Life Rating for Gears

[Intermesher]

Can anyone advise on how gear sizes are determined for aerospace application?

When I reverse engineer a gear used in a helicopter and then use catalog calculations, the safety factor comes in a 1 or less. The safety factor must obviously be greater than 1, therefore I assume that there is an adjustment made, which is related to the life of the gear.

My questions are;
~ How is the life factor entered in to the calculations?
~ Is the life factor based on Durability or Strength?

Thanks

Dave J.

 

[israelkk]

Look for AGMA standards.

 

[plasgears]

The PowerGear program for gear design handles these questions with authority. Gear teeth fatigue of course is the limiting element.

What you may be missing is the principles of modified gears, like extended addendum on pinions, full fillet radius, thicker pinion tooth/thinner gear tooth, etc. When you iterate your design based on various mods, you will be surprised at the reductions in stress. I have found 1.2 extended addendum and 54% pinion tooth thickness to be very beneficial.

 

[Intermesher]

Thank you gentlemen.

Dave J.