Thorp Air Command - T18.net

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Forum Administrator

Jeeez, even with 2 model A engine blocks, a weekend of cloths, shampoo tub/toiletries, full fuel, a case of 24 beers and a no small healthy cook, you can still do gentleman aerobatics!!!

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Fraser MacPhee
N926WM
Serial #279-1
Angel Fire, NM (KAXX)

All you girly men start to gray out at 2.5 G's...especially those wearing kilts ! [:X] If you are not G tolerant (when was the last time you pulled 6 G's ?), then I would stick to the Transport Cat. G limits. Nice data to keep as reference on the Thorp interest page or the data page ?

Keep the turn coming

RB

As I understand it, the S18 wing has even higher limit load factors. The center section is shorter, making it inherently stronger. I read somewhere that the outboard panels and outboard attach points were stressed at 6g X 1500 lbs., or greater.

But, it was not widely publicized, either because there are fewer S18's, because the fuselage and fuselage attach points were not beefed up, or just to remain conservative in design. I'm sure there's enough historical knowledge on this site to say whether increasing the Aerobatic "G" limit to 1500# on a properly built S18 (no play in the attach points) is "foolish" or "maybe OK." For example, on T18/S18's that have been overstressed in flight, where did the damage occur?

Can someone shed some light on this?

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Rich Woodcock
N114RW - T18CW

You are correct. The "C" wing was designed to for aerobatic limits +6.0 -3.0 at 1500 lbs. This was done simply due to the fact that T-18's emerged as a little more complex (thus heavier) then John Thorp intended. In order the keep the GW at 1250 you needed to fly solo with minimal fuel. With this in mind, part of Lu Sunderland's design criteria for the new wing was to up the gross weight at aerobatic limits. I don't think this was kept under wraps at all. We do not have a break down at increased gross weights for the C wing available though (to my knowledge).

As far as where a T-18 bends when stressed out. I have first hand knowledge of this as my airplane had been overstressed at one point in time. It happens at the 525 frame, you can tell by looking for buckles in the skin right above the spar.

I of course have pics of the damage and repair ...

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

Lee,
Thanks, for both the clarification and photos. That's clear. The wing is not the weakest point, in either a T18 or S18. Do you know if John Thorp and Lou Sunderland felt the fuselage was sufficiently strong to handle 6 g's at 1500 lbs.?

As to revised load limits with weight, the math isn't difficult - "G" loading for an S18 wing would be:
Wt. +Lim. -Lim.
1500 6.00 -3.00
1600 5.63 -2.81
1800 5.00 -2.50
2000 4.50 -2.25
2200 4.09 -2.05

Of course, FAA Standard Limits are +6/-3 Aerobatic (meets 1500#), +4.4/-2.2 Utility (meets at 2045#), and +3.8/-1.5 Normal (meets at 2368#).

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Rich Woodcock
N114RW - T18CW