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Low Density EPP Foam for Crashable AWECS

There is one current kind of ultra-lightweight foam composite wing or turbine-blade construction that can take severe abuse- Low-density Expanded Polypropylene (EPP) with internal tubular carbon fiber spars. EPP can be cut with a hot-wire from large blocks into good airfoils with minimal wastage. Such construction is very cheap compared to hand-laid monocoque composite shells. Mass production would be easy. Should a carbon spar break, its a COTS product, easily replaced. This sort of construction is ideal for small AWECS and might scale to about 100 kW rated "crashable" wings, provided overall flying mass is kept very low.


In the late eighties Brooks and I had early access to Ethafoam (expanded polyethylene) to make robust small UAVs years before EPP became available. Joel Sholtz turned us onto EPP, which is even better. EPP is revolutionizing model aviation.

A basic KiteLab AWE method is to separate lift and control from power harvest. A single-line soft kite acts as a pilot-lifter to safely suspend a hot airfoil that is allowed to "go nuts" in self-oscillation to drive a load. Normally the system lands gently in lulls with the hot-wing self-parked. In turbulent conditions the hot wing could hit the ground at high speed (not yet observed). EPP hot wings take this sort of punishment without damage.

Conventional wind turbine blades are not optimized for AWE flying weight or crashing. EPP-based turbines would be far better.

CoolIP                       ~Dave Santos            October 2 , 2010                    M2269

Comment and development of this topic will be occurring here.       
All, send notes, drawings, and photographs!

Terms and aspects:   

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Related links:

Commentary is welcome: (distinguish EPP and EPS foams  Art1, EPP wiki, EPS wiki,    )

  • M3867   NASA enters exploration of EPP arc hybrid wings with unidirectional fiberglass members on lower surface.     July 2011
  • DaveN,   Yes, EPP foam is wonderfully crashworthy and its easy to insert a carbon tube
    for extra stiffness (stock tube sleeve-sets for tapered COTS spars). Bonding a
    fabric skin to EPP is harder, but it can simply be stretched on. A
    foam/spar/skin composite is super for a versatile triple load-path structural
    system, with the spars easily replaced and skin patched. Even EPS foam becomes
    robust in this sort of composite. This is KiteLab's basic construction method
    for high L/D powerwings deployed under soft pilot-lifters,    ~daveS