(11)EP 2 573 321 B1


(45)Mention of the grant of the patent:
24.06.2020 Bulletin 2020/26

(21)Application number: 12185421.0

(22)Date of filing:  21.09.2012
(51)International Patent Classification (IPC): 
F01D 5/14(2006.01)





(84)Designated Contracting States:

(30)Priority: 23.09.2011 US 201113241868

(43)Date of publication of application:
27.03.2013 Bulletin 2013/13

(73)Proprietor: United Technologies Corporation
Farmington, CT 06032 (US)

  • McKaveney, Christopher S.
    East Hartford, CT Connecticut 06118 (US)
  • Murdock, James R.
    Tolland, CT Connecticut 06084 (US)

(74)Representative: Dehns 
St. Bride's House 10 Salisbury Square
London EC4Y 8JD
London EC4Y 8JD (GB)

(56)References cited: : 
EP-A1- 2 014 386
EP-A2- 0 926 312
EP-A1- 2 239 043
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).



    [0001] This application relates to a hollow fan blade for a gas turbine engine, wherein a unique rib geometry is utilized.

    [0002] Gas turbine engines may be provided with a fan for delivering air to a compressor section. From the compressor section, the air is compressed and delivered into a combustion section. The combustion section mixes fuel with the air and combusts the combination. Products of the combustion pass downstream over turbine rotors, which in turn are driven to rotate and rotate the compressor and fan.

    [0003] The fan may include a rotor having a plurality of blades.

    [0004] One type of fan blade is a hollow fan blade having a plurality of channels defined by intermediate ribs in a main fan blade body. An outer skin is attached over the main fan blade body to close off the cavities. The blades are subject to a number of challenges, including internal stresses that vary along a length of the fan blade.

    [0005] A prior art fan blade having the features of the preamble of claim 1 is disclosed in EP0926312 A2. A prior art method of manufacturing an aerofoil for a gas turbine engine is disclosed in EP2014386 A1. A further prior art fan blade is disclosed in EP2239083 A1.


    [0006] The present invention provides a fan blade, as recited in claim 1.


    [0007] The invention will be described with regard to the specific and drawings, the following of which is a brief description.

    Figure 1A shows a fan blade.

    Figure 1B shows another feature of the Figure 1A fan blade.

    Figure 2 is a cross-sectional view along line 2-2 as shown in Figure 1A.

    Figure 3 shows a main body of the Figure 1A fan blade.

    Figure 4 is a simplified view of one rib.

    Figure 5A is a first arrangement taken along line 5-5 of Figure 4.

    Figure 5B is a second arrangement taken along line 5-5 of Figure 4.

    Figure 5C is a third arrangement taken along line 5-5 of Figure 4.

    Figure 6A is a first embodiment rib break-edge.

    Figure 6B is a second embodiment rib break-edge.

    Figure 7 shows another area within the fan blade.

    Figure 8 shows a radially inner end of the channels.


    [0008] A fan blade 20 is illustrated in Figure 1A having an airfoil 18 extending radially outwardly from a dovetail 24. A leading edge 21 and a trailing edge 22 define the forward and rear limits of the airfoil 18.

    [0009] As shown in Figure 1B, a fan rotor 16 receives the dovetail 24 to mount the fan blade 20 with the airfoil 18 extending radially outwardly. As the rotor 16 is driven to rotate, it carries the fan blades 20 with it. There are higher stresses adjacent to the rotor 16, than occur radially outwardly of the rotor.

    [0010] Figure 2 shows a cross-section of the fan blade 20, at the airfoil 18. As shown, the leading edge 21 carries a cap 37 secured to a main body 28. A cover skin 32 closes off cavities or channels 30 in the main body 28. The main body 28, the cap 37 and the skin 32 may all be formed of various aluminum alloys. While aluminum alloys or aluminum may be utilized, other materials, such as titanium, titanium alloys, or other appropriate metals may be utilized.

    [0011] As shown, a plurality of ribs 26 separate channels 30 in the cross-section illustrated in Figure 2. These channels 30 are closed off by the skin 32.

