Abstract:
Aircraft systems having baffle seals with low coefficients of friction and methods of assembling aircraft systems are disclosed herein. In one embodiment, an aircraft system includes: (a) an aircraft baffle; (b) an aircraft cowl separated from the aircraft baffle by a gap, the aircraft cowl having a contact surface; and (c) a flexible aircraft baffle seal extending from the aircraft baffle to the aircraft cowl to seal the gap, the aircraft baffle seal having a contact side for contacting the contact surface of the aircraft cowl, the contact side having a kinetic coefficient of friction that is not more than 0.4, the aircraft baffle seal comprising an elastomer sheet and a laminate, the laminate being the contact side.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation application claiming priority to U.S. patent application Ser. No. 11/361,734, filed Feb. 24, 2006, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Most modern aircraft with reciprocating engines employ a cooling system known as “pressure cooling”. Pressure cooling is accomplished by placing a cowling around an engine and then using a system of baffles and seals to induce airflow around the engine cylinders to achieve even cooling with minimum drag. Most pressure cooling systems are “down-draft” type systems where, in conjunction with the placement of the air inlet and outlet, the baffles and seals create a high pressure region above the engine and a corresponding low pressure region below the engine. The resulting pressure differential between the two regions produces a top-to-bottom airflow around the engine cylinders. 
         [0003]    The baffles are typically of aluminum sheet metal construction and attach to brackets on the engine. The baffles extend from the engine almost to the engine cowl, and there is normally a small gap (1 to 4 inches is common) between the baffle and the cowl to allow for engine vibration and movement. This gap is sealed by baffle seals. 
         [0004]    Baffle seals are typically made from a flexible material, such as neoprene or silicone rubber, and they are sometimes reinforced with fiberglass. The baffle seals are commonly stapled or riveted to the baffles and extend to the cowl to prevent air from by-passing the baffles. The baffle seals are typically wider than the gap they must seal, and the excess seal material bends forward such that the pressure differential between the high pressure and low pressure regions forces the baffle seal against an inner surface of the cowl (also referred to herein as “cowl contact surface”). 
         [0005]    Due to constant flexing, mishandling during cowl installation, and a harsh operating environment, baffle seals have a limited useful life and must be replaced as part of regular maintenance. There are currently three types of baffle seal material commonly used to replace baffle seals: 1) un-reinforced silicone rubber (e.g., Federal Specification ZZ-R-765 Class 2B Grade 60 Silicone); 2) fiberglass reinforced silicone rubber (e.g., AMS 3320 Glass Cloth Reinforced Silicone Sheet); 3) neoprene coated fiberglass (e.g., AMS 3783 Chloroprene Coated Glass Cloth, a.k.a., T8071). All three of these materials are available in bulk from many aircraft supply companies. Replacement seals ordered from aircraft manufacturers appear to be either AMS 3320 Glass Cloth Reinforced Silicone Sheet or AMS 3783 Chloroprene Coated Glass Cloth, depending on the manufacturer and the aircraft vintage. 
         [0006]    All three types of baffle seal material have a common shortcoming; they do not have a sufficiently low coefficient of friction. A low coefficient of friction is especially important, not just to extend the life of the baffle seals, but also to prevent damage to the cowl and attaching hardware. Friction between the baffle seal and the cowl contact surface transfers engine vibration to the cowl. This vibration locally erodes the cowl where the baffle seal contacts it and fatigues the cowl and all hardware attached to it, which eventually necessitates costly repairs. 
         [0007]    Using the ASTM D 1894-01 test method with an opposing surface of stainless steel with a #8 finish, a cross head speed of 6 inches per minute, and modified with 0.25 psi surface pressure instead of 0.07 psi to more accurately reflect the conditions under which the materials are used, we found AMS 3783 Chloroprene coated fiberglass to have a static coefficient of friction of 0.616 and a kinetic coefficient of friction of 0.495. We found ZZ-R-765 Class 2b Grade 60 Silicone to have a static coefficient of friction of 2.28 and a kinetic coefficient of friction of 3.02. 
