US2111975A - Rotative-winged aircraft - Google Patents

Description

March 22, 1938.

A. E. LARSEN ET AL ROTATIVB WINGED AIRCRAFT :5 Shets-Sheet. 1

Filed Dec. 19, 1935 ATroR'NEYJ March 22, 1938. A E LARSEN ET A 2,111,975 I I ROTATIVE WINGED AIRCRAFT Filed Dec 19, 1955 3 sheets-sheet '2 mcmsuca INVENTORS 60 90 5 11 W Wvfiw ATTORNEYS go 5o BLADE LENGTH March 22, '1938. A. E. LARSEN ET. AL 1,

ROTATIVE WINGED AIRCRAFT I Filed Dec. 19, 1935 P s Sheets-Sheet z INVENTORS WTMM ATTORNEYS Patented Mar. 22, 1938 UNITED STATES ROTATIVE -WINGED AIRCRAFT Agnew E. Larsen, Huntingdon Valley, aiulPaul H. Stanley, Glenside, Pa., assignors to Autogiro Company of America, Willow Grove, Pa",

' i a corporation of Delaware Application December 19, 1935 Serial No. 55,142

20 Claims. (01. 244-18) This invention relates to aircraft having rotative sustaining blades or wings, and is especially concerned with that type of. craft in which a sustaining rotor is employed incorporating a plurality of blades which are pivotally connected with a common generally upright axis mechanism. I

One of the major objects of the invention is to increase the efilciency of craft of this type, more particularly to increase the rotor efliciency.

The invention also overcomes a diving tendency sometimes experienced at high forward speeds. I

Still further, it is an object of the inventio'nto provide a rotor the blades of which are of reduced .weight as compared with prior constructions and which are further of simplified construction.

The foregoing important and more or less general objects are served by various features of construction such as the following:

The invention contemplates a blade of novel form, more specifically, the improved blade hasa thickness ratio varying by steps which is conveniently obtained with maintenance of uniform chord, thus without necessarily reducing the solidity of the rotor. According to the invention, the blade is composed of several portions, preferably three, each one of which is of substantially uniform thickness but the several portions, respectively, being of diflerent thicknesses, an out:

board portion, for example, being of reduced thickness ascompared with the adjacent inboard portion. v

Similarly, the invention contemplates the employment of a spar of stepdown construction, the several portions of the spar preferably being substantially coextensive with the portions'of the blade mentioned above as being of diflerent thicknesses.

In addition to the above, the construction of this invention involves a blade of substantially fixed center of pressure (preferably well forward or at about 25% of the chord from the leading edge) for all normal angles of attack above a predetermined minimum, for example, 2 positive. The blade section employed in accordance with this invention further has a rearward travel of the center of pressure below said predetermined minimum; This type of blade we have foundto provide very material improvement in smooth ness of operation, especially when maintaining the sectional center of gravity substantially coincident with or slightly ahead of the sectional center of pressure, this latter also constituting an important feature of the invention.

The improved blade herein disclosed is; also characterized by a novel incidence relation between inboard and outboard portions thereof.

Special arrangements in the structure, such as features of the spar, nose, ribs, ballast weights, etc., are also of importance in the working out 5 of the primary objects, as will appear more fully Y hereinafter.

How the foregoing, together with other objects and advantages are" attained, willappear more fully in the following description referring to the accompanying drawings, inw'hich- Figure 1 is a plan view of the structural members of a blade according tov the invention, the outer covering being removed;

Figure 2 is an enlarged sectional view of the 15 blade taken substantially as indicated by the section line 2-2 on Figure 1;

Figure 3 is a top plan view of one of the ribs employed in building up the blade; Y

Figure 4 is a partial sectional view takenas indicated bythe section line 44 on Figure l and illustrating a ballast weight and the mounting therefor; v

Figure 5 is a fragmentary top view of structural members of the blade, this view also showing the ballast weight;

Figure 6 is a view containing a graph and a blade'in outline and illustrating a number of features discussed fully hereinafteryand Figure 7 is a view of the blade section (in outline) at various points along the length of the blade, particularly illustrating the relation of incidence settings of diflerent portions of the blades.

