Maglin:

I am quite surprised you have not yet received replies to your original post. It has some interesting points.

First of all, I looked at the Skyraider MK1 and it looks like a nice aircraft. If you have 20 flights on your previous trainer, can take off and land successfully (well, all except your last flight that is), you should do ok with that plane.

I am a tad bit hesitant to go ahead and acknowledge the Four Stroke engine for a new student. Four stroke engines can be a bit more difficult to set up than two strokes, but I think once you get the hang of it, it will be ok. But, the focus here is to get you flying and "qualified" to continue on your own. If it's power you are worried about, well, you can get a good two stroke, such as an OS AX engine, in the .46 to .55 cu. in. range. The AX series of engines are powerful engines and will give you good overall power for just about anything in the size range of the Skyraider MK1 or even larger. One of the mods here put an OS .55 AX in a plane that I thought would be much better off with a 70 size engine, but it flew just fine with the .55 AX so that would be my recommendation.

That is not without saying that the four stoke won't do, as it will do just fine. The low end torque, especially when prop'ed correctly, will give you lots of take off power although it may not give you the RPM for high end speed as a two stroke would, but, it will do just fine for a trainer, especially if you have several friends at your field that are experienced with four stroke engines. Just be careful when buying them that you don't just opt for price versus brand and quality. Just remember that cheap is usually that, cheap, although I must admit that I am not familiar with that particular engine. I hope someone here will post as to their experineces with the ASP four stroke engines and can fill in the gaps.

I am somewhat partial to two strokes (as you can probably imagine from the content of this reply) because I've flown just about everything I have with two strokes with on exception, and that was quite a few years ago.

As far as prop size is concerned, go with what is recommended for that engine and stick with that for a few flights to get the feel of what it has to offer. When I started out, I did what I assume you are probably doing, and trying to find the right fit for your engine-plane combination, and I bought a boat-load of props. Added to that was, well, hard landings caused me to break a few props, so I bought several spares of what I was using, and, at the price, heck they were only a couple of dollars each, I bought them 5 at a time. And, I bought several sized and played around with props of different width and pitch. Just remember that lower pitch will give you more RPM, more power, but less speed. Going higher in pitch could load the engine down to the point where it does not operate in it's optimal RPM range, whatever that may be.

You are probably aware of this, but think of the prop pitch as gears in a standard shift car (automatic too, but it's more obvious in a standard shift). Lower gears will pull harder but you are limited in speed.. 20 mph may be top speed in first gear at the red-line RPM). Higher pitch will give you more speed, but it takes longer to get there. an 11-6 prop, the 6 is the pitch means, that in ideal conditions, one rotation of the prop will move 6 inches of air through the prop, or will move the plane 6 inches. If you work that out, at 10,000 RPM, you would move 60,000 inches per minute (6 X 10,000) which works out to just over 83 feet per second or just under 60 statute miles per hour at max RPM, and as I said, ideal conditions, which is not realistic, but good enough for explanation. Changing that to an 11-4 prop changes those numbers to an end product of 55.5 feet per second. I'm sure you get the idea, or probably already knew this, so I won't digress.

If you want to experiment with prop selection, why not do it while having some fun.. buy a few of different sizes and go ahead and see how it works out for you.

Anyway, best of luck.

CGr.