Performance Changes with Design Variables: An Analytical Method of Rapidly Assessing the Effect on Performance of Changes in Design or Conditions of Flight

THE use of an analytic method of aircraft performance calculation allows certain calculation facilities denied to normal graphical method. The analytic method has to make certain basic assumptions but justification for these can be claimed in that at the design stage the overall drag can never be exactly summed from the individual component drags and in the ‘flown’ stage a normal scatter of results always occurs, the analysis values should always lie within such scatter. Analytical methods have been put forward in the past by Bailey Oswald and R. M. Clarkson amongst others for the airscrew propulsion type aircraft and recently by R. K. Page for use with turbine jet propulsion. The airscrew propulsion case is more difficult to deal with than the turbine jet case as the level speed is derived from the solution of a cubic equation of the powers involved. At the higher speeds possible with jets, compressibility effects may be involved, in which case an analytical approach is not practical.