Aerial propellers more especially for aircraft propulsive units

The invention provides improvements to aerial propellers, particularly for aircraft propulsive units, wherein the cowling of the propeller is defined by a meridian line having: at its origin (B) a maximum curvature greater than 15; then a curvature decreasing rapidly from the maximum value to a value of 7; then a curvature decreasing linearly from the value 7 to a value of 0; than a curvature decreasing more slowly from the value 0 to a minimum value between -3 and -5; then a curvature increasing rapidly from the minimum value to a value of 0.

The present invention relates to aerial propellers, particularly for 
aircraft propulsive units. 
It is known that the theoretical efficiency of a propeller, for a given 
disk loading C=P/D.sup.2 (P being the power on the propeller shaft and D 
the diameter), increases with the rotational speed of the propeller. But 
the adoption of a high rotational speed comes up against a problem: the 
composition of the speed due to rotation of the propeller and the 
advancing speed of the aircraft leads to relative MACH numbers which 
increase progressively from the base of the blade to its end. In these 
conventional propellers, the MACH number frequently reaches values of the 
order of 0.9 even when the advancing speeds are moderate, of the order of 
M=0.6. At these relative high Mach numbers there already appear, on thin 
conventional profiles, intense shock waves causing lamina separation and 
leading to high loss levels. Consequently, the propulsive efficiency of 
conventional propellers decreases rapidly, at a given propeller speed, 
when the speed of the aircraft increases, which leads to replacing 
propulsive units using propellers by other types of units, particularly by 
turbojets, when the speed of the aircraft exceeds about M=0.65. 
Considerable work has already been carried out to try and increase the 
field of use of propellers towards much higher Mach numbers. 
Propellers have been proposed such as the one shown (in a perspective view) 
in FIG. 1 of the accompanying drawings; this propeller includes a large 
number of blades 1 (with a number of blades generally greater than 8), 
projecting from a cowling 2, at a distance from the leading edge B of the 
cowling. This cowling 2 is joined to the engine nacelle (not shown), fixed 
against rotation. 
The blades 1 of this propeller have a special shape in that their end is 
curved rearwardly, with regard to the direction of rotation of the 
propeller, and downstream, with respect to the plane of rotation of the 
propeller. 
In propellers of this type, the flow in the blade portions (bases) the 
closest to the rotational axis of the propeller risks being blocked in the 
channels defined by the blades, such blocking causing considerable shocks 
reducing the theoretical efficiency of the propeller, with the risk of 
generating lamina separation on the blades and on the cowling. One of the 
aims of the invention is to slow down the flow locally at the base of the 
blades by using an appropriate form of cowling. 
The cowling is defined as a body of revolution generated by the rotation of 
a meridian line about the axis of rotation of the propeller, this meridian 
line being referenced by its coordinates X and Y plotted on the axis of 
rotation of the propeller and on a radical axis and referenced to the 
diameter of the propeller, namely: 
##EQU1## 
x designating the abscissa, r the radius and D the diameter of the 
propeller. 
This meridian line is characterized by its curvature C defined by: 
##EQU2## 
The position of the blades with respect to the cowling is referenced by the 
distance L separating the leading edge of the cowling and the plane of the 
blades defined as being the plane perpendicular to the axis of rotation of 
the propeller and passing through its center. 
The propeller of the invention comprises a plurality of blades leaving a 
cowling at a distance L from the leading edge of the cowling, said cowling 
being defined by a meridian line having: 
at its origin, forming the leading edge of the cowling, a maximum curvature 
greater than 15, 
between its origin and a first relative abscissa point X=x/D equals 0.05, a 
curvature decreasing rapidly from the maximum value to about a value of 7, 
between this first point and a second point situated at a distance from the 
leading edge between 0.5 and 0.7 times the leading edge--blade plane 
distance L, a curvature decreasing substantially linearly from a value 7 
to a value 0, 
between this second point and a third point situated in the plane of the 
blades, a curvature decreasing more slowly than said linear decrease, from 
value 0 to a minimum value between -3 and -5, 
between this third point and a fourth point situated in the rear plane of 
the cowling, a curvature increasing rapidly from the minimum value to a 
value of 0. 
