GB2229230A - Ring for supporting aircraft propeller - Google Patents

Description

1 -l- RING FOR SUPPORTING AIRCRAFT PROPELLER 13-DV-9575 The invention

relates to the mounting of propeller blades in aircraft engines. In one type of mounting system, the centrifugal load of the propeller blades i distributed as hoop stress in a ring, the ring in turn being supported by a turbine which the ring surrounds.

Should the ring break during operation, the centrifugal load of the propeller blades can cause the ring to -unwrap from the turbine. The invention protects against such unwrapping.

S Figure 1 illustrates an aircraft engine 3 of the unducted fan type, in which the invention can be used. Region 6 is shown in Figure 2, wherein contra-rotating turbines 9 (hatched) and 12 (plain) are driven by a hot gas stream 15 provided by a core engine (not shown). The turbines 9 and 12, in turn, drive contra-rotating fan (or propeller) blades 18 and 21. (The term llcontra-rotatingll means that turbines 9 and 12, as well as blades 18 and 21 to which they are attached, rotate in opposite directions, as shown by arrows 24 and 27 in Figure l.) A view of sub-region 6A in Figure 2 is shown in Figure 3, and in more detailed form in Figure 4. The turbine blades which are located, but not shown, in sub-region 6B in Figure 2 are shown schematically in X 13-DV-9575 Figure 3 as blades 28 and in detail in Figure 4. The turbine blades 28 extend between a casing 24 and an inner barrel 92 in Figures 2, 3, and 4. The turbine blades extract energy from the airstream 15 in Figure 2, and also act as a stiff connecting web between the casing 24 and the barrel 92.

The fan blades 18 in Figure 3 are supported by a structure which is shown as a ring 22 in Figure 4, and which is fastened to the casing 24 by brackets 25.

During operation, the centrifugal load of the fan blades 18 is carried by the ring 22 as a hoop stress.

The actual structure used is not the idealized ring 22 shown in Figure 4, but is what is termed a polygonal ring 22P shown in Figure 4A. The polygonal ring 22P includes two types of sections: one type is a blade support section 22B, or "hub." A hub is also shown in Figure 5, which includes thrust and torque bearings 22D which transmit the centrifugal load imposed by the fan blade 18 to the ring 22P. The thrust bearings 22D allows pitch'change of the blade to occur, as indicated by arrow 23.

The other type of ring section is a connector 22A which connects neighboring hubs 22B. The connector includes rails 29 (Figure 6) which are in tension because of the centrifugal load of the blades 18.

One type of polygonal ring is described in the U.S. Patent 4863352 entitled 'Slade Carrying Means" issued to Hauser, Strock, Morris and Wakeman. the description in which is hereby incorporated by reference.

If one of the rails 29 should break, as shown by break 31 in broken rail 29B Figure 6, the hoop stress which was previously shared as tension in both rails 29 is now totally applied to the remaining, intact rail 291. Further, the breakage causes a torsional load to be applied to the intact rail 291, as indicated by torsion arrow 33. because the centrifugal load 35 13-DV-9575 (which can be viewed as.a force 35 in Figure 7 applied at the center of mass 18M of the blade 18) is separated by distance 36 from the line of action 38 of the intact rail 291. The blade 18 becomes displaced to phantom position 18P in Figure 7. The added tension and torsion can be cluite large, as an example will show.

it is assumed, for example, that the propeller diameter, dimension 42 in Figure 1, is 12 feet. It is assumed that each fan blade can be treated as a point mass 45 weighing 54 pounds and located on the circumference of a circle 46 which is six feet in diameter. It is also assumed that the speed of rotation is 1200 rpm, or 20 revolutions per second, which corresponds to (2)(pi)(20) radians per second, i.e., about 126 radians per second.

