US 1909186 A
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IRPLANE WING File d Fe
@ets-S heet May 16, 1933 v. L OUGHEED 1,909,186
AIRPLANE WING Filed Feb. 9, 1951 2 Sheets-Sheet 2 INVEN-ron Patented May 16, 1933iy UNITED STATES I VICTOR LOUGHEED, OF WASHINGTON, DISTRICT OF COLUMBIA AIRPLANE WIN'G;V
Application filed February 9, 19x31. Serial No. 514,619.
My discovery or invention thus relates primarily to the sustaining elements of air'- planes, since it has for its obj ect the provision of a novel type of sustaining element,`of increased lift and decreased drag-With application to control surfaces, to render them also more effective, as a secondary object-all for the purpose of improving, and rendering4 more efficient and safe, airplane performance and operation.
ln its essential features, my discovery, or
invention consists in the combination, with sustaining surfaces of suitable cross-sectional forms, of coverings therefor possessed of teX- 5 ture characteristics which exert a positive and beneficial control upon the relative airfiow over and beneath such surfaces.
While, to yield its greatest gains in the way of improving airplaneefficiency, my discovery or invention demands combination With the most suitable Wing plan forms and sections, of the most suitable textures of coverings, its application even in inferior embodiments can be of some benefit, for which reason I do not limit this specification or the vclaims hereof to its best embodiments alone.
As pointed out at greater length in the specification of an earlier rUnited States patent application, Serial Number 328,982, filed by me on December 28, 1928, and also relating to the control of airflow `over airplane surfaces, all natural flightis accomplished with Wings provided with very deep undercamber or concavity, whereas all established artificial flight depends upon the use of sustaining elements the undersides of Which are only most slightly undercarnbered, if at allbeing more often flat or even convex. The reason for this is that, in designing his Aartificial sustaining elements, man has not heretofore learned how to control the relative airflow to the contour of an undercambered wing. And I have discovered that such flow ycontrol is a means for rendering the deeply undercambered wing-useless without it-a much safer and more efficient device for transporting a load upon the air than it is possible to make of the conventional, substantially fiat-bottomed airfoils of present ,cross section, quite similar to the cross section accepted and universally-prevailing airplane practice.
With the above and other objects in View, my invention consists in the construction and arrangement of parts as will be described more fully hereinafter. l i
Reference is to be had to the accompanying drawings forming a partof the specification,- inwhicli like reference characters indicate corresponding partsfthroughout the several views, and in which:
Figure 1 shows a cross-sectional and partial-plan view of an airplane wing embodying features of my discovery or invention.
Figure 2 is a cross-section of adeeply canibered wing with airfiow'around it indicated by streamlines and arrows, showing the desirable type of flow produced when the fiow is controlled. K ,n
Figure 3 represents the same wing cross section of Figure 2, but in this case surrounded by airflow of the undesirable type which normally occurs inthe absence of flow control.
Figure 4 shows a ,conventional air'foil,
of Figure 3 excepting that in this case vsolid structure is substituted for turbulent air, the
airflow in Figure l being substantially the same as in Figure 3. f
Figure 5 shows the cross section of Figure inclined at the stalling angle, and depicts the resulting appearance of a zone of turbulence, Within the streamlines, above the section.
Figure 6 is designed to indicate the manner in which the Wing of my discovery or invention rides upon a solitary Wave of` translation?7 through the air.
Figure 7, in contrast to Figure 6, shows how a Vconventional airfoil section must progress against what might be called a wave of defiection, through the air.
Figure S, in contradistinction to Figure 1,
is designed to explain objections to attempts to control flow around a structure which is feature of a movable front edge, as a substitute for ailerons and as a means for controlling camber.
Figure l0 shows a wing section, embodying a modified form of my discovery or invention.
Figure ll shows a wing section embodying my discovery or invention as applied to a structure which is doubled surfaced.
