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Rotor Egg Drop B

Posted: August 14th, 2012, 11:22 pm
by Jim_R
Discussion for Rotor Egg Drop B

Rotor Egg Drop Wiki
2012 Thread

Re: Rotor Egg Drop B

Posted: September 15th, 2012, 10:11 pm
by Itsanthonguise
Hi guys, do any of you have any tips for me?

Re: Rotor Egg Drop B

Posted: September 16th, 2012, 7:32 am
by jander14indoor
Kind of generic, works better if you have more specific questions.

But, as it is a new event, here's some pointers.

The science behind this is aerodynamics, the basic principles behind Wright Stuff, Balloon Launch Glider, Helicopgter Duration & Gliders all broadly apply.

Keep it LIGHT. You are trying to minimize descent rate to reduce impact to the egg, that's the same as maximizing flight time. KEEP IT LIGHT. For everything that flies weight is critical to increasing flight time.

The rotor is a wing flying in a tight circle. This is the same thing as a propellor. See last years helicopter discussions for hints and tiops on rotor design and construction. You'll need to maximize rotor size to minimize descent, challenge will be to do so with minimum weight gain.

Like the other flying events you are trying to get the most flight out of limited energy. You need to really understand that your ONLY source of energy is the potential energy from your drop height. You have to use it efficiently if you want to maximize flight time.

Since you are starting from a complete stop, there is one big difference from helicopter rotor design. Lower pitch results in slower flights, but take longer to spin up. Higher pitch spins up faster, but doesn't slow as much. Depending on drop height, you may not reach full speed with a low pitch before hitting the ground so may still be dropping fast. Optimum pitch will be a tradeoff and require experimentation to figure out.

This a need to spin up also affects design. It takes energy (altitude) to spin up the egg, so why do it? You should have the rotor spin independant of the rest of the device.

So, start designing, start experimenting, and start modifying.

Oh, suggestion on the test process. You don't need to risk an egg every flight. Use an equivalent mass to the egg, similar shape for dynamics. Judge design by flight time and maybe speed (if you can measure it) at impact. Do most of your testing that way and then confirm with eggs when you are satisfied.

Jef Anderson
Livonia, MI

Re: Rotor Egg Drop B

Posted: September 16th, 2012, 7:55 pm
by CMShong

Re: Rotor Egg Drop B

Posted: September 25th, 2012, 8:29 pm
by hebblethwaite
Do you have any ideas on how to or what materials to use on the rotor egg drop.

Re: Rotor Egg Drop B

Posted: October 21st, 2012, 5:46 am
by InfiniCuber
hebblethwaite wrote:Do you have any ideas on how to or what materials to use on the rotor egg drop.
I remember last year I helped my bud a lot in this event... I agree on the materials he used, they were logical. Just use some thin balsa wood and make the thing with that and super glue (don't use gorilla glue) and use Mylar for the rotor covering things.... :D

Re: Rotor Egg Drop B

Posted: October 23rd, 2012, 4:24 am
by JimY
I built a couple prototypes for this event last season, as it was a trial event in Indiana. I can't say they were that great, as drop times from 6 meters were not that high. We used golf balls instead of eggs for testing the devices, even though they are about 10 grams lighter. You could add a 10 gram lump of clay to one side of the ball, but we didn't do that. Ours had either 6 or 8 blades. As Mr. Anderson says, you need to experiment with the blade pitch to get the slowest descent time. Our builds were tested three times in competition (two for two teams at our regional and one at state), and while the shell cracked two of three times, it did not leave a wet spot on a paper towel. One time, the egg did not crack. So, it is possible to not get stuck in tier 2. Maybe this part will end up being quite easy, especially if you have some good ideas to start with and spend enough time working on it.

I don't have a copy of the rules for the event this season, since I do C division instead of B. One construction rule that bugged me like crazy last season was regarding placement of the egg. We used the Indiana rules, which at one point said "The bag will be mounted or suspended from the bottom of the helicopter device in such position that the egg it contains is the first thing to contact the floor." I saw a draft set of national rules for the event over the summer, and they had the same sentence. I could 't believe it. So, can someone quote for me what the final rules say on this? I hope that the first part of the sentence was simplified, as to me, the second part (beginning after "in such position") is the part that really matters.

Re: Rotor Egg Drop B

Posted: October 25th, 2012, 8:49 am
by qiqishi
Can anyone help me with what designs I should use for the propellers?

Re: Rotor Egg Drop B

Posted: October 25th, 2012, 1:42 pm
by InfiniCuber
qiqishi wrote:Can anyone help me with what designs I should use for the propellers?
Well i know that some sorta square wings in the aerofoil shape works (curve the rotor). Cover it in Mylar and it works pretty well. Make it out of balsa. This worked well last year as my friend got 1st at state. But it could definitely be improved on, so try different variations.

Re: Rotor Egg Drop B

Posted: October 26th, 2012, 8:12 pm
by e_sully
Be very careful with laminated rotors that they are not arched, or at least have a solid bottom. A curved rotor will act like a parachute and can get you DQ'd.