Propeller with removable and adjustable blades

A propeller according to the invention has a hub centered on and rotatable about a hub axis and formed with a bore extending along the axis and with a plurality of identical, radially outwardly open, and angularly equispaced sockets centered on socket axes extending at least generally radially of the hub axis. Respective identical blades each have a base complementary to and snugly fittable in the respective socket and an outer part extending radially outward from the hub along the respective socket axis when the respective base is fitted therein. Respective locks are provided in the hub for releasably fixing the bases in the respective sockets against relative movement between the respective blades and the hub. The sockets and bases are normally complementarily cylindrical and both centered when the bases are in the sockets on the respective socket axes. Thus the blades can turn about the respective socket axes on the hub when released by the respective locking means. In addition each socket is formed with an annular groove open inwardly radially of the respective socket axis and each base is formed with a similar annular but outwardly open groove confronting the respective inwardly open groove when the base is fitted in the respective socket and forming with the respective inwardly open groove an annular chamber. The system for locking includes a respective plurality of balls generally filling the chamber and something that can press the balls tightly against the respective grooves.

FIELD OF THE INVENTION 
The present invention relates to a propeller. More particularly this 
invention concerns a propeller with removable blades used for instance as 
a watercraft drive screw, mixer element, turbine rotor, air fan, or the 
like. 
BACKGROUND OF THE INVENTION 
A standard propeller such as usable as the drive screw of a watercraft 
comprises a central hub centered on and normally rotated about a hub axis, 
and a plurality of identical blades extending radially at equiangular 
spacing from the hub. Such a propeller is invariably made by casting from 
one piece of metal, either stainless steel or a cuproaluminum alloy, as it 
must be very strong and must also be capable of being finished to very 
close tolerances. 
The rough casting from which the propeller is eventually made is cast in a 
mold that is made from a model supplied to the foundry either in wood or 
in metal. The wood model normally has a single blade but the metal one is 
complete. 
The wood-model route is most popular because the model costs the least to 
make. The foundry has to make up individual molds for each blade. In this 
there is a possibility of modifying the pitch by inclining the axis of the 
propeller hub relative to the original setting, but this possibility is 
limited and anyhow the new value of the pitch is really only obtained on a 
single radius normally equal to seven-tenths of the radius of the 
propeller. 
Once the rough casting for a given propeller is completed it is subject to 
a complex and expensive machining operation that must be carried out by 
hand by skilled workers. The propeller must be ground and eventually 
statically and even dynamically balanced. As a result a propeller is 
expensive to manufacture. In addition propellers must also normally be 
produced in a wide range of sizes. 
It is fairly common for a propeller to be damaged, in particular in inland 
waterways, so that the propeller must either be repaired or replaced. 
Repair is extremely exacting work, and replacement is also expensive 
because of how much a propeller costs to make in a group of different 
sizes and then to stock in this range of sizes. 
It is also common that a change in engine or operating conditions requires 
that a different type of propeller be used. In this situation a perfectly 
good propeller must be replaced with the needed type, or inferior 
operating performance with the existing but now mismatched propeller must 
be tolerated. 
OBJECTS OF THE INVENTION 
It is therefore an object of the present invention to provide an improved 
propeller. 
Another object is the provision of such a propeller which overcomes the 
above-given disadvantages, that is which is inexpensive to manufacture and 
which is not difficult to adapt to a range of sizes. 
SUMMARY OF THE INVENTION 
A propeller according to the invention has a hub centered on and rotatable 
about a hub axis and formed with a bore extending along the axis and with 
a plurality of identical, radially outwardly open, and angularly 
equispaced sockets centered on socket axes extending at least generally 
radially of the hub axis. Respective identical blades each have a base 
complementary to and snugly fittable in the respective socket and an outer 
vane part extending radially outward from the hub along the respective 
socket axis when the respective base is fitted therein. Respective locks 
are provided in the hub for releasably fixing the bases in the respective 
sockets against relative movement between the respective blades and the 
hub. The sockets and bases are normally complementarily cylindrical and 
both centered when the bases are in the sockets on the respective socket 
axes. Thus the blades can turn about the respective socket axes on the hub 
when released by the respective locking means. In addition each socket is 
formed with an annular groove open inwardly radially of the respective 
socket axis and each base is formed with a similar annular but outwardly 
open groove confronting the respective inwardly open groove when the base 
is fitted in the respective socket and forming with the respective 
inwardly open groove an annular chamber. The system for locking includes a 
respective plurality of balls generally filling the chamber and something 
that can press the balls tightly against the respective grooves. 
