Aeronautics and astronautics – Aircraft power plants – Mounting
Reexamination Certificate
1999-02-26
2001-02-20
Swiatek, Robert P. (Department: 3643)
Aeronautics and astronautics
Aircraft power plants
Mounting
C248S554000
Reexamination Certificate
active
06189830
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field Of The Invention
The present invention relates to a tuned engine mounting system for a jet aircraft, and more particularly to an engine mounting system in which an aft engine mount is provided with spring beams for damping pivotal movement of the engine.
2. Background Information
It is a design goal that when an aircraft wing is subjected to a momentary force in flight which causes the wing to oscillate between a bent state and an unbent state, that in the absence of this force, the oscillations will damp out and the wing will return to a steady, unbended state. On the other hand, “wing flutter” refers to a phenomenon in which the wing oscillations between the bent state and the unbent state do not damp out. Rather, the amplitude of these oscillations either remains constant or increases over time.
Wing flutter is an aeroelastic instability produced by the coalescing and proper phasing of two or more structural vibration modes of an aircraft in flight. A flutter mode usually involves both bending and torsion-types of motion in which the torsional motion extracts energy from the airstream and drives the bending mode to increasingly higher amplitudes. In other cases, these oscillations are lightly damped, but stable, within the operating speed envelope of the aircraft and can cause a reduction in riding comfort of the aircraft.
The location of the engine nacelle relative to the wing, the mass properties of the engine, and the stiffness of the strut which attaches the nacelle to the wing are factors which influence the flutter characteristics of the wing. More specifically, the natural frequency of the nacelle and the manner of strut installation can influence the mode and air speed at which the wing oscillations become unstable (flutter).
Conventionally, in order to avoid wing flutter, the natural frequency of the nacelles and nacelle struts are restricted within a narrow range. For example, in earlier models of the Boeing 747 aircraft, the outboard engine nacelles are permitted to oscillate at a natural frequency of about 2 cycles per second in a lateral direction. If the outboard engine nacelle lateral frequencies are significantly above or below 2 cycles per second, then wing flutter can result at an unacceptably low air speed.
However, in some newer aircraft which feature stronger but less stiff lifting surfaces, flutter can occur at air speeds below that required by government regulations. In this case, the avoidance of wing flutter requires the unsatisfactory solution of reducing the maximum operating speeds of the aircraft.
U.S. Pat. No. 4,917,331 discloses a method for preventing wing flutter in an aircraft, wherein the lateral natural frequencies of the left and right engines are sufficiently different so that when subjected to a time varying disturbance in flight, the flutter speed of the aircraft is increased. In this design, spring beams are attached at the interface between the pylon structure and the wing for damping movement of the engine. The spring beams may be tuned to provide the desired lateral frequency.
FIG. 1
shows a prior art engine and wing structure, wherein a wing
10
supports a pylon structure
12
, which supports the engine
14
. The pylon structure
12
is attached to the wing
10
at the upper link interface
16
and mid-spar fittings
18
. The spring beam structure described in U.S. Pat. No. 4,917,331, referenced above, would be attached at the interface between the wing
10
and the pylon structure
12
, such as in the areas of the upper link interface
16
or mid-spar fittings
18
shown in FIG.
1
. The spring beam attachment structure would replace such attachment devices
16
,
18
. Because the spring beams are spaced substantially from the center line
20
of the engine (the center of mass), the placement of such spring beams is limited, and the size of the entire spring beam attachment structure is significant as a result of strength requirements. Accordingly, the spring beam attachment structure generally defines the placement of the engine
14
. In other words, as a result of the strength limitations of the attachment, the engine
14
may not be positioned where desired to optimize efficiency.
SUMMARY OF THE INVENTION
The present invention provides a significant improvement over the prior art described above by providing a spring beam attachment located at the aft engine mount, such as aft engine mount location
22
shown in FIG.
1
. The aft engine mount
22
shown in
FIG. 1
is replaced by a spring beam structure on opposing sides of a pivotal connection. Because the aft engine mount location
22
is substantially closer to the center line
20
of the engine
14
in comparison with the attachments
16
,
18
, the moment arm length is reduced by approximately 3 feet and the size of the spring beam attachment structure may be substantially reduced. This smaller structure is therefore not limiting upon the placement of the engine
14
, thereby allowing optimization of engine placement for improved efficiency. Also, the placement of the spring beams at the attachment between the pylon structure
22
and the engine
14
, as opposed to the attachment between the pylon structure
12
and the wing
10
, provides the same advantage of enabling lateral frequency tuning to minimize flutter.
More specifically, the present invention provides an aircraft assembly including a wing, a pylon structure attached to the wing, an aft engine mount attached to the pylon structure, and an engine attached to the aft engine mount. The aft engine mount includes a pivotal attachment to the pylon structure and first and second spring beams operatively connected to the pylon structure at opposing sides of the pivotal attachment for damping pivotal movement of the engine with respect to the pylon structure to enable tuning of lateral frequency of the engine.
Objects, features and advantages of the invention are readily apparent from the following detailed description of the best mode for carrying out the invention.
REFERENCES:
patent: 2891743 (1959-06-01), Bligard et al.
patent: 4917331 (1990-04-01), Hager et al.
patent: 5054715 (1991-10-01), Hager et al.
patent: 5065959 (1991-11-01), Bhatia et al.
patent: 5181675 (1993-01-01), Lardellier et al.
patent: 5238206 (1993-08-01), Pachomoff
patent: 5687948 (1997-11-01), Whiteford et al.
patent: 5871177 (1999-02-01), Demouzon et al.
Powell Donald T.
Schnelz James R.
Brooks & Kushman P.C.
Swiatek Robert P.
The Boeing Company
LandOfFree
Tuned engine mounting system for jet aircraft does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Tuned engine mounting system for jet aircraft, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Tuned engine mounting system for jet aircraft will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2590003