Thorp Air Command - T18.net

This is off a Grumman Cheetah/Tiger. Might have some clues as to Hoerner profile.

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Bob Highley
N711SH
SN 835
KLAL

Ah, I see the difference now in what I have. Thanks for posting

Has anyone built the Hoerner tips out of fiberglass? And if so how hard is the process? My tips are 40+ years old and the fiberglass is going bad so it might be time to replace the original tips with a new style.

Paul McMicheal in Seattle built a pair quite recently and he raved about the performance improvement.

There is a good article in one of the newsletters describing how to build them. It may have been written by John Evans, but I’m not sure.

I would be all over buying a set of Hoerner wing tips if anyone has a set. As far as me building them, that's too much for my current fiberglass skill level.

Cubes sells them .. there's also a great 'how to' out there ... I can probably track down the exact newsletter. If I had to guess it's in the '90s era.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

Didn't, think of Thorp Central. Well, I guess they will get some more of my money.

Don’t hesitate to spend money at Thorp Central!!!! We need TC to stay in business.

Our Hoerner tips are in the S18 profile. They would make a great start for someone who wanted them on a T18. All you would have to do is cut the splice about 1/3 of the way back, pull them down to the T18 profile, and reglass them.
For the T18, we stock the original profile tips.
Cubes

Tried to upload John Evens article but failed (maybe too big)
Author date was Sept. 2003 if it helps.

Here's a drop box link
https://www.dropbox.com/sh/o403ydna8v66 ... r6_Za?dl=0

Forgive my ignorance, but advantages of Hoerner on the T-18 are...?? According to https://www.aircraftspruce.com/catalog/ ... ngtips.php which is for C-150/172/etc:

Typical Improvements are:
• Increase cruise 3-6 mph
• Increase rate of climb 75-100 ft./min.
• Increase stability with more positive aileron control
• Decrease stall speed 4-5 mph
• Decrease distance for take-off
• Gives a modern, more aerodynamic profile

And according to https://www.eaa.org/eaa/news-and-public ... troduction --

"The result is a 5 percent improvement in cruise speed." (at least on a Sonerai, obviously much slower than our birds)

Does anyone have actual numbers/advantages -- meaning measured, real world, not theory -- for the T-18? Please convince me that I want them. Very intriguing!
(PS: My A&P would do all the modifying ("cut the splice about 1/3 of the way back, pull them down to the T18 profile, and reglass them"), fitting, painting, etc. I have zero ability in that regard, but he does.)

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Philip Mandel
N118BC
S/N 957
Beaverton OR

FWIW - here is a portion of an email I recently sent to a couple of other Thorp owners...

"There was no particular subjectivity in my testing of their performance. As I reported at the time I actually flew with one of the new and one of the original tips, with the new one on the left wing - the wing that normally was "heavy" with just me onboard, requiring a bit of the original roll trim (slightly lowering the position of that flap). Not only did I not need the trim, but I had to hold a considerable amount of left aileron pressure to compensate for what was obviously greater lift. It was surprising, right from lift-off, but increased as speed increased. Then I installed the other one and it was nicely balanced again. It's a little surprising and I have no explanation for it, but I saw no discernible difference in my full-throttle top speed - approximately 204 mph TAS at 7500' MSL. The biggest difference in handling was then during landing & especially when getting into ground effect... that extra lift was very obvious and I grew to like it a lot. I ended up lowering my approach/landing speeds quite a bit... seriously, about 10 mph.

Richard Eklund had a friend who was quite a good metal-worker - I don't recall his name, but you probably know who I'm talking about. He & Richard carefully studied and took careful measurements of my tips one year at OSH. He then proceeded to build a set out of metal. They were very well done and matched the fiberglass ones pretty closely, except for a more rounded outer edge. He sold that first set to my best friend and hangar-mate, Dean Cochran. Dean put just one on at first, and performed the same test that I had. He actually took a spring scale up with him and measured the force needed to hold that wing down & level. I don't recall what it was but it was considerable, and he documented it in the newsletters I believe. Richard's friend later built a second set for Richard's airplane, and he confirmed similar results."

I had enough Thorp time with the original design tips at the time to be able to make a good comparison of the new ones with my airplane. I can't attribute all of the decreased landing speed to the new tips, but they definitely made a very noticeable difference for me, making the landings more comfortable at those speeds. The level WOT speed referenced may have varied a couple of MPH one way or the other, but 204 is very close, with or without the "new" tips. 160 hp O-320-D2A and Aymar-Demuth prop.

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

That is seriously cool info, John. Thank you.

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Philip Mandel
N118BC
S/N 957
Beaverton OR

There is a series of videos on YouTube showing how to build Hoerner tips.... similar methods as what is described in the Newsletter article.

https://m.youtube.com/watch?v=sDHynvw9Ozo
https://m.youtube.com/watch?v=RoOh-fgI8oU
https://m.youtube.com/watch?v=ULhZchv7ito

D