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Effect of engine placement on aeroelastic trim and stability of flying wing aircraft
Mardanpour, P; Hodges, DH; Neuhart, R; Graybeal, N
The aeroelastic trim and stability of an aircraft with a backswept flying wing configuration is investigated us-ing the computer program NATASHA (Nonlinear Aeroelastic Trim and Stability of HALE Aircraft). Results obtained for divergence instability, modal frequency, and damping agree very well with those from a recently developed aeroelasticity analysis of the classical Goland wing, the aerodynamics of which is based on a continu-um formulation. Then, the effect of engine placement on flutter characteristic of a backswept flying wing resem-bling the Horten IV is investigated using NATASHA. The stability studies showed that the flying wing exhibits a so-called body freedom flutter with very low frequency and non-oscillatory yawing instability (flight dynamic mode), which is expected in aircraft with neither a vertical tail nor yaw control. The effect of the backward sweep for three engine locations is presented. The maximum flutter speed was captured for engine placement just outboard of 60% span, with a forward offset of the engine's center of gravity from the wing elastic axis. This study showed that the body freedom flutter mode was largely unaffected by the engine placement except for the case when the engine is placed at the wing tip and close to elastic axis. Aircraft c.g. location was held constant during the study, which allowed aircraft controls to trim similarly for each engine location, and seemed to mini-mize flutter speed variation along the inboard span. In the absence of aerodynamic and gravitational forces for the flying wing, and without the engines, a region of minimum kinetic energy for the first symmetric bending mode was also determined to be around 60% span. Possible relationships between the favorable flutter character-istics obtained by placing the engines at that point and the area of minimum kinetic energy are briefly explored. © 2012 by Pezhman Mardanpour and Dewey H. Hodges.
December 1, 2012