Mounting structure for a turbojet engine

An engine mounting structure for a turbojet engine is disclosed which incorporates a safety rod in addition to the normal support rods used to attach a turbojet engine to a mounting structure. Under normal conditions, the safety rod is unstressed and supports none of the engine's weight. Upon rupture of one of the support rods, a tensile or compressive force exerted on the safety rod will move it into an active position so as to assume support of the engine's weight. A locking structure is also disclosed which will securely lock the rod in its active position such that it assumes the portion of the engine weight normally undertaken by the ruptured support rod.

BACKGROUND OF THE INVENTION 
Turbojet engines mounted beneath aircraft wings are typically suspended 
from a strut by a suspension means adjacent the front and rear of the 
engine. The suspension means comprises members to support the weight of 
the engine and to resist the rotational torque generated by the engine. 
Such suspension means typically comprise support bars or rods having one 
end fixed to the suspension means and the other to the engine. The rear 
suspension of the turbojet engine typically comprises three such bars or 
rods attached by hinge means to an engine casing ring and to three points 
on a rear strut of the aircraft suspension pylon. 
In the event that one of the three suspension rods breaks, the two 
remaining rods must withstand the entire load which was previously spread 
over the three rods. This presents the danger of consecutive breaking of 
the two remaining rods thereby causing the total failure of the engine 
support system. Even in the event that the two remaining rods fail to 
break, the rotational torque generated by the engine and applied to the 
anti-torque bars may become excessive, thereby causing damage to the 
engine. 
In order to prevent such a catastrophic failure of the engine support 
system, safety systems have been proposed. One such solution consists in 
doubling the rear suspension rods in the three axes. However, this 
solution to the problem has generated suspension systems with excess 
weight and complexity due to the necessity of forming the spare support 
elements of sufficient size and strength so as to enable it to withstand 
the maximum forces generated upon failure of the primary suspension 
system. 
British Pat. No. 1,236,917 describes a turbojet engine suspension system in 
which an additional safety rod is incorporated into the normal three rod 
suspension system. However, no means are described for changing the 
position of the safety rod fro a normal, non-supporting position, to one 
in which it serves to support at least a partial engine load. 
Other engine suspension systems are known in which an additional, safety 
rod normally performs no suspension function, however, should one of the 
normal support rods fracture, the safety rod then absorbs at least a part 
of the engine weight. However, these systems typically involve fixed 
clearances in the rod mounting such that these clearances are maintained 
during the normal suspension operation to prevent the rod from bearing any 
engine loads. Upon failure of one of the other suspension rods, the 
clearancese are taken up by engine movement such that the safety rod 
performs a support function. 
SUMMARY OF THE INVENTION 
The present invention relates to a suspension system for supporting a 
turbojet engine below an aircraft wing, more particularly to such a 
suspension system for the rear part of the engine. 
The invention provides a safety support rod in addition to the plurality of 
support rods which normally serve to attach the engine to the aircraft 
support strut. The three conventional suspension rods, in normal 
operation, support all of the engine loads while the fourth, safety rod is 
non-existent in regards to the suspension forces. The safety rod becomes 
active only if one of the three rods of the normal suspension system 
should break. 
Another object of the invention is to provide the suspension system with 
means for generating an alarm system to the aircraft pilot or to act 
directly as a control signal to regulate the engine to decrease its speed 
so as to reduce the stresses on the suspension system. 
It is an object of the present invention to provide a safety suspension 
system which, in the event of a fracture of the normal suspension rod, is 
capable of withstanding the maximum stresses for which the normal 
suspension system is rated. 
The invention also emcompasses means to move the safety from its passive 
position, wherein it is free from any loads generated by the engine, to an 
active position wherein it supports at least a portion of the engine 
loads. The drive means includes means for locking the safety rod in the 
active safety position once the safety rod has been moved to that position 
by failure of one of the normal suspension support rods. 
