Prop Bolt Torque

[Twister]

Who here torques prop bolts? and what setting do you use? Up til now the biggest engine I have is a 60cc and I just used an allen wrench but I'm moving up to a 120cc and thought it would be better to torque the bolts. any thoughts.

 

 

 

Thanks Jim

 

[Ohio AV8TOR]

I still do and probably not necessary.  For wood I use 30 in/lbf, any more and the wood compresses.  Carbon I use 50 in/lbf.  I remember when I first got my DA60 I followed the manual recommendation of 75 in/lbf for a wood prop and it always seemed to loosen up so I would tighten it again......and again, until I realised I was just compressing the hub.  

 

[wesley.]

I set mine at 50 in/lbs for wood.  Never had any trouble.  I get to that 50 in a couple of steps though not all at once.

 

[Ohio AV8TOR]

wesley. said
I set mine at 50 in/lbs for wood.  Never had any trouble.  I get to that 50 in a couple of steps though not all at once.

Is that on a laminated prop?  I could never get that on a 4-bolt beechwood.  Lams did not compress as much for me.  

 

[reyn3545]

I've always gone 50 on a wood prop and 80 on carbon fiber.

 

[stangflyer]

reyn3545 said
I've always gone 50 on a wood prop and 80 on carbon fiber.

Size of prop and displacement of motor make much of a determining factor in torque values?

 

[Ohio AV8TOR]

stangflyer said
reyn3545 said
I've always gone 50 on a wood prop and 80 on carbon fiber.

Size of prop and displacement of motor make much of a determining factor in torque values?
Torque is more about the screw diameter and class of bolt.  Keep in mind that there are basic number values then it can get real complicated  even thread lubricant.   Just use a basic chart but it looks like this if you want to go crazy

T= cDF

T= Torque required

F= Bolt tension required (axial load in pounds)

D= Nominal bolt diameter (major diameter)

c= friction component

 

 

[wesley.]

Ohio.AV8TOR said
wesley. said
I set mine at 50 in/lbs for wood.  Never had any trouble.  I get to that 50 in a couple of steps though not all at once.

Is that on a laminated prop?  I could never get that on a 4-bolt beechwood.  Lams did not compress as much for me.  
Yes Zoar laminated is pretty much all I run

 

[Ohio AV8TOR]

wesley. said


Ohio.AV8TOR said


wesley. said
I set mine at 50 in/lbs for wood.  Never had any trouble.  I get to that 50 in a couple of steps though not all at once.

Is that on a laminated prop?  I could never get that on a 4-bolt beechwood.  Lams did not compress as much for me.  


Yes Zoar laminated is pretty much all I run


Laminated props while not as stiff as carbon can take more torque than beech without crushing.  After that beech I was mentioning I went Xoar laminated before going with a carbon Vess Stealth.  My Xoar laminate held up very good.  
 

 

[CatalinaWOW]

Ohio.AV8TOR said 

Torque is more about the screw diameter and class of bolt.  Keep in mind that there are basic number values then it can get real complicated  even thread lubricant.   Just use a basic chart but it looks like this if you want to go crazy

T= cDF

T= Torque required

F= Bolt tension required (axial load in pounds)

D= Nominal bolt diameter (major diameter)

c= friction component

 

All this is absolutely true, but doesn't tell you much.  The required force is one key, and there is really no way for most of us to know that.  The thrust loads on these bolts are negligible.  Dominant loads are probably vibration and unbalance loads.  Desired load is probably what is required to keep the prop from sliding around relative to the bolts.  The friction terms depend on a lot of things, including but not limited to lubricants, thread lockers, number of times the bolt and hub have been used, surface finish and materials of both hub and bolt and ....

Unless you have a mechanical engineering lab and instrument your bird to measure all of these things the rules of thumb are probably the best way to go.  The rules of thumb apply roughly the most load that the material of the prop can take, which is well under the tensile capability of the bolt.