Rotor Egg Drop B

[Bozongle]

Participated at the northridge invite today in Indiana. Just finished our competition rotor yesterday after procrastinating. The height was 4m and it got 2.7 seconds, however the egg cracked on the bottom. I believe it was because we didn't get all the air out of the bag when we put the egg in and it was inflated, or we used too much tape. Either way is that a good time?

[SOCoach]

Do ribs on the rotors (like helicopters) have a noticeable effect on times?

[Skink]

I, too, would like to know about that. I have rarely seen ribs on egg drop devices, so what would be the purpose for using them when they are?

[Adi1008]

Do ribs on the rotors (like helicopters) have a noticeable effect on times?

If you use light wood (1/16" square balsa), I doubt it would amount to much more than a gram or two (including glue). Hence, given the fact that most of the devices I've seen are around 20-30 grams, I don't think it would have a significant impact (if you are asking as to whether it lowers the times). In regards to how it may increase the time: that depends on the design, size, shape, and weight of the blades.

I, too, would like to know about that. I have rarely seen ribs on egg drop devices, so what would be the purpose for using them when they are?

I personally use them to make curved blades (blades that are in three dimensions rather than two). However, I'm sure that there are better, more creative ways to utilize them.

[ckssv07]

Do ribs on the rotors (like helicopters) have a noticeable effect on times?

They probably would but I believe that it would be counted as a parachute, because of the curve.

[SOCoach]

We are getting times of 2.4 - 2.6 seconds at heights of 14 feet. (Without breaking the egg obviously) Any feedback as to how competitive this would be?

[Bozongle]

In terms of weight, what would be a good weight for a device with 11 rotors, or a rotor egg drop device in general? Mine yesterday weighed in at 31g after putting on some new rotors and fixing up the device, but some excess glue is there that I'm going to be getting off soon and I could probably shave it off to around 25g. Would that be a good weight or should I try to get it a bit lighter?

[NASA123]

Just got back from a regional tournament and I got 2nd place! My design had two 24x24 rotors with curved ribs set at about a 10 degree angle. It weighed in at about 12 grams and got a time of 3.05 seconds on a 17 foot drop. The egg survived as well. A good weight would be around 15 grams or less and a good time should be almost 3 seconds on that drop. Also, how do you even fit eleven rotors onto one device? The highest I've tried is eight. Having more rotors on the device lowers the efficiency like crazy. There should be sufficient space between the rotors to let turbulent air calm down. When a rotor goes through the air, it leaves turbulent air behind it, which lowers the efficiency of the rotor behind it. I am not saying that more rotors will make your device worse, I am saying that it does not use every rotor to the maximum potential.

[Mixadoodle]

The instructions say that the device can't contain a balloon, but is it allowed to cut a mylar balloon and use pieces of it to cover the blades?

[jander14indoor]

As usual, the best place to get official answers about the rules is to ask on the NSO website, www.soinc.org because that's the ONLY official place to get answers. What follows is JUST an opinion.

Assuming all other rules are met (no parachute is the one to watch with flexible coverings) that should be OK. You can buy the exact same material mylar balloons are made of in sheet stock form. Why should it make any difference if you cut it from a balloon? Consider, you can make a perfectly good balloon out of any non-permeable flexible membrane material. If the ability to make a balloon from the covering eliminated it, it would also eliminate Japanese tissue, grocery store bags, plastic wrap, etc.

Warning though, are you sure the balloon material is the lightest covering you have access to? I haven't weighed it, but just handling it, seems like some of the grocery store or produce bags are lighter. Before you use it, consider weighing equal size pieces of different coverings and select the lightest.

Jeff Anderson
Livonia, MI