Fluid reaction surfaces (i.e. – impellers) – Specific working member mount – Adjustable
Reexamination Certificate
1999-07-28
2001-04-10
Verdier, Christopher (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Specific working member mount
Adjustable
C416S20400A, C416S22000A
Reexamination Certificate
active
06213719
ABSTRACT:
TECHNICAL FIELD
This invention is directed to preloading propeller blade bearings of aircraft in preparation for centrifugal and bending forces which develop during operation, and more particularly, to a bar wedge preload and retention device.
BACKGROUND ART
With the invent of the composite propeller blade, which are lighter than the earlier metal and/or metal-composite hybrids, blades in operation experience reduced centrifugal loading. Accordingly, the loading is typically insufficient to prevent rocking caused by high bending loads. Many current designs use a retention assembly that includes one or more bearings that must be preloaded by some means. The rocking effect caused by the bending loads is alleviated in many current designs by use of pitch change bearings with increased diameters. Often, these designs also use extra rows of bearings. However, these additions add to the weight and complexity of the blade and retention assembly design, thereby increasing costs and potential for mechanical failure. In addition, many composite propeller blades attach through a shear bond joint to a metal retention member. This is an inefficient means for load transfer and requires a secondary mechanical backup.
As indicated, the existing solution to prevent rocking is to use a preloaded bearing assembly so as to provide a compensating load. For example, the double row bearing design, used by the assignee of the present application, is preloaded by a large mechanical nut through a very stiff load path, making the application of preloading somewhat difficult. In addition, it is difficult to monitor and retain the initial preload over long periods of service time. Also, current designs require the use of special tools to apply the high preload necessary. And, some form of load monitoring is required to prevent the loss of foundation/attachment stiffness at the base of the blade. Without such monitoring and means for adjusting the preload, a potentially dangerous change in blade resonant frequency can arise undetected. And, since the most current designs use a mechanical nut, small amounts of fretting or wear on the threads that engage the nut can lead to this loss of stiffness. In addition to the above, replacement of blades with these types of retention designs is cumbersome and requires a significant amount of time. U.S. Pat. Nos. 4,850,801 to Valentine and 5,118, 256 to Violette et al, both assigned to the assignee of the present application, provide examples of such designs.
Blade retention may also be achieved by using a pin assembly at the base of the blade for attaching the same to a receiver portion attached to the hub of the propeller assembly. A plurality of patents has issued with respect to such designs. Examples of such designs are shown in U.S. Pat. No. 5,163,817 to Violette et al, U.S. Pat. No. 5,02,824 to Violette et al and U.S. Pat. No. 4,877,376 to Sikorsky et al.
Sikorsky et al is particularly interesting and describes a method of attachment of a rotor blade of fiber reinforced plastic to a metal rotor hub. The shank of the propeller blade attaches to the hub through a connection. Prestress can be applied through the connection to the propeller to assist in resistance of lateral impact force. In this design, the blade
4
connects to a tubular body B of the hub by means of bolts or screws. In addition, the blade includes a tubular shank
18
b
that extends into the tubular body and which further connects to the tubular body via an attachment or tensioning means
5
b
. The tensioning means
5
b
comprises a tensioning bolt
21
rotatably arranged in a transverse bore in shank
18
b
. The tensioning bolt includes pivot pins
22
and
23
extending from each end thereof and which are eccentric to the centerline of the bolt. Each pivot pin
22
and
23
resides in a support disk
25
and
26
, respectively, which mount in circumferential slots
27
and
28
, respectively, in the wall of tubular body
8
b
. When turning the tensioning bolt
21
via head
24
of pin
23
, support disks
25
and
26
travel in slots
27
and
28
. By this process, tension is applied to shank
19
in a direction of arrow
29
to press the blade against an upper flange of body
8
b
. This tensioning produces a prestress in the blade
4
that opposes stresses developed in the blade due to lateral impact forces during operations. While a cam or a center pin design is used to apply the downward force to the shank
18
b
, no locking mechanism is provided for maintaining the prestress on the shank. This shortcoming could potentially allow loss of the prestress and/or require that the bolts
6
maintain the prestress, which may also give rise to a prestress loss by their loosening.
An alternative embodiment is shown in FIG.
4
and in this embodiment, a retaining pin
32
resides in a transverse opening
31
in shank
18
c
. The pin includes end portions received in holes
34
a
and
34
b
in a tension sleeve
33
that surrounds shank
18
c
. The tension sleeve includes two spirally ascending semi-annular cam faces
35
and
36
that inversely conform to cam faces on an additional coaxially arranged rotary sleeve
37
. The tension sleeve and rotary sleeve are arranged one above the other for axial displacement in the tubular body
8
c
. Tubular body
8
c
includes circumferential slots
38
a
and
38
b
to permit access to positioning holes
39
a
and
39
b
in the rotor sleeve
37
. A tool, not shown, may be used to engage the positioning holes
39
a
and
39
b
such that the rotary sleeve
37
is rotatable to tension the shank
18
c
. Similar to the embodiment discussed above, there appears to be no means for locking the prestress position of rotary sleeve
37
and tension sleeve
33
to ensure maintenance of the preload. Again, the design uses bolts
36
to lock the preload position into place, which as discussed above, presents questionable preload security.
There exists a need, therefore, for an improved pin type retention and preload assembly for retaining a propeller blade to a hub and for preloading the same, whereby the preload position of the blade relative the hub is locked into place.
DISCLOSURE OF THE INVENTION
The primary object of this invention is to provide an improved pin type preload and retention assembly for retaining a propeller blade to a hub.
Another object of this invention is to provide a bar wedge preload and retention assembly for simultaneously preloading and retaining the blade to a receiving portion of a propeller hub without the use of additional fastening means.
Still another object of this invention is to provide an improved preload and retention assembly which uses a bar wedge tool in combination with a pinned retention device, wherein the bar wedge tool may be removed from the propeller blade assembly after the preload is applied thereby and the pinned retention device is secured.
The foregoing objects and following advantages are achieved by the composite propeller blade and hub attachment assembly of the present invention. The assembly includes a blade root having a first connecting member and a hub arm having a second connecting member. The first connecting member meshingly engages the second connecting member. A device preloads the blade root and the hub arm. The first and second connecting members form a slot for receiving the preloading device. The preloading device includes an outer movable unit, an inner movable unit, and a mechanism for displacing the outer and inner movable units relative each other. As the mechanism for displacing relatively moves the inner and outer units, the preloading device is caused to expand and tension the blade root and hub arm for centrifugally preloading the blade.
REFERENCES:
patent: 2980395 (1961-04-01), Rubbra et al.
patent: 4850801 (1989-07-01), Valentine
patent: 4877376 (1989-10-01), Sikorski et al.
patent: 5022824 (1991-06-01), Violette et al.
patent: 5118256 (1992-06-01), Violette et al.
patent: 5163817 (1992-11-01), Violette et al.
Nagle David P.
Shattuck Coleman D.
Violette John A.
United Technologies Corporation
Verdier Christopher
Woo Richard
LandOfFree
Bar wedge preload apparatus for a propeller blade does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Bar wedge preload apparatus for a propeller blade, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Bar wedge preload apparatus for a propeller blade will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2542730