GB2130158A

GB2130158A - Deicing aircraft surfaces

Info

Publication number: GB2130158A
Application number: GB08315935A
Authority: GB
Inventors: Lawrence E Mcallister; John N Pepin
Original assignee: Fiber Materials Inc
Current assignee: Fiber Materials Inc
Priority date: 1982-11-15
Filing date: 1983-06-10
Publication date: 1984-05-31
Also published as: JPS5992300A; FR2536037A1; DE3322431A1

Abstract

The leading edge of an airfoil surface comprises a rigid self- supporting, porous, nonmetallic composite fabric material and is adapted for use with reservoir means for containing a fluid and means for pressurizing the fluid so as to cause it to flow over the outer surface thereof at a predetermined flow rate, means being provided for controlling the flow of pressurized fluid through the material to the outside surface. The flow controlling means is a microporous plastics membrane 28. <IMAGE>

Description

SPECIFICATION Deicing aircraft surfaces This invention relates to an aircraft deicing and debugging system, and more particularly, it relates to the use of lightweight, self-supporting, rigid, non-metallic composite materials as the leading edge of an airfoil surface, as well as a component of a novel wind deicing and debugging system.

Deicing the leading edge of an aircraft airfoil, or wing, to remove or prevent accumulation of ice on the leading edge of a wing by flooding the surface thereof with glycol and other antifreezing liquid chemicals is well known, Deicing systems of this type normally utilize means for storing the glycol, a subsystem for delivering the glycol to the leading edge of the aircraft wing, and means for controlling the flow rate and distribution of the glycol over the leading edge.

One problem of some prior art deicing systems of the type described is that they may not be appropriate for modern aircraft designs. Another problem of some prior art systems is that their weight may be excessive when added to the airfoil surfaces, so that use on small aircraft is precluded.

This problem usually is due to the utilization of heavy metal components in the deicing system.

Another problem in some prior art deicing systems of this type is the inability of the glycol distribution subsystem to ensure uniform distribution of the glycol over all portions of the leading edge so as to inhibit all ice formation there. As a result it is necessary to utilize an excessive amount of deicing fluid to insure that proper deicing occurs.

For example, many prior art deicing systems utilize an unrigidized fabric to form the leading edge of an airfoil surface and control the flow of glycol to that edge. See for example, U.S. Patent Nos.

2,200,838 and 2,075,659. Such unrigidized fabric constructions do not appear appropriate for modern aircraft, particularly jet aircraft. U.S.

Patent No. 2,249,940 shows a composite of closely woven cloth, formed partly of metal or alloy wire and partly of yarn, applied over the surface of an airpiane wing. The patentee states that the metal or alloy wires prevent stretch of the fabric, while the yarn provides the necessary permeability for the deicer fluid. It is believed, however, that effective control of the flow of deicer fluid with such construction would be difficult. Further, such a fabric can add excessive weight so that its use on small aircraft is undesirable, if not precluded. The more modern prior art deicing systems shown in U.S. Patent Nos. 2,843,341 and 3,423,052 utilize a rigid airfoil surface, but the deicerfluid is dispensed through discrete hole patterns which may provide uneven distribution of the deicer fluid.One of the systems shown in U.S. Patent No. 3,423,052 includes the use of stainless steel sheathing of porous construction to form the leading edge of the wing. However, this stainless steel metal sheathing is heavy in weight and may not provide the even distribution of fluid, as desired due to the lack of control over poor size and density in the sheathing.

Still another problem with some of these prior art deicing systems is the lack of satisfactory means for controlling the flow rate of the glycol from storage means to the leading edge of the aircraft.

Although accumulation of insects on the leading edge of a natural laminar flow airfoil can destroy the laminar flow over the surface thereby increasing airfoil drag, there appears to be no prior art which discloses that such an airfoil can be debugged by flooding with a liquid exuded through a porous surface.

Accordingly, a general object of this invention is to provide an improved deicing and debugging system which eliminates, or substantially reduces, the problems noted above.

A more specific object is to provide a deicing system for distributing the deicing fluid over the leading edge of an airfoil in a uniform manner, while minimizing the amount of deicing fluid required to prevent ice formation.