Advantageously the engine nacelle which is joined to the cowling has a 
meridian line, extending that of the cowling, whose curvature increases 
from the value 0 to a value of about 3 at a relative distance of 0.10 to 
0.15 downstream of the rear plane of the cowling, then decreases from 
value 3 to a value of about 1 at a relative distance of 0.40 to 0.45 
downstream of the rear plane of the cowling. 
The invention consists, apart from the arrangements already discussed, of 
several other arrangements which are preferably used at the same time and 
which will be described in greater detail hereafter.

Referring to the above defined system of coordinates and to FIGS. 2 and 3, 
the propeller of the invention has a plurality of blades 1 projecting from 
a cowling 2 at a distance L from the leading edge B of said cowling, said 
cowling being defined by a meridian line having: 
at its origin O, forming the leading edge of the cowling, a maximum 
curvature greater than 15, 
between its origin O and a first point M.sub.1 with relative abscissa X=x/D 
equal to 0.05, a curvature decreasing rapidly from the maximum value to a 
value of about 7, 
between this first point M.sub.1 and a second point M.sub.2 situated at a 
distance L.sub.2 from the leading edge between 0.5 and 0.7 times the 
leading edge--blade plane distance L, a curvature decreasing substantially 
linearly from the value 7 to a value 0, 
between this second point M.sub.2 and a third point M.sub.3 situated in a 
plane of the blades P.sub.P, a curvature decreasing more slowly than said 
linear decrease, from the value 0 to a minimum value between -3 and -5, 
between this third point M.sub.3 and a fourth point M.sub.4 situated in the 
rear plane P.sub.A of the cowling, a curvature increasing rapidly from the 
minimum value to the value of 0. 
The cowling has then: 
a first zone Z.sub.1, between the leading edge B and the second point 
M.sub.2, in which the curvature decreases first of all fairly rapidly from 
its maximum value to a value of about 7, then decreases less rapidly, from 
a value of about 7 to its zero value, 
a second zone Z.sub.2 between the second point M.sub.2 and the plane of the 
blades P.sub.P, in which the curvature is negative and decreases even more 
slowly to its minimum value, and 
a third zone Z.sub.3, between the plane of the blades and the rear plane 
P.sub.A of the cowling, in which the curvature increases rapidly from its 
minimum value to a zero value. 
The engine nacelle 3 which is joined to cowling 2 has a meridian line, 
extending that of the cowling, whose curvature increases from value 0 to a 
value of about 3 at a relative distance of 0.10 to 0.15 downstream of the 
rear plane of the cowling, then decreases from the value 3 to a value of 
about 1 at a relative distance of 0.40 to 0.45 downstream of the rear 
plane of the cowling. 
The engine nacelle has then a zone, called fourth zone Z.sub.4, extending 
the last zone Z.sub.3 of the cowling whose curvature varies fairly rapidly 
following first of all an increase then a decrease. 
This variant of the curvature of the meridian line forming the cowling of 
the propeller and the beginning of the engine nacelle is clearly shown in 
FIG. 3 in which the relative distances (X/D) reckoned along the axis of 
rotation of the propeller are plotted as abscissa and the curvature C as 
ordinates. 
By way of example, the meridian line forming the cowling of the propeller 
and the beginning of the engine nacelle may be formed by the following 
curve sections, in the cartesian system X, Y in which X=x/D and Y=r/D. 
for 0&lt;X.ltoreq.0.3 
EQU Y=0.3271995X.sup.1/2 -2.422616X.sup.2 +5.697069X.sup.3 
for 0.3.ltoreq.X.ltoreq.0.55 
EQU Y=2.996639-38.21174X+200.4801X.sup.2 -538.7765X.sup.3 +794.8556X.sup.4 
-615.5586X.sup.5 +196.3246X.sup.6 
Another example gives, for the cowling and the engine nacelle, the meridian 
line defined in the table below which takes up point by point the 
coordinates of this line in the same carthesian system X, Y, the notation 
E.+-.W signifying 10.sup..+-.W. 
