US1872337A - Air screw with automatically variable pitch - Google Patents

Description

%!LLARD AIR SCREW WITH AUTOMATICALLY VARIABLE PITCH Aug. 16, 1932. 1,872,337

' Filed April 16, 1930 3 Shets-Sheet 1 pmuw nm'mtwbf.

Aug. 16, 1932. I M. PIILLARD 1,372,337

AIR SCREW WITH AUTOMATICALLY VARIABLE PITCH Filed April 16. 1930 :5 Sheets-Sheet 2 IHH IIHH

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Aug. 16, 1932.. LLARD AIR SCREW WITH AUTOMATICALLY VARIABLE PITCH Filed April 16. 1950 s Sheds-Sheet, s

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Patented Aug. 16, 1932 UNITED STATES PATENT-OFFICE 1 IABCEL PILLABD, F MAZRSEILLE, FRANCE, ASSIGNOB TO LHELICE METALLIQUE,

BRE'VETS IPAULH.AN-I?ILLAIRD,- SOCIETE ANONYME, 0F MARSEILLE, FRANCE.

AIR .scaEw wI'r AUTOMATICALLY VARIABLE rrrcn Application filed April 18,1930, Serial No. 444,856, and i France m 17, 1929.

In order to produce a screw with auto-' For this purpose it is sufii'cient to articulate the blade upon an axis which should not be confused with the neutral axis of the -blade,. i. e., the line connecting the-centers of gravity of the sections of the blade in such a manner as to permit of a forward inclina- 16 tion of the neutral axis when the traction effort increases to a larger extent than the centrifugal .force or-of a rearward inclination as soon as the traction effort decrease more than -.the centrifugal force. 20 If this axis of articulation is perpendicular ,to the neutral axis, the blade may be inclined forwards or rearwards without its pitch varying within the small limits of inclination which'occur in practice.

If'said'axis is inclined relatively to the neutral axis, but form with that neutral axis a considerable angle, for instance 45 to 90 the variation of the blade pitch is slight and is not sufficient to be effective.

This is not the case if the axis of articulation is slightly inclined with regard to the -,neutral axis of the blade as in that case a comparatively small inclination of the neutral axis forwards or rearwards corresponds to a variation of theblade pitch which is sufficiently great to be effective.

Various arrangements based on this principle may be made; One may provide for a turning of the blade around an axis having actual shape, or one may provide for a turning of the blade on a joint and add to this arrangement a device which'immobilizes another point of the blade, but the latter arrangement is equivalent to the former, as the blade then moves around two fixed points, that is, aroundan axis connecting the points.

However, in these constructions, care must be taken to take into account a very important point which has a series bearing upon the strength and efficacy of the blades;

namely that the neutral axis should :pass through the axis of the driving shaft.

In fact, if the neutral-axis of ,thejblade' passes on one side of the axis of the driving shaft, the occurring centrifugal forces all have a transverse component which-deforms the blade, alters its characteristics jand is even liable to break the blade, because at the occurring peripheral speeds the centrifugal forces are enormous.

In order to counteract the'defo rma tion of the blade, it-is a rule in connection with all blades having a fixed pitch to' give the neutral axis of screw blades a curved form which is obtained by calculation and is called the compensation curve, this methodv of construction having for its object only the elimination of the transverse forces just referredto. V The calculation shows that the extension of the neutral axis of the blade should ass through the axis of rotation of the sha in order that the blade be compensated.

This very important consideration leads to the particular construct-ion of a 'variable pitch arrangement forming the subject of the present invention, one form of which is shown by way of constructional example in the accompanying'drawings, and is substantially characterizedby the fact that the neutral axis of the blade passes through the axis of the driving shaft and that the blade turns about an axis which is slightly inclined both in the direction of propulsion and in the direction of rotation of the screw to the neutral axis of said blade.

In the drawings:

Fig. 1 shows in half elevation and longitudinal section the internal arrangement of a hub of an air screw with automatically variable pitch.

' Fig. 2 is a half cross view and also section of the same hub.

Fig. 3 is a section on line IIIIII of Fig. 5, gig. 4 is a section on line IV-IV of Fig. 5, an

Fig. 5 is a detail sectional elevation showin the stop for limiting the rotation of the blade.

, The hub 2 carries one pivot member 3 for each blade 4 the pivotal axis II of. which pivot member is inclined to the neutral axis II-II of the blade" (which neutral axis is perpendicular to the axis of the shaft) by a small angle in the sense of the rotation (Fig. 2) and also by another small angle in the direction of propulsion, i. e., the direction of the flight (Fig. 1). These inclinations are calculated in such a manner that at any inclination of the blade't due to a variation between the tractive effort and the couple of the engine on the one hand, and the centrifugal force on the other hand, the required alteration of the pitch is obtained.

Each of the inclined pivot members 3 carries upon its lower portion a ball or equivalent step bearing 5 of known typeand upon its upper portion a ball or equivalent journal bearing 6, also of known type.