According to further features of this invention the hub is formed at each 
socket with a loading passage having an outer outwardly open and threaded 
end and an inner end opening at the respective inwardly open groove and 
each passage is sufficiently large that balls can be introduced through it 
into the respective chamber. The means for pressing the balls are screwed 
into the respective outer ends to bear on the balls therein. A plug is 
threaded into the outer end of each passage and bears on a locking ball 
that in turn bears on two of the respective set of balls. This presses the 
balls apart and wedges them in the respective chamber thereby solidly 
locking the blade in the socket. When not under such compression each set 
of balls acts like a rotary roller bearing to permit the respective blade 
to rotate in the respective socket. 
Each socket in accordance with this invention has a face directed radially 
outward from the hub axis and each blade has a face directed radially 
inward toward the hub axis and directly confronting the respective socket 
face when the respective blade base is fitted in the respective socket. At 
least one stop pin projects radially of the hub axis at each socket from 
one of the respective faces into the other respective face. This locks 
each blade against rotation relative to its socket even if the locking 
balls are not under compression. The use of a pin like this allows exact 
pitches to be set by aligning factory-precise bores and pins. Normally a 
given blade is only meant for use at a given pitch, so the correct setting 
can be established at the factory, although a series of holes on either 
face would allow for some range of adjustability through a series of 
accurately determined positions. 
To allow the system to be emptied of balls or the balls to be freed up 
after they have been compressed to lock a blade, the hub is formed at each 
socket with another passage offset from the respective loading passage, 
opening into the respective chamber, and normally blocked by a respective 
plug. A tool or a fluid under pressure could be admitted to the chamber 
through this passage to free up or push the balls out the other passage 
which is unblocked. This other passage can be of larger diameter than the 
chamber, and the auxiliary locking ball in this passage can be similarly 
large to facilitate filling and emptying of each chamber. 
Furthermore seals are provided between each plug and the respective passage 
and between each socket and the respective base when fitted therein to 
prevent leakage therebetween. These seals also allow the joints between 
the base and socket to be greased. 
A main advantage of this invention is that both the hub and the blades can 
be made very inexpensively. A crude casting of the hub can be finished 
entirely by turning and boring, machine operations that can be automated 
and carried out by relatively unskilled operators. Even most of the work 
on a blade is similarly reduced to turning and boring, as compared to the 
hand milling of the prior art, for relatively inexpensive manufacture. 
Furthermore a small series of differently sized hubs can be combined with a 
small series of differently sized blades to produce virtually any desired 
propeller size with any desired number of blades. To make up a given 
propeller size a chart is consulted so that the blade and hub can be 
selected, whereupon they can be put together using parts--balls and plugs 
mainly--that are standard for all propeller sizes. 
Even at the foundry it is possible to cut down long blades to make short 
blades if the socket and base sizes are standardized. The initial model 
can also be simplified, as only one blade model need be made for each of 
the different sizes needed. The original casting can also be made to much 
tighter tolerances than has been the case hitherto, because the parts are 
fairly simple castings. In fact the vane parts of the blades can be cast 
so that once scraped and shot-peened they merely need some milling to get 
them to the right weight and pitch. The system of the invention therefore 
greatly simplifies the problems of manufacturing and maintaining a stock 
of propellers.

SPECIFIC DESCRIPTION 
As seen in FIG. 1 a propeller according to this invention has three 
identical blades 1 and a single hub 2, although of course more or fewer 
than three blades is of course possible. 
The hub 2 is a massive metal casting formed with a central bore 3 centered 
on a hub axis 4. It has a pair of axially opposite faces 12 and 17 and is 
formed with three identical sockets 5 of cylindrical shape centered on 
respective socket axes A.sub.5 that extend perpendicularly from a common 
point on the axis 4 and that are angularly equispaced about this axis 4. 
Each socket 5 is further formed at around its midlength point with an 
annular groove 6 that opens radially inward is of semicircular section. 
Extending in one direction parallel to the hub axis 4 from the groove 6 to 
the face 12 is a large-diameter threaded passage 11. A smaller-diameter 
threaded passage 16 extends in the opposite direction from the groove 6 to 
the other face 17. 
The blades 1 each extend along respective blade axes A.sub.1 and have at 
one axial end a cylindrical base 8 complementary to any of the identical 
sockets 5 and centered on the respective axis A.sub.1. Each base 8 is 
formed with a radially outwardly open semicircular-section groove 9 
substantially identical to any of the identical grooves 6. 
Thus as seen in FIGS. 1 and 2 each blade 1 can be fitted to a respective 
socket 5 of the hub 2 by moving it along the respective socket axis 
A.sub.5 until the base 8 is seated in the socket 5 with the grooves 6 and 
9 aligned. 
In addition the hub 2 is formed around each socket 5 with a respective 
annular and planar face 25 perpendicular to the respective axis A.sub.5 
and each base 8 springs from a shoulder portion 7 formed with an annular 
face 24 perpendicular to the respective axis A.sub.1 and centered thereon. 
The shoulder 8 is axially traversed by at least two bores 20 that open at 
the face 24 spaced angularly about the axis A.sub.1 from each other. Pins 
19 project outward from the axis 4 and along the axis A.sub.5 from the 
face 25 and can fit into the holes 20 to lock a blade 1 fitted to a socket 
5 against relative rotation about the now coaxial respective axes A.sub.1 
and A.sub.5. 
The blades 1 are fixed in the hub 2 against displacement along the 
respective axes A.sub.1 from the hub axis 4 by respective pluralities of 
substantially identical steel balls 10 filling the chambers formed by the 
juxtaposed grooves 6 and 9 of each socket 5. Each passage 11 houses 
another ball 13 which is pressed radially of the axes A.sub.1 and A.sub.5 
as indicated by arrow P between two adjacent balls 10 of the respective 
set by a respective plug 14 threaded into the outer end of the passage 11. 
Thus pushes half the balls 10 of the respective set in one angular 
direction and the other half in the opposite one, wedging these balls 10 
tightly between the grooves 6 and 9 and thereby solidly locking the 
respective blade 1 in the respective socket 5. If the balls 10 are 
somewhat undersized they will wedge alternately against opposite sides of 
the passage 6, 9 for very uniform holding of the blades 1 on the hub 2. 
Thus once a blade 1 is fitted in the desired angular setting to produce 
the desired pitch it can be locked solidly in place by screwing in the 
respective plug 14. A cap 15 can be threaded over the projecting threaded 
end of this screw 14 to engage the face 12 of the hub 2 and, like a 
locknut, prevent it from loosening. 
The opposite passage 16 from each groove 6 is too small to let the balls 10 
through and is normally blocked by a screw plug 18 so as to be used to 
admit something to free and/or remove the balls 10 if subsequently it is 
necessary to adjust or remove the blade 1. For adjustment it is merely 
necessary to back off the screw 14 and then free up the balls 10, as for 
instance by poking a pointed rod into the hole 16 to push the balls 10 
back toward the now retracted ball 13. Once thus loosened the blade 1 can 
rotate about the respective socket axis A.sub.5 so long as the pins 10 
have been retracted. To empty the balls 10 out of the joint for complete 
removal of the respective blade the plug 14 is removed completely and 
compressed air or high-pressure water can be injected into the opposite 
passage 16 to flush the thus loosened balls 10 out the open passage 11. 
Once all the balls 10 are out, the blade 1 can be pulled axially out of 
the socket 5. 
In addition the entire joint can be lubricated with a heavy grease via the 
hole 11 or 16. To maintain such a body of lubricant inside the assembly, a 
seal 21 is provided at the inside peripheries of the faces 24 and 25, a 
seal 22 is provided around the plug 14, and another seal 23 is provided 
around the screw plug 18. 
The propeller according to this invention can of course be used as the 
rotor of either a motor or a pump. It could be used on a kneading or 
mixing machine, or anywhere it is necessary to have a plurality of blades 
on a normally rotating hub for transmission of mechanical energy between 
torque in the hub and movement in a fluid moving through the propeller 
past its blades.