I have a DVD of a History channel program on MAV's and they highlight the ARA BATCAM which has become the Nighthawk. They describe the wings as a combination of carbonfiber and ripstop nylon so they can fold up and fit in a tube. That's cool, but how do they combine ripstop with carbonfiber and get it stiff but flexible?

Here's the link which shows a picture of the wings bending to fit in a tube.

http://www.ara.com/robotics/Nighthawk.html

I'm guessing it's the "glue", but what kind of resin will hold a shape and be flexible like tupperware? Is it somehow infused with a flexible plastic? I'm not looking for their trade secret, just a general idea of a material.

I am using ripstop nylon for live hinges in some of my planes.
The trick is ,You have to make a sandwich ,for instance,carbon/nylon/glass,so nylon sits in between other materials.
Laminating resin is MGS
Yuri.
http://yuricomposites.com

Very cool. My guess is that the carbon is in the form of carbon fiber rod in a sort of "skeleton" arrangement. I would love to know details though.

It's neat alright, MAV in a tube. On the show, a soldier reaches in the tube pulls it out and the wing pops into shape. It still has flex to it and I saw a paper on the stability benefits of that wing with some flex. Seems it dampens it some so it isnt all twitchy.

I can understand how they sandwich the nylon, maybe even have a thicker area near the LE. I just dont understand how a regular resin could bend like that without cracking.

Easy! the carbon is so thin that you can fold it down around itself due to the shape. It keeps its rigid shape the other direction due to the shape of the airfoil. Its a thin foil like an old school hangglider. Meaning the top skin is also the botton skin. Plain weave it very flexible. this wouldn't work well if it was made with uni.

Brandon

Interesting...maybe it gets its strength from its geometry like a tape measure does.

Very thought provoking!

Originally Posted by Ward Hagaman

Interesting...maybe it gets its strength from its geometry like a tape measure does.

Very thought provoking!

Thats exactly what I was talking about! Thats the prefect example!!

Brandon

Some shops use Gorilla Glue instead of epoxy for flexible carbon parts

Originally Posted by JIM CALDWELL A

Some shops use Gorilla Glue instead of epoxy for flexible carbon parts

I should have figured that as a possibility. I'm sitting hiere looking at my plane and that is exactly how I did the pod, except it is glass. It was painted in the mold and you cant see that immediately until the cowl is pulled and the ugly yellow is visible. As a method, it is strong and flexible and I've crashed enough to prove it is tough and still very light.

As for the Nighthawk, maybe they use a clear polyurethane.

http://morse.colorado.edu/~timxb/Aiaa.pdf

Here is a description of the wing construction (on page 4):

The wing is fabricated with a carbon fiber skeleton, containing a main spar running the length of the span with thin battens attached, and nonbreathable rip-stop nylon skin. This construction technology, developed in part at the University of Florida results in a flexible wing design providing two features key to the success of this small UAV. First, the elastic properties of the wing battens, constructed of unidirectional carbon fiber strips, allow passive adaptive
washout, improving stability and gust response. Much like the feathers of a bird, the battens near the wing root are stiffened with an increased number of layers of carbon fiber, while the tip battens remain thin to promote flexibility.
The second feature is the ability to fold the wings. The main spar of the wing uses a bidirectional carbon fiber mesh with the fibers oriented ±45 deg relative to the span. The fabrication technique, combined with the geometry of the
airfoil camber, results in a structure that is stiff in the upward direction and flexible in the downward direction, allowing the wings to be rolled underneath the fuselage. This wing design, along with a non-rigid V-tail design, allows the BATCAM to be stored, fully assembled and ready to fly, inside a tube less than six inches in diameter.