WO1997021543A1

WO1997021543A1 - Aircraft pneumatic deicer repair method

Info

Publication number: WO1997021543A1
Application number: PCT/US1996/019028
Authority: WO
Inventors: Leslie D. DEES (Deceased)
Original assignee: Boots, Incorporated; DEES, Dorothy, Sue
Priority date: 1995-12-01
Filing date: 1996-11-27
Publication date: 1997-06-19
Also published as: AU2188697A

Abstract

An aircraft pneumatic deicer (20), formed of a fabric-reinforced elastomer (40), which has surface damage characterized by small cracks (80) or pinholes (70), is repaired by a process of filling the damage site with a compound composed of ethyl cyanoacrylate adhesive and, if necessary, ethylene copolymer rubber as filler material. A damage site having no material loss is cleaned with a solvent, the adhesive compound is applied to the sides of the crack, and the sides are taped together to reinstate the deicer pre-damage configuration. A damage site having material loss is filled with a combination of an adhesive compound and a filler compound and is not taped. In either case, the compound is cured at ambient temperature. The repaired damage site is then sanded to reinstate its pre-damage profile. This process can be used with deicers made of rubber, neoprene, or 'ESTANE'.

Description

AIRCRAFT PNEUMATIC DEICER REPAIR METHOD

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority based on the following two provisional applications: Serial No. 60/007879, filed December 1, 1995, and Serial No. 60/009916, filed January 16, 1996.

TECHNICAL FIELD

This invention relates generally to the repair of flexible, inflatable pneumatic objects which are cyclically inflated to low pressures and then deflated over a relatively short time span. More particularly, the present invention provides a method for the surface repair of cracks and punctures in flexible, inflatable aircraft deicers to prevent aggravation of the cracks and punctures as a result of fluid flow across the surface.

BACKGROUND ART

Accumulation of ice changes the physical characteristics of an aircraft airfoil (e.g. wing, winglets, horizontal stabilizer, vertical stabilizer) , resulting in loss of lift and a hazard to efficient flight. A pneumatic deicer for aircraft is a device installed on the leading edge of an airfoil and is used to prevent the accumulation of ice on those surfaces.

A typical pneumatic deicer consists of a fabric- reinforced elastomer containing a plurality of parallel, individually inflatable airways, or tubes, which can be oriented to the airfoil either spanwise along its longitudinal axis or chordwise along its chord. In operation, the airways are either simultaneously or alternately briefly inflated and quickly deflated during a nominal operational cycle to mechanically break off the surface ice from the leading edge of the airfoil and to restore normal airflow over the airfoil. The brief cycle of deicer inflation/deflation cycle operation prevents a shell of ice, conforming to the inflated shape of the deicer, from forming. If the inflation cycle time is extended, an ice shell, conforming to the inflated shape could form, thus rendering the deicer ineffective, because the deicer would inflate and deflate within the ice shell without ever applying sufficient pressure to break the ice. The timing of the inflation/deflation cycles and the time interval between them is controlled by each individual aircraft manufacturer. A representative example of a typical deicer operation might be a cycle comprising a seven second inflation followed by a five second deflation repeated at five minute intervals. A majority of aircraft deicers are manufactured by the B. F. Goodrich Company and are composed of neoprene or "ESTANE" elastomers. Neoprene is designated as polychloroprene, or 2-chloro-1, 3 -butadiene. "ESTANE" is a registered trademark of the B. F. Goodrich Company and identifies a class of elastomers used as coatings in sheet or liquid form for providing deicer and corrosion protection to transportation vehicle surfaces. The inner surface of each of the deicer airways is formed of a fabric designed to stretch only in the direction of inflation (i.e. radially) and not longitudinally. Each airway cavity is lined by the fabric, which is encased in the elastomer to provide protection from the environment and to provide an airtight seal.

An aircraft pneumatic deicer has superficial similarities to a conventional pneumatic tire, but it is actually quite different in many ways. A tire is a thick elastomeric pressure container which: (1) is designed to operate continuously at a predetermined pressure which varies only in a failure mode of deflation;

(2) when inflated, does not appreciably change shape, volume or surface area from its uninflated state;

(3) is designed to continuously support great weights; (4) is designed to experience continuous frictional mechanical wear during operation and normally requires periodic replacement;

(5) when deflated, disables operation of the vehicle mounting the tire.

