US2440240A - Protective covering for preventing accumulation of ice on airfoils - Google Patents

Description

April 27, 1948. J. o. ANTONSON PROTECTIVE COVERING FOR PREVENTING ACCUMULATION OF ICE ON AIRFOILS 3 Sheets-Sheet 1 Filed Dec. 29, 1944 April 27, 1948. J. G. ANTONSON PROTECTIVE COVERING FOR PREVENTING ACCUMULATION OF ICE ON AIRFOILS Filed Dec. 29, 1944 s Sheets-Sheet 2 n E'FZZZZEL... John Ufinibnsm P 1948- .a. 5. ANTONSON 2,440,240

PROTECTIVE COVERING FOR PREVENTING ACCUMULATION OF ICE ON KIRFOILS Ill/ll EJZELFTZYEL i527 02 27227275027 Patented Apr. 27, 1948 PROTECTIVE COVERING FOR PREVENTING ACCUMULATION OF ICE ON AIRFOILS John 0. Antonson, Akron, Ohio, assignor to The B. F. Goodrich Company, New York, N. Y., a corporation of New York Application December 29, 1944, Serial No. 570,308

This invention relates to protective coverings for the surf-aces of structures such, for example, as aircraft and other vehicles, and especially to covering apparatus for preventing the accumulation of ice on the leading edges of wings and other airfoils, empennage fin structures, struts, and other structures of aircraft.

It is an object of the invention to provide a protective covering having inflatable passages positiioned over the chordwise extent of the leading edge coverage, which passages are of a size and expansive excursion commensurate with the thickness of ice at the respective positions so that the individual passages are most effective for-ice removal at their individual positions and at the same time offer minimum aerodynamic disturbance. Related objects are to provide for maximum effectiveness of ice removal throughout the extent of the covering together with maximum security of attachment against objectionable lifting under aerodynamic forces, and to provide for cleanliness of aerodynamic design.

Other objects are to provide inflatable coverings adapted for arrangements of varied chord- Wise extent as desired, especially for thick-section airfoil-s; to provide for distending such coverings at chordwise positions in accordance with the requirements of the ice formations at such positions for effective removal of the ice; to provide for removing effectively heavy ice-caps over the central zones of the inflatable coverings and for removing effectively very thin ice formations throughout the extent of such coverings; to provide inflatable ice-removing means of varied expansive excursion in adjacent portions of the coverings for outwardly distending the coverings into spanwise ridges in series, which ridges in the central zones of the coverings at the regions of sharp curvature of the leading edges are relatively larger than the ridges in the rearward portions of the coverings at the regions of lesser curvature of such leading edges; to provide inflatable passages in the coverings which passages are of uniform size along their extent but are decreasing in width as the radii of curvature of the leading edges increase; and to provide for simplicity of construction, efficiency. of operation, and facility of installation.

Further objects of the invention are to provide for distending the central zones of the coverings with little or no exertion of stretching force on portions of such coverings extending rearwardly from the central zones; to provide for preventing objectionable lifting of the coverings away from the supporting surfaces despite the distention of the coverings and especially such lifting at the rearward portions thereof; to provide for venting Claims. (Cl. 244-134) the coverings; to provide for the secure attachment of the coverings, especially along the margins of the central zones thereof; and to provide for maintaining the aerodynamic characteristics of the airfoils.

These and other objects and advantages of the invention will be apparent from the following description.

In the accompanying drawings which form a part of this specification and in which like numerals are employed to designate like parts throughout the same,

Fig. l is a perspective view from above of a twin engine aircraft having protective coverings disposed thereon and constructed in accordance with and embodying the invention, parts being broken away,

Fig. 2 is a plan view from above of the covering before attachment to the leading edge of a wing or other airfoil of the aircraft,

Fig. 3 is a sectional view on an enlarged scale taken along line 3-3 of Fig. 2,

Fig. 4 is a view like Fig. 3 taken along line 4-4 of Fig. 2,

Fig. 5 is a perspective view showing a manifold arrangement for inflating a series of tubes, parts being broken away and in section,