Figure l2 shows a section of surfacing as applied to a wing embodying my discovery or invention.
Referring now to Figure 1, it is to be noted that in two essential respects the wing of this illustration uniquely differs from wings of present accepted and universally prevailing airplane practice` p The first of these differences is that, in its cross section from its chord A to B it is deeply concaved beneath, or undercambered, being arched to such an extent that the vertex of the undercamber, at 20 may advantageously be, for some application at least, at a height above the chord line A-B of even as much as one sixth of the chord length AWB.
Now, to explain more in detail, it is well known, and it is a fact derived from all flight experience and wind-tunnel investigations by others to date, that in any attempted application to artificial flight such a cross section as the one shown in Figure l, considered merely as such a cross section., will not, when operated at optimum incident angles to the relative airflow, afford high lift/clingl ratios-though it will commonly afford high lift coefficients, but the value of which is offset by the excessively high drag coefficients. It is also well though perhaps not so widely known, that the high drag of such curved surfaces is primarily consequent upon a failure of the streamlines of the relative airflow to follow with any parallelism the contour of the undersurface of the section. Instead of flowing as shown at D, Figure 2, they take a tangent course, parallel to the chord line as depicted at E, Figure 8. The hollow undercamber or concavity then fills up with dragged air, as at F, Figure 3, which fairly boils or seethes with turbulence, so wholly destroying all ltendency towards the smooth laminar flow which is illustrated at D in Figure 2, and so wastefully consuming energy.
It is this sort of situation, convincingly den'ioi'istrated to exist both by wind tunnel research and by mans flight experience, and never in any artificial flight structure escaped from by any discovery or invention that has been made heretofore, which has forced upon modern flight-engineering practice, as the best type of sustaining element heretofore available, such airfoil sections as that shown in Figure ll. And a most significant feature of this type of surface is its resemblance to the wing of Figure 3, with the place of the useless, turbulent air at F 4sealed over or filled up with solid structure,
which at worst is less detrimental than the turbulent airit takes the place of, and which at least possesses the positive merit that it conduces to a maximum combination of needed strength with lightness.
lV ith this section of Figure, il, the problem of securing laminar flew is much simpler than it is with the section of Figure This is because, .regardless of surface texture-within the limits of reasonable smoothness-the streamlines at incident angles appropriate to normal operation take naturally the courses LE shown in Figure 4, which are quite the same of those of Figure 3. But, differing from the case of Figure 3, that of Figure l involves little or no turbulence excepting at very high incident or stalling angles, when the upper flow L breaks away somewhat as depicted in Figure 5, with the consequent development of the turbulent zone at H.
The other respect in which the wing of Figure l difl'ers uniquely from wings of present and universally prevailing airplane practice, resides in the novel coniibinatien it pre scnts, of the deeply-arched or cambered slction, having a hollow or concave underside, with th month or predominantly-impcrvious portion 2i forward of the vert-cx of the iuidcrcaniber, and with the predominantlypervious portion 22 rearward of the vertex of the undercainberthe latter constituted of a relatively-thin single or 1multi-ply surface penetrated with a great number of tiny porclike vesicles 23.
The effect of this novel combination, during the functioning of the wing along a path of air, is to control the relative airflow in such a manner that the streamlines adopt the laminar paths, close to the wing substantially parallel to the contours of the section, which are portrayed in Figure Q., and which by so hugging the profile of the section eliminate the zone of turbulence shown at F, Figure 3.
