I've decided to try my hand at building a helicopter completely from scratch. The part I've started with and am having trouble with is the rotor.
It has mostly to do with the fact that I dont know whether what i'm doing produces any lift. But I feel as if i'm doing something fundamentally wrong.
Does a helicopter stay aloft by producing lift with its rotors as air foils? or are they more like some sort of extremely efficient fans that induce an air mass flow downwards that has a reaction on the blades themselves and is transmitted to the body of the helicopter to keep it aloft?
I made a 4 blade rotor that was like 10 inches in diameter and turned it with a DC motor and it produced enough wind to feel it like 6 or 7 feet away. it was just a flat piece of metal that i curved so it would have some pitch.
The other thing I did was to make something that came out to roughly 2 feet long but only 2 bladed instead of 4 like the preceding one. The special thing about this one however was that instead of being a curved flat piece of metal, it was an air foil (or at least an approximation of one). What I did was to cut 2 pieces of metal to be 3 inches wide and 12 inches long, bent them at a point 1.25 inches into their width, and then curve the 1.75 inch part of the resulting L shape so that it matched with the 1.25 inch part. This basically created a flat that was 1.25 inches wide, with a curved top and a flat bottom and a huge amount of camber. I made a coupling piece out of two aluminum plates and 4 4-32 screws and 2 brass screwsand an inch long steel rod of 3/8th inch diameter (which is what I put into the drill when I tested it). When I put this on my electric drill, it didnt make such a lot of wind as the other simpler thing even though they were moving theoretically the same speed.
I think my problem is making a test stand that I can use to measure the force produced by these things tangent to their axes of rotation. but I'm just curious if anyone has any thoughts on how to improve the way i'm making these things.
I realize that it wasnt exactly logical in an experimental sense to make a rotor that was twice as long and had half as many blades and compare it to the first one, but I am operating with a limited supply of this aluminum (which is this really great stuff they use to cover exhaust pipes on building generator units that I grabbed some scraps of when we were done).
I figure it might have something to do with the tip effects or the fact that I held off on taping the two edges that are supposed to meet together. I havent taped it yet because I dont want to make it sticky and have to deal with the parasitic drag that might create.
Another thing that's bothering me is the fact that the curvature of the top is very circular. as I recall, airfoils i've seen in the past are more flat towards the back and curved towards the front.
If you have a flat piece of metal and you curve it so it looks like the top part of an airfoil, can you approximate it as an airfoil? I didnt think so, which is why I made the second one the way I did.
Also, Could it be that what i'm doing is actually too heavy to be practical even though it's hollow. I know that the most common material in use is balsa wood.