Fig. 6 is a view like Fig. 3 taken along line 6--'5 of Fig. 4,

Fig. '7 is a view like Fig. 3 taken along line 1 of Fig. 2,

Fig. 8 is a View showing the covering installed on the airfoil and showing distention of the covering at the central zone thereof, parts being broken away and in section,

Fig. 9 is a view like Fig. '7 but showing distention :of the covering in portions thereof extending rearwardly from the central zone,

Fig. 10 is aplan view like Fig. 2 showing a modification of the covering,

Fig. 11 is a sectional view on an enlarged scale taken along line 'll-Il of Fig. 10, parts being broken away, and

Fig. 12 is a view showing the modified covering installed on the leading edge of an airfoil, parts being broken away and in section.

In the illustrative form of the invention shown in Figs. 1 to 9 inclusive, protective coverings l5, l5a, each comprising a body 25 of elastic material such, for example, as resilient rubber or other rubber-like material having inflatable passages extending spanwise therein, may be positioned at the leading edge of an airfoil or wing ll of an aircraft l8, which aircraft includes a fuselage IS, a streamlined motor housing 20 at such leading edge, and a propeller 22. The coverings are desirably of generally rectangular shape but may be tapered or other suitable shape, the ends of which, for example, at I50! and We of the covering l 5, may be tailored to fit as desired especially along the sides of the fuselage or the motor housing, or both, in order to conform to the curvature thereof and for facilitating venting at such ends, if desired, by virtue of the interference eflects which cause greater negative pressure closely adjacent such sides than are present around the profile of the wing at a distance from the junction of such parts and the wing. The coverings l5, l5a, are constructed alike except with respect to the tailoring at the ends thereof, in view of which only the construction of the covering IE will be described in detail hereinafter.

For effective ice removal substantially through-- out the extent of the covering [5, the invention provides spanwise-extending inflatable tubes 3t and 31 having walls of suitable resilient rubberlike material, which walls may be reinforced with highly extensible fabric therein, the tubes being positioned in series within the covering and over the chordwise extent of the leading. edge coverage and being of a size and expansive excursion commensurate with the thickness of ice deposited at the respective positions so that the individual tubes are most effective for ice removal at their individual positions and at the same time offer minimum aerodynamic disturbance. The highly extensible reinforcing material in the walls of the tubes may be stockinette or other knitted or otherwise stretchable fabric, preferably of nyion-or rayon, although cotton or other suitable material may be used. The nylon sto'ckinette fabric is stretchable both circumferentially and longitudinally of'the tubes-Which permits stretching of the tube walls for expanding the covering locally at such tubes to break and loosen the ice thereon.

The inflatable tubes '36" are disposed spanwise along a front portion or central zone [5f of the covering l5 for positioning at the region of sharp curvature of the leading edge of the wing I! where heav ice-caps graduated-in-thi'ckness substantially symmetrically about the chord line of the wing tend to be deposited. The tubes 36 in such central zone are arranged in series'chordwise for positioning symmetrically about the chord line 38 of the leading edge, the widths of the tubes being graduated so that such widths decrease with the increase in radius of curvature of such leading edge and hence are proportioned in accordance with the change in thickness of the ice deposited thereon. Such an arrangement toether with the extensible wall construction makes possible a change in the extent of the local distention of the covering at each of such tubes with respect to that of an adjacent tube and a corresponding change in the extent of stretching of the outer surface material of the covering for effective ice -removal at such central zone 151. In the preferred constructioma plurality of graduated tubes 36' are provided in the rubber material of and substantially throughout the extent of the central zone, the adjacent tubes of greatest width, which, for example, may be 2 inches, being disposed symmetrically about the longitudinal center line of such zone, which center line corresponds to the chord line 38 when. the covering is mounted on the airfoil.

