Thorp Air Command - T18.net

Dang, that looks sharp!

Hi all, I hope everyone had a nice Thanksgiving! N12055 is nearly ready. We did the weight and balance last night after getting the interior put in. Empty weight is 888 lbs with 47 lbs of that on the tail wheel. Prop ground clearance in level configuration is 13.25”. Still a few more punch list items to finish (aren’t there always it seems ).

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John Twigg N12055 SN.79 Pittsburgh, PA (KFWQ)

Looking great! It is kind of interesting to lift the tail (hang on cause it will try to over center) until the prop is about 2 inches from terra firma just to see the extreme nose low attitude you have to be in to hit the prop. Of course the gear could spread a little on a nose low hard bounce, but the Thorp gear isn't going to flex much! Even sinks in a little more if you can be sitting in the cockpit when someone else lifts the tail. Helps to reduce the pucker factor if you are apprehensive about raising the tail during wheel landings or correcting small bounces.

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Bernie Fried
N18XS

888#. I am sure you are happy with that. I bet she will perform great.

Hi all, I'd like to get ahold of Les Krumel (@ljkrume) or anyone else who has cut belly access holes in their plane. I'd like to find out how they did it and how/if they needed to reattach the belly longerons when the put the access cover back on. I'm in the process of reattaching my cover, which is about 28" x 18" give or take (I haven't measured it yet). Any thoughts or NL articles I haven't known about? It's the last piece of the puzzle before flying.

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John Twigg N12055 SN.79 Pittsburgh, PA (KFWQ)

Happy New Year, everyone! N12055 has been getting ready with instrument panel labels, and other punchlist items being done. I've been doing taxi testing the past couple of weeks. She rolls straight and true with no tendency to veer one way or the other. Just touched 50 MPH last weekend.

The engine runs a little rougher than I'd like at idle with the original plugs, so she's getting new plugs. Anyone have a favorite plug for the Lycoming O-290-D?

Last weekend, I was testing the max RPM and got only slightly over 1800 RPM. Scratched head several times and then borrowed an optical RPM instrument and found that the installed tachometer reads 190 - 260 RPM too low. For example, 1000 indicated is actually 1260. I found out that the problem was magnets - many mechanical tachs have magnets in them and will read lower and lower as these magnets age. I think mine is 45 years old - but it looks great - haha. So, the tach is being replaced with a new 3.25" Mitchell tach from Aircraft Spruce with the green arc and redline option as well as them setting the hours for me.

I also found that the right brake wouldn't hold the aircraft still during run-up. It failed completely back in the hangar a day later while investigating, testing, and topping off the brake fluid. I think there is some sort of poppet or compensator valve in the brake's piston that failed. Anyway, both brake master cylinders are getting replaced perhaps with Matco MCMC-5A (Aircraft Spruce p/n 06-00375) units if they match the correct hole-to-hole length of the existing brake cylinders. What master cylinders (with Reservoir) works best for you guys?

P.S. I don't know why these pictures are coming out upside-down, sideways, etc. If you click on them though, then they seem to be correctly rotated.

John

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John Twigg N12055 SN.79 Pittsburgh, PA (KFWQ)

I currently have master cylinders like yours, if I were to replace them I would go with a remote reservoir on the firewall, would make servicing them easier. Ya I know, more work for the install.

My O290 has Unison UREM38E plugs installed, they were in the engine when I purchased the airplane and have not changed them yet. Note: Lycoming SI 1042Y specs all of the massive electrode plugs except the Unison UREM38E, go figure, they're working just fine for me.

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

Hey John,
FYI, we are a MATCO dealer.
Cubes

Bruce - thanks for the info about your plugs - I’ll look them up tomorrow. You’re right about more wok for the install. I’m done for now (I hope) with more install work.

Cubes - that’s cool that you are a Matco dealer - I’ll get them from you on Tuesday.!

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John Twigg N12055 SN.79 Pittsburgh, PA (KFWQ)

Hey John,

Just noticed you asked about floor panels. Maybe I got the image properly attached, but in case it failed I also added it to my album in the photo section. I can't speak for other concepts, but for mine, I was intent to maintain shear strength of the original design; the floor panel is a critical structural item. I didn't really cut the panel for access, but kept it whole (I can crawl up inside with it removed). Instead, I replaced a screw for every rivet used to attach it. For the same reason, I used flat-head screws and dimpled the panel and (crosswise) mating joints, which is good for shear strength. Corresponding longerons for R&L edges of the fuselage are countersunk with locking nut-plates. This was extra work but handy for under the panel maintenance. You'll also see scuff plates for pilot and pax heels. There is a small access hole at center only to inspect rudder cable connection and springs inside the forward tunnel. The right pedal is notched to clear the fuel tank support as you'll see in early newsletters. External R & L ports are a redundancy to a single vent line going to the fuel tank. Brake lines are nylon with additional protective plastic tubing (Brake lines down the gear legs are aluminum tubing with a flex-bow on each end). The whole thing is a sub-assembly itself as the photo indicates.

Yeah, kudos to Cubes too. He's great.

Hope this helps,
Les

Now THAT, folks, is what craftsmanship looks like. I sure wish I had your patience and talent Les.
Cubes

Les that looks great but I have what may be a silly question because mine looks a little different. In addition to being the floor, is that also the belly skin?

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

Can't recall the dwg no. but the floor under the pilots feet is according to plan. It runs from the firewall to the bulkhead just in front of the wing spar. I could have made it go to the one behind the spar.

Les

I need to quit scanning the forums when I am frustrated with something in the shop. I didn’t read the post with the picture thoroughly before I asked the question. Asking if your removable floor was the belly was indeed a silly question.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

Thanks Les! Absolutely beautiful and ditto what Cubes said!

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John Twigg N12055 SN.79 Pittsburgh, PA (KFWQ)