B340

If the bearing is stationary for long periods or rotates slowly and is subject to shock loads then the bearing selection procedure is based on the Static Load Carrying Capacity. For an operation that is more continuous the bearing is selected on the Dynamic Load Carrying Capacity.

Rotor Hub:

Blade Pitch Mounting: [Source ~ MDD p.17]

Bearings:

A bearing should be selected and its rated thrust capacity calculated for an average life of 2500 hours and at 500 rpm. For light series bearings, 60 percent of this calculated capacity may be used as the allowable operating load to which it should be subjected.

DBJ ~ From all the information I've come across, that 'rated thrust capacity' is the dynamic basic load rating and the selection is only based on the axial (centrifugal) load on the blade. In other words, torque is not considered and the blades flap to position. Of course, rigid hubs such as the UniCopter's and the SynchroLite's with hub spring will require that radial loading be taken into account.

Teetering Bearing:

It looks like bushing (composite bearings) are the optimal ones for teetering bearings, in the SynchroLite/Dragonfly teetering, teetering with offset and CVJ(CDUJ) hubs.

See; Rexnord Tuflite composite bearings with unique journal bearing bores; http://aerospace.rexnord.com/CatalogPDF/tuflite.pdf Have hard copy.

Also look into GRAPHALLOY bearings.

Transmission: [Source ~ MDD p.68]

Transmission Bearings:

"Where feasible, it is desirable to provide a minimum life of 1000 hours for the bearings of a transmission. This will give upward of 2,500 hours average life. ... inspected only at about 500 hour intervals.".

Life Adjustment Factor:

For Reliability:

The most commonly used reliability level for bearing life calculations is L10 (rating life).

A 1972 report by Kaman says that for Life Criteria - Bearings are sized for 4000 hours L10 using a life enhancement factor of 3. I believe that a life enhancement factor of 3 is the same as L2, which is a life adjustment factor for reliability of [x 0.33]. This is the same as a reliability of 98%.

This is my thinking ~ Go 99% [x 0.21] for the critical rotor intermeshing bearings and 98% for the remainder. all at a minimum of [4000 * 0.21 / 0.33] = 2545 hours.

For more information, see the Engineering section in the Torrington catalog.

Posting on Eng-Tips ~ Bearing design, manufacture and maintenance:

Bearing manufactures list Static Load Rating and Dynamic Load Rating. They are used for completely separate things.

You always use Static Load Rating to determine the factor of safety for an application. Find the worst case loading condition and use that for Factor of Safety calculations.

You use dynamic load rating to calculate the theoretical L10 life of a bearing.

For most applications, to get decent life out of bearing you end up with a factor of safety of 4-5. Depends though.

Four-Point Contact Ball Bearing: (from Net)

A single row angular contact bearing with the inner ring made of two parts. The inner rings are machined such that when forced together all the bearing clearances are removed and the correct per-load in installed in the bearing. Thrust loads in both directions. The arrangement shown uses the four-point contact bearing for axial location and a non-locating roller for the radial loads. Note the radial clearance on the four-point contact bearing.

The angular contact ball bearings can be used to carry both radial and axial loads simultaneously, and is subjected to high-speed rotation. The contact angle of this type of bearing have five; !5, 25, 26, 36 and 40-degrees. The bigger the degree of contact angle. The larger the capacity of axial loading. This type of bearings used in carrying radial loads will implicate additional axial thrust. Therefore it is in duplex arrangement in general. The duplex bearings can be preloaded or with axial clearance adjusted in order to increase the stiffness of the spindle. Four-point contact ball bearings. Type QJ composed of a pair of double combined bearings is suitable to carry axial loads in either direction. As well as to restrict the axial displacement in either direction.

DK says that this bearing is no good for mast/crown single bearing application since there must be preloading and thus the bearing will wear. Consider Crossed Cylindrical Roller Bearing below.

Crossed Cylindrical Roller Bearing:

See: OTHER: Mechanics - Bearing - Crossed Cylindrical Roller

Delrin AF

Here is where you can buy it: http://www.polymerplastics.com/mecha...delrinaf.shtml
Here is a sheet with a list of it's properties: http://www.portplastics.com/download...ngAndWear2.pdf

I have info, somewhere, on a material that I think is better than Delrin. This maybe it; Tuflite Composite Bearings

Gyrocopter Mast Bearings:

Equivalent Dynamic Bearing Loads: (approximate value)

Model:	Bensen	Two seater
Gross Weight:	550 lbs., 2446 N	1200 lbs., 5338 N
Bearing Part Number:	5206CZZ ⁽¹⁾	5206CZZ ⁽²⁾
Basic Dynamic Load Rating:	26100 N	26100 N
Radial Load Factor:	1
Axial Load Factor:	1
Actual Radial Bearing Load:	1
Actual Axial Bearing Load:	2446 N * ⁽³⁾ of 4 = 9785
Equivalent Dynamic Bearing Load:	9785
Basic Life Rating (in millions of revolutions)	19
Rotor Revolutions per Minute	335 rpm	300 rpm
Basic Rating Life [in hours] [L10h]	944
Reliability:	98 ⁽³⁾
Adjusted Rating Life [in hours] [Ln]	312

Double row Conrad caged bearing (not slot filled)

This may have two bearings.

This could or should be adjusted by; an overload factors * % of time; reliability, a safely factor (1.5?)

Last Revised: October 9, 2009