When the tubes 36- are inflated, preferably simultaneously, they distend outwardly from the wing ll, as shown especially in Fig. 8, and assume a relatively sharp curvature afforded by a semicircular shape in sectionby virtue of the uniform and high stretchability of the walls thereof. As the tubes 36 are thus highly distended, they operate not only to crack the heavy ice-cap on the leading edge but also operate to shift the pieces of the cracked ice-cap somewhat in the chordwise direction so as to subject such pieces to the force of the airflow rather than to permit the pieces of ice to remain static especially in the stagnation region immediately at the chord line'38;

The local outward distention and stretching of the series of symmetrically graduated tubes 36 aboutthe chord line at the region of sharp curvature of the leading edge has been found to be especially elfective in the full and prompt removal of the heavy ice-caps which tend to form at such region. By virtue of such localized distention and stretching of the tubes especially along. the oppositemargins of the central zone I57, little or no exertion of stretching force is imparted to rearwardly extending portions" l'5g and l57r of the covering l5. Also, such local action of the tubes 36 avoids to a; large extent outward movement of such rearward portions relative to the supporting surface of the wing l1 thereby avoiding entrapment of substantial quantities f air beneath the covering and preventing objectionable bulging thereof.

In prior constructions of protective coverings in which a stretchable rearward portion between a central inflatable tube zone and an attached margin has been subjected to stretch for removing ice from such portion upon the inflation of each tube in such zone; the action of such coverings under some ice conditions of particular severity has not been effective to obtain full cleanliness of ice removal in the stretchable portion and. the tube zone. The rapidly repeated stretching of the stretchable rearward portion has under some ice conditions tended to" craz'e or merely crack theice repeatedly rather than break or remove it thoroughly from the surface of the covering. To'the end of overcoming such difficulties, the invention further provides inflatable tubes 3! in series and extending spanwise substantially throughout the extent or the rearward portions lbg and I'5h of the covering between the central zon'e I5fand attaching margins 26 and 21. The tubes 31 which are positioned preferably closely adjacent one another, may be of the same construction as the tubes'36 except that each of thetubes 31 may be of the same diameter such, for example,- as inch and relatively small in width as compared to that of the large tubes 36. By virtue of their construction, the respective series of tubes 31, which tubes are desirably inflated simultaneously, distend locally at each tube 31 and. distend the outer surface of the covering at suchv rearward portions into ridges of relatively small radius of curvature thereby effectively breaking the bond of the ice deposited. and lifting and rocking the latter for removal by the scavenging action of the flow of the ambient air.

For inflating the'tubes 3'! in each of therearward portions [5g and l5h, the invention provides respective manifolds 40 and M of suitable construction, desirably in the covering, in communication with the respective series of. small tubes 37. Such manifold construction may comprise locally slitted portions of the tubes including annular tape reinforcing elements 31a of suitable fabric at the junctions of such portions adhered thereto whereby the walls of the tubes define the interconnecting manifold passageway,

as shown especially in Figs. 2, 4, 5 and 6, in which Figs, 4 and 5 the tube walls, for purposes of clarity, are shown in separated relation although they may be contacting one another for the defiated condition of the covering. A manifold 42 of similar construction to the manifolds 46 and 4| and within the covering in communication with the tubes 36 in the central zone [5 provides for inflating such tubes simultaneously. The manifolds 40, 4| and 42 are connected to a suitable source of air :under pressure, which may be disposed, for example, within the fuselage of the aircraft, by means of suitable conduits (not shown) extending from connection members 43, 44, 45 and 46 to such source of air, the respective connection members being in communication with the respective manifolds 46, M and 42 as shown especially in Figs. 2, 4 and 5.

The covering [5 may be provided with a highly elastic fabric reinforcement 54 in the rubber body thereof substantially throughout its entire extent, which reinforcement is adjacent the under surface of the covering and beneath the inflatable tubes 36 and 31. This highly elastic fabric is stretchable chordwise and such result may be provided by a woven fabric having straight warp threads with adjacent filling threads highly twisted in reverse directions, which fabric has extensive stretchability along the filling threads,

being stretched, being in itself highly resilient.