As mentioned at the outset, the invention is 35 concerned with a blade for an aircraft sustaining rotor of the type incorporating an axis mechanism, thisbeing shown at i in Figure l, to which a plurality of blades are pivoted. The blade appearing in Figure 1 is secured to the axis or hub I by means of a flapping articulation 8, extension link 9 and drag" articulation Ill. The blade is thus free to "fiap in a direction generally transverse the mean rotative path of travel and also to move fore and aft substantially within the path of travel. The articulations, of course, serve to interconnect the hub member and the main structural element of the-blade which takes the form of a spar ll. At the inner end of the spar a fitting l2 may be provided, this fitting having fork or equivalent parts adapted to cooperate with the pivot Hi. The fitting I 2 and also an additional sleeve B at the inner end of thespar serve to increase rigidity toward the root end of the blade, this being of importance in the 5 cantilever support of the blade and for other reasons. In general, moreover, it might be said that because of bending and tension loads at the root, greater strength and related characteristics are required toward the root end, whereas aerodynamic efficiency, because of the high speed,

is of greatest importance toward the tip of the blade. Numerous features of the present inven- -tion carry out the relationships just mentioned more completely than has been possible heretofore.

Turning again to the spar, attention is called to the fact that the inboard portion of the spar designated by the arrows lid, is of substantially uniform cross-section or diameter but larger than the intermediate and outboard sections I lb and I I0. Sections lib and lie are also respectively of uniform diameter, although portion 0 is-of smaller diameter than portion Ilb, so that the spar is of stepped construction. The spar, moreover, is preferably composed of a single drawn tube and has short tapered sections l4 and I5 joining sections lia-Ilb, and Ilb-llc, respectively.' At the outer end of the section Ilc an extension i6 is provided, and this extension carries a tip part I! shaped to conform with the desired tip-taper.

The spar carries ribs I811, I82) and l8c, each group being apertured to engage the spar in the respective sections thereof, The attachment of the ribs to the spar may be accomplished (see Figures 2 and 3) by means of a fitting l9 riveted latter object is also served by location of the spar well forward in the blade section. More specifically, it will be noted that the center of the spar is located less than 25% of the chord from the leading edge. These features of construction,

together with fairly robust ribs, particularly in the trailing edge portions thereof, may afford sufiicient rigidity in the path of rotation even without the necessity of employng a supple-' mentary spar or stringer which heretofore has been located intermediate the main spar and the trailing edge. The rear ends of the ribs are embraced by a trailing edge stringer 24 which may be applied in'the form'of a trough or V and then pinched together at its front edges as at 25. The nose of the wing is preferably also surrounded by a plywood covering 26 which, as clearly seen in Figure 2, is recessed into the edges of the ribs. This nose covering also adds considerable rigidity in the path of rotation.

The blade, of course, is covered with a fabric 21 which may be suitably doped.

As seen in Figure 1, the blade further incorporates a plurality of ballast weights 28, one of which appears to best advantage in Figures 4 and 5. This weight, it will be observed, is disposed well forward in the nose of the blade and is preferably supported on the spar by means of a pair of bolts 29 which pierce the spar horizontally at the neutral axis and thus result in minimum weakening thereof. A pair of spacer sleeves 30 are disposed between the spar and the outline.

, weight itself, and a web ll, lying in the plane of the blade, is welded to the sleeves 30. This construction provides a rigid mounting for the weights 28 which ishighly effective as against the action of centrifugal force, in spite of the fact that the weight is. spaced a substantial distance from the spar.

From Figures 1 and 6 it will be seen that the weights 28 are all located in the outer half of the blade. It is the-outboard portion of the blade that requires ballasting, but the distribution disclosed, while concentrating the weight in the outer portion of the blade, does not impose the total centrifugal load thereof on the outermost section of the spar which, as already noted, is of reduced size.

