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Helicopters B

Posted: August 4th, 2013, 3:22 pm
by Jim_R

Re: Helicopters B

Posted: September 11th, 2013, 8:13 pm
by silverheart7
How would you even go about building a single bladed rotor? It doesn't sound (conceptually) easy to make balanced.

Re: Helicopters B

Posted: September 12th, 2013, 6:58 am
by jander14indoor
Ahh, you've found our devious challenge for this year. And thus the bonus for figuring out how to make it work, kind of like the Chinook challenge to div C two years ago that students blew rule writer expectations away.

More practically, you will need a counterbalance, trick is it has to work in two dimensions.
First it has to balance the mass of the rotor spinning around the axis. That's pretty simple. Just put a mass equal to the blade at the same center of gravity radius as the blade. This is easy to do statically, just like balancing a 'normal' two blade rotor.
Second, you need to balance the thrust of the blade as it rotates around the axis. This is the hard part both conceptually and physically. The single blade's force is no longer balanced by the opposite blade so it pushes off to one side as it spins around the axis. If you locate that counter balance behind the plane the blade travels through, as it spins centripedal (or is it centrifigal I tend to get those two confused) force creates an outward force. Since the mass is behind the plane of the blade that means a forwards force similar to the force from the blade. At any single rpm you can find the right offset for the mass to just balance the blade. Trick is your rotor doesn't operate at a single rpm, so you need to find the best compromise to sort of balance across the flight range. Or figure out a self adjusting mechanism that doesn't otherwise violate the rules.

Old time free flight planes used to do this all the time because theoretically a single blade prop is more efficient. Some flying events today still do so. Google it.

http://www.outerzone.co.uk/plan_details.asp?ID=3582
http://www.hippocketaeronautics.com/hpa ... =59&page=2
http://www.ultraligero.net/Cursos/vario ... a_pala.pdf

Jeff Anderson
Livonia, MI

Re: Helicopters B

Posted: October 8th, 2013, 4:56 pm
by Olympian_Cau2134
Does any body know if an air screw would be allowed? Like daVinci's design, but with the same diameter all around :D

Re: Helicopters B

Posted: October 9th, 2013, 11:03 am
by chalker7
Does any body know if an air screw would be allowed? Like daVinci's design, but with the same diameter all around :D
This has come up in the past. This is not official, but I do not see a clear statement in the rules that would prohibit an air screw.
More importantly, why do you want to make an air screw? If you look at all modern helicopters and vertical take-off aircraft, they follow very similar design strategies.

Re: Helicopters B

Posted: October 9th, 2013, 4:23 pm
by Olympian_Cau2134
Does any body know if an air screw would be allowed? Like daVinci's design, but with the same diameter all around :D
This has come up in the past. This is not official, but I do not see a clear statement in the rules that would prohibit an air screw.
More importantly, why do you want to make an air screw? If you look at all modern helicopters and vertical take-off aircraft, they follow very similar design strategies.
I don't know if it would help, but I was going to make a prototype

Re: Helicopters B

Posted: October 10th, 2013, 10:22 am
by coppersquirrel
I'm new at ordering materials for science olympiad events and I've noticed that some in the past (on this forum) have recommended Roy White as a source for mylar for helicopters/egg drop in prev. years. Does anyone by any chance have his contact email/phone? I've had no luck trying to locate him on google data search. Thanks so much.

Re: Helicopters B

Posted: October 10th, 2013, 11:39 am
by Balsa Man
I'm new at ordering materials for science olympiad events and I've noticed that some in the past (on this forum) have recommended Roy White as a source for mylar for helicopters/egg drop in prev. years. Does anyone by any chance have his contact email/phone? I've had no luck trying to locate him on google data search. Thanks so much.
Hmmm...,
If you Google "mylar roy white", 3rd hit is:
http://www.indoorspecialties.com/articl ... 20Them.pdf

His, and many other supplier's addresses are on the last page.

