US2630709A - Pitching moment recorder - Google Patents

Description

INVENTORS AGENT ANTONR. HOFFMANNR WALTER J. CRUMP A. R. HOFFMANN ETAL PITCHING MOMENT RECORDER 1 Filed Jan. 29, 1946 STICK LOCKED TAB ADJUSTED NO RESULTING MOMENT STICK FREE March 10, 1953 NEG POS

Patented Mar. 10, 1953 PITCHING MOMENT RECORDER Anton R. Hoffmann, Southport, and Walter J. Cramp, Stratford, Conn., assignors to United Aircraft Corporation, East Hartford, Conn., a

corporation of Delaware Application January 29, 1946, Serial No. 644,016

'5 Claims. 1

This invention relates to means for measuring the moments of a rotor blade or blades for helicopters, or the like, and for adjusting the blade or blades in accordance with such measurement.

In helicopters, during flight, certain vibrations may be present due to unbalance of the rotor blades with respect to each other. Such vibrations will cause an unbalanced resultant moment acting on the control system felt in the control stick as a one per revolution shake and may render the controls inaccurate or difficult to operate or fatiguing to the operator.

Hitherto, devices have been built to measure such vibrations so that corrections could be made in the rotor blades therefor. Such devices have included synchroscopes and electrical recorders and have been bulky and diiii-cult of manipulation, and not suited for use away from factories or completely equipped airport services.

It is an object of this invention to provide a simplified, but very accurate, means for balancing rotor blades for helicopters, or the like.

Another object is to provide a device as set forth in the above object that may be readily installed and used by a person not necessarily skilled in the measuring arts.

Other objects reside in the details of construction, arrangement of parts, and will be either obvious or pointed out in the following specification and claims, in view of the drawing of a presently preferred embodiment, in which:

Fig. l is a diagrammatic plan view of a threebladed rotor type of helicopter;

Fig. 2 is an elevational view *with parts broken away and non-essential parts omitted for clarity;

Fig. 3 is a diagrammatic view of the chart and stylus arrangements;

Figs. 4: and 5 are sample charts; and

Fig. 6 is a diagrammatic illustration of a modified form of the indicating mechanism of Figs. 1 through 3.

Referring first to Figs. 1 and 2, a helicopter has a body ill in which an engine 12 is mounted. The engine l2 turns a drive shaft 14 through suitable reduction gearing Hi to turn several rotor blades [8 carried above the body 10. The rotor blades are mounted upon the drive shaft M by universal hinges, not shown, but which may be substantially the same as those shown in application Ser. No. 592,862 of Igor I. Sikorsky, filed May 9, 1945, now Patent No. 2,517,509 of August 1951. The rotor blades are equipped with tabs 26 which may be bent by suitable tools between limits indicated at 22, Fig. 2, to change the pitching moment of a blade due to aerodynamic forces.

Each of the rotor blades 18 is provided with a control arm. 24 which is connected by a push-pull rod 26 to a whiflletree 2B. The whifiletree 28 is connected at its inner end to amovable plate 30 which can be moved up and down to change the pitch of all of the blades [8 by total pitch control means, not shown. The outer end of the whiflletree 28 is connected by push-pull rod 32 to a plate to which is driven around with the shaft [4. The plate 34 is connected by suitable bearings with a non-rotatable tilt plate 315 which can be tilted in any direction in azimuth by a plurality of push-pull rods 40, only one of which is shown. When the rod 40 is moved up or down, the plates 34 and 3B are tilted correspondingly and the pitch of the blades [8 Will be controlled cyclically in accordance with such tilting. When the rod 40 is in a mid or neutral position, the blades maintain the same pitch during an entire revolution.

The rod 40 is positioned by a crank 42 pivoted upon the framework of the body Ill, and is moved up and down by a rod 44 connected at its lower end to a bell crank 46 pivoted by its mid pivot to a fixed portion of the craft. The bell crank 46 is rocked by a rod 48 which in turn is moved by a control stick 50 in the occupants portion of the body It. As the control stick 50 is pushed forwardly, the rod 40 will be moved upwardly through the linkage above described, and as the control stick 50 is moved 'backwardly, the rod is pulled down. With the stick 50 held in the neutral position shown, the rod 40 will likewise remain substantially in the position shown in which the blades I-B have a constant angle of incidence through their entire revolution. Lateral control is effected by similar linkage, not shown.

