Thorp Air Command - T18.net

Thanks Bob that sounds like a handy trick for filling in bonus holes! I'm still not sure how I managed to get them wrong in the first place but at least that seems to be the only hiccup we have come across with the side skin CAD drawing. Guess it was always going to be a risk on the first attempt with this approach.
Stuart

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Stug

Or you can simply put rivets in them. It's area is under a lot of stress during landings. I would use the top row with a 3/4 by 1 inch angle. On the bottom, I would dimple and rivet the existing holes and drill new ones after everything else lines up. Rivets are as strong or stronger than bare skin.
Cubes

When I started my "project" I asked an A & P..."what if I misdrill a hole ? " What do I do ? He said put a rivet in it . BOOM ! >:D

RB

Would it be prudent to go ahead and put a stiffener on the inside of the fuse on the row of misaligned rivets? I mean since your considering filling the holes with rivets anyway....I'm just thinking out load....I'm not a builder.

There are two very important stiffener angles that connect the 527/firewall to the lower forward fuselage longerons. That is what those holes are for. The angles are riveted to the skin then bolted to the longerons.
Cubes

Thanks for all the suggestions guys. I have decided to use Cube's suggestion and go with the 3/4* 1 angle on the top and use those holes. On the lower angle I will go with 3/32 flush rivets in the incorrect holes and drill a new row of holes in the correct location. Due to the location of the misplaced rivets I will probably include a spacer/doubler plate between the skin and the 3/4 angle. After a lot of head scratching and double checking I think I have resolved the error in the side skin drawing and am now ready to cut the second side skin.

Today I was putting the shear plates into position and after drilling the 601 beam to plan dimensions off the airframe I noticed that one shear plate was under a bit more tension when it was being cleco'd into position, the tension I suspect was due to some uneven curvature in the 1" longerons. There is still a lot of flex in the airframe at present since nothing is riveted but it made me wonder, how best do I check the alignment of the fuse in this area, at this stage? I don't recall reading anywhere in the newsletters what the recommended method was.
I can hope that the matched hole tooling will resolve some of twist along the way but does anyone have any hints or tricks for checking alignment and resolving the twist as we go?
Stuart

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Stug

All you can do is keep everything in alignment as best you can. Once all parts are made, the fuselage is leveled, and you can dimension everything. That is why I recommend making the parts and not drilling until everything is set up. I bent, drilled and clecoed my side skins on the flat. Actually, I riveted the longerons to the side skins on the flat. Then put all formers in, align everything and start drilling.
Cubes

Cubes I think it sounds like you have taken the opposite approach to me. Wherever possible I am trying to pilot drill parts while still flat and separate. For those parts CAD drawn and machine cut it turns out near on perfect, just so long as the bends are where they should be. For the frames and some of the smaller parts like the shear plates which came with the project I bought, not so good and I can't trust the centre punch marks that they came with, so seem to end up doing a lot of double checking before drilling.

I'm currently using #40 pilot holes and assembling, hoping that there will be enough scope to take out any twist, when finally drilling everything out to #30.
I'm planning to borrow a self levelling laser soon to help with the alignment checks, hopefully it will give some confidence that we have managed to keep everything in line!

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Stug

Stug,
You are definitely out on your own with your methods. I'm not at all saying they are wrong! They are very right, and quite cool. I am very interested in how all this turns out for you. However, you may find some issues that I did not run across just because of the difference in methods. Ill tell you what I did, and hopefully it may help. If not, that's why they are called experimentals!
Pretty neat. Good luck.
Cubes

Have been doing some research in preparation for preliminary fitting the 580-2 Top skin. The skin that curves over the top of the fuel tank.
It has prompted a couple of questions, (again) Sorry.

1. John Thorp revised the windshield design very early on to remove some hollows in the top skin and avoid the need for stretching the material, he mentioned this in part 11 of his building instructions. However some time later in 1979 newsletter 48 pg.2-3 a builder reported how to stretch form this skin.
Is some stretching actually still required in this area?

2. I can find only one drawing #487-Windshield Installation that provides a view of the curve in the lower outer section of the windshield and there is virtually no information on the drawing by way of co-ordinates or formula the Thorp instructions make no reference to it and there are no newsletter references about how the curve is formed. Can I assume drawing 487 as a true side view and that the limited detail allows freedom in the precise location and shape of the curved section of the windscreen? Am I missing some detail here or something else obvious?

3. Also what is the current fashion and what is easier to build. Windscreen tucked in under the skin OR per plans with the skin under the windscreen and an external trim strip over the top to seal it.

Any pearls of wisdom!

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Stug

Stug,

Stretch-forming is not necessary. I remember Dick Cavin talking about that in the newsletters long ago, and was always a little confused as to why he thought it necessary. Mine's a flat piece & it fits just fine.

I'm an advocate of putting the windshield under the skin. It can be a little tight between the plexiglas & the center tube of the roll-bar structure, but that's easily dealt with. It's not necessary, but you can slightly modify the attach point of that tube to get a little more room if you think ahead, and especially if you make your own roll-bar like I did.

I used a pattern from another T-18 project to get that curve - sorry I can't shed any other light on that.

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

Thanks John

I put together this preliminary flat layout of the top skin into CAD,it's not finished yet and took a bit of thinking to get the curves right. Hopefully I got that windscreen curve close enough.
Any comments on the drawing does it look about right?

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Stug

. I placed my windscreen between the skin and the windshield frame. Used a tool John Kerr showed me to gently bend up the skin around the top . Nothing more than a hardwood handle with a groove cut in it . Take small progressive bends to avoid too much stretching . I placed a EPDM weather strip on the bottom of the skin and then placed the glass into position . I did not use any screws on the top and about 3/4 of the way down the sides . Instead I used what Danny Boy used on his installation . I fabed aluminum angle brackets to hold the glass into position . They are attached to the bulkhead aft of the fuel tank...can't remember what bulkhead it is , but it is between the tank and the instrument panel . The only screws I have on the fus. holding the glass are 4 along the sides. Where the skin was "bent" up I used a high grade auto filler (no BONDO !) to smooth it out . No cracks with 110 hours . BADA BING , BADA BOOM !

RB

Thanks Rich helpful pictures, From the look of it I need to tidy up my drawing across the bottom of the windscreen so that there is a smooth flow from side of the screen through to the centre line.
You must dislike screws, although it does make for a very clean finish. That bracket you made must have come of the 603 frame. I'd be interested to see a pic of that
Do you recall if you modified the centre tube of the roll bar like John mentioned, to provide more space for the glass?
Thanks

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Stug

You should not need to modify the roll bar. Bill Williams posted a thread a while back on making a roller to bend that skin up. Other than that, it's a flat piece. My comments on your drawing would include eliminating the notches where the boot cowl forms around the glass. And Eliminate the notches on the top side of the side aft section. I brought mine all the way up to the canopy rail.
Cubes