US2124760A - Propeller blade pitch setting device - Google Patents

Description

Patented July 26, 1938 UNETED STATES PROPELLER BLADE PITCH SETTING DEVICE Walter W. Burrington, Seattle, Wash., assignor to Northwest Air Service Inc., Seattle, Wash, a corporation of Washington Application February 11, 1936, Serial No. 63,310

Claims.

This invention relates to propeller blade pitch setting devices and a primary object of this invention is to provide a propeller blade pitch setting device of simple and efficient construction 5 which. is quickly and easily applicable to a propeller blade and which will save a great deal of time and labor in imparting a proper pitch to a propeller blade.

Another primary object of this invention is to provide a propeller blade pitch setting device which is adapted to be mounted on a propeller blade alone without being connected to any other support and which is operable to twist or pitch said propeller blade in either direction and which leaves said propeller blade free to assume its natural angle when no torque is being exerted on said pitch setting device thus making it possible to obtain a correct measurement of the pitch of the propeller blade without disconnecting, or loosening the pitch setting device.

Another object is to provide a propeller blade pitch setting device comprising two relatively strong frame members pivotally connected together for relative angular movement, said two frame members being interconnected by power step-up means by which they may be angularly moved relative to each other and each of said frame members being provided with means for engaging a propeller blade, said two blade engaging means being spaced from each other.

A further object of the invention is to provide a propeller blade pitch setting device which is equally well adapted for initially putting the correct pitch in a propeller blade or for restoring the correct pitch to a propeller blade which has been damaged.

In the methods heretofore commonly employed of imparting pitch to metal airplane propeller blades by exerting a torque or twist on the blades it has been common practice to use clamping devices engaging the propeller blade at two locations and to secure one of said clamping devices to a fixed support or have the same held by an operator while the other clamping device is being angularly moved to twist or pitch the blade. This method consumes a great amount of time because it is often necessary to twist the blade and then measure the pitch angle of the blade several times at one station before 50 the correct pitch is obtained and obviously it is necessary to disconnect a fixedly secured clamping device either from the blade or from its support and relieve the blade from strain each time before the pitch angle can be correctly measured. Where two operators are used, one

on each clamping device, it has also been found necessary to disconnect the blade clamping devices, which are usually in the nature of long levers, before the pitch angle of the blade can be correctly measured.

This invention overcomes the objectionable features hereinbefore pointed out by providing a propeller blade pitch setting device which is supported on the propeller blade only and is not secured to any other support and which is positioned so that it does not affect the pitch angle of the blade when no torque is being exerted by the pitch setting device.

Other and more specific objects of the invention will be apparent from the following description taken in connection with'the accompanying drawing.

In the drawing Fig. 1, is a side elevation of a propeller blade pitch setting device constructed in accordance with my invention.

Fig. 2 is a front elevation of the same.

Fig. 3 is a plan view of the same.

Fig. 4 is a sectional View substantially on broken line 44 of Fig. 2. 1

Fig. 5 is a somewhat diagrammatic side elevation on a smaller scale showing this propeller pitch setting device applied to a propeller supported on a pitch table.

Like reference numerals designate like parts throughout the several views.

This device embodies a channel shaped frame member having a base portion 6, a side portion 1, and a top portion 8. Another frame member, hereinafter termed a front frame member, is operatively positioned at the open side of the channel shaped frame member. This front frame member consists of a relatively strong base por tion 9, two upright portions It and an arcuate top portion H. The base portion 9 of said front frame member is pivotally connected by a pivot bolt I2 with the base portion 6 of the channel shaped frame member. As there is very little strain on this pivot bolt l2 said bolt may be of relatively small diameter. The base portion 9 of the front frame member is of strong and substantial construction and is preferably provided on its bottom side with two rigidly connected propeller blade engaging plates [3 of metal which is softer than the metal ordinarily used in the construction of propellers. A transverse clamp bar H! has its two end portions connected with the base portion 9 of the front frame member by bolts E5. The upper surface of the bar I4 is preferably curved to conform, in a general way,

to the transverse curvature of a propeller blade 29, Fig. 2, and is preferably provided with two rigidly secured propeller blade engaging plates it of soft metal positioned opposite to the plates l3. The plates I3 and I6 being of softer metal than the propeller blade will not mar the propeller when they contact the same. When the device is in use on a propeller blade the nuts on the bolts IE will preferably be tightened just enough to lightly clamp the blade and yet permita slight slippage of the blade between the plates l3 and It as a twist or pitch is put into the a blade.

