What kind of a Prop is ideal for my rascal 40 's OSFX40 engine? Some say 11x7, is it right?
thanks

Yes, you can use an 11x7 prop. You can consult the engine manual to get the recommended prop sizes for this motor.


Ken

So is prop size dependent on engine type and /or Plane size ?

747,
Yes, the prop size will depend the engine you have. It can also depend on the plane in the fact that you sometimes can't mount bigger props on some planes because of ground clearance.

Ken

747,

Also, while you would use a 9 X 6 with that engine on a Quickie 500, you probably don't want to do that on the big ol Rascal.

Ken, AMA 19352

You could get by with a 12x6 and it would look more scale on the front end of that bird.Don't that thing fly sweet!I miss mine.

For an OS 40 you need to run a 10" prop (unless you are racing, then a 9" prop).

A 46 would use an 11" prop (except for racing or 3D).

These prop sizes are suggested to keep the engine from over revving (prop to small ) or bogging down from too much of a prop load (prop to large ).

The Rascal 40 is a "floater". Even with a low idle plan on having A LOT of runway to land.

Because the Rascal is such a floater, I recommend a Master Airscrew (the black one) 10x5 prop.

An APC is to efficient and will not allow the plane to slow down enough to land. The MAS are less efficient so the plane will slow down enough to land. I have an OS 46FX on my Rascal and I use a MAS 11x5 on it. It is either that or kill the engine in order to land (had to do that before I got the MAS prop for the plane).

Hope this helps and answers your questions.

FWIW - The Rascal will do a nice knife edge and other basic aerobatic manuvers. Depending on your skill level AND radio, I suggest low rates while learning and high rates for the aerobatic manuvers.

They do a nice flat spin too. I also was able to get it to rotate on the wings axis at knife edge.

Wouldn't a 10x5 be a bit underpropped for this engine? I run this size on my Webra .32.

I've always found that if you want to slow down a plane it's better to go with a larger diameter and smaller pitch. This would indicate that an 11x5 might be a better choice, although that's still a bit below the smallest recommended by OS for this engine. if the plane has enough ground clearance, a 12x5 or 12x4 could even be worth trying. The larger diameter seems to create a bit better flywheel effect, which can help reduce the idle RPMs.

Wouldn't a 10x5 be a bit underpropped for this engine? I run this size on my Webra .32.

I've always found that if you want to slow down a plane it's better to go with a larger diameter and smaller pitch. This would indicate that an 11x5 might be a better choice, although that's still a bit below the smallest recommended by OS for this engine. if the plane has enough ground clearance, a 12x5 or 12x4 could even be worth trying. The larger diameter seems to create a bit better flywheel effect, which can help reduce the idle RPMs.

< Message edited by piper_chuck -- 4/19/2006 2:19:22 PM >

I agree with you on the flywheel effect. It can allow you to get a lower idle. However, an 11" prop (for general flying) on a 40 has a high probability of bogging the engine down. Remember, you are talking about a SIG Rascal, not a 3D plane.

I'm not convinced that an 11" prop with the right pitch would be a problem for this engine. Have you taken the opportunity to review what props OS recommends for the engine?

Last time I looked (a couple of years ago ), for a 46 they recommended an 11x5 - 11x7 for sport flying (although some of the older manuals say 10x5 - 10x7). For a 40 they recommended a 10x5 - 10x7 for sport flying. This may very well have changed since I last looked it up.