Building a Kaman free flight helicopter

Thanks for answer.
That would be the best way but i don't now anything about the power in detail.
But I think that the engine has enough power to fly with the helicopter. What would you think?
The engine has enough power to bring a rc airplane in the air. Then it should also get free flight hlicopter in the air right?

bnitram

Hi bnitram,

And if I haven't said so, Welcome to the Forum! I'm not involved in a lot of rotorywing flying, but here are my thoughts:

Engine sizes/ratios between airplanes and helicopters don't transfer equally because of the different characteristics of the two...especially in THIS type where the engine is essentially dead-lifting the helicopter with it's little prop. An .020 on an airplane just pulls it forward and lets the wings do the lifting. The rotors on this type basically provide stability by spinning while the propeller does all the lifting. With the engine out of fuel, the rotors then do their thing in gently lowering it to the ground.

Cox marketed an .020 type called a "Sky Copter" which flew so well, there was a chance that it'd take off and leave you. Perhaps Mark or some other collector here would measure and weigh theirs to give you some workable numbers to shoot for. Hope this might help.

Good Luck with your project ! Kim

Thanks for answer.
So the size and weight are very important.
Do you think if I take the right size and weight it will work?

bnitram

Does anyone here know the power output of these engines? I would wild guess that a Babe Bee is around 40 watts. There is at least one member at RCG that has done extensive power measurements on engines. I'll try to find one of his threads. I don't even remember his name right now. He built a device with a swing arm he mounts the engine to and measures how much it can pull.

bnitram wrote:Thanks for answer.
So the size and weight are very important.
Do you think if I take the right size and weight it will work?

bnitram

If you know the watts per pound of the original, then yours will scale directly.

Hello! Thank's.
I think I found a table with performance disclosures.
http://www.mh-aerotools.de/airfoils/cox_performance.htm

Can it help?

bnitram

You could set the engine up on a balance beam and weigh the thrust...

With many models, the density decreases as volume increases. This means a larger model ends up with lighter loading due to proportions.

Phil

Re:

bnitram wrote:http://www.mh-aerotools.de/airfoils/cox_performance.htm

Looks like the horizontal axis is RPM so if you got the right prop on tweaked for max horsepower, you likely get 26 watts out of the 0.020, and roughly twice that out of a typical 0.049. So just go for 1/2 the weight I'd guess = 1/2 the size.

I remember as a kid putting an 0.020 on a scratch hovercraft and it just sitting there stuck to the ground... But the cox helo flew nice.

Show us your result! BTW anyone ever see an engine tied to a rag fly like a helo?

daddyo wrote: BTW anyone ever see an engine tied to a rag fly like a helo?

like this
https://www.youtube.com/watch?v=ph2PMs2-7G4

https://www.youtube.com/watch?v=67PUWyKdqjI

cheers
a

So you think that it works well with a half size and the Cox PeeWee.
Just as I thought. But not with the power but the size of the engine.

bnitram

Since things don't always scale exactly, you might consider building it with a bit longer main rotor blades. Then you can cut them back if needed to get the desired lift. Easier to cut them down than adding length....

ado1974 wrote:

daddyo wrote: BTW anyone ever see an engine tied to a rag fly like a helo?

like this
https://www.youtube.com/watch?v=ph2PMs2-7G4

https://www.youtube.com/watch?v=67PUWyKdqjI

cheers
a

Ya! Haven't seen that in a while! Amazingly cheap, ultimate quick build haha.

I'm sure things don't scale exactly but my thought is that were not going 1/20th scale or the like, just 50%. Looks like horsepower is kinda proportional to displacement, but that can sure vary alot depending on model/brand. Also since the helo is mostly made of material along the length of the body, which might likely be most of the weight aside from the motor, that cutting the length in 1/2 would be 1/2 weight. Might want to see what the weight of the motor is between the two sizes to see if that might affect things (are they 2:1 ratio?). If you want to be certain it'll have enough lift, maybe you would make it even smaller than 50%.

Many thanks for the answers.
I think I will begin in a few weeks and i will build the blades a bit larger than normal to test it out.

bnitram