I have a new MVVS 58cc that has 2 gallons of fuel through it at this time. I am running a NX 24X8 prop, but it is turning to many rpm's on the ground. 7830 rpm's on the ground, no telling what in the air. What I need to know is what size prop do I need to get the rpm's down to where they need to be. These props are too expensive to experiment with to find the right size. Also, NX does not make a 25" diameter prop, they go from 24" to 26". I was thinking of trying the 24X10 but I don't think it will drop the rpm's that much. I do know one thing, this is one powerful engine!!! I am really happy with it, it cranks easily and runs great. Has not dead sticked me yet.

YOU ARE OVER-SPEEDING YOUR ENGINE!!!!

This engine reaches its peak HP number at only 6,700 RPM (or only 6,200, if it is the ProSport), so you are over 1,100 RPM over the top with this 'puny' prop. And the is a ground figure...

The engine should be propped to spin around 6,000 RPM on the ground, which means a 26x10 (Mejzlik), or a slightly smaller Menz, or Bolly.

You should try to prop for about 6000 rpm static. That can be achieved ith 24x12 up to 26x8-10
For three bladed props, 22 x10-12.
The large 26" prop should be of the narrow blade type.
I turned a Menz-S 24x12 at 6050 rpm using a Krumscheid 50-70cc pipe without tuning the length for best rpm.
Look at the power curves on [link=http://mvvs-nl.com]my web site [/link] and you wll see what rpm are best suited.
I hope this helps.

Sorry guys, I typed in the wrong rpm's, it is 6830 instead of 7830.

Flyer,


It is still too small a prop.

We both wrote the RPM should be set to around 6,000, in ground static conditions.

Dar, I definitely agree with you, this prop is too small. That is why I posted my question here, to see what size prop I needed to get the rpm's down to the proper level. I have ordered an NX 24X12 and will try it. If it turns 6000 static, will unload in the air and turn 6800? I guess that should have been my original question, how many rpm's does a prop gain unloaded in the air vs. static.

Flyer,


Unloading is a function of you model's aerodynamics.

The faster it can fly, the greater the unloading, on a given prop.


If your plane is a slow flying 3-D model, you may prefer a larger diameter, smaller pitch prop, than the 24x12 you suggested in your last post.

A 26x10 may serve this purpose better.

If your plane is a sleek, fast model, you may want a 22x14-16 prop.
All should be close to 6,000 RPM, but do take a reading.

All will unload similarly in level flight, each at its plane's respective version of 'fast' flying.