A BLADE-PROFILE BLANK FOR A PROPELLER

Abstract: A blade-profile blank for a propeller comprises a first elongate, non-twisted part (1) of streamlined cross-section and of constant cross-sectional area and constant shape from one end of said part to its other, and a second, planar part (2) which connects with one longitudinally extending edge of the first part and which is of constant thickness and breadth. The second part (2) has a surface (5) which merges at least substantially tangentially with one, convex single-curve surface (3) of the first part, and a surface (6) which merges smoothly with the other surface (4) of the first part (1).

Description: A blade-profile blank for a propeller. The present invention relates to a blade-profile blank for a propelle It is well known that for each engine used to drive, for example, a light aircraft, a hydrocopter or the like the engine speed and the engine power constitute those parameters which determine the de¬ sign of the propeller blade. A normal propeller blade is twisted so that its pitch is constant at any given transverse section, which mea that a propeller becomes very expensive unless it can be manufactured in great numbers. Consequently, a prime object of the invention is to provide a blade*- profile blank which is particularly cheap to manufacture and which can be readily worked to obtain practically any desired constant pitch within a very wide range. Such a propeller blade can be produced cheaply and enables propellers for light aircraft, wind-power plants, industrial fans etc. to be manufactured at relatively low costs. This object is realized with the blade-profile blaruk set forth in the following claims. The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 is a sectional view of a blade-profile blank according to the invention, taken at right angles to the longitudinal direction of the blank, Figure 2 is a perspective view of a blade profile according to the O PI invention, shown in larger scale than in Figure 1, Figure 3 is a sectional view of a conventional propeller blade and of a corresponding propeller blade produced from a blcπk according to the invention, Figure 4 illustrates part of a two-bladed propeller produced from blanks according to the invention, Figure 5 is an axial sectional view of the propeller hub of the pro¬ peller illustrated in Figure 4, and Figure 6 illustrates a hub for a three-bladed propeller, seen in the direction of the axis of rotation. Figure 1 is a sectional view of a blade-profile blank according to the invention in approximately double scale. The blade profile illustrated in smaller scale in Figure 2 comprises, for example, a hardened alu¬ minium alloy which has been drawn to produce straight profiles of uni- form thickness and breadth and a cross-sectional shape such as that shown by way of example in Figure 1. The profile comprises a first, streamlined part 1 which along one imaginary edge merges with a second part 2 of constant thickness and width. The second part 2, which by suitable working is to provide the desired pitch angles along the blade, is made as thin as possible, to facilitate removal of material and to make it as light as possible. The thickness of the second part 2 of the profile illustrated in Figur 1 may be 1.5 mm. The first part 1 has a maximum thickness of 4 mm and a width of 50 mm. In the illustrated embodiment, the upper surface 3 is defined by a circular arc whose centre lies in a plane passing through the centre of the first part 1, while the lower surface 4 of " * said first part 1 is also defined by a circular arc whose centre lies ^ in said plane. As will be understood, however, the surfaces 3 and 4 c be formed in any suitable manner whatsoever. The second blade part 2 5 has two planar, mutually parallel, or at least substantially porσllel surfaces 5 and 6, of which the surface 5 merges substantially tangen¬ tially with the surface 3, to provide the desired streamline proper¬ ties of the blade. The surface 6 merges with the surface 4 through a smooth curve 7. In the illustrated embodiment, the part 2 of the 10 profile has a width of about 45 mm. The angle between the second part 2 of the illustrated profile and the lower surface 4 is about 20 , bu can be varied according to the rotational speeds for which the finish propeller is intended. 