Centrifugal acceleration is equal to w 2 r, wherein w is angular velocity (radians per second) and r is radius. In this example, the acceleration is about 47,374 feet per second 2:

47,374 = [126/sec] 2 x 3 feet Dividing this number by the acceleration due to gravity, 32.2 feet per second 2, gives a quotient of about 1471. The quotient is the g field experienced by the point masses. 1 Stated another way, each point mass 45 (representing the weight of each blade), which originally weighed 54 pounds, now weighs about 80,000 pounds under centrifugal force (1471 x 54 = 79,434). Consequently, the additional tensile force acquired by the intact rail 291 in Figure 6 is in the range of one-half of 80,000 pounds. Further, assuming distance 36 to be six inches, the torsional load on the intact rail 291 becomes approximately 80,000 x 6, or 480,000 inch pounds. (The torsional load is not exactly this value, because the neighboring unbroken rails 29N in Figure 6 assist the intact rail 291 in resisting the torque.) Therefore, breakage of rail 29B applies large 13-DV-9575 tensile and torsional loads to the remaining, intact rail 291, which can cause deformation and damage. In addition, if the travel of the broken rail 29B, indicated by distance 49, is sufficiently great, both undesirable imbalance-in the rotating system, as well as breakage of rail 291, can occur.

Further, the deformation of the polygonal ring 22P can cause failure in the pitch change mechanism (not shown) of the aircraft. The pitch change mechanism is lo that which rotates the fan blades about axis 23A in Figures 3 and 5 in order to change the pitch angle. The detailed operation of the mechanism need not be und erstood, but only that the pitch change mechanism must remain operational in order to pitch the blades properly. Proper blade pitch is necessary for good performance, safe operation, and prevention of overspeed of the propeller.

It is an object of the invention to provide an improved blade retention system for use in aircraft.

In one form the invention provides a redundant support system for aircraft propeller blades supported or carried by a ring which surrounds a turbine which rotates the ring and the blades. The invention concerns a system for preventing the centrifugal load of the blades from unwrapping the ring from the turbine if the ring should break. one such system includes a band surrounding the ring, which adopts part or all of the hoop stress of the ring if the ring should break.

In the accompanying drawings:

Figure 1 illustrates an aircraft powered by contra-rotating propellers.

Figure 2 is a simplified cross-sectional view of the aircraft engine 3 of Figure 1.

13-DV-9575 Figure 3 is a simplified view of region 6A in Figure 2.

Figure 4 is a more detailed view of Figure 3.

Figure 4A illustrates the actual polygonal ring 22P which supports propeller blades 18. The polygonal ring 22P is shown in simplified form as a circular ring 22 in Figure 4.

Figure 5 illustrates bearings which allow pitch change of propeller blade 18.

Figure 6 illustrates a break 31 in the polygonal ring which can cause torsion indicated by arrow 33 in an intact rail 291.

Figure 7 illustrates dislocation of a propeller blade 18 which can occur because of the torsion shown is in Figure 6.

Figure 8 illustrates one form of the invention, in which bands 50 surround the ring 29.

Figure BA is a cross-sectional view of Figure 8, taken along lines BA.

Figure 9 illustrates how band 50 prevents dislocation of a broken rail 29 to phantom position 29PH.

Figure 10 illustrates unwrapping of the polygonal ring 22P which can occur because of break 31.

Figure 11 illustrates another form of the invention, in which bands 50 are contained in channels 56.

Figure 11A is a cross-sectional view of Figure 11, taken along lines IIA-11A.

Figure 12 illustrates wrapping of foil 65 around polygonal ring 22P in order to construct the bands 50 (not shown).

Figure 13 illustrates a stack of foil layers 65 which form the band 50.

Figure 14 is a simplified cross-sectional view of the polygonal ring 29P of Figure 4A, taken along lines 14-14. In addition, casing 24 of Figure 4 is shown, together with catchers 70.

L 13-DV-9575 Figure 15 illustrate's deformation of catcher 70 which can occur when rail 29 is forced to move in direction 77.

Figures 16A, 16B, and 16C illustrate alternate forms of catchers 70, which eliminate the deformation of Figure 15.

Figure 17 illustrates a stack of foil layers-forming a band 50. and located within a channel 56.

Figure 18 illustrates dislocation of foil layers 65 which can occur when the attempt is made to wind the layers onto a polygonal ring in the absence of channel walls 120 in Figure 17.

