At 05:04 PM 28/04/2008, you wrote:
>This is precisely what the British team did before going to Sweden.
>Got an old plane and landed it in a lake. 4 times. Wheels up and
>wheels down. If you want, I can get chapter and verse from someone
>who was in Germany and witnessed the experiments.
>
>
>
>
>_______________________________________________
I have no doubt that wheel down is the way to go.
Let's put some numbers on the suck down force if the curved undernose
area hits the water.
Assume a 0.3 x 1m area of fuselage bottom.(It's probably more than this)
So we have about 0.3 m^2 of area. The wing area of a glider we'll
call 10m^2. so we have about .03 times the lift force of the wings
multiplied by the density ratio of water/air which is around 800. At
touchdown the weight of the glider = lift force generated by the wings.
The fuselage probably won't provide quite as much lift as a properly
designed airfoil. Call it about 0.25 as much for the same area.
Call the glider mass 350Kg, so we have 350 x0.03 x 800 x 0.25
Near enough to 2100Kgf of suck down force on the cockpit. Feel free
to argue the exact amount. It does seem high. This will be offset by
the displacement of water as the glider dives.
You are now in a submarine.
The effect of the wheel down is to create a spoiler for the "lift" surface.
It would be really interesting to see what happens when the wheel
brake is applied before touchdown as to whether the aquaplaning trick
will work. If so the glider should be going somewhat slower when it
finally settles in the water which can only be good. Wa this tested
in the above mentioned case?
Mike
Borgelt Instruments - manufacturers of quality soaring instruments
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