Structural Aspects of the Do 31 Jet-Lift VTOL Aircraft

Abstract

SummaryThe special structural problems of VTOL aircraft are examined, taking the Do 31 as a basis and it is shown how these problems can be solved without significant weight penalties.After a short description of the aircraft and the systems associated with aircraft testing, the structural design of the Do 31 is described.The effect of special VTOL load cases on the individual aircraft components are illustrated and it is shown where these are critical. The methods used in the calculations are explained briefly and theoretical results are compared with tests.Special emphasis is given to the lift pod structure and its structural analysis.There are special problems with VTOL aircraft which must be considered during the structural design phase. The effects of temperature on the engine pods, wing and fuselage are shown and the solution of the associated design problems are indicated. The results obtained are compared with a number of Do 31 test results.If conventional British or US fire requirements are applied to the design of lift pods, there is a possibility of some weight penalties. Fire problems and fire requirements for lift pods are discussed with reference to test results. Recommendations for minimising the danger of explosions and for the use of fire detecting devices are also made.A great advantage of VTOL aircraft is their ability to use unprepared sites. Debris may be thrown up by the downward deflected jet exhausts and strike the aircraft. Calculations and test results show the effect of impact velocities, stone shape, etc. Structural optimisation for withstanding debris impact is considered.Noise problems have to be investigated during the aircraft design phase because of the high engine thrust installed in a VTOL aircraft. Results of the Do 31 tor near field noise levels are given. Particular attention is given to the proportion of overall noise level which affects the airframe.