Accession Number:



Measurements and Analysis of the Forces Acting on a Small Aircraft Flying in the Upwash of a Large Aircraft.

Descriptive Note:

Final rept. 1 Jan 76-31 Dec 77,

Corporate Author:


Report Date:


Pagination or Media Count:



A study has been made of the forces and moments acting on a small aircraft while it is flying in the upwash field adjacent to and behind the wing tip of a larger airplane. Preliminary analysis of the expected ranges of forces and moments were made using available theoretical methods and confirming experiments were performed in the Hydronautics Ship Model Basin. The tests used a large model of the Boeing 747 transport aircraft and a smaller model typifying a fighter-type aircraft. The range of positions of the small model relative to the large model extended laterally 30 full-scale feet from the wing tip or from the tip vortex and downstream roughly 80 feet behind the wing tip. Consideration was given to the problem of maintaining steady position at a point that provided a maximum increase in the lift to drag ratio LD of the small aircraft. The model tests have shown that an increase of 50 in LD can be obtained by a small fighter-type aircraft flying close to the tip trailing vortex of a larger aircraft. Higher increases in LD for the same relative aircraft positions would result if the smaller aircraft exhibited higher performance maxim LD was 8.9 in free air. Calculations made for the models tested indicate that control power of typical fighters would be sufficient to maintain level flight in the favorable positions close to a tip vortex. No influence of the small aircraft on the large should be felt because the most favorable locations for the small aircraft are well behind the wing tip of the large aircraft.

Subject Categories:

  • Fluid Mechanics

Distribution Statement: