Difference in Wet and Dry Screen Height

[Piltdown Man]

I think the answer is buried in the sands of time. When Perf. A as is it is called in this part of the world was introduced, four pistoned engined aircraft were the order of the day and they had a great deal of trouble flying safely with an economic payload following an engine failure. They needed more runway both to stop and fly. Lowering the screen height gave them the margin they needed. This fudge has stayed with us today and the errors associated. I can remember being able to lift more weight from some wet runways than dry ones - clearly a ridiculous situation.

So simply put, a kluge from history!