Figure 19 illustrates deformation of hub region 22B which occurs when a propeller blade (not shown) has a pitch angle such that the load on the hub region 22B can be viewed, in a simp lified manner, as forces 130.

Figure 20 illustrates a guide 130 which can be used to align the foil layers 65 of Figure 17 into a stack during winding.

Figure 21 illustrates the absence of a channel 56 in hub region 22B.

Figure 22 illustrates an alternate form of the invention, in which rings 155 are placed into rails 29.

Figure 23 illustrates buckling of a layer 183 which occurs when a laminate is bent.

Figure 24 illustrates a tapered end of a foil layer 65.

Figure 25 illustrates an alternate to catchers 70 in Figure 14.

Figure 26 illustrates an alternate form of the invention, in which the polygonal ring 22P surrounds a gear transmission 305, instead of a turbine as in Figure 4.

As discussed above, the break 31 in Figure 6 causes the remaining, intact rail 291 to carry all of the centrifugal load, indicated by arrows 35, of the 13-DV-9575 propeller blades 18 in Figure 4A. Further, because the centrifugal force 35 of the propeller blade is displaced from the rail 29 by distance 36, the centrifugal load 35 of the blade applies a moment to the rail 291: the rail is placed into torsion, as indicated by arrow 33. The ring 22P becomes twisted such that the broken rail 29B becomes displaced upward, as indicated by arrow 49. The blade 18 shifts as shown in Figure 7.

A simplified form of the invention is shown in Figure 8, and in cross-section in Figure SA, wherein a pair of parallel bands 50 are fitted around the polygonal ring 29. If one of the rails 29 should break, as indicated by crack 53, the band 50 surrounding that rail adopts much of the hoop stress formerly borne by the rail, thereby preventing the broken rail from attaining a large distortion, indicated by phantom rail 29PH in Figure 9. That is, the band- 50 in Figure 10 prevents the ring 22P from distorting to position 22PH because of break 31. The large distortion, if attained, could induce a damaging torsion in the intact rail 291 in Figure 6.

Another form of the invention is shown in Figures 11 and 11A, wherein a pair of annular channels 56 are machined into the polygonal ring 22P. In Figure 11, the bands 50 discussed in the paragraph above lie within the channels 56. The positioning of the bands within the channels serves to assist in manufacturing the bands, as will now be explained.

The bands 50 can be constructed of metallic foil, such as a foil of titanium 17. The foil 65 in Figure 12 is pre-stressed by winding it around the ring, within the channel 56 (not shown in Figure 12), under tension: the band 50 comprises a pre-stressed winding.

Arrow 58 indicates rotation of the ring 22P and arrow indicates tension applied to the foil. The tension is preferably 3,000 to 5.000 pounds per square inch.

13-DV-9575 The foil 65 is about 0.olo inches (ie lo mils) thick, and about 3/4 inch wide(dimension LL, later explained, in Figure 11A.) The layers of foil are bonded together with an epoxy adhesive, such as that sold by DuPont, located in Wilmington, Delaware, as product number NR150-256X. The foil 65 is wrapped until the desired number of layers of foil 65 in Figure 13 is attained, which is preferably 50 layers. Accordingly, the band 50 has a cross-sectional area of 1.5 square inches.

Since Titanium 17 has a failure strength of 150,000 pounds per square inch, the band 50 will have a failure strength of 225, 000 pounds.

one reason for pre-stressing the band 50 is that when the hoop stress of the rail 29B in Figure 6 becomes acquired by the band upon breakage of rail 29B, the added stress on the band will cause it to stretch. in the absence of pre-stressing, the stretch can allow the broken rail to move radially outward to phantom position 29PH in Figure 9. This movement reduces the dynamic balance of the system, as stated above. Further, the greater is the outward excursion 49 in Figure 6 of the broken rail 29B, the greater is the torsion on the intact rail 291. Pre-stressing the band 50 in Figures 11 and 18 reduces the stretch occurring in the band after a rail failure and thus reduces torsional load upon the intact rail 291.

