Chinook Chat!

[bjt4888]

1k carbon tow, applied with two coats of duco thinned 50/50 with acetone, also pre glue wood with one coat of the glue adds 0.005 grams per inch. Start with very light 1/16" square wood (less than 5.0 lb per cubic foot) and apply the carbon to two sides.

Brian T

[vjindal]

1k carbon tow, applied with two coats of duco thinned 50/50 with acetone, also pre glue wood with one coat of the glue adds 0.005 grams per inch. Start with very light 1/16" square wood (less than 5.0 lb per cubic foot) and apply the carbon to two sides.

Brian T

Where do you buy 1k Carbon Fiber Tow?

[bjt4888]

vjindal,

1k carbon tow, and many other lightweight composite materials, can be purchased at "CST - The Composites Store".

Brian T.

[Ash123]

Does anyone have any ideas on how to use a single rubber band for the chinook? All of my designs utilize two rubber bands- one for each prop. Also, I noticed on some online videos that people use drinking straws for the body of the helicopter. Would that work here? Finally, would it be wise to try and include a third prop for extra lift?

[retired1]

Anything is possible, but is it practical. It takes a large amount of energy from the rubber band(s) to achieve a competitive time. I doubt if a lite chopper could withstand the force of a single band. Turning the corner to vertical will drain a large amount of the energy, requiring a stiffer chopper and thus heavier and thus probably not competitive.

[Unome]

Finally, would it be wise to try and include a third prop for extra lift?

Several competitive designs in 2012 were three or four prop chinooks. The highest-scoring chinook at 2012 Nationals was just over 3 minutes raw time, and most top chinooks were over 2 minutes. The rotor size was 5 cm longer back then, but the minimum mass was 3.5 grams. Consider that the FFM kit already has proven times over 2 minutes by students, and according to Dave can fly for 2:30. I wouldn't recommend trying three or four props unless you really know what you're doing.

[Ash123]

Anything is possible, but is it practical. It takes a large amount of energy from the rubber band(s) to achieve a competitive time. I doubt if a lite chopper could withstand the force of a single band. Turning the corner to vertical will drain a large amount of the energy, requiring a stiffer chopper and thus heavier and thus probably not competitive.

Oh ok, thanks! That really helps. As far as the body of the chinook goes, what type of wood do you think is best? I’ve heard a lot of people say they are using balsa wood but I’m wondering if there is something better. Could carbon fiber work well? I’ve heard some people are using that.

[coachchuckaahs]

A "single rubber band" Chinook would be difficult, as you need counter-rotating. Some have used a horizontal rubber, but it is pinned at the center and each half wound opposite, so no advantage over 2 pieces.

Light balsa is needed, 5-6pcf range, with judicious use of carbon reinforcement such as that noted by Brian in other posts in the heli forum. You may be able to use pure carbon for some parts, but I suspect the motor stick best strength to weight will be either balsa/carbon or balsa with rigging.

3.5g should be fairly reachable. 3,0g is possible, but takes careful wood selection, very careful gluing, and a good design.

Coach Chuck

[Ash123]

A "single rubber band" Chinook would be difficult, as you need counter-rotating. Some have used a horizontal rubber, but it is pinned at the center and each half wound opposite, so no advantage over 2 pieces.

Light balsa is needed, 5-6pcf range, with judicious use of carbon reinforcement such as that noted by Brian in other posts in the heli forum. You may be able to use pure carbon for some parts, but I suspect the motor stick best strength to weight will be either balsa/carbon or balsa with rigging.

3.5g should be fairly reachable. 3,0g is possible, but takes careful wood selection, very careful
gluing, and a good design.

Coach Chuck

Thanks! That really helps a lot. As far as the rubber band goes, how would you recommend picking a thickness for them? I’m a little confused by that.

[Ash123]

Also does anyone know how to actually build the perpedicular motor stocks that hold the rubber bands? I thought about just doing two motor sticks that are used on axial helicopter designs, but I think that would weight too much. Also how would I reinforce it with carbon fiber? And what could I use as hooks for the rubber bands?