Thorp Air Command - T18.net

This may have already been tried before, but I

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In theory, theory and practice are the same. In practice, they are not.

I'll give you my 2 cents work Dick ...

As you know the Thorp cowl is very tight underneath, there is not really enough room to have and airbox - scat - carb setup down there. In addition, you really don't want to have to disconnect controls etc when taking the cowl off;

1.) you're likely to forget and although carb heat is not a life and death thing, it would get annoying when you forget, and

2.) It's tight down there and you ARE going to have to pull the cowl with the engine hot someday and sticking your hands in there to attach scat tube/hook up CH controls etc ... with a hot engine does not sound fun.

The way I see it things are likely to get a little complicated in there. Box attached to cowl, scat from box to exhaust shroud, scat from box to carb (still need a box or something to hold a flange here), carb heat secure on box, carb heat control to carb heat lever.

That's a min of 4 things to disconnect/reconnect every time you pull the cowl.

There are several airbox designs that use element filters that work just fine. The old Leider airbox is used on a large number of T-18's, we have one on N51863 and it works great. I may still have the form blocks and some hardware to make one of these if you're interested.

Also, I looked at your pics of the carb heat wear, the trick there is to have a good bearing surface. Either an actual bearing plate or something like a micarta block for the door hinge (shaft) to pivot on. From the pics it looks like it was just steel against aluminum.

If it were me I'd save the extra work and clean up/re-build the existing box with a good CH pivot and keep moving forward getting that airplane in the air.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

Thanks, Lee; all good points. I was trying to think outside the box, if you'll pardon the pun.

I would be interested to find out more about the Leider airbox. Maybe that's an option for me for a winter project. Where can I find out more info? Does it incorporate an filter element of some sort? One of the problems with my current setup is that a 2" x 4" x 1" THK piece of foam is all that is doing the filtering. I'd like to improve that.

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In theory, theory and practice are the same. In practice, they are not.

I'd be happy to find the airbox drawings but your still going to use an element filter with it. I was suggesting the different airbox only to solve your carb heat wear issue. If it makes you feel any better I have a 3" diameter element filter on mine. The trick is to keep it clean and replace it as necessary.

It's just an opinion but I really think your best off rebuilding the box you have rather than re-engineer the intake system. The original builder of that airplane knew what he was doing. That was his third T-18 and maybe his 6th or 7th homebuilt (I think he made it to the double digits before he passed).

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

Well, the carb heat pivot wear was only one of several problems I was trying to solve. If anyone has a picture posted of a Leider Airbox, I'd like to see what it looks like just to satisfy my curiosity. I couldn't find anything by search.

You're probably right about working with what I have. The airplane has gotten this far with that airbox. There are plenty of other problems that need to be addressed this winter.

After spending many hours close up and personal with my particular Thorp, disassembling, inspecting, and analyzing why things were done the way the were done, I'd have to say that a more accurate statement is that the original builder "knew what he could get away with." Then there are the things that were and weren't done since he sold it, but I'm not going to go there.

DW
edwolff at brucetelecom dot com

Jan 18, 2011 --> That was an arrogant thing to say. I've come to appreciate Bill Cox's work. The original build was good for the most part. I have great admiration for builders. dw

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In theory, theory and practice are the same. In practice, they are not.

Happened to be out at the airport working on N51863 today. I snapped a couple of pics of the Leider style airbox.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

Wow! I've never seen anything quite like that before. Thanks for the shots. I don't think I'd have enough room for that in my airplane, but I could use one of those blue rubber sleeves. Is that neoprene?

DW

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In theory, theory and practice are the same. In practice, they are not.

Lee...that is quite the bomb ! NASA would like to talk to you !

RB

Thanks Rich, but in full disclosure that was built by my dad John Walton, I was present but the credit goes to him. Ill brag a little bit about my dad for a sec., everytime I work on his old airplane it reminds me of how far I have to go. Everything on that airplane just glides together as if was pulled from a mold! He was a heck of a craftsman and a heck of a guy.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

Hi Dick,

I think its the same material as mine... a scuba suit sleeve. Mines red though (matches the airplane)

Image Insert:

Nice. Where can I get a yellow and blue wetsuit? ;-)

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In theory, theory and practice are the same. In practice, they are not.

Ah@! and Tim is sporting a Leider style box as well! Yes ours is wet suit material too, we ended up finding a wet suit manufacture here in town and just grabbed some remnants (30 years ago) I still have some blue left, if you like I can see if there's enough for another go.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

Thanks for the offer. Let me look around the house first. Seems to me I had a long-john wetsuit left over from the sailboat racing days. I'm sure it's too small for me now.

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In theory, theory and practice are the same. In practice, they are not.

Hey, flipping through the Thorp drawings I came across an interesting set up that might work for me. I don't have the drawing number at my finger tips (will edit this tonight), but it was a banjo box with an automotive ring-type filter. The unique feature was a deep drawn cup that went around the carb and a rubber seal between the carb to the banjo box, presumably sealed with one big hose clamp. The air box part was supposed to be fixed to the cowl.

Does anyone actually have a set up like this? The rubber seal had a drawing number reference, but I couldn't find the drawing. I wondered if it was a commercial part or DIY. Also, nothing looked hard to make except the cup. I think it was 3" deep and 6"? in diameter, straight vertical sides, one piece, flat bottom 0.06" aluminum, can't remember the alloy. I'm in Sheet Metal 101; this looks like a Post Doctoral Thesis part to me. Has anyone made one?

Will add some more detail to this post later.

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In theory, theory and practice are the same. In practice, they are not.

DWG-781

Dick,

I believe Bruce Finney still has one on his airplane.

If you're wanting to go that route you've got some fiberglass work in front of you. The per plans Thorp Banjo box setup requires a pretty good sized donut on the lower cowl.

The 2010 version of that is the Van's airbox ..

http://www.vansaircraft.com/cgi-bin/cat ... b-vertical

Of course you're going to be cutting the cowl open for that too. According to Gary Green this is a superior airbox setup to anything else out there for the updraft carb. To save yourself some trouble you could buy their intake scoop as well (of course fitting that to the cowl is another project).

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Lee Walton
Houston, TX
N51863,N118LW
KEFD