Before considering the effect of these weights and also of various other factors already mentioned, reference is now made to the incidence setting of the blade. As will best be understood from examination of Figures 6 and 7, the blade has a progressive decrease in incidence or washout from the root end thereof outwardly toward the tip. This primary washout, if carried to the extreme tip of the blade, would give the blade about 7 lower incidence at the tip than at the root. An additional washout of 1, however, is superimposed on the primary washout, this additional decrease in incidence commencing at a point about 85% of the blade length from the root. In consequence, the tip has 1% lower incidence than the root. As indicated in the graph of Figure 6, the blade is set on the hub with its root end at an incidence of approximately 4 above zero lift, and in view of this, the tip setting approximates 2% above zero lift. The incidence settings just mentioned (see also Figure '7) are the positions of the blade section (at different points along the blade) measured from that position which, with airflow perpendicular to the axis of rotation, would give zero lift. As seen in Figure 7, with a blade section of the type shown, the chord line of the blade in zero lift position (represented by line zz) is slightly negative with respect to the plane a:.1: perpendicular to the axis of rotation r-r, the negative angle being about 1.2" as shown.

Attention is now directed to the fact that in Figure 7 the full line blade outline A is taken at a point toward the inner end of the blade and that the chord line H of this section is positioned at it positive angle with reference to the line 22-22 representing the zero lift position. Figure 7, it will be noted, also shows two additional blade sections B and C in dot-and-dash Sections B and C both have substantially the same chord as section A, although section B is of reduced thickness as compared with section A and section C, in turn, is of reduced thickness as compared with section B. The points at which these three sections are taken is also indicated by corresponding letters on the blade appearing in Figure 6, and from this latter view it will be seen that section A is taken in the region where the spar has largest diameter, section B in the region where the spar has intermediate diameter, and section C in the outer section of the blade where the spar is of smallest diameter.

Turning again to Figure 7, it will be noted that the chord line b-b of the section B is positioned at a 4 positive angle with reference to line z-z, and from comparison with Figure 6 it will be seen that section line b-b is positioned at the point where the graph shows 9. 4 incidence. Similarly, the chord line 0-0 of section C is positioned at about a 3 4 angle with reference to line e--z, as also appears from the graph of Figure 6. 1 From the foregoing it will be seen that al though the same chord dimension is maintained substantially throughout the entire length of the blade, the thickness ratio of the blade is varied, with the section of least thickness at the tip and the section of greatest thickness at the root. Ac-' thickness being located inboard and the portion of least thickness toward the tip, as is desirable from the standpoint of structural and aerodynamic emciency of the rotor. The present stepped construction, in contrast with a gradually tapering shape, is of substantial advanta e since, with the varying oblique flow of air encountered during rotation of the rotor, the effective blade section is distorted to a much smaller degree than with prior forms of blades. The only points of material distortion, in fact, are those at the junction points between adjacent portions of the blade, at which points the blade tapers rather sharply from the. larger thickness to the next smaller thickness. This tapering at the junction points is substantially coextensive with the tapered portions l4 and iii of the spar.

The step-down blade construction, while maintaining uniform chord dimension, is of further advantage since it provides a material and highly desired reduction in drag in the outboard portion of the blade without a noticeable reduction in lift and further without reducing the solidity of the I rotor, i. e., the ratio of the total blade area to the disk area swept by the blades.

Maintenance of the solidity is of advantage chiefly .in retaining the desired low flight speed characteristics of the rotor.

In considering some further features of the in-, vention, it shouldbe noted that the section employed in all portions of the blade is preferably one of several known forms having a substantially .fixed center of pressure located well forwardly, for'example, at about 25% of the chord dimension from the leading edge. This condition is substantially maintained throughout the several steps of the blade, although the thickness ratio is slightly modified. By way oi example, the thickness ratio in the innermost portion of the blade may be about H l /2%, in the intermediate portion about 11 /2%,jand in the outboard portion about 10%.

