Why Big Props

[xptical]

Hi all,

I love my EPP Sniper 3d. The plane performs wonderfully. However, despite my best efforts, I can't hover her.

A friend pointed out that my motor was too high KV and too small prop.


I run a 9*6 on a 1200KV. He runs 11*4.7 on 800KV. Both planes *fly* very much the same. Our vertical performance is about the same. We can both launch vertically and climb forever. But he can hover while I can't.


All things being equal, I can hover no problem in the sim.



Why do big props make it easier to hover?

Why can't I just put a big prop on a higher KV motor?

[cryhavoc38]

the rule of thumb on props and motor kv is this.

The higher the kv of the motor, the smaller the prop should be used due to amp draw.
lower KV motors are suited to swing bigger props where you get more thrust, but somewhat less speed, depending on the pitch of the prop.

Your 1200KV motor, not knowing which one it is, is going to want to swing a smaller prop given the same amp draw as your friends, 800kv motor swinging a larger prop.

Your motor would be best suited to swing a 9" prop, of say 5 or 6 pitch and you are going to have some good speed out of it.

For instance, one of my strykers is using a helimax 2580kv motor swinging a 6x5.5 prop and at WOT It pulls in excess of 42 amps. It has unlimited verticle and pretty good speed.

If I put a 5x5 prop on the same setup, using the same 11.1v 2100 lipo, my WOT amp draw is sub 30 amps, I don't have unlimited vertical, and my speed is much higher, however it takes a bit longer to get up to speed since the thrust is much lower with a 5x5 prop than what the 6x5.5 prop gives me. Speed is great with the 5x5, but I like the combination of thrust and speed I get with the 6x5.5 apc prop.

So if you put an APC 10x5 or 11x6 prop on your motor, you will have alot more thrust, but be mindfull of WOT flying. Your hovering may be easier since you have more thrust, and get out of trouble down low thrust/power. Speed is unimportant when you are trying to hang off the prop down on the deck.

[sidnam]

try a 10X4.7 slofly prop :) BTW i also fly a sniper3d

[HELINHAWAII]

I run an 11x7 on my 1200kv with no problem. It's an Electrifly 36-35-1200 and pulls 34 amps WOT. Great little motor for $36.

My plank hovered at 3/4 throttle with a 10x7 but does even better with the bigger prop.

[Pinecone]

Larger diameter gives higher thrust due to larger area.

To select a prop for electric, eitehr select pitch for speed (pitch speed) or diameter for hovering, then tune the other for the current draw.

Old rule of thumb on props is +1 inch diameter, reduce pitch by 1.

Try an 11 x 4.7 or 11 x 4.