Thrust mounting arrangement

Mounting of gas turbine engines in aircraft requires use of thrust struts associated with mountings. It is important should there be failure that a load path is maintained. Furthermore, on a wing or in-situ inspection is highly desirable with respect to reducing maintenance costs. Of particular concern is failure as a result of cracking both sideways and vertical which may result in loss of all load paths through the mounting. By provision of independent cranks which are associated through crank pivots in apertures of the cranks and then articulation about central pivots provided in apertures and a central element along with pivot association of the struts through pivots created about apertures in the cranks load paths are maintained. By independent provision of the cranks sideways and vertical cracking cannot cause failure in both load paths to the arrangement from the struts. Furthermore, gaps between the cranks and the mounting and in particular snubber surface can be monitored to indicate component failure.

The present invention relates to thrust mounting arrangements and more particularly to a thrust mounting arrangement to secure a gas turbine engine to an aircraft utilising thrust struts.

Referring toFIG. 1, a gas turbine engine is generally indicated at10and comprises, in axial flow series, an air intake11, a propulsive fan12, an intermediate pressure compressor13, a high pressure compressor14, a combustor15, a turbine arrangement comprising a high pressure turbine16, an intermediate pressure turbine17and a low pressure turbine18, and an exhaust nozzle19.

The gas turbine engine10operates in a conventional manner so that air entering the intake11is accelerated by the fan12which produce two air flows: a first air flow into the intermediate pressure compressor13and a second air flow which provides propulsive thrust. The intermediate pressure compressor compresses the air flow directed into it before delivering that air to the high pressure compressor14where further compression takes place.

The compressed air exhausted from the high pressure compressor14is directed into the combustor15where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive, the high, intermediate and low pressure turbines16,17and18before being exhausted through the nozzle19to provide additional propulsive thrust. The high, intermediate and low pressure turbines16,17and18respectively drive the high and intermediate pressure compressors14and13and the fan12by suitable interconnecting shafts26,28, and30.

It will be appreciated that the gas turbine engine10must be secured by an appropriate mounting on an aircraft wing or otherwise. Typically, such mountings include thrust struts which are connected via a yoke that pivots through a central pin to transmit engine thrust loads to a mounting block. Such articulation accommodates for tolerance variation and for thermal growth as well as engine deflection in use. Such thrust arrangements should also provide an indication as to failure. Should one thrust strut or corresponding yoke end fail then the arrangement will pivot about a centre pin such that a catcher pin associated with the arrangement will continue to provide a thrust load path. Such a failure can also be noted upon inspection in situ or on an aircraft wing by checking for catcher pin clearances. In normal use each catcher pin will be locate within an oversized hole. If the catcher pin is forced into providing the thrust load path then this clearance within the hole will be lost. If a rear mounting block was to develop cracks from the centre pivot for the yoke then these could propagate to both the catcher pin holes resulting in a complete failure with no reliable thrust path. Such a situation or potential for such a situation would be generally unacceptable. The potential for such a failure can be detected by inspecting the rear mounting block for cracks at regular intervals but such inspection requires the thrust mounting arrangement to be removed with the engine. Furthermore additional crack growth analysis and substantiation testing may be required at inspection intervals for sure detection of any cracks before failure in use occurs.

In view of the above it is clearly desirable to appropriately provide a thrust mounting arrangement for gas turbine engines and the like but similarly in safety critical situations it is also important that these thrust mounting arrangements are readily visually inspectable in situ.

In accordance with the present invention there is provided a mounting arrangement for mounting a gas turbine engine to a pylon of an aircraft, the gas turbine has a rotational axis the mounting arrangement comprises a mounting block, two thrust struts and two cranks each pivotably attached to one of the thrust struts and pivotably attached the mounting block, characterised in that a gap is provided between the two cranks and the mounting block.

Preferably, the two cranks are pivotably attached to one another.

Preferably, a centre link pivotably connects between the two cranks.