Another object is to provide a system for effectively controlling the flow rate of the deicing or debugging fluid from storage means to the wing's leading edge.

And another object of the present invention is to provide a deicing and debugging system utilizing lightweight components especially suitable for small modern aircraft.

Still another object is to provide a deicing system (which term hereinafter is intended to include a debugging system) that overcomes the problems listed above at a relatively low cost and with a relatively simple design.

Attainment of these and other objects is achieved by an improved wing deicing system comprising storage means for storing an antifreeze or deicing liquid, a lightweight, rigid, self-supporting, porous non-metallic, fiber composite material formed in the shape of a leading edge of an airfoil, and means for controlling the flow of the antifreeze or deicing fluid from the storage means to the exterior surface of the composite material. Forming the leading edge from a non-metallic composite material provides structural and thermal compatibility with a wing made from a similar composite. For laminar flow to be maintained over a wing's surface, the airfoil cross-section must not change substantially with wing loading. Fiber composite materials afford a superior opportunity to construct a very stiff wing which does not change shape under aerodynamic loading.

In the preferred embodiment of the invention, the means for controlling the flow rate of deicing fluid includes a microporous plastic membrane positioned between the storage means and the composite material. The composite material is preferably a 3-D fabric made of woven fiberglass partially impregnated with resin. Preferably, distribution means in the form of a layer of an aramid fiber fabric, is laminated to the exterior surface of the composite so as to provide a more uniform distribution of antifreeze solution to the exterior airfoil surface.

Fig. 1 is a plan view of a typical small aircraft showing suggested locations where porous leading edge elements of the deicing system of the present invention are used; Fig. 2 is a cross-sectional view, partially cut away, of a porous leading edge element, taken along line 2-2 of Fig. 1; Fig. 3 is an isometric rear view of the interior of a porous leading edge element; Fig. 4 is a fragmentary plan view of a single layer of the preferred 3-D composite utilized in the present invention; and Fig. 5 is a partial cross-sectional view taken along line 5-5 of Fig. 4.

The deicing system of the present invention includes a tank mounted somewhere for convenience in the aircraft for storing an antifreeze fluid such as glycol. A pump is utilized to pump this fluid from the tank to the porous leading edge elements. Fluid proportioning units are typically utilized to provide a more uniform distribution to all of the porous leading edge elements. To the extent described, the system is known to those skilled in the art. In accordance with the present invention, an improved, lightweight, rigid, self-supporting, porous non metallic composite material is utilized to form leading edge elements of an aircraft as well as provide a porous surface through which the antifreeze material can be fed.

As shown in Fig. 1, locations on a small aircraft 12 are designated to show where the leading edge elements of the deicing system of the present invention can be utilized. Primarily designed for installation along edges 20 of aircraft wings 14, the leading edge elements of the deicing system may also be utilized as other airfoil leading edges such as those on the aircraft's tail assembly, e.g., edge 22 on each horizontal stabilizer 1 6 and front edge 24 on vertical stabilizer 1 8. For purposes of simplifying the description of the deicing system of the present invention, only the leading edge element forming the leading edge 20 of the aircraft wings 14 will be described.The structure and operation of each of the leading edge elements of the system, when installed as the leading edges on other airfoil surfaces, are substantially the same as those provided on wings 14, although the size and shape of each leading edge element may vary.

As shown in Fig. 2, the leading edge element 26 of the deicing system comprises (1) a self supporting, porous, nonmetallic composite material sufficiently rigid and yet relatively lightweight so as to be particularly useful for the aerodynamic needs of modern aircraft, and (2) means for controlling the rate of flow of antifreeze solution through the element to the exterior surface of the element. In the preferred embodiment, lead edge element 26 comprises an outer shell 36 and an inner shell 38, shells 36 and 38 being secured together so as to form a cavity 32 therebetween. Shells 36 and 38 provide the self-supporting rigidity needed to define the leading airfoil surface.Cavity 32 is adapted to contain fluid (1) under positive pressure with respect to the exterior surface of the outer shell 36 and (2) pumped to it from the reservoir tank (not shown) of the system through an inlet nipple 44.

The preferred lead edge element 26 also comprises a microporous plastic membrane 28 laminated in cavity 32 between the outer and inner shells for controlling the flow of fluid through the lead element.

