Rotor Egg Drop B

[jander14indoor]

Actually, balsa is almost a wonder material, hard to improve on good balsa. Problem is, being a natural product, not all balsa is equal, to get good results you have to select carefully.
As an alternative, I've seen light RC planes made with carbon fiber frames for their wings. They take thin, straight, carbon fiber rods and bend them into a loop/oval and glue the covering to that. Here's an example http://www.microflight.com/Carbon-Butte ... room-Flyer
Here's one randomly picked source for carbon fiber rods/tubes/other: http://www.cstsales.com/products.html

Note, I didn't say cellophane, that stuff is CRAZY heavy as a covering material. About 15+ gm/m2
Better, consider grocery store bags, particularly produce bags. The lightest, flimsiest stuff you can find. ranges from 15 gm/m2 down to 7 gm/m2
Better still, consider the light mylar made for free outdoor free flight planes, the light stuff, 0.0005 or 0.00025 thick. around 2 gm/m2 Here's one source http://www.modelresearchlabs.com/using_ ... rials1.htm
Best, but hard to work with, is indoor free flight covering, .000059 thick. This is getting in the range you can judge thicknes by the diffraction color! VERY light. Search for Penny Plane Film. <1 gm/m2
Another source for info on covering weight: http://www.freeflightsupplies.co.uk/lightweight.htm

Jeff Anderson
Livonia, MI

[VikP]

Hello, I am new to rotor egg drop this year and I am just wondering what average times of the rotors are at regionals, states, and nationals (mainly looking at regionals). Also, any design methods or tips that can increase the time it stays up would be appreciated.

[TrueshotBarrage]

Do you think larger wings are better than smaller wings? I am not too concerned about the weight and my coach said that bigger wings are better (shown in the picture) but I heard differently from various sources. I wanted to make sure on the scioly forums, thank you.

[jander14indoor]

First, this is a flying event, you must always, Alway, ALWAYS be concerned about weight. If you double the weight while doubling the area you gain NOTHING. And when you compare two alternative designs, if the weight isn't the same you won't be able to tell if the improvement is from lighter weight, or better lift.

Second, this is science, the only way to be REALLY sure is to test it yourself!! We so-called 'experts' on this forum can be wrong. Remember, the experts once thought the earth was flat, didn't move, and the sun and planets revolved around us!

Now, some theoretical considerations.

To a point, yes, bigger wings are better. But since the diameter is limited for this event, that means you get short, low aspect ratio wings (rotor blades) as area increases. For the same area, a long skinny wing is more efficient than a short fat one. This means in practice, the long skinny wing can have LESS surface area than a short fat one and give the same lift in the same conditions. Where that tradeoff is depends on a lot of details and the best way to figure it out is to try it.

Next, the blades in a rotor don't work in isolation. Each blade travels in the turbulent wake of the blade in front of it and leaves a turbulent wake behind. A wing flying through turbulent air does not provide as good lift as one traveling through smooth air. Thus, the more blades, the less separation, the less efficient the rotor SYSTEM. At some point again the added area does not compensate for the lost efficiency. Again, you'll need to experiment to figure that optimum point.

There is another way to increase area without making short fat blades or trying to have too many blades too close to each other. Add another rotor. Coaxial rotor systems have some interesting properties where the rotors interact in positive ways and the pair more than doubles the lift of the individual rotors. Again details need to be experimentally determined.

Finally, DON'T NEGLECT WEIGHT!!!! This past weekend I was coaching a team that couldn't get their helicopter to fly. There was nothing wrong with their winding or the aerodynamic configuration of the blades. The thing was just TOO HEAVY! Even with a very fat rubber band it could not generate enough lift to rise above launch height. My demo helicopter with less area, but similar rotor properties on the other hand flew to the ceiling on a thinner band because it weighed half what the student's did! And I guarantee the aerodynamics of helicopter duration are transferable to Rotor Egg Drop.

Jeff Anderson
Livonia, MI

[Bozongle]

I have a few questions regarding size limitations and performance.

First off, my current rotor design consists of four rotors, make it a total length of 64 cm by a width of 64 cm and a height of 10cm. I made this rotor with the rule stating "any orientation" in mind, would this design fit in the 51x51x51 cube? I don't have a box on hand to try it out. Also, would I be able to drop it normally? I've heard some discussion regarding "flying configuration" and that if you were to put the rotor in the box diagonally, you would have to drop it diagonally as well. Is this true?

Also, I haven't had access to my 4.75m testing site, so I used an alternative one at around 3.4m and got a time of 2.51 seconds on one drop and 2.56 on a second. How would this performance rank at competitions? Good? Bad? Any feedback would be greatly appreciated

Thanks

[TrueshotBarrage]

I'm pretty sure you have to drop it the same way you put it in the box. However, since a 51 cm cube is a cube, you can use 45-45-90 degree triangles and their properties to roughly figure out if you need to reduce the size.

[Bozongle]

I'm pretty sure you have to drop it the same way you put it in the box. However, since a 51 cm cube is a cube, you can use 45-45-90 degree triangles and their properties to roughly figure out if you need to reduce the size.

Yeah I used that to figure out it can be a max of 70cm, but still confused about the "flying configuration"

According to the soinc website:
"Students will be the ones who choose the orientation of their device in the cube and place it in the cube for verification. Students must be the only ones to touch their device. As long as it fits into the allowed dimensions of the cube,in flying configuration which means with the cup attached, then it passes."

So it seems like it only has to fit with the cup attached rather than having to be dropped in the same orientation that you put it in the box

[jander14indoor]

As per usual, opinion, not official, etc.

I suspect that if they'd meant drop configuration they'd have said drop configuration. By flying configuration I suspect they mean as it flies, not as held in some orientation when dropped.

For most rotors I've seen (it is possible to design otherwise) that would mean with the rotor in horizontal plane.

I believe (wait, checks FAQs on the soinc.org website, yes I'm correct) there is a FAQ that says the rotor does not have to rotate in the box.

So yes, you can have a four bladed rotor stretching from corner to corner of the 51 by 51 cm box horizontal cross section. Note, the corners are pointy, you won't fit broad round tips out there at the extreme.

Regards,

Jeff Anderson
Livonia, MI

[Bozongle]

Ok, sounds good. I currently have a makeshift box which is roughly 51x51x51 and my rotor fits pretty well. Hopefully I don't run into any problems with the event supervisor having conflicted views at State this weekend.

I also finally tested my rotor at a good height today, and from a height of 4.75m it averaged a time of 3.6s. This is a lot better than my older rotors, however I still don't know how this will fare competitively. Good/Bad? Thanks

[Somicvs]

Can someone give me some times for egg drop for this year?