FR2784960A1 - Supersonic airplane with low fuel consumption, utilizes low bypass ratio jet engines in conjunction with high bypass ratio engines - Google Patents

Abstract

Engines with very small bypass ratio (21) are dimensioned for transonic ascent and optimized for supersonic cruise. These engines are operated at a lower power setting so as to limit noise and are also used for take off. Several engines with large bypass ratio (11) are used alone for subsonic cruise and approach. They are used with the small bypass ratio engines at take off and retracted inside the aircraft at supersonic cruise.

Description

 The present invention relates to a new concept of supersonic aircraft whose fuel consumption is much lower than that of existing or planned aircraft.

This concept is characterized by the use of motors with very different characteristics. Small section motors with high ejection speed are used in transonic climb and supersonic cruise; at low speed to limit noise, they are also used for takeoff. Large section engines with low ejection speed are used for takeoff, subsonic cruising and approach; they are retracted inside the plane in supersonic cruise.

 Current projects for supersonic transport aircraft use engines of the same type which adapt to the different flight phases. It should be foreseen that, the supersonic overflight of the grounds being prohibited because of the sonic boom, these planes will have to carry out a significant fraction of their journey in subsonic cruise for many missions. However, compared to the only existing supersonic transport aircraft, the Concorde, future aircraft will already, despite advances in technology, have a specific consumption (mass of fuel consumed per unit of thrust and per unit of time) when cruising supersonic rather increased because of various complications allowing a less noisy takeoff. As for the subsonic cruise, their specific consumption will be approximately double that of modern subsonic planes.

 Like the European variable-cycle engine airplane project, the American mixer-ejector projects do not make it possible to meet current noise standards and a fortiori future reinforced standards, according to the results currently known. This is why the recent patent WO 97/48600 (Rudolph), after having made a very complete reminder of the current state of the art, proposes the use at takeoff of retractable subsonic auxiliary engines.

The proposals made in this patent (aircraft and method) are only intended to reduce noise; with regard to the specific consumption on a subsonic cruise, it says there
explicitly on pages 43 and 44 (with reference to Figures 23 and 24) that the use of the retractable motor (s) does not lower the specific consumption. Although claim 18 of this patent relates to a thrust ratio of subsonic to supersonic motors at least equal to 1 in 10, this lower limit is indeed much too lower than what is proposed in the present invention to allow a reduction in specific consumption in subsonic cruise flight. In addition, all the descriptions made in this prior patent, with or without reference to the figures, do not allow all the solutions proposed in the present invention to be obtained. Even more clearly, its claim 1, repeated in all of the following, specifies in paragraph c that the only supersonic engines used at full speed can provide the nominal thrust necessary for takeoff (even if they then produce too intense noise), when they cannot according to certain specifications of the present invention.

 This is why it is proposed here to obtain the different thrust conditions with different motors and not with configuration changes of the same motors or with auxiliary motors.

 Furthermore, current engine projects involve considerable study and development costs with high risks of failure while the present invention uses existing engines (or those close to those which already exist).

The aircraft according to the present invention is therefore characterized by:
-one or fixed motors with low dilution ratio (or rate), -one or retractable motors with high dilution ratio.

 Low-ratio engines (with a dilution ratio of less than 3 and preferably less than 0.5) are optimized for supersonic cruising for which their specific thrust is around 300 to 600 m / s. Their specific consumption (engine installed) can then be around 1.1 kg / daN. h. These same motors are dimensioned so as to ensure only the transonic rise. For subsonic cruising, they are put at low speed or stopped, so that the thrust is provided exclusively or almost by engines with a high dilution ratio at least equal to 3, and preferably greater than 6, which can have a consumption specific (motor installed) close to 0.5 kg / daN. h. At takeoff, the ejection speed of engines with a low dilution ratio is reduced (without the need to modify their air intake geometry or to use an ejector) to the value required by the desired noise level, for example about 300 m / s. Engines with a high dilution ratio are dimensioned so as to provide the additional thrust necessary for takeoff with this same average ejection speed. In practice, these latter engines provide more than half of the total take-off thrust and their diameter can be such that they must be retracted one behind the other (if there are two of them), in a section that is not too narrow. of the fuselage, during the supersonic flight.

