Thorp Air Command - T18.net

I was looking over 'Feisty' the other day, and noticed the flaps are not up against the fuselage flap fairing.
In fact, they don't look fully retracted. The left flap roll trim is fully retracted.
Both flaps are just 'a bit' down.
Would you experienced guys talk about this?
I would like to know of any accumulated knowledge before I try retracting them to the wing profile.
Will it handle differently? will it go faster? will it fly with the nose higher? will it stall faster?
Inquiring minds and all that.

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Scott Emery
EAA Chapter 326
T-18 N18TE

I found it a challenge to get the flaps to fair full up . The problem I found with the S-18 is the AN bolts used to attach the rear folding wing fittings to the rear spar created a clearance problem. They would interfer with the flaps going "full up." Can't remember if the Standard T-18 used AN bolts on the rear spar ? I removed the bolts during the building process and replaced them with NAS Flush head screws . I also had to reposition a few of the flap hinges to get as much up travel as I could . The flaps now "hit" the back of the rear spar in the full up position. I did put a thin (PSA) chaff strip on the rear beam to help protect the flap from rubbing . Seems to be working . Not only was this a challenge , but also trying to mate the (2) S-18 flaps and keep the clearance to a mniumum with the rear spar . BOOM ! I am sure there are other ways to tackle this problem , but this was my route to success.

RB

This is a common problem. I originally tried the rear wing/fus filet and could not get a satifactory full up fit. I abandoned the filets.

One trick I have used is to make eccentric bushings for the flap hinges and rotate them around until the flaps fit full up while resting on the rear spar (with some teflon tape to stop chaffing). You should see better performance with the flaps full up. I doubt you see a difference in stall speed, but the wing will stall from the inboard out. giving better control at high alpha.

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Bob Highley
N711SH
SN 835
KLAL

Good idea about the bushings ! Yep I used the teflon tape as a rub strip . My main problem was getting all the Monkey motion to line up with the S-18 flaps ! Rear beam clearances, clearance between the two flaps and lining up the rear joint (I call it a swival joint) for the two flaps and having min. play and having them go to full up ! Not an easy process !

RB

I used a thin strip of silicone rubber foam to "seal" & cushion the leading edge of the flaps against the rear wing spar. You may find that you have a similiar rubber strip that may be thicker than it needs to be. I like Bob's idea of the eccentric bushings if you need to do that.

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John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

The teflon rub strip (PSA) will get you as close to the rear spar as you can get . I got mine from VAN's . Probably 1/32nd " thick ? If you are using the AN bolts for the S-18 wing then all bets are off . I believe the plans call for some type of "rubber" chaff strip between the rear spar and the leading edge of the flaps ? Been a while since I looked .

RB

I would dust off the plans and look to see exactly what the chord line looks like. Anything off the chord line is drag. I drew that line on all my ribs for the new plane. It makes it easier to see what is going on.
Cubes

Not sure if this even applies , but I put a straight edge along the bottom of the wing and along the bottom of the flaps to line them up flush to try and eliminate any drag . Flush = min. drag ? Best I could do with a BA degree in Liberal Arts ! BOOM !

RB

Another trick, from the newsletters, is to wrap a piece of string around the wing, with the two ends coming together at the trailing edge of the flap. Then you will REALLY see how well the flaps fair. BING.

So I'll look for the thickness of chafe strips & bolt heads, use string and a straight edge, and check the adjustment on the lever & mechanism.
BIFF!

_________________
Scott Emery
EAA Chapter 326
T-18 N18TE