How to calculate the applied radial load on a bearing?

  • #1
Hi,

I am doing design calculations for a Variable Pitch Propeller and I have to calculate bearing life. A deep groove ball bearing is used for a mainshaft (driveshaft). And the mainshaft is connected to the propeller hub.
I know the basic formula for calculating the bearing life but I am having trouble in regards with determining the equivalent dynamic load needed for the calculation. This equivalent dynamic load can be calculated by knowing the applied axial load on the bearing (due to thrust) and an applied radial loading.

I am able to calculate the axial loading due to thrust but not sure on how to go about determing the radial load on the bearing nor what is the factor the causes this load. Can anyone help me on how to go about this?

Below is an illustration of the arrangement.

image.jpeg


Thank you
 

Answers and Replies

  • #2
Tom.G
Science Advisor
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2,147
Can you consider the shaft as a lever and the bearing as either a fulcrum or the fixed end of the lever? Then calculate the worst case loading for various combinations of weight and end points of the lever. Remember to include vibrations from out-of-balance rotating parts (a bird strike, etc).
 
  • #3
Nidum
Science Advisor
Gold Member
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Many load cases possible . Most relevant ones usually are g and blade off . Sometimes gyro .
 
  • #4
Many load cases possible . Most relevant ones usually are g and blade off . Sometimes gyro .
Can you consider the shaft as a lever and the bearing as either a fulcrum or the fixed end of the lever? Then calculate the worst case loading for various combinations of weight and end points of the lever. Remember to include vibrations from out-of-balance rotating parts (a bird strike, etc).
Thanks for the reply! I did look around a bit more and found that the radial load on the bearing would be due to forces perpendicular to the shaft. So would it be reasonable if I just used the weight of the shaft + the weight of the propeller?
 
  • #5
billy_joule
Science Advisor
1,200
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Thanks for the reply! I did look around a bit more and found that the radial load on the bearing would be due to forces perpendicular to the shaft. So would it be reasonable if I just used the weight of the shaft + the weight of the propeller?
Well what's the specs? Does it's need to survive a worst case scenario? What are the forces in this case? Ie blade failure/ out of balance at max rpm.
 
  • #6
Tom.G
Science Advisor
3,398
2,147
When/if the prop hits something there will be a large radial force on the bearing. Do you care if it disintegrates then?

I've destroyed the ball bearings in an 80mm computer fan by getting my finger in the blades while it's running. Wasn't comfortable but it didn't damage my finger or the blades at all; not so the bearings (R.I.P).
 

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