WO2005044662A1

WO2005044662A1 - Aircraft power assembly and aircraft provided with such an assembly

Info

Publication number: WO2005044662A1
Application number: PCT/GB2004/004584
Authority: WO
Inventors: Ronald Frederick Ayers
Original assignee: Advanced Creative Engineering Ltd.
Priority date: 2003-10-31
Filing date: 2004-10-29
Publication date: 2005-05-19
Also published as: GB0325510D0

Abstract

An aircraft propulsion system comprising two uncoupled separately operable turboprop gas turbine engines (1, 2), the rotary axes (5, 7) of which are inclined to each other in a horizontal and/or vertical plane and each of which is connected by a drive shaft to a compound gearbox (6) which drives a pair of coaxial contra-rotating airscrew shafts (11, 13).

Description

AIRCRAπ POWER ASSEMBLY AND AIRCRAFT PROVIDED WITH SUCH AN ASSEMBLY

This invention relates to air aircraft power assembly and an aircraft incorporating such a power assembly.

At the present time most passengers are transported in large aircraft which means that they must operate from large airfields with runways which are sufficiently long to accommodate them. This has led to airports of increasing size and complexity and over centralisation of the industry and which results in long delays for passengers at airports and the associated difficulties of reaching the airport concerned and moving within it.

It is not possible to operate these large modern aircraft from small airfields with, for example, runways of only 2,000 yards, and because the aircraft are large their capacity for passengers requires the large airport facilities referred to above.

It is possible to operate smaller aircraft from small airports or airfields but the public are suspicious of single engined aircraft which have no engine redundancy or small multi-engine aircraft which may suffer severe handling issues given an engine failure. The safety factors inherent in large aircraft which can fly with engine failure of one or even more engines is lost and the passenger public are well aware of this.

Operating from small airfields would reduce the crowding at large airports and, moreover, allow passengers easier access to the point from which they are to fly and delivery nearer to the point of destination.

The requirements of an aircraft to provide relative safety can however be achieved if there is more than one engine and each engine is powerful enough to enable the aircraft to take off and sustain safe flight. The normal way of incorporating two engines in a small aircraft would be to provide an engine in a nacelle on each wing but again there are problems if an engine fails because there is the asymmetric drag of the failed engine and its nacelle.

Under certain circumstances maintaining safe flight with the remaining engine may be dangerous or marginal.

The present invention is intended to overcome some of the problems referred to above and to provide an aircraft propulsion system which can be incorporated into any suitable aircraft design and is more especially, although not exclusively, applicable to relatively small aircraft of up to ten tons and with a load carrying capacity of up to 20 passengers.

In the present Application the word 'airscrew' is intended to also include any complex multibladed variable and/or fixed pitch propeller system, that is a propfan.

According to the present invention an aircraft propulsion system comprises two uncoupled separately operable turboprop gas turbine engines, the rotary axes of which are inclined to each other in a horizontal and/or vertical plane and each of which is connected by a drive shaft to a compound gearbox which drives a pair of coaxial contra-rotating airscrew shafts, one engine being discretely coupled to each airscrew shaft.

According to one aspect of the invention the compound gearbox can connect each engine separately to one of said coaxial contra-rotating airscrew shafts.

Thus, with the construction set forth above many of the problems referred to are overcome, each engine can be arranged to be sufficiently powerful for the aircraft to take off, fly and land safely by driving through only one airscrew. With both engines operating and both airscrews in use sufficient power can be developed for short take off which allows for the use of short runways and thus a relatively small airport.

Cruise flight can be maintained economically by running both engines at low power or using only one engine and airscrew.

A further advantage of the construction is that with the engines being inclined to each other in a horizontal and/or vertical plane the assembly can be conveniently incorporated in the nose or tail with a frontal area which is very little more than that of using a single engine.

According to another aspect of the invention the compound gearbox can be arranged to selectively connect both, or only one, engine to both coaxial contra- rotating airscrew shafts.

Preferably the axes of the pair of coaxial contra-rotating airscrew shafts is at an equal angle to the rotary axis of each of the engines.

The included angle between the rotary axes of the engines can be between 1° and 30°.

The airscrew on one airscrew shaft can have more blades than the other, for example, the front airscrew can have three blades and the rear airscrew four to provide better airscrew efficiency and noise reduction when both airscrews are in use.

A rotary journal bearing can be provided between the coaxial airscrew shafts and said bearing preferably includes two radially or axially displaced coaxial rows of rotary bearing elements which can, for example, be balls or rollers, open or caged. The use of a double row of bearings reduces the possibility of seizure and shaft displacement caused by a single bearing failure and ensures continued operation. The invention also includes an aircraft provided with a power assembly as set forth above and in which the power assembly is mounted in the nose or tail.

Separate engine controls will be provided for each engine, if desired these can be selectively interlinked..

The invention can be performed in various ways and one embodiment will now be described by way of example and with reference to the accompanying drawings in which :

Figure 1 is a diagrammatic plan view showing the aircraft power assembly according to the invention; Figure 2 is a diagrammatic part cross-section of a rotary journal bearing bearing having two axially displaced coaxial rows of bearing elements according to the invention; and Figure 3 is a diagrammatic part cross-section of a rotary journal bearing having two radially displaced coaxial rows of bearing elements according to the invention.

