Helicopters C

[Ten086]

I'm sure it's somewhere in the forums, but could someone remind me how increasing vs decreasing pitch affects lift?

[bjt4888]

Ten086,

Good question; For a particular free stream flow rate, increased rotor pitch (which likely produces increased angle of attack) increases lift and increases drag. Related to this aspect of the Helicopter event, what you would want to determine by experimentation is the rotor blade angle/pitch (area, shape, pitch distribution, etc.) that produces the best Lift/Drag ratio for your particular helicopter.

More important than this rotor aerodynamics analysis, would be to find the best possible motor length and thickness for a particular rotor set, minimizing overall weight and learning to get the greatest number of turns into your motors.

Good luck and keep building and testing.

Brian T

[izzanom]

Hey guys, I'm using the FFM chinook kit this year and I was wondering what others with same model were using for rubber bands. Dave supplied .094" and .1024"(or something similar I can't remember) but they seem rather thick. He says in his instructions that each rubber band should be about 1 gram but that requires each band to be rather short which means I can't do many winds without having a really high torque. I've been trying .072" since I can do more winds but I was wondering what other people were doing. I'm not sure what the "optimal" length and width would be.

[bjt4888]

Izz,

I would suggest that Dave Ziegler has given teams a major start in the right direction with the rubber supplied in the kit. The answer is to test, and test, and test, etc. As this is a major piece of the problem solution, I'm thinking that teams would be reluctant to share very much detail.

Knowing the average rotor revolutions per second (by testing and measuring turns wound and turns remaining and duration) and knowing the duration of the best flights so far at Invitationals and having knowledge of one of the "turns calculation formulas", you can back into the likely rubber motor length and "thicknesses" used by these best flights.

I posted a .pdf of the turns formula that my teams use (John Barker's formula: famous U.K. propeller engineer) in this wiki under a previous year's Wright Stuff thread. If someone wants to find it, I'll cheer them on from the sidelines. Or, you can do what I did as I prepared for my first year coaching Science Olympiad and read every post on every forum for every year (this is a tongue-in-cheek, sort of, challenge for the teams want to accept it).

Brian T.

[glouthan]

Hello all,

I've recently purchased some carbon fiber tow (3K) so that we can use it to reinforce our motor sticks, but our team is not quite sure the most effective and weight efficient way to attach the carbon fiber tow. We've read that whatever glue we use it needs to be applied so that the carbon fiber is fully immersed in the glue for the carbon fiber to be effective in strengthening the motor stick. However, after reading though the forums and other sources the most common method seems to be to use CA glue, but we can't help but imagine that it would add so much weight to the structure, so does anyone know of any other glues we can use to attach the carbon fiber that would be less heavy? We are looking for a solution that would be pretty readily available from stores as we have a competition coming up soon so we probably do not have time to order something online such as a specific epoxy, etc.

Thanks for the help!!

[CrayolaCrayon]

Your best bet would be CA glue from my experience. Other guys on here with more experience could probably tell you more about the glues they use. For me, I personally use Duco in some spots, and CA in others, depending on the area.

[bjt4888]

Glouthan,

Yes, CA glue to attach 3k carbon to will add quite a bit of weight. However, if you start with very light wood for your motor sticks, the end result will be reasonable. For example, the FF kits that my students have built had motor stick wood that ranged from 4.5 lb cu ft to about 6.0 lb cu ft. The lightest kit wood meant that the bare wood before carbon sticks weighed less than 0.18 grams. Attaching 3k carbon tow to both sides of The lightest of these sticks brought the weight up to a very reasonable 0.45 grams each.

Carbon tow is not absolutely necessary though. Sticks a little thicker than those supplied in the FF kit are strong enough to only require the truss arrangement that has been used for Heli construction in the past.

Brian T.

[glouthan]

Thanks CrayolaCrayon and bjt4888 for the advice.

Your best bet would be CA glue from my experience. Other guys on here with more experience could probably tell you more about the glues they use. For me, I personally use Duco in some spots, and CA in others, depending on the area.

When you say Duco are you referring to the Duco cement or another product?

[CrayolaCrayon]

Duco cement. It's a very strong glue. I do know however that there are varied types of CA. I'd take a look at some of those if you're interested. I know there are a couple different kinds.


Good luck with your building!

[daydreamer0023]

Duco cement. It's a very strong glue. I do know however that there are varied types of CA. I'd take a look at some of those if you're interested. I know there are a couple different kinds.


Good luck with your building!

Keep in mind that, although Duco is lighter, Duco isn't as strong as CA...and that Duco does not seep into the wood like CA does. Therefore, CA would be better for attaching carbon fiber tow so it stays better. Duco is better for applications that need removal or adjustment or wood on wood connections - it comes off more easily with acetone than CA.