seancorder

My Feedback: (1)

A gentleman at the field suggested I go from an 11X5 prop on my OS 46 FX to an 11X7. I Did so, and the difference it made was phenomenal , especially considering the amount of noise was far less annoying, changing the propeller was worth it right there... But once I saw the flight difference, I am amazed.

Can someone point me to an article, or articles that I can learn "WHY" the pitch change works the way it does?

Thanks!
Sean Corder

dr_wogz

My Feedback: (3)

IN Prop numbers, the first is teh prop diameter, 11=11" diameter

the second number is teh pitch, or the amount of 'bite' the prop has in teh air. the higher the number, the more 'bite'.

Ideally, the second number indicates how far the prop would travel in one rotation. So, the 11-7 would travel 7" forward. At least taht's teh idea. Also, the prop tip travels faster than the center, so the 'angle of attack' is les than at teh vcenter, where the prop is not turning as fast as teh tips. But air can be a funny thing, and swish around in eddies, currents, turbulence, and vorticies. all these add to the 'inneffeciencies' of teh prop.

But with more bite comes more drag. and that stresses the engine. Changing to big a diameter, and/or too much 'bite' and the engine will be under powered. Same is true for an undersized and/or little pitch. the engine has no resistance (load) and works overtime!

seancorder

My Feedback: (1)

Thanks for the info.

Tell me, what is the best way to determine the best prop for a specific task?

scubyfan

Trial and error.

seancorder

My Feedback: (1)

I was afraid that was going to be the case!

Thanks!

dr_wogz

My Feedback: (3)

Yeah, the good-ole 'TE' method. try it, try it, try it...

Different planes will yeild differnt results with the same prop. Also, one brand '11x7' prop will not perfom the same as the next brand '11x7' prop (nor will it fit the spinner!!)

Air quality on the day will affect the prop's performance, as well as altitude, barometric pressure, humidity, etc...

There are many, many factors to choosing a prop. As long as you are in the 'ballpark' for the reccomended prop size, all you can do is try..

If you search this site for 'prop size' and 'which prop to go faster' you'll get some other explanaitions (not the exact search string, but along those lines.. There are many threads about choosing props...)

bojangle

This is the way I approach props. Every plane, as mentioned is different, and by its design, has a certain speed it wants to fly. The prop has to be able to keep up with the plane, and vice versa. Try to force a "high drag" plane to go faster than it wants, the drag coefficient goes up exponentially and you open up a whole new can of worms. You apparently have a cleaner, lower drag plane, and have been holding it back. Now you are simply letting the plane do what it wants to do. Enjoy it

There is nothing so scientific about this. A prop unloads in flight, but you don't want it to unload to the point where the "plane is pushing the prop" through maneuvers. Any engine is more efficient when the proper load is applied to it. As mentioned, don't underload or overload it.

Having said all that, it's still trial and error from the starting point, you will know when you get it right. You have apparently worked it out just fine, don't mess it up by reading a bunch of prop theory. And I agree with all the other posts above about all the variables.

BO "Your plane is your friend, listen to it. It will tell you what it needs"