US2404522A - Pitch control means for sustaining rotors - Google Patents

Description

Jaws, 1946.

. S. P. NEMETH PITCH CONTROL MEANS FOR SUSTAINING ROTORS Filed Aug. 20, i945 SPNEMETH FIG .4

Patented July 23, 1946 "PITCH CONTROL MEAN no'roas s FOR SUSTAINING Stephan Paul N emeth, Chicago, Ill. Application August 20, 1943, Serial No. 499,340

I the control of the pilot.

The pitch angle variation-features under the control of the pilot are intended to reduce the flapping angle and to provide pitch and roll control of the aircraft in a known manner. The flapping is principally relied on for stabilizing the rotor and for preventing excessive centrifugal loads and stresses. A periodic pitch angle variation of a period equal to that of the rotor rotation having an amplitude under the control of the pilot is used'for providing an approximate balance between the left side and the right side of the rotor, that is to say for an approximate equalization of the lift of the advancing blade and of the retreating blade. A variation of the average blade pitch angle under the control of the pilot is provided for goveming the mode of flying, whether the aircraft is predominantly flying forwardly with its best speed or whether it shall predominantly climb or hover at a lesser or no speed.

The inner portions of rotating blades do not produce lift commensurate with the lift produced by their outer portions, because the velocity of rotation of the inner blade portions is much smaller than the velocity of rotation of the outer blade portions. The lift production is therefore practically concentrated within an outer ring portion of the circular disc" area through which the blades rotate. In consequence, there is produced on the left side and on the right side of the aircraft more lift, and at the center portion of the disc circle, near the fuselage path, less lift than would be desirable for best efficiency. It

is a first object of my invention to provide a sustaining rotor producing a more advantageous lift distribution crosswise the aircraft, favoring the portion near the flight path of the fuselage to a larger extent than present rotors do.

4 Claims. (01. 244-173 pacitycan-not be fully utilized because the lift of the advancing blade must balance and not over balance the lift of the retreating-blade. Thus, the lift capacity oi'the advancing blade is partly wasted, to the detriment of its efficiency. This particular-shortcoming also inherent in the presently described improved rotor. But furthermore, with conventional rotors, the blade when pointing forwardly into the direction of flight, .or rearwardly into a tailwise direction, is arranged to produce a lift half waybetween the lift corresponding to the true lift capacity of the advancing blade and the true lift capacity of the retreating blade. In other words, the effective pitch'angle of the blade in forward and in rearward position is substantially the arithmetic mean of thepitch angles of the blade when in advancing or in retreating relation. This arrangement utilizes the lift capacity of the blades in their-fore aft;p0sitions'below full capacity, thereby further reducingtheefliciency of the rotor. There is no compelling reason for this additional lift capacityre- .The retreating blade has a very small lift cayelocity relative to the air. :But this larger-cad duction. The lift production fore and aft is substantially equal, and balance is provided at a lift production at full capacity as well as at a lift production 'at' part capacity. It is a further object of my invention to'provid'e' a sustaining rot'or utilizing the lift capacity of the bladesin their fore and aft position fullest without'regard to the lateral balance requirement. 1

The blades of conventional rotors change their effective angle of incidence relative to the moving airrperiodically, once during each revolutionbf the blade. I have found that a more frequent change of the. incidenc angleQat least twice' during each blade revolution, and one with an amplitude of the angle variation beyond that necessary for the lateral control greatly benefits the aerodynamic action of the blades, reducing the blade resistance and increasing the. blade lift capacity. It is a third object of my invention to provide a sustaining rotor having blades arranged to change their effective incidence angle.

periodically at least twice during each revolution of theblades with considerable amplitude variation. 7 These and other desirable objects and advantages of the presentinvention will be illustrated in the accompanying drawing and described in the specification, a certain" preferred embodiment being disclosed by way ofillustration only, for,

since" the underlying principles-may be incor porated in other specific dev1ces;it.is not intended to be limitedxtothe oner-hereshown; exceptas structure I I aircraft.

Mo ses such limitations are clearly imposed by the ap-' the aircraft having said rotor hub assembly in? corporated, and

The hub assembly broadly designated'by I13 comprises a housing I 4 fastened to the f-use'lage.

Asleeve I5 is mounted in said housing adapted to slide up and down and held in vertical position relative to the housing by I screwfn'ieans 32' under the" control of the pilot, I A cam track drum" I1 is tiltably mounted on top of sleeve 'I5' by meansofa universal joint I6,

its'tilting position being controlled by means of control'lever I9' extending downwardly through the housing I4 and having its end adapted to be manipulated or controlled by the pilot. Rotor hub 23'is mounted rotatably about a substantially vertical axis 'on-and aroundhousing I4. At its lower end it forms a gear wheel 24in mesh with the :gear wheel 25 mounted on casing l l'and adapted to'be driven by an engine.

