Helicopters B

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NASA123
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Re: Helicopters B

Post by NASA123 » February 5th, 2014, 6:58 am

You also have to keep in mind that the motor stick should be strong as well as light. A good weight does not mean much because the strength is what counts. If you have, suppose, a .9 gram balsa motor stick, you would be risking your entire device if the stick snaps. I'd say a good weight would be around 1 - 1.1 grams so you can try more types of rubber motors without worrying about it snapping.

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Re: Helicopters B

Post by jander14indoor » February 5th, 2014, 10:49 am

And it depends on how light you can build your rotors!

When I built my demo copter this fall, using very sturdy balsa for rotor spars and grocery store bags for covering, my rotors were a pretty surdy 1.4 gm. That was a four bladed upper, and a two bladed lower, complete. I could get it down to 1.0 gm with still pretty sturdy balsa (8 lb/ft3 vs 12 for the spars). If I wanted to go crazy and use up some of my good wood and specialty indoor covering material I could hit 0.8 gm or less all up for the rotors. I might not use those in a site with a nasty ceiling, but they'd be fine in a smooth ceiling site.

Since the minimum weight this year is 3.0 gm that leaves 1.6 to 2.0 gm (no ballast) all up weight for the motor stick.

As coaching advice, I'd suggest you build moderately sturdy upper rotor, light as you can make lower. Target 1.0 to 1.2 gm for the set.
Build a stout motor stick to 1.6 to 1.8 gm to handle whatever rubber you through at it. Several ways to get there. You can use a REALLY large cross section low density stick. You can make a hollow tube stick. You can use a really light density smaller stick and reinforce with Carbon Fiber. What I wouldn't suggest is to use a skinny, but very hard stick. It will turn out to be bendier due to the low cross section/low moment of inertia.

OH, if anyone wants to know how to build light, I can share my Bill of Materials where I plan out how to hit a weight target. Might need help posting atable on this thing. You can also dig back through prior year posts on Helicopter, Glider & Wright Stuff on how to build to a target weight.

Jeff Anderson
Livonia, MI

lyleis
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Tool for Motor Transfer

Post by lyleis » February 12th, 2014, 6:43 pm

Hello Coaches!

I'm told there is a simple, household tool that is ideal to use to transfer the motor from the winder and onto the hook on the thrust bearing. However, a search of the forums yielded nothing. Can anyone point me in the right direction?

Thanks!

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Re: Tool for Motor Transfer

Post by helicpters_rule » February 12th, 2014, 6:47 pm

lyleis wrote:Hello Coaches!

I'm told there is a simple, household tool that is ideal to use to transfer the motor from the winder and onto the hook on the thrust bearing. However, a search of the forums yielded nothing. Can anyone point me in the right direction?

Thanks!
I've seen people use pliers.

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Re: Helicopters B

Post by TrueshotBarrage » February 16th, 2014, 3:05 pm

How can I view images from the Image Gallery?
2015 Regionals
It's About Time - 3rd
Compound Machines - 1st
2015 States
Bridge Building - 3rd

2016 Regionals
It's About Time - 1st
Air Trajectory - 1st

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Re: Helicopters B

Post by jander14indoor » February 17th, 2014, 3:10 pm

Click on the Image Gallery pick you should be able to see at the top of the page?

Of course that assumes you are using a browser similar to mine (Mozilla Firefox 27.0.1 on a MS compatible desktop or laptop), but you didn't give any detail on that.

Regards,

Jeff Anderson
Livonia, MI

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Re: Helicopters B

Post by bjt4888 » February 20th, 2014, 9:03 am

I am judging this event at a local invitational tournament this weekend and am wondering if the experienced competitors or coaches among you could answer a couple of questions. First, I'm wondering what is the typical device used to judge rotor span. I have a couple of ideas based upon my experience as a long-time indoor free-flight modeler, but am sure that members of this forum can guide me.

Also, I am wondering what the typical process is for judging rule 4(j)..."the rotors no longer support the weight of the helicopter". I can envision that a helicopter may lodge itself in a ceiling obstruction for a few tenths of a second and then break free and continue flying. I would be inclined as a judge to allow the flight timing to continue in this case, but if the helicopter is stuck in a girder for more than a few tenths, I would declare the flight ended. Is this procedure the common practice? If so, how long is too long for a helicopter to be stuck, if it subsequently frees itself and continues flying? Also, if the helicopter is stuck in ceiling obstructions for .5 or .7 seconds before the flight is declared ended, is it necessary to measure and deduct this "stuck time" from the total flight time? This would of course require a separate watch and I could see this happening multiple times during any single helicopters flight.

Thanks for the help,
Bjt4888

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Re: Helicopters B

Post by abby1kanobe » February 20th, 2014, 9:59 am

I have seen several methods to measure rotor spans from using a large caliper to a large cardboard cutout with a hole with a diameter of 25 cm. One event even used a ruler.

I wonder myself about the timing and how arbitrary it can be in reference to the helicopter no longer being supported by its own power. How can you determine that the lower rotor is not pushing the upper rotors on the ceiling rendering the upper rotor motionless??? My idea would be to have one stop watch stop when you think it may have gotten stuck and others keep going just in case the copter begins it desent. Other than that I wish you the best of luck. I am sure more experienced event proctors will have some better ideas.

Good luck!

