i decided getting the o.s 75ax and i was EXTREMELY confused on what prop i should get..14x6/14x8/15x7....now what are the differences between those and which do you guys prefer THANKS!!!!!!!!!!!!!!!!



-RYAN

A lot depends on your particular style of flying. for example, for 3-D flying, you usually want a long prop (The first number) with a low pitch (The second number). So if you're using an OS 75 for 3-D, you'd want something like a 16x4

With a low pitch, you get more power but less speed - Higher pitch, more speed, less power (Like first gear vs forth gear on a car)

But for those of us who prefer planes that FLY (as opposed to 3-D planes that just power themselves through the sky) something in the 14x7 range is good for the 75AX.

Personally, I am using a Graupner 14x7 on my 75AX and I wouldn't dream of using anything else. People can talk about their APC props all day long, but for pure stump-pulling power, I'll take a Graupner any day. I rarely use anything else.

http://www.hobby-lobby.com/grprop.htm#2%20Blade

The answer to your question is "yes". Buy a bunch of props of different brands in those size ranges, and fly and try. You will find that one or two are the best for that particular airplane/engine combo. Keep the others as you will likely find one of them the best for anther combo.

My Godlberg Skylark 70 has the OS .75 AX which has an APC 14-6 prop. The reason is that it is what I had and that's what I used. It works, so I leave it alone... if it ain't broke, don't fix it. But, there are so many different sizes and manufacturers that you can try any of them in your range and find at least one that will work out. As Minnflyer said, it just depends on what you wish to do with your aircraft.

I usually equate prop choices to the gears on a car. While they're not exactly the same, they are close enough to get a fairly good mental picture of how this works. Lower diameter, higher pitch props are like a higher gear in a car - you get better top speed, but slower acceleration and diminished vertical performance. Higher diameter, lower pitched props are more like a lower gear - you don't get the high speed, but acceleration is improved along with climb/vertical performance.

The prop must impose a certain load on the engine in order to keep the RPMs within the specified range. Too little load and you'll rev up the engine too much. Too much and you won't get enough RPM along with overworking the engine. This is why when you increase the diameter you must decrease the pitch, or vice versa.