The preferred outer and inner shells each preferably comprise one or more layers of fabric material, with each layer woven as a 3-D fabric.

3-D fabrics are well-known. In addition to 3-D fabrics, other multi-directional fabrics could be utilized, e.g. seven directional (7-D) or eleven directional (11 -D) fabrics as described in U.S.

Patent No. 3,949,126. As shown in Figs. 4 and 5, such a 3-D fabric material 48 comprises four separate groups of yarns. Two groups of yarn 50 and 52 extend in the Y-direction (see the coordinate system legends accompanying Figs. 4 and 5) and form two parallel layers of yarn as shown. The yarns 54 of a third group extend in the X-direction and form a third layer of yarns sandwiched between the respective layers of yarn 50 and 52, while the yarns 56 of a fourth group are each interwoven in the Z-direction with the yarns 50 and 52 so as to interlock yarns 50 and 52 (see Fig. 5) and thereby bind all four groups of yarn together. The weave construction, yarn size, and yarn distribution of the fabric 48 can be varied so as to achieve a fabric with the desired mesh and porosity distribution. The preferred material of yarns 50, 52, 54 and 56 is fiberglass.The fabric of the outer shell 36 is impregnated with a resin material so as to form a rigidized composite material 40, but not fill all of the existing pores in the fabric so that composite material 40 is foraminous. Outer shell 36 also preferably includes at least one other layer 30A of fabric disposed on the exterior surface of the shell to form an outer skin and made of a material (such as any one of several aramid fibers of the type manufactured by E. l. du Pont de Nemours a Co.

of Wilmington, Delaware under the trademark KEVLAR) which will add abrasion resistance, toughness and aerodynamic smoothness to the airfoil surface, and which is of a sufficiently fine weave so as to provide a more uniform distribution of antifreeze solution to the exterior surface. Likewise the interior surface of outer shell 36 can be provided with a layer of material 30B, similarly to layer 30A, to provide even greater rigidity. The inner shell 38 is sufficiently impregnated with a resin to make it completely nonforaminous so as to prevent any flow of fluid through it.

Microporous membrane 28, for controlling the flow rate of antifreeze solution through the outer shell 36, preferably comprises at least one thin film or sheet of polyvinylidene fluoride of substantially uniform microporosity, such as the type manufactured by the Millipore Corporation of Bedford, Massachusetts under the trade designation HVLP 00010, although it will be appreciated that other microporous films of the same or different material can be utilized. The membrane 28 is preferably attached to the inside surface of the outer shell 36 by bonding the outer edges of membrane 28 to shell 36 with a suitable adhesive.

Referring to Fig. 3, each leading edge element 26 is preferably formed in section 42 with each section forming a separate cavity 32, adjacent cavities being separated by a boundary depression 46. An inlet nipple 44 for each cavity 32 is bonded to the inner shell 38, is adapted to be connected to a fluid conduit (not shown) and provide fluid communication between such conduit and the cavity 32.

The following is an example of a method of making the lead edge element 26, it being understood that the example is for the purpose of illustration and not limitation.

Outer shell 36 is vacuum bag molded in a female mold. A layer of dry fine weave aramid fiber fabric (purchased from E. I. du Pont de Nemours of Wilmington, Delaware under the trade designation &num;120 KEVLAR 49 fabric) is first placed in the mold to form the outer skin layer 30A. Next a 3-D woven glass tape prepreg, 40 mils thick, is placed in the mold over layer 30A.

This 3-D glass prepreg is previously made by soaking the tape in DER 331 epoxy resin, manufactured by Shell Chemical Company of Houston, Texas (with NMA and BDMA curing agents), cut with 50% MEK, and staging or advancing the resin cure in an oven at approximately 2500 F for approximately sixteen (16) minutes. Finally, another layer of aramid fiber fabric identical to layer 30A is placed over the 3-D woven glass tape prepreg to form the inner layer 30B of outer shell 36. The resulting structure in the mold is thus a resin starved sandwich of aramid fiber fabric/fiberglass/aramid fiber fabric.

