Helicopter B/C [Trial]

masterhat
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Re: Helicopter B/C [Trial]

Postby masterhat » March 8th, 2010, 3:27 pm

wlsguy wrote:
jander14indoor wrote:Who said solid prop? Not required in the rules...


The rules say that "Helicopters must be constructed only from wood, paper, plastic film covering and glue."
I think this pretty much rules out using plastic for the props.
The items left are solid balsa prop blades or something built up (like an indoor duration plane).

Anyone disagree? Do you think it needs a clarification?

Thanks.


There is an Illinois State rule clarification that allows plastic but I'm not sure for Nationals (which is held in Illinois...)
http://www.illinoisolympiad.org/tournaments/state/

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Re: Helicopter B/C [Trial]

Postby baker » March 9th, 2010, 3:52 pm

Well, we built two new helio's, ceiling walker design, the small one (9.5 in dia.) weighs in just above 4 grams and the other larger one (14.5 in dia) weighs 9.2 grams. The smaller one flys, or I should say climbs straight up until it hits something, then it just goes whatever way it is facing at the time it gains thrust again. The larger one requires a much larger motor to spin the prop fast enough for thrust. Tried to flatten the pitch but still same problem. Can't get many winds on a larger motor to give a good flight time. We've flown in approx 28 ft ceiling and get to the roof in about 5 seconds and then bing, bing, bing... Question, is there suppost to be a "cruise" phase with these things? Or do they just go up and then come down?
Jander, with all due respect, you seem to be one in the know of this event...how about shareing your experiances with these...designs, time, height, does it fly around the room..you know stuff..

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Re: Helicopter B/C [Trial]

Postby jander14indoor » March 10th, 2010, 6:40 pm

masterhat wrote:There is an Illinois State rule clarification that allows plastic but I'm not sure for Nationals (which is held in Illinois...)
http://www.illinoisolympiad.org/tournaments/state/


Now why the heck did they do that? Are they trying to allow Ikara props? Anyway, DON'T expect that to be a clarification for Nationals, even if held in Illinois. I mean, it could happen, but not if I...

baker wrote:Jander, with all due respect, you seem to be one in the know of this event...how about shareing your experiances with these...designs, time, height, does it fly around the room..you know stuff..


Ohh I HATE questions like this. Absolutely open ended. Tempts me to say everything so I end up saying nothing after spending an hour writing a long note that I'm not satsified with. OK, lets try a shorter answer and you guys throw out more specific questions.

BTW, you give me WAY too much credit. I actually have very little experience with helicopters, especially compared to Wright Stuff. Part of the attraction of this event is that while the skills of WS mentors are still valuable, few, if any, have the same level of expertise as they have with WS. Leaving more for the students to discover!

But, I'll briefly share my observations and some truisms.

First, what part about weight being CRITICAL to Wright Stuff didn't you get, and why don't you think it applies to helicopters? In building real, working flying machines the first, most important thing is to minimize weight. And so is the second and third! You can get a brick to fly, but you better have a LOT of power, and don't expect it to fly well! The rules require, what, 4.0 gms minimum weight. Your copters MUST weigh very close to 4.0, certainly less than 5.0 gms to be successful.

Second, think of the rotor and blades as a wing. Bigger rotors and bigger blades will give more lift, allowing the rotors to turn slower to lift that 4.0 gm, allowing longer flights. Now, there is a limit on blade size for a number of reasons that tempted me to write an encyclopedia, but that starts getting beyond my expertise fast. As a practical matter you want your rotor diameter to be the maximum allowed, like you want a WS wing to be the maximum span allowed. You probably want widish blades, and possibly more than two for your rotor, but the true optimum is not clear to me at least. I've seen two-bladed rotors with tip chords on the order of 10 to 20 percent of chord diameter seem to fly pretty well. I can't say they are optimum.

Third, the top rotor starts the air moving down, the second is in that moving stream and has to move it faster, the bottom rotor will work best if slightly higher pitch than the top. Not sure how much is best.

Fourth flight pattern. Ceiling walkers fly straight up and descend straight down. I suspect they'll 'cruise' if you get the rubber/rotor combination just right and have enough height to fly in, but haven't had enough experience to get there. This matching will probably be more critical than Wright Stuff. I also suspect winding to torque will be even more critical with these copters. They aren't real stable so if they hit the ceiling so the blades flip them around, the behavior can be exciting. Consider adding a stick to the top rotor shaft to hit the ceiling first so it can spin on that point and keep the blades from hitting the ceiling. I've seen copters with this feature fly to the ceiling and just sit there twirly till the rubber wound down and they descended.

Fifth, construction. With weight so important, expect to need and use building skills very similar to Wright Stuff and the best bridges. You have to build light and strong and straight with great control. You have to build to a specific weight. You have to create an intended shape.

Some broad hints, hope that helps, if not try more specific questions. And for a while, don't expect the degree of expert help you have available for Wright Stuff. Again, that's one of the reasons for trying to introduce this event.

