THE EFFECT OF HEAVY RAIN.
The FAA sponsored a research programme to discover the effect that heavy rain has on aircraft performance. The results showed that:
1.- The impingement and rapid accumulation of water sufficiently distorts the shape of upper wing surface, albeit only temporalily, to diminish the total lift developed by up to 30% of its normal value.
2.- The impact of the rain on the aircraft and its lowered undercarriage increases drag to such an extent that it decreases the aircraft´s forward speed.
3.- When operating in such conditions a jet engine is slow to respond to rapid demends for power.
4.- The weight of the rain can momentarily adversely affect the aircraft weight.
Quote from "AIRCRAFT PERFORMANCE THEORY FOR PILOTS"
Author: P.J. Swatton. ISBN 0-632-05569-3