Thus, both the rubber and the fabric are better able to resist the development of objectionable permanent set. The elastic fabric is advantageous in giving added resistance throughout its coverage to objectionable lifting of the covering in any part of its extent and also is not subject to objectionable contraction spanwise of the covering. Such an arrangement, by virtue of the elasticity of the reinforcement 54, further facilitates maintaining the covering in the desired condition of relatively uniform stretch between the attaching margins '26 and 21 and also minimizes objectionable restriction to the expansive excursion of the tubes with respect to the leading edge.

To facilitate the attachment of the covering l5 to the wing 11 along spanwise margins 26 and 21, each such margin 26, 21 includes desirably a bead reinforcement 28 of stiff material such, for example, as flat steel wire imbedded in the rubber body 25 and around which bead wire may be positioned a folded strip 29 of relatively nonstretchable fabric material such, for example, as square-woven bias-cut fabric of cotton, rayon, silk and other filamentary material. The covering I5 is mounted on the leading edge of the wing l1 in a condition of stretch between the margins '26 and 21 and secured thereto as by suitable spaced-apart screw fasteners 30 and 3| extending through fairing strips 33 and 34 of aluminum or magnesium alloy, for example, seated in marginal recesses 35, 35 in the rubber body, through the covering inwardly of the bead wires 28, 28, and engaging threaded members 32, 32 suitably attached to the skin or other structure of the wing H, as shown especially in Figs. 8 and 9. Such marginal arrangement makes possible substantially smoothv surfaces across th margins 26 and 21 whereby turbulent rality of spaced-apart chordwise-extending venting grooves such, for example, as the grooves designated by the numerals 49, 56, 5| and 52, although a greater or lesser number of grooves may be provided, if desired. The venting grooves are each in communication with the atmosphere through suitable apertures 53 in the rearward portions I50 and. l5h, as shownespecially in Figs. 2 and '7. Thus all parts of the undersurface of the covering are in communication with the outside atmosphere through such channels and venting grooves, the air flowing therethrough in directed paths from such parts of the undersurface to the outer regions of lesser pressure. This arrangement provides effectively for venting the covering including the central zone and preventing objectionable lifting thereof relative to the airfoil.

.In the operation of the rotective covering [5,

the series of tubes 36 in the central zone I5 are desirably inflated simultaneously and first in the cycle of inflation. The tubes 36 distend locally outward relative to the wing, as shown especially in Fig. 8, with little or no exertion of stretching force imparted to the rearward portions 159 and i5h. Such distention distorts the covering at the region of sharp curvature of the leading edge into symmetrically graduated ridges about the chord line and correspondingly stretches the material of the outer surface of the covering at such region, thereby effectively cracking and breaking the ice deposited into pieces and moving such pieces especially chordwise into the flow of air for subjecting such pieces of ice to the scavenging action of the air, The respective tubes 36 coact one with another in effectively removing the ice at such region of sharp curvature even though the ice be in the form of heavy ice-caps or a relatively thin film.

In the second phase of the cycle of inflation, the respective series of tubes 31, 31 in each of the rearward portions l5g and [5h are desirably inflated simultaneously distending the covering locally at such portions into substantially uniform and relatively small ridges as compared to those at the central tube zone, as shown especially in Fig. 9. Such inflation of the small tubes 31, 31 also stretches locally the material of the outer surface of the rearward portions I 5g and l5h. In this manner the relatively thin ice deposited at such portions is removed effectively by the breaking and cracking action of the tubes 31, 31 permitting the flow of ambient air to remove the cracked pieces therefrom throughout the extent of the rearward portions.

Since the covering is in a condition of relatively uniformly transmitted stretch throughout the rubber body 25 especially at the elastic fabric 54 beneath the tubes, the inflation of the tubes '36 and 31 causes only minor inward distention relative to the wing, which inward distention is resisted by the stressed fabric 54 and rubber material at the undersurface; hence the covering 7 may be lifted away from the wing only a relatively small extent thus avoiding entrapment of harmful quantities of air between the covering and the wing skin. However, the relativelysmall quantity of air which-may be entrapped beneath the covering, quickly flows in directed paths through the venting channels andgrooves in such undersurface and through the respective venting apertures to the outer atmosphere. Also, when the channels i8 extend to the ends 1511 and le of the covering, the entrapped air is vented additionally at such ends by virtue of the changing negative pressures around the profile of the wing especially when such ends are "positioned to take advantage of the interference effects at the junctions of partsoi the aircraft, as described hereinabove. Thus, the respective elements comprising the covering coact one Withal'lothfii' in combination to provide a covering capable of removing .efiectively ice deposited on'the leadin edge of the wing regardless of-the thicknesscharacteristics of such ice.

