Abstract:
Performance reduction methods will soon be required for routine tests of turbopropeller aircraft. A survey of the types of methods available has therefore been made to find which type seemed likely to be most useful. The purpose of performance reduction is briefly examined. Methods in use are classified into experimental methods, which require no advance numerical data, and analytical methods, which require such data. The latter class is sub-divided into methods based on small corrections and methods based on performance analyses. The suitability of each class of method is discussed. Experimental methods are only practicable if any engine control linkage scheme is such as to impose dimensionally correct relations between the linked variables. They are convenient if data are required over a range of all variables or if, of the non-dimensional groups which result from dimensional analysis, all or most are susceptible to precise control. If such methods are practicable and reasonably convenient they are very attractive and probably the best to use on turbo-propeller aircraft, particularly at high altitude or Mach number, because of the lack of knowledge, as yet, of aircraft and engine characteristics under these conditions. If experimental methods are impracticable or very inconvenient, analytical methods based on performance analyses are probably the best substitute, at least for tests at high altitude or high Mach number, until such time as numerical data on engine and airframe kehaviour are available and can be easily used.