When the rotor blades it are turned by the engine I2, or due to aerodynamic action in the autorotation state, the control rod 4!] will be subjected to cyclical vibrations if the pitch of the rotor blades it differ with respect to each other, or if the aerodynamic pitching moments of these blades are difierent. In order to measure the different aerodynamic pitching moments of the several blades, an indicating mechanism is provided as generally indicated at 52 in Fig. 2. This mechanism 52 comprises a chart 54 that is driven by and may be secured to the drive shaft 14 and a stylus arm 56 mounted upon the pushpull rod 44 by a pivot bracket 58. The stylus arm 55 is equipped with a marking device, or stylus, til at its outermost end for marking the chart 54. The arm 56 is pivoted at a point between its ends by a multiplying mechanism comprising a slip friction device including a spring 32 cooperable with a clip 64 carried by a pivot 65, which spring and clip restrain the pivot to a position along a Wire 68 that is secured at its upper and lower ends to fixed parts of the body of the helicopter. The slip friction device may be moved along the wire 68 so that the marking point Gil of the stylus arm 56 may register with a fixed mark around the chart 54, or to a position in which new marks may be made upon the chart 5d, and allows for movement of the controls.

As best shown in Fig. 2, each blade when in the position shown will have its push-pull rod 32 in substantial registry with the push-pull rod 40 at one position in its cycle, so that any net difference of the pitching movements of the three blades at this time will be transferred through the rod 50 to therod M to cause the stylus arm 56 to be moved. The resulting chart when utilized as set forth hereinafter, permits appraisal of the pitching moments of all the blades and, therefore, it is necessary to use but one indicating mechanism 52.

In Figs. 4 and 5, the charts 54 are shown as they would appear if unrolled and after marks have'been made thereon by the marking point 60 of the stylus arm 56. As the shaft I4 moves through a complete revolution from to 360 on the chart, a push-pull rod 32 of a blade lines up with control rod 60 at the 0", 120, 240 and 360 positions on the chart. In Fig. 4, a straight line marked stick-locked could be made by holding the control stick by a suitable fastener and operating the rotor blades I8 and placing the marking point 60 against the chart 54. Under such conditions, any vibration of the rotor blade cannot be transferred to the marking point 60 because of the locked stick. The line marked stick free is irregular and indicates variations in the pitching moments of the several blades between zero degrees and 360 degrees on the chart.

At the zero position on the chart 54, the line marked stick free indicates that there is a positive pitching moment of the blade I8 which has its control linkage in registry with the rod 40. Inasmuch as there are three blades I8 spaced substantially 120 degrees apart, substantially 120 degrees later, the indication of the stick free line on the chart 5% at 120 degrees will indicate positive pitching moment for the second blade of the three. 120 degrees still later, the third blade I8 will have its control linkage in registry with the push-pull rod 50 and the chart indicates a negative pitching moment.

Upon examining a chart as described above, an operator will be apprised of the fact that the first and second blades have a positive pitching moment, with the second blade having a slightly greater moment than the first blade. Each blade may be marked with a distinguishing color and, v

if desired, the lines denoting the degree position upon the chart may be of the same color, and the operator, by moving a blade to a position in which its control linkage is in registry with pushpull rod 40, will then know that the corresponding line on the chart beneath the marking point 60 should correspond to this color. With such information, the operator will then be able to bend the tab of the first and second blades downwardly to a required degree to give a more negative pitching moment to such blades. The third blade shows a negative pitching moment so that its tab 20 will need be bent upwardly, but to a lesser extent than the other two tabs were bent downwardly because this moment is of a lower magnitude than the positive moments of the first two blades. Thereafter another run may be made and a new tracing made by the marking point 60 upon the chart 54.