         [0008]    Replacement baffle seals are commonly coated with a powder for shipping purposes, but this powder is quickly rubbed off, either before or during installation or when the baffle seal interacts with the cowl. This powder is not part of the baffle seals, and it offers no sustained reduction in the material&#39;s coefficient of friction. It should be understood that “baffle seal” and “sheet of material” as used herein do not include powders used topically for shipping or otherwise that do not provide more than a momentary reduction in coefficient of friction. 
       SUMMARY 
       [0009]    An aircraft system having a baffle seal that reduces the high baffle seal friction that is common in the prior art would reduce the amount and magnitude of repairs associated with high baffle seal friction. Accordingly, innovative aircraft systems and methods of assembling aircraft systems are disclosed herein. An aircraft system of one embodiment includes: (a) an aircraft baffle; (b) an aircraft cowl separated from the aircraft baffle by a gap, the aircraft cowl having a contact surface; and (c) a flexible aircraft baffle seal extending from the aircraft baffle to the aircraft cowl to seal the gap, the aircraft baffle seal having a contact side for contacting the contact surface of the aircraft cowl, the contact side having a kinetic coefficient of friction that is not more than 0.4, the aircraft baffle seal comprising an elastomer sheet and a laminate, the laminate being the contact side. 
         [0010]    In another embodiment, an aircraft system includes: (a) an aircraft baffle; (b) an aircraft cowl separated from the aircraft baffle by a gap, the aircraft cowl having a contact surface; and (c) an aircraft baffle seal extending from the aircraft baffle to the aircraft cowl to seal the gap, the aircraft baffle seal comprising a sheet of material having a flexible primary layer and a flexible contact layer presenting a contact side for contacting the contact surface of the cowl, the contact side having a kinetic coefficient of friction that is not more than 0.4. 
         [0011]    In yet another embodiment, a method of assembling an aircraft system includes the step of fastening a flexible baffle seal having a contact side with a kinetic coefficient of friction that is not more than 0.4 to an aircraft baffle such that the contact side contacts a contact surface of an aircraft cowl. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  shows an uninstalled baffle seal separated from a larger sheet of material in accordance with an illustrative embodiment of the invention. 
           [0013]      FIG. 2  shows the baffle seal of  FIG. 1  installed. 
           [0014]      FIG. 3  shows a side view of  FIG. 2 . 
           [0015]      FIG. 4  shows a side view of a baffle seal constructed from a sheet of material in accordance with an illustrative embodiment of the invention. 
           [0016]      FIG. 5  shows a side view of a baffle seal constructed from a sheet of material in accordance with an illustrative embodiment of the invention. 
           [0017]      FIG. 6  shows a side view of a baffle seal constructed from a sheet of material in accordance with an illustrative embodiment of the invention. 
           [0018]      FIG. 7  shows a side view of a baffle seal constructed from a sheet of material in accordance with an illustrative embodiment of the invention. 
           [0019]      FIG. 8  shows a side view of a baffle seal constructed from a sheet of material in accordance with an illustrative embodiment of the invention. 
           [0020]      FIG. 9  shows a side view of a baffle seal constructed from a sheet of material in accordance with an illustrative embodiment of the invention. 
           [0021]      FIG. 10  shows a side view of a baffle seal constructed from a sheet of material in accordance with an illustrative embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIG. 1  shows an uninstalled baffle seal  100  that has a low coefficient of friction. Baffle seal  100  is generally elongate and is dimensioned to seal a gap between an aircraft&#39;s baffle and cowl so that air does not escape between the baffle and the cowl. Baffle seal  100  may be manufactured having appropriate dimensions, or baffle seal  100  may be cut (or otherwise separated) from a larger sheet of material  10 . “Baffle seal” and “sheet of material” as used herein do not include powders used topically for shipping or otherwise that do not provide more than a momentary reduction in coefficient of friction. 
