GB2096776A

GB2096776A - Improvements in or relating to thrust stands

Info

Publication number: GB2096776A
Application number: GB8107888A
Authority: GB
Original assignee: FROUDE ENG Ltd
Current assignee: FROUDE ENG Ltd
Priority date: 1981-03-12
Filing date: 1981-03-12
Publication date: 1982-10-20

Abstract

A thrust stand is provided for testing an aero-engine, such as a jet engine 1. The stand comprises a first support 16 to which the engine is fixed. The first support is connected to a second support 20 by means of flexure plates 19. Transducers 32 are connected between the first and second supports for measuring the thrust produced by the engine. Each flexure plate 19 is perpendicular to the thrust direction and is clamped along opposite sides to the first and second supports by clamping plates. The plates 19 may thus be made from stainless steel sheet and do not require machining. The second support 20 is suspended from fixing pads 25 by means of torsion bars 21. The resonance frequency of this suspension may thus be adjusted to avoid vibration problem areas and to match airframe installation stiffnesses for flight simulation testing. <IMAGE>

Description

SPECIFICATION Improvements in or relating to thrust stands The present invention relates to thrust stands.

Such thrust stands may be used for the development or testing of aero-engines, such as turbo-jet or turbo-fan engines, for measuring the thrust produced by such engines.

According to one aspect of the invention, there is provided a thrust stand comprising a first support arranged to be fixed to an engine, a second support connected to the first support by means of a plurality of flexure plates, and at least one transducer connected between the first and second supports for measuring thrust produced by the engine, each flexure plate being disposed substantially perpendicular to the direction of thrust and being fixed along opposite first and second sides to the first and second supports, respectively, by means of respective clamping plates.

Such an arrangement allows the flexure plates to be produced from stainless steel sheet without requiring any machining, such as necking of relatively thick plates as was required with previously known flexure plates. Thus, the cost of such flexure plates can be substantially reduced.

According to another aspect of the invention, there is provided a thrust stand comprising means for fixing the stand, means for supporting an engine, and at least one torsion bar connected between the support means and the fixing means.

The use of the torsion bar arrangement provides a suspension arrangement whose natural resonant frequency can easily be changed.

Thus, it is possible to avoid vibration problem areas in development testing. Also, for the purpose of flight simulation testing, it is possible to match an airframe installation stiffness.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view, partially cut away, of a thrust stand constituting a preferred embodiment of the invention; Figure 2 is a side view of the thrust stand of Figure 1; Figure 3 is an end view of the thrust stand of Figure 1; Figure 4 is a plan view of the thrust stand of Figure 1; Figure 5 is a side view to an enlarged scale of a detail of the thrust stand of Figure 1; Figure 6 is a transverse sectional view of the detail shown in Figure 5; and Figure 7 is a cross-sectional view to an enlarged scale of another detail of the thrust stand of Figure 1.

A thrust stand is shown in the accompanying drawings for use during testing or development of an aero-engine such as a turbo-jet engine 1 as shown in Fig. 1. The aero-engine 1 is fixed to a test cradle 2 which comprises an upper frame 3 made of square section tubular metal rigidly connected to a lower plate 4 by brackets 5 provided with bracing struts 6. The engine 1 is provided with a ring which is connected to the plate 4 by means of a pair of struts 8. The engine 1 is connected to the frame 3 by means of a pair of brackets 9 fixed to the compressor housing of the engine 1 and two pairs of brackets 10 arranged as V-shaped brackets on respective opposite sides of the engine. Couplings such as 11 and 12 are provided on the plate 4 to allow the various services, such as fuel lines and the like, to be connected to the engine 1 and a development or test.

Each corner of the frame 3 is provided with a pair of upstanding parallel plates 13 interconnected at their upper ends by respective bolts 14 or similar members which are readily removable to allow the cradle 2 and engine 1 to be connected or disconnected easily and quickly to and from the remainder of the thrust stand.

Four plates 1 5 are fixed to respective corners of a frame 1 6 constituting a first support. These plates 1 5 extend downwardly from the frame 1 6 and, at their lower ends, have holes through which the bolts or elements 14 pass so as to fix the frame 3 of the cradle 2 to the fram 1 6 constituting the first support.

The frame 1 6 is provided adjacent its respective corners with saddles 1 7 which are rigidly connected to the frame 1 6. Each of the saddles 1 7 is connected to a corresponding saddle 1 8 by means of a respective pair of flexure plates 19. The saddles 18 are rigidly connected to another frame 20 which, like the frames 3 and 16, is made of square section tubular metal and constitutes a second support.