In contrast, a deicer is a thin elastomeric pneumatic container which:

(1) experiences rapid inflation and deflation during normal operation and is designed to operate intermittently in an inflated condition, but exists primarily in an inoperative deflated condition;

(2) when inflated, balloons and undergoes a significant change in shape, volume and surface area;

(3) is non weight bearing;

(4) does not normally experience frictional mechanical wear during operation and does not normally require replacement; (5) when deflated, has no effect on vehicle operation.

Thus, it is seen that tires and deicers have little in common. However, heretofore, the only method of repairing deicers was an adaptation of the method used to repair tires and tire tubes. Conventionally, when the surface of a deicer is damaged, it is repaired, if possible, by using special, orientation dependant patches supplied by the manufacturer, much like a tire patch.

Deicers sustain many different types of damage during normal operation. Damage may take the form of cracks due to aging, accidental mechanical tears, or weakening through exposure to corrosive aviation solvents or acids from dead insects. If such damage is allowed to endure, then the deicer damage is aggravated and can result in destruction of the deicer by the motion of air over the airfoil during flight. Since removal and replacement of a damaged deicer from an airfoil is an expensive and time-consuming process, the deicer is normally repaired while on the aircraft, provided that the damage is not so extensive as to necessitate replacement .

Pneumatic deicers are delivered with proprietary instructions from the manufacturer for the repair of the deicer. Heretofore, the method for repairing deicers has been essentially the same method as is conventionally used to patch a pneumatic tire. This method currently consists of applying a patch from a repair kit supplied by B. F. Goodrich, i.e. the 74-451-C Kit for neoprene deicers or the 74-451-H Kit for ESTANE deicers. These kits have limitations concerning the number of patches of a certain size which are permitted within a given twelve inch square area. They also require maintenance personnel to be aware of the direction in which the patch can be stretched so that it can be applied with the correct orientation to the deicer surface because patches installed with the wrong orientation fail more rapidly than those that are installed with the proper orientation.

This conventional type of repair has the following disadvantages :

1. When applied, the repair patch alters the normal profile of the airfoil, which disrupts the flow of air over the airfoil and thus increases drag.

2. When repair patches are applied in this manner, the flow of air over the airfoil often tears the protruding patch loose over time, rendering the this type of repair temporary, at best.

3. The conventional repair patch is directional since it can only stretch in one direction. Thus, it must be applied with the proper orientation to be effective. In practice, human error causes a significant number of patches to be misapplied with the wrong orientation, necessitating deicer replacement or re-repair, when it is discovered; otherwise, the deicer will fail to operate properly. These disadvantages result in a repaired deicer which is defective, since it is not returned to its pre-damage functioning condition.

A new method or process for repairing pneumatic deicers is needed which provides a more permanent repair, does not affect airflow, is inexpensive, cannot be applied with a wrong orientation, and returns the deicer to its pre-damage functioning condition.

DISCLOSURE OF THE INVENTION

It is therefore an object of this invention to provide a new method or process for repairing deicers which provides a more permanent repair, does not affect airflow, cannot be applied with a wrong orientation, and returns the deicer to its pre-damage functioning condition.

This invention provides an improved method of repairing pneumatic deicers, wherein the damage to the deicer is repaired by rebonding the site of the damage and, if necessary, replacing lost deicer elastomer with a suitable filler, rather than covering the damage site with a patch, as is the conventional practice. A liquid adhesive is introduced into the damage site and allowed to cure at ambient temperature, thereby sealing the damage and rendering the deicer air tight. This method of repair does not require curing of the surface with an oxidant prior to application of the adhesive, and returns the deicer to its pre-damage functioning condition.

Further objects and advantages of this invention will become more readily apparent upon reference to the following detailed description of a preferred embodiment, as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a typical pneumatic deicer as configured for the airfoil of a wing or horizontal stabilizer, with the individually inflatable airways oriented transverse to the airfoil;

FIG. 2 is an enlarged sectional view of the pneumatic deicer, taken along line 2 - 2 of FIG. 1, shown in an uninflated, or rest, state;

FIG. 3 is a view similar to FIG. 2, but with the pneumatic deicer shown in an inflated, or active, state, and illustrating damage sites; and

FIG. 4 is a flow diagram for the aircraft pneumatic deicer repair process according to this invention.

BEST MODES OF CARRYING OUT THE INVENTION

FIG. 1 illustrates generally a typical airfoil 10 to which a pneumatic deicer 20 has been installed to its leading edge. Deicer 20 includes a plurality of airways 30 of the deicer 20 which have a transverse orientation along airfoil 10. Damage to a deicer 20, which is repairable by the process according to this invention, falls into two classes. What is known as "Class 1" damage consists of damage which does not involve the removal or loss of deicer material. Such damage is characterized by cuts which create openings that can readily be pulled together by hand. Cuts include tears and gouges caused by mechanical damage or foreign object damage .

