The present invention relates to an aircraft having an airframe configuration, engine orientation and engine mounting that precludes the ingestion of foreign objects, for example, birds, into the aircraft's engines yet maximizes the flow of air to the engine inlets 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, inwardly of the free or external stream, termed the boundary layer. The boundary layer exists in several states, namely, laminar, turbulent, and wake. 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 to a point beyond the engine air inlets, orientation of the aircraft engine in a manner that precludes ingestion of relatively heavy foreign objects, for example, birds presents a more difficult problem.

SUMMARY OF THE INVENTION The present invention is based on the premise that relatively heavy objects tend to flow rearwardly of the aircraft outside the cytindricat surface defined by the maximum cross section of the fuselage due to their large inertia forces. Accordingly, the engines of the jet aircraft of the present invention are mounted on pylons extending from the vertical stabilizer of the aircraft with the engine air inlets 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. Air flow to the engines is maintained by orientating the engine inlets in the external stream between boundary layer air flow and said rearward fuselage projection.

More specifically, the jet aircraft of the present invention solves the problem of foreign object ingestion by utilizing a conical aft fuselage or taif 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 thereby permitting the engine air inlets to be positioned within a rearward projection of said maximum fuselage cross section. Engine inlet airflow is optimized by mounting the engines on pylons in spaced relation to the vertical stabilizer so as to permit boundary layer air to pass between the vertical stabilizer and the engine air inlets.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a"T-tail"aircraft in accordance with embodiment of the present invention ; Fig. 2 is a front view of the aircraft of Fig. 1 ; Fig. 3 is a rear view of the aircraft of Fig. 1 ; Fig. 4 is a top plan view of the aircraft of Fig. 1 ; Fig. 5 is a side elevational view of the aircraft of Fig. 1 ; Fig. 6 a view taken along the line 6-6 of Fig. 5 ; Fig. 7 is a view, similar to Fig 4, of the invention applied to an aircraft having conventional vertical and horizonta ! stabifizers ; and Fig. 8 is a view taken in the direction of the arrow"8"of Fig. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) As seen in the drawings, a twin engine jet aircraft 10, comprises a fuselage 12 having a generally conical nose section 14, a generally cylindrical center section 16, and a generally conical aft fuselage section or tail cone 18.

In accordance the embodiment of the invention seen in Fig. 1-5, the aircraft 10 has a vertical stabilizer 20 with a horizontal stabilizer 22 at the top thereof in a "T"configuration. Alternatively, as seen in Fig. 7 and 8 conventional horizontal stabilizers 23 and 24 are mounted on the vertical stabilizer 20. In both embodiments, forwardly swept wings 26 and 28 are joined to the fuselage 12 at the aft end of the center section 16, thereof.

In accordance with the present invention, a pair of jet engines 30 and 32 are mounted on pylons 34 and 36 extending from the vertical stabilizer 20. The engines 30 and 32 have air inlets 38 and 40, respectively disposed in spaced relation to the vertical stabilizer 20 but entirely within a theoretical rearward projection of the cylindrical center portion 16 of the fuselage 12.

Engine combustion air flowing externally of the boundary layer enters the engine air inlets 38 and 40 while the inertia of heavy objects forced into the external air stream by the center section 16 of the fuselage 12 will preclude ingestion thereof into the engine air inlets 38 and 40.

While the preferred embodiments of the invention have been disclosed, it should be appreciated that the invention is susceptible of modification without departing from the scope of the following claims.