Another form of the invention is shown in Figure 14, which is a crosssectional view of part of Figure 4A, taken along lines 14-14. Rails 29 are shown in Figure 14. The invention includes a pair of catchers 70 which act as hooks and catch a flange 73 (built into the polygonal ring) when a rail 29 breaks. That is.

catcher 70 engages the flange 73 upon rail breakage, and limits the outward travel (ie, in the direction of arrow 115) of a rail 29 if breakage occurs. The catchers 70 are annular about, and fastened to, the turbine casing 24. Modifications can be made to the 1 -g- catcher system shown in Figure 14, as will now be 13-DV-9575 discussed in connectionwith Figure 15.

In that Figure, the radially outward force 77, which is applied by the flange 73 to the catcher 70, causes a moment to occur in the catcher, as indicated by arrow 80. one reason for the moment is that the point of contact 83 between the flange and the catcher is displaced from the point of attachment 86 of the catcher to the casing 24 by distance 89. The moment induces rotation of the catcher 70 into phantom position 70P, which can release the flange 73.

Several types of modification, shown in Figures 16 A-C, can prevent this release. For example, (1) buttresses 90 in Figure 16A can extend between the catchers 70 and the casing 24. (2) The catcher and the flange can be in the form of wedge-shaped claws 95 as shown in Figure 16B. When the claws engage upon rail failure, the wedge surfaces 98 tend to draw the catcher toward the flange, as indicated by arrows 100. (3) Either the catcher or the'flange can contain a tongue, or hook, 105, shown on the catcher 70 in Figure 16 C, which engages a groove 107 upon rail failure.

Several important features of the described embodiments of the invention are the.following:

1. As discussed above, the bands 50 in Figures 8 and 11 are pre-stressed in order to limit the size 49 of the deformation in Figure 6 of the broken rail 29B.

However, deformation should not be completely eliminated. Some deformation is desirable in order to intentionally throw the rotating propeller system off balance in order to create a vibration which will draw the attention of the pilot to the engine. A deformation indicated by distance 49 in Figure 6 of 0.050 inches, or less, should be allowed.

2. Similarly, a space 110 in Figure 14 exists between catcher 70 and flange 73. The space 110 allows the rail 29 which breaks, together with the propeller 13-DV-9575 blades near it, to move radially outward, in the direction of arrow 115 and to introduce imbalance into the system, as in the paragraph above.

3. The pair of catchers 70 can be viewed as defining a channel within which the rails 29 are held captive. The channel is annular and generally c-shaped in cross-section, as indicated by dotted C 300 in Figure 14.

4. The discussion above stated that the band 50 should be wound into a channel 56 in Figures 11 and 11A which has been cut into the ring 22P. One reason for doing this is that the walls 120 of the channel in Figure 17 serve to keep the layers of foil aligned vertically, and prevents them from becoming misaligned during construction, as shown in Figure 18.

However, forming a channel 56 in the hub section 22B in Figure 11 involves removal of material from the hub, thus weakening it. This weakening is undesirable because the hub carries the centrifugal load of the propeller, which can be about 80,000 pounds per blade, as discussed earlier. The centrifugal load, together with the aerodynamic load of the propeller blades, cause a complex, non-uniform, stress distribution within the hub.

As an oversimplified example of the effects of this stress, the propeller blade can be viewed as applying two point loads as indicated by arrows 130 in Figure 19. These point loads are resisted by the tensile forces applied-by the rails, as indicated by arrows 133. one can see that the hub 22B tends to bend into phantom shape 136 under these loads. Removing material from the hub, as occurs when the channel 56 in Figure 11 is cut, reduces the stiffness of the hub and worsens the bending shown in Figure 19. At least two solutions exist to this problem.