The longitudinally opposite sides of the frame 20 are provided with respective torsion bar suspensions in the form of two torque tubes 21 which extend transversely of the frame 20. The opposite ends of the torque tubes 21 project from either longitudinal side of the frame 20 and are rotationally rigidly connected to links 22. The upper ends of the links 22 are pivoted by means of holes to pins 23 which extend between and are fixed to respective pairs of parallel plates 24 of fixing pads 25. The pads 25 are fixed to a sufficiently strong overhead structure, such a ceiling or frame, which is capable of withstanding the thrust provided by the engine 1.

The frame 20 includes a plurality of transverse members 26 which interconnect the two longitudinal sides of the frame 20. A central box section 27 is fixed to the central bracing member 26 and extends downwardly therefrom so that its lower end is disposed adjacent the centre of the frame 1 6. The box member 27 is further braced to the other bracing members 26 by means of triangular plates 28. The lowe end of the box member 27 is provided with two oppositely extending pairs of plates 29 which are pivoted to respective annular members 30 by means of respective pins 31. Each of the annular members 30 is fixed to one end of a respective load cell 32.

One of the load cells 32 which constitutes a test load cell has its other end fixed to an annular member 33, which is pivoted by a pin 34 to a pair of parallel plates 35 fixed to the frame 1 6.

The other end of the other load cell 32 which constitutes a calibration load cell is provided with a longitudinal extension 36 which is held against a member 37 pivoted by means of a pin 38 to a pair of parallel plates 39 fixed to the frame 1 6.

Figures 5 to 7 show in more detail the arrangement of the flexure plates 29 and the torque tubes 21. The flexure plates 19 are made from stainless steel sheet and are each provided with four holes whose edges are pressed into respective cones 40 (only one shown in Fig. 5).

Each cone 40 is clamped between corresponding mating conical surfaces of a locking stud 41 and the saddle 18. The flexure plate 19 is clamped between the stud 41 and the saddle 18 by means of the nuts 42. When the nuts 42 have been tightened and locked, a fixing of the flexure plates 19 is provided which is capable of carrying the whole of the live loading experienced by the thrust stand when an engine whose thrust is within the rating range of the thrust stand is operating.

The flexure plates 1 9 are clamped to the saddles 17 and 18 by means of clamping plates 43. In particular, the clamping plates 43 are clamped against the flexure plates 19 by means of nuts 44 screwd on to the studs 41. This position thus accurately defines the point of flexure or pivoting of the flexure plates 1 9 at the position indicated at 45.

A downwardly extending rod 46 is fixed to each of the upper saddles 1 8 and has at its lower end an enlarged head 47. A housing 48 is fixed to the lower saddle 17 and surrounds the head 47 with clearance. The clearance is arranged so that engagement of the rod 46 or the head 47 with the housing 48 prevents further deflection of the flexure plates 29 so that their normal range is not exceeded.

Each torque tube 21 comprises a cylindrical rod or hollow tube, each of whose ends is provided with a diametrically opposite pair of flattened surfaces 49. A generally rectangular cutout, having rounded internal corners 50 for reducing stress and raised surfaces 51 for locating vertically the torque tube 21, is formed in the link 22. One of the surfaces 49 abuts against the innermost surface of the cut-out whereas a locking plate 52 is rigidly screwed to the link 22 so as to clamp the link rotationally rigidly with the end of the torque tube 21.

The torque tube 21 passes through the square section making up the frame 20 and is held rotatably therein by means of plain bronze bearings 53. A pin 54 is fixed to the inner one of the pair of plates 24 and extends with clearance into an aperture in the frame 20 arranged so that the pin 54 abuts against the frame 20 so as to limit twisting of the torque tube 21 to within its normal operating range.

The middle of each of the torque tubes 21 is provided with a torque reaction clamping arrangement as shown in Figure 7. The clamping arrangement comprises a first member 55 having formed therein a cut-out substantially identical to that formed in each link 22. Similarly, a second member 56 in the form of a clamping plate is provided, the first and second members being clamped to a middle portion of the torque tube 21 provided with diametrically opposite flat surfaces 57 and 58. The members 55 and 56 are further clamped to a frame member 59 by means of bolts 60, the frame member 59 being fixed to the frame 20. Thus, each torque tube 21 is divided into two substantially independent halves which may be placed separately in portion when the thrust stand is in use. (For the sake of clarity, the torque reaction clamping arrangement of Fig. 7 is not shown in the other drawings).

