Rotors

[lllazar]

You should try 1/8 x 3/16, 1/4 x 1/16 seems like it'd be kinda flimsy.

[illusionist]

I can also agree that 1/16 x 1/16 square balsa spars are definitely strong enough (if you sort out the best ones). For the ribs, I also use 1/16 square balsa pieces, but these are usually among the lightest/flimsiest ones I can find. You won't need much strength for them. So, using those dimensions, it's quite easy to build a sub 1 gram rotor.

[lonestar]

You should try 1/8 x 3/16, 1/4 x 1/16 seems like it'd be kinda flimsy.

Yeah, 1/4×1/16 broke. Would 1/8×3/16 be stripped from a 1/8 sheet? Or is it okay to layer two 1/16 strips together?

[lllazar]

Well you could strip it from a 1/8 sheet or strip it from a 3/16 sheet, but layering two 1/16 sheets isn't something i'd suggest, as there is a difference in strength and stiffness between a solid stick of 1/8 vs two layered 1/16.

Also, if your worried about weight, i wouldn't worry too much, it's not too tedious to find a stick 1/8 x 3/16 that is 12 inches long (and im being generous with that figure, most helis do shorter than that i believe) that's under .5 grams, and theres not much of a reason to go even lighter than that. If your rotors total 1g, and your motor stick weighs in at .5g, that's still .5g left for the rotor assembly parts such as the prop hanger and rear hook.

[smartkid222]

If your rotors total 1g, and your motor stick weighs in at .5g, that's still .5g left for the rotor assembly parts such as the prop hanger and rear hook.

The motor sticks being described are WAY to flimsy for these helicopters. There is no way anything with 1/16 thickness will will work and you are much better off using 1/8 than laminating two 1/16.

According to your math (copied above)
1g+1g+.5g+.5g =3g
there is one whole gram missing in that. That 1 gram should go towards the motor stick which idealy should weigh around 1.5 grams.

[lllazar]

Gasp. Sorry, that was a miscalculation on my part, and i was discouraging the 1/16" motor sticks. For some reason i thought the heli excluding the motor had to weigh under 2 grams - crazy, i don't know how i got that number.

But ya, definitely use 1/8" a motor stick.

[lllazar]

Sorry for double post, but i've figured out and built a jig for our rotors, and i had a few questions regarding it.

The basic appearance of the jig looks like the one pictured here:

http://www.freedomflightmodels.com/imag ... 0Large.jpg

Mine in actuality is different in dimensions and also i added a few things to for better pitch, but it helps to see the pic to answer thq questions:

1. So what's the difference between making completely balsa rotors (Balsa sheet curved into a helical shape) and making "ribbed" rotors with mylar? I suppose experimentation is the key to figuring that out, i think ill make a jig for that as well, but it seems like the "ribbed" rotors would be lighter...correct me if im wrong.

2. Would there be any advantage to not make the rotors 40cm in diameter - larger surface would produce more lift, no?

3. What kind of glue should we use as we will most likely disassemble parts quite often? Now, id say im pretty good at taking a sharp box cutter in between the joint and gently separating the two pieces, even when connected with super glue, with no damage to either part, but to be on the safe side should we use some sort of water soluble adhesive? Any suggestions?

[blue cobra]

I wouldn't disassemble glued parts all that often. I can't imagine that's too good for the strength and weight of the joint. For Wright Stuff I could build each piece separately and connect them with rubber bands, making it easy to switch out and adjust each part, but for helicopters that is much more difficult. I'd definitely try to come up with a way to adjust whatever it is you want to adjust without de-gluing. I was able to solve pretty much every problem in Wright Stuff with rubber bands and tissue tubes. It'll take some adaptation to get it to helicopters, but I'm sure it can be done.

But in the mean time, I think CA dissolves in acetone.

[illusionist]

One suggestion ( I have no idea how well it will work), is to attach the rotors to the rotor spar with plastic tubes, similarly as in Wright Stuff wing posts. You may have to glue it in, but it should be easy to remove/adjust by pulling or twisting the rotor.
Here is an example of what I believe to be that method: http://vimeo.com/12109667 Take a look at when they attach the rubber and before launch.
As for the solid vs ribbed blades, I would recommend going for the ribbed as there is no advantage to the solid ones. Both will have the same lifting surface area, and the solid one only adds more weight to your rotors compared to the ribbed one. (Especially if you are using 1/16 balsa to build both, the ribbed one will be much lighter)

[illusionist]

2. Would there be any advantage to not make the rotors 40cm in diameter - larger surface would produce more lift, no?

Here is a post from the old Helicopter thread by jander14indoor:
Second, think of the rotor and blades as a wing. Bigger rotors and bigger blades will give more lift, allowing the rotors to turn slower to lift that 4.0 gm, allowing longer flights. Now, there is a limit on blade size for a number of reasons that tempted me to write an encyclopedia, but that starts getting beyond my expertise fast. As a practical matter you want your rotor diameter to be the maximum allowed, like you want a WS wing to be the maximum span allowed. You probably want widish blades, and possibly more than two for your rotor, but the true optimum is not clear to me at least. I've seen two-bladed rotors with tip chords on the order of 10 to 20 percent of chord diameter seem to fly pretty well. I can't say they are optimum.