Thorp Air Command - T18.net

I have been doing some preliminary firewall planning and put this flat layout drawing together to help start thinking things through.
I can't seem to locate a dimension drawing online for the commonly available Odyssey PC980 battery holder or the standard cabin heat valves. Would anyone happen have dimensions or drawings of these items that they would be willing to share?
Thanks
Stuart

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Stug

Stuart,
If you search for PC680 rather than PC980 I think you'll have unlimited success.

Stuart - I am at that stage in my restoration... I can offer some thoughts on the subject:
- Plan your control exits carefully... they probably shouldn't exit in a horizontal line like on your PDF,
especially if you are using the Van's cable bracket between the carb and the engine. My throttle cable wants to come through at the bottom right, and my mixture wants to come through about 9" above that.
- Personally, I wouldn't run any wires over the top of the tank; however, if you did, plan for plastic conduit of some kind. Don't just drape the wires over the aluminum. You might get away with it for signal wires like CHT and EGT.
- Real Estate is at a premium on the firewall, espcially if you have a heater valve. Consider putting the spin-on oil filter and/or the cooler on the engine. (There are great arguments for hanging them on the firewall too, but if you can save space, why not?)
- Accepted practice now (in Canada, anyway) requires that all penetrations be sealed and oil and fuel bulkhead fittings must be steel. Consider one or two of those SS "pass throughs" from Aircraft Spruce and others with the fireseal tubing and the fireproof caulking. Also consider SS shields to protect grommets. (After I tore mine apart, looking through my firewall from the inside was looking at a starry night!)

Hope that helps!

Stuart : Attached are 2 pics . One showing the Vans carb/engine bracket . It makes attaching the mixture and throttle cables very easy and secure . You can also see the warm/cool air selector/mixer on the firewall . It is very compact and also has the ability to shut off all air entering the cockpit on the cockpit side . I think I got mine from Spruce ? P/N 08-00629 . I ran the mixture and throttle cables between the mixer and the gascolater , it turned out to be an almost straight shot to the carb . The carb air cable was run on the left side of the firewall to line up with the carb air box . As it turned out with my custom made throttle quadrant I was able to use the same length cables and P/N's . The carb air cable did need a short extension . The PC-680 goes in the blank space upper right on the firewall .

RB

Thanks for the hints and suggestions guys. It's great to hear the all.
At this stage engine choice for me is undecided so control cable locations are just on the plan as place holders. It sounds like there are a least 2 votes for the vans bracket so I will need to look into that some more.
I anticipate using an engine mounted spin on oil filter and probably oil cooler as well as S. Steel pass throughs and fire sealed grommet covers.

The "PC680" battery. Yes that was the one I was referring too, I can find lots of pictures and also pictures of the bracket but still haven't come across any online source of the dimensions for the bracket. I might just have to go ahead and buy one to get the size. Same thing with some of the cabin heat boxes.

The comment about bulkhead fittings for fuel and oil being steel makes sense. I hadn't yet got to thinking about it but was assuming alloy ones would have been adequate, I'd expect Oz will have the same standard.

I'm curious, why no cables across the top of the tank! Assuming cables were in a conduit fixed to the fuel tank brackets, what is the main concern here, maintenance, access, potential for sparks or some other concern?

Rich, I notice what appears to be a small doubler on the side skin near the landing gear attachment beam. Is that cosmetic recommended mod or did you just want to beef up the structure?

Stug

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Stug

The small doubler was there when I got the project . Not sure why it was added .

RB

The doubler is required. It is only shown in one drawing, but its purpose is to tie the two vertical angles on the back of the firewall to the horizontal angle riveted to the top of the landing gear beam ot prevent flexing here. It is not dimentioned, but I used .090 aluminum and proper edge distances for the rivets it picks up. I think it is shown on the 580 series of drawings and not the firewall layout. You could probably get away with .063 plate as this is the thickness of the angles.

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Bob Highley
N711SH
SN 835
KLAL

The doubler is required, Bob?... that's going to raise some eyebrows across the land! I've never noticed them before on any T18; I don't have them on mine either. Good timing for me though... my interior is still open. Thanks! Good to know!

So aside from these doublers, the extra diagonal angles ahead of the dash, and the double row of rivets on the spar box corner doubler, are there any other under documented or undocumented mods we should know about?

Stuart - cables just draped across the tank could be a sparking hazard if the insulation wore off a wire. Unlikely, maybe, especially with Tefzel or Teflon insulation, but on the other hand it's not very easy to inspect up there once the soundproofing is in place. A fuel leak and a spark could ruin your day! Up hear in the Great White North, they check for stuff like this on imported amateur builts.

d

I have some sensor wires running across the top of my tank. I see no issues.
Cubes

The majority of my wiring, sensors and such (low amperage) runs across the top of the tank in a schedule 200 3/4" pvc conduit. The big wires (starter, alternator) run through the side wall on the right side of the cockpit under the tank.

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Bruce Finney
N18JF T-18C #262
Yelm, WA USA

The "doubler ?" I often wondered about that little critter . Out of the few T-18 Fly In's I've been to , I think I saw it on 3 aircraft...one of which was mine . I think I saw it at KVIS on John Evens AC ? Maybe not ? I looked thru the drawings and could not find that little beasty ? All the 580 drawings and all the fus. mod drawings . Is it possible some folks put it inside the skin ? Anywho it appears to be a good addition at that location . BOOM !

RB

I've not seen these doublers either, and I just checked my drawings and cannot find any trace of them. I've got 580A & 580C. Is there a 580B? I can tell you one thing, having seen a gear leg hit so hard that it was bent back over 45 degrees (striking the bottom of the wing) & completely cracking the outer gear leg tube (it was a Ken Brock gear), also mashing the lower corners of the firewall & side skin below that area - the airplane had approximately 1200 hours at the time & the 580A & 580C modifications had been done. There was absolutely NO deformation or distress in the area where you say this doubler is needed. The other T-18 in my hangar has over 1800 hrs., has .025" side skins, and doesn't have them, and it's gear was bent with a very hard landing one time. Unless this was specified by John Thorp (& it may well have been - I don't know) I would question the need for them, especially considering the number of ships which I believe do not have them.

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

I certainly can't see it hurting the airframe . I bought the project from an owner that had died ( Ken Hamilton ) and the project was a basic fus. with a butt load of skins, ribs, etc. When I picked it up from Dick Cavin (he was selling it for the Mom of Ken) I didn't know enough questions to wet a Monkey diaper let alone ask about the doubler . That was in 1984 . I still don't know enough questions to wet a Monkey diaper ! I do get asked at fly in's about the little bugger ! My answer...ask the Monkey ! BOOM !

RB

Looks like doublers are a popular topic.
Pretty sure Bob was talking about this doubler, and he is right it only shows up on one drawing, 580.
The side skin doubler doesn't appear on any plans I have. Agree it would be hard to see it doing any harm and it could be a option I need to look at, given I have extra holes in that area that I need to sort out.

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Stug

My mistake!? I thought you guys were talking about the one Stug shows. I would like to see the other one you are talking about.

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Bob Highley
N711SH
SN 835
KLAL