Power plants – Reaction motor – Interrelated reaction motors
Reexamination Certificate
2002-10-21
2004-06-22
Freay, Charles G. (Department: 3746)
Power plants
Reaction motor
Interrelated reaction motors
C060S226200, C060S770000, C239S265250
Reexamination Certificate
active
06751944
ABSTRACT:
BACKGROUND OF THE INVENTION
Exhaust nozzles are used on business and commercial aircraft for reducing the noise produced by the engine at take-off, as well as for optimizing the aircraft take-off, climb and cruise performance, and for decelerating the aircraft at landing.
Variable area exhaust nozzles are known in the art. For example, U.S. Pat. No. 5,221,048 describes a variable exhaust area nozzle comprising a fixed structure or nacelle on which are hinged two pivoting half shells or nacelle extensions including an exit nozzle that cooperate radially and longitudinally with the nacelle. Fluid tightness between the two half shells and the fixed part is ensured through a sealing arrangement. Actuating means control the opening position of the shells to their fully opened position or to their fully closed position or to any intermediate position, allowing the adjustment of the nozzle exhaust area to the particular value required for achievement of optimum performance for the particular flight conditions.
The system described in patent '048 is advantageous because it has a relatively low number of moving parts, and at the same time it allows the area variation of the exhaust of the nozzle. Therefore, at take-off, with the variable nozzle opened, meaning that the value of the nozzle throat area is increased, the noise generated by the engine is decreased. During climb, with the variable nozzle closed, meaning that the nozzle throat area is reduced to its minimum value, climb performance is improved, and at cruise with the variable nozzle set to its nominal position, cruise performance is optimized.
However, the adjustments of the two shells that control the value of the area of the throat of the variable nozzle to any position between its two extreme positions, necessitate the use of actuating means with rather sophisticated control logic if the adjustments are fully integrated to the engine computer. This has a direct consequence of increasing the cost of the technology. Also, when the shells move away from their nominal position, they modify the outer mold line (OML) of the rear part of the nacelle.
While, from a performance point of view, this is not critical, as when this happens, the aircraft is at rather low speed, and for cosmetic reasons it is desirable that the OML not be altered by the operation of the variable nozzle. Also, while the variable nozzle described in patent '048 is attractive and readily applicable to business aircraft using engine with long nacelle, it has been found that it is more difficult to use this technology on short nacelle, a more commonly used installation on commercial aircraft.
Another limiting factor to the use of the variable nozzle described in patent '048 is that it is difficult to integrate it on a nacelle equipped with a target type thrust reverser and that its delta weight with a fixed nozzle tends to increase as the engine thrust category is greater than 40,000 pounds.
In order to reduce the landing distance of a turbofan engine powered aircraft as well as to increase the level of safety when the aircraft is landing on a wet or icy runway, thrust reversers are utilized to re-direct forward the flow of engine exhaust gases in order to provide a braking thrust for the aircraft.
There are basically two main types of thrust reversers used on turbofan engines. A first type reverses the total mass flow, core and fan flows, while the second type reverses the fan flow only.
As disclosed in the detailed description, the variable exhaust nozzle according to the present invention is applicable to both types of thrust reversers. The exhaust nozzle can be installed on nacelles of turbofan engines that are fitted on the fuselage or under the wings of an aircraft. The nacelles may or may not be equipped with a thrust reverser, and they can be of the long, short, or C-duct types.
Typically, the thrust reversers that reverse the total mass flow of the engine are more commonly called target reversers or pivoting doors reversers, and are generally composed of at least a pair of thrust reverser doors capable of pivoting about axes which are substantially transverse to the axis of the engine, between a stow position for forward thrust and deploy position for reverse thrust. While most of these target reversers constitute a portion of the exhaust nozzle when they are in their stow configuration, very few of them have the capability for adjustment of the throat of the exhaust nozzle for optimizing the aircraft performance during take-off climb and cruise, or for reducing the noise emitted by the engine during take-off.
Typical examples of target or pivoting door reversers are described in U.S. Pat. Nos. 5,779,192, 5,826,823, 5,819,527 and 5,875,995. In U.S. Pat. No. 5,779,192, the depicted apparatus has two reverser doors
17
a
,
17
b
which are pivotally mounted respectively about stationary axis
18
a
,
18
b
. With the reverser doors in the stow position, they form the exhaust nozzle for the engine gases, and the throat is not adjustable and is located at the trailing edge
19
of the reverser doors.
In U.S. Pat. No. 5,826,823, typical of a pivoting doors type reverser, the apparatus has a fixed structure that cooperates with at least two reverser doors
26
,
28
. The fixed structure
20
includes side beams
22
that terminate in an annular aft portion
24
. It is the fixed annular portion
24
that forms the exhaust nozzle for the jet engine, and the nozzle throat located at the trailing edge of the fixed portion is not adjustable.
In U.S. Pat. No. 5,819,527, the structural composition of the apparatus is very similar to U.S. Pat. No. 5,779,192, i.e., the exhaust nozzle is formed by an aft fixed, non-adjustable structure
3
. In U.S. Pat. No. 5,875,995, a fixed non-adjustable rear annular portion
34
forms the exhaust nozzle.
A typical example of a target reverser with throat adjustment capability is described in U.S. Pat. No. 5,181,676. When the reverser doors
30
are stowed, a pair of shells
44
that cooperates with the pair of thrust reverser doors forms the exhaust nozzle. The pivots
40
of the reverser doors, which are linked to the corresponding pivots
58
of the shells via arms
56
, have the capability of undergoing a radial and longitudinal displacement that confers the adjustment of the area to the throat of the exhaust nozzle.
While this arrangement is attractive by its simplicity, the amount of throat area variation capability is limited to about 10% over the nominal value. The limitation is a consequence of the mechanical arrangement that necessitates, in forward thrust, the radial and longitudinal displacement of the thrust reverser doors so that the throat area of the exhaust nozzle can be adjusted to the desired value. Also, when the reverser doors and shells move away from their nominal position, they modify the outer mold line of the rear part of the nacelle.
While, from a performance point of view, this is not critical, as when this happens, the aircraft is at rather low speed, and for cosmetic reasons it is desirable that the OML be not altered by the operation of the variable nozzle. Also, while the thrust reverser with variable nozzle described in patent '676 is attractive and readily applicable to business aircraft using engine with long nacelle, it has been found that it is more difficult to use this technology on short nacelle, a more commonly used installation on commercial aircraft.
Typically, the thrust reversers that reverse the fan flow only can be classified into three main groups: the cascades type, the pivoting doors type and the fan reverse pitch mode type. With reference to the cascades type, for example, U.S. Pat. Nos. 3,779,010, 4,922,713 and 5,655,360 show a cascades type fan thrust reverser with a variable nozzle for the fan flow only. A cascades type fan thrust reverser function and operation being well known in the art, no further comments will be offered on that particular aspect.
However, it is important to concentrate on the variable nozzle portion of these fan reversers to understan
Conte Francis L.
Freay Charles G.
The NORDAM Group, Inc.
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