|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
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
(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
Conventional wind turbine blades are not optimized for AWE flying weight
or crashing. EPP-based turbines would be far better.
~Dave Santos October
2 , 2010
Comment and development of this topic will be occurring here.
All, send notes, drawings, and photographs!
Terms and aspects:
Commentary is welcome: (distinguish EPP and EPS foams
EPS wiki, )
M3867 NASA enters exploration of EPP arc hybrid wings
with unidirectional fiberglass members on lower surface.
- 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).
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
system, with the spars easily replaced and skin patched. Even EPS
robust in this sort of composite. This is KiteLab's basic construction
for high L/D powerwings deployed under soft pilot-lifters,