CA1165299A - Reduced stress aircraft propeller blade root structure - Google Patents
Reduced stress aircraft propeller blade root structureInfo
- Publication number
- CA1165299A CA1165299A CA000390158A CA390158A CA1165299A CA 1165299 A CA1165299 A CA 1165299A CA 000390158 A CA000390158 A CA 000390158A CA 390158 A CA390158 A CA 390158A CA 1165299 A CA1165299 A CA 1165299A
- Authority
- CA
- Canada
- Prior art keywords
- shell
- spar
- collar
- root
- closure member
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000000945 filler Substances 0.000 claims description 6
- 239000000463 material Substances 0.000 claims description 4
- 238000012423 maintenance Methods 0.000 claims description 3
- 239000003733 fiber-reinforced composite Substances 0.000 claims description 2
- 239000011257 shell material Substances 0.000 description 74
- 239000006260 foam Substances 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 4
- JOYRKODLDBILNP-UHFFFAOYSA-N Ethyl urethane Chemical compound CCOC(N)=O JOYRKODLDBILNP-UHFFFAOYSA-N 0.000 description 3
- 239000002131 composite material Substances 0.000 description 3
- 239000004744 fabric Substances 0.000 description 3
- 238000010276 construction Methods 0.000 description 2
- 238000005520 cutting process Methods 0.000 description 2
- 239000011159 matrix material Substances 0.000 description 2
- 230000002787 reinforcement Effects 0.000 description 2
- 238000007789 sealing Methods 0.000 description 2
- 239000004593 Epoxy Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 239000003365 glass fiber Substances 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 238000004321 preservation Methods 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 239000013585 weight reducing agent Substances 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64C—AEROPLANES; HELICOPTERS
- B64C11/00—Propellers, e.g. of ducted type; Features common to propellers and rotors for rotorcraft
- B64C11/16—Blades
- B64C11/20—Constructional features
Landscapes
- Engineering & Computer Science (AREA)
- Aviation & Aerospace Engineering (AREA)
- Structures Of Non-Positive Displacement Pumps (AREA)
- Toys (AREA)
Abstract
Abstract of the Disclosure A propeller blade of the type having an airfoil shell bonded to a spar received within the interior of the shell is provided with a shell closure member which covers the root end of the shell and includes an opening therein which receives the spar. The closure member enhances the structural integrity of the shell, redistri-buting and minimizing stresses in the shell root and includes a collar upstanding therefrom, the spar being received through the collar and bonded to the inner surface thereof, thereby increasing the area of the shell-to-spar bond for stress reduction therein.
Description
~L~ti5~3~or3 This invention relates in general to propellers such as aircraft propellers and specifically to such propellers comprising an airfoil shaped shell fixed to and supported by an elongate structural spar received longitudinally within the interior of the shell.
For purposes of weight minimization, various modern aircraft propellers comprise a lightweight shell filled with a foam such as urethane foam for maintenance of the shape of the shell under operating conditions, and an elongate spar longitudinally received within the shell and attached thereto substantially along the entire length of the shell. For further enhancement of weight reduction, the shell is often formed from a light-weight composite such as an epoxy matrix provided with a plurality of glass fiber reinforcements disposed there-within.
Operation and testing of such propellers have shown that the most highly stressed area is the bond joint between the shell and spar at the root end of the blade. It was recognized in the prior art that blade root stresses could be redistributed from the spar-to-shell bond area to other, less highly stressed areas of the shell and reduced in magnitude by the removal of portions of the shell from that bond area adjacent the bond area edges. However, the criticality of precisely locating the removed shell portions with respect to the bond area, demands that such shell material removal be carried out subsequent to the bonding of the shell to the spar and therefore, to avoid damage to the shell, spar or foam filler, the removal of the shell material is carried out predominantly by hand, involving various hand scribing, cutting, grinding and sanding operations which are not only tedious for the operator but contri-bute substantially to the cost of the blade Such a propeller shell structure is commonly known as a Biot shell structure after the originator thereof. Once the shell material is removed, to maintain the con-`~ ~
529'3 tinuity of the airfoil surface at the blade root, thevoids in the shell resulting from the removal of material therefrom are later filled, and a non-structural covering is applied to the shell root portion to seal the root end of the blade. Such filling and covering involves additional hand labor and therefore is also inimical to the economy of blade manufacture.
