GB2209370A - Propeller - Google Patents

Description

r ,,-2093710 PROPELLER This invention relates to a propeller, particularly

although not exclusively for a propulsion system, for example of an aircraft.

It has long been attempted to reduce the fuel consumption of propulsion systems especially for aircraft, to save operating cost and also to economise energy.

Savings can be achieved from the thermodynamic cycle of the engine, but to a large degree also from the propulsion system (propulsive coefficient). The propulsive coefficient increases with decreasing velocity difference between exit velocity from the main propulsor and and flight speed. With a conventional propeller, however, considerable losses are encountered in the flight mach range M > 0.7, which greatly reduce the total efficiency.

These losses result from the fact that.the static pressure level decreases when the relative velocity between the propeller blade and the air reaches the unfavourable supersonic range. This is why conventional propeller engines will not at reasonable expense give higher speeds than practically M=0.7.

For moderately low flight mach numbers, socalled propfan engines were developed, which have a more favourable propulsive coefficient than fan engines. A typical propfan engine has been described in DE-OS 33 04 417.

In FR-877 989 a propeller is disclosed the blades of which are curved in a circumferential direction to give improved efficiency plus reduced noise at high Mach numbers.

In FR-1 047 583 a propeller is disclosed the blades of which are inclined in an axial direction. This, together with a pointed shaft cone, is to give an improved flow pattern. More particularly, the streamlines are to be deflected radially inward. These two arrangements are disadvantaged by the fact that the center of gravity of a blade then no longer lies exactly radially above the mounting point. The blade fixing accordingly becomes subject to considerable bending moments necessitating heavy blade fixings to absorb the high centrifugal loads.

Embodiments of the present invention provide a propeller blade producing a radially inward directed flow profile without causing mechanically unfavourable moments to act on the blade fixings.

In a particular aspect of the present invention the propeller blades are curved such that the force acting on the surrounding air in a direction normal to the blade back and face surfacesgenerates, when integrated over propeller span, a static pressure that increases in the direction of the hub, and the center of gravity of the propeller blade is situated radially above the blade fixing.

An advantage afforded by the present invention is that it permits a radially inwardly increasing static pressure to be generated. This reduces both the level of the relative propeller speed and the angular momentum.

The force exerted by the propeller blade on the air flowing through the propeller extends approximately normal to the face of the blade. Its radial components cause a rise in static pressure in the direction of the propeller hub; the tangential component causes the thrust force. The "packing effect" resulting ahead of the propeller from the radial pressure rise causes an advantageously reduced velocity level in the flow around the propeller blade. The advantageously reduced velocity level advantageously avoids the abruptly growing losses at relative velocities in the supersonic range (conventional propeller), so that higher flight speeds can be attained.

Arrangement of the propeller blade center of gravity radially above the propeller fixing prevents bending moments from acting on the blade fixing. The latter, therefore, can be continued in its conventional design, where the advantageous effects of a profile designed in accordance with the present invention can additionally be achieved.

The objective is a maximally large pressure rise from the outer section towards the inside. As a result the angle of lean the blade axis forms with the radial direction is selected as wide as possible at the propeller tip.

The advantages associated with the embodiments of the present invention, such as reduced losses and reduced noise, or increased thrust at the same propulsive power and the same propeller diameter, or reduced propeller diameter at the same thrust and propulsive power, can be' achieved using a variety of electric motor or combustion engine-based propeller drives.

A further advantage provided by embodiments of the present invention, therefore, is a substantially increased number of applications for such a propeller engine, specifically in the design of blowers, fans, etc., where such fan engines or blowers can be used not only for aircraft, but also for ground vehicles or combined-mode vehicles, such as hovercraft, especially for generating a traction, thrust and/or lift force.

The invention may be put into practice in many ways but certain embodiments will now be described by way of example of the present invention, represented is schematically in the accompanying drawings, in which:

FIG.1 is a front view illustrating a propeller, FIG.2 is an elevation view illustrating the propeller, FIG.3 is an elevation view illustrating a propeller, FIG.4 is a plan view illustrating a propeller with a rising pressure gradient, FIG.5 is a plan view illustrating another propeller variant, FIG.6 is a front view illustrating a propeller actuating mechanism, and FIG.7 is a longitudinal sectional view of the actuating mechanism in accordance with FIG.6.