The modified construction 60 ofthe covering shown in Figs. 10, 11 and. 12 is in many of its aspects like the covering I5 and isapplicable especially to the leading edges of thick-section wings and where extensive chordwise coverage maybe required. The covering '60 includes abody 61 of suitable resilient rubber-like material and also includes a front or central tube portion or zone 62 for the sharply curved region of the leading edge and rearwardlyextending portions-63 and for the relatively less-sharply curved regions of the leading edge.

For efiectively removing the ice deposited at the "front portion or central tube zone 52 by the outward distention of the latter, two relatively large inflatable tubes '66 and 6] having walls of suitable resilient reinforced-rubber construction may be positioned within the covering symmetrically about the longitudinal center line 65 of said zone and extending in side-by-side relation in the spanwise direction along such zone, as shown especially in Fig. 10. However, a greater or lesser number of such tubesym'ay be provided in such zone 62. The width of each of the tubes 63 and 51 is desirably such that their combined width coverage includes the major part of the chordwise extent of the zone 62 betweenattaching margins 68 and 69 providing relatively narrow venting regions adjacent such margins, in which regions may be respectively a series of spaced-apart venting apertures 10 and ll extending through the covering.

The large tubes 66 and B1 are preferably inflated simultaneously and for this purpose a suitable manifold i2 and connection member 13 arrangement in communication with the tubes is provided, the connection member 13 being interconnected With a suitable source of air under .pressure, as described hereinabove for the covering 15. When the tubes 66 and 61 are inflated, they distend locally outward from the leading edge and assume a relatively sharp curvature afforded by a semi-circular shape in section by virtue of the uniform and high stretchability of the walls thereof. For thedistended condition of such tubes, they operate not only to crack the heavy ice-cap on. the leading edge, but also operate to shift the pieces of the cracked icecap somewhat in the chordwise direction so as to subject such pieces to'the force of the airflow rather than to permit the pieces of ice to remain static especially in the stagnation region immediately at thechord line 14 of the lead- 8 ing edge. Such chord line corresponds to the center line 65 of the'covering 60 when the latter'is mounted on the leading edge.

The coveringfifl at the central zeneiiZ is maintained in a condition of stretch between rearwardly extending underlying portions or attaching margins 68 and 69. To the end of providing uniformity of stretch throughout the extent of the zone togetherwith reinforcing the rubber body of such zone, it is desirable that a suitable highly elastic fabric reinforcement 15 be disposed in such rubber body adjacent the undersurface thereof and *beneath the inflatable tubes-66 and '61, such fabric reinforcement extending around reinforcing metal bead wires 68a and 69a and between the attaching margins 68 and "69. The zone62 of the covering 60 is attached to the leading edge of the wing as by suitable screw fasteners extending through the underlying portions 68 and 69 and bead Wires 68a andBHa and engaging interiorlythreadedhollow rivets 18 sultably attached to the skin or otherstrueture'of the wing, as shown especially in Fig. 12.

For'coacting with the venting apertures H! and H to vent the zone 62, the rubber undersurface 0f suc'hzone maybe provided with a multiplicity of suitable spanwise ribs 62a and venting-channels 16% throughout the extent thereof and the venting channels may also be in communication with the atmosphere at the ends 16 and T! of the covering for advantageously permitting endventing action by virtue of interferenceefiects at such ends in the manner described above for the covering l5. It has been found that chordwise venting grooves may be dispensed with, if desired; since the aforesaid end-venting action in combination with the venting of the respective series of venting apertures 10 and H is usually sufficient to accomplish the desired venting.