______________________________________ 
X Y 
______________________________________ 
0. 0. 
.1250000E-01 .3621461E-01 
.2500000E-01 .5030967E-01 
.3750000E-01 .6025554E-01 
.5000000E-01 .6781963E-01 
.6250000E-01 .7372742E-01 
.7500000E-01 .7838351E-01 
.8750000E-01 .8205535E-01 
.1000000E+00 .8494048E-01 
.1125000E+00 .8719646E-01 
.1250000E+00 .8895621E-01 
.1375000E+00 .9033639E-01 
.1500000E+00 .9144257E-01 
.1625000E+00 .9237234E-01 
.1750000E+00 .9321749E-01 
.1875000E+00 .9406537E-01 
.2000000E+00 .9499998E-01 
.2125000E+00 .9610265E-01 
.2250000E+00 .9745259E-01 
.2375000E+00 .9912732E-01 
.2500000E+00 .1012030E+00 
.2625000E+00 .1037544E+00 
.2750000E+00 .1068558E+00 
.2875000E+00 .1105801E+00 
.3000000E+00 .1150000E+00 
.3104167E+00 .1192282E+00 
.3208333E+00 .1237836E+00 
.3312500E+00 .1284998E+00 
.3416667E+00 .1332382E+00 
.3520833E+00 .1378875E+00 
.3625000E+00 .1423614E+00 
.3729167E+00 .1465950E+00 
.3833333E+00 .1505422E+00 
.3937500E+00 .1541728E+00 
.4041667E+00 .1574703E+00 
.4145833E+00 .1604294E+00 
.4250000E+00 .1630536E+00 
.4354167E+00 .1653538E+00 
.4458333E+00 .1673461E+00 
.4562500E+00 .1690503E+00 
.4666667E+00 .1704886E+00 
.4770833E+00 .1716840E+00 
.4875000E+00 .1726598E+00 
.4979167E+00 .1734383E+00 
.5083333E+00 .1740401E+00 
.5187500E+00 .1744838E+00 
.5291667E+00 .1747857E+00 
.5395833E+00 .1749592E+00 
.5500000E+ 00 .1750155E+00 
______________________________________ 
In FIG. 4 a graph has been shown with the relative distances (x/D) reckoned 
along the axis of rotation of the propeller shown as abscissa and, at the 
lower part of the ordinate axis, the relative distances (r/D) reckoned in 
the plane of the blades as ordinates, and at the upper part of the axis of 
the ordinates, the relative Mach number (local Mach number/Mach number 
characterizing the speed) for a Mach number of 0.7. 
The lower curves are the median lines of the cowling of the invention 
(continuous line) and of a conical conventional cowling (broken line). 
The upper curves are the relative Mach variations in the case of a cowling 
of the invention (continuous line) and of a conical conventional cowling 
(broken line). 
It can thus be seen that in the plane of the blades we have a substantial 
slowing down of the local Mach number, which contributes to avoiding the 
risk of blocking of the flow in the channels defined by the blades. 
In so far as the different profiles are concerned which should be given to 
each blade associated with a cowling having the above characteristics, 
modern profiles may be used such as those usually established for 
transonic propellers. 
Finally, and whatever the embodiment adopted, a propeller is obtained which 
may be used at high Mach numbers (greater than 0.65) and in which, because 
of the shape of the cowling, the phenomena of blocking of the flow in the 
channels defined by the blades at their bases are avoided. The efficiency 
of the propeller is therefore not diminished by shocks or lamina 
separation which such blocking phenomena risk causing.