FIG.8 shows a perspective view of the propeller blade according to the invention showing the pressure side 8 and the suction side 9 of the propeller 1.

FIGS.9 and 10 show a further embodiment.

Y Z With reference to FIG.1 showing a propeller in front view. two propeller blades 1 and 2 are mounted by means of blade fixings 4 on a rotating propeller hub 3, in which the two propeller blades 1 and 2 are identical in construction and are curved in the direction of rotation.

Thus, each blade has, as viewed on a circumferential plane, a sickle-shaped curvature, with the cutting side (edge) of the sickle arranged, i.e. directed towards, the direction of rotation. As will be seen in Fig.1, the radially inward part of the blade 1 is inclined at an angle to the radial direction so that the blade presents a radial outward component; whereas on the radially outer part of the blade 1, the tangent to the curve of the blade is inclined at an angle to the radial direction so that thatpart of the blade presentS a radially inward component.

Fig.2 shows the propeller in side elevation, normal to the hub axis, from which it is seen that the blades are also curved relative to the plane perpendicular to the axis of the hub 3. Thus, the blades are also given an axially sickle-shaped curvature, with the cutting side (edge) of the sickle arranged, i.e. directed, counter to the direction of thrust.

FN here indicates the direction of the force exerted on the air in a direction normal to the blade face of propeller 1. E indicates its radial component. R To avoid stress problems caused by bending moments, the center of gravity S is located radially above the propeller blade fixing 4. In this arrangement the pressure gradient reduces from radius Rx towards the inside, because the normal on the blade face is given an outwa"rdly directed radial component. But owing to the lower peripheral speed the inwardly generated, oppositely directed pressure gradient is smaller than the outwardly g(nerated gradient. so that on balance the desired pressure rise towards the inside is still achieved.

is In the propeller-variant shown in FIGS.1 and 2 the decrease in pressure gradient at the hub can be avoided if the inner lean + P(in accordance with FIG.2) is selected such that its pressure gradient (rising towards the inside) compensates or exceeds the gradient caused by the peripheral direction at the hub (FIG.1).

FIG.3 illustrates three sections through a propeller blade 1, namely a hub section N, a mean section M and a tip section G. In FIG.4 these sections N, M and G are plotted one over the other from a radial perspective, i.e. in plan view, with the respective centroids SN, SM and SG being indicated.

6 M 1 In accordance with the present invention the (radial) course of the center of gravity axis is selected such that the downwardly directed area projection of individual sections (left-hand hatching) becomes so large that when totaled over the propeller 1 (propeller span), an inwardly increasing pressure gradient results (FIGA). Displacement of the G section is circumferentially (U) as well as axially (Z). Both give the desired inwardly directed surface is normal (left-hand hatching).

If the blade fixing is to be free of bending moment, "negative lean" is required between sections N and M (right-hand hatching), whereas "positive lean" is required between N and G (left-hand hatching with inwardly directed component of the surface normal), as long as on balance the static pressure rises in an inward direction. The total center of gravity of the blade coincides with the centroid SN Of the hub. section.

The radial pressure gradient is presented when the force exerted by the propeller 1 on the surrounding air or medium has a radial component, i.e., when the surface normal in the respective propeller blade section is inclined relative to the radial. The propeller force proper naturally rises with lift coefficient, velocity head and chordal length of blade. This is why also the effectivity of the lean will grow in a direction from inside to outside. This is made possibly by the arrangement shown in FIG.5.

In this arrangement little "negative" pressure gradient (right-hand hatching) is anticipated between sections N and M despite large "negative" projection area, whereas a large "positive" pressure gradient (left-hand hatching) can be gen- erated between M and G with a relatively modest shift in center of cjravity, so that on balance the desired pressure rise in an inward direction is achieved.