Fig. 5 discloses what is considered to be a desirable trace of the resulting moments of all blades as recorded with proper trim tab adjustment thereof and the stick free. The line bearing the legend tab adjusted-no resulting moment is substantially horizontal and the irregu- 4 larity thereof is: caused only by engine vibration due to explosions, and gear tooth vibrations in the reduction gearing I6.

The indicating mechanism 52 of this invention is of such simple construction that it may be made part of the regular equipment for the helicopter so that periodically it may be used to correct the blade action. When not in use the slip friction device may be slid along the Wire 68 so that the stylus is out of the way of other operating parts of the machine, or the entire mechanism can be easily removed and replaced, if desired. It is also obvious that the chart 54 might be operated by different parts of the mechanism associated with the rotor drive and that the stylus could be actuated from other of the rods connected between the control stick 50 and the tilt plate 36, and that the choice of position for this mechanism may be left with the mechanic who is to use the device.

It will be understood that in testing the rotor of a helicopter as above described the helicopter would be held stationary 0n the ground either by loading it with sufiicient weight or by using tiedown cables.

In Fig. 6, a modification of the indicating mechanism for performing the functions outlined above is shown and comprises a drive shaft I I4, which may be the rotor drive shaft I4 of Fig. 2, mounting a plate II6 which turns cam projections I I8, one of which is shown in engagement with a breaker switch generally indicated at I20. The breaker switch I20 engages three times in each revolution of the rotor for a threebladed rotor at the time that the rotor control mechanism is in registry with a control rod I 14 corresponding to rod 44 of Fig. 2. At the time of engagement of the switch I20 the force in the control rod I44 due to the action of a rotor blade will be reflected in a strain gauge I46, or the like, which registers the strain in the rod I44. Obviously, other pressure responsive electrical means could also be used to generate a signal. Wires from the breaker switch I20 and the strain gauge I46 lead to a suitable recorder I25 which may carry a chart I26 driven by the shaft I IE or otherwise. Current for the circuits to the breaker switch I20 and the strain gauges I45 are supplied from suitable sources, not shown, through wires I28. The breaker switch I20 may energize a spring biased solenoid I30, or the like, to move a stylus I32 to make a mark I34 on the chart I26. Peaks I36 on the mark I3 3 will occur degrees apart upon energization, of the solenoid I30 by the breaker switch I20 under the influence of the cams H8. 1

To obtain a trace upon the chart I26, of the force caused by blade action, the strain gauge I 36 may operate a solenoid I40, or the like, to make a mark I42 upon the chart I26. The mark I42 will accurately indicate upon the chart the force upon the control rod I44. With such structure, by providing an external driving means for chart I26 the chart and mechanism containing the chart may be removed from the body of the heli copter so that a ready field test may be obtained merely by plugging into the circuits of the breaker switch I20 and the strain gauge I35. Obviously, electrical equivalents could be used for the various parts of the combination to obtain the same result as obtained by the means explained.

While we have shown and described two modifications of our invention and the method for using the same, it will be understood that modified means and methods will occur to those skilled in the art within the spirit and scope of the following claims:

We claim:

1. Apparatus for testing helicopter rotors, in combination, a drive shaft, a plurality of variable pitch blades driven by said shaft, a rotating pitch control mechanism driven by said shaft and connected to said blades, a non-rotating pitch control mechanism connected to said rotating mechanism for controlling the pitch of said blades, a movable chart, a stylus for making a trace on said chart, means responsive to vibrations and the dynamic pitching moment of each blade as it passes a given point during each revolution, said last mentioned means being connected to said non-rotating control mechanism, means operatively connecting said responsive means and said stylus so that said stylus marks and records on said chart the combined pitching moments for all of said blades, and means including an element driven by said shaft for indicating on said chart the points on the trace of said stylus at which each of said blades passes said given point.