To facilitate mounting the rearward portions 63 and 54 after the central zone or portion 62 has been attached to the leading edge and to make possible continuity of smooth surface-over the attaching margins, in continuation with the 'outersurface of the central zone, the rubber body of the covering is divided into rearwardly extending underlying and overlying portions Stand 69, and 63a and Ma, respectively, and the oppos- .ing areas ofsuc'h portions are in unadhered relation immediately at the respective attachin margins, as shown especially in Fig. llat 19 for the margin '68. The overlying portions or inner marginal-23a, 64a of the rearward portions extend over the attaching margins and are secured integrally to the rubber body of the central portion '82. With this divided marginal arrangement, the underlying attaching margins and screw fasteners are covered by the overlying portions 63a and 64a of the rubber body at such marginal regions; thus providing the desired smooth outer surface continuity.

The rearward portions 63 and -34 including the overlying portions 153a and 64a are each provided with a series of inflatable tubes 81 tin-therein having walls of suitableresilient reinforcedrubber construction which tubes are relatively small in width as compared to the large tubes 63 and 5?. The tubes :89 in each of the rearward portions extend desirably spanwise in side-byside, closely adjacent relation throughout chordwise coverage of such rearward portions, except at rearward margins 8i and 82 of such portions 63 and, which latter margins are desirably tapered to a relatively thin edge, as shown especially in Fig. 12, for facilitating smooth flow of air thereover. To provide continuity of ice removal from the central tube zone rearwardly, the respective series of inflatable tubes 80, 80 in each of the rearward portions 63 and 64 begins with respective tubes 83 and 84 positioned in the overlying portions 63a and 64a of the covering at the attaching margins 68 and 69 where the distending and stretching action of the large tubes 68 and 61' may not be entirely effective to remove ice by virtue of such attachment and the local distending action of such tubes 66 and 61. Each of the respective series of tubes 89, 80 are desirably inflated simultaneously and for this purpose suitable manifolds 85, fitand connection members 81, 88 in communication with such series of tubes 80, 80 and with a suitable source of air under pressure are provided.

The rearward portions 63 and B4 are adhesive- 1y or otherwise suitably secured to the wing throughout their extent and may be reinforced in the rubber body thereof by a reinforcement 89 of relatively non-stretchable fabric material such, for example, as square-woven bias-cut cotton fabric. The rearward portions 63 and 64 may be slightly tapered in section, as shown especially in Fig. 12, for providing continuity of relatively smooth curvature of the covering 68 around the profile of the leading edge thereby facilitating maintaining the aerodynamic characteristics of the wing.

In the operation of the covering 6E1, the large tubes 68 and 61 are desirably inflated first distending the covering at the central tube zone into relatively large spanwise ridges for breaking and cracking the ice thereon and. permitting its removal by the flow of ambient air. Such distendlng action of the tubes being localized between the attaching margins 68 and 69, imparts little or no stretching force to the rearward portions. Air, which may be trapped within the central portion upon inflation of the large tubes, is vented rapidly to the atmosphere through the venting channels at the respective ends 16 and 11 and the series of venting apertures 10 and H thus preventing objectionable bulging at such zone.

In the second phase of the inflation cycle, the tubes 80, 80 in the rearward portions are desirably inflated simultaneously thereby distending such portions outwardly into a series of relatively small spanwise ridges beginning at the attaching margins 68, 69 which effectively cracks and breaks the icedeposited thereon into pieces for removal by the flow of air. Since the rearward portions are adhesively secured to the wing, objectionable bulging and movement of the rearward portions is effectively eliminated regardless of the chordwise extent thereof and venting of such rearward portions is likewise eliminated. Thus the construction of the covering 6|] provides advantageously for effectively removing ice from the leading edges of thick-section airfoils and facilitates providing chordwise coverage of the leading edge to any desired extent in addition to facilitating installation thereon.

The fabric and rubber parts of the coverings l and BI] are united desirably by vulcanization under heat and pressure.

Variations may be made without departing from the scope of the invention as it is defined in the following claims.