To achieve an optimum pressure gradient for the respective flight speed and propeller speed, a lean change mechanism-as illustrated in FIGS. 6 and 7 will be advantageous. Center of gravity shift can be influenced in both the U- and the Z-axes. Rotating a ring 5 in the direction of the arrow causes a change in propeller lean in the direction U (FIG. 6).

Rotation of the screw 6 in the hub 3 on the spindle 7 urges the propeller blade 1 against the moment of centrifugal force Z into a lean position, with a resultant shift relative to the Z axis as described in the example above (see arrows in FIG. 7).

Actuation is severally or jointly, preferably by electric/electronic provision and infinitely variable (e.g. as taught in EP 154 808). Variable-geometry blades can equally find application (e.g. as taught-in EP 166 104). The inventive concept also embraces further variants on the embodiments shown without departing from the inventive principle.

According to a further embodiment, the downwardly directed area projection of the propeller pressure side between a mean section M at 50% of the propellers height and a mean section G at 90% of the propellers height is 10-30% of the propeller pressure side surface A.

It was found that the relation according to this further embodiment it is especially adequate to achieve a flow line configuration similar to that of a cowled propeller. Preferably, the relation is 2025%.

The embodiment example of the invention will be explained by means of a propeller blade of the invention shown in two views, FIGS.9 and 10.

FIG.9 shows a radial plan view of a propeller blade which rotates about the axis X in the circumferential direction. Three substantially horizontal sections can be seen, referenced N, M, S spaced from the acis of rotation X. The profiled front edge V and the profiled rear edge H of the propeller blade are also shown.

FIG.10 shows the propeller blade according to FIG.9 in front view, in which N^S and H are also drawn on.

The essential projection surface A1 of the invention between M and S can be seen in FIG.9 in its true size as a hatched surface. Taking into account the approximate lengths of N, M and S at about Ne'63 LE, M!n8.5 LE, N!29.5 LE there is an approximate surface Al228 FE. (LE: length units, FE: surface units).

The surface A2 of the propeller pressure side can not be shown in twodimension in its true size since the propeller blade is greatly twisted threedimensionally. A2 can be approximated as a trapezoidal surface, with N and S as approximately parallel base lines and the average (middle) propeller blade height h as the trapezoidal height:

The propeller blade height h can be taken from FIG.10 at about h214 LE. There is an approximate propeller pressure side surface A2 = 6.3+9.5. 14=110FE. 2 Thus the essential ratio (proportion) of the invention is: A1: A2 = 28: 100 = 0.254t25%

Claims (7)

CLAIMS:

1. A propeller having at least two propeller blades mounted on a hub by means of propeller blade fixings, in which the propeller blades are curved such that the force acting on the surrounding air in a direction normal to the blade face and back surfaces results in a static pressure which when integrated over propeller span rises towards the hub, and in which the centre of gravity of each propeller blade lies radially above the propeller blade fixing.

2. A propeller as claimned in claim 1, in which the propeller blades are curved in the direction of rotation.

3. A propeller as claimed in claim 1 or 2, in which the propeller blades each have, as viewed on a circumferential plane, a sickle-shaped curvature, with the cutting side (edge) of the sickle arranged in the direction of rotation.

4. A propeller as claimed in claim 3, in which the propeller blades each have as viewed in axial section a sickle-shaped curvature, with the cutting side (edge) of the sickle arranged counter to the direction of thrust.

5. A propeller as claimed in any one of claims 1 to 4, in which the propeller blades are fitted with an actuating mechanism to adjust the propeller blade lean (inclination) in the direction of rotation and/or in the direction of thrust.

6. A propeller substantially as sE)6cifically described herein with reference to any one of the embodiments illustrated in the drawings..

7. A propeller according to claim 1, wherein the downwardly directed area projection of the propeller pressure side between -a mean section M at 50% of the propellers height is 10-30% of the propeller pressure side surface A.

Ptiblished 196B at The Patent "Ice. State House 6671 HiCh Londor. WC1R 4TP F1jrther ccpies rnk%, be obtained f-cn.The Patent Office.

Wes Branch. St Mary Cray. Orpington. Kent BM 3AD. Printed by Multiplex techniques ltd, St Mazy Cray, Kent. COIL 1137.