In use, with the engine 1 mounted as shown in Fig. 1, the thrust produced by the engine is transmitted via the cradle 2 directly to the first support comprising the frame 1 6. The flexure plates 1 9 bend of flex under the loading caused by the thrust so that the frame 16 moves by an amount substantially proportional to the thrust with respect to the frame 20 of the second support. The test load cell 32 which essentially has one end connected to the frame 16 and the other end connected to the frame 20 provides an electrical signal corresponding to the amount of thrust, and the direction thereof, produced by the engine 1.

The effect of the thrust produced by the engine 1, the frame 20 is similarly caused to move with respect to the fixed pads 25. This movement causes the links 22 to rotate, thus applying a torsion to the torque tubes 21. Longitudinal vibration is similarly communicated to the torque tubes 21.

The arrangement of the flexure plates 1 9 allows simple stainless steel sheets to be used without requiring any substantial machining, thus substantially reducing the cost of the flexure plates, eight of which are required in the embodiment shown in the accompanying drawings.

The naturai resonant frequency of the suspension system provided by the torsion bar arrangement may readily be altered if necessary.

For instance, each torque tube 21 may be provided with a pair of clamping arrangements as shown in Figure 7 which can be slid along the torque tube in respective opposite directions so as to change the length of the section of the tube in torsion, or the torsional stiffness of the tube may be varied by selection of bore size. Thus, vibration problem areas which might be encountered during development testing of an engine 1 may be avoided. Further, the airframe installation stiffness may be matched to allow simulation testing of the engine 1.

Claims

1. A thrust stand comprising a first support arranged to be fixed to an engine, a second support connected to the first support by means of a plurality of flexure plates, and at least one transducer connected between the first and second supports for measuring thrust produced by the engine, each flexure plate being disposed substantially perpendicular to the direction of thrust and being fixed along opposite first and second slides to the first and second supports, respectively, by means of respective clamping plates.

2. A thrust stand as claimed in Claim 1, in which each of the said opposite sides of the flexure plates is clamped by means of the respective clamping bar to a saddle which is fixed to the first or second support.

3. A thrust stand as claimed in Claim 2, in which each of the said opposite sides of the flexure plates has formed therein a plurality of holes surrounded by conical portions pointing towards the saddle, which has formed therein corresponding holes surrounded by corresponding conical surfaces, there being provided a plurality of studs having conical shoulders which clamp the conical portions of the flexure plates to the corresponding conical surfaces of the saddle.

4. A thrust stand as claimed in any one of the preceding Claims, in which at least one rod extends from one of the first and second supports and enters an opening in, or in a member fixed to the other thereof with a clearance such that abutment of the rod on the edge of the opening limits flexing of the flexure plates within a normal working range thereof.

5. A thrust stand as claimed in Claim 4, in which the rod has an enlarged head which is larger than the opening so as to limit movement between the first and second supports in the event of failure of a flexure plate.

6. A thrust stand as claimed in any one of the preceding Claims, including means for fixing the stand and at least one torsion bar connected between the second support and the fixing means.

7. A thrust stand comprising means for fixing the stand, means for supporting an engine, and at least one torsion bar connected between the support means and the fixing means.

8. A thrust stand as claimed in Claim 7, in which the support means comprises first and second supports with at least one transducer connected therebetween, the second support being connected to the or each torsion bar and the first support being arranged to be fixed to an engine.

9. A thrust stand as claimed in any one of Claims 6 to 8, in which the fixing means comprises a plurality of fixed pads, each pivotally connected to a link which is rotationally fixed to a respective torsion bar.

10. A thrust stand as claimed in any one of Claims 6 to 9, in which each torsion bar comprises a solid or or hollow cylindrical torque tube.

11. A thrust stand as claimed in Claim 10, in which the or each torque tube is clamped at its middle portion to the support means or second support to provide two portions arranged to function as independent torsion bars.

12. A thrust stand as claimed in Claim 11 when dependent on Claim 9, in which each end of the or each torque tube has opposite flattened surfaces to which the respective link is clamped.

13. A thrust stand as claimed in Claim 12, in which each link has a substantially rectangular cut-out for receiving the end of the torque tube and a clamping plate is fixable to the link to clamp the end of the torque tube.

14. A thrust stand as claimed in any one of Claims 12 or 13 in which each link has a fixed pin which projects into an opening in the support means or second support with a clearance which is such as to limit movement between the link and the support means or second support within the normal working range of the torque tube.

1 5. A thrust stand as claimed in any one of Claims 1 to 6 and 8, and any one of Claims 9 to 14 when dependent on Claim 8, in which a cradle for receiving an engine is detachably rigidly connected to the first support.

1 6. A thrust stand substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.