It is therefore a principal object of the present invention to provide a propeller root structure wherein stresses at the interconnection of the shell and spar are minimized.
It is a further object of the present invent-ion to provide such minimization of stresses at the interconriection of the shell and spar in an economical manner.
It is a further object of the present invention to provide such stress minimization without adversely affecting the airfoil shape or root end sealing of the blade.
In accordance with a particular embodiment of the invention there is provided a highly loaded aircraft propeller blade. The blade includes a fiber reinforced composite airfoil shaped ~hell and a spar received longitudinally within the shell and fixed thereto along substantially the sntire length of the spar. Filler material is disposed within the shell for maintenance of the shape thereof. The propeller blade is character-ized by a closure member being integral with, and enclosing a root end of the shell. The closure member includes a collar outstanding therefrom and integral~
therewith. The collar is attached to a root portion of the spar along substantially the entire inner surface of the collar. Preferably the closure member is provided with a collar portion upstanding therefrom in alignment 5;Z~3 with the closure member opening, the spar being bonded to the shell along the airfoil portion thereof and along the length of the sleeve inner surface. In the preferred embodiment, the shell, closure member and sleeve are integrally formed from a lightweight composite such as a matrix of epo~y resin having glass filament reinforcements disposed therewithin.
These and other objects will become more readily apparent from the following detailed description taken in connection with the appended claims and accom-panying drawings wherein:
Fig. 1 is a fragmentary, perspective view of a prior art, Biot-type shell closure propeller blade root structure, portions of the blade root being broken away to show details of construction; and Fig. 2 is a fragmentary, perspective view of the propeller blade root structure of the present invention, portions of the blade root being broken away to show details of construction.
Referring to Fig. 1, the root portion of a typical prior art, Biot-type shell closure propeller blade root i8 shown generally at 10 and comprises, an airfoil shaped shell 15 filled with a material such as urethane foam 20 to preserve the shell's shape during operation- The ghell ig carried by a 9tructural spar 25 which ig attached to the propeller's hub (not shown) by an elongate spar 25. The spar is received within the shell longitudinally thereof and is bonded thereto along the length of the spar, the bonded spar-to-shell jointg being opposite each other generally centrally to the interior of the shell camber and face. Analysis of such prior art blades has indicated that the areas of highest shell stress exist in the shell root at the edge of the bonded connection between the shell and the spar.
To reduce such blade stresses by rèdistributing the stresses to other less highly stressed portions of the , ,, ;
?PJ ~ ~ ~' ;h ,~
, . ~ ~ .
'` 11~5299 shell, as discussed hereinabovel it has been the practice to remove those highly stressed shell portions subsequent to the bon~ing of the shell and the spar.
As shown in Fig. 1, removal of the highly stressed shell root portions results in two recesses 30 and 35 in mirror-image relation to one another. The recesses are formed by hand by such hand processes as scribing, cutting, grinding, and sanding so as not to ; damage the spar and foam filler. Recesses 3~ and 35 are shown for a blade having a lightweight composite shell. Were the shell to be formed from metal, inner oblique surfaces 40 and 45 of recesses 30 and 35 would extend outwardly to the leading and trailing edges of the shell whereby the leading and trailing shell root portions would be removed entirely. To preserve the airfoil shape of the shell, once the shell material is removed, recesses 30 and 35 are filled with a filler which is contoured to provide a smooth continuation of the airfoil surface. The root of the blade is then covered with a fabric covering and molded rubber boot shown together at 50 to seal the shell and protect the edge of the shell from damage due to, for example, handling and/or impact with foreign objects.
