Prop for OS 35 AX

[Pilot Ben 28]

 

The recommended props for it are

10 x 6

10 x 7

11 x 6

12 x 7

 

I'm wondering which one is best for funfly?

Thanks

 

B

 

[Bravedan 106]

I would say for most of the events where speed is not required the lowest practical pitch in order to be able to twitch the throttle and blast a pulse of air across the surfaces without accelerating the plane unduly.

[Pilot Ben 28]

So.... An 11x3 is best?

[Bravedan 106]

 

Look at that list. How on earth do they expect one engine to cope with a 10x6 AND alternatively a 12x7??

 

There are all the other factors, noise, swinging space (undercart clearance), etc. so bIggest practical diameter, lowest practical pitch.

 

[Emay 2]

 

According to this link http://www.os-engines.co.jp/english/line_up/propelle/proindex.htm the sugeted prop is 10x6-7,11x6 or 12x6.

I would go with a 12x4 APC for fun fly.

 

[Pilot Ben 28]

I ended up getting a 12.25x3.75 because Weston didn't have a 12x4. I also have an 11x3 and a 11x4 in case the noise is too high or the engine won't cope

[Martin 0]

 

I think 12x7 in that list has to be a mistake. I'd expect to see a 12x7 on a .55 not a .35!

 

12.25x3.75 might be a bit on the heavy side. I used a 12x4 on several different .46 engines (albeit not an AX) and it was fine there but it appeared to be at the upper end of what the engine could cope with. That said, the other propellers in the recommended list (e.g. 10x7, 11x6) are also ones I'd expect to see on a .40 or .46.

 

There is a useful rule of thumb to compare the rough load that a propeller places on the engine or motor, which is to take the square of the diameter multiplied by the pitch. (This is proportional to the notional "pitch volume" swept by the propeller.) You can use whichever units you want (inches, millimetres, etc) as long as you're consistent between the ones you're comparing. This is only a rough approximation - many engines have quite a limited rpm range for good torque so you're more limited in prop choice than you might think. It's more useful for working out what diameter/pitch you should be looking at when you decide to try going up or down on one or other.

 

For example, based on the list you posted:

* 10 x 6 -> load value 600 (10 * 10 * 6)

* 10 x 7 -> load value 700

* 11 x 6 -> load value 726

* 12 x 7 -> load value 1008 (note how this is MUCH more than the others)

 

The others discussed:

* 12 x 4 -> load value 576

* 12.25 * 3.75 -> load value 563

 

As Dave said, for a fun-fly type plane (and indeed anything else that you want to fly slowly but with max control), you want to be looking at the largest practical diameter and the lowest practical pitch. The prop you have sounds like a good option if the engine is happy with it.

 

[Pilot Ben 28]

 

I think I'll give it a go and if that doesn't work I'll just put a 11x3 which is an inch down from the other. If OS say it'll work, it might work ! As you say, if the engine is happy with it then that should be good!!!

 

 

B

 

[funflyjames 19]

 

The 12.25x3.75 is a great fun fly prop, give it a try, though it might be a bit big for your 35. It will give you lots of breaking effect when you throttle back though which is just what you want on a fun fly.

James.

 

[Martin 0]

Yes, my main concern with that prop on a 35 was how quickly the engine would be able to spin it up on demand. A 12in IC prop has a fair amount of momentum.