Aircraft propulsion system arrangement

In an aircraft arrangement comprising an aircraft fuselage provided with a wing on either side thereof and provided with a propeller propulsion system at the rear of the fuselage, the improvement comprising a propulsion system comprised of at least two independent propulsion units each mounted in its individual lateral fuselage section in a rear fuselage part formed by the central fuselage section originating from the outer contour of the main fuselage section and tapering toward the fuselage end, the lateral fuselage sections having an outer contour tapering in spindle form toward the fuselage rear to the diameter of the propeller spinner of each propulsion unit and propellers on each propulsion unit arranged behind the fuselage and the air frame.

STATE OF THE ART 
Various arrangements of propeller propulsion means for an airplane are 
known, particularly for turboprop propulsion systems, depending on the 
given layout criteria for an airplane. One example is to place one 
propulsion unit on each wing at both sides of the fuselage, but this type 
of arrangement has the disadvantage of the sudden appearance of a large 
disturbing moment about the yaw axis, especially when there is a sudden 
failure of one of the engines of the propulsion units. Moreover, this 
arrangement causes noise problems due to the propeller sound waves 
entering the passenger compartment and the twisted air streams from the 
propeller have an adverse effect on the airflow over the wings. Another 
problem with the engines arranged on the wings is that the propellers have 
a destabilizing effect on the airplane. One attempt to reduce these 
adverse effects consists in increasing the vertical tail surface but this 
leads to a greater airplane weight and a larger surface flown around by 
the air streams. 
Another known arrangement for the propulsion means of an airplane 
comprising having a propulsion unit in both the nose of the fuselage and 
stern area of the fuselage but this arrangement results in aerodynamic 
problems caused by the influence of the flow of the propeller air stream 
of the nose propeller about the wing and fuselage. Thus, no laminar flow 
can be obtained with this type of arrangement and the arrangement of the 
drive means inside the fuselage consumes a large amount of the fuselage 
space. 
A further known arrangement for the propulsion means for airplanes 
comprises housing the propulsion means in the so-called "tail-twin" 
arrangement in the rear portion of the fuselage but both propulsion units 
drive a common propeller which overcomes the disadvantage of the previous 
discussed arrangements but despite two propulsion units, there are safety 
problems in case of failure of the propulsion transmission means to the 
common propeller or in the event of damage to the propeller. Also, the 
diameter of the propeller circle is limited by the .beta. angle of 
rotation (clearance angle) to be initially maintained. The specific 
propeller load is defined by the ratio (KW/D.sup.2) where D is the 
diameter of the propeller circle and KW is the propulsion power. Since the 
jet efficiency decreases with increasing propeller load, there are 
relatively narrow limits to propeller layout with respect to propeller 
disk D.sup.2. 
OBJECTS OF THE INVENTION 
It is an object of the invention to provide a novel airplane design with an 
arrangement of at least two completely independent propulsion units in the 
rear area of the fuselage free of prior art disadvantages and having 
improved stability behavior and favorable aerodynamic flow conditions. 
It is another object of the invention to provide an improved structural 
design of the rear fuselage component of an air plane to accommodate the 
propulsion units. 
These and other objects and advantages of the invention will become obvious 
from the following detailed description. 
THE INVENTION 
In an aircraft arrangement of the invention comprising an aircraft fuselage 
provided with a wing on either side thereof and provided with a propeller 
propulsion system at the rear of the fuselage, the improvement resides in 
a propulsion system comprised of at least two independent propulsion units 
each mounted in its individual lateral fuselage section in a rear fuselage 
part formed by the central fuselage section originating from the outer 
contour of the main fuselage section and tapering toward the fuselage end, 
the lateral fuselage sections having an outer contour tapering in spindle 
form toward the fuselage rear to the diameter of the propeller spinner of 
each propulsion unit and propellers on each propulsion unit arranged 
behind the fuselage and the air frame. 
The arrangement of the invention ensures a considerable increase in safety 
in the event of a failure of the airplane propulsion by the completely 
independ driving units, each consisting of a drive unit with its own 
transmission means and adjoining propeller. Because of the special 
arrangement of the drive units, interruptions caused by the flow of the 
propeller air streams around the fuselage and wings are avoided and the 
boundary layer flow on the fuselage is received and conveyed by the 
propellers rotating behind the air frame. Due to the design of the central 
fuselage section with the lateral sections, the air flow in the area above 
the central section is delayed in an advantageous manner by the diffusor 
formation effect. Furthermore the arrangement of the driving system in the 
rear fuselage part has a stabilizing effect by the propellers, 
particularly in a lateral approach. 