The inner shell 38 is vacuum bag molded in the same female mold with the modification that a layer of cork 0.059 inches thick is placed in the mold to simulate the outer shell 36 during the molding process of the inner shell 38. Rectangular cork pads of the same material are secured to this layer of cork in a spaced apart manner to simulate the spaced apart cavities 32. The inner shell laminate comprises three layers of fiberglass, Style 7500-38 finish #162 boat cloth prepreg, manufactured by Northern Reinforcements, of Exeter, New Hampshire, impregnated with 100% epoxy resin solids.

Specifically, the three layers of fibreglass were each made by soaking 3-D woven glass tape prepreg, 40 mils thick, in 100% DER 331 epoxy resin with NMA and BDMA curing agents.

The resin cure is then staged or advanced in an oven at 2500 F for sixteen (1 6) minutes.

After the inner laminate was molded and cured, a small hole was drilled in the location of the corner of each cavity 32 so as to provide an inlet for the deicing fluid. A polyethylene nipple 44 is bonded over each hole with a structural adhesive such as EA 934 manufactured by Dexter Hysol Corporation of Pittsburg, California.

The inner and outer laminate shells 38 and 36 are then bonded together with two layers of the polyvinylidene fluoride membrane sandwiched inbetween. The outside edges and boundaries between the cavities are bonded with the EA 934 adhesive and clamped during the adhesive cure.

After curing, the edges can be sanded and any leaks sealed with a suitable sealant such as Hysol R9-2039 room temperature curing epoxy resin.

A description of the operation of the deicing system of the present invention follows. An antifreeze fluid such as glycol is transported under some positive pressure, e.g., by a pump, from a centralized storage container (not shown) through conduit (not shown) to each nipple 44 so as to cause the glycol to flow into each cavity 32. Inner shell 38 is nonforaminous so that the pressurized glycol flows through the microporous plastic membrane 28 at a rate determined by the pressure of the fluid and the nature of membrane 28 and thence through the outer shell 36 of element 26. After the glycol passes through the foraminous composite material 40 of the outer shell, it encounters the finer mesh covering 30A (Fig. 2) which allows for a very uniform distribution of the glycol over the outside surface of element 26.The pressure of the glycol is controlled so as to cause the glycol to bleed through the covering 30A at an adequate rate to ensure that no ice will build up on the leading edge 20 of the wing 14. The glycol bleed rate is also kept as low as practicable in order to minimize the quantity of glycol required to attain the goal of no ice formation mentioned above.

While the preferred embodiment of the present invention has been described, it will be evident that lead element 26 can be modified without departing from the scope of the invention. One possible modification to the present invention is to remove the microporous plastic membrane 28 from leading edge element 26 and control the fluid flow rate with the composite material 40 of the outer shell 36 of element 26. The resin content, resin composition, and fabric construction of material 40 can be varied to control the porosity and porousness of the outer shell 36, thereby controlling the flow rate of the glycol through outer shell 36.

Other possible methods of controlling the fluid flow rate through the composite material 40 of outer shell 36 include (1) the use of a fugitive filler in the resin matrix, and (2) the use of fugitive fibers in material 48, both as described in greater detail below: (1) The composition of the resin in material 40 could be modified to include soluble or volatilizable fillers that would leach or vaporize out of the resin after molding the composite material 40. The particle size distribution of such a fugitive filler could be varied so as to result in a porous and foraminous composite material 40 that would control the fluid flow rate as desired.

(2) Fugitive fibers, such as polyvinyl alcohol, could be included in the fabric weave composition of material 48 in some predetermined pattern.

When the fibers leached out of the material 48, a composite material 40 would remain having the desired porous and foraminous structure to properly control the fluid flow rate through the outer shell 36 of element 26.

In addition to its use specifically in a deicing system for airfoil leading edges, the present invention as previously noted has other uses, one of which is to provide for increased laminar flow across aerodynamic surfaces on a routine basis by maintaining the leading edge of an airfoil in a smooth condition. The constant uniform bleeding of a fluid (not necessarily glycol) over the outside surface of the airfoil leading edge would tend to prevent particulate materials, particularly insects, from adhering to the leading edge and thereby maximize laminar airflow over the airfoil, while minimizing turbulent airflow.