Withfurther reference to the blade section, while the center of pressure as above indicated is substantially fixed, this condition is maintained in a highly eflicient section only above a predetermined minimum aerodynamic angle of-attack. This minimum, according, to the present invention, preferably approximates 2 positive.

It is here to be noted that the expression angle of attac is not to be confused withthe .incidence setting" of the blade which in the present description refersto'the angle of the chord line above zero lift position. The expression angle of attac is'herein usedto define the angle between the chord line and the line of airflow at any given instant. For various reasons (notably the effect of .blade flapping and attitude and direction of flight of the craft), the angle of attack is almost continuously fluctuating and may assume a value which is eithergreater or less than the incidence setting.

Reverting now to the characteristics of the blade section employed, below approximately 2 positive, the center of pressure of the section adopted moves rearwardly from the 25% position quite rapidly. V 1

The reduction in the incidence settingof the blade toward thetip, as herein contemplated, has been found to materially reduce vertical fluctuation in forces or "bouncing" transmitted 1 from the rotor to the machine. By the difference in incidence setting, a more uniform lift distribution is applied to the blade throughout its cycle, and, in consequence, bending moments in the blade arereduced. Reduction in bending moments in-the blade is of importance since this reduces fluctuation i'n lift delivered to the'hub. Furthermore, under certain conditions of flight, the advancing blade of a rotor having flapping blades, will, through a restricted range of positions, be operating at a low angle of attack.- A

negative torsional moment would normally occur as a result of this in a blade having an aerofoil section of the general character used in accordance with the present invention. However, the reduction in blade incidence toward the tip has an advantageous eiiect in minimizing this torsional moment and thus reducing any diving tendency produced by the moment.

The location of the sectional center of gravity coincident with or slightly ahead of the center of pressure of the blade, as herein contemplated, is also of importance, and with a blade of the type herein shown, the ballast weights aid in providing the relation of center of gravity to center of pressure just referred to. The relation of the C. G. and C. P. overcomes detrimental cumulative action producing torsional deflection of the blade and causing undesirable loads on the machine under the effect of vertical accelerations. due to maneuvers or bumps.

Another advantage ofthe blade structure herein disclosed, particularly the employment of a rather robust leading edgestrip, a plywood covering for the nose part of the wing, and other features increasing the stiffness of the'blade in the plane of rotation, is that the increase in stiffness in the plane mentioned increases the natural vibration frequency in this plane and this, in tum,- reduces tendency toward'grou'nd resonance in the rotor. V

The step-down construction of the blade and other features thereof which reduce thenecessity for employing a secondary spar as hereinbefore referred to, is of substantial advantage in simplifying construction. Note particularly that with the step-down construction, the number of different types of ribs is reduced, since all ribs in the region of each of the spar sections Ila, llb and llc may be of one type, both as to external contour as-well as to diameter of spar receiving aperture.

1n summarizing the advantages, it should be noted that various features of the structure, in-

cluding the step-down spar, the reduction in thickness ratio of the blade, the C. G. and C. P. relation, and incidence settings are of importance V in reducing weight while providing adequate strength, even where ballast weights are employed, improving the smoothness of rotor operation, reducing the tendency to set up torsional or other vibrations due to periodic fluctuation in the position of the center of pressure, and substantially eliminating bouncing" of the rotor.

We claim:-

1. A blade for an aircraft sustaining rotor, an inboard portion thereof being of substantially uniform thickness, and an outboard portion thereof being of smaller but substantially uniform thickness, the two portions being joined by a relatively short tapered portion.

2. A blade for an aircraft sustaining rotor, said blade having a spar, an inboard portion of which is of substantially uniform cross-section and an outboard portion of which has a smaller but substantially uniform cross-section, and means defining the blade surface, an inboard portion thereof being of substantially uniform thickness, and an outboard portion thereof being of smaller but substantially uniform thickness, the two portions being joined by a relatively short tapered portion.