    [0012] As shown, the channels 30 extend from an open end inwardly to a closed side. The open end is closed off by skin 32. It is within the scope of this invention, however, that the channel extends across the width of the main body 28, and there are two skins on opposed sides of the main body 28.

    [0013] In addition, the channels may be filled with lighter weight filler material to provide stiffness, as known.

    [0014] A contact area 132 at the forward face of the ribs 26 serves as a mount point for the skin 32, and receives an adhesive. Chamfers 38 are formed at the break-edges, or the edges of the ribs 26, and will be described in more detail below. As shown, the channels 30 have a side extent formed by a compound radius 34 and 36, again to be described in greater detail below.

    [0015] Figure 3 shows the main body 28. There are a plurality of channels 30 from the front or leading edge 21, to the back or trailing edge 22, and varying from the radially inner end toward the radially outer tip. As shown, some of the channels 30 extend generally radially upwardly. Other channels, such as channel 40, bend toward the leading edge 21. Other channels 41 simply extend generally from the middle of the main body 28 toward the leading edge 21.

    [0016] To reduce the weight, it is desirable to maximize the amount of channels and minimize the amount of rib. However, there is also a need for additional stiffness adjacent the radially inner edge 42, to provide greater durability, and minimize blade pull. Thus, the ribs 26 may be formed such that they tend to be thicker adjacent a radially inner edge 42, and become thinner when moving toward the radially outer portions 44.

    [0017] It is also desirable to form a blade which avoids certain operational modes across the engine operational range. Additional mass toward the tip or outer end of the blade raises challenges against tuning away from fundamental modes.

    [0018] As shown schematically in Figure 4, ribs 26 are thinner at radially outer end 44 than at the inner end 42. A thickness t1 at the radially inner end 42 is greater than the thickness t2 at the tip or radially outer end 44. In embodiments, a ratio of t1 to t2 may be between 1.1 and 8. As can be appreciated from Figure 3, the variation need not be linear as shown in Figure 4, and may be different across the several ribs.

    [0019] As shown in Figure 5A, a cross-section through the rib could be a trapezoid as shown in Figure 5A, wherein the bottom 50, which extends into the main body 28, is larger than the outer end 48 which attaches to the skin 32. Sides 46 are angled between the two ends 48 and 50.

    [0020] Figure 5B shows a rectangular cross-section for the rib 26 wherein the ends 52 and 54 are generally of the same thickness, and the sides 56 are generally perpendicular to those ends.

    [0021] Figure 5C shows yet another embodiment, wherein the ends 58 and 60 are of different thicknesses, and the sides 62 curve relative to each other along a particular radius.

    [0022] By modifying these several variables, a designer is able to tune or optimize the operation of the fan blade for its use in a gas turbine engine.

    [0023] Notably, as will be explained below, it is desirable that the upper end 48/52/58 actually has a more complex surface at its break-edges.

    [0024] Figure 6A shows the actual break-edge 38 on a rib 26. The contact area 132 which will actually contact the skin, and provide a surface for receiving adhesive and securing the skin should be maximized. On the other hand, there are stresses which are induced at the break-edges, and thus a chamfer 38 is formed in this embodiment.

    [0025] As shown in Figure 6A, the rib 26 has a nominal thickness t3 at the upper end, if not for the chamfers 38. Stated another way, t3 is the distance between sides 200 at the end of chamfers 38. The chamfers 38 extend for a thickness c measured in a plane perpendicular to the top edge 132.

    [0026] A ratio of c to t3 according to the invention is between 0.02 and 0.15. The use of the chamfer at the break-edge location reduces the stress. There would otherwise be stress concentrations at that area. On the other hand, by utilizing a chamfer within the disclosed range, the amount of surface area available to provide a good adhesion to the cover is still adequate.

    [0027] Figure 6B shows an embodiment of a rib 64, wherein the break-edges are provided along a radius r1. According to the invention, the ratio of r1 to t3 is between 0.02 and 0.15.