The rear portion of the channel shaped frame member, at the junction of the base 6 and side i, is provided with an integral transverse bar portion ll which is connected with a clamp bar it by bolts l9 and cooperates with said clamp bar a propeller blade. Opposed plates 20 of softer material are secured to the bar portion I7 and clamp bar l8 so as to engage with the propeller blade and avoid marring the same. Preferably the plates I3 and i6 which cooperate with the front frame member and the corresponding plates 2% which cooperate with the channel shaped frame member are positioned so that they engage with the propeller blade inwardly from the edges thereof. This avoids injury to the thin edges of propeller blades. Also it provides a propeller blade engaging means which has sufficient contact with propeller blades of the different widths and transverse curvatures usually encountered to adapt this device for use on blades covering a wide range of sizes.

Power multiplication or step-up means is provided for angularly moving the two frame members relative to each other. One preferred power multiplying or step-up means is in the form of a gear segment 2! secured to the arcuate top portion 5 l of the front frame member and meshing with a gear pinion 22 secured to a stub shaft 23 which is jcurnaled in the top portion 8 of the channel shaped frame member and in an L shaped bracket 24 which is rigidly secured to the channel shaped frame member by screws 25. The L shaped bracket 24 extends partially around the gear segment 2! and arcuate top portion II of the front frame member and forms a guide and support and completes a structure which securely holds the gear segment 2i in mesh with the pinion 22. This structure also permits free angular movement of the two frame members relative to each other. The stub shaft 23 has an integral portion positioned above the channel shaped frame member and this integral portion preferably is of square cross section for engagement within a square opening in the end of a lever arm 26. A tube 27 may be slipped over the end of the lever arm 28, as shown in Fig. 5, to provide any desired length of lever arm.

In the operation of this device a propeller which is to be bent to a predetermined pitch or which is to have its pitch altered or corrected is placed on a horizontal pitch table 28 with its hub portion secured upon an upright axle member 3E which is rigidly mounted on the pitch table 28 near one end thereof and extends upwardly from the table at'right angles thereto. This positions and holds the axis of the propeller at right angles to the table and makes it possible to measure the pitch of the blades relative to the horizontal top of the pitch table. In setting the pitch of a propeller it is common practice to read the pitch at intervals of six inches on the IE) to form a clamp for securely clampingpropeller blade and for this reason it is preferable to mark off the pitch table at intervals of six inches by marks 3| shown in Fig. 5. In restoring the proper pitch to a bent or damaged propeller the propeller is first straightened longitudinally to restore the proper alignment. Said propeller is then mounted on the upright axle member 30 so that one blade which is to be straightened is positioned above the pitch table 28 and the other blade extends beyond the end of the pitch table. The pitch setting device is then placed on the blade to be straightened, usually by slipping it over the end of said blade, the channel shaped frame member being nearest to the hub of the propeller. Starting at a station on the propeller blade nearest to the hub of the same and usually about eighteen inches from said hub, the pitch of the blade is measured with a protractor and if the pitch at this station is found to be wrong the pitch setting device is positioned with the blade engaging elements of the front frame portion at this station and the other set of blade engaging elements between this station and the hub. The blade engaging elements ll and I8 are then clamped tightly on the blade and the blade engaging elements 9 and i5 clamped somewhat loosely on the blade. The operator who is correcting the pitch of the blade then preferably stands in a position so that he can hold another blade of the propeller to prevent the .propeller from turning on the axle 30 and at the same time angularly move the lever 26 in either desired direction to exert the desired twisting and bending force on that portion of the propeller between the two clamps. As the propeller is bent or twisted at any station it may be checked from time to time with a protractor to ascertain whether or not the correct angle for this station has been attained. This checking can be done without loosening the clamps or removing the pitching device, as said pitching device is not connected to anything except the propeller and does not exert any twisting strain on the propeller when the lever 2621 is released.