Blade roots 2B aremounted on the hub 23 tatable' about substantially horizontal axes in atrailing edge 30. 'Theyrotate in clockwise di-" rection whenseen from above. The tail unitof the aircraft is broadly designatedby I2; 7 l

Blade roots 2IihaVe lever arms. projecting therefromin trailing relation to the blade ,mo-

'angle relative to the air.

the production of the lift, the former does not.. The flapping motion is-the outcome of an added,

4 about hinges 21, and this introduces a phase difference between the variation of their pitch an-' gle and the variation of the effective incidence Th latter determines up effect of the lift produced and tends to counteract 'or neutralize the pitch. This counteracting takes place with time delay by virtueof the mass effects of the blades. Hence, in order to obtain the largest effective incidence angle at the forward and rearward positions of the blades, it 7 Fig.7 4 represents a plan view 'of'the rotor hub is necessary that the pitch an les have their maxassembly shown in Fig. 1.

imum at angular positions assumed after these forward and rearward positions have been passed by the blades. Ihave obtained excellent results by arranging themaximum pitch'angles to take place at the 0 and 190 azimuth position of the blades, with the forward position of the blade being considered at zero azimuth. That is to say, the bladeassumesthe maximum pitch angle as far as traceable to the sinuosity of the cam tion. Connecting rods 2| are hinged to said levers and guidedby rod guides 22 for upand down mo.- tion. Attheir upper. endsthey are provided with camfollowers 20. in operative contact with the cam trackIB of cam track drum ;II. Cam track I8 issinuous havingtwo valleys and two peaks,

as shown in Fig. 2. As the blades rotate, their pitch angle is periodically changed in conserotation; Moving sleeve I5 by means of screw 32 changes the average pitch angle of the blades.

.Superposed to these known control and adjustment variations of the pitch angle isa periodic variation comprising two pitch angle increases and two pitch angle decreases during each blade rotation. The amplitude of this variation is governed by the amplitude of the sinuosity of the cam. track I8. I obtained excellent results by varying the pitch angle during, each half revolution by plus andminus 3 /2 degrees It is essential for this invention that the blade produce its largestlift near its mostforward position and near, its most rearward position relative to the aircraft, and that it produce its smalltrack while occupying the front quadrant and the rear quadrant of the blade rotation circle, more particularly while occupying thesecondhalf of these quadrants, the first half of these quadrants having already been passed through by the blade.

This isv represented in the drawing. Since the levers 3| trail the roots 26, contact of follower 28 with the lowest point of. track; I8 will produce the highest pitch angle. The contact points trail the root positions by 45. Hence, the lowest pointof 1 track I 8 must be at or near the azimuth positions 325 and 145. As indicated in Fig. 3, track I8 of Fig; 2 is represented as seen by an observer 7 the portion of the blade course nearer the fuselage axis. f

1 i r (I 1. In an aircraft sustained by a bladed rotor having blades mounted with freedom for flapping movement, and having controllable mechanism for shifting the line of action of therotor force to maneuver the aircraft, automatic mechanism operative in different positions, of adjustment; of

said controllable mechanismyto periodicallyvary the geometric pitch, angle *ofithe'blades, said automatic mechanism being constructed and arranged so as to impartmaximum increment of pitch angle to the bladesiwhile they are passing through the quadrants of. the circle of rotation in forward and in rearward relation to the: aircraft.

2. In an aircraft sustained bya bladed rotorhaving blades mounted with freedom for flapping movement, and having controllable mechanism for shifting the line of action of'the rotor force to maneuver the aircraft, automatic mechanism. operative in different positions of adjust- 'ment of said. controllable mechanism. to periodically vary. the geometric pitchangle of the blades,

est lift near its lateral position relative to the This 'does not necessitate the. largest pitch angle'at'the fore and aft positions northe said automatic mechanism being constructedand arranged so as to impart maximum incrementof pitch angle to the blades while they are passing through thequadrants of the circle of rotation in and after theyihavepassed positionp 3;stln"anaircra'ft, a sustainingretbr coat-ssing a'hub rotatable about a substantially verti'-' cal axis, a blade root projecting substantially radially from said hub and mounted rotatably for variation of its geometric pitch angle, a blade hinged tosaid root, a slidable and. universally tiltable drum mounted in said aircraft centrally to said rotor, a sinuous cam track in said drum, a cam follower in operative contact with said cam track and in operative linkage with said root, the cam track and the linkage being so dimensioned, arranged, and adjusted so as to impart to the blade a maximum increment of geometric pitch angle while it is passing through the quadrants of the circle of rotation in forward and in rearward relation to the aircraft.

4. In a rotary aircraft, a sustaining rotor hav- 6 ing radial variable-pitch blades, a circuitous sinuous cam track with two valley portions and two peak portions, and mechanism linking the cam track to the blades constructed and arranged so as to cause automatically periodic variations of the geometric pitch angle of the blades, so as to associate a predetermined value of the increment of geometric pitch angle with each angular station of the blade, and so as to associate the maximum increment of geometric pitch angle of the blades with blade stations within the two quadrants of the blade rotation circle in forward relation and in rear relation to the aircraft.

S'I'EPHAN PAUL NEMETH.

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