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-   -   NEW! Ultimate C/S Prop Wrench Anti Splat Aero (https://vansairforce.net/community/showthread.php?t=82592)

Bob Kuykendall 02-24-2012 09:53 AM

Quote:

Originally Posted by PerfTech (Post 630093)
...I graduated top of my class at MIT with three degrees in mechanical engineering...

Not that I put much emphasis on credentials, but just to clarify this point: When you say MIT, do you mean Massachusetts Institute of Technology?

Thanks, Bob K.

fatherson 02-24-2012 05:01 PM

I answered this question from Mike Starkey in another thread on this debate:
Quote:

Originally Posted by Mike S (Post 630311)
If I use an electric motor, with an adjustable clutch set to slip at 100 lb/ft of torque on the output shaft, and then attach the 3" tool at the end of that shaft, how much torque will the end of the tool see????

I can't see anywhere Mike's question was addressed, so let me repeat my answer here:
The nut will see absolutely no torque at all.
Think about it or try it out to prove to yourself that it's true. I think this proves the correction multipler cannot be a constant.

Hope that helps.

--
Stephen

speyers 02-24-2012 07:10 PM

90 degrees
 
For the love of mary, put the thing on 90 degrees and be done with it! Or calibrate your elbow... seriously. Does anybody really torque spark plugs, an 3 bolts, brake backing plates or mag attach nuts?

PCHunt 02-24-2012 09:09 PM

I torque spark plugs every time. One stripped thread in the cylinder isn't worth it to me. Without a torque wrench, I tend to over-torque stuff, especially AN-3 stuff.

I really have to watch it!........ :o

BillL 02-24-2012 09:12 PM

Sorry to do this, but . . .
 
Quote:

Originally Posted by fatherson (Post 632812)
I answered this question from Mike Starkey in another thread on this debate:


I can't see anywhere Mike's question was addressed, so let me repeat my answer here:
The nut will see absolutely no torque at all.
Think about it or try it out to prove to yourself that it's true. I think this proves the correction multipler cannot be a constant.

Hope that helps.

--
Stephen

Actually I was wondering when this could come up. There are two rules of statics, 1. summing forces about a point = zero 2. a pure moment can be located anywhere on the plane.

So . . . Mike's pure torque of 100 will result be resisted by an equal torque at the nut. There are no force couples involved. the distance is not relevant since there is no force couple involved.

OK, all ready to pull your hair out now?

Think about it . . . if you applied a pure torque to that wrench and it was not attached, what would happen - it would spin, right? So the reaction at the nut can NOT be zero and the real answer is it is equal to that applied.

For the extension - use the FAA and torque wrench book formula.

Why? Lets say the FAA is correct - the factor is not fixed at 0.8 . But I use the 0.8 anyway. The prop torque needs 60-70 ft-lb of torque. I usually use the middle number since i don't know which way my tool may be inaccurate. So let's use 65 ft-lb. If I use a 16.5 inch wrench ( my real number) and using the .8 factor, I will be actually 6.7% low, according to the FAA formula. What if my click wrench is 4% low? Then I am 10.7% low now, or only 58 ft-lb of real torque on the nut. That is 2 ft-lb below the low end of the range. Is that enough to worry? I don't know, so I will be using what my engineering training, experience, and the FAA formula tells me.

Wayne Gillispie 02-24-2012 10:47 PM

It is after midnight...
 
I just had to see what all the huboob was about and clicked on this thread. I read every post to page 11. I said to my aching brain...let's skip to the last page and there I will find out if the length really does matter. Okay, I can sleep tonight since I have been flying behind my prop that was torqued with a 90 deg adapter. We used the same formula that is in AC43.13 in the military. I would hate to have to go back and recheck torques from 23 years ago. I am going to bed, my calibrated elbow is hurting too.

Now I figured out why Mike Starkey was recommending to a new builder "torque wrench how-to lessons" before starting his -10 emp. I was wondering what kind of crazy recommendation was that.:D

Mike S 02-24-2012 11:56 PM

Quote:

Originally Posted by Wayne Gillispie (Post 632894)
Now I figured out why Mike Starkey was recommending to a new builder "torque wrench how-to lessons" before starting his -10 emp. I was wondering what kind of crazy recommendation was that.:D

That recommendation was to help him sleep.

PCHunt 02-25-2012 12:56 AM

Found a nice online calculator
 
It even (correctly) takes into account the angle-off of the adapter.

http://www.cncexpo.com/TorqueAdapter.aspx

Try putting an angle of 180 degrees in, see what happens. You can change the length to see the results as well.

fatherson 02-25-2012 01:00 AM

Quote:

Originally Posted by BillL (Post 632870)
Think about it . . . if you applied a pure torque to that wrench and it was not attached, what would happen - it would spin, right? So the reaction at the nut can NOT be zero and the real answer is it is equal to that applied.

You know, even as dusty as my statics and four years of physics are, Bill's counterpoint to my claim above sounds right. I'm tired and just checked into VAF for a few seconds on my way to bed, but I couldn't let my probable error stand overnight unchecked. I'll revisit this again once I have time to sketch a proper force diagram to figure out where my intuition went wrong. At least Bill and I agree that trusting the science is the right approach.

--
Stephen

scsmith 02-25-2012 01:31 AM

Both could be right! Advanced Statics....
 
Quote:

Originally Posted by fatherson (Post 632910)
You know, even as dusty as my statics and four years of physics are, Bill's counterpoint to my claim above sounds right. I'm tired and just checked into VAF for a few seconds on my way to bed, but I couldn't let my probable error stand overnight unchecked. I'll revisit this again once I have time to sketch a proper force diagram to figure out where my intuition went wrong. At least Bill and I agree that trusting the science is the right approach.

--
Stephen

Actually, depending on how you hold the impact wrench, either solution is possible.

In case 1, you do your best to hold the impact driver still. In doing so, you provide a reaction force that counters the wrench interaction on the nut. You get a force couple that cancels the moment, with no torque on the nut.

In case 2, you do not resist the motion of the impact wrench, only its rotation. The wrench will try to orbit the nut, and in doing so, transmit the pure torque to it with no force couple. This assumes it does not orbit so fast that centrifugal force throws it off the nut though! :rolleyes:


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