I claim:

1. Apparatus for preventing the accumulation of ice on a surface exposed to ice-forming conditions in airflow, said apparatus comprising a covering of elastic material for said surface ineluding a front portion and a rearward portion and including a plurality of inflatable passages in each of said portions for distending said covering into a series of ridges, said plurality of passages in said front portion being wholly disposed within the latter said portion and of widths gradually narrower throughout their lengths toward said rearward portion, and said plurality .of passages in said rearward portion being wholly disposed therein closely adjacent one another and being of less width throughout their lengths than the width of each of said passages in said front portion, whereby said covering is distensible into ridges relatively small and closely adjacent one another in said rearward portion as compared to the ridges in said front portion.

- 2. Apparatus for preventing the accumulation .of ice on the sharply curved and relatively lesssharply curved regions of the leading edge of an airfoil, said apparatus comprising a covering for said leading edge including a distensible portion for said sharply curved region and. a second distensible portion for said less-sharply curved region, said portions having a chordwise series of inflatable passages extending spanwise thereof and said second portion having a plurality of said passages wholly disposed therein closely adjacent one another, a passage in the first said portion being of a greater width than the width of individual passages in said second portion, and the closely adjacent passages in said second distensible portion having aligned openings directly through the adjacent Walls thereof for simultaneous inflation of said passages.

3. Apparatus for preventing the accumulation of ice on the sharply curved and relatively lesssharply curved regions of the leading edge of an airfoil, said apparatus comprising a covering for said leading edge including a distensible portion for said sharply curved region and a second distensible portion for said less-sharply curved region, said portions each having a plurality of inflatable passages extending spanwise thereof for distending the latter, said passages in the first said portion each being relatively greater in width than the width of individual passages in said second portion, and said plurality of passages in each of said portions being wholly disposed closely adjacent one another in the portion and having aligned openings directly through the adjacent walls thereof for simultaneous inflation of the passages of the portion.

4. Apparatus for preventing the accumulation of ice on the sharply curved and relatively lesssharply curved regions of the leading edge of an airfoil, said apparatus comprising an elastic covering for said leading edge including a zone for said sharply curved region and a portion extending rearwardly from said zone for said lesssharply curved region and said covering including a plurality :of inflatable passages wholly disposed in said zone closely adjacent one another and being of widths gradually narrower toward the rearward portion, the closely adjacent pas sages in said zone having aligned openings directly through the adjacent walls thereof for simultaneous inflation of said passages, and a plurality of inflatable passages wholly disposed in said rearward portion closely adjacent one another for distending said covering into ridges closely adjacent one another in said rearward portion, the latter said passages in said rearward portion being individually of less width than the width of a passage in said zone and having aligned openings directly through the adjacent 11 walls of the closely adjacent latter saidpassages for simultaneous inflation of the latter said passages.

5. Apparatus for preventing the accumulation of ice on the sharply curved and relativelyv lesssharply curved regions of the leading edge of an airfoil, said apparatus comprising a covering for said leading edge including a distensible portion for said sharply curved region and a second distensible portion for said less-sharply curved region, said portions each having a plurality of inflatable passages wholly disposed thereon and extending generally parallel to one another for distending said covering into ridges, said passages in the first said portion each being relatively larger in width than the width of each of said passages in said second portion, and said plurality of passages in said second portion being disposed closely adjacent one another and having aligned openings directly through the adjacent walls thereof for simultaneous inflation of said passages. a

6. Apparatus for preventing the accumulation of ice; on asurface exposed to ice-forming conditions in airflow, said apparatus comprising. a coveringof elastic material for said surface divided at a margin thereof into an underlying portion and a portion. overlying the same and extending rearwardly of saidmargin, portions of the covering: forwardly and rearwardly of said margin being distensible' and having a; plurality of inflatable passages therein for distending the covering into a series of ridges, a plurality of passages in. the rearward distensible portion wholly disposed within the latter said portion closely adjacent one another and being individually of less width than a passage in the forward distensible portion whereby said covering is distensible into ridges closely adjacent one another. in said rearward. distensible portion and relatively small. in said rearward distensib'le portion as compared to a'ridge in. said forward; dist'ensible,portionv of the covering, and means for mounting the covering by attachment through said underlying portion.

