I'm planing to get some type of trainer/high wing plane to convert to taildrager and mount skis on to use through the winter.
I've never had a four-stroke engine, and I'm dying to get one for my "snow-bird" project.

Normally you see the normal 40 size trainer having a .40 or .46 two-stroke engine, right.
What size 4-stroke would be wise to get?
Would a OS 70 surpass ll be way to big for a normal .40 trainer? (Prop-ground-clearance, too heavy etc...)
I want to get a fourstroke that's beginner-friendly, will fit on this winter-plane, and later have power to spare for some more acrobatic plane.

Do you know what plane you want?

Prefered engine would be an OS 70 or 52 four stroke.


The two configurations I'd expect to use it in would be:

1. My winter-plane project. Perhaps a high wing 40 size trainer, a 4*40, sportster or stick type of plane with skis.

2. Warbird, I think the future home for this engine will likely be a warbird ARF. (Some 40 size warbird ARF from World models or Great Planes)

I'd go with the 70 size. It'll give you more power off the rough ground and has more utility after you move on to more aerobatic airplanes. Lot of good prices on used 50s though, so price may be a consideration.

Definately go with the 70. It will give you much more room to grow. (And it's a wonderful engine!)

This would be a great project. How about the LT-40. Very durable trainer. Or how about a Stik

The 52 would probably work, but the 70 will work better. As others have said, the extra power will help for both this plane and other planes you may decide to put the engine in. The weight won't be an issue for a 40 sized trainer, they have a large wing area.

Something to keep in mind for winter flying. Be careful of your fingers when tuning the engine. There's the obvious problem of accidental contact with a moving prop. Don't forget the not so obvious problem of frostbite. One person here (on RCU, not in North Carolina) said he stopped flying in the winter because he got frostbite on his fingers while tuning his engine. The extra wind from the prop makes for a significant wind chill.

I agree with Stu on the LT-40, great trainer and i'm sure i've seen threads around on converting this to run on ski's. Sig's specs on their web page quote a 4-stroke upto a .50 but i'm sure you could get away with a 70.

I was all set to endorse the .52, because I think training is best accomplished with a little less power than is usually used.

Then you said, If you're buying an engine for a future aerobatic warbird, I think the minimum is probably that .70 fourstroke.

But I still recommend the smaller engine for the plane you learn on.

Just my opinion. Good luck,
Dave Olson

Ordered the O.S FS-70.
Thanks for your input guys!

I actually got to fly an LT-40 with an OS .52 4-banger in the nose, one of my student's planes. Great flying plane, plenty of power. It actualy felt better in the air than the ones with the .46 two-strokes. I'd say the LT-40 is a natural fit to the .52.

However, your comment about wanting it for acrobatic planes later makes me agree that the .72 is probibly your better bet.

If your headed for warbirds, the extra weight of a .70 size would be better utilized. A good top wing plane for would be the Seagull Decathlon or GP or H9 Piper Cub. The are not 'trainer' planes, but would be a good stepping stone to warbirds.

Reviving this thread again...

I bought a OS 70-fs II and a high wing De-Havilland Beaver from Falcon trading (Known as 'Modelfly' or 'ARC' here in Europe).
This combo works great as my winterplane, but I still want a trainer with a fourstroke to fly on lazy afternoons ar to introduce my friends to RC flying.

I'm about to order the LT-40 and a OS .52-fs as soon as the current project leaves the building board (4*60)
This seem to be a perfect combo with the qualities I like!