ESDU TM 192:2018

The additional decelerating force that affects an aircraft when rolling on a runway contaminated by a layer of water consists of two components: the displacement force, which is the major component, and the impingement force, which is a minor but significant component. The latter component arises from the impingement of any spray (generated in the process of displacing the fluid contaminant) on to parts of the airframe. In ESDU TM 165 a speed-related function is identified for the form of the impingement force. Such a concept, if it were sufficiently broad in its application to a range of aircraft, may be useful in developing a general (algebraic) treatment of spray.

In this document, the aforementioned concept is developed as part of an empirical scheme and is then considered as an aid to analysing aircraft tests. Data from testing one aircraft when rolling (but not braking) in troughs filled with significant depths of water are appraised. Displacement forces are calculated using the methods of ESDU 05011, ESDU 10015 and ESDU 11004 and are subtracted from the total fluid forces. The residual (impingement) forces are then studied in terms of the algebraic description introduced in ESDU TM 165.