GB2083420A

GB2083420A - Disposition of engines on aircraft

Info

Publication number: GB2083420A
Application number: GB8124046A
Authority: GB
Original assignee: Messerschmitt Bolkow Blohm AG
Current assignee: Airbus Defence and Space GmbH
Priority date: 1980-09-03
Filing date: 1981-08-06
Publication date: 1982-03-24
Also published as: DE3033101A1; JPS5777295A; FR2489245B3; FR2489245A1; DE3033101C2; GB2083420B

Abstract

A method for increasing the resultant propulsive thrust of a combination of propulsion unit 10 and wing 14 on an aircraft has the propulsion unit nacelle 10 mounted on the aircraft and the thrust nozzle 11 designed so that the propulsion unit jet in the reduced pressure zone in front of and above the wing 14 is mixed with the incident airflow, the air-flow mixture being intensified on the reduced pressure side of the wing. The jet nozzle may include vortex generators 15 or be multi-lobed or star-shaped. <IMAGE>

Description

SPECIFICATION Aircraft propulsion systems This invention relates to aircraft propulsion systems and to a system for increasing the resultant propulsive force in a combination of a propulsion unit and a wing.

The interaction between thrust jets of an aircraft and the airframe has been investigated in numerous wind tunnel tests and also simulated by computer. In general, however, these operations deal with the effects on lift, on the lateral force and on the moments of an aircraft configuration, little attention has been given to the drag aspect of the interaction between a thrust jet and the adjacent aerofoils or control surfaces.The conclusion has been reached, in theory, that the resultant propulsive force of a combination of propulsion unit and wing can be increased if a system is used in which the thrust of the propulsion unit interacts with the air flow above the wing, but this effect has been incorrectly attributed on one hand to the increase in the wing air flow velocity due to the jet and on the other hand to a reduction in the boundary layer separation in the zone of the trailing edge of the wing.

In practice, propulsion units have hitherto been arranged in such a way that the jet interaction takes place either in the over pressure zone underneath the aerofoil or outside the zone of aerodynamic influence of the air-frame altogether. The drag interaction of these systems is either unfavourable or insignificant.

An object of this invention is to provide a system in an aircraft, particularly a transport aircraft which can be made more economical than hitherto.

According to this invention there is provided a method for increasing the resultant propulsive force of a combination of a propulsion unit and wing in an aircraft, wherein the propulsion unit nacelle is mounted on the aircraft and the thrust nozzle thereof is such that the propulsion unit jet in the reduced pressure zone in front of and above the wing is combined with incident airflow, to effect an increase in the combined jet on the reduced pressure side of the wing.

The Invention is further described with reference to the accompanying drawings showing preferred embodiments by way of examples. In the drawings: Figure 1 shows a schematic part cross section through a combination of a propulsion unit and wing according to the invention, Figure 2 shows a jet mixing effect obtained with a star nozzle, Figure 3 shows a part cross section through a multitubular nozzle of a propulsion unit, Figure 3a shows a view looking in the direction A of Fig. 3, Figure 3b shows a detail of the upper portion of Fig. 3a to a larger scale, Figure 4 shows a diagram of the jet mixing effect obtained by vortex generators on the end of the thrust nozzle of a propulsion unit, Figure 5 shows a diagram of the distribution plot for iso-Mach numbers on a wing profile of a known type, Figure 6 shows a graph of the increase in the thrust in a multitubular nozzle assembly, and Figure 7 shows in perspective the structure of a model for calculating the flow in a jet exhaust in the wash from an aerofoil.

Wind tunnel measurements, tests and calculations have shown that the resultant propulsive force from a combination of a propulsion unit and aerofoil, hereinafter called an depends to a very large extent on the way in which these two components are relatively arranged.

It has been found that the nearer the jet exhaust approaches the low pressure side of the aerofoil and the greater the wing lift and the jet velocity ratio Vs/V, the greater will be the most favourable drag interference between jet and aerofoil.

With the arrangement of this invention it can be proved that the increase in the propulsive force is due to an increase which takes place in the jet impulse thrust and this is due to the mixing of the jet in a low-pressure zone. The interaction force appears as a reduction of the drag of the adjacent surface and is caused by the low pressure effect of the jet undergoing a combining or by the venturi effect of the wing on the jet. In simplified terms, the wing "sails" as it were, in the up-wind area which is created in the vicinity of the jet as a result of the combining process.

It has been found that the increase, by reference to the nett thrust S, in the propulsive S-W force with reference to the nett thrusts for a given power output of the propulsion unit can be calculated from the formula:

wherein: V = Flight velocity, V5 = jet exhaust velocity,

q(x) = local value of the reduced pressure on the axis of the jet.

u(x) = X-induction of the wing on the axis of the jet.

XA = rearward position of the jet outlet.

