Rotors

Re: Rotors

Postby mrsteven on Mon Feb 27, 2012 2:22 am

chia wrote:
thsom wrote:When you guys use helical rotors, what are your main beams? If they are 1/8 by 1/8 wouldn't that get really heavy because you would have four pieces of 1/8 by 1/8 balsa wood of say 36-37 cm length each?
I use 1/16 by 1/16, though I believe some use 1/32 by 1/16. I can't imagine 1/8 by 1/8 is terribly aerodynamic, and the extra strength really isn't necessary.

I've be surprised you could get 1/8^2 off the ground without a super high pitch and super thick rubber for a super short time

Usually 1/16^2, however you can down that a little if you feel lucky. I like to play it safe, any thinner I would be frightened of, i break enough 1/16^2 easily by accident. any smaller the few close calls you get = baaaaaaaad
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Re: Rotors

Postby MrX on Tue Mar 13, 2012 10:39 pm

Have anyone considered using a 3D printer to make carbon fiber rotors. My reasoning is that a single piece of rotor would be much lighter than making a balsa rotor from parts and perhaps aerodynamically more favorable.
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Re: Rotors

Postby chalker7 on Tue Mar 13, 2012 10:48 pm

MrX wrote:Have anyone considered using a 3D printer to make carbon fiber rotors. My reasoning is that a single piece of rotor would be much lighter than making a balsa rotor from parts and perhaps more aerodynamically more favorable.

Couple of issues. The first is that you can't 3D print carbon fiber (yet). All 3D printing processes are additive and either granular or filament based. In order to get the fibers aligned properly, someone would have to invent a new process. The best you can do is to 3D print a negative/blank upon which you could mold carbon fiber.

Second, carbon fiber is actually extremely dense. The benefit you get from it is that its strength to weight ratio is very high. However, due to its density, you would have to use extraordinarily thin sheets (less than 0.001") of carbon fiber to compare on a weight comparison with built up balsa and mylar rotors. Carbon fiber this thin does not exist (as far as I'm aware of) in complete sheet form.

You may want to experiment with forming thin sheets of balsa. Various classes of indoor free flight models require solid wood propellers (such as EZB), and those do have the benefit of being both more aerodynamically more efficient as well as slightly stronger.
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Re: Rotors

Postby sr243 on Sun Mar 25, 2012 9:01 am

I tested two different helicopters with two different rotors. One was 8cm from one rotor stick to the other(width). The other was 9cm. I noticed with the 8cm, the top propeller would spin super fast and I felt like I could get longer times if it slowed down a bit. However, with the 9cm one, the propeller would spin but too slow. The helicopter would descend with over 200 winds left which is just too much. The 9cm is heavier but still 3.55g. The 8cm is 3g without the weight. I was just wondering if this seemed correct. I thought rotors should be even larger than these, but maybe the 9cm is just constructed poorly? I didn't expect it to have such a large impact because the times for the 9cm is about 1 minute while the 8cm can get 1minute 20seconds.
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Re: Rotors

Postby thedoctor on Sun Mar 25, 2012 10:25 am

sr243 wrote:I tested two different helicopters with two different rotors. One was 8cm from one rotor stick to the other(width). The other was 9cm. I noticed with the 8cm, the top propeller would spin super fast and I felt like I could get longer times if it slowed down a bit. However, with the 9cm one, the propeller would spin but too slow. The helicopter would descend with over 200 winds left which is just too much. The 9cm is heavier but still 3.55g. The 8cm is 3g without the weight. I was just wondering if this seemed correct. I thought rotors should be even larger than these, but maybe the 9cm is just constructed poorly? I didn't expect it to have such a large impact because the times for the 9cm is about 1 minute while the 8cm can get 1minute 20seconds.

8-9 cm for the chord at the ends of the rotor (what i'm guessing you mean) is a lot...i don't think you really need to go any larger than that. Then again, I might be misunderstanding what you said.
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Re: Rotors

Postby sr243 on Sun Mar 25, 2012 10:37 am

Okay, thx. So should I increase pitch of the 8cm rotor to decrease its spin speed? It unwinds at almost 10 spins per second when I wind it to 800 winds. If I were to increase the pitch, it would slow down the spin speed right? However, it would also have more winds left over, am I correct?
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Re: Rotors

Postby chia on Sun Mar 25, 2012 12:55 pm

sr243 wrote:Okay, thx. So should I increase pitch of the 8cm rotor to decrease its spin speed? It unwinds at almost 10 spins per second when I wind it to 800 winds. If I were to increase the pitch, it would slow down the spin speed right? However, it would also have more winds left over, am I correct?

That's what I would do. 10 spins/sec is waaay fast. And yeah, It could have more winds left over; it depends on how quickly they run out now, and how quickly your helicopter falls on less winds.
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