 Two embodiments of the invention are now described in detail with reference to the figures.

The numerical values mentioned result from the state of the prior art and from the inventor's research activities.

 Figure 1 is a bottom view of the rear tip of the aircraft described in the first example, showing the configuration of subsonic flight with two engines with high dilution ratio and two engines with low ratio.

 FIG. 2 is a bottom view of the same airplane, showing the supersonic configuration with the two engines with large dilution ratios retracted into the fuselage; the first reentry has undergone a rearward translation.

 FIG. 3 is a partial front view of the same aircraft in the same configuration as in FIG. 1.

 FIG. 4 is a partial front view of the same aircraft during the re-entry operation of an engine with a large dilution ratio.

 FIG. 5 is still a partial front view of the same aircraft corresponding to the configuration of FIG. 2.

 Figure 6 is a partial front view of the aircraft described in the second example, in subsonic flight configuration.

 FIG. 7 is a side view of the rear of the same airplane in a supersonic configuration with the engine having a large dilution ratio retracted.

Figure 8 is a side view similar to the previous one where the retracted motor feeds a base nozzle
We first consider a transport aircraft of about 300 passengers with a total transonic climb thrust of 560 kN. With a specific thrust close to 640 m / s, each of the two motors with a low dilution ratio (zero or less than 2) has an air inlet diameter of 2 m. The total thrust of 290 kN in supersonic cruising corresponds to an optimized specific consumption of approximately 1.1 kg / daN. h. These engines with low dilution ratio, even used at their maximum nominal thrust, are possibly insufficient to ensure takeoff of the aircraft at its nominal thrust. To have a total takeoff thrust of 1,120 kN at an average ejection speed of 300 m / s on all engines, the diameter of the two retractable engines is 2.9 m and their dilution ratio is close to 10. The the total air intake section of all the motors is then more than three times that of the fixed motors alone. The two motors with a high dilution ratio can alone provide the total thrust in subsonic cruising of 250 kN so as to obtain a specific consumption of around 0.5 kg / daN. h. At takeoff, the thrust of engines with a high dilution ratio is more than double that of engines with a low dilution ratio. The retractable motors are therefore the main motors and not auxiliary motors.

This propulsion system has a noise lower by 10 decibels than the current certification standards (ICAO, Annex 16,
Chapter 3). In a fuselage of the order of 4 m in diameter, the two motors with a high dilution ratio cannot be stored side by side. Their working position could be offset axially but, in the present example, it is considered preferable to have the same axial working position. It is therefore necessary to enter the fuselage, preferably downstream of the hold of the main landing gear, a first engine and to move it axially along one or more rails to make room for the second. Figures 1 and 3 show the subsonic cruise configuration, also used for take-off and on approach. In FIG. 1, all the engines, with a high dilution ratio (11 and 12) and with a low dilution ratio (21 and 22) are in the working position, shown in a bottom view of the rear of the aircraft . Figure 3 shows, from the front, the fuselage (1) and the left wing (2); the left engine with high dilution ratio (11) has its profiled support (4) fixed to its operating arm (3); all the cavity shutters (G, 7 and 9) are closed. FIG. 4 represents the engine with a large left dilution ratio (11) during its movement for retraction. All the shutters are open. The operating arm (3) moves the motor (11) in rotation about the axis (5). In FIG. 5, the motor (11) has completed its rotation and is fixed to the rail (8) for its translation towards the rear of the hold; the operating arm (3) has been detached from the profiled support (4) and has returned to the wing (2), cover (6) closed. After translation of the engine (11) and retraction of the second engine with large dilution ratio (12), Figure 2 shows a schematic bottom view (i.e. engines drawn although they are hidden by the flaps d (shutter) configuration of transonic rise and supersonic cruise. The engine compartment is separated from the passenger cabin by the watertight bulkhead (10). The engines with high dilution ratio (11 and 12) are used for the final subsonic cruise and for the approach.