What is known as "Class 2" damage is characterized by the removal or loss of deicer material. This type of damage consists of small openings (i.e. splits and pinholes) which cannot be readily closed by hand. Pinholes may be caused by insect acids which partially dissolve the deicer material over time, imperfections in the deicer material, or punctures by sharp objects. Splits are generally caused by aging of the deicer and appear in areas where the deicer is installed in tension, especially on the leading edge of an airfoil . The repair process of this invention applies to Class 2 damage, where no appreciable amount of material is removed by the damage.

FIG. 2 illustrates a deicer airway in a deflated state, while FIG. 3 illustrates the same deicer airway in an inflated state. Deicer 30 comprises a sheet of elastomer 40 having a plurality of transverse airways 30, each of which is defined by an elongated cavity 60 that is lined with a fabric sheath 50. Damage sites which are reparable by practicing this invention include such material loss damage as pinholes and splits (shown at 70 in FIG. 3) , and no material loss damage, such as cuts, gouges and tears (shown at 80 in FIG. 3) , located in the surface of elastomer 40 . Certain types of damage which extend into the fabric 50 can be repaired by the method described herein. However, damage to the elastomer and fabric backing which occurs within 1/2 inch of the boundary of an airway is too extensive to be repaired by this method.

A flowchart illustrating the general repair process is shown in FIG. 4. The repair method for repairable types of deicer damage, as practiced by this invention, consists of the following steps:

1. Each deicer is inspected to determine if it can be repaired under this process. Cuts, splits, tears, and gouges, which are observed to extend into fabric 50 and which are within 1/2 inch of an airway boundary, which separates the airways 30, are not repairable by this method and must be repaired according to the manufacturer's instructions. Damage extending into the heating elements of propeller deicers is also not repairable by this process and must be repaired according to the manufacturer's instructions.

2. A determination is made as to the composition of the deicer in order to use the correct cleaning solvent in subsequent steps of this process, since use of an inappropriate cleaning solvent will result in chemical deterioration of the deicer. For deicers composed of neoprene or rubber, the preferred cleaning solvent and best mode is methyl ethyl ketone (MEK) . For deicers composed of "ESTANE", the preferred cleaning solvent and best mode is toluene.

3. The deicer surfaces are cleaned by wiping with a clean shop rag wetted with the cleaning solvent. A pad of Scotchbrite 07447 abrasive material is then wetted with the cleaning solvent and the surface is rubbed with sufficient pressure to loosen surface contamination. A paper towel is used immediately after rubbing the surface to remove loose material from the surface. This cleaning process is continued to the end of one surface of the deicer and then repeated for the other surface of the deicer.

4. The cleaned deicer is inspected to locate specific damage sites to be repaired. Using a flashlight, the deicer is closely examined for Class 1 and Class 2 types of damage. A chalk line is drawn around each damage site to mark it, but with sufficient clearance to preclude contaminating the treatment of the damage site.

5. Each damage site is then repaired according to a determination of whether the damage site consists of Class 1 or Class 2 damage or of minor imperfections, as follows:

A. Class 1. The damage site is filled with an adhesive material to bond the sides of the site together. No chemical preparation of the surface is necessary. The preferred adhesive compound and best mode for repair consists of an adhesive whose active ingredient is ethyl-2- cyanoacrylate. After application of this bonding material, a piece of black vinyl electrical tape is applied in tension across the edges of the damage site to close the opening and return the deicer to its pre-damage configuration. This restores its structural integrity. The bonding material cures at ambient temperature.

B. Class 2. The damage site is filled with a composition including, but not limited to, an adhesive which bonds to the sides of the damage site and a filler material which fills the damage site to the level of the airfoil. No chemical preparation of the damage site is 5 necessary. The preferred material and best mode for repairing Class 2 damage sites consists of a preparation containing ethyl cyanoacrylate adhesive and ethylene copolymer rubber as filler material. Other materials may

10 be added to the preparation, such as carbon black to cosmetically color the repair so that the repair is not noticeable. When using this preparation for splits, an accelerator compound may be required to speed the drying and curing

15 process. The preferred compound and best mode for accelerating the curing process is a chemical composition, the primary component of which is N,N-Dialkyltoluidine in nominal concentrations of from 0.1% to 3%. The actual