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Re: Helicopter B/C [Trial]

Postby baker » March 10th, 2010, 7:33 pm

Good come back, I told you "all due respect".. Thanks

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Re: Helicopter B/C [Trial]

Postby bchero » March 11th, 2010, 2:56 pm

I'm back and I have a few questions. On the rules sheet, what do they mean by three fixed pitch rotors? I need to know so I can build some during the weekend. Also, (forgive me if this is a very stupid question) what exactly is the motor (the rubber band right ?)? Finally, how exactly do I calculate the motor size? I really appreciate the help here mates.

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Re: Helicopter B/C [Trial]

Postby masterhat » March 11th, 2010, 3:19 pm

Does anyone know if this will be held as a trial event at nationals? How about towline glider?

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Re: Helicopter B/C [Trial]

Postby smartkid222 » March 11th, 2010, 6:11 pm

bchero wrote:I'm back and I have a few questions. On the rules sheet, what do they mean by three fixed pitch rotors? I need to know so I can build some during the weekend. Also, (forgive me if this is a very stupid question) what exactly is the motor (the rubber band right ?)? Finally, how exactly do I calculate the motor size? I really appreciate the help here mates.


The motor is the ruber band. Motor size should be writen on the box/bag/whatever when you buy the rubber. If you have rubber that you dont know what size it is, you would have to use some type of microcalipers to get an approximation.
Im interested in Jandor's description of "fixed pitch rotors"

If anyone cares supervised this event for a div b regionals a week or two ago. There were 5 entries. The flight times ranged from approximatly 1-2 seconds.
If it becomes an event next year, I expect interesting interpretation of the rules by the students, mostly due to the fact that it will be a new event.
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Re: Helicopter B/C [Trial]

Postby jander14indoor » March 11th, 2010, 6:24 pm

bchero wrote:I'm back and I have a few questions. On the rules sheet, what do they mean by three fixed pitch rotors? I need to know so I can build some during the weekend. Also, (forgive me if this is a very stupid question) what exactly is the motor (the rubber band right ?)? Finally, how exactly do I calculate the motor size? I really appreciate the help here mates.


A rotor is a set of blades spinning together around a single axis. Think of a propellor. Might have 1 to any number of blades. Fixed pitch means the pitch (or angle of blade) doesn't change in flight. The rules allow from one to at most three rotors.

Yep motor = rubber band. Note, fuel tank = rubber band too.

The motor size has two parameters. Total mass. This is important because the total energy (fuel) stored by the motor is directly proportional to to mass. The other important parameter is the cross sectional area. Since most motors use the same thickness rubber most shorten this to motr width. This is important becasue the cross section sets the power available for flight.

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Re: Helicopter B/C [Trial]

Postby jander14indoor » March 11th, 2010, 6:26 pm

masterhat wrote:Does anyone know if this will be held as a trial event at nationals? How about towline glider?


Helicopter Duration is planned as a trial at nationals leading to an official event, probably next year.

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Re: Helicopter B/C [Trial]

Postby smartkid222 » March 11th, 2010, 6:35 pm

jander14indoor wrote: Fixed pitch means the pitch (or angle of blade) doesn't change in flight.


How would you have the blade changing pitch? You would have to have a complicated VP prop setup right?
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Re: Helicopter B/C [Trial]

Postby jander14indoor » March 12th, 2010, 7:39 am

The added complexity of variable pitch props is the reason they are banned.

If you want to see one method, look at the indoor discussion lists for examples of F1D variable pitch systems.

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Re: Helicopter B/C [Trial]

Postby StampingKid » March 12th, 2010, 9:03 am

Would fixed pitch eliminate a blade cut out of a sheet of balsa as they tend to flex like a broad blade Ikara prop?
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Re: Helicopter B/C [Trial]

Postby jander14indoor » March 12th, 2010, 10:20 am

I'd expect that kind of variable pitch to be treated like WS treats it. OK as long as no active pitch control. Of course that's why we trial these events is to flush out these questions.

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Re: Helicopter B/C [Trial]

Postby bchero » March 12th, 2010, 4:23 pm

I just got my Penni kit a few hours ago and saw that it contained washers, lead shots, and torque springs. Is this okay, or is there a way to build this thing without these materials? Thanks for the help!

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Re: Helicopter B/C [Trial]

Postby jander14indoor » March 12th, 2010, 6:28 pm

Well, I don't see lead as an allowed material specifically, but it was allowed to balance WS planes. Hmmm, note to self...
As to a replacement, if its just used for balance, you could use a dense piece of wood. Wouldn't be as convenient, but it would work.

Are the washers used as low friction bearings? If so, clearly allowed. If not, how are they used?

Torsion springs. Hmmm, how used in that design. I've seen them but not up close. How they are used would determine if legal.

Comment, is the rogor in that kit pre-made, or do you have to shape it? If premade, its not legal, if you have to shape it, no problem.

Hope that helps,

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