Consequently this wing, as it is translated along through a mass of air, efficiently resists the gravitational stress, ever acting to pull it down, by riding smoothly on a solitary wave of translation (of the type first described by the great Scottish engineer, John Scott Russell, in his book The lVave Translation in the Qcean of 1Water, Air and llther) as at LD, Figi'lre (i, produced by the action of the wing in the oncoming strata of air K, which after the smooth passage of the wing are restored to their original level P, at a point proxil'nate to the trailing edge of the wing. Hthin the wa ve LD` both ben neath and over the wing, the sums ofthe aerodynamic actions and reactions on the wing so nearly cancel eac-h other out that the economics ,of available energy untiliZa-tion are of a extraoriflinarily superior order. The resulting condition as respects powerinput becomes quite different from that crudely invoked in the greatly inferior principle of sust-entren by the treadmill effect of an inclined plane,
or its close relative, 'an airfoil, in the functiolnng of which the gravitational stress is inefhciently fought by forcibly driving downward at LE the oncoming strata of air K, Figure 7, to a new and lower level M as the plane passes over and leaves it. e
In the final restorations of atmospheric equilibrium which of coursemust follow even such inefiicient flying, these occur too remote in space and time from the airplane structure itself to yield back to it any return of the energy its violent passing has squandered.
The exact mechanism 4of the flow control, attained by the means provided by my discov-ery or invention, remains to be described. It is based upon thevfact that minute vesicles 23 within a wing surface, or surfacing, trapping or containingair which is attenuated to a. degree of subnormal pressure, relative to the pressure of the airflow across the vesicle mouths, becomes an effective corrective of the baffling boundary-layer problems, existence of which have been so long recognized to constitute one of the greatest obstacles in the way of further progress in flight engineering.
For such vesicles. by their suppression, or draining or blowing of the boundary layer, seem to substitute for the turbulence and velocity gradients that are properties of the boundary layer, a condition which may be termed gaseous shear, maintained or constan tly reformed, between the denser flowing air and the thinner trapped air, with the consequence that the flow becomes adherent to the vesicular surface-is subjected to flow controland, apparently, through some such phenomenon as gaseous shear is at the same time made to occasion less than the usual skin-frictional drag.
earlier patent application, Serial No. 328,982,
filed December 28, 1928, and shown in Figure 10,; or, in different areas, with both.
The surfacing of Figure 1 can'be slightly modified as shown in Figure 12 wherein the forward impervious portion 21 is provided with zones that have pervious surfacing 24 secured thereto and the rear portion 22 is provided in a similar manner with Zones of impervious surfacing 25. In the forward -portion 21 it is desirable to have all o at least a predominating part of the surfacing impervlous, while 1n the rear portion the surfacing 1s predominantly pervious with the possible exception of strengthening zones, cross strips or ribs as shown by surfacing 25. Certain details ofthe structure are of the utmost importance.
The part 2l of the wing of Figure 1, neces sarily somewhat vaguely defined herein as the forward portion, must be regarded substantially that portion forward of the vertexr of the undercainber, but it Vdoes not necessarily follow that the division between the impervious and the pervious portionsr of the wing must be made exactly at this vertex. The best place for the line of demarkation can be ascertained for any given case, of a.A
minate, the rearward portion 22 also is not l absolutely determinate, except by empiricism applied tothe given case.
The whole matter .is in no sensek a simple one of merely providing a wing with a porous surface. In addition tov the necessity for restricting thel porosity to a defined zone or Zones of a wing, the new combination involved in my discovery or invention requires that both the rate of air seepage throughthe surface and the texture of the surface be controlled within definite limits. Still more important the leak through thesurface must be straight through a single surface, and cannot be allowed to occur first into one element of a double surfacing, thence into a relatively extensive hollow space between such surfacings, and finally out through the other element of surfacing; with thecertainty that between the two surfaces much of the air will pursue lateral paths, parallel to the surfacings, and thence ultimately to escape at points not opposite to those of ingress, or even not through the opposite surfacingv at all, but on the same side as the side of ingress, as suggested by the curved arrows QR, Figure 8, instead of as at T, Figures 1 and 10.
