Several AWE starts are betting on their proposed composite airframes to live outdoors for years in all conditions, but risk of hailstorms will be a major economic factor. Aircraft hull insurance exists to protect capital investment in the airframe but rates are much higher to cover hail risk.

The American Midwest is considered the most hail prone place on earth, with around ten hailstorms a year not uncommon. Hail is also occurs regularly around the world at mid-latitudes & tropical higher-altitudes. Aircraft that live outside are particularly at risk to hail damage.

Hail has the worst effect on composite aircraft skins, with severe damage hidden under a smooth surface, while a metal wing clearly reveals damage by denting. Composite damage can allow water infiltration, resulting in worse damage. Eventual total failure of the airframe is possible. Total write-off of a damaged aircraft will not be too unusual. Metal wings dinged by hail are often only cosmetically affected & still meet airworthiness standards. Composite repair is complex and expensive; the affected airframe is never again quite as sound or light as the original condition. Composite airframe damage would commonly not be field repairable; the aircraft would need to be moved to a repair facility.

Composite AWE designs such as those of Makani Power, Joby Energy, and  Ampyx are the most exposed to hail expense/risk. Of course, membrane wings are also vulnerable, but safety is less compromised, and repair is relatively cheap and simple.

Dave Santos                      November 3, 2010

Commentary is invited

• Site experiences are invited.
• Wing materials perhaps intended for "membrane" may include textile, film, laminate sheet, ...
• Collect hail aloft and use its altitude-base potential energy for driving generator?
• Collect hail aloft and use its melt for splitting to get hydrogen for use in onboard energy systems?
•  

Links:     

• Hail
• Membrane wings
• Bristled wing:    Fluid-dynamic characteristics of a bristled wing    "Thrips fly at a chord-based Reynolds number of approximately 10 using bristled rather than solid wings."
• Feathered wings
• Textile wings
• Film wings
• Future graphane or graphene in wings
• Soft wings
• Hard wings
• Composite aircraft skins
• v