Thorp Air Command - T18.net

Check out the lightning holes. Are they even safe???
I wonder if the center wing is made the same?

I think this is the same one listed on barnstormers just today and now its showing sold. asking price was $3500. If i recall, this is the one that came out of somebody's basement when he died and it has gone through a couple of different owners pretty quickly.

Bob,

It's a good thing you asked about those lightening holes. I hope someone can answer that for you, but it's probably not something anyone can simply say, yes or no. I have seen that style in books but not on a Thorp. It's definitely not per plans, so I'm sure you'll get the warning. This grabs my attention because I put lightening holes in mine and wonder now, how big is too big? Mine are the typical round ones with a 45 degree flange. Not per plans either, but I know it can be done to some degree and they're pretty handy for reaching inside. I won't do aerobatics, etc.

Books often show the typical steady state pressure distribution over a common airfoil, with a major part of it centered over the spar. Hence, that's how the spar got placed. But not so common is the redistribution of those loads with flaps deployed, or deflected ailerons. I almost forgot that. And the farther fore or aft such loads get from the spar, the greater moment they create. I can't give you an answer either, but these are some of the same thoughts I had to process. If anyone has rules for size I'd like to know.

It looks like those in the picture have flanges, which is important. If they were mine, I'd add a wide vertical channel across each opening, about mid-span, or close them off altogether to improve the strength. My guess is there is a way to get in and do it, even with pop rivets if you have too. Use plenty. If there's such a departure from plans you might look around for other things too. Not necessarily bad, this is experimental, right? The reason I chose the T-18 is that the plans have been well proven by those ahead of us.

Les Krumel,
Albuquerque

Les,

I talked to the gentleman that sold this T18. He said the inner wing has the same ribs. Somebody sure did a lot of work. I guess that is what JT ment by weakening holes.
He said he had a list of five names waiting to purchase this T18.

Bob MO