20 concentration of N,N-Dialkyltoluidine is not significant. When using this material for pinholes, the accelerator compound is not required. C. Minor Imperfections. Insect stains and

25 other minor deicer imperfections not requiring repair by either of the two abovementioned processes are treated by sanding the surface of the deicer with 400 grit wet/dry sandpaper. 6. After all repairs have cured, the surface of each repaired damage site is lightly sanded with 400 grit sandpaper to remove any ridges and to smooth the resulting repair. This conforms the surface of the deicer to its pre-damage profile to restore the airfoil and prevent any superficial irregularities which could disturb the airflow or become the site for ice formation. The damage site is inspected, and if it requires further repair, then the previous step is repeated according to the type of damage being repaired.

7. After all repairs have been made, any remaining chalk marks are removed by rubbing the with a clean paper towel wetted with water.

8. Since the deicer surface is porous, it is then waxed with a commercial wax for protection and for reducing the tendency of ice to adhere to the surface during operation. The preferred wax compound for this purpose is any silicon- free preparation conventionally used in aircraft maintenance facilities .

Thus, this invention describes a method for repairing deicers which provides a more permanent repair than was previously available, which returns the surface of a damaged deicer back to its pre-damage shape, so that the repair does not affect airflow, and which cannot be applied with a wrong orientation so as to reduce the effectiveness of the repair. The repaired deicer is returned to its pre-repair functioning condition.

While only a preferred embodiment has been illustrated and described, obvious modifications are contemplated within the scope of this invention and the following claims. For example, other adhesive and filler materials may be used to seal the damage sites. Also, this method may be applied to the repair of other similar damaged elastic articles which operate by cyclically inflating and deflating and which have a fabric backing. Accordingly, the scope of the invention should be determined not by the embodiments illustrated but by the appended claims and their legal equivalents .

Claims

What is claimed is:

1. A method for repairing a damaged deicer, which is formed of a fabric-reinforced elastomer, to a condition in which the deicer is returned to its pre- damage configuration and its surface is brought into conformance with its pre-damage profile, said deicer having a damage site characterized by a surface break defined by two opposed sides and characterized by no loss of elastomer material, said method comprising the steps of

(a) cleaning the damage site with a cleaning solvent, to remove oils and foreign matter from the sides of the damage site; (b) applying an adhesive to the opposed sides of the damage site, (c) engaging said opposed sides to eliminate the surface break and to conform the deicer to its pre-damage configuration; (d) taping the opposed sides together to maintain the deicer in its original configuration during the subsequent curing step; (e) curing the damage site at ambient temperature; and (f) sanding the damage site to conform the surface of the repaired deicer to its pre-damage profile.

2. The process recited in claim 1, wherein the elastomer is neoprene and the cleaning solvent is methyl ethyl ketone.

3. The process recited in claim 2, wherein the active ingredient of the adhesive is ethyl-2- cyanoacrylate.

4. The process recited in claim 1, wherein the elastomer is "ESTANE" and the cleaning solvent is toluene.

5. The process recited in claim 5, wherein the active ingredient of the adhesive is ethyl-2- cyanoacrylate.

6. A method for repairing a damaged deicer, which is formed of a f bric-reinforced elastomer, to a condition in which the deicer is returned to its pre- damage configuration and its surface is brought into conformance with its pre-damage profile, said deicer having a damage site characterized by a surface break defined by two opposed sides and characterized by a loss of elastomer material, the method comprising the steps of (a) cleaning the damage site with a cleaning solvent to remove oils and foreign matter from the sides of the damage site, (b) applying to the damage site a preparation composition comprising an adhesive compound and a filler compound, whereby the preparation composition functions to fill the damage site, to conform the deicer at the damage site to its configuration prior to the occurrence of the damage, and to bond the filler compound therein to the sides of the damage site;

(c) curing the damage site at ambient temperature; and

(d) sanding the damage site to conform the surface of the repaired deicer to its pre-damage profile .

7. The process recited in claim 8, wherein the elastomer is neoprene and the cleaning solvent is methyl ethyl ketone.

8. The process recited in claim 9, wherein the preparation composition consists of ethyl cyanoacrylate as the adhesive compound and ethylene copolymer rubber as the filler compound.

9. The process recited in claim 8, wherein the elastomer is "ESTANE" and the cleaning solvent is toluene .

10. The process recited in claim 12, wherein the preparation composition is comprised of ethyl cyanoacrylate as the adhesive compound and ethylene copolymer rubber as the filler compound.