3. A blade for an aircraft sustaining rotor, an inboard portion thereof being of substantially uniform thickness, and an outboard portion thereof being of smaller but substantially uniform thickness, the two portions being joined by a relatively short tapered portion, and the two portions further having substantially the same chord.

4. A blade for an aircraft sustaining rotor, an inboard portion thereof being of substantially uniform thickness, and an outboard portion thereof being of smaller but substantially uniform thickness, the two portions being joined by a relatively short tapered portion, and said two portions further having a gradual or progressive incidence washout providing relatively positive incidence toward the inboard end of the blade.

5. A blade for an aircraft sustaining rotor, an inboard portion thereof being of substantially uniform thickness, and an outboard portion thereof being of smaller butsubstantially uniform thickness, the inboard and outboard portions both having a substantially fixed sectional center of pressure at about 25% of the chord from the leading edge throughout at least a major part of the normal range of angles of attack.

6. A blade for an aircraft sustaining rotor, an inboard portion thereof being of substantiallyuniform thickness, and an outboard portion thereof being of smaller but substantially uniform thickness, the inboard and outboard portions both having a substantially fixed sectional center of pressure at about 25% of the chord from the leading edge throughout at least a major part of the normal rangeof angles of attack, and each portion further having its sectional center of gravity sub-' stantially coincident with the center of pressure.

'7. A blade for an aircraft sustaining rotor, an

inboard portion thereof being of substantially uniform thickness, and an outboard portion thereof being of smaller but substantially uniform thickness, the inboard and outboardportions both having a substantially fixed sectional center of pressure at about 25% of the chord from the leading edge throughout at least a major part of the normal range of angles of attack, each portion further having its sectional center of gravity substantially coincident with the center of pressure, and said two portions still further having a gradual or progressive incidence washout providing relatively positive incidence toward the inboard end of the blade.

8. For an aircraft sustaining rotor, a generally upright axis mechanism and a sustaining blade secured to the axis mechanism with freedom for movement in a direction generally transverse the mean rotative path of travel of the blade, said blade having an airfoil section with a substantially fixed center of pressure throughout a range of aerodynamic angles of attack above a predetermined angle, the blade setcion further having a rearward travel of'the center of pressure at angles of attack below said predetermined angle, an outboard portion of the blade being set at a positive incidence with respect to its zero lift position, which incidence, however, is such that when the blade is on the advancing side of the rotor during high speed forward flight, the aerodynamic angle of attack of the outboard portion is below said predetermined angle, and an inboard portion of the blade being set at a positive incidence with respect to its zero liftposition, which incidence is sufficiently above said predetermined angle to maintain an angle of attack above the predetermined angle when the blade is on the advancing side of the rotor during high speed forward flight.

9. For an aircraft sustaining rotor, a generally upright axis mechanism and a sustaining blade secured to the axis mechanism with freedom for movement in a direction generally transverse the mean rotative path of travel of the blade, said blade progressively decreasing in incidence from a point toward the root end thereof outwardly substantially to the tip, the decrease in incidence in about the outer 15% of the blade length being substantially uniform per unit of length and being greater per unit of length than the decrease in the inner 85% of the blade length, and the decrease of incidence in the inner 85% of the blade length also being substantially uniform per unit of length of the blade.

10. For an aircraft sustaining rotor, a generally upright axis mechanism and a sustaining blade secured to the axis mechanism with freedom for movement in a direction generally transverse the mean rotative path of travel of the bIade said blade progressively decreasing in incidence from a point toward the root end thereof outwardly substantially to the tip, 'the decrease in incidence in about the outer 15% of the blade length being substantially uniform per unit of length and being greater per unit of length than the decrease in the inner 85% of the blade length,

and the decrease of incidence in the inner 85% of the blade length also being substantially uniform per unit of length of the blade, the total decrease in incidence from the root to the tip of the blade being approximately 1%, the blade being mounted on the axis mechanism with its root end portion set at approximately l positive lift incidence with respect to its zero lift position and the section of the blade substantially throughout the length thereof having a substantially fixed center of pressure at angles of attack above approximately 2 and further having a rearward travel of the center of pressure at angles of attack below approximately 2.