Experiments so far conducted indicate that, at any rate for certain contemplated applications, a seepage of about two cubic feet per square foot (.61 cubic meter per square meter) per minute is fairly close to the optimum. But slower seepage will control flow to a valuable degree, particularly if the wing velocity is low; and greater seepagewill only subtract more or less from the maximum attainable wing loading. Also there may be some reason for supposing that a higher rate of leak is desirable with large wings than for small wings. And of course Ythe rate of leak varies with the pressure differential.
Obviously, any sjiiecited rate of leak, such as that suggested in the preceding parairraph for a given case, could be provided either by numerous smaller holes or by a few larger holes. And, with holes of any given size, the rate of leak will vary, even with the pressure differential constant, with any change of the length of the holes.
Here again there is found to be an optimum. It seems that the hole size must be appropriate to the known viscosity of the atmosphere-and in line mesh fabrics, thick and strong enough safely to carry the load upon them, it is found effective to have the spacing of the warp and weft threads such as to leave holes between them of effective area ranging from l/GO inch square to l/lQO inch square (.42 mm sq. to .21 mm sq.). There is some indication that fabrics woven of soft and rough threads are better than those constituted of hard tight threads. This may be because the openings in the first case are subdivided by numerous spray fibers, in which case it is to be taken as an indication that openings of even smaller dimensions than those suggested may be best.
The effect of water upon such porous surfacing, should it be allowed to close the pores in consequence of swelling of the threads, will spoil the eflieiency of the surface. There fore waterproofing or watcr-repellant treatment of the fabric, as by prolonged soaking in kerosene, for airplanes which are to be operated in wet weather, is a necessity. Manifestly, Such waterproofing must treat the fibers as individuals, as in cravenetting processes, rather than the fabric as a whole, since any partial or complete closing of the porcs, as by rubberizing, must impair or desti-oy the desired functioning.
As nearly as ,it can be analyzed and explained, the immediate interaction with the atmosphere of a wing designed as in Figure l, or in any other embodiment of my structure or invention, is both to improve the lift coefficient and to produce a powerful propelling pressure against the underside of the downcurved forward portion, which greatly reduces the drag coefficient. This seems to be because the seepage of the more highly compressed air from beneath the rear portion of the wing, through the tubular vesicles of its rearward surface, into the region of lessl1ighly-coinpressed air above the rear portion of the wing, constantly draws oilI the underside boundary layer and blows off the topside layer, and so controls the flow of the desirable type of Figure 2 instead of allowi d it to assume the undesirable type of Figure 3. rlhe flow control beneath is essential to eiiiciency; that on top is of greatest importance only as stalling angles are approached.
Making the entire forward Figure l, of the wing porous portion 21, seems ordinarily to have little effect in controlling flow, and ma y be damaging to su stention, therefore it may act to injure performance rather than to improve it.
A matter of great importante is that the rear portion 22 of the wing, Figure l, must not be double surfaced, unless its resulting hollow interior Q6 can be partitioned. as at 27, Figure 11, a structure somewhat difficult to carry out, and hence objectionable from the standpoint of practical structural engineering as applied to wing design.
The reason for this partitioning will become more clear upon reference to Figure 8, in which a wing similar to that of Figure l, but with the rear portion having an upper surface 28 and a lower surface Q9, is shown. In this, as in Figure l, the forward portion 2l is made impervious to air, while the two surfaces 29 and 29 of the rearward portion are pervious. But now, contrary to the case in Figure l, due to the space 2G between the two surfaces, the air passing' 'through the wing, as suggested by the arrow Il, Figure 8, under the influence of the positive underside pressure as expressed by the gradient J, and the negative topside pressure eX- pressed by the gradient O, no longer constrained to pass substantially straight through the wing, as at T Figure l, or as at S, Figures S and 1l, but may now distribute itself throughout the space 2G, after it has entered through the lower surfacing and bcfore it has emerged from the upper. Hence the certainty of transverse flow within the space 26, and, still worse, the certainty that much air passed through one surfacing may never pass clear through the wing, but may simply recirculate out through the same surface through which it entered, as suggested by the recurved arrows at Q. The result is that the beneficial functioning which is attained with the structure of Figure l may in that of Figure 8 be more or less completely or largely lost. Partitioning the hollow interior 26, Figure 11, as at 27, will reduce such objectionable recirculation of the air as is indicated by arrows S, but cannot wholly suppress it because of the structural impossibility of providing such partitions close enough to produce finel enough texture.