It will be appreciated that the manufacture of such a prior art Biot-type shell closure propeller blade, involving extensive handwork is therefore, expensive and time consuming. To reduce the amount of time and handwork, and therefore expense, in manufacturing a shell type propeller blade, and to enhance the reduction of shell root stresses, such a blade may be manufactured in-accord-ance with the present invention by providing the propeller shell with a root and closure member having an opening therein which receives the ~par which is bonded to the inner surface of the opening for enhanced strength and 8tress reduction. Referring to Fig. 2, the propeller blade of the present invention is shown generally at 100 and as prior art blade 10, includes an airfoil shaped , . ..
.
ilf~;52 shell 115 filled with a filler such as urethane foam 120 for preservation of the shell's shape under operating conditions. Likewise, the blade is provided with a structural spar 25 received longitudinally within the shell and konded thereto along the length of the spar. However, unlike the prior art Biot-type shell closure blade wherein the shell is closed by a fabric covering and rubber boot after removal of the highly stressed shell material, the shell of the present invention is formed with closure member 130 integral with the shell for sealing the root end of the shell. The closure member also enhances the struc-tural integrity by integrally connecting the camber and face of the shell thereby reducing the stresses in those shell portions at the root thereof. Closure member 130 is provided with an opening 135 therein, which receives the spar therethrough, the spar being bonded to the closure member about the inner surface of the opening.
To increase the bonding area of the highly stressed shell-spar interconnection to lower stresses at that interconnection, closure member 130 is provided with a collar 140 upstanding from the closure member in align-ment with opening 135. In the preferred embodiment, the height of the collar is approximately 0.3-0.5 times the blade thickness at the collar center although it will be understood that the invention is not so limited to such relative proportions.
It will be appreciated that enclosing the root end of shell 115 not only enhances the stress distribution within the shell but eliminates the necessity of sub-stantial amounts of handwork associated with the manu-facture of prior art Biot-type shell closure propeller blades. Thus, where in the Biot-type shell closure blade, recesses 30 and 35 were required to be formed by hand, in the present invention, the shell with closure member 130 and, if desired, collar 140 are integrally molded in one molding operation about the spar 125 thereby requir-., ~ i.~ ,., i5Z99 - 6 - ;
ing no removal of shell material by hand. Moreover, it will be recognized that closure member 130 provides an effective seal for the root end of the shell whereby the fabric covering and rubber boot 50 are no longer required. The collar substantially increases the area of bonding between the shell and spar thereby further contributing to the reduction of stresses in the blade root portion.
Although this invention has been shown and described with respect to a detailed embodiment thereof, - it will be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention. Thus, for example, it will be under-stood that the invention herein is not limited to blades employing spars extending the entire length of the blade, but rather encompasses blades employing spars extending only partially into the shell interior.
, ~ " ....
. .
. ,
For purposes of weight minimization, various modern aircraft propellers comprise a lightweight shell filled with a foam such as urethane foam for maintenance of the shape of the shell under operating conditions, and an elongate spar longitudinally received within the shell and attached thereto substantially along the entire length of the shell. For further enhancement of weight reduction, the shell is often formed from a light-weight composite such as an epoxy matrix provided with a plurality of glass fiber reinforcements disposed there-within.
Operation and testing of such propellers have shown that the most highly stressed area is the bond joint between the shell and spar at the root end of the blade. It was recognized in the prior art that blade root stresses could be redistributed from the spar-to-shell bond area to other, less highly stressed areas of the shell and reduced in magnitude by the removal of portions of the shell from that bond area adjacent the bond area edges. However, the criticality of precisely locating the removed shell portions with respect to the bond area, demands that such shell material removal be carried out subsequent to the bonding of the shell to the spar and therefore, to avoid damage to the shell, spar or foam filler, the removal of the shell material is carried out predominantly by hand, involving various hand scribing, cutting, grinding and sanding operations which are not only tedious for the operator but contri-bute substantially to the cost of the blade Such a propeller shell structure is commonly known as a Biot shell structure after the originator thereof. Once the shell material is removed, to maintain the con-`~ ~
529'3 tinuity of the airfoil surface at the blade root, thevoids in the shell resulting from the removal of material therefrom are later filled, and a non-structural covering is applied to the shell root portion to seal the root end of the blade. Such filling and covering involves additional hand labor and therefore is also inimical to the economy of blade manufacture.
