I'm am curious that it is often stated that multiple propellers are less efficient than multiblade props.
What I am curious about is why multi blade props and contra rotating props are used on real aircraft ?
Is that the only way to use enough power with the high hp that the airgraft has ?
Kind of like putting a lawnmower engine in a 1/2A model?

Jim,
In general you start adding blades when you have extra hp and not enough ground clearance to use a two blade prop or the power plant needs to turn at a higher speed that would push the blade tips faster than Mach 1. Another thing that is done is to go to wider blades but that is not the best way, in some designs they (the designer) was willing to give up some top end performance. Some of the turbo prop designs have so much power multi props were used to absorb it while maintaining tips speeds and ground clearance (on some of the bombers you can't lift the ship to high because of having ground crews loading it).

For stunt multi blades are used for ground clearance to avoid having a ship look like its on stilts.

Best,        DennisT

I was talking all multi blade simge engine as in the bouton paul defiant with conter or contra rotating props.
I knew that for speed they say 1 blade but I have never seen a real 1 blade aircraft at all. NOT MODEL that is.
So I kinda wondered why they never tried a 1 blade prop in any kind of real aircraft racer.

Guys,
I've flown stunt with props having from one to four blades.

I flew my canard with a one blade prop, just to see if I could. It was no problem.  The model didn't accelerate real quick on release for take off, but once up to speed, the was no problem flying the pattern. I've always thought that you simply have to trim what you have, to do what you what you want it to do.
I personally like 3 blades, the way they look and being able to make a shorter landing gear.
Of course now that we're using electric power and left hand props, I have to now make my own left handed 3 blade.

     Arch

Thanks Bill for explaining the move. I really did not know what to put the question under.
May a topic area for random thoughts ?
Merry Xmas!