The attaching means for attaching the safety rod to the support strut 
includes an intermediate position, in which the safety rod is not 
subjected to engine stress loads and two extreme positions in which the 
rod will support at least a portion of the engine loads. The extreme 
position to which the safety rod is moved is determined by whether the 
initial force on the safety rod is in tension or compression. This, of 
course, depends upon which of the normal support rods has ruptured. 
The movable end of the safety rod is supported on a shaft rotatably mounted 
on an eccentric cam which, in turn, is attached to a shaft rotatably 
mounted on the support strut. When the safety rod is in the intermediate 
position, the central axis of the eccentric cam, which is laterally 
displaced from the rotational axis of the shaft, is disposed such that the 
axis of symmetry of the safety rod passes through the central axis of the 
eccentric cam, but does not intersect the rotational axis of the shaft. 
When the safety rod is moved to its active position, the eccentric cam and 
shaft rotate such that the axis of symmentry intersects or passes near the 
rotational axis of the shaft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a turbojet engine 1 suspended from a pylon 2 attached to the 
wing 3 of an aircraft. The engine 1 is suspended by front suspension rods 
4 attached to the front part 5 of the pylon 2 and connected to a front 
attaching ring 6 on the fan stator casing 7. A rear support strut 8 is 
attached to the pylon 2 and is connected to a rear suspension flange 9 of 
the engine by three support rods 10. Thrust absorbing bars 11 connect the 
rear strut to the engine case and are symmetrically arranged on either 
side of a vertical diametrical plane of the engine. 
FIG. 2 shows a view of the rear support strut 8 viewed in the direction of 
arrow G in FIG. 1. The strut 8 is located on pylon 2 by studs 12 and is 
fixed to the pylon by bolts passing through vertical bores 13 which 
cooperate with holding shafts 14. The strut 8 comprises a generally 
horizontal portion 8a and two angularly inclined portions on either side 
8b and 8c so as to encircle an upper portion of the engine. The strut 8 
comprises symmetrical forged elements 15 and 16 (see FIG. 4) which makes 
up the portion 8a, 8b and 8c. The elements 15 and 16 define clearances 18, 
19, 20 and 21. Clearances 18, 20 and 21 define a clevice-type joint for 
the attachment of rods 10 by hinge menas 22 and shafts 23 provided with 
shoulder bearings 24. The joints for attaching the rods 10 to the strut 8 
are shown in detail in FIGS. 2a and 2b. Support rods 10, which are 
normally three in number are attached to elements 25 formed on suspension 
flange 9 of the engine casing by known means. 
As shown in FIG. 2, each of the support rods 10 may be formed in two 
portions joined together by a universal type joint 26. The universal joint 
26 will allow the support rods 10 to accommodate axial expansion and 
contraction of the engine due to the changes in engine temperature during 
its operation. 
A safety rod 27 is also attached between the support strut 8 and the flange 
9. A fourth hinge connection 28 serves to attach one end of the safety rod 
27 to the flange 9 such that it may pivot about a Z--Z axis. The other end 
of the safety rod 27 is attached to the support strut 8 by shaft 29 which 
is rotatably mounted in bore 31 (defined by strut 8) by bearings 30, as 
illustrated in FIG. 4. Eccentric cam 29a is mounted on shaft 29 such that 
its central axis Y--Y is laterally displaced from the axis of rotation 
X--X of shaft 29. The end of safety rod 27 is attached to the eccentric 
cam 29a by universal socket joint 32 between a shoulder 29a of the cam and 
a washer 33. 
When the safety rod 27 is in its intermediate, inactive position (the 
position in which it assumes no load from the engine) the longitudinal 
axis of symmetry of the safety rod 27, indicated at 27c in FIG. 3, passes 
through the central axis Y--Y of eccentric cam 29a. In the intermediate 
position, the axis of symmetry 27c is displaced from the axis of rotation 
X--X of shaft 27 such that a line 27d passing through both the axis of 
rotation X--X of shaft 27 and the central axis Y--Y of the eccentric cam 
29 will be substantially orthoganal to the axis of symmetry 27c. Thus, the 
safety rod 27 does not take any of the stresses caused by the suspension 
of the engine which is totally affected by the support rods 10. 