The control umbilics and the fuel lines are possibly disconnected and reconnected automatically. The total mass of this power plant is around 30 tonnes divided into 10 tonnes for all supersonic engines and 20 tonnes for subsonic engines with their operating devices.

 We now consider a business aircraft of about 20 passengers with a takeoff weight of 34 tonnes.

Its total thrust in transonic climb is 56 kN.

With a specific thrust close to 640 m / s, each of the two monoflux motors (zero or practically zero dilution ratio) has a diameter of 0.63 m. The total thrust of 29 kN in supersonic cruise at Mach 2 corresponds to an optimized specific consumption of around 1.1 kg / daN. h. To have a total take-off thrust of 112 kN at 300 m / s ejection speed on all engines, the retractable engine diameter is 1.31 m and its dilution ratio is close to 10. This engine can only provide the total thrust in subsonic cruising of 25 kN with a specific consumption of around 0.5 kg / daN. h. In this example, rather than a rotation movement, it is proposed to retract the engine with a high dilution ratio by a displacement in vertical translation. In a fuselage of the order of 2 m in diameter, the engine with a large retracted dilution ratio occupies an entire section of the fuselage. Figures 6 and 7 illustrate the arrangement of these engines during the different flight phases. FIG. 6 represents a front view of the subsonic cruise configuration, also used for takeoff and on approach; all the engines with a high dilution ratio (11) and a low dilution ratio (21 and 22) are in the working position under the wing (2) and the fuselage (1). Figure 7 shows, from the side, the supersonic configuration with the motor (11) retracted thanks to the telescopic support (13). The total mass of this power plant is approximately 6 tonnes divided into 3 tonnes for supersonic engines and 3 tonnes for the subsonic engine with its operating device.

 The two examples described in detail above are not limiting. According to variants not illustrated, one or more motors, with large or low dilution ratio, can be placed above the wing, on the sides of the fuselage, at the foot of the fin, on any masts, etc. The axial positions of the motors can be different from those shown in the figures.

 In an alternative embodiment it is proposed to operate at reduced speed one or more motors with a high dilution ratio while they are retracted and to reject their gases (the primary flow alone preferably) at the rear tip of the fuselage. This base blowing makes it possible to shorten the tapered rear part of the aircraft and therefore to lighten it while reducing the base drag. FIG. 8 shows a retracted motor (11) supplied by a grouping of the air samples (31) through a stilling chamber (3 2) and discharging into a base nozzle (33).

 Another variant, complementary to the previous one, consists in supplying one or more retracted motors with boundary layer samples taken at various locations (taken together or one of them only or several of them) such as the vicinity of the leading edge of the wings, the cockpit, different positions along the fuselage, the fin. According to the known state of the art, these boundary layer samples are likely to reduce the drag of the aircraft and therefore its consumption; in addition, those carried out along the cockpit and the fuselage can reduce the internal noise of the aircraft and all contribute to the reduction of external noise.

 Unlike current projects, the supersonic aircraft according to the present invention does not require major developments of entirely new engines. For example, in the case of the heavy aircraft described above, engines with a large dilution ratio exist; in the case of a business aircraft, the engine with a high dilution ratio also exists and the engines with low dilution ratio can be a simple adaptation of an existing military engine. The technology of telescopic or rotary cylinders exists, as well as that of chains with stiffened unwinding. The application of the invention to industrial production will therefore require only a mechanical study of the devices for deploying and retracting engines with a high dilution ratio as well as examining its consequences on the market study linked to construction and operating costs.