11. A blade for an aircraft sustaining rotor, said blade incorporating a spar, an inboard portion of which is of substantially uniform section and an outboard portion of which is of smaller but substantially uniform section, means carried uniform thickness throughout a portion of the blade substantially coextensive with said inboard portion of the spar and further being of reduced but substantially uniform thickness throughout a portion of the blade substantially coextensive with said outboard portion of the spar. I

12. A blade for an aircraft sustaining rotor, said blade incorporating a spar, an inboard portion of which is of substantially uniform section and an outboard portion of which is of smaller but substantially uniform section, means carried on said spar and defining the surface or formof the blade, said means being of substantially uniform thicknessthroughout a portion of the blade substantially coextensive with said inboard portion of the spar and further being of reduced but substantially uniform thickness throughout a portion of the blade substantially coextensive but substantially uniform section, means carried on said spar and defining the surface or form of the blade, said means being of substantially uniform thickness throughout a portion of the blade substantially coextensive with said inboard portion of the spar and further being of reduced but substantially uniform thickness throughout a portion of the blade substantially coextensive with said outboard portion of the spar, and a ballast weight secured to the spar adjacent the outer end of said inboard portion of the spar.

14. A blade for an aircraft sustaining rotor, said blade incorporating a spar, an inboard por tion of which is of substantially uniform section and an outboard portion of which is of smaller but substantially uniform section, means carried on said spar and defining-the surface or form of the blade, said means being of substantially uniform thickness throughout a portion of the blade substantially coextensive with said inboard portion of the spar and further being of reduced but substantially uniform thickness throughout a portion of the blade substantially coextensive with said outboard portion of the spar. and a plurality of ballast weights carried by the spar, one in the outboard portion thereof and another adjacent the outer en'd of the in board portion.

15. A blade for an aircraft sustaining rotor, portions of said'biade being of diiferent thickness but substantially the same chord, each of said portions further beingof substantially uniform thickness throughout its length and an outboard portion being of reduced thickness as compared with an inboard portion, and a ballast weight in the blade toward its leading edge in theoutboard portion thereof.

16. Ablade for an aircraft sustaining rotor, said blade incorporating a spar and means defining the blade shape, substantially coextensive portions of said means and of the spar being of different thickness and cross-section, respectively, an outboard portion having substantially uniform blade thickness and spar cross-section but being smaller than the blade thickness and spar section in an inboard portion.

17. For an aircraft sustaining rotor, a blade of spar andrib construction, an. inboard portion of the spar being of substantially uniform crosssection, an outboard portion thereof being of reduced but substantially uniform cross-section, and an intermediate portion of the spar being tapered to join said inboard and outboardportions, and a plurality of ribs mounted on said spar in spaced relation, the length of said intermediate section and the spacing of said ribs being approximately the same.

18. For an aircraft sustaining rotor, 'a generally upright axis mechanism and a sustaining length, and the decrease in incidence in the inner portion of the blade length also being substan- L tially uniform per unit of length.

19. A blade for an aircraft sustaining rotor,

the blade being composed of at least three portions' of different thickness each of which is of substantially uniform thickness throughout its length.

20. A .blade for an aircraft sustaining rotor, said blade including a spar, means carried by the spar and defining the blade contour, a ballast weight at least the majpr mass of which lies in the plane of the blade chord, the ballast weight further being horizontally offset from the spar,

and means interconnecting the ballast weight and the spar. AGNEW LARSEN. PAUL H. STANLEY.

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