1. Field of the Invention
The present invention relates to an aircraft configuration, and more particularly to an aircraft configuration where propellers are mounted adjacent to the fuselage of the aircraft.
2. Background Art
To optimize the airflow around the fuselage of an aircraft, it is desirable to contour the aft portion of the fuselage in a manner that the surface of the fuselage aft portion tapers inwardly with a desired aerodynamic contour to a closure location. A typical closure configuration is in the form of an ogive where the length to width ratio is about three-to-one, this representing an optimum balance between pressure drag and skin friction drag. However, when engines are mounted to the rear fuselage portion, the effect of these engines can be such to disturb the optimized pressure distribution pattern resulting from the flow over the fuselage aft portion. This can result in an accelerated growth in the boundary layer over the surface of the rear fuselage portion, so as to cause increased drag. This problem can be exacerbated when the engines have propellers. In general, the diameter of a propeller for an engine of a given horsepower would be greater than the diameter of a fan for a fan jet engine of the same horsepower. Further, with the fan of a fan jet engine being enclosed in a nacelle or shroud, the disturbance in the flow field adjacent the aft fuselage surface is reduced somewhat, in comparison with propellers. For these reasons, as well as others, it is important to consider the effect of rear engine mounting as it relates to optimized airflow over the aft portion of the fuselage, particularly where there is an unshrouded propeller.
A search of the patent literature has disclosed a number of U.S. Patents, these being the following.
U.S. Pat. No. 1,386,493 discloses an aircraft or dirigible having a cooling system for a motor that drives the propeller. Air is introduced into the nacelle and this passes over the radiator of the motor. The air then passes rearwardly out from the nacelle. For example, in FIG. 1 air is introduced through aperture "a" and into chamber "c" enclosing motor "d". The air then flows along passage "e" and exits through the aperture "f". Also, air is inducted through the aperture "h", passes across the radiator "i" and is expelled through the aperture "j". In FIG. 1, the propeller is mounted at the rear of the aircraft. Other configurations show the propeller mounted at the forward end of the aircraft.
U.S. Pat. No. 2,385,499--Garvy discloses an aircraft having a propeller positioned at the forward end of the fuselage. The rear end of the fuselage has lateral portions which bulge outwardly. As shown in FIG. 7, when the airplane is turning so as to be in a yaw condition, the air flowing over the rearwardly positioned bulging portions on the fuselage acts in a manner to create a pressure differential along the opposite sides of the rear portion of the airplane, thus making it easier to turn the airplane.
U.S. Pat. No. 2,874,922--Whitcomb deals with the overall shaping of the airplane to reduce the effects of drag when the airplane approaches and exceeds the speed of sound. This relates to the well-known "area ruling" concept.
U.S. Pat. No. 2,956,760--Attinello discloses an airplane where the side portions of the fuselage have the capability of blowing air outwardly or sucking air inwardly. This is done to affect the local pressure along the fuselage, thus obtaining some of the aerodynamic benefits which might otherwise be obtained by modifying the actual contour of the fuselage.
U.S. Design Pat. No. 211,426--Smith discloses an aircraft configuration where the propeller is mounted rearwardly of the wing and is centered on the fuselage. At the location of the propeller, the diameter of the fuselage is made smaller than that of the main portion of the fuselage.
U.S. Pat. No. 3,455,523--Hertel discloses an aircraft where a cantilever support 2 is affixed to the rear end 7 of the fuselage 9. A plurality of jet engines are mounted to this cantilevered support member 2. This patent points out the difficulty of prior art configurations where the engines are mounted under the wing or laterally of the fuselage, in that the streams of air flowing along the engine and along the aircraft part on which they are mounted interfere with each other and cause an increased resistance and drag. The patent in column 1, beginning on line 64, discusses the invention disclosed therein as follows, "Due to the fact that the engines are carried by a rearwardly projecting spear-like support spaced from the fuselage, detrimental effects of the engine on the fuselage are avoided, and neither interference of airstreams, nor impingement of the walls of the fuselage by high pressure sonic waves takes place."
U.S. Pat. No. 3,476,336--Hertel relates to the contouring of a body, such as a fuselage of an aircraft, traveling at high subsonic speeds. The body has a transverse thickness gradually increasing from the nose of the body to an intermediate portion and gradually decreasing from the intermediate portion to the tail of the body. In FIGS. 15, 16 and 17, there is shown an arrangement somewhat similar to the earlier Hertel patent (U.S. Pat. No. 3,455,523), where a plurality of jet engines are mounted to a thin support 51 extending rearwardly from the fuselage.