2. Apparatus for testing helicopter rotors, in combination, a drive shaft, a plurality of variable pitch blades driven by said shaft, a rotating pitch control mechanism driven by said shaft and connected to said blades, a non-rotating control mechanism connected to said rotating mechanism for controlling the pitch of said blades, a movable chart, a stylus for making a trace on said chart, means responsive to the combined dynamic pitching moments of said blades as they pass a given point during each revolution, said means being connected to said non-rotating control mechanism, means operatively connecting said responsive means and said stylus so that said stylus marks and records on said chart the combined pitching moments of said blades, and means including an element driven by said shaft for indicating on said chart the point on the trace of said stylus at which each of said blades passes said given point.

3. Apparatus for testing helicopter rotors, in combination, a shaft, a plurality of blades mounted on said shaft for pitch varying movement, means for varying the pitch of said blades including a swash plate mechanism having relatively stationary and rotatable parts, control members connecting the pitch varying elements of each of said blades with said rotatable part, means including a pilot operative member connected to said relatively stationary part, and recordin means for registering forces set up in said pilot operative member and in the connections between the latter and said stationary part by the dynamic pitching moments of the several blades as the control member associated with each blade moves past said pilot operative member including, a movable chart, a stylus for marking said chart, means carried by said pilot operative memher and responsive to the combined dynamic pitching moments of said blades, means operatively connected to said last mentioned means and to said stylus for moving the latter to mark said chart in proportion to the magnitude of said pitching moments, and means including an element driven by said shaft for indicating on said chart the points on the trace of said stylus at which said control members pass said pilot operative member.

4. Apparatus for testing helicopter rotors, in combination, a shaft, a plurality of blades mounted on said shaft for pitch varying movement, means for varying the pitch of said blades including a swash plate mechanism having relatively stationary and rotatable parts, generally upright members connecting the pitch varying elements of each of said blades with said rotatable part, means including a generally upright pilot operative member connected to said relatively stationary part, and recording means for registering forces set up in said pilot operative member by the pitching moments of the several blades as the upright member associated with each blade moves past said pilot operative member including, a movable chart, a stylus for marking said chart, means carried by said pilot operative member and responsive to the forces exerted on said member due to the combined pitching moments of said blades, means operatively connected to said last mentioned means and to said stylus for moving the latter to mark said chart in proportion to the magnitude of said pitching moments, and means including an element driven by said shaft for indicating on said chart the points on the trace of said stylus at which said upright members pass said pilot operative member.

5. Apparatus for testing helicopter rotors, in combination, a shaft, a plurality of blades mounted on said shaft for pitch varying movement, means for varying the pitch of said blades including control mechanism having relatively stationary and rotatable parts, control members connecting the pitch varying elements of each of said blades with said rotatable part, means including a pilot operative member connected to said relatively stationary part, and recording means for registering forces set up in said pilot operative member by the pitching moments of the several blades as the control member associated with each blade moves past said pilot operative member including, a movable chart, a stylus for marking said chart, means carried by said pilot operative member and responsive to the forces exerted on said member due to the combined pitching moments of said blades, means operatively connected to said last mentioned means and to said stylus for moving the latter to mark said chart in proportion to the magnitude of said pitching moments, and means including an element driven .by said shaft for indicating on said chart the points on the trace of said stylus at which said control members pass and pilot operative member.

ANTON R. HOFFMANN. WALTER J. CRUMP.

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

UNITED STATES PATENTS Number Name Date 815,303 Mason Mar. 13, 1906 981,989 Fitch Jan. 17, 1911 1,316,260 Zahm Sept. 16, 1919 1,457,629 Lawaczeck et a1. June 5, 1923 2,151,728 Baker Mar, 28, 1939 2,166,932 Keinath July 25, 1939 2,252,464 Kearns et al. Aug. 12, 1941 2,291,475 Kellogg et a1 July 28, 1942 2,343,383 Martin et a1 Mar. 7, 1944 2,361,990 Brown Nov. 7, 1944 2,380,582 Cierva July 31, 1945 2,385,881 Peterson Oct. 2, 1945 2,415,148 Sikorsky Feb. 4, 1947 2,451,541 Doman Oct. 19, 1948

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