Duration

[illusionist]

Do you mean like the one they picture here, but with a twist so that it acts like a rotor?
http://www.illinoisolympiad.org/iso/fil ... copter.pdf

[lllazar]

Yep that's the one. Of course everything is bigger, to fit the dimensions of this year.

[jander14indoor]

Commonly called a Wright Bat because they (the Wright brothers) invented/played with that layout a lot.

Works OK, got to wonder about the efficiency since the only thing the vertical section is providing is drag, no lift. But they are a little simpler to build.

Jeff Anderson
Livonia, MI

[illusionist]

How about modifying that design so that the vertical surface is twisted, similarly to a rotor?

[lllazar]

Hmm the thing is, lately we haven't been able to get the copter flying. I don't know what it is but it certainly isn't our building technique or the design that is the problem. Now granted it is 4.6 grams, it's still the basic two rotor design that most people use. Can anyone think of any reason for this?

Also is the tail fin necessary?

[jander14indoor]

Is this a new copter that isn't flying, or one that's been flying and quit? More details are needed to diagnose.

Jeff Anderson
Livonia, MI

[lllazar]

New copter, the old one got stuck in the rafters at school. I can't see any difference between the two - it's the usual two rotor 1 fixed one free design, the fixed rotor is about halfway between the bottom and top of the rotor stick. We use .125 rubber at around a 1000 winds...

[jander14indoor]

OK then, something HAS to be different, its probably staring you in the face but hard to see if you are too close. Excess weight is bad, but I hope your design has enough margin to carry an extra .6 and at least fly a little. Though it seems these copters aren't as forgiving as Wright Stuff for excess weight.

Some things that are easy to miss. Are the rotors oriented correctly? One clockwise and one counter? Or both the same? Are they wound in the right order to provide lift or wrong and they provide down force? Rotor orientation is tricky to start, and easy to mess up. Is something hanging up and causing unsuspected drag? Are the pitches REALLY the same as the last one? Curve of ribs? Are you really winding as hard? Have you tried fresh rubber? Is one of the spars cracked and its flexing unexpectedly? Are the spars less stiff and you are getting unexpected flexing?

Probably more things, but check those first. Especially rotor orientation vs winding direction.

Jeff Anderson
Livonia, MI

[lllazar]

Well...by rotor orientation and whether both are spinning in the same direction, what do you mean? The motor stick spins in the opposite direction of the free rotor, and since the fixed rotor is attached to the motor stick, wouldn't it make sense that the fixed rotor spins in the opposite direction of the free rotor?

And anyway, it was the winding direction. Im sad and quite disappointed that i didn't catch my partner winding the wrong way, i wanted both of us to get pretty good at it so ya...but thanks a lot Mr. Anderson, it's actually doing really well now!

[jander14indoor]

Yes they'll spin opposite ways, but in this case I meant the actual rotor orientation or twist itself. Is it correct to the direction of spin to create lift. Of course if you wind it backwards the answer is no but easy to correct. Glad you figured it out, and I bet your partner won't do THAT again.

Jeff Anderson
Livonia, MI