The arrangement of the driving units in the area of the rear fuselage part 
has the further advantage that, compared to the propulsion means arranged 
on the wings, the passenger compartment is outside the range which is 
admitted by the propeller sound waves and this results in a considerable 
reduction of the noise in the passenger compartment. 
Another feature of the invention comprises the outer contour of the central 
section of the rear fuselage part having an increasingly flattened form 
with regard to the z-coordinate starting from the outer contour of the 
main fuselage part. This flattening of the central section in connection 
with the lateral, spindle-shaped fuselage sections results in an 
aerodynamically favorble tail design and an advantageous design of a rigid 
fuselage unit which is particularly suitable to receive the propulsion 
means and their auxiliary devices.

Referring in detail to the embodiment of FIGS. 1 to 4, the fuselage 1 is 
divided into main fuselage portion 2 containing the payload compartment 
and rear fuselage portion 3 carrying the tail unit and drive system 4, and 
the wings 5 are secured to the sides of fuselage 1. The propulsion system 
incorporated into rear fuselage portion 3 contains two propulsion units 8 
and 8' at either side of the vertical longitudinal center plane E-E of the 
airplane inside the rear fuselage portion 3. 
The rear fuselage portion 3 has an air frame contour to accommodate 
propulsion units 8 and 8' which is comprised of a central fuselage section 
11 and lateral fuselage sections 12 and 12' formed as a unit. The central 
fuselage section 11 has an outer contour which, starting from the outer 
contour of the main fuselage part 2, has a flattened form increasing in 
the direction of the fuselage end relative to the z-coordinate. The 
central section 11 passes over the area of the fusealge end from the 
increasingly flattened form into a sharp rear edge 14 which widens in the 
direction of the y-coordinate. The lateral fuselage sections 12, 12' have, 
starting from the main fuselage part 2, a spindle-shaped contour extending 
to the rear and serve to accommodate the propulsion units 8 and 8'. At the 
rear end of the lateral fuselage sections and behind tail unit 6, there 
are arranged the propulsion propellers with the propeller disks 34 and 34' 
extending in a common turning plane E1-E1 perpendicular to the 
longitudinal axis of the airplane without overlapping. The spindle-shaped 
outer contour of the lateral sections 12 and 12' tapers in the direction 
of the fuselage tail to a diameter which corresponds to the diameter of 
the propeller spinners 32 and 32' of propellers 31 and 31' of propulsion 
units 8 and 8'. The drive plants 9 and 9' of the driving units 8 and 8' 
are arranged at a minimum distance with regard to the vertical 
longitudinal center plane of the airplane and also at a minimum distance 
following the main fuselage part 2, that is, behind the payload 
compartment relative to the longitudinal axis of the airplane. 
To connect the propellers 31 and 31' to the drive plants 9 and 9' there are 
arranged inside the lateral fuselage sections 12 and 12' extension shafts 
25 and 25' which are connected by clutches 26 and 26' and 27 and 27' to 
the output shafts of the drive plants and through reducing gears 28 and 
28' resp. with the propellers 31 and 31'. 
For air supply and waste gas exhaust in the drive plants, designed in this 
embodiment as turboprops, the lateral sections 12 and 12' of the rear 
fuselage part 3 surmount with their outer contour of the main fuselage 
part 2 for the receiving an air inlet and gas outlet system 20 and 20' and 
21 and 21' resp. with the respective air inlet orificies 19 and 19' and 
the air supply channels. The air inlets 24 and 24' of the drive plants 9 
and 9' are connected with orifices 19 and 19' by feed channels inside 
sections 12 and 12'. 
As it can be particularly seen from FIG. 2, the drive plants 9 and 9' and 
their respective extension shafts 25 and 25' assume with respect to their 
longitudinal axis of position deviating from the longitudinal center plane 
E-E in the direction of the tail end so that, despite the arrangement of 
the drive plants 9 and 9' at a minimum distance from the vertical 
longitudinal center plane E-E, propulsion propellers 31 and 31' with 
relative large disk diameters in the common turning plane E1-E1 can be 
provided as long as the propeller disks 34 and 34' do not overlap. The 
rearwardly tapering contour of the lateral sections 12 and 12' extends so 
that the cross sectional contour of the rear fuselage part 3 remains 
substantially constant over the entire longitudinal extension. The center 
fuselage section 11 has to this end a width which diverges in the 
direction of the fuselage end. 
