I am new to R/C and am a little confused about engines.

From what I understand, two strokes have higher power to weight ratio than four-strokes, yet many aerobatic and 3D pilots use four strokes. I assume that they have a broader power band so provide more usable power. Is this correct?

Which would generally be better suited to 3D flying and why?

You are correct. Generally speaking, four stroke glow engines have more usable power. The maximum power output of a four stroke motor is in a practical rpm range, whereas the maximum output of most two stroke glow motors is generally in a prohibitively hi rpm range. That being said, people fly 3d with both kinds just fine. The argument for four strokes is that the torque and lower rpm they provide allows a greater diameter propeller, which in turn provides greater low speed thrust, (desirable for 3d flying). And since the rpm range of the four stroke is smaller, the throttle response and spool-up time is quick. Two strokes on the other hand are generally lighter, so if the usable power is enough for the application, and they are propped well, they can work great too. In the end it's personal preference. I use both two and four stroke engines for 3d flying.

I have an evolution .40 engine. I have been using it for about 4 months. The rear bearing is bad. I have disassembled the engine and found the crank shaft a little rusty. What might have caused the rusting since it has been kept oiled and in use. 2nd should the bearing have gone out this quick.3rd how do you get that rear bearing out. Thanks Sam

If the crank was a little rusty, so was the bearing. That's why the bearing went bad. The rust formed from some of the oxides created by nitro in the fuel and the afinity for water by alcohol.

You should always run your engine out of fuel in the pits when you are done flying and put some after run oil in the engine venturi and flip the engine over several times. There is always a big discussion as to which oil is best but most universally people don't use anything that resembles WD40 oil. Use oils like air tool oil, Dexron, Mobil 1, and there are many others.

You will need help to change that bearing. Either get the local engine expert to do it, send the engine in for repair or get back on here to find out how to change your bearing which is no easy task for someone who's never done it before.

Happy Holidays,

Jim

Thanks Astroman,

Any recommendations for a profile aircraft (TopCap)?

The Top Cap is a good choice as well as the Lanier Pro Twister. I like the TT Extra ARF since it has the larger control surfaces. Most profiles have almost the same wing, so it comes down to a preference of the fuse. outline you like.

I'm a big fan of profile fun-flys, and there are several I like. You should check the Profile Brotherhood forum (if you haven't already) for a consensus on the best profiles. I haven't flown one, but alot of guys there seem to like the OMP Sledge.