Gunner is great, gunner is good, let us thank him for… what he says makes sense.
Plus, he has supporting evidence regarding the cause.
But, I’m not sure if the specific ‘ailment’ has been identified.
I do like Scuba’s assessment that it is also related to foil properties. Either nicks in the surface or an excessively sharp leading edge. ..Particularly, if you combine that with gunners concern over twisting of both strut and wings.
Cavitation is a possibility, but that would be accompanied by significant noise and vibration would be readily detectible if damaging enough to cause a crash, imo.
Laminar separation is one guess. Sharp leading edges, smooth profiles , shiny surfaces and low Reynolds number are good conditions to support laminar boundary layers. However, laminar BL are sensitive to laminar separation. This could lead to complete loss of lift on top surface, similar to stalling.
As Scuba noted, rounding the LE, makes the foils less sensitive to AOA. sanding the surface causes early transition to a turbulent BL which is much more resistant to separation of the boundary layer ( a legit analogy to the reason for dimpled golf balls)
I'm sure Peter can recall many stories of airplanes when laminar flow wing profiles were initially implemented. Despite the low drag, many fell out of the sky at inconvenient times.
Turbulent boundary layer separation (stall) still happens, but usually a higher AOA that the 'sweet spot' for foils
All pretty interesting.
I would like to ask for more details if possible.
What was the ‘fast’ speed (or range of speeds where this happened)?
What was heading (upwind, downwind etc)?
Any particular maneuver involved?
Wing profile (eppler, naca, DIY, etc)?
Strut profile (eppler, naca, DIY, etc)?
Surface condition of foils?
Any comparative values for stiffness of wing or strut?
Wings on top of fuselage?
were Top of Wings well faired with fuselage (possible interference effects)?
Wing loading (weight/area)?
Can your description of ‘loss of lift’ also be described a significant increase in drag?
Just prior to event, did you feel you had ability to alter AOA and jump or dive at will?
lastly, are you still convinced that ventilation from the air/water interface is not happening?
...and all this time I thought crashing was my fault.