A first solution involves cutting the channel 56 such that the material left beneath (ie, radially 13-DV-9575 inward of) the channel, in rectangle 125 in Figure IIA, has an aspect ratio (ie', TT/LL) equal to the aspect ratio of of the rail itself (ie, T/L). The aspect ratio, in the case of beams of rectangular cross-section, indicates the moment of inertia of the beam, and thus gives an indication of the bending-versus-shear loads within the respective rectangles. One wishes to keep the relative bending/shear ratio the same in both rectangles, even though the total load-bearing capability of the rail having a channel will be less than that of the rail without a channel.

Restated, even though total bending and total shear within the smaller rectangle 125, per unit cross-section, will be greater than the total bending and total shear, per unit cross-section, within the larger rectangle of the rail 29 itself, the ratio in both rectangles should be the same.

A second solution involves either the elimination or reduction in depth of the channel 56 in the hubs. As stated above, the channels serve to facilitate stacking of the foil strips during construction. The absence of a channel 56 in the hubs can be accommodated by the use of temporary jigs 130, such as shown in Figure 20, which are clamped to the ring by clamp 135 duringband construction. The jigs provide, temporarily, the function of the channel walls 120 in Figure 17 for aligning the foil layers 65. One form of this second solution is shown in Figure 30 20, wherein the band 50 is located within channel 56 in the rails 29, and, in contrast, atop the hub 22B, which lacks a channel. The band 50, after construction, occupies the dashed surface 140. 5. The use of laminated foil bands has been discussed above. Alternately, metal discs 155 can be pressed into annular grooves 157 cut into the face of a rail 29 as shown in Figure 22.

13-DV-9575 In either case of the metal discs 155 of Figure 22, or laminated foil bands 50'of Figure 18, covers 160 and in Figures 17 and 22, respectively, can be used to restrain the discs or band.

6. The polygonal ring 22P in Figure 4A is preferably constructed of titanium, as are the bands 50 in Figure 8 and the discs 155 of Figure 22. Accordingly, the thermal expansion of the two components will be almost identical, which is desirable. If there is a differential in thermal expansion, one component will slide along the other during temperature changes and cause friction and wear.

7. As discussed above, the bands 50 in Figure 17 are pre-stressed. Consequently, they compress the bottom 170 of the channel 56. When a hub section deforms under centrifugal load, as described in connection with Figure 19, the band 50 will slip with respect to the channel 56. An exaggerated example of why slip occurs during deformation is shown in Figure 23.

If two pieces 183 and 185 of flat material are glued together along a seam 180 and then bent, the bottom piece 183 will buckle as shown, while the top piece 185 will stretch. A shear load exists at the seam 180.

The seam is analogous to the interface between the band 50 and the channel bottom 170 in Figure 18.

In order to reduce wear caused by the slippage, a lubricant is introduced into the channel, such as by coating the channel with a solid bearing surface of poly-tetrafluoroethylene, which can be purchased from the DuPont Company, under the name of Teflon(P-Tfl), Slip is not so great a problem within the channel 56 located in the rails 29, because the rails are predominantly loaded in tension, and do not bend significantly.

8. The end of the outer layer 195 of the foil winding in Figure 17 is tapered as shown in Figure 24 z 1 -13- 13-DV-9575 over the final few (ie, Aess than six) inches, indicated by dimension 201, in order to attain a better stress distribution within the foil. Such tapering is also desirable at the initial few inches of the 5 winding.

9. The use of multiple elements in the bands (eg, the. foil layers 65 in Figure 17. and the titanium discs 155 in Figure 21) provide redundant load-carrying capability when a breakage occurs. That is. if the bands were instead solid, a single crack can sever the entire band. However, in the case of a layered band, a single crack can sever only one layer.

Viewed another way, the invention reduces the danger which a single crack poses. With the unprotected ring of Figure 4A, a single crack can propagate through and break a rail, thereby causing unwrapping of the ring. However, with multiple- element bands, a single crack cannot cause unwrapping.

10. The catchers 70 in Figure have been described as annular. However, they need not be continuous, but can be segmented, as shown in Figure 25, which shows only one set of catcher segments 70A.

11. Bands 50 in Figure 8 and discs 155 in Figure 22 can be viewed as hoops or rings which act in redundance to polygonal ring 22P in Figure 4A. If the polygonal ring 22P should break, bands 50 and discs 155 provide a back-up function.

