prop size calculator

[choppergabor]

Hello everyone. I am trying to find a size calculator that would allow me to use more than one prop. Multiple props calculator. All I found is this so far and it would calculate only one piece of propeller. Lets say I want to use rather two smaller props instead of one large sucker.
http://www.pponk.com/HTML%20PAGES/propcalc.html
If anyone has anything of that sort I would appreciate a link to it.
Thank you in advance.
Gabor

[scottessex]

Multiple props on the same engine?

[Timchick]

At the same time?

[choppergabor]

Yep say to replace a 60 inch prop with two smaller but keeping the efficiency percentage, ultimately changing the rpm and maybe the pitch..... I know I am difficult

[scottessex]

You will lose efficiency, The prop is the most efficient with the least number of blades, when you add blades you do so because you are limited by diameter and are trying to soak up horsepower.
You could put a 6 bladed prop on a rotax 447 but the pitch would be almost flat.
At 15mph you would run out of effective thrust.
Another way to look at it is if I had a rotax 618 with a 50 inch prop......I would have to add blades to soak up the HP because a 2 bladed prop at that small diameter would be pitched so much that the prop blades would stall. So you add blades to keep a good pitch and absorb HP so you can regulate the engine speed.

[Passin' Thru]

Originally Posted by scottessex

Multiple props on the same engine?

Hey, Wilber and Orvile did it!

[scottessex]

Yes they did Pete, but oh...That chain.....how long will that last? scares me!

[WHY]

Since finding "exactly" the right prop for an engine and application is near "black magic" you would probably have try and make contact with "Marie Lavue", last know address was in the Everglades. There are many different numbers for even just one application.

You've got blade material, blade profile, diameter, rpm, round tip, square tip, P-tip, number of blades just for starters and a prop maker could probably add a lot more factors, like I said, "it aint just diameter and pitch".

Tony

[choppergabor]

Exactly! It is an artform to find the proper propeller for the application, but I have to think there is a better way than keep trying different props till one's happy with the results. That's why I am wondering if there was a calculator or rather a prop designer software for multiply props.....

[RotoPlane]

Gabor - Are you thinking two props on one shaft….or two props separated on two shafts, turning opposite directions….to clear the keel…..or one pusher and one tractor? Or with two engines?.......
Just wondering .

[choppergabor]

Ed I am thinking one engine two props on two separate shafts counter rotating
Just to make it easy Oh thanks for the pdfs I got a good view now of the concept! I like it! Can't wait to see the thing materialize. Ok I am off to help the Queen to clean.....I feel your pain Stan LOL. I ain't gonna pretend hovering I rather bitch.....

[RotoPlane]

Okay…put your foundry skills to work and make a gear box where one gear is on a 582 engine shaft and two gears mesh on either side of it. These "obit" gears size would be larger and the ratio would depend on the prop size.

Ask Ron at Warp Drive what thrust could be expected from one large prop, reduce that by say 10% for gearbox and prop gear-belts losses and divide that by 2 (I'm just thinking out loud). Then ask him what the two smaller props size should be for that divided thrust and their best rpm….see, it's easy .

[brett s]

A single larger one will always be more efficient than two smaller ones at the low airspeeds & power we're talking about here.

As Ed pointed out, you can't forget about drivetrain losses either - more gears or belts means more power wasted, more weight & things to break too.

[choppergabor]

Thanks guys for the thoughts. Certainly making this idea not as great sounding anymore..... LOL

[StanFoster]

Gabor...Just put a 2.5 Subby on it....


Stan