The maximum increase in propulsive force is obtained when the jet combining process takes place in the zone of maximum wing induction, that is maximum reduced pressure. Based on this fact the method of the invention arranges the propulsion unit nacelle 10 on the aircraft and designs the thrust nozzle in such a way that the propulsion unit jet in the reduced pressure zone in front of and above the wing 14 will be combined with ambient air and the jet combining process will in addition be increased on the reduced pressure side.

This intensification of the jet combining process can be obtained, as shown in Fig. 1, by providing vortex generators 1 5 at the end of the nozzle 11. Fig. 4 is a schematic diagram of the resulting jet combining effect. In an alternative arrangement star-like nozzles 20 can be fitted to the thrust nozzle, as sown in Fig. 3. In this case the shape of the nozzle can also be varied, for example the cross section can be oval or conical, as shown in Fig. 3b. With this arrangement it is found that the jet combining effect was completed after 1 to 2 jet diameters had been covered.

With regard to the average pressure reduction in the combining zone it is known that the reduced pressure side of the wing, under cruise conditions, is surrounded by an extensive supersonic zone. In this connection Fig. 5 shows the distribution of lines of equal Mach number values for one of the well known conventional wing profiles at a cruise Mach number of 0.72.

Modern wing profiles result in a far more extensive supersonic zone and in a considerable increase in the average reduced pressure.

The calculations shown in the graph of Fig. 6 are based on the assumption that the effective wing induction in the x direction is Ueff = (Vsound that is the jet combining operation takes place at an average velocity of Sound. The greater part of the jet combining operation is completed about half-way along the width of the wing and as the wing induction under cruise conditions can quite easily reach 2 X (Vsound - V locally the above assumption is to be regarded, if anything, as conservative. On this basis and assuming a modern double-flow propulsion unit (ducted fan jet) the relative thrust increase shown in Fig. 6 is obtained as a function of the design Mach number.As the critical reduced pressure decreases with increasing flight Mach number, the gain obtainable by the jet combining process on the reduced pressure side rapidly falls with an increasing design Mach number.

With an angle of sweep-back of 40 and a cruise Mach number of 0.85, a reduction of at least 11% in the fuel consumption may be expected. If the design Mach number is reduced to M = 0.7, the interaction force becomes as high as 20% of the nett thrust. Similar increases in thrust are obtained on take-off and on landing.

These values are obtained by the construction shown in Fig. 1, in which the propulsion unit 10 is connected to the structure of the aircraft via a streamlined pylon 1 2 with a flexurally and torsionally rigid torpedo-shaped support 1 3 connected to the front and rear spar of the wing 14, in such a way that the propulsion unit jet in the reduced pressure zone in front of and above the wing is mixed with ambient air. Under the circumstances shown the suggested increase in the jet combining process is brought about by the provision of eddy or vortex generators.

Fig. 7 shows schematically and theoretically the incompressible flow parameters of the propagation of a jet in the pressure zone of the aerofoil. In this instance the propulsion unit nacelle is represented by a floating long pipe F of constant cross-sectional area. By means of a loss-free fan blower the volumetric air flow is taken in by suction from the unimpeded incident air flow, subject to an over-all pressure increase and exhausted at the nozzle at the end of the pipe at a velocity of V5 and at a corresponding pressure.

The meanings of the symbols in Fig. 7 are as follows: S: Nett thrust of propulsion unit.

x,, y,, z Coordinates of a point on the wing surface.

XA, y z Coordinates of the central point of A' A the nozzle outlet.

:u: Induction of the aerofoil at the locus of the jet in the X direction.

W: Wing drag.

x,y,z: Coordinates of which the point of origin is the wing leading edge, the x axis being parallel to V and the z axis perpendicular to the plane of the wing.

a: Angle of incidence of the wing.

dr: Rotation rate of an element in the boundary vortex layer.

The method of the invention makes an aircraft more economical through the intensive mixing of the propulsion unit jets in the reduced pressure zone in front of and above the wing, which latter acts in respect of the propulsion unit as a unilateral venturi.

Claims

1. A method for increasing the resultant propulsive force of a combination of a propulsion unit and wing in an aircraft, wherein the propulsion unit nacelle is mounted on the aircraft and the thrust nozzle thereof is such that the propulsion unit jet in the reduced pressure zone in front of and above the wing is combined with incident air-flow, to effect an increase in the combined jet on the reduced pressure side of the wing.

2. A method in accordance with Claim 1, wherein the increase in the jet in front of and over the wing is effected by providing vortex generator means on the end of the jet nozzle.

3. A method in accordance with Claim 1, wherein the increase in the jet is effected by a use of star-like nozzles.

4. A method in accordance with Claim 1, wheein the increase in the jet is effected by a multitubular thrust nozzle system.

5. A method in accordance with Claim 1, wherein the propusion unit is connected to the aircraft structure by a pylon through a flexurally and torsionally rigid torpedo-shape support mounted to the front and rear spars of the wing.

6. A method for increasing the resultant propulsive force of a combination of propulsion unit and aircraft wing substantially as herein described with reference to the accompanying drawings.

7. An aircraft constructed and arranged to function substantially as hereinbefore described and claimed.