    [0028] Figure 7 shows the surfaces 34 and 36 as illustrated in Figure 2. The areas at that side of the channels 30 are prone to stress concentrations. A typical fillet, or single curve, may be considered for formation at that area to reduce stress. However, in the disclosed embodiment, a compound fillet having two curves 34 and 36 is utilized. Curve 34 is formed along a radius r2 while curve 36 is formed along a radius r3. A ratio of r3 to r2 is between 0.03 and 0.25. As is clear, r2 is greater than r3. More narrowly, it may be between 0.06 and 0.13. The use of the compound fillet provides a great reduction in stress concentration, which would otherwise be maximized at the general location of the curve 36.

    [0029] Finally Figure 8 shows a radially inner end, bottom or termination 100 of a channel 30. As shown, there is a compound curve or fillet including a bottom portion 104 formed at a radius r4 and a side portion 102 formed at a radius r5, which merges into the side of the ribs. As is clear, r5 is greater than r4. Again, this arrangement reduces a stress concentration at the corners which would otherwise be induced into the cavity terminations. In embodiments, a ratio of r4 to r5 is between .03 and .25.

    [0030] The compound fillets as disclosed in Figures 7 and 8 reduce stress concentrations with minimum weight increase. Further, the compound fillets may be provided with minimal additional cost, because multi-pass machining is not required. Instead, a cutter with a compound radius shape may be utilized.

    [0031] The fan blade as described above reduces stresses that are raised during operations when mounted in a gas turbine engine.

    [0032] Although embodiments have been disclosed, a worker of ordinary skill in the art would recognize the modifications which come within the scope of this Application. Thus, the following claims should be studied to determine the true scope and content.


    1. A fan blade (20) comprising a main body (28) extending between a leading edge (21) and a trailing edge (22), and having channels (30) formed into said main body (28) from at least one open side with a plurality of ribs (26) extending across the main body (28) intermediate the channels (30), with said fan blade (20) having a dovetail (24), and an airfoil (18) extending radially outwardly from said dovetail (24), said ribs (26) having a thickness defined as measured from said leading edge (21) toward said trailing edge (22);
    characterised in that:

    said ribs (26) have break-edges (38;66) at edges of said thickness, said break-edges (38) being formed to extend away from an outer face (132) at said open side,

    wherein said break-edges (38) are respectively formed by a chamfer, wherein a nominal thickness (t3) of the rib (26) may be defined as a thickness between sides (200) of the rib (26) beyond the chamfer (38), and the nominal thickness (c) of the chamfer (38) may be defined in a plane perpendicular to said outer face (132) of said rib (26), with a ratio of said nominal thickness (c) of the chamfer (38) to the nominal thickness (t3) of the rib (26) is between 0.02 and 0.15; or

    said break-edges (66) are curved, wherein a ratio of a radius (r1) of said curved break-edge (66) to a nominal thickness (t3) of the rib (26) measured between sides (200) of the rib (26) at locations beyond the curved break-edge (66) is between 0.02 and 0.15.

    2. The fan blade (20) as set forth in claim 1, wherein a cover (32) closes off said at least one open side, said cover (32) being attached to said ribs (26) at said outer face (132).
    3. The fan blade (20) as set forth in claim 1 or 2, wherein said at least one open side extends to a closed side within said main body (28).


    1. Gebläseschaufel (20), umfassend einen Hauptkörper (28), der sich zwischen einer Vorderkante (21) und einer Hinterkante (22) erstreckt und Kanäle (30) aufweist, die von mindestens einer offenen Seite mit einer Vielzahl von Rippen (26), die sich quer über den Hauptkörper (28) zwischen den Kanälen (30) erstrecken, im Hauptkörper (28) geformt sind, wobei die Gebläseschaufel (20) einen Schwalbenschwanz (24) aufweist und wobei sich ein Schaufelprofil (18) radial auswärts vom Schwalbenschwanz (24) erstreckt, wobei die Rippen (26) eine Dicke aufweisen, die als von der Vorderkante (21) in Richtung der Hinterkante (22) gemessen definiert wird;
    dadurch gekennzeichnet, dass:

