Pointy props
 

I have a Hobbyzone Super Cub. It comes with a prop that has a rather square end. Some people are replacing them with props that have a very narrow ending, almost tapering to a point.

It seems like to me that sort of prop would not grab as much air as the square-ended prop, since out toward the ends, there just isn't much prop to grab air with.

Is my thinking right? Why use pointy props, when a squared-end would have lots of blade all the way to the ends of the prop? Should I stay away from the tapered end prop style?

Thanks.....

RE: Pointy props
 

The prop tips generate induced drag way out of proportion to the lift they generate. By narrowing the blades to a point, the tip vortices are smaller leaving more power available for the more efficient inner part of the blades.

RE: Pointy props
 

Pointy props also produce less noise in flight than "square" or "blunt" props.

RE: Pointy props
 

Thanks, what a great answer.

It seems counterintuitive that the outside part of the blade (drag aside) would be less efficient in pulling air than the inside portion, since the outside portion travels faster. But a 10x8 square end prop will have less thrust than a 10x8 tapered prop? I wonder what the motivation is to even make the square-tipped props?

Thanks....

Jim

RE: Pointy props
 

Actually, I'd be happy if the SC made a little MORE noise :-).

Jim

RE: Pointy props
 

I've noticed that 4 stroke props have flat ends. Can anyone explain why?

RE: Pointy props
 

Because 4-stroke engines have the balls to swing them :D

But don't forget, because the tip is... well... at the tip, The air slips off the end.

This is why you see a lot of commercial airliners now with winglets on the wingtips. This prevents air from sliding off the end of the wing so the wing produces more lift.

Similarly, I see a few electric props now with "winglets" at the tips.

RE: Pointy props
 

Actually, the outer area of the prop is where most of the lift is created. But, right, not right at the tips.

Truth is, with props, none of the sound byte wisdom is of much real value. Yeah, all are somewhat true, but props aren't so simple that just the tips, or just the shape, or just the composition, or chord, or area, or what rpm they turn on the ground, or their weight, do enough by themselves to decide how any prop matches your engine/airplane. Have I mentioned the airfoil matters and it's chord and thickness.

It's kewl to talk about the details but with a prop, the details don't decide spit.

For a couple of reasons. For one thing, if you did a pitch check on any make of prop that was say a 6" pitch, you'd find a bunch of different pitches all the way out the prop. Why? Because to get the prop to pull the airplane through the air 6" for every revolution, the speed of the prop matters, and is different at each radius. And a lot of props change airfoil with radius. And that's just the beginning...................

Don't get fixed on any detail about props. Try everyone that seems suited to your engine. You'll be surprised. Almost all will work good. No matter what their tips look like. Some will work better. But lots of times the best one won't be much different than the average ones.

And did you know that very often the best summer prop isn't the best winter prop? It's the different tip shapes that do that, right? ;)

RE: Pointy props
 

Which brand of prop are you looking at?

The pitch of any location along the radius is determined by what the mfg wants out of that location.

4strokes usually turn a prop more slowly than 2strokes. But there is nothing about running a prop at lower speed that demands the pitch at the tip be flatter or have greater AOA either.

The ones you've seen look that way simply because the mfg was getting enough lift out of the rest of the prop that he could use less at the tips. For the speed he expected each station to experience with the engines he thought would probably be spinning that prop on the airplanes that might be hanging behind those engines.

There are a number of 4stroke props that have very much greater pitch going out the blade.

Ain't no sound byte wisdoms large enough to cover prop details.