The adjustable stop device is constructed as follows:

Into a bore 17 of the hub 2 is screwed a stop 12, a transverse screw 18 preventing any accidental'unscrewing of the stop. The stop 12 is formed with two lateral flat surfaces 14:

adapted to co-operate with-set screws 15-, 15 inserted into bores 16 of the socket 7 By adjusting the screws 15 in their respective bores 16 the angle of adj ustmentof the blade from a middle position may be determined in both directions.

The step bearing is arranged within a socket iforming an extension of the blade,

and the journal bearing is arranged on a transverse partition 11 fixed to the socket of the blade.

The socket and its partition are arranged in and the fixed ring of the step bearing 5, forces the whole blade and the partition towards a conical portion 10 of the stop of the hub 2 so long as the centrifugal force has not reached a minimum predetermined value, this arj rangement having for 1ts' ob ect to fix the blades in a fixed position upon the ground and at the moment of starting'and also having for its object to provide a tight joint.

In addition there is provided a stop device 12 adjustable between a maximum and a minmum position which enables the automatic variation of the pitch to be stopped, or enables the blade to be given the necessary amplitude of pitch variation according to the mode of use of the air screw and more-parnon-supercharged motor and for flights with reduced supply.

' There is also provided a fixed safety stop device 13 in case one. or more balls or rollers of the step bearing should break.

The forms of construction and arrangement above described do not restrict the scope, they may vary according to the power and the type of the aircraft without departing from the general arrangement of the invention.

I claim:

1. In an air screw having automatically variable pitch thecombination of: a driving shaft; a hub on said shaft; a blade arranged on said driving shaft in such manner that its neutral axis normally passes through the axis of said shaft; and a pivot member interposed between said hub and said blade, and

otally mounted on said pivot member and turning on the bearings thereof, said pivot memberbeing so constructed and arranged that its pivotal axis, about-which said blade turns is slightly inclined both in the direction of propulsion and in the direction of rotation of the screw to the neutral axis of said blade, which latter normally passes through the axis of said blade, substantially as described.

3. In an air screw having automatically variable pitch, the combination of: a driving shaft; a hub on said shaft; a blade arranged on said driving shaft in such manner that its neutral axis normally passes through the axis of said shaft; a pivot member interposed between saidhub and said blade, and so constructed and arranged that its pivotal axis about which said blade turns is slightly inclined both in the direction of propulsion and in the direction of rotation of the screw to the neutral axis of said blade; and a spring member on said pivot member constructed and arranged so as to prevent said blade turning and thereby altering its pitch when the centrifugal force of the screw is low, substantially as described.

4:. In an air screw having automatically variable pitch, the combination of: a driving shaft; a hub on said shaft; a blade arranged on said driving shaft in such manner that its neutral axis normally passes through the axis of said shaft; pivot member interposed between said hub and said blade, and so conticularly for flights at high altitude with Stlucted and arranged that its pivotal axis of said shaft; a pivot member interposed between said hub and said blade, and so constructed and arranged that its pivotal axis about which said blade turns is slightly inclined both in the direction of propulsion and in the direction of rotation of the screw ,to the neutral axis of said blade; vand an adjustable stop member on said pivot member pivot member; and an adjustable stop member on said pivot member constructed and arranged so as to limit the turning move-v ment of saidblade, substantially as described.

constructed and arranged so as to limit the turning movement of said blade and consequently the variation of pitch, substantially as described.

6. In "an air screw having automatically variable pitch, the combination of: a driving shaft; a hub on said driving shaft; a pivot member comprising an upper roller bearing and a lower ball bearing constituting a step bearing mounted on said hub; a blade artic;

ulated to said pivot member and turning about the bearings thereof, said pivot memher being so constructed and arranged that its pivotal axis, about which said blade turns is slightly inclined both in the direction of propulsion and in the direction of rotation of the screw to the neutral axis of said blade, which latter normally passes through the axis of said blade; :1 spring member on said pivot member co-operating with said step bearing and constructed and arranged so as to prevent said blade turning when the centrifugal force of the screw is low; and a pitch-adjusting device associated with said blade and said pivot member, substantially as described.

7. In an air screw having automatically variable pitch, the combination of: a driving shaft; a hub on said driving shaft; a pivot member comprising an upper roller bearing and a lower ball bearing constituting a step bearing mounted on said hub; a blade articulated to said pivot member and turning about the bearings thereof, said pivot member being so constructed and arranged that its pivotal axis, about which said blade turns is slightly inclined both in the direction of propulsion and in the direction of rotation" of the screw to the neutral axis of said blade, which latter normally passes through the aXis of said blade; a spring member on said pivot member co-operating with said step bearing and constructed and arranged so as to prevent said blade turning when the centrifugal force of the screwis low; a pitch-adjusting device associated with said blade and said ,In testimony whereof I have affixed my signature.

l MARCEL PILLARD.

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