    die Rippen (26) Bruchkanten (38; 66) an den Kanten der Dicke aufweisen, wobei die Bruchkanten (38) geformt sind, um sich von einer Außenfläche (132) an der offenen Seite weg zu erstrecken,

    wobei die Bruchkanten (38) jeweils durch eine Schrägfläche geformt sind, wobei eine Nenndicke (t3) der Rippe (26) als eine Dicke zwischen den Seiten (200) der Rippe (26) jenseits der Schrägfläche (38) definiert werden kann und die Nenndicke (c) der Schrägfläche (38) in einer Ebene senkrecht zur Außenfläche (132) der Rippe (26) definiert werden kann, wobei ein Verhältnis der Nenndicke (c) der Schrägfläche (38) zur Nenndicke (t3) der Rippe (26) zwischen 0,02 und 0,15 liegt; oder

    die Bruchkanten (66) gebogen sind, wobei ein Verhältnis eines Radius (r1) der gebogenen Bruchkante (66) zu einer Nenndicke (t3) der Rippe (26), die zwischen den Seiten (200) der Rippe (26) an Stellen jenseits der gebogenen Bruchkante (66) gemessen wird, zwischen 0,02 und 0,15 liegt.

    2. Gebläseschaufel (20) nach Anspruch 1, wobei eine Abdeckung (32) die mindestens eine offene Seite verschließt, wobei die Abdeckung (32) an den Rippen (26) an der Außenfläche (132) angebracht ist.
    3. Gebläseschaufel (20) nach Anspruch 1 oder 2, wobei sich die mindestens eine offene Seite zu einer geschlossenen Seite innerhalb des Hauptkörpers (28) hin erstreckt.


    1. Aube de soufflante (20) comprenant un corps principal (28) s'étendant entre un bord d'attaque (21) et un bord de fuite (22), et ayant des canaux (30) formés dans ledit corps principal (28) à partir d'au moins un côté ouvert avec une pluralité de nervures (26) s'étendant à travers le corps principal (28) entre les canaux (30), ladite aube de soufflante (20) ayant une queue d'aronde (24), et un profil aérodynamique (18) s'étendant radialement vers l'extérieur à partir de ladite queue d'aronde (24), lesdites nervures (26) ayant une épaisseur définie telle que mesurée à partir dudit bord d'attaque (21) vers ledit bord de fuite (22) ;
    caractérisée en ce que :

    lesdites nervures (26) ont des bords de rupture (38 ; 66) au niveau des bords de ladite épaisseur, lesdites bords de rupture (38) étant formés pour s'étendre à l'opposé d'une face extérieure (132) au niveau dudit côté ouvert,

    dans laquelle lesdits bords de rupture (38) sont respectivement formés par un chanfrein, dans laquelle une épaisseur nominale (t3) de la nervure (26) peut être définie comme une épaisseur entre les côtés (200) de la nervure (26) au-delà du chanfrein (38), et l'épaisseur nominale (c) du chanfrein (38) peut être définie dans un plan perpendiculaire à ladite face extérieure (132) de ladite nervure (26), un rapport de ladite épaisseur nominale (c) du chanfrein (38) à l'épaisseur nominale (t3) de la nervure (26) étant compris entre 0,02 et 0,15 ; ou

    lesdits bords de rupture (66) sont incurvés, dans laquelle un rapport d'un rayon (r1) dudit bord de rupture incurvé (66) à une épaisseur nominale (t3) de la nervure (26) mesurée entre les côtés (200) de la nervure (26) à des emplacements au-delà du bord de rupture incurvé (66) est compris entre 0,02 et 0,15.

    2. Aube de soufflante (20) selon la revendication 1, dans laquelle un couvercle (32) ferme ledit au moins un côté ouvert, ledit couvercle (32) étant fixé auxdites nervures (26) sur ladite face extérieure (132).
    3. Aube de soufflante (20) selon la revendication 1 ou 2, dans laquelle ledit au moins un côté ouvert s'étend jusqu'à un côté fermé à l'intérieur dudit corps principal (28).


    Cited references


    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description