Thorp Air Command - T18.net

Has any one looked into installing a Yamaha Apex 4 stoke or other than 0290/0320/0360 engine. I am a year or until the House is done until I start putting 27AL Back together. Happy Wife! Happy Life! Al Pros and Cons welcome.
Thanks
Dave.

The plane was designed around the Lycomings. They dominate this hp range and have the weight the plane is meant for. I can't think of a good alternative off the top of my head.

The new Rotax is rather light and will require a long engine mount. It will also be low on hp if your plane is as heavy as most T-18 airframes. The mouse-motor guys have always striven for extra light construction.

I suppose the larger Rotec radial could be made to work. The hp and weight are about right, but there's a lot of cowling design hassle. It's a geared motor and swings a larger prop, so beware ground clearance.

The Delta Hawk is a bit heavy, but maybe the CG could be made to work out.

D-motor and ULpower are the correct hp but wrong weight, and I've seen reports they don't make advertised hp. They'd save weight but not much money.

Verner Motors: http://www.vernermotor.com/7H.html
Seems to be the best direct drive Radial Engine, I just don't think a T-18 would look good nor go fast with one.
The D-motor: https://d-motor-usa.com/ has the advantage of being a "Boxer" engine like a Lycoming, but narrower because it's a flathead.
I like that because the advantage of overhead valve engines are slight @ 2700 RPM 8:1 compression. The narrow engine would make a T-18 cleaner, the cheek cowls would be smaller and nearly closed at the front. Too bad they are expensive, higher RPM and not quite powerful enough...
Yep, Lycoming again. I'm collecting parts for my esoteric Lycoming. Maybe it will be a O-290G case with GO-480 cylinders and an O-340 crank?
Mind you; I built a Turbo Mazda Rotary and an RV-8, which I flew for 16 hours, then changed it to an O-360 Lycoming. I'm all in favor of experimenting. T-18s are especially bound to Lycoming engines and are especially happy birds. Some historical photos of alternate powered T-18s can be found....to my eye they look 'troubled'. I know Cubes is building a special monster, that's a different category and engineered for it's unique purpose. Understand that these projects add years or decades to the build time.
I hope I have not stepped on any toes.

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Scott Emery
EAA Chapter 326
T-18 N18TE

Mine had a Ford V-6 for a long time before the builder went back to a Lycoming. Looking at the W&B history it appears The V-6 was 200 pounds heavier.

I always thought a Thorp would make a great mini-Hellcat with the way the wings are built. After seeing the RV-8 with a radial engine I became even more convinced. It takes more money and skill than I have to do a radial engine conversion and there would likely be penalties in weight and speed defeating my reasons for owning the Thorp.

I have a buddy rebuilding a Rearwin Sporster as an experimental who he has a Verner on order. I am looking forward to seeing it in action.

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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

I have been looking at the Yamaha forum and the folks that are building them are saying that the complete weight of a 150hp apex engine including accessories is at around 180lbs. That and 10 to 15k including prop is perking my interest.

That would make for a 50 pound decrease in weight from the O-290 the airframe was built around. That’s a lot of ballast to hang on the engine mount. Alternatively, the engine mount and cowl could be extended forward. I am not familiar with the Yamaha engine. Maybe it is a smaller profile and could be mounted farther forward without extending the cowl. It could be done with enough time and effort. My guess is that the little bit of money you save on the engine will be ate up by trying to make it fit.

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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

Stick to a Lycoming and get it flying instead of trying to get the Yamaha to work right in your Thorp. You may well find no money saved trying to do it cheaper after all the "I didn't know that wouldn't work" gets added up. Time is your most valuable commodity.

I agree with Dana . Stick with what's been a proven design . Good thing they didn't try something different than the Saturn V rocket !

RB

I love the idea of conversions, when there is no Lycoming/Continental offering that is practical. Under 65hp and over 300hp. In a fast cruise airframe like the Thorp not so much. These mid hp engine/psru combos are best left with aircraft that are short, unimproved field capable. You WILL need that if you want to use one of these engines.
Ask your spouse if your life is worth TRYING to save maybe $3k and an extra year figuring out how to make it work in your airframe. Pick up a O-290 for cheap, bore the cases, install O-320 cylinders, sump, carb and you have a budget O-320. Just some thoughts.

All good things to think about. Never herd if a cheep way of building a 0290 up. That and boring and moding a gpu or run out cessna 0290 d2 doesnt sound like a reliable choice. I have a 320 that needs to be completely gone thru but was told that i could easily spend 15k-20k. The nice thing is that i have atleast a year to mull it over until i can start putting 27AL back together.

I haven't actually done an O-320 but I have had overhaul shops quote $15K. I think $3K-$5K of that would likely be labor based on my experience overhauling an IO-520 and an O-200. Case work and getting the steel parts inspected and/or ground eat up a chunk of money and, if doing a true overhaul, the "mandatory" replacement items add up too. There is money to be saved if you have the skills and tools to assemble an engine yourself. Money can also be saved by going the "IRAN" route. That is inspecting and replacing/repairing as necessary instead of doing a full overhaul.

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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

If you already have a O-320 then it's a no-brainer. Yes, you could spend that much but even if you do the value will be in having a reliable strong running engine. Have Performance Aircraft Powerplants do the cylinder work and stick some 9 or even 10:1 pistons in and enjoy 180hp.