Building materials (excluding covering)

[illusionist]

When you guys mention "music wire", what are you referring to? Is it like guitar strings? Going with that, what size would be best to make a rotor shaft?

[calgoddard]

Music wire, as I understand it, refers to high-carbon steel strings used in pianos and guitars. 0.020" diameter music wire is typically the wire used in Wright Stuff airplanes for the propeller shaft, and similarly used in the Parlor Copter kit with the Harlan bearing.

As to what size of balsa to use in a helicopter for SciOly, the answer is that you use the size that will give you the greatest strength but still allow you to achieve a total weight at, or slightly above 4.0 grams, not counting the rubber motor.

Typically the rotor spars will be made of 1/16" square balsa, and the ribs for the rotors will be cut from 1/16" balsa sheet. The motor stick could be 1/8" x 3/8" inch suitably stiff balsa. Any stabilizer will normally be cut from 1/32" balsa sheet. Of course the size of the balsa will be somewhat dictated by its weight, calculated in pounds per cubic foot. Ordinarily 6 - 8 pound balsa would be used, with care in selection for the appropriate stiffness. Leading edge rotor spars, for example, can be heavier and stiffer than trailing edge rotor spars. Ribs can be lighter than leading edge spars. I hope this helps

[eta150]

I remember that there was a downside to one of the Harlan bearings last year, but I can't remember what that downside was. Anyone remember?

[jander14indoor]

One (the one sold for SO) doesn't have a slit pigtail that allows you to remove and change the rotor. Have to cut the rotor shaft to remove and replace.

Jeff Anderson
Livonia, MI

[eta150]

One (the one sold for SO) doesn't have a slit pigtail that allows you to remove and change the rotor. Have to cut the rotor shaft to remove and replace.

Jeff Anderson
Livonia, MI

Does anyone know which is the bearing sold by the turnertoys.com website? I can't figure it out.

[ironchef48]

What exactly does a thrust bearing do? Does it function with the same purpose as a prop hanger?

[jander14indoor]

Colloquially, as used in this thread, yes, generally the same as a prop hanger.

Technically a thrust bearing is any rotary bearing where the primary vector of force is along the axis of rotation. Its purpose is to reduce the friction from this axial force.

In these strings it is somethimes the more technical definition referring to the bead, brass washer or teflon washer between the rotor and the prop hanger.

Jeff Anderson
Livonia, MI

[lllazar]

I have a few questions regarding the attachment of the free motor to the body stick. Would you use the "front hook" depicted on this page:

http://www.freedomflightmodels.com/paypal.htm

So basically i was thinking i'd attach the front hook to the front of the body stick, get some sort of wire, bend it and poke the straight end out through the front hook, so that it is pointing up if the helicopter was held about a vertical axis. Then attach the rubber motor to the bent end. The question i have now is, how do i attach the free rotor to the straight end of the bent wire - also, the rubber is going to cause the wire hook to pull back, how do i keep the free rotor completely "free", as in its not actually in contact with the front hook, that would cause a lot of friction.

Also, where can i get the right type of wire for the hook? I ordered some stuff from that website, such as the hooks, the mylar, and the winder. I got rubber...but what thickness should i get? I feel like got the wrong thickness. Its was .088.

Edit: Is the use of those plastic hooks legal?

[jander14indoor]

You cannot prevent the rotor from contacting the prop hanger, as you said, the rubber pulls the rotor to the body. You need to add the nose button one picture down to the front hook on that website, it acts as the thrust bearing and reduces the friction to acceptable levels.

Wire size. For the rubber sizes used in this event, range of 0.020 inch (which fits that button) to 0.025 inch (for thicker rubber bands) music wire is appropriate. Connected by either gluing the wire to the rotor, or inserting through a SMALL hole in the spar, maybe both to maintain alignment, and bending back over to catch the rotor spar.

Legal, well, usual caveat about this not being a clarification site, but I think the rules specifically allow commercially available bearings/hangers.

Jeff Anderson
Livonia, MI

[lllazar]

Thanks Mr. Anderson, i understood most of that...what is a the rotor spar?

Also, i think i have an alternative for the nose bead - but wat could i use instead of the glass bead? I forgot to order that for some reason, but could i make something in place of that for the meantime?