Locking arm 35 is fixedly attached to end 34 of shaft 29 by a splined or 
fluted connection such that arm 35 rotates with shaft 29. Locking arm 35 
extends generally perpendicular to the shaft 29 and lies adjacent to an 
outer surface of support strut 8. The distal end portion of arm 35 defines 
a longitudinally extending bore 36 in which a generally cylindrical stud 
37 is slidably retained. Spring 38 is interposed between the innermost 
portion of stud 37 and the bottom of bore 36 so as to exert a biasing 
force on the stud 37 tending to move it outwardly from the bore 36. Screw 
40 is inserted through the wall of shaft 35 such that its innermost 
portion engages a longitudinal groove 39 formed in stud 37. This serves to 
guide the motion of the stud 37 with respect to the arm 35 and to limit 
its inward and outward movement. 
An arcuate flange 42 whose center of curvature coincides with the X--X axis 
of shaft 29 is mounted adjacent the distal end of the locking arm 35 on 
support strut 8. A wheel 41 is rotatably mounted on the exposed end fo 
stud 37 such that it bears against the inner arcuate surface of flange 42 
and is biased against this surface by spring 38. The arcuate flange 42 
defines openings 44 and 45 adjacent either of its ends, the openings being 
sized so as to accommodate the end of stud 37. Microswitches 46 are 
mounted on plate 43 attached to support strut 8 such that their actuating 
levers 47 are aligned with openings 44 and 45, respectively. Thus, when 
locking arm 35 is rotated with the shaft 29, stud 37 will enter either of 
the openings 44 or 45 when the arm approaches its extreme operating 
positions such that the end of stud 37 will pass through either one of the 
openings 44 or 45 and actuate the levers 47 of either one of the 
microswitches 46. The microswitches may operate an alarm signal in the 
aircraft cockpit to advise the pilot that the safety strut has been moved 
into an operative position, or the circuit may directly control the 
turbojet engine to reduce its output so as to prevent damage to the 
structure. 
As best seen in FIGS. 3 and 5, when the safety rod 27 is in its 
intermediate position, the central axis of eccentric cam 29a is in the 
position y shown in these figures and the locking arm is in the position 
indicated by solid lines in FIG. 5. If one of the normal support rods 10 
should rupture, a portion of the engine weight will then be supported by 
safety rod 27. This initial force, which may be tensile or compressive, 
depending on which of the normal support rods 10 has ruptured, applied to 
safety rod 27 causes the eccentric cam 29a to rotate in such a manner that 
its central axis Y--Y will pass sinto the y1 position, shown in FIGS. 3 
and 5, if the initial force on the rod 27 is tensile, or into the y2 
position if the initial force is compressive. Movement of eccentric cam 
29a causes rotation of shaft 29 which, in turn, drives locking arm 35 
until stud 37 comes into alignment with one of these openings, stud 37 is 
forced through the opening due to spring 38 so as to activate the 
microswitch 46. Engagement of the stud 37 in the opening 44 or 45 also 
serves to lock the arm 35 into its extreme position. It also serves to 
lock the shaft 29 in one of the two active extreme positions such that the 
rod 27 will then continue to function as a stressed engine support in the 
same manner as previously performed by the ruptured rod 10. 
In order to allow for axial engine displacement, safety rod 27 may be 
formed by elements 27a and 27b interconnected by a universal type joint 
47. As indicated in FIG. 3, element 27a is attached to support strut 8 via 
shaft 29, while second element 27b is attached to flange 9 via hinge 28. 
The safety system according to the invention provides a turbojet engine 
mounting structure having the requisite safety characteristics, but also 
one having a low weight, relatively simple construction. The engine 
mounting structure also provides the advantage of having means to generate 
an alarm signal to alert the aircraft pilot or one to act directly on the 
engine to reduce it power output to prevent further damage. 
The foregoing description is provided for illustrative purposes only and 
should not be construed as in any way limiting this invention, the scope 
of which is defined solely by the appended claims.