How to calculate the applied radial load on a bearing?

In summary, the designer is trying to calculate the bearing life for a Variable Pitch Propeller and is having difficulty determining the equivalent dynamic load needed. The designer is considering the shaft as a lever and the bearing as either a fulcrum or the fixed end of the lever. The designer calculates the worst case loading for various combinations of weight and end points of the lever. The designer remembers to include vibrations from out-of-balance rotating parts (a bird strike, etc). The designer also considers the shaft as a lever and the bearing as either a fulcrum or the fixed end of the lever when calculating the worst case loading for various combinations of weight and end points of the lever. The designer is concerned if the bearing disintegrates
  • #1
Dency Dela Cruz
2
0
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
 
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  • #2
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
Many load cases possible . Most relevant ones usually are g and blade off . Sometimes gyro .
 
  • #4
Nidum said:
Many load cases possible . Most relevant ones usually are g and blade off . Sometimes gyro .
Tom.G said:
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
Dency Dela Cruz said:
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
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).
 

1. How do I determine the applied radial load on a bearing?

To determine the applied radial load on a bearing, you need to know the bearing's load rating, dimensions, and the type of load it is designed to handle. The formula is F = (C/P) x Fr, where F is the applied radial load, C is the bearing's dynamic load rating, P is the equivalent dynamic bearing load, and Fr is the radial load acting on the bearing.

2. What is the difference between static and dynamic load ratings for bearings?

The static load rating is the maximum load a bearing can withstand without permanent deformation, while the dynamic load rating is the maximum load a bearing can withstand for one million rotations without failure. The dynamic load rating is typically used for calculating the applied radial load on a bearing.

3. Can I use the same formula for calculating the applied radial load on all types of bearings?

No, different types of bearings have different formulas for calculating the applied radial load. For example, deep groove ball bearings use a different formula than spherical roller bearings. It is important to consult the manufacturer's specifications for the correct formula for your specific type of bearing.

4. How does the speed of the bearing affect the applied radial load?

The speed of the bearing can affect the applied radial load by increasing the equivalent dynamic bearing load. The faster the bearing rotates, the greater the applied load will be. It is important to consider the speed when calculating the applied radial load to ensure the bearing can handle the load at that speed.

5. Are there any safety factors to consider when calculating the applied radial load on a bearing?

Yes, it is recommended to use a safety factor when calculating the applied radial load on a bearing. This ensures that the bearing is not operating at its maximum load capacity and allows for any unexpected changes in load. The recommended safety factor is typically between 1.5 to 2 times the calculated load.

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