Would depron foam work well for a large flat blade helicopter?

[BABAR]

Was thinking of upscaling whopper flopper chopper. https://www.rocketryforum.com/showthread.php?28904-Build-Thread-for-Whopper-Flopper-Chopper

Launch length would be 6 feet.
Each hinged folding blade would be 6 feet closed 12 feet open for a 24 foot diameter (probably 20' with dihedral.)
It would not rotate very quickly.
Also what could I use to reinforce it along the length to prevent bending?

 

[TheAviator]

Depron would work in terms of holding the chordwise forces, but it would certainly bend over itself along the span as soon as the blades open. If you use 3mm depron, I would run 3mm carbon along the edge of your blade and make all of your structural connections to the carbon.

 

[neil_w]

I just went and read the original thread... that's amazing. An upscale would be totally off the charts. Good luck!

op:

 

[Crawf56]

Hmmm....first of all, I recommend talking to Frank at Dynasoar Rocketry. He is smarter than your Average Bear.

Given my experience in building several foam rc models, here are some thoughts:

A) For a depron 'blade' that is 3 inches wide, with a carbon fiber rod, what "feels" right to me is about 2 ft. long (to have the strength you need). Assuming the rod is glued to the bottom center of a blade.

carbon rod/tube: https://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXJDP7&P=0

B) Might try a carbon strip. But don't lay it flat on the blade; cut a small slit in the middle (chord-wise) the whole length of the blade, and glue it end PERPENDICULAR to the surface of the blade (making a "T" of sorts). I don't know how long this could be; 3 feet?

Carbon fiber strip: https://www3.towerhobbies.com/cgi-bin/wti0093p?&C=RFZ&P=7&D=Graphite---Miscellaneous

C) Rigging? Could you incorporate string (or elastic chord) to help support the rotors when fully extended?

Best of luck.

 

[burkefj]

I think that's going to be tough even in reinforced depron, especially tying the hinge mechanisms and deployment springs/elastic, I would think it would have a lot of flex, you'd have to keep extremely light as well. Maybe some sort of lamination with some carbon fiber inbetween might work?

Frank

 

[BABAR]

Hmmm.
4 rotor design, each rotor with two sections, each section 5 feet long (have to fit this in my car!)
Will have 2 sets of hinges, 4 central rotor hub hinges, and 4 mid-rotor hinges to allow for folding the rotors.
Rotors are 4 inches wide. Each section would have a 2" segment of say.... 1/4" plywood to make the hinge attachment.
so need a structural support for each section
Trying to keep costs down. ? 6 foot bamboo poles? 2 Each segment, one front and one back, with depron foam on the outside?
Although this will rotate as a helicopter (won't go very fast) the basic concept is airbrake recovery, so there is no need for any type of airfoil.
What thickness of Depron would I need? Monokote would also work, but I haven't used it before, and the shrinkage might be a problem.

 

[BABAR]

Is this the foam I need?

https://www.rcfoam.com/index.php?products_id=1256

 

[burkefj]

That is what remains of the 6mm depron in the country. Again, I'm not sure how you are going to make the hinges and stiffness work out with those dimensions you are using, I'd have to see what you are planning, or you need to get some of the foam and see how it works for you. Depron is good for certain things but it is not magic. It's good for short span flat plate wings with carbon reinforcing like I use in my kits, or for built up structures, in long flat strips it's not good by itself.

Frank

 

[TheAviator]

That is what remains of the 6mm depron in the country. Again, I'm not sure how you are going to make the hinges and stiffness work out with those dimensions you are using, I'd have to see what you are planning, or you need to get some of the foam and see how it works for you. Depron is good for certain things but it is not magic. It's good for short span flat plate wings with carbon reinforcing like I use in my kits, or for built up structures, in long flat strips it's not good by itself.

Frank

What do you mean "what remains... in the country?"

 

[burkefj]

The European manufacturer changed its process to make it cheaper to make and it changed the consistency and also means the sheets come out with a curve in all four corners that does not come out with heat. That means for flat foamies it is worthless, rcfoam had so many complaints that they are not importing it any more. The manufacturer doesn't care because they make it for floor insulation and that application doesn't need it to be flat.

What rcfoam has is the curved depron and are just selling it out. It's very unfortunate because there isn't a good replacement. Model plane foam is not an exact substitute and I've tried foam board, the foam board from flite test and cellfoam88 and none of them are a good substitute. MPF has variable thickness and is soft and too flexible, cellfoam 88 is brittle, foam board is heavy. At least for my kits there is no substitute yet that is workable as they are designed. They would require more expensive carbon reinforcement, or the use of heavy hot glues or other unfortunate side effects.

What do you mean "what remains... in the country?"