Rotors

[thewinner]

It was a trial event this year, at least in NJ since Bottle Rocket was cancelled due to inclement weather.

[thewinner]

And, Helicopters is just an awesome event in general so I wanted to try it.

[illusionist]

And, Helicopters is just an awesome event in general so I wanted to try it.

That's a perfectly acceptable reason

[jander14indoor]

Also, do you think Helicopters is going to be a B event next year?
Sorry if this isn't the right thread.

I cannot say for sure because MANY people are involved with rules decisions. The high level plan is another year for helicopters in C, then rotate it to B and bring some form of Wright Stuff back to C. Unless folks perceive helicopters as too difficult for B in which case you might see balloon launch gliders. Or it might go some other way entirely. Like I said, MANY folks have a say.

Jeff Anderson
Livonia, MI

[lllazar]

Just wondering, how can it be too difficult? I mean, the basic mechanical concepts such as torque, friction, etc, aren't all that difficult to understand, and if B division kids could do Wright Stuff i'm sure they'd handle heli just fine. And Wright Stuff is coming to C division?? That'll be my senior year,

Also, i've been reading in some posts that the pitch of the bottom rotors vs top rotors should be different. Some have said more pitch on bottom, others have said more pitch on top. Can anyone explain 1. Why the pitches should be different and 2. Which of the above configurations is actually correct?

[jander14indoor]

Dang, I left out the key word perceived. Personally I think div B students can do it just fine, but others have to agree with me. Having done it in NY and at the national trial last year, should be sellable though.

OK, different pitch. Like most things it depends. The correct pitch for any rotor depends on the speed of the rotor through the local air stream, NOT the absolute speed. IF your rotors are close enough together, the top rotor accelerates the air before it hits the lower rotor. For the lower rotor to contribute equally (and you NEED it to as it has equal torque applied, think about it), it either has to turn faster (tough to arrange, lowering the pitch may let it spin a little faster, but the increased drag at the high speed means it doesn't spin enough faster to work efficiently) or have a higher pitch to add its component of acceleration to the air stream. If there is large separation, this effect is less important. This effect is real and has been verified many times on full scale double propellor systems. I also verified it in static testing I did last year as I was developing this event.

Jeff Anderson
Livonia, MI

[lllazar]

Thanks Mr. Anderson.

One more question: I don't know if this has been discussed, or evne if this is the right place to post, but how tight should the covering be on our rotors? I feel like if they aren't tightly covered then i won't get as much lift, but would too tight be a bad thing?

[illusionist]

Thanks Mr. Anderson.

One more question: I don't know if this has been discussed, or evne if this is the right place to post, but how tight should the covering be on our rotors? I feel like if they aren't tightly covered then i won't get as much lift, but would too tight be a bad thing?

If you try to get it too tight, you could easily warp your rotor blade. The pitch could be higher on one side of the rotor. So I cover mine with the same amount of tightness as a wright stuff wing.

[kjhsscioly]

Thanks Mr. Anderson.

One more question: I don't know if this has been discussed, or evne if this is the right place to post, but how tight should the covering be on our rotors? I feel like if they aren't tightly covered then i won't get as much lift, but would too tight be a bad thing?

They can have a little give, it would catch air better than a rigid rotor, and illusionist is right, it isn't worth th risk of warping to get perfect covering. I am curious as to whether we need to cover that little middle segment that is always too hard to cover.

[lllazar]

Hmm. Interesting new find, at least for me, but maybe for others as well. Regarding covering, i made two rotors today and applied the mylar covering by using spray on adhesive. Before this, i had always used super glue. Bad idea.

Rotors covered with super glue: .6-.65 g before covering, .9-.95 grams after
Rotors covered with spray on: .6-.65 g before covering, .7 g after covering.

The mylar adds exceptionally low weight. I weighed an excessive amount of mylar that would easily cover 2 rotors, and it massed out at about .13g. I realized that the glue was at fault. So i tried the spray on and these are my results. With these new rotors, and even a 2g motor stick, i easily build out to about 3.5g total, allowing me to strengthen other parts and have a significant ballast.

O, and build time with the spray on is a lot shorter. However, note that the spray on adhesive should be used with caution, i used a loctite repositionable adhesive and here was my basic method:

I got a fairly large box with an open top. Get your uncovered rotor, and place it inside. Now, go outside to your patio/backyard. Do not do this in your room...the area needs to be ventilated and outside is the best.

Just mist the entire rotor for a few seconds, and take the rotor to the area where you will be doing the covering. Now go about covering however you did before, and keep in mind you can (if you get the right glue) reposition the mylar a lot better than you can with mylar.

I used a surgeon's mask and gloves for the spraying part because im paranoid like that, but hey the back of the bottle said one of the chemicals could potentially cause cancer....o wat we do for science