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Re: Helicopters B

Post by jander14indoor » February 20th, 2014, 1:16 pm

Measurement. I'm an engineer. Measurements introduce errors, I use a VERY good ruler once to make a GO/NOGO gage and then compare everything to the gage. As an event supervisor it is not important that you know how big the rotor is, just that it isn't too large.

For the multi-blade rotors of para 3.e I use quarter inch foam board and VERY carefully measure and cut a circle to 25.0 small as I can measure just over 25.0 cm. I have a set of calipers good to a couple of tenths of a mm. But a good straight edge should keep you between 25.00000 and 25.1 cm. Just be fair to the students and don't make a gage at 24.9 cm.

Students, this doesn't mean you should make a helicopter to exactly 25.0 cm because you may not use the same ruler and the consequences to you are to be tiered, no matter how good your time is. The judges ruler gage will win EVERY time. And there just ISN'T that much time to be gained between a 24.8 or 24.9 cm diameter rotor's performance and one at 25.0 cm. Don't do it.

For the single bladed rotor of para 3.f a circle won't work, that's why the radius is specified. For that I use foam board and cut out a 15.00 wide gap or notch. Start with one straight edge. Use a square to draw a line perpendicular to the edge, say 2 to 4 inches deep. Measure over 15.00000 cm plus as close as you can measure to just over 15.000000 cm and mark a second perpendicular line. Now carefully cut along those lines. At the bottom, you only need a rough cut to clear the material between your parallel lines. Check that measurement again.

In use, the ES holds the gage and the students move their helicopter through the gage. Unless you are VERY experienced with handling these copters under no circumstances do so. They are fragile and it would be a shame if a team couldn't compete because the judge broke the copter. Even if you ARE experienced, avoid it strongly

For multi blade rotors the rotor must fit through the gage with the plane of the blades parallel to the gage, no tilting or tipping, without bending or distorting the blades to pass through. The rotor can touch at the tip on one point of the circle, but the other tips shouldn't touch this. Check each rotor.

For the single blade rotor, the student holds the axis at one edge of the notch and the tip should pass the far edge cleanly. The axis point and the far tip should both pass the gap along a line parallel to the original straight edge.

Weighing the copter. Remember, no rubber.
I like to use a simple knife edge balance. On one end is a simple counterweight, the other a generous hook made of fine wire. The counterbalance is selcected/adjusted to JUST balance the 3.00 gm minimum mass. In use the student suspends their helicopter from the hook and it is good to go if it either balances or overbalances the counterweight.
If you use a scale, you'll need one good to hundredths of a gram. Its hard to set the helicopter on most scales so make a stooge. A padded spring clothes pin with the spring replaced to lower the force works. Attach one leg to a stick, attach the stick to the center of a flat plate as large as the platform on your scale. Set stooge on scale, tare the weight to zero. Let the student clip their helicopter into the stooge to weight. If they have their own stooge, let them use it, just remember to retare the scale.

This note is long, I'll address timing on another.
Jeff Anderson
Livonia, MI

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Re: Helicopters B

Post by jander14indoor » February 20th, 2014, 2:08 pm

OK, timing.
I like to have three timers on every flight. If all three good, use the middle one. If someone misses and knows it, throw out the bad one and average the other two. If two bad, use the good one. Three bad has been very rare.

As long as your eyes are pretty good, you won't find it that hard to figure out if the helicopter is supporting its own weight, but this is why I recommend a site with a smooth ceiling when available. I'll take a smooth reasonably tall site over a nasty but very tall site for helicopters any day. Racquet ball courts turn out to be pretty nice. Generally easy for spectators to see, especially the glass wall ones and easy to seperate competitors from inappropriate coaching.

Warning, following is opinion, how I do it, not official. A helicopter with the upper rotor stopped but not caught on anything is OK (opinion), that's why we added the disk to address the concern about pins sticking into a ceiling (that was sometimes hard to evaluate). If it is hanging over something though, sorry, SOME of the weight is being held by building structure, time stops. If no blades are turning, it aint self supporting, timing stops.

Temporary stops. If the blades bump a vertical wall say and stop turning for a moment or possibly longer as the helicopter slides down, timing continues until it hits the ground. If it bumps into a rafter and bounces back, timing continues. If it hits the rafter and hangs more than very momentarily, stop your watch, count 10 Mississippi's. If it restarts in that time, restart time. If not, they are done.

Dang, just noticed you have indoor free flight experience. You know all about gages and balances to check indoor planes, same techniques for these helicopters. Timing isn't much different except there will be more bouncing around in the rafters (why I like racquet ball courts). Generally if it is moving around in space, you are good. When they are caught, they stop moving around, even if some parts are still spinning. Typically the rotors wrap themselves around a rafter or wire and its obvious.
Another big difference, large floor space isn't nearly as important as a plane or glider. These things MOSTLY go fairly straight up and down. Back to the racquet ball court, you wouldn't want to fly a plane in one (maybe a mini-stick) but helicopters rarely hit the walls, you can even fly several at once for practice with little risk.
Good/bad air doesn't seem to be as critical with these things. STRONG breezes that move them around a lot are bad, but air movement that messes up a Penny Plane doesn't seem to bother these things. Just keep the air consistent,good or bad.

If you are flying in a raftered ceiling, bring a pole if you have one. Some WILL get caught. I give the students the choice of using pole to get it down or having me do so. I may have more experience and reach, but its their helicopter.

Good luck, you'll enjoy it.
Jeff Anderson
Livonia, MI

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