Alternatively, the two cranks overlap one another and are joined by a pivotable attachment.

Alternatively, the centre link is integral to one of the cranks and pivotably attached to the other crank.

Preferably, the crank extends either side of its pivotable attachment with the mount block.

Preferably, the crank or mount block define snubbers either side of the pivotable attachment with the mount block; the snubbers define at least a part of the gap.

Preferably, the pivotable attachment between the cranks is forward of the pivotable attachment of to the mounting block.

Preferably, the pivotable attachment of the thrust struts are forward of the pivotable attachments to the mounting block.

Preferably, the pivotable attachment(s) between the two cranks are circumferentially between the pivotable attachments of the thrust struts.

Preferably, each pivotable attachment to the mounting block is located circumferentially between the pivotable attachments of the thrust strut(s) and the pivotable attachment between the two cranks.

In accordance with aspects of the present invention there is provided a thrust mounting arrangement comprising of mounting having spaced apart pivot mountings for receiving a respective thrust strut secured through a pivot pin and a load device across the pivot mountings, the arrangement characterised in that the load device comprises a respective crank portion for each pivot mounting, each crank portion pivoted upon its respective pivot mounting about a crank pivot with the pivot pin for the thrust strut to one side of the crank pivot and a centre pivot to the other side of the crank, the cranks coupled between the centre pivot, each crank having a gap relative to a part of the mounting whilst the crank pivot, the centre pivot and the pivot pin retain their relative positions within the arrangement.

Generally, one gap closes towards an end of the respective crank if the relative position is lost by structural failure at least of position of one or more of the pivot pin and/or the pivot crank and/or the centre pivot.

Generally, the mounting has a snub element to oppose a part of at least one crank to define the gap.

Possibly, the respective cranks are directly coupled through the centre pivot. Alternatively, cranks are coupled by a centre element extending between centre pivots. Possibly, the centre element and associated centre pivots for the respective cranks are configured whereby structural failure of the centre element causes the gap to open or close.

Possibly, the cranks are provided by plates. Possibly, each crank comprises two plates extending either side of the mounting. Generally, the plates are independently associated with the pivot mounting and the thrust strut and the other crank.

Possibly, part of the mounting or crank has a witness surface to highlight any contact between the part of the mounting and the crank.

Possibly, the gap is filled with a displaceable element to identify by displacement of the displacement element closure or opening of the gap. Possibly, the displaceable element comprises a fluid. Possibly, the fluid is located within a burstable element to indicate opening and closing of the gap.

Possibly part of the mounting or the crank is frangible and an opposed part of the crank or mounting is arranged to cause detachment of the part which is frangible if the gap opens or closes.

Also in accordance with aspects of the present invention that is provided a gas turbine engine incorporating a thrust mounting arrangement as described above.

Aspects of the present invention provide a thrust mounting arrangement in which two cranks are independently attached to a mounting by means of a pin and clevis joint. In such circumstances the cranks can rotate about the pin. Each crank is also associated with a respective thrust strut in use which transmits thrust load through the crank to the main mounting and onto a support structure. The cranks are connected through the pin and clevis joints to a common centre element in the embodiment depicted in order to provide stability through a linkage system. The complete linkage system allows articulation to compensate for tolerance variation with respect to the constituent components, relative thermal growth and engine movements to be expected in normal use. In a failure scenario a gap between the mounting and one of the cranks is utilised as an indicator. The gap will normally close as a result of an engagement between the crank and the mounting on one side and open on the other side relative to the other crank. Such engagement will provide an auxiliary load path to allow continuous operation of the thrust mounting arrangement despite such failure. The crank and main mounting are separate so that any cracks which may occur cannot grow sideways or vertically within the mounting arrangement or vice versa. In such circumstances the mounting arrangement in accordance with aspects of the present invention avoids the necessity for routine inspection and analysis for cracks within the mounting arrangement required with previous arrangements.

