ENGINE/PROP RELATIONSHIP
 

Are there some simple rules to establish the best propeller/engine combination? I know that there are recomendations in the instruction manual that comes with the engine, but I have noticed that opinions are varied about which prop size is the best for the job. As an example let me tell you, I have a Four Star 60 which I plan to fly with a K&B 65 ( I was planning to use a Magnum 1.08 but I was told it was an overkill - what do you think?), how can I determine the best match for this combination?

RE: ENGINE/PROP RELATIONSHIP
 

http://www.rcuniverse.com/forum/fb.asp?m=2437687

RE: ENGINE/PROP RELATIONSHIP
 

Go with an 11/7apc. The charts and graphs are nice for general flying around but they don't have a guide for specializing like speed or 3d.

RE: ENGINE/PROP RELATIONSHIP
 

Hello!
The Old K&B plain bearing engine doesn't like to rew hard so put on a little bigger prop than the 11x7...say a 12x6 or 13x5 or even a 13x6 or 14x5 APC.
Regards!
Jan K
Sweden

RE: ENGINE/PROP RELATIONSHIP
 

To all who answered, THANKS GUYS! This is one of the things that make this hobby unique, people helping each other.

RE: ENGINE/PROP RELATIONSHIP
 

Hey Bolt,

Think of your prop as a transmission.

In real airplanes you hear folks speak of "climb" props and "cruise" props.

You guessed it, a climb prop has less pitch. It enables the plane to maitain a better rate of climb.

And a "cruise" prop has more pitch. They don't climb as good or accelerate as good, but they give you a higher cruise speed.

So a climb prop is like "low" gear. Less pitch give better acceleration and climb.

Cruise props are like high gear. And have more pitch.

If a plane is very streamline , it will actually fly well with a prop with very high pitch. The same prop and engine would be overloaded on a bluont and slow plane.

Aerobats like to go straight up and straight down. They use climb props, less pitch. And the prop can act as a brake on the down leg as well.

The charts listed above show a range. Just what you use in that range depends on your plane and your needs.

Often I will play around with 4 o5 props until I find the one with the best performance for a particular application. When it is right, the difference is more than just noticable.

RE: ENGINE/PROP RELATIONSHIP
 

The 1.08 may be over kill, but with a 14 or 15X6 prop you would definitely have vertical acceleration. I had several of these planes and loved them with a 1.20 four stroke on them. Many folks run .91 FX's on them and have no problems. The 1.08 would require more throttle management, but you wouldn't be disappointed with it's perfomance protential. You can always throttle down, but if you're under powered, you can't get more power when you could need it the most. If you go with the bigger engine, then use heavier duty servos and hardware to avoid flutter potential.

Good luck with you 4*60.

RE: ENGINE/PROP RELATIONSHIP
 

To all you guys out there. Thanks a million for your information. The concept of the prop as a transmission cleared a lot of things for me. I plan to use the 1.08 in my Tiger 60 which is more or less the same thing as the 4* 60. I think that experimenting is another fun part of our hobby.

Merry Xmas to all the pilots in this R.C. Universe !!!!!!!

RE: ENGINE/PROP RELATIONSHIP
 

Don't expect the Mag 1.08 to be a high revving engine. It likes a 15-8 or 16-6 prop best. They are nice running engines. The 2 my buddy and I have are excellent. On the initial run, his took twice as long to start-2 flips vs. 1. Ours always hand start after a choke of 3 turns and 6 flips to prime, then battery and usually 1 flip.

I would build your Tiger 60 without the elevator & rudder servos and install the engine. Then rubber band the servos on the see where they should be placed. You might end up with 1 or both in the rear for correct balance without adding weight.

RE: ENGINE/PROP RELATIONSHIP
 

Like he said. I have two OS 1.08s. Great engine but more of a Torquer than rpms. Frankly yo have too much engine (size) on that thing which can be pulled equally well with a G90 at a lot less the cost.

RE: ENGINE/PROP RELATIONSHIP
 

Thanks for your input. My Tiger 60 is a pretty tail heavy airplane.Having the 1.08 doing nothing in the box for a time, I decided to experiment with the engine in this plane, I rather have power in the nose than dead weight, anyway, I can still (hopefully) control the beast with my throttle.

Thanks again for your input people. I'll keep you poster when I use the 1.08

Death to styrofoam, Long live balsa!