlet completely.
Don’t forget/ignore - its as much about exit air (if not more) than inlet air
Re: Aileron Gap Seals
Posted: Mon Dec 20, 2021 4:24 am
by sonex1566
Hi everyone, I read the post before last regarding only relying on a top oil cooler. I did that originally on my Aerovee powered Sonex and suffered scary high oil temps that just wouldn’t go down unless I throttled right back and levelled off. I ended up cutting a small hole about 1"x 2" right in front of the oil pump and instantly dropped the oil temp by 20 degrees F. I ended up making a baffle to direct air around the sump and made the hole approx 1 1/2" x 3". I reckon that no matter what you need to have air flowing around the lower cases. I changed over to a Jabiru 3300 as I consume too many donuts.
Re: Aileron Gap Seals
Posted: Mon Dec 20, 2021 7:45 pm
by karmarepair
sonex1566 wrote:Hi everyone, I read the post before last regarding only relying on a top oil cooler. I did that originally on my Aerovee powered Sonex and suffered scary high oil temps that just wouldn’t go down unless I throttled right back and levelled off. I ended up cutting a small hole about 1"x 2" right in front of the oil pump and instantly dropped the oil temp by 20 degrees F. I ended up making a baffle to direct air around the sump and made the hole approx 1 1/2" x 3". I reckon that no matter what you need to have air flowing around the lower cases.
Where was the oil temperature sensor in this scenario?
Re: Aileron Gap Seals
Posted: Tue Dec 21, 2021 5:19 am
by sonex1566
I had the temp sensor fitted to the blanking plate on the L/H front cases facing forwards under the exhaust pipe. Initially the only air flowing over the lower cases was what leaked past the heads and cylinders. The coldest ambient temp that I’ve ever flown in is about 60 deg F and froze my butt off as well. I initially thought that a top mounted cooler would work better as it is in the fresh 'high pressure ’ area of the cowl, but it didn’t work for me on it’s own. I know that this has nothing to do with gap seals, sorry to go off sideways…again!