FIG. 2provides a perspective view of a thrust mounting arrangement31in accordance with aspects of the present invention. The arrangement31comprises a mounting32associated with pivot mountings33,34. The pivot mountings33,34have an aperture35,36to receive a respective crank pin (not shown). The crank pins in the apertures35,36allow and provide a crank pivot for crank elements37,38. The crank elements37,38in such circumstances can pivot and articulate about the mountings33,34.

The cranks37,38define further apertures39,40within which a respective pivot pin for locating thrust struts41,42is provided. Thus, the thrust struts41,42are associated with a respective crank37,38through the pivot pins and in turn the cranks37,38are associated with the mountings33,34for pivot articulation.

In accordance with aspects of the present invention the cranks37,38are also arranged to pivot around a central pivot or with central pivot combination as illustrated between them. In the embodiment depicted inFIG. 2this central pivot combination is achieved through a centre element43which is secured at each end through a central pivot44,45.

In the above circumstances the arrangement31through the articulation provided by the respective pivots created in apertures35,36,39,40,44,45allows assembly adjustment for tolerance variation between the various components, relative thermal growth and expected normal engine movements. However, throughout such expected movements a gap46between opposed parts of the cranks37,38and the mounting32is maintained. As illustrated generally snub surfaces47,48are provided in order to define the gap46between the cranks37,38and the snub surfaces47,48. Monitoring of the gap46will allow determination as to structural failure in the form of cracking or otherwise with regard to component parts of the arrangement31in accordance with aspects of the present invention.

Of particular importance with regard to aspects of the present invention is the independence and isolation of the respective cranks37,38and associated crank pivots provided in the apertures35,36from each other. In such circumstances structural cracks resulting in failure cannot grow sideways or vertically ensuring that failure from such cracks cannot result in failure of both potential auxiliary thrust load paths provided through the thrust struts41,42and associated pivot pin to the respective cranks37,38abutting the mounting32. In such circumstances the arrangement31will remain operational until inspection of the gaps46indicates such failure and therefore remedial action can then be taken.

FIG. 3provides a plan view of the arrangement31as depicted inFIG. 2with pivot mountings33,34removed for clarity. As indicated above in normal use the pivot mountings33,34as depicted inFIG. 2will overlay the cranks37,38in order to allow pivoting about apertures35,36. The thrust struts41,42as indicated are associated through pivot pins in apertures39,40with the cranks37,38to allow articulation in use for expected operational tolerance variation. However, should there be structural failure of the components then a load path is maintained. This load path is generally achieved through one or other of the cranks37,38engaging an opposed part or snubber of the mounting32. In such circumstances changes in the gap46will provide an indication as to structural failure or cracking which can be identified by on wing or in situ inspection rather than demounting for appropriate analysis and inspection. The scenarios with respect to failure are outlined below.

If the centre element43or associated centre pivots fail then the cranks37,38will respectively engage at ends B, C if there is a forward thrust or ends A, D if there is a reverse thrust in terms of the load applied by the thrust struts41,42.

If thrust strut42structure fails or its related pivot pin in aperture40or crank pin in aperture36fails then end B of crank37will engage the snubber48ain forward thrust or end B of the snubber46in reverse thrust.

Alternatively, if left hand thrust strut41or associated pivot pin in aperture39or crank pin in aperture35should fail then crank38will engage end C of snubber surface48bin forward thrust or end D in reverse thrust.

If the right hand crank pin in aperture36fails then all the load will be taken by the left hand crank pin in aperture35such that end B of the snubber surface48awill be engaged in forward thrust and end B will be engaged in reverse thrust.

Should the left hand crank pin in aperture35fail then all of the load will be taken by the right hand crank pin in aperture36such that end C of the snubber surface48bwill engage in forward thrust and end D in reverse thrust.