As shown in Figure 1, the aircraft power assembly according to the invention comprises two uncoupled separately operable turboprop gas turbine engines indicated by reference numerals 1 and 2. The rotary axis of engine 1 is indicated by reference numeral 3 and the rotary axis of engine 2 by reference numeral 4. It will be seen that these rotary axes 3 and 4 are inclined to each other in a horizontal and/or vertical plane. The engine 1 is connected by a drive shaft 5 to a compound gearbox 6 to which the drive shaft 7 of engine 2 is also connected. The gearbox provides an appropriate gearing assembly to convert the drive from the shafts 5 and 6 through, for example, shallow angle bevel gears to a pair of coaxial contra-rotating airscrew shafts 8. The outer shaft 9 can, for example, be connected to engine 2 and the inner shaft 10 to the drive shaft 5 of engine 1. The inner shaft 10 carries a multibladed airscrew 11 and the outer shaft 9 carries an airscrew 13 with a similar or different number of blades..

The relative angle between the axes 3 and 4 can be between 2° and 60° and preferably they are equally angled in relation to a thrust axes indicated by reference numeral 14.

A rotary journal bearing 15 is provided between the coaxial airscrew shafts 9 and 10, alternative constructions of which are shown in more detail in Figures 2 and 3. In Figure 2 the bearing includes two axially displaced coaxial rows of rotary bearing elements 21 and 22 and in Figure 3 the bearing includes two radially displaced coaxial rows of bearing elements 23 and 24. in the construction shows in Figures 2 and 3 the bearing elements are shown as balls but they could be rollers, taper rollers, open or caged. Due to the coaxial rows of bearing elements, if one row is damaged or seizes the other can still operate thus providing a safety factor in the bearing itself and reducing the possibilities of damage, especially if one airscrew is used by itself which might tend to increase the loading on the bearing.

The use of turboprop gas turbine engines enables their high power to be employed and to couple two separately operable engines into a single thrust axis which thus reduces the frontal area of an aircraft fitting with such a construction but provides increased safety factors over known aircraft.

Due to the angled engines the power assembly is particularly suitable for mounting into a streamline shape at the nose or tail of the aircraft.

The construction could also be used on the wing of an aircraft so that four engines were employed but the particular advantage of enabling a relatively small aircraft, compared with modern two, three or four engined aircraft at present in use, is the ability to provide a safety factor in a small aircraft which can operate from a relatively small airfield with a short runway of, for example, only 2,000 yards.

In the construction shown in Figure 1 separate engine controls indicated by reference numerals 17 and 18 are provided. Although shown spaced apart in Figure 1 they can be arranged side by side so that they can be selectively interlinked in known fashion for multiple engine throttle controls. Thus, the controls can be used together to operate the engines when both engines are in use but each engine can be operated separately if required.

The design and configuration of the airscrews will depend upon their requirements. Thus, in the construction shown in Figure 1 the forward airscrew has three blades and the rear four. The diameters, axial spacing, pitch and other parameters will depend upon the aircraft design and the requirements of the airscrews themselves. The relative speeds of the airscrews for given flying requirements will also be predetermined and will form a part of the aircraft management system for particular situations and the flight envelope.

Again, the number of blades on each airscrew will be determined according to requirements to minimize noise and the relatively power deliveries of the engines.

The engines could have similar power outputs but in certain circumstances it may be advantageous to provide one engine with more power than the other to be able to maintain the necessary flight characteristics of the aircraft.

It will be appreciated that in the construction shown in Figure 1 each engine 1 is connected through the gearbox 6 to one of the coaxial contra-rotating airscrew shafts 8 but in a second embodiment in which the layout is similar to that shown in Figure 1 the compound gearbox 6 is designed to selectively connect both or only one engine 1 or 2 to both coaxial contra-rotating airscrew shafts 8. The construction of the gearbox can take many forms, depending upon design parameters and the load which it has to carry.

With this arrangement the aircraft can be flown with both engines driving their power to both airscrews 11 and 13 or, for cruising or in an emergency and the failure or loss of power of one engine, the other engine can be employed to drive both airscrews thus overcoming any handling problems which can arise if one airscrew is stopped and all the power is carried to the other airscrew thus creating a torque effect. This will not occur if both airscrews are still driven.

The engine control systems can be similar to those described in Figure 1.

Claims

1. An aircraft propulsion system comprising two uncoupled separately operable turboprop gas turbine engines, the rotary axes of which are inclined to each other in a horizontal and/or vertical plane and each of which is connected by a drive shaft to a compound gearbox which drives a pair of coaxial contra-rotating airscrew shafts.

2. An aircraft propulsion system as claimed in claim 1 in which the compound gearbox connects each engine separately to one of said coaxial contra-rotating airscrew shafts.

3. An aircraft propulsion system as claimed in claim 1 in which the compound gearbox is arranged to selectively connect both, or only one, engine to both coaxial contra-rotating airscrew shafts.

4. An aircraft propulsion system as claimed in claims 1 to 3 in which the axis of the pair of coaxial contra-rotating airscrew shafts is at an equal angle to the rotary axis of each of the engines.

5. An aircraft propulsion system as claimed in claim 4 in which the included angle between the rotary axes of the engines can be between 3° and 60°.

6. An aircraft propulsion system as claimed in claims 1 to 4 in which each airscrew shaft carries an airscrew, one airscrew having more blades than the other.

7. An aircraft propulsion system as claimed in claims 1 to 6 in which a rotary thrust bearing is provided between the coaxial airscrew shafts, said bearing including two radially displaced coaxial rows of rotary bearing elements.

8. An aircraft propulsion system as claimed in claim 7 in which the rotary bearing elements are balls or rollers, open or caged.

9. An aircraft provided with a power assembly as set forth in claims 1 to 8.

10. An aircraft as claimed in claim 9 in which the power assembly is mounted in the nose or tail.

11. An aircraft as claimed in any one of the preceding claims in which separate engine controls are provided for each engine.

12. An aircraft as claimed in claim 11 in which the engine controls can be selectively interlinked.