It is therefore a principal object of the present invention to provide a propeller root structure wherein stresses at the interconnection of the shell and spar are minimized.
It is a further object of the present invent-ion to provide such minimization of stresses at the interconriection of the shell and spar in an economical manner.
It is a further object of the present invention to provide such stress minimization without adversely affecting the airfoil shape or root end sealing of the blade.
In accordance with a particular embodiment of the invention there is provided a highly loaded aircraft propeller blade. The blade includes a fiber reinforced composite airfoil shaped ~hell and a spar received longitudinally within the shell and fixed thereto along substantially the sntire length of the spar. Filler material is disposed within the shell for maintenance of the shape thereof. The propeller blade is character-ized by a closure member being integral with, and enclosing a root end of the shell. The closure member includes a collar outstanding therefrom and integral~
therewith. The collar is attached to a root portion of the spar along substantially the entire inner surface of the collar. Preferably the closure member is provided with a collar portion upstanding therefrom in alignment 5;Z~3 with the closure member opening, the spar being bonded to the shell along the airfoil portion thereof and along the length of the sleeve inner surface. In the preferred embodiment, the shell, closure member and sleeve are integrally formed from a lightweight composite such as a matrix of epo~y resin having glass filament reinforcements disposed therewithin.
These and other objects will become more readily apparent from the following detailed description taken in connection with the appended claims and accom-panying drawings wherein:
Fig. 1 is a fragmentary, perspective view of a prior art, Biot-type shell closure propeller blade root structure, portions of the blade root being broken away to show details of construction; and Fig. 2 is a fragmentary, perspective view of the propeller blade root structure of the present invention, portions of the blade root being broken away to show details of construction.
Referring to Fig. 1, the root portion of a typical prior art, Biot-type shell closure propeller blade root i8 shown generally at 10 and comprises, an airfoil shaped shell 15 filled with a material such as urethane foam 20 to preserve the shell's shape during operation- The ghell ig carried by a 9tructural spar 25 which ig attached to the propeller's hub (not shown) by an elongate spar 25. The spar is received within the shell longitudinally thereof and is bonded thereto along the length of the spar, the bonded spar-to-shell jointg being opposite each other generally centrally to the interior of the shell camber and face. Analysis of such prior art blades has indicated that the areas of highest shell stress exist in the shell root at the edge of the bonded connection between the shell and the spar.
To reduce such blade stresses by rèdistributing the stresses to other less highly stressed portions of the , ,, ;
?PJ ~ ~ ~' ;h ,~
, . ~ ~ .
'` 11~5299 shell, as discussed hereinabovel it has been the practice to remove those highly stressed shell portions subsequent to the bon~ing of the shell and the spar.
As shown in Fig. 1, removal of the highly stressed shell root portions results in two recesses 30 and 35 in mirror-image relation to one another. The recesses are formed by hand by such hand processes as scribing, cutting, grinding, and sanding so as not to ; damage the spar and foam filler. Recesses 3~ and 35 are shown for a blade having a lightweight composite shell. Were the shell to be formed from metal, inner oblique surfaces 40 and 45 of recesses 30 and 35 would extend outwardly to the leading and trailing edges of the shell whereby the leading and trailing shell root portions would be removed entirely. To preserve the airfoil shape of the shell, once the shell material is removed, recesses 30 and 35 are filled with a filler which is contoured to provide a smooth continuation of the airfoil surface. The root of the blade is then covered with a fabric covering and molded rubber boot shown together at 50 to seal the shell and protect the edge of the shell from damage due to, for example, handling and/or impact with foreign objects.