As indicated above structural failure of components within the arrangement31will in such circumstances result in maintenance of a load path to the mounting32for continued operation. This continued operation will be maintained until the gap46is again inspected in situ or on wing. Upon inspection of the gap46engagement of the snubber surfaces48a,48bwill be identified. Such identification of narrowing or engagement across the gap46will indicate failure or early stage failure such as preliminary cracking and therefore weakness in the respective components allowing appropriate maintenance and remedial action to be taken.

By aspects of the present invention articulation and linkage is provided through the respective cranks37,38and the pivots created about apertures35,36,39,40,44,45and it will be appreciated that on wing inspection of a mounting arrangement31is achievable. Furthermore, the failure modes as indicated above are symmetrical and deterministic from the respective closure or engagement at the ends A, B, C, D on the snubber surface48allowing ready analysis and verification of failure within the arrangement31and so remedial action to be taken.

Generally in forward thrust the centre element43is loaded in compression by the thrust loads presented through the thrust struts41,42to the cranks37,38. Such compression will inhibit crack growth within the centre element43and therefore restrict exposure to tensile loads in reverse thrust to only a fraction of the fatigue spectrum so improving the component life or offering a reduced weight component for the centre element43.

As indicated above generally a centre element43is provided to allow for the articulation about the centre pivot combination created within apertures44,45. The centre element43may be removed and so a direct association between the cranks37,38in forward thrust achieved. Elimination of the centre element43may provide savings with regard to cost and weight. In reverse thrust with such direct association and coupling between the cranks37,38it will be understood that the cranks will move and so cause contact with respect to ends A, D. In effect by eliminating the centre element43an arrangement configuration is provided where effectively the centre element and its associated pivots have failed resulting in an indicative scenario for reverse thrust which is compensated for in initial configuration of the arrangement.

As indicated above aspects of the present invention are particularly relevant with regard to ensuring an appropriate load path is provided consistently despite component failure. In such circumstances by creating the cranks37,38of separate plates associated either side or appropriately to the mountings33,34(FIG. 2) and the thrust struts41,42it will be understood that even greater durability may be achieved. If the respective plates are independently mounted, should one plate fail then the other is still in place to carry thrust loads at least temporarily until remedial action can be taken at next inspection. The plates may be designed to provide sufficient strength to continue with full loads or to precipitate a partial narrowing of the gap46indicative of failure of one plate and therefore a requirement for remedial action.

To further improve robustness the crank pivots provided in the apertures36may be of a double concentric pin nature so that if the outer pin fails the inner pin will still transmit applied load. However, outer pin failure will generally result in an asymmetric positioning of the inner pin resulting in again a reduction or alteration in the gap46. This reduction or alteration in the gap will be detectable at next inspection.

Generally arrangements in accordance to aspects of the present invention as indicated will be configured to ensure a load path is provided should one or other of the components fail. By such a configuration it will be understood that in normal operation the gap46will be maintained through the respective component positioning particularly of the cranks37,38. Failure will open or close the gaps46allowing identification at maintenance inspection and remedial action to be taken. Provision of snubber surfaces48allows accurate determination of the gap46for comparison of such inspections. Such determination may be through a feeler gauge of the correct width. In order to further emphasise changes, in particular closure of the gap46parts of the snubber surfaces48may be arranged to provide witness of such closure such that in operation failure and therefore engagement by a respective crank37maybe identified by such witness surfaces. Thus, upon maintenance should the gap re-open as a result of residual torsion or other biases within the mounting arrangement identification of the engagement during operational periods can be notified. This witness surface may comprise a compliant surface which is compressed by the engagement and therefore noticeable once the engagement is removed. A further alternative may be to provide a displaceable element with the gap46. This displaceable element and its removal will therefore be seen at inspection. The displaceable element may force the element out of the gap and therefore provide a noticeable feature. Alternatively, the displaceable element may comprise a fluid or gel which is squeezed from the gap and therefore becomes identifiable upon inspection. However, with respect to provision of witness surfaces and of displaceable elements it will be appreciated that generally the engagement as a result of closure of the gap46will be utilising to create a load path. This load path must be sufficiently robust to transfer thrust loads and therefore care must be taken in weakening the snubber surface48. However, where such weakening of the snubber surface may be acceptable a proportion of the snubber surface48may be frangible so that it becomes detached upon in engagement and therefore again be more readily identifiable upon inspection. It will also be understood that use of a witness surface or other indicator of engagement may be capable of indicating an imbalance in the load applied through the thrust struts.