The thinness of the portion 22 of Figure 1, which if not single-layer should at most not exceed that of a few close and thin layers of suitable fabric, quilted together to avoid having space between them, of course de- 1n ands that the structural ribbing of the surface be external to rather than within it. I prefer to provide such structural stiffenirg in the forni of ribs 30, Figure l, which for best results should closely parallel laterally the relative airflow, which is not necessai-ily at all points parallel to the flight axis.
Such a structure can be easily made a flexible or deformable structure, and the combination of iexibility in the trailingportion,
with the other features of my discovery or invention, presents several important advantages.v F or one thing, a deformable elastic structure by yielding to shocks reduce their effect. F or another, a exible trailing edge tends to suppress center of pressureshifts consequent upon changes in angle of incidence, and thereforeto maintain balance and to suppress stalling. The change of form under excessive load further tends to spill off such load. And, finally, avery yielding trailing edge, by deforming when the wing is moved the wrong way-when it is backed into the relative wind-strongly resists autorotation, and so becomes an efectivecure for spinning.
Since an exceedingly thin and ieXible elastic 'trailing edge to a wing renders very diiicult and unsatisfactory the provision of aileronsof the common typebesides which there are other objections to such aileronsand because it is desirable in the use of a deeply-cambered wing to be able to alter the depth of the camber,it is a needed or at least a desirable element of the'combination, in at least some embodiments of my discovery or invention, to have the entering edge of the wing movable. Accordingly, therefore, I include structure illustrated in Figure 9, an important feature of which is the movable forward element 31. By moving such an entering edge through the range of positions suggested by the dotted lines, the camber is changed, as well as the angle of incidence. Produced symmetrically, in the two halves of a wing pair, such change of camber and of incident angle is useful for increasing speed range, from fastest top speed to slowest landing speed. Changed unsymmetrically, the effect is to afford a powerful lateral control, for balancing and steering.
i Utilized for the latter purpose, that side of the wing which has'the camber deepened has the anglek of incidence decreased, while its drag and lift increase and its speed lowers, in exact contradistinction to the effect of manipulating the usual rear-edge aileron,
the use of which calls for a powerful vertical rudder control, to prevent the unsymmetrical drag of the ailerons from steeringl an airplane in exactly the contrary direction to that intended.
The preferable type of my surfacing is single, without interior hollow; the small seepage of air necessary to maintain` its functioning is supplied naturally by the movement of the wing, with only the smallest consumption of energy and with -immense reduction in the resistances against which the wing must `be propelled.
It will be understood that the above de- 4 scription and accompanying drawings comprehend only the general and preferred emchanges in construction, proportion and arrangement ofl parts may bemade within the scope of the appended claims, and without sacrificing any of the advantages of my invention.
What I claimis:
1. An aircraft wing comprising a. thick forwardportion impervious to air at the normal pressure gradient adjacent to it anda thin fiexible rear portion having a surfacing a fine-grained porous surfacing permitting seepage of air therethrough.
(l. In a deeply-undercambered aircraft wing, ribmembers, an impervious vesicular surfacing secured to said rib members forward of the vertex of the undercamber and a vesicular surfacing pervious to air secured to said ribs rearward of the vertex of the c: mber of the wing. I
5. An'k aircraft wing comprising a forward portion having a vesicular surfacing impervious to air of the normal operating pressures adjacent to it and a rear portion having a vesicular surfacing pervious to air of the normal operating pressures adjacent to it.