As soon as the proper pitch is imparted to the bladeat one station the pitch setting device is moved outwardly on the blade to the next station and the process repeated. By working from the hub portion of the propeller outwardly it is possible to accurately pitch all of the stations on a blade in a short period of time. Also it is found that after the pitch of a station is properly set, such pitch will not be disturbed by the setting of subsequent stations, due to the fact that the cross sectional area and strength of the propeller blade decreases from the hub toward the tip.

From the foregoing description it will be seen that this pitch setting device is supported entirely on the blade which is being pitched during operation and is not secured to the pitch table 28 or to any fixed support. For this reason the part of the blade which is being set will always assume its natural angle when no torque is being exerted on the pitch setting device and the angle of the blade may always be measured without disconnecting the pitch setting device or loosening the clamps.

The foregoing description and accompanying drawing clearly shows a preferred embodiment of my invention but it will be clearly understood that this disclosure is merely illustrative and that such changes in the invention may be made as are within the scope and spirit of the following claims.

I claim:

1. Propeller blade pitch setting devices for use on a propeller which is supported on a pitch table With a blade thereof in close proximity to the table comprising two frame members; pivotal means connecting said two frame members for relative angular movement; blade engaging means connected with each of said frame members and positioned external to said frame members and at one side of said frame members and adjacent the pivotal connection of said frame members and adapted to receive and hold a propeller blade which is positioned in close proximity to the pitch table whereby the pitch of the blade may be measured with reference to the table; and frame member moving means operatively connected with said two frame members for relatively moving said frame members angularly in opposite directions.

2. In a propeller blade pitch setting device, for use on a propeller which is supported on a pitch table with a blade thereof in close proximity to the table, a channel shaped frame member; blade clamp means connected with one end of said channel shaped frame member; a front frame member pivotally connected with said channel shaped frame member; blade clamp means connected with an end of said front frame member in spaced relation from said blade clamp means on said channel shaped frame member said two blade clamp means being adapted to receive a propeller blade which is positioned externally of said two frame members and in close proximity to the pitch table; and frame member moving means operatively connecting said two frame members whereby said two frame members may be relatively moved angularly in opposite directions on their pivotal connection.

3. In a propeller blade pitch setting device, for use on a propeller which is supported on a pitch table with a blade thereof in close proximity to the table, a channel shaped frame member having a base portion an upright portion and a top portion, another frame member positioned at the front of said channel shaped frame member in substantially parallel spaced relation to the upright portion of said channel shaped frame member; pivot means connecting the bottom portions of said two frame members permitting relative angular movement of said two frame members; power step-up devices interconnecting said two frame members for angularly moving the same; and two spaced apart propeller blade clamping devices connected with the bottom portions of the respective frame members externally of said frame members.

4. In a propeller blade pitch setting device, a channel shaped frame member having a base portion an upright portion and a top portion; another frame member positioned at the front of said channel shaped frame member in substantially parallel spaced relation to the upright portion of said channel shaped frame member; pivot means connecting the bottom portions of said two frame members permitting relative angular movement of said two frame members; a gear rack secured to one of said frame members; a gear pinion rotatably mounted on the other frame member and operatively meshed with said gear rack; gear pinion rotating means connected with said gear pinion; propeller blade engaging means connected with the lower portion of said front frame member; and propeller blade clamp means connected with the lower portion of said channel shaped frame member in spaced relation from the propeller blade engaging means on the front frame member.

5. In a propeller blade pitch setting device, a channel shaped frame member having a base portion an upright portion and a top portion; another frame member positioned at the front of said channel shaped frame member in substantially parallel spaced relation to the upright portion of said channel shaped frame member; pivot means connecting the bottom portions of said two frame members permitting relative angular movement of said two frame members; a gear rack secured to said front frame member; a gear pinion mounted on the top portion of said channel shaped frame member and meshing with said gear rack; a bracket secured to said channel shaped frame member extending over said gear rack supporting said gear rack for movement; gear pinion rotating means connected with said gear pinion; propeller blade engaging means connected with the lower portion of said front frame member; and propeller blade clamp means connected with the lower portion of said channel shaped frame member in spaced relation from the propeller blade engaging means on the front frame member.

WALTER. W. BURRINGTON.

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