Re: Helicopters B

Posted: October 11th, 2013, 8:32 am
by jander14indoor
Does any body know if an air screw would be allowed? Like daVinci's design, but with the same diameter all around :D
Start with usual comments about not offcial, this isn't a clarification, just one guys opinion, etc...

I assume you are doing this as a way to get the single blade bonus. As I read the rules, there are no restrictions on Chord (not what I recommended, but that's why I preface my messages about not official, my suggestions aren't always followed, nor should they be) so a diVinci airscrew should be legal.

BUT, as chalker7 said, there is a good reason you don't see daVinci air screws in real life. While propellors are often called airscrews that is REALLY misleading. The whole screw concept falls apart when you take it out of a solid. Propellors and rotors don't work like a screw at ALL in fluids. They act like a wing flying in a really tight circle. All validated models, theory, analysis, etc are based on that, NOT a screw.

Now, why do chalker7 and I suspect a daVinci screw won't work well. Take that screw surface and unwrap it from the axis. It becomes a very long, not very broad surface. Something called VERY low aspect ratio. This is a VERY bad thing in theory and practice for a lifting surface in a fluid. Their is a reason the wings on a man-rated glider are VERY long and skinny (high aspect ratio), this turns out to be the shape needed for an efficient wing. See, what happens on all real wings is that nice theoretical straight air flow isn't, straight that is. Some of the airflow spills over the tips of the wing and reduces the available lift. A wing with LONG tips in relation to their width (span) spills a LOT of air, those with short tips vs width (span) spill relatively less air. The wing that spills less air is more efficient. And an efficient airfoil is much of the game in these endurance events (the rest is LOW WEIGHT).

So, what happens with a daVinci screw? Instead of the air being driven down, creating a reaction force upwards called lift, most of it spills outward in all directions creating little net force.

Now, feel free to prove me wrong, science wouldn't advance otherwise. But you should understand where you are starting from when you set out to prove conventional wisdom wrong.

Good Luck,

Jeff Anderson
Livonia, MI

Re: Helicopters B

Posted: October 12th, 2013, 3:44 pm
by Olympian_Cau2134
Does any body know if an air screw would be allowed? Like daVinci's design, but with the same diameter all around :D
Start with usual comments about not offcial, this isn't a clarification, just one guys opinion, etc...

I assume you are doing this as a way to get the single blade bonus. As I read the rules, there are no restrictions on Chord (not what I recommended, but that's why I preface my messages about not official, my suggestions aren't always followed, nor should they be) so a diVinci airscrew should be legal.

BUT, as chalker7 said, there is a good reason you don't see daVinci air screws in real life. While propellors are often called airscrews that is REALLY misleading. The whole screw concept falls apart when you take it out of a solid. Propellors and rotors don't work like a screw at ALL in fluids. They act like a wing flying in a really tight circle. All validated models, theory, analysis, etc are based on that, NOT a screw.

Now, why do chalker7 and I suspect a daVinci screw won't work well. Take that screw surface and unwrap it from the axis. It becomes a very long, not very broad surface. Something called VERY low aspect ratio. This is a VERY bad thing in theory and practice for a lifting surface in a fluid. Their is a reason the wings on a man-rated glider are VERY long and skinny (high aspect ratio), this turns out to be the shape needed for an efficient wing. See, what happens on all real wings is that nice theoretical straight air flow isn't, straight that is. Some of the airflow spills over the tips of the wing and reduces the available lift. A wing with LONG tips in relation to their width (span) spills a LOT of air, those with short tips vs width (span) spill relatively less air. The wing that spills less air is more efficient. And an efficient airfoil is much of the game in these endurance events (the rest is LOW WEIGHT).

So, what happens with a daVinci screw? Instead of the air being driven down, creating a reaction force upwards called lift, most of it spills outward in all directions creating little net force.

Now, feel free to prove me wrong, science wouldn't advance otherwise. But you should understand where you are starting from when you set out to prove conventional wisdom wrong.

Good Luck,

Jeff Anderson
Livonia, MI
I asked someone in my science group, and he said it would be terrible too :D