6. An aircraft wing comprising arelatively-thick forward portion substantially impervious to air of normal operating pressures adjacent to it, avesicular surfacing secured to a section of said forward portion, and a relatively-thin rear portion having a vesicularl surfacing freely pervious to'air ofthe normal operating pressures adjacent toit.
7. An aircraft wing comprising supporting members, a forward portion having a vesicular surfacing impervious to air secured to saidk supporting members and a rearward portion consisting ,of-a relatively-thin'surfacing, having vesicles pervious to air of the normal pressure gradient adjacent to it, securedlto the supporting members.
8. A deeply-undercambered aircraft wing comprising a thick forward portion having a surfacing substantially-impervious to air of the normal pressure gradient adj acent' to it, a thin surfacing pervious Lto airof the normal pressuregradient adjacent to it extending rearward from said thick forward portion to the trailing edge of the wing to control the relative airflow to the contour of the wing and Yrib members having fiexible elastic rear portions, extending rearward from said forward thick portion substantially parallel to the airflow and supporting said thin pervious surfacing.
9. A deeply-undercambered aircraft wing comprising a thick forward portion having a surfacing` substantially-impervious to air of the normal pressure gradients adjacent to it7 and a. pervious rear portion consisting of a porous top surfacing, a porous bottom surfacing and means forming cellular divisions between said top and under surfacings whereby air of the normal pressure gradient adj acent to the under surfacing will pass from the underside of the wing substantially straight through the cellular divisions to the top of the wing.
l0. An aircraft wing comprising a thick forward portion having a vesicular surfacing impervious to air of the normal pressure gradient adjacent to it and a rear portion consisting of partition members forming small cellular divisions and a porous surfacing pervious to air of the normal pressure gradient adjacent to it secured to the top and to bottom of said partitions whereby air will pass from the underside of the rear portion of the wing substantially straight through the cellular division to the top surface of the wing. j
l1. A concave-convex cambered aircraft wing section comprising a thick forward portion having a surfacing innliervious to air of the normal pressure gradient adjacent to it, means for moving said surfacing at the leading edge, to change the camber7 and a relatively-thin rearward portion having a fabric surfacing pervious to air of the pressure gradient adjacent to it.
12. A concave-convex aircraft wing comprising a thick forward portion having a vesicular surface impervious to air of the normal pressure gradient adjacent to it, means for moving said surfacing at the leading edge to change the camber of the wing, and a relatively-thin rearward portion consisting of supporting members having f1eX- ible elastic rear ends and a fabric surfacing pervious to air of the pressure gradient adjacent to it, secured to said supporting members.
13. In an aircraft wing a forward portion having a surfacing impervious to air of the normal pressure gradient adjacent to it and a rearward portion pervious to air of the normal pressure gradient adjacent to it, consisting of supporting members and a porous fabric having a waterproof surfacing for repelling water without damage to the porosity of the fabric, secured to said supporting members.
14. In an undercambered aircraft wing, a thick forward portion having a surfacing impervious to air of the normal pressure gradient adjacent to it, supporting members extending rearward from said thick forward portion and a porous fabric having a waterproof surfacing, secured to said supporting members whereby air will pass through said porous fabric unhindered by moisture.
l5. In an aircraft wing, a forward portion impervious to air, and a rear portion having a pervious vesicular surfacing with openings the area of which range between l/O inch square to 1/120 inch square.
16. In an aircraft wing, a forward portion having a vesicular surfacing impervious to air, and a rear portion having a vesicular surfacing pervious to air, wherein the aggregate area of the vesicular openings of said vesicular surfacings exceeds 8O percent of the total area of the top surface and the aggregate area of the top edges of the walls forming the vesicles is less than 20 percent of the total top surface area.
17. In an aircraft wing, a forward portion impervious to air, and a rear portion having a pervious vesicular surfacing with substantially uniform openings the area of which maj7 be set between the range of l/GO inch square and l/ 120 inch square.