Aspects to the present invention have particular applicability with regard to mounting gas turbine engines through thrust struts and rear mountings with an aircraft. The mounting arrangement allows for reliable and continued operation through a thrust path should there be a failure of one or other of the thrust strut41,42load paths in the arrangement. The arrangement31ensures such a load path is provided whilst also through the variations identifiable at inspection in the gap46notification available as to requirement for remedial action.

The present invention may be summarised as a mounting arrangement31comprising a mounting block32, two thrust struts41,42and two cranks37,38each pivotably attached39,40to one of the thrust struts and pivotably attached35,36the mounting block, characterised in that a gap46is provided between the two cranks and the mounting block. The mounting arrangement31is intended for mounting a gas turbine engine to a pylon of an aircraft. The gas turbine has a rotational axis X-X to which the term circumferential applies. The two cranks, although there could be more where further thrust struts are employed, are pivotably attached to one another and as shown inFIGS. 2 and 3via the centre link43. Alternatively, the two cranks could extend and overlap one another and be joined by a pivotable attachment such as a pin as is well known. Furthermore, the centre link could be integral to one of the cranks and be pivotably attached to the other crank.

Importantly, the cranks extend either side of their pivotable attachment35,36with the mount block. This is so that in the event of failure of a part of the mounting arrangement the ends A, B, C, D of the cranks can bear against the mount block and create a reasonably sized moment arm to keep stresses in the crank and bearing stress on the mount block within stress limits. Preferably, the snubbers48are specifically designed to be load bearing elements and are positions at the ends A, B, C, D of the cranks. Therefore the snubbers each define at least a part of the gap between each crank and the mounting block.

The relative locations of the pivotable attachments are important to ensure the arrangement is stable during normal engine operation and to react as required in the unlikely event of failure of the mounting arrangement. To this end the pivotable attachment43,44,45between the cranks is forward (towards the front of the engine) of the pivotable attachment35,36to the mounting block. Further, the pivotable attachment39,40of the thrust struts are forward of the pivotable attachments35,36to the mounting block. Still further the pivotable attachment(s)43,44,45between the two cranks are located circumferentially between the pivotable attachments40,41of the thrust struts. Yet still further, each pivotable attachment35,36to the mounting block is located circumferentially between the pivotable attachments40,41of the thrust strut(s) and the pivotable attachment43,44,45between the two cranks.

Modifications and alterations to aspects of the present invention will be appreciated by those skilled in the art. Thus for example it will be understood that the cranks37,38are essentially bell cranks associated with pin and clevis joints and the respective apertures35,36,39,40,44,45. The respective size and distribution of the crank pivots provided in the apertures35,36, centre pivots through pivots in apertures44,45as well as pivot association between the thrust struts41,42with the cranks37,38can all be adjusted to provide the degree of articulation necessary to precipitate engagement between the cranks and the mounting across the gap46and typically against snubber surfaces48of the mounting32. It is by positioning the pivot pins in the apertures39,40associating the thrust struts41,42within the arrangement31that it will be understood the articulation to cause displacement to engagement with the ends A to D of the snubber surfaces48can be achieved and which allows witness of failure. Positioning of the respective pivots to cause articulation in such circumstances will depend upon operational requirements in terms of thrust load transfer in normal use as well as creation of a sufficiently robust load path in failure and identification through changes in the gap46in use.