Aeronautics and astronautics – Aircraft – heavier-than-air – Airplane sustained
Reexamination Certificate
1998-08-11
2001-03-13
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Aircraft, heavier-than-air
Airplane sustained
C244S05300R, C244S055000, C244S130000
Reexamination Certificate
active
06199795
ABSTRACT:
The present invention relates to an aircraft having an airframe configuration and engine orientation that precludes the ingestion of foreign objects, for example, birds, into the aircraft's engines yet minimizes side line noise due to the reflection of jet exhaust on the vertical stabilizer of the aircraft.
BACKGROUND OF THE INVENTION
The propulsion system of an aircraft must be capable of ingesting foreign objects without engine damage. The problem of foreign object ingestion has been solved in the past by merely increasing the strength of the engine components exposed to impact damage. However, strength can be equated with weight, which, in turn, compromises performance of the aircraft. Reconciliation of such seemingly divergent performance and safety requirements requires careful integration of the aircraft's propulsion system with airframe aerodynamics.
The basic model of air flow past an aircraft fuselage assumes that air viscosity acts over a relatively thin region termed the boundary layer. The boundary layer exists in several states, namely, laminar, turbulent, wake and the external stream. In the laminar state, flow is stratified. Farther aft, laminar flow transforms into a turbulent state which is eddying in character. Turbulent flow subsequently transforms into a wake wherein the direction of flow may actually reverse.
While careful aerodynamic design can cause the boundary layer, whether laminar or turbulent, to remain attached to the aft fuselage at least to a point beyond the engine air inlets, relatively heavy foreign objects, for example, birds, tend to flow rearwardly of the aircraft outside the cylindrical surface defined by the maximum cross section of the fuselage due to their large inertial forces.
Thus, placement of the engines so that their inlets are entirely within the area defined by the forward (passenger) section of the fuselage (i.e., so that they cannot be seen by an observer located forwardly of the aircraft on the extended axis of the fuselage) precludes foreign object ingestion. At the same time, careful aerodynamic design can limit the boundary layer thickness at the engine inlet plane to a finite value so that a reasonable gap between the inner boundary of the inlet and the fuselage will permit the boundary layer to pass between the inlet and the fuselage and permit the inlet to ingest only high velocity free stream air thereby maintaining the high efficiency of the installation.
It is to be noted, however, that any solution to the problem of foreign object ingestion must take into consideration the problem of side line noise induced by close proximity of airframe appendages to high density or velocity airflow.
SUMMARY OF THE INVENTION
In accordance with the present invention, the engine air inlets of a jet aircraft are positioned within a rearward projection of the maximum lateral cross section of the center section of the fuselage so that ingestion of foreign objects into the engine air inlets is precluded while air flow to the engines is maintained. Side line noise is minimized by eliminating the effect of high velocity exhaust gases on the vertical stabilizer of the aircraft stabilizer by extending the engine nacelles and exhaust nozzles along both sides of the vertical stabilizer to the rearmost extremity thereof. More specifically, the jet aircraft of the present invention solves the aforesaid problems of foreign object ingestion and side line noise by (a) utilizing a conical aft fuselage or tail cone that, in a lateral plane containing the engine inlets, is significantly smaller in radial cross section than the maximum cross section of the main fuselage section (b) separating the engine air intakes from the fuselage to permit boundary layer air to pass between the fuselage and the engine air inlets, (c) placing the engine air inlets radially inwardly of a rearward projection of the main fuselage section yet in of the rearward flowing external stream and well forwardly of the separation point between turbulent flow and the wake and preferably forwardly of the separation point between boundary air flow and turbulent flow, and (d) extending the exhaust nozzle of each engine to the rear of the fixed portion of the vertical stabilizer.
REFERENCES:
patent: 3060685 (1962-10-01), Tonnies et al.
patent: 3455523 (1969-07-01), Hertel
patent: 5114097 (1992-05-01), Williams
patent: 1756250 (1970-03-01), None
patent: 945365 (1964-04-01), None
patent: 1041132 (1966-09-01), None
Barefoot Galen L.
Lyon P.C.
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