It will be appreciated that the manufacture of such a prior art Biot-type shell closure propeller blade, involving extensive handwork is therefore, expensive and time consuming. To reduce the amount of time and handwork, and therefore expense, in manufacturing a shell type propeller blade, and to enhance the reduction of shell root stresses, such a blade may be manufactured in-accord-ance with the present invention by providing the propeller shell with a root and closure member having an opening therein which receives the ~par which is bonded to the inner surface of the opening for enhanced strength and 8tress reduction. Referring to Fig. 2, the propeller blade of the present invention is shown generally at 100 and as prior art blade 10, includes an airfoil shaped , . ..
.
ilf~;52 shell 115 filled with a filler such as urethane foam 120 for preservation of the shell's shape under operating conditions. Likewise, the blade is provided with a structural spar 25 received longitudinally within the shell and konded thereto along the length of the spar. However, unlike the prior art Biot-type shell closure blade wherein the shell is closed by a fabric covering and rubber boot after removal of the highly stressed shell material, the shell of the present invention is formed with closure member 130 integral with the shell for sealing the root end of the shell. The closure member also enhances the struc-tural integrity by integrally connecting the camber and face of the shell thereby reducing the stresses in those shell portions at the root thereof. Closure member 130 is provided with an opening 135 therein, which receives the spar therethrough, the spar being bonded to the closure member about the inner surface of the opening.
To increase the bonding area of the highly stressed shell-spar interconnection to lower stresses at that interconnection, closure member 130 is provided with a collar 140 upstanding from the closure member in align-ment with opening 135. In the preferred embodiment, the height of the collar is approximately 0.3-0.5 times the blade thickness at the collar center although it will be understood that the invention is not so limited to such relative proportions.
It will be appreciated that enclosing the root end of shell 115 not only enhances the stress distribution within the shell but eliminates the necessity of sub-stantial amounts of handwork associated with the manu-facture of prior art Biot-type shell closure propeller blades. Thus, where in the Biot-type shell closure blade, recesses 30 and 35 were required to be formed by hand, in the present invention, the shell with closure member 130 and, if desired, collar 140 are integrally molded in one molding operation about the spar 125 thereby requir-., ~ i.~ ,., i5Z99 - 6 - ;
ing no removal of shell material by hand. Moreover, it will be recognized that closure member 130 provides an effective seal for the root end of the shell whereby the fabric covering and rubber boot 50 are no longer required. The collar substantially increases the area of bonding between the shell and spar thereby further contributing to the reduction of stresses in the blade root portion.
Although this invention has been shown and described with respect to a detailed embodiment thereof, - it will be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention. Thus, for example, it will be under-stood that the invention herein is not limited to blades employing spars extending the entire length of the blade, but rather encompasses blades employing spars extending only partially into the shell interior.
, ~ " ....
. .
. ,
Claims
1. A highly loaded aircraft propeller blade comprising:
a fiber reinforced composite airfoil shaped shell, a spar received longitudinally within said shell and fixed thereto along substantially the entire length of said spar;
filler material disposed within said shell for maintenance of the shape thereof;
said propeller blade being characterized by a closure member being integral with, and enclosing a root end of said shell, said closure member including a collar outstanding therefrom and integral therewith, said collar being attached to a root portion of said spar along sub-stantially the entire inner surface of said collar.
