Analysis of Empty Weight of General Aviation Piston Engine Aircraft

Abstract

Regression analysis of weight data of general aviation piston engine aircraft (single engine with fixed and retractable gear and twin engine aircraft) with a Pax capacity of 4 to 9 suggests that airworthiness requirements for increased occupant protection introduced during the later half of 1980s have resulted in empty weight growth. It is interesting to note that weight penalty due to cabin pressurization on twin-engine aircraft manufactured before 1986 is about the same as that due to increased occupant protection. Potential reductions in the empty weight of all composite piston engine aircraft are not realized. The cause plausibly is that cumulative weight arising from a) minimum gauge requirements, b) conservative design and certification process, c) damage tolerant design requirement, d) lightning protection system e) poor impact resistance and f) manufacturing deficiencies, offsets the weight reduction achieved through high specific strength and high specific stiffness of composite materials. I. Introduction Airplane design is an iterative process. Convergence of the end result, therefore, depends on the initial inputs, which are derived from past experience. The closer the initial inputs are to the final values the lesser would be the number of iterations and the lesser would be the time required for conceptual design phase. References 1 and 2 constitute the primary source of design information for estimating take-off gross weight and standard empty weight of aircraft ranging from homebuilt to jet transport. Reference 3 provides regression analyses for weight estimation of light general aviation aircraft. However, there has been paradigm shift in occupant protection, through introduction of regulatory requirements, a) installation of shoulder harness on previously certificated aircraft manufactured after 1986 and b) design of seat and restrain system capable of surviving a 21g horizontal and 15g vertical impact for the passenger and 26g horizontal and 19g vertical for the pilot for aircraft certificated after 1988. The market for composite aircraft structures in general aviation has been rapidly growing since 1990 as evidenced by all composite Diamond Aircraft DA 40 and DA 42, Cirrus Design Corporation’s SRV, SR20 and SR 22 and Lancair International Incorporation’s Columbia 350 and 400 aircraft. Cabin pressurization is incorporated in a design for passenger comfort and to provide the capability to fly over most weather. Cabin pressurization, therefore, is being included in the mission requirements for the new piston twins (Adam A500 and Diamond DA42 NG Diesel Twin). There is, therefore, a need to develop design tools for computation of empty weight of aircraft taking into consideration effect of these three phenomena. Regression analyses of weight data of general aviation piston aircraft (Refs. 4-7) with a Pax capacity of 4 to 9 are carried out. Influence of a) increased occupant protection and b) cabin pressurization in piston twins and c) application of composite materials, on standard empty weight of general aviation piston aircraft is assessed. Regressed equations in terms of take-off weight are derived.