7; Apparatus for preventing. the accumulation of. ice: on a surface exposed to. ice-forming conditionsin airflow, saidapparatus comprising a coverin-g ofv elastic material for said surface divided at a. margin thereof into an underlying portion and a portion overlying the same and: extending rearwardly of said margin, portions of the covering forwardly and rearwardly of said. margin including said portion overlying the margin being distensible and having a series of inflatable passages therein for distending. the covering into a series of ridges, a plurality of passages in. the rearward portion including a passage in said portion overlying said margin wholly disposed therein closely adjacent one another and being individually of less width than. each of the passages inthe forward portion of the covering, whereby said covering is distensible. intoridges relatively small and closely adjacent one another in said rearward. portion including the overlying-portion as compared to the ridges in said forward portion of the covering; and. means for mounting the covering by attachmentthrough saidu-nderlying portion.

8. Apparatus for preventing the accumulation of: ice on the sharply curved and: relatively lesssharply curved regions of the, leading edge of an airfoil; said apparatus comprising a covering of elastic material for said leading. edge including a portion for said sharply curved. region having a rearward marginfor attachment of the covering to said leading edge and aportion overlying said margin and extending rearwardly from the first said portion for coverage of said less-sharply curved region, said portions being distensible and having a plurality of inflatable passages extending spanwise therein for distending the covering into a series of spanwise ridges, a plurality of passages in the rearward distensible portion wholly disposed therein closely adjacent one another and being individually of less width than a passage in the first said portion whereby said covering is distensible into ridges closely adjacent one another in said rearward portion and relatively small in said rearward portion as compared to a ridge in the first-said portion, and means for attaching the covering at said margin to said leading edge.

9. Apparatus for preventing the accumulation of ice on the sharply curved and relatively lesssha'rply curved regions of the leading edge of an airfoil, said apparatus comprising a covering of resilient rubber-like material for said leading edge having, attaching margins and including a central zone .for said sharply curved region, rearward portions extending-from the margins of said zone for said less-sharply curved regions, means for attaching the covering at said. attaching margins to said surface, .anda plurality of inflatable tubes extending spanwise in said zone and: said rearward portions, said tubes in said zone being of widths gradually narrower toward therearward portions, and said tubes in said rearward portions. being less in width than the width of each tube insaid. zone whereby the expansive excursion .of said tubes in said Zone and said portions is in accordance with the thickness of the ice deposited at-the respective positions of i the tubes.

10. Apparatus for preventing the accumulation of ice .on thesharply curved and relatively less-sharply curved regions of the leading edge of an airfoil, said apparatus comprising a covering of resilient rubber-like material for said leading edge including a central zone for said sharply curved region and portions extending rearwardly from said zone for said less-sharply curved regions, said covering at said zone comprising spaced-apart attaching margins, a pair of" inflatable tubes extending spanwise between said margins and a layer of said material thereover, each of the rearward portions comprising a plurality of inflatable tubes extending spanwise closely adjacent one another each of which being relatively small as compared to the first said tubes, and a second layer .of said material thereover in continuation of the first said layer and overlying said attaching margins for presenting a substantially smooth outer surface of the covering at the attaching margins, and means for mounting said covering at, said attaching margins tosaid leading edge and, for securing said rearward portions to said leading edge.

JOHN 0-. ANTONSON.

REFERENCES CiTED' The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,990,866 Gregg Feb. 12, 1935 2,3210% Geer Aug. 17, 1943 2,306,759 Sears Dec. 29, 1942 1,998,809 Geer Apr. 23, 1935 Certificate of Correction Patent No. 2,440,240. April 27, 1948.

JOHN O. ANTONSON It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 11, line 12, claim 5, for the word thereon read therein;

and that the said Letters Patent should-be read with this correction therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 1st day of March, A. D. 1949.

THOMAS F. MURPHY,

Assistant Gammz'ssioner of Patents.

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