12. The polygonal ring 22P has been described as surrounding a rotor in the form of a turbine, which supplies motive power to the propeller blades 18, as shown in Figures 2, 3, and 4. However, such is not strictly necessary. The ring 22P can instead surround a gear transmission 305 as shown in Figure 27. A turbine 307 is driven by the hot gas stream 15 of Figure 2, but rotates at such a high speed and low torque, that the transmission 305 is required in order to reduce the speed and increase. the torque as required f -14- 13-DV-9575 to drive the propellers blades 18.

is Moreover, the invention need not be used in an engine of the dual Unducted Fan type. It can be used with a single fan or propeller, which may be ducted or unducted.

13. The preceding discussion has been made in the context that the bands 50 in Figure 8 back up the polygonal ring 29P in case of ring breakage. In another form of the invention, the hoop stress of the ring 22P is shared during normal operation by both the bands 50 and the rails 29 in Figure 8. However, each is constructed with sufficient strength that each alone can carry the load of the blades. Consequently, each backs up the other: if a band breaks, a rail backs it up, while if a rail breaks, a band backs it up.

14. In the situation where the bands 50 are preloaded, the bands 50 and the ring 22P share the hoop stress during operation. Thus, the hoop stress borne by the ring is reduced as compared with that borne by a ring having no band 50. If a ring 22P fails, the hoop stress in the pre-loaded band increases. This increase can still be viewed as adoption of hoop stress by the band 50.

Numerous substitutions and modifications can be undertaken without departing from the true scope of the invention.

4 -is-

Claims (11)

CLAIMS:

1. An aircraft propulsion system comprising:

rotor; ring surrounding said rotor for carrying a plurality of propeller blades; and apparatus for preventing centrifugal load from causing detachment of the ring from the rotor when the ring fails.

2. The apparatus of Claim 1, in which said apparatus comprises:

a band surrounding the ring for adopting at least part of the hoop stress when a failure occurs in the ring.

3. The apparatus of Claim 2, in which said apparatus comprises:

an annular channel fastened to the rotor within which the ring is captive for preventing escape of the ring upon failure of the ring.

4. The apparatus of Claim 2, in which said apparatus comprises:

a plurality of annular channel segments fastened to the rotor within which the ring is captive for preventing escape of the ring upon failure of the ring.

5. The apparatus of Claim 1, in which said apparatus comprises:

a band disposed ' about said ring for adopting centrifugal load when failure occurs in the ring.

6. The apparatus of Claim 1, in which said apparatus comprises:

a second ring disposed circumferentially about said ring for carrying a plurality of propeller blades for adopting centrifugal load when failure occurs in the ring for carrying propeller blades.

7. The apparatus of Claim 1, in which said apparatus comprises:

first and second generally parallel bands surrounding said ring for adopting at least part of the centrifugal load when a failure occurs in the ring.

8. The apparatus of Claim 2, in which said apparatus comprises:

a catcher system for preventing separation of the ring from the rotor when a failure occurs in the ring, and including a plurality of hooks upon the rotor for catching the ring when failure occurs.

9. The apparatus of Claim 2, in which said apparatus comprises:

an annular hook (105) fastened to the rotor; and an annular groove (107) fastened to the ring which engages part of the annular hook when a failure in the ring occurs.

10. The apparatus of Claim 2, in which said apparatus comprises:

flange of the ring; and hook on the rotor for catching the flange when a failure occurs in the ring.

n

11. An aircraft propulsion system in which a blade carrying rotor ring is provided with ring failure protection substantially in accordance with any of the alternative modes of such protection hereinbefore described with reference to Figures 8-25 of the accompanying drawings.

1 PubUshed 1990atThe Patent Otrice,State House.6671 High Holborn. LondonWC1R4TP.PurLher copies maybe obtained from The Patent Office. Wes Branch. St Mary Cray. Orpngton. Rent BR5 3RD. Printed by Multiplex techniques ltd. St Mary Cray. Kent, Con. V87