I would image a fair bit of force on that panel during flight...someone calculate that for me....
weight of the aircraft/wing area would give the weight per square inch then multiply by the area of the hatch...
What's the number?
You are talking about the aerodynamic forces?, if so the Calculation is more complex than working out wing loading and dividing by area
Firstly, its only the top skin missing, the underside of that area is still contributing a large percentage of the lift that it would produce, if the upper surface was intact.
Also it is apparently about 60% chord so aft of the CP and flow disruption
may well be quite minimal.
In all it probably had a far smaller effect on L/D than you might imagine
As for the percentage of structural strength of the wing it contributes, would, for me be a guess, so I wont bother....OK I'll bother...< 3%