A Flight Determination of the Tolerable Range of Effective Dihedral on a Conventional Fighter Airplane

Charles J. Liddell · Rudolph D. Van Dyke · Donovan R. Heinle

Jan 1949 · National Advisory Committee for Aeronautics

About this ebook

The results of an investigation to determine the tolerable (safe for normal fighter operation) range of effective dihedral on a conventional fighter airplane are presented. The test airplane was equipped with a special device for varying the effective dihedral in flight over a large range of positive and negative values. The results of quantitative flight measurements of the effective dihedral and the dynamic-lateral-stability characteristics are shown. A survey of pilots' opinions was made to determine which values of effective dihedral were intolerable. It was found that small amounts of negative dihedral (of the order of -5 deg) could be tolerated by the pilots at both landing-approach and cruising speeds and that values of positive dihedral greater than 20 deg could be tolerated. It was found, in fact, that at landing-approach speeds, an effective dihedral high enough (28.4 deg) to produce oscillatory instability could be tolerated. The occurrence of rolling velocity reversals during rudder-fixed aileron rolls with high positive values of dihedral did not adversely affect the pilots' opinions of the over-all lateral handling characteristics. The relation between the findings of this investigation and the present Air Force-Navy stability and control specifications is discussed.