Hi again Arie

I would just match the prop to the engine and throttle back. You don't have to drive a hotrod flat out, but you might need the power for fun. Also keeping the motor cool and running for a long time is at the top of my "to do" list.

You will almost always have more power and speed than you need when you first start out.

The power to weight ratio for RC planes is a little unreal, but everybody likes as much power as they can get. (goes double for me). :greedy:

If you figure it up, you are running about 5 to 10 times the power as compared to a real airplane. The thing is going to move out!!!

On your 45, I would go to the 11X7 or 12X6, but I would take the sage advice of the more experienced modelers at your field over what is said here. Nothing like being there.

If you put on a bigger prop you will need to lean out your motor to get it to come alive and this ups the chance of burning up a motor. :cry:
I would stay within the manufactures recommendations and let the motor run at its best, then just use less throttle.

At your field you will find a lot of different opinions, but generally small diameter and high pitch is a high speed prop and a bigger diameter with a lower pitch will slow the plane down and let it climb a little better.

After you find a size that the engine likes you can move the diameter and the pitch together increasing one and decreasing the other to get the same load with a different characteristics. The prop will still be matched to the engine.

An easy way to do it is to just multiply the thing out 11X6 is 66 and 12X5 is 60, so if you went to a 12X5.5 you would have about the same load on the engine. (They don't always make the prop with the numbers that you will come up with).

You can take this to extremes and though it is not the perfect formula it will put you in the ball park as too the size you will need.

It also will come in handy when you want to use a three bladed prop. Just add up each blade and the totals will tell you which prop will work. 11X7X2= 154 for a 11X7 two blade and 9X6X3=162 for a 9X6 three blade. This shows that the motor will be a little over propped with the three blade as compared to the two blade. Not a perfect method but close.

My best guess is a 11X7 apc for the engine, yes it will be fast and powerful, but you will love the plane later, but for now I would use a 12X6 master airscrew.

The apc is a much better prop but the master airscrew is great for a trainer. The apc is like a piece of glass, one little touch and it is junk, but the master airscrew is very tough and will take a lot of abuse. They will take prop strikes on the ground and with a file and balancer you are still in business.

Again just one opinion,
MR Flyer57