a fiber reinforced composite airfoil shaped shell, a spar received longitudinally within said shell and fixed thereto along substantially the entire length of said spar;
filler material disposed within said shell for maintenance of the shape thereof;
said propeller blade being characterized by a closure member being integral with, and enclosing a root end of said shell, said closure member including a collar outstanding therefrom and integral therewith, said collar being attached to a root portion of said spar along sub-stantially the entire inner surface of said collar.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US20993980A | 1980-11-24 | 1980-11-24 | |
| US209,939 | 1980-11-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1165299A true CA1165299A (en) | 1984-04-10 |
Family
ID=22780956
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000390158A Expired CA1165299A (en) | 1980-11-24 | 1981-11-16 | Reduced stress aircraft propeller blade root structure |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS57114795A (en) |
| BR (1) | BR8107571A (en) |
| CA (1) | CA1165299A (en) |
| DE (1) | DE3146048A1 (en) |
| FR (1) | FR2494663B1 (en) |
| GB (1) | GB2087981B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2279114A (en) * | 1993-06-15 | 1994-12-21 | Nuaire Ltd | Fan impeller blade |
| US5660527A (en) * | 1995-10-05 | 1997-08-26 | The Wind Turbine Company | Wind turbine rotor blade root end |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2623599A (en) * | 1947-11-26 | 1952-12-30 | United Aircraft Corp | Propeller blade stress distributing means |
| GB659344A (en) * | 1948-05-04 | 1951-10-24 | United Aircraft Corp | Improvements in or relating to hollow aircraft propeller blades |
| US3161238A (en) * | 1962-07-05 | 1964-12-15 | Howard P Key | Helicopter rotor blade |
| US4169749A (en) * | 1977-09-21 | 1979-10-02 | The United States Of America As Represented By The Secretary Of The Navy | Method of making a hollow airfoil |
-
1981
- 1981-11-16 CA CA000390158A patent/CA1165299A/en not_active Expired
- 1981-11-20 BR BR8107571A patent/BR8107571A/en not_active IP Right Cessation
- 1981-11-20 DE DE19813146048 patent/DE3146048A1/en not_active Ceased
- 1981-11-20 GB GB8135116A patent/GB2087981B/en not_active Expired
- 1981-11-24 JP JP18904681A patent/JPS57114795A/en active Pending
- 1981-11-24 FR FR8121938A patent/FR2494663B1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS57114795A (en) | 1982-07-16 |
| FR2494663B1 (en) | 1985-10-11 |
| DE3146048A1 (en) | 1982-08-19 |
| BR8107571A (en) | 1982-08-17 |
| FR2494663A1 (en) | 1982-05-28 |
| GB2087981B (en) | 1984-02-08 |
| GB2087981A (en) | 1982-06-03 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4213739A (en) | Helicopter rotor blade | |
| US3799701A (en) | Composite fan blade and method of construction | |
| US4806077A (en) | Composite material blade with twin longeron and twin box structure having laminated honeycomb sandwich coverings and a method of manufacturing same | |
| US5885059A (en) | Composite tip cap assembly for a helicopter main rotor blade | |
| US5392514A (en) | Method of manufacturing a composite blade with a reinforced leading edge | |
| US6000911A (en) | Blade with swept-back tip for the rotary wings of an aircraft | |
| US6976829B2 (en) | Rotor blade tip section | |
| US4696623A (en) | Helicopter rotor blade made from a multispar composite material with torsion compartments and a process for manufacturing same | |
| US5346367A (en) | Advanced composite rotor blade | |
| US7758312B2 (en) | Main rotor blade with integral tip section | |
| US6132857A (en) | Hybrid component with high strength/mass ratio and method of manufacturing said component | |
| KR100311562B1 (en) | Fiber reinforced composite spar for a rotary wing aircraft and method of manufacture thereof | |
| US5269658A (en) | Composite blade with partial length spar | |
| US4083656A (en) | Composite rotor blade | |
| US3237697A (en) | Helicopter rotor blade | |
| US5320494A (en) | Helicopter rotor blade having a replaceable anhedral tip | |
| US20030129061A1 (en) | Multi-component hybrid turbine blade | |
| US5193982A (en) | Separate inter-blade platform for a bladed rotor disk | |
| US2954828A (en) | Laminated airfoil structure | |
| US5421704A (en) | Inter-blade platform for a bladed disc of a turbomachine rotor | |
| US5462409A (en) | Leading edge weight retention assembly for a helicopter rotor | |
| CA1165299A (en) | Reduced stress aircraft propeller blade root structure | |
| CA1101817A (en) | Roll formed blade structure | |
| US2574651A (en) | Sustaining rotor blade | |
| US11371357B2 (en) | Fabric comprising aramid fibres for protecting a blade against impacts |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |