BACKGROUND TO THE INVENTION

THIS invention relates to propeller flange lock arrangement and more particularly but not exclusively, to a propeller flange lock arrangement suitable for use with a variable pitch propeller system.

Safety is of utmost concern in the design and construction of aircraft components. Failure mode classification therefore greatly influences the control and cost of each component within a sub-assembly, and in order to reduce this classification rating, as much redundancy as feasible must be designed into each sub-assembly.

One of the many critical aspects when it comes to aircraft design, and in particular in this case in the design of a propelfer-driven aircraft, is to ensure that the propeller flange, to which the individual propellers are secured, are properly secured to the propeller shaft. In some designs the flange forms part of the crankshaft. More particularly, in some existing designs the propeller flange is located on the propeller shaft by means of a spline, and a flange lock nut is then screwed into an internal thread of the propeller shaft, thus locking the flange relative to the shaft. The thread arrangement is in an opposite direction to the rotation of the propeller shaft rotation to ensure that the flange lock nut does not become loose during rotation of the propeller shaft. Although this arrangement effectively secures the propeller flange to the propeller shaft, increased safety redundancy would be beneficial in order to ensure that the propeller flange remains secured to the propeller shaft.

A variable-pitch propeller is a type of propeller with blades that can be rotated around their long axis to change their pitch. The rotation can be mechanically, electrically or hydraulically actuated. In the case of hydraulicaily actuated variable pitch propellers, a hydraulic fluid feed tube extends through a bore of the propeller shaft towards the front end of the propeller shaft, with an end of the feed tube typically terminating at the flange lock nut. The feed tube is, however, not secured to the flange lock nut, and merely constitutes a hydraulic fluid conduit without contributing to the mechanical integrity of the propeller flange lock arrangement.

It is accordingly an object of the invention to provide a flange lock arrangement that will, at least partially, alleviate the above disadvantages, and which provide additional redundancy to that found in conventional designs.

It is also an object of the invention to provide a propeller flange lock arrangement which will be a useful alternative to existing flange lock arrangements. SUMMARY OF THE INVENTION

According to the invention there is provided a propeller flange lock arrangement for use in a propeller rotation unit that includes a propeller drive shaft and a propeller flange located on the propeller drive shaft, the propeller flange lock arrangement comprising:

a flange lock nut having a head formation for securing the propeller flange relative to the propeller drive shaft, and a tubular spigot extending from the head formation, with the spigot including a first threaded section for engaging a complementary thread provided in an end zone of the propeller drive shaft;

characterized in that the tubular spigot extending from the body of the flange lock nut also includes a second threaded section suitable for engaging a complementary thread provided on a cylindrical element located inside a bore of the propeller drive shaft.

There is provided for the first threaded section of the spigot to be an externally threaded section, and for the complementary thread provided in an end zone of the propeller drive shaft to be an internal thread.

There is provided for the second threaded section of trie spigot to be an internally threaded section, and for the complementary thread provided on a hydraulic fluid supply tube to be an external thread.

The cylindrical element may be a hydraulic fluid supply tube.

There is provided for the thread on the flange lock nut, the thread on the propeller drive shaft, as well as the thread on the fluid supply tube to be configured in a direction opposite to the direction of rotation of the propeller shaft. There is provided for the hydraulic fluid supply tube to include a first end and a second end, with the first end in use extending into the hollow spigot of the flange lock nut, and the second end protruding from an opposing end of the propeller drive shaft.

A feed tube lock nut is provided for securing the second end of the feed tube to the end of the propeller drive shaft.

Preferably, the feed tube lock nut is provided with an internal thread that engages a complementary external thread provided on the second end of the propeller drive shaft, with the feed tube lock nut sandwiching a circumferential flange extending radially outwardly from the feed tube between the feed tube lock nut and the second end of the propeller drive shaft.

According to a further aspect of the invention there is provided a propeller rotation unit including the propeller flange locking arrangement as described above.

According to a still further aspect of the invention there is provided an engine arrangement including the propeller rotation unit and the propeller flange locking arrangement as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention is described by way of a non- limiting example, and with reference to the accompanying drawings in which: Figure 1 is a side view of an airplane including a propeller flange lock arrangement in accordance with the invention;

Figure 2 is a cross-sectional side view of the propeller rotation unit incorporating the propeller flange lock arrangement; and

Figure 3 is an enlarged view of the forward end of the propeller rotation unit of Figure 2.

DETAILED DESCRIPTION OF INVENTION

Referring to the drawings, in which like numerals indicate like features, a non-limiting example of propeller rotation unit incorporating a flange lock arrangement in accordance with the invention is generally indicated by reference numeral 20.

The invention finds application in the propulsion arrangement of an airplane 10, and in particular a propeller 12 driven airplane. In this example the propeller 12 is driven by way of a piston engine 11.

Referring to figures 2 and 3, the propeller rotation unit 20 incorporates an advanced propeller locking arrangement that constitutes an improvement over the prior art. The propeller 12 is driven by a drive shaft 30, which is supported by way of bearings 22, and which is in turn driven by the engine via a drive gear arrangement 21. The drive shaft 30 is in the form of an elongate body 31 having a hollow longitudinal bore 31.3, the body having a first end 31.1 and a second end 31.2. An internal thread 32 is provided at the first end 31.1 drive shaft 30, and an external thread 33 is provided at _{the second end 31.2. The purpose of these threads is described in more detail below.}

_{A hub 80 of the propeller 12 is secured to a propeller flange 40. The propeller flange 40 includes an annular disc 41 for receiving the propeller hub 80, as well as a securing sleeve 42 extending from the disc 41 , and which is in turn locatable inside the first end 31.1 of the drive shaft 30 by way of a spline arrangement (not shown) that secures the propeller flange 40 to the drive shaft 30 and prevents relative rotation between the two. A shoulder formation 34.1 prevents linear displacement of the propeller flange 40 towards the engine, while a propeller flange lock nut 50 secures the flange 40 against displacement in an opposite direction.}

_{The propeller flange lock nut 50 comprises a body having a head formation 51 that secures the propeller flange 40 in position by trapping the same between the head formation and the shoulder 34.1 provided on the propeller drive shaft 30. A tubular spigot 52 extends from the head 51 of the lock nut 50. Both external thread 53 and internal thread 54 are provided on the spigot. The propeller flange lock nut 50 engages the first end 31.1 of the propeller drive shaft 30 by engaging the complementary internal thread 32 provided on the first end 31.1 of the drive shaft, which then prevents linear displacement of the propeller flange lock nut 50, and hence the propeller flange 40, relative to the drive shaft 30. Importantly, the threads on the drive shaft and flange lock nut are configured in a direction opposite to the rotation of the drive shaft.}

_{A hydraulic fluid supply tube 60, for use in supplying hydraulic fluid as actuation medium for the variable-pitch blades, extend through the bore 31.3 of the drive shaft 30. The supply tube 60 is in the form of an elongate tube having a first end 61 and a second end 62. External thread 61.1 is provided on the first end 61 , and a circumferential, radially outwardly extending flange 62.1 is provided towards the second end 62. The first end} 61 protrudes into the bore of the propeller flange lock nut 50, and the thread 61.1 engages the thread 54 provided inside the spigot 52 of the lock nut 50. This therefore constitutes a further securing mechanism, resulting in increased redundancy, and which has not previously been known in the art.

The second end 62 of the feed tube protrudes from the second end 31.2 of the drive shaft 30, and is secured to the drive shaft by way of a supply tube lock nut 70 that traps the flange 62.1 between the lock nut 70 and the end of the drive shaft 30. in this way the supply tube 60 therefor doubles up as a mechanical anchor for the propeller flange lock nut, and does not merely fulfill the function of conveying a hydraulic medium as is known in the art.

It will be appreciated that the propeller flange 40 is therefore secured to the drive shaft 30 by way of a lock nut 50, and the lock nut is in turn secured by both the drive shaft 30 and the supply tube 60, thus resulting in the desired securing redundancy without adding significant complexity.

It will be appreciated that the above is only one embodiment of the invention and that there may be many variations without departing from the spirit and/or the scope of the invention.