         [0023]      FIGS. 2 and 3  show the baffle seal  100  in an exemplary method of use—fastened to an aircraft&#39;s baffle  2  and pressed against a contact surface  4   a  of the aircraft&#39;s cowl  4  to keep air from escaping between baffle  2  and cowl  4 . Baffle  2  is attached to the aircraft&#39;s engine (e.g., by mounting brackets  6 ). Baffle seal  100  is shown fastened to baffle  2  by rivets  8 , though other fasteners (e.g., staples) may alternately or additionally be used. Baffle seal  100  has a contact side  100   a  that contacts the cowl contact surface  4   a , as shown in  FIG. 3 . Contact side  100   a  has a low coefficient of friction (i.e., not more than 0.4), and the low coefficient of friction reduces the transfer of engine vibration to cowl  4  and extends the life of baffle seal  100 , cowl  4 , and other attaching hardware. “Coefficient of friction” as used herein includes only kinetic coefficient of friction unless specifically noted otherwise. 
         [0024]      FIG. 4  shows a side view of a baffle seal  100 ( 1 ) constructed from a sheet of material  10 ( 1 ). Sheet  10 ( 1 ) comprises a flexible primary layer  12  and a flexible contact layer  14  that presents contact side  100   a . Flexible primary layer  12  includes an elastomer sheet  402  (e.g., a silicone sheet), and flexible contact layer  14  includes a thin laminate  404  at contact side  100   a . Thin laminate  404  has a low coefficient of friction (i.e., not more than 0.4), and may include, for example, polytetrafluoroethylene (PTFE), fluorinated ethylene propylene copolymer (FEP), a copolymer of ethylene and tetrafluoroethylene (ETFE), a proprietary blend of fluoropolymers and other high-performance resins (such as Teflon®-S), or a perfluoroalkoxy polymer resin (PFA) (all of the above are commonly sold under the registered trademark “Teflon”) at contact side  100   a . While it is presently preferred (according to one embodiment) that flexible primary layer  12  is from 0.06 to 0.13 inches thick and flexible contact layer  14  is from 0.002 to 0.010 inches thick, other dimensions may also be suitable. Similarly, it is presently preferred (according to one embodiment) that elastomer sheet  402  includes silicone having a minimum tear strength of 140 lb/in using the tear strength test method of ASTM D624 Die C, though other elements or compositions having a similar tear strength or silicone having a different tear strength may also be suitable. 
         [0025]    Using the ASTM D 1894-01 test method with an opposing surface of stainless steel with a #8 finish, a cross head speed of 6 inches per minute, and modified with 0.25 psi surface pressure instead of 0.07 psi to more accurately reflect the conditions under which the materials are used, we found a sample of material  10 ( 1 ) having a flexible primary layer  12  of ZZ-R-765 Class 2B Grade 60 Silicone 0.120 inches thick and a flexible contact layer  14  of DuPont® FEP Type C film 0.003 inches thick to have a static coefficient of friction from 0.18 to 0.21 and a kinetic coefficient of friction from 0.22 to 0.25. DuPont® FEP Type C film indicates that one side of the film is cementable; the non-cementable side was contact side  100   a.    
         [0026]      FIG. 5  shows a side view of a baffle seal  100 ( 2 ) constructed from a sheet of material  10 ( 2 ). Sheet  10 ( 2 ) comprises flexible primary layer  12  and flexible contact layer  14  that presents contact side  100   a . Flexible primary layer  12  includes an elastomer sheet  502  (e.g., a silicone sheet), and flexible contact layer  14  includes a fiber cloth  504  at contact side  100   a . Fiber cloth  504  has a low coefficient of friction (i.e., not more than 0.4) at contact side  100   a , and may include, for example, fiberglass, woven polyamide fibers such as those commonly sold as “nylon”, or woven para-aramid fibers such as those commonly sold as DuPont™ Kevlar® at contact side  100   a.    
