Thorp Air Command - T18.net

I saw this recently and thought it was worth passing along.

This is a shot of the fuselage skin on a Thorp. A good reminder for the builders and or re-builders out there to deburr those holes (everywhere!) and make sure those skins are tight. One would not think the fuselage skin works enough to develop cracks like this but it does (look at an in-flight pic of a T-18 and notice the side skins). This particular airplane had diagonal stringers added in between the fuselage bulkheads to mend oil-canning. I can only assume that it was bad enough initially to cause this.




Note: the braizer head rivets were added in response to the cracks.




Note: Here the braizer head rivets here tie into the stringers that were added to mend oil-canning.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

I would assume at a certain point it would become a structural matter with this much cracking ? Not an engineer, just asking.

RB

Indeed RB,

On this particular airplane these the cracking was isolated to the two spots pictured above.

A few things going for the airplane ..

1.) The overall workmanship is quite good, much above par.
2.) It has a new owner is going down for a serious going over right now where I'm sure these areas will be addressed.
3.) The guy doing the "going over" will be mentored by one of our best. (hint ... it's going to IL)

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

On my initial first glance it appears to me that the added stringer in the bottom pic does not tie in to the bulkhead, just butts up, thus the skin carries the load between then. A little piece of angle can fix that. It does look like it has oil canned in several places. Do you suppose that just the oil canning is what cracked the bottom edge in the other pic? I agree that it has the potential to be a really nice plane though I have to question your assesment of the mentor. Thanks for your help so far.

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David Read
Olney, Illinois
N718DR

Yeah that's what I thought too, not sure why he went to the trouble of installing those stringers and not going to the trouble of drilling out a couple of bulkhead rivets and tying it together. While we're at it, why didn't he dimple the stringers? In my opinion the stringers give it a little character, they're straight and in a way look like they could have been per-plans (see pic .. look at the "second WL-42") ... I like the airplane although I'm getting a bit envious of you guys up there. Olney, IL is quickly becoming T-18 central!!

I know your modesty is genuine but we've all seen your airplane and work, and so have the EAA judges ... my friend, you do great work!

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

Before "we" were smart enough to rivet the 42 stringers to the side skins while flat, we would see a lot of ill fitting side skins. This would lead to gaps and bulges between the the skin and the stringer. The bottom angle and the 1" angle that runs on top of the wing channel still need to be formed a bit for a good fit.

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Bob Highley
N711SH
SN 835
KLAL

Just chiming in with my .02 cents here.

Recently had a helicopter return from contracted maintenance with 2 cracked ribs and vertical fin with enough damage to have to be re-skinned due to smoking rivets.

The point that I am trying to make here is not all smoking rivets can be just ignored.

In the first picture shows the result of leaving smoking rivets unattended. This started from one rivet loose ending up with 2 rows of rivets loose. There is 2 ribs showing damage from a Bell 412 helicopter. The rivets, outer skin and supporting ribs in time all showed signs of looseness.


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2nd picture shows the 2 rows of rivets worn. Note ribs could not be viewed above or below or from the front due to boxed in structure.

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3rd picture shows rib with approx 2.5 feet of rib structure cracked and broken off providing no support.

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4th picture show the inner skin damage where the rib would vibrate damage between .015 to .025 on a .080 aluminum skin on the load bearing side.

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Victor J Thompson
C-GIRQ
"In Memory Of Dad"

Wanted to add,...

While it is acceptable to monitor aircraft damage that is minor in nature, in this case, maintenance personnel had several opportunities to inspect this aircraft and repair this area on schedules inspections. This was not pursued and the resulting damage occurred. Food for thought.

_________________
Victor J Thompson
C-GIRQ
"In Memory Of Dad"

Another reason NOT to fly Helos.

RB