Claims (15)

 1) Supersonic aircraft, with low fuel consumption but also produced according to the prior art, characterized by one or more turbojets (11-12) with a dilution ratio at least equal to 3 ensuring almost all of the thrust during the subsonic cruise , the other engine (s) (21-22) with a dilution ratio of less than 3 then being stopped or at very low speed.  2) supersonic aircraft according to claim 1 characterized by the use of one or more fixed engines (21-22) with a dilution ratio of less than 3 such that their total nominal maximum thrust is insufficient to ensure takeoff of the aircraft at its nominal thrust (even with noise exceeding the standards).  3) supersonic aircraft according to claim 1 characterized by the use of one or more fixed engines (21-22) with a dilution ratio of less than 3 ensuring only the transonic rise and supersonic cruise phases while the engines (11- 12) with a dilution ratio greater than 3 are retracted inside the structure.  4) supersonic aircraft according to claims 1 and 3 characterized by one or more fixed motors (21-22) with a dilution ratio of less than 3 dimensioned to ensure only the transonic rise and optimized only for supersonic cruising, that is to say say not having take-off noise reduction devices such as variable geometry, scoops or an ejector.  5) supersonic aircraft according to claim 4 characterized by a noise level chosen elsewhere and obtained by the only limitation of the average speed of ejection of all engines, for example to 400 m / s and preferably to about 300 m / s.  6) supersonic aircraft according to claim 1 characterized in that the engine (s) (11-12) with a dilution ratio greater than 3 ensure takeoff more than half of the total thrust and preferably about two thirds, it is that is, the total air intake section of the retractable motor (s) (11-12) is then approximately double that of the fixed motors (21-22).  7) supersonic aircraft according to claim 1 characterized by the use of one or more fixed engines (21-22) having a dilution ratio of less than 0.5.  8) Supersonic aircraft according to claim 1 characterized by the use of one or more retractable motors (11-12) having a dilution ratio greater than 6.  9) supersonic aircraft according to claims 1 and 3 characterized in that two large retracted motors (11-12) are stored one behind the other along the axis of the fuselage, the first retracted having undergone translation by rails (8).  10) supersonic aircraft according to claims 1 and 3 characterized in that the displacement of the engine or engines with high dilution ratio (11-12), from their working position when re-entering their hold, is ensured by pivoting arms ( 3), these being able to be separated from the profiled supports (4) to facilitate their own retraction, for example in the airfoil (2), and to allow the translation of the first retracted motor.  11) Supersonic aircraft according to claims 1 and 3 characterized in that the retracted motors (11-12) have their control navel and their fuel supply line possibly disconnectable and reconnectable automatically.  12) supersonic aircraft according to claims 1 and  3 characterized in that one or more motors (11-12) in the retracted position operate at reduced speed to eject their gases at the rear tip of the aircraft so as to reduce its base drag while reducing its rear tip.  13) supersonic aircraft according to claims 1 and  12 characterized in that one or more motors (11-12) in the retracted position draws part or all of its supply air near the leading edge of the wing and / or near the cockpit and (or) in different positions along the fuselage and / or on the vertical stabilizer in order to reduce the friction drag (therefore to save fuel) and to reduce the interior and exterior noise of the aircraft.  14) Method for greatly reducing the fuel consumption of a supersonic aircraft characterized in that an aircraft according to claim 1 uses at low speed, or stops, its engines with low dilution ratio (21-22) during the phases of subsonic cruise, almost all of the thrust being then supplied by the motors (11-12) with high dilution ratio so as to obtain a specific consumption of 0.5 kg / daN. h approximately, and in that it uses for supersonic cruising, the engines (11-12) with high dilution ratio then being retracted into the structure of the aircraft, engines with low dilution ratio (21-22) optimized by the fact that they do not have to be modified at takeoff to lower their noise (this noise reduction is then obtained by their operation at low speed).  15) Method for obtaining noise levels of approximately 10 decibels below current international standards (ICAO, Annex 16, Chapter 3) characterized in that all the motors (11-12) and (21-22) of the aircraft according to claims 1 and 3 have an ejection speed of less than 400 m / s, and preferably close to 300 m / s, on takeoff and on approach, the thrust required for takeoff being then provided by a section of air intake of all motors approximately 3 times greater than that of stationary motors alone (21-22).