FIGS. 3 and 4 shows the transition of the outer contour of the rear 
fuselage portion 3 starting from the outer contour of the mainfuselage 
part 2 in the area of the cross section III--III of FIG. 1 into the 
lateral sections 12 and 12' and the central section 11. 
FIGS. 1 to 3 and 9 as well as FIGS. 5 to 8 show two different embodiments 
for the arrangement and design of the tail unit with the special design of 
the rear fuselage portion 3. In the embodiment of FIGS. 1 to 3, the tail 
unit 6 is designed as a so-called Y-tail unit in which each of the 
spindle-shaped sections 12 and 12' carries the outwardly inclined tail 
unit fin 40 with its respective rudder 41, and the central section 11 
carries a vertically downward pointing fin 43 with control surface 44. In 
the design of FIGS. 5 and 6 which relates to the design in FIGS. 1 to 4, 
the propellers 31 and 31' are arranged behind the fuselage tail, that is, 
behind the fuselage air frame. 
The design of the tail unit is based on a so-called T-tail unit form in 
which the vertical rudder fin 45 is directed with control surface 46 to 
the central section 1 of the rear fuselage portion 3. Rudder fin 45 
receives in a known manner in the T-tail arrangement elevator fin 48 with 
elevator control surface 49 and 49'. In this tail unit arrangement, the 
tail unit 6 surmounts the propulsion propellers 31 and 31', but here too 
propellers 31 and 31' are behind the fuselage air frame. 
In the embodiment of FIG. 9, propellers 31 and 31' are staggered relative 
to the longitudinal axis of the airplane so that the propeller disks 34 
and 34' extend in parallel, but staggered planes E1-E1 and E2-E2, 
respectively. In this design, overlapping of the propeller disks 34 and 
34' is also conceivable and the rest of the design of the rear fuselage 
portion 3 corresponds to the embodiment of FIGS. 1 to 8. 
FIG. 10 shows an advantageous design of the wing unit or tail unit wherein 
the design is based on a generally known "canard wing-configuration" in 
which wings 50 are arranged in the area of rear fuselage portion 3 in 
connection with the lateral section 12 and 12'. The canard wings 51 are 
arranged in known manner in the front area of the main fuselage part 2. 
and in this configuration, the propeller gear directly engages the drive 
plant with no extension shafts and clutches. 
FIG. 11 shows the air frame structure of the rear fuselage portion 3 for 
suspension of the drive plants 9 and 9'. In the side walls 54 and 54' 
which extend in the longitudinal direction of the fuselage of the central 
section 11 there are provided yoke parts 55 and 55' with the usual 
suspension members 56 and 56' and 57 and 57' which cooperate with 
corresponding members on the drive plants 9 and 9' for their suspension on 
the air frame structure. The walls 54 and 54' form the lateral boundary of 
the central fuselage section 11 and the structural connection of the 
lateral fuselage sections 12 and 12'. 
FIG. 12 shows an embodiment with a synchronous connection 60 between 
propellers 31 and 31' in which extension shafts 25 and 25' are connected 
by overrunning clutch means 61 and 61' and reduction gears 62 and 62' with 
propeller gears 28 and 28' and propeller spinners 32 and 32' in drive 
connection. The reduction gears 62 and 62' establish through a connecting 
shaft 64 a connection between propeller gears 28 and 28' of the drive 
means 9 and 9'. In the event of a drive means failure, both propellers 31 
and 31' are available for production of the thrust power through reduction 
gears 62 and 62' and connecting shaft 64. 
If one of the drive means 9 and 9' fails, this results in an improved 
thrust from the intact drive means. Furthermore, if one of the drive means 
9 and 9' fails, the formation of a disturbing moment about the vertical 
axis of the airplane is avoided by the driving transmission from one of 
the drive means 9 and 9' to both propellers 31 and 31', where propeller 
blades 33 and 33' of the drive means 9 and 9' are so staggered in their 
rotation direction that the propeller blades of propellers 31 and 31' are 
positioned to fill gaps. It is possible by this means to obtain a 
reduction of propeller noise. 
Finally, FIG. 13 shows an arrangement of propellers 31 and 31' wherein 
propeller disks 34 and 34' extend in planes E3-E3 and E4-E4 respectively 
which are vertical and form an angle phi with each other. 
Various modifications of the propulsion system arrangement and airplane 
design of the invention may be made without departing from the spirit or 
scope thereof and it should be understood that the invention is intended 
to be limited only as defined in the appended claims.