The numbers in the prop selection mean something. I will use the 10-4 prop mentioned in the previous post as an example.

10 (diameter) means the diameter of the prop... the length from tip to tip of the prop.

4 (pitch) means the amount of theoricical air that the prop will pass through in one complete revolution. So, for each revolution, the prop will pass throug or pass (if standing still) 4 inches of air.

That still counts for the diameter... meaning that it will still only pass 4 inches of air per revolutino, even at 15000 RPM, but because of the more RPM, more will pass through.

The diameter of the prop comes into the equation because the longer the prop is, of course, it will pass through more air per RPM.

Think of changing the pitch as though you were changing gears in your car or truck. In first gear, the car or truck won't go very fast, but it will pull very hard. Second gear, less pull but more speed. Third gear.. more speed, less pulling power and so on. So, for a given prop diameter, changing the pitch will cause that prop to pull more but do so at a slower rate of speed. So, you will accelerate much more quickly with a smaller pitch prop than with one with a larger pitch.

Then the flex comes into the picture. Props that flex during pulling will tend to not pull as hard, will slip, so to speak as it trys to gain thrust or pulling (pushing) power. Carbon composite props are considered the most efficient props because they do not flex, but the expense is also quite a bit more.

The APC props are generally considered good because they are pretty much consistent in weight and usually are in balance when you get them off of the shelf. That does not mean that you should not check the balance, but you are less likely to find one that is badly out of balance when new, usually acceptable enough off the shelf to use right away. And, they are pretty stiff and good for just about most of our sport flying.

They do not tend to break as easy as wood props do. That could be good and that could be bad. Getting your finger in the way of any rotating prop will ruin your whole day no matter the composition, by the way.

So, Mr Maggot, you may want to leave the diameter alone and go to a different pitch. But, also consider that your motor may not be enough to power that midwest aerobat. I had one and used an OS 46 for power and a 10-8 prop which worked out just fine.

DS.