stangflyer
I like 'em "BIG"!
I think I will just stay with my original method. It seems to work.... If it's not broke, don't fix it right? LOL
Prop Bolt Torque
- Thread starter Twister
- Start date
Rolling.Circle
100cc
The DA manuals have different torque settings for the various motors and for the material the prop is made from as well...
DA 120 Steel prop bolts: M5x 50mm 75 in. lbs. / wood props, 90 in. lbs. /carbon props.
Looks like the 150 and 170 aren't much different so everything above is in the ballpark but 50lb/in. may be taking chances. Is the consensus that overtight will cause bolts to sheer off? Man, haven't had that happen yet and don't want to either. Must be a PITA
DA 120 Steel prop bolts: M5x 50mm 75 in. lbs. / wood props, 90 in. lbs. /carbon props.
Looks like the 150 and 170 aren't much different so everything above is in the ballpark but 50lb/in. may be taking chances. Is the consensus that overtight will cause bolts to sheer off? Man, haven't had that happen yet and don't want to either. Must be a PITA
CatalinaWOW
50cc
While the formula above doesn't dial in an exact torque, you may use it to feel better about sheering bolts.
Your DA 120 bolts have a pitch diameter of about 0.19 in. The friction factor can vary from about 0.15 up to about 0.85, but most sources will tell you that it is typically from 0.5 to 0.7. The low value comes when you have a well greased bolt with good fits and smooth finishes, non galling surfaces and run in and out a number of times, and the high values are from other pathological cases. Using 0.5 friction and the 90 in. lb. torque number the tension in the bolt comes out to a little over 900 lbs, and the stress to around 34 ksi. There are large error bars around this number, but even really crummy bolt steel has strengths double this so there is lots of margin.
Strangely, the guy most likely to sheer bolts would be a highly meticulous guy. He runs the bolts in and out a few times getting the prop and hub setup just right. Then he applies loktite to the bolts (loktite is an excellent lubricant pre-cure) and snugs the torque down to the top allowed value. Under these conditions you could approach the tensile strength of standard bolts. Even this guy wouldn't approach the strength of high grade bolts.
Your DA 120 bolts have a pitch diameter of about 0.19 in. The friction factor can vary from about 0.15 up to about 0.85, but most sources will tell you that it is typically from 0.5 to 0.7. The low value comes when you have a well greased bolt with good fits and smooth finishes, non galling surfaces and run in and out a number of times, and the high values are from other pathological cases. Using 0.5 friction and the 90 in. lb. torque number the tension in the bolt comes out to a little over 900 lbs, and the stress to around 34 ksi. There are large error bars around this number, but even really crummy bolt steel has strengths double this so there is lots of margin.
Strangely, the guy most likely to sheer bolts would be a highly meticulous guy. He runs the bolts in and out a few times getting the prop and hub setup just right. Then he applies loktite to the bolts (loktite is an excellent lubricant pre-cure) and snugs the torque down to the top allowed value. Under these conditions you could approach the tensile strength of standard bolts. Even this guy wouldn't approach the strength of high grade bolts.
stangflyer
I like 'em "BIG"!
Hmmm! Super good information.
Robotech
70cc twin V2
That's my method. Grunt tight. It's never failed, but I only use CF props.
That is my method also. My right arm is my torque wrench. Never had a bolt loosen up on me.
Decal Dennis
TEAM EP&G
Snug down in a criss cross pattern. No specific torque need, some will disagree with that tho!!