15 In Figure 2, the part 8 shown in dash lines illustrates the area to removed from the second part 2 in order to obtain a desired pitch on propeller. On the left of Figure 3 there are shown four sections of a conventio 20 nal, twisted propeller blade, said sections being taken from the blad tip at a distance of 100 % of the blade length from the hub (section at a distance of 75% of the blade length frσ ~ the hub (section ,C), at the centre of the blade, 50 of the blade length (section B) , and at a distance of 25 % of the blade length from the hub (section A). Show - 25 to the right of Figure 3 are corresponding blade sections A, B, C and Λ . D of a blade profile according to the invention, said second blade part 2 being worked by removing material from within, for example, the region 8 shown in Figure 2. In order to obtain a constant pitch, the angle of attack <r_ will, as is known, vary along the whole of the 30 blade length and increase towards the hub, because the speed of rota¬ tion of the blade is greatest at the blade tip, i.e. at section D. OMFI The angle a is measured between a line drawn between the longitudina edges of the blade, the chord 9, and a line 10 extending at right ang les to the axis of rotation of the propeller. It will be seen that a propeller blade having the same constant pitch as the twisted conventional blade shown to the left of Figure 3 and the same anales of attack a. - a,. can only be obtained from the A D J straight, non-twisted profile blank according to the invention, by removing material from the thin profile part 2 of uniform thickness. It should be emphasized here that the profile of the illustrated part 1 can be modified in many different ways, and the surface 4, for exam may be made completely flat if desired, or may, for example, have the same radius as the curved surface 3. The convex, single-curve surface 3 need not be symmetrical as described, but may, for example, have a wing profile form of the kind illustrated in section D to the left of Figure 3. When practicing the invention, a propeller can be produced very quickly, even by unskilled workmen, since all that is required is access to the relatively inexpensive blade blank according to the in¬ vention and data concerning the width of the blade at some sections . If a blade should become damaged, all that is necessary is to take the width measurements of the undamaged blade and mark these measure- ments on a blade blank, and then saw and grind the part 8 (Figure 2) away. Figure 4 illustrates part of a propeller having two blades 11 and 12 and manufactured from a blank according to Figures 1 and 2. The two blades 11 and 12 are twistably mounted on a hub 13. As will be seen from Figure 5, the hub comprises a cylindrical body 14 having α central bore 15 for receiving the engine shaft. Provided in the cylindrical body 14 are two cylindrical recesses 16 arranged to ro- tatably receive a cylindrical part 17 of a head 18. The head 18 forms part of a bifurcate element having two legs 19 and 20 which form therebetween a gap 21 into which one end of respective propeller blad 11, 12 can be inserted and fastened by means of bolts 22, 23 (Figure The head 18 has an outer part in the form of a straight truncated con which is co-axial with the cylindrical part 17 and which co-acts with a conical surface located on the inner surface of a cover plate 24. The cover 24 is secured to the cylindrical body 14 by means of bolts 25 and is through-passed by respective bifurcate elements. By loose¬ ning the bolts 25, a bifurcate .element together with its associated propeller blade 11, 12 can be rotated continuously and smoothly to adjust the pitch for optimal use of the engine. Subsequent to setting the desired pitch, the head 18 of respective bifurcate elements is secured by tightening the bolts 25, the conical surface on said head 18 being urged against the conical surface 26 on respective covers 24, so as to positively lock the head 18 in the set position. Figure 6 is a simplified view of a hub 26 of the same kind as that illustrated in Figure 5, but intended for a three-bladed propeller. The hub 26 has a central bore for receiving the engine shaft, and sunk into the hub are three pressure plates or cover plates 28 corre¬ sponding to the cover plates 24 of the Figure 5 embodiment. Propeller blade attachment means 29 may also have the form of the bifurcate elements 19,20 shown in Figure 5, or any other suitable form. Each attachment means 29 has an inner head with a conical surface arranged to co-act with a conical surface in respective covers 28, as described with reference to Figure 5. OMPI

Claims: CLAIMS :- 1. A propeller-blαde profile blank, comprising a first, elongate, πoπ-twisted first port which is streamlined in cross-section and is o constant cross-sectional area and of constant shape from one end of said part to the other: and a second, planar part which merges with one longitudinal edge of said first part and extends along the whole of said edge, said second part having substantially constant thicknes and breadth and a first surface which merges at least substantially tangentially with a convex single curve surface of said first part, and a second surface which merges smoothly with the other surface of said first part. 2. A blank according to Claim 1, in which the convex, single- curve surface of the first profile part is defined at right angles to the longitudinal direction of the blank by a circular arc. 3. A blank according to Claim 1, in which said other surface of said first profile part is defined at right angles to said blank by a circular arc. 4. A blank according to Claim 1, in which said other surface of said first profile part is planar. ONPI

Inventors: KOLECKI JERZY
Applicants: KOLECKI JERZY
Application year: 1982
Main classification: B21D53
IPC codes: B64C11