         [0027]      FIG. 6  shows a side view of a baffle seal  100 ( 3 ) constructed from a sheet of material  10 ( 3 ) that includes an elastomer sheet  602  (e.g., a silicone sheet) compounded with an antifriction additive  604 . The antifriction additive may include, for example, a fluoroadditive (e.g., DuPont™ Zonyl® or another PTFE, FEP, ETFE, Teflon®-S, or PFA powder) or molybdenum disulphide. Elastomer sheet  602  compounded with antifriction additive  604  has a low coefficient of friction (i.e., not more than 0.4) at contact side  100   a.    
         [0028]      FIG. 7  shows a side view of a baffle seal  100 ( 4 ) constructed from a sheet of material  10 ( 4 ). Sheet  10 ( 4 ) comprises flexible primary layer  12 , flexible contact layer  14  that presents contact side  100   a , and a flexible third layer  16  inside primary layer  12  for reinforcing and increasing the durability of primary layer  12 . Flexible primary layer  12  includes an elastomer sheet  702  (e.g., a silicone sheet), and flexible contact layer  14  includes a thin laminate  704  at contact side  100   a . Third layer  16  includes a fiber cloth  706  inside elastomer sheet  702 . Thin laminate  704  has a low coefficient of friction (i.e., not more than 0.4) at contact side  100   a , and may include, for example PTFE, FEP, ETFE, Teflon®-S, or PFA. Fiber cloth  706  may include, for example, fiberglass cloth, and fiber cloth  706  may reinforce elastomer sheet  702  to increase the strength and durability of elastomer sheet  702 . 
         [0029]      FIG. 8  shows a side view of a baffle seal  100 ( 5 ) constructed from a sheet of material  10 ( 5 ). Sheet  10 ( 5 ) comprises flexible primary layer  12 , flexible contact layer  14  that presents contact side  100   a , and flexible third layer  16  for reinforcing and increasing the durability of primary layer  12 . Flexible primary layer  12  includes a standard elastomer  802 , flexible contact layer  14  includes a low-friction elastomer  804 , and third layer  16  includes a fiber cloth  806 . Standard elastomer  802  and low-friction elastomer  804  are on opposed sides of fiber cloth  806 . Low-friction elastomer  804  is at contact side  100   a . Standard elastomer  802  may include, for example, silicone; low-friction elastomer  804  may include, for example, a fluoroelastomer with antifriction additives; and fiber cloth  806  may include, for example, fiberglass cloth. Low-friction elastomer  804  has a low coefficient of friction (i.e., not more than 0.4) at contact side  100   a.    
         [0030]      FIG. 9  shows a side view of a baffle seal  100 ( 6 ) constructed from a sheet of material  10 ( 6 ). Sheet  10 ( 6 ) comprises flexible primary layer  12  and flexible contact layer  14  that surrounds primary layer  12  and presents contact side  100   a . Flexible primary layer  12  includes an elastomer sheet  902  (e.g., a silicone sheet), and flexible contact layer  14  includes a parylene conformal coating  904 . Coating  904  has a low coefficient of friction (i.e., not more than 0.4) at contact side  100   a.    
         [0031]      FIG. 10  shows a side view of a baffle seal  100 ( 7 ) constructed from a sheet of material  10 ( 7 ). Sheet  10 ( 7 ) comprises flexible primary layer  12 , flexible contact layer  14  that presents contact side  100   a , and flexible third layer  16 . Flexible primary layer  12  includes a standard elastomer  1002  (e.g., silicone), flexible contact layer  14  includes a laminate  1004 , and third layer  16  includes a fiber cloth  1006 . Standard elastomer  1002  and laminate  1004  are on opposed sides of fiber cloth  1006 . Laminate  1004  has a low coefficient of friction (i.e., not more than 0.4), is at contact side  100   a , and may include, for example, PTFE, FEP, ETFE, Teflon®-S, or PFA. 
         [0032]    Those skilled in the art appreciate that variations from the specified embodiments disclosed above are contemplated herein and that the described test results are not limiting. The description should not be restricted to the above embodiments or test results, but should be measured by the following claims.