The invention illustrated and described above has a number of advantages. First, it allows the leading edge of an airfoil to also function as a portion of a deicing system, while minimizing the weight added to the aircraft when compared to similar deicing systems which employ metal fabric. The leading edge element 26 of the deicing system of the present invention can provide weight reduction of up to 50%. The use of the lightweight, rigid, nonmetallic composite material 48 could also allow the deicing systems to be manufactured at a lower cost than is presently possible.

Additionally, the use of the rigid, nonmetallic composite material 40 provides adequate structural strength for the leading edge element 26, as well as providing a foraminous structure that facilitates uniform distribution of the fluid.

Furthermore, the covering 30 provides a smooth aerodynamic surface for element 26 so as to maximize the laminar flow of air over wind 14 while minimizing turbulent airflow. In the preferred embodiment of the invention, covering 30 is made from a fine weave aramid fiber fabric that also provides added abrasion resistance to element 26.

The fine mesh of the aramid fiber fabric also provides for a very uniform distribution of antifreeze fluid over the outer surface of element 26, thereby minimizing the opportunities for ice to build up anywhere on the surface of element 26.

Other modifications and advantages of the invention will be obvious to persons skilled in the art.

Claims

1. An article made of a rigid, self-supporting, porous nonmetallic composite fabric material comprising an outer surface formed as the leading edge surface of an airfoil and adapted for use with reservoir means for containing a fluid and means for pressurizing the fluid so as to cause it to flow over the outer surface at a predetermined flow rate, means being provided for controlling the flow of pressurized fluid through the material to the outside surface.

2. An article as claimed in claim 1 in which the material is of at least a 3-D construction.

3. An article as claimed in claim 1 or 2, in which the means for controlling the flow comprises a microporous membrane.

4. An article as claimed in claim 1,2 or 3, in which the rigid, self-supporting, porous nonmetallic composite material forms an outer shell for defining the outer surface, a nonporous inner shell co-operating with the outer shell so as to form a cavity between the outer and inner shells for retaining the pressurized fluid.

5. An article as claimed in claim 4, in which the means for controlling the flow comprises a microporous membrane in the cavity disposed between the outer and inner shells.

6. An article as claimed in claim 5, in which the microporous membrane is secured to the outer shell.

7. An article as claimed in claim 6, in which the membrane includes polyvinylidene fluoride.

8. An article as claimed in any preceding claim, in which the composite material is resin impregnated fibreglass.

9. An article as claimed in claim 8, in which a fabric layer of aramid fibres is disposed over the composite material to as to form the outer surface.

10. An article as claimed in claim 9, in which the fabric layer is fine weave so as to provide an abrasion resistant surface and a more uniform flow of fluid over the outer surface.

11. An article as claimed in claim 10, in which a second fabric layer of aramid fibres is disposed over the composite material on the surface opposite the outer surface.

12. An article as claimed in claim 11, in which the composite material includes a layer of fabric of at least 3-D construction.

13. An airfoil wetting system, comprising in combination a holiow airfoil leading edge element formed from a rigid, self-supporting, non-metallic, porous and foraminous composite material, which element is attached to a nonporous backing and having a hollow space forward of the backing for receiving a fluid under positive pressure, means for controlling the flow of fluid from the hollow space through the element, means for transporting the fluid into the space and means for pressurizing the fluid.

14. A system as claimed in claim 13, in which the composite porous and foraminous material is a resin impregnated 3-D fabric of woven fibreglass, the composite material having a predetermined mesh and porosity.

1 5. A system as claimed in claim 14, in which the porosity of the composite material is determined by the amount of resin in the material.

16. A system as claimed in claim 14, in which the porosity of the composite material is a function of fugitive material removed from the resin in the fabric.

17. A system as claimed in claim 14, in which the porosity of the composite material is a function of fugitive fibres removed from the fabric.

1 8. A system as claimed in claim 14, in which the porosity is a function of the viscosity of an antifreeze type of the fluid.

19. An article constructed and arranged substantially as herein described with reference to and as illustrated in Figs. 2 to 5 of the accompanying drawings.

20. A system constructed and arranged to operate substantially as herein described with reference to and as illustrated in Fig. 1 of the accompanying drawings.