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02-14-2012, 03:09 PM
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Join Date: Feb 2006
Location: East Texas
Posts: 192
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Larry
You are correct. Using your example, at 12" the applied force required is 64lbs. The three inch extension will experience 80 FT-LBS of torque. Your math example assumes a torque wrench that is calibrated at 12 inches.
The problem arrises when Tim (380mxc) has a torque wrench that calibrated at 22.57 inches.
Torque = force X distance
For a 12" torque wrench with a 3" extension, setting 64 FT-LBS results in 80 FT-LBS at the bolt. 64LBS x 1.25feet = 80 FT-LBS
For the 22.57" torque wrench with a 3" extension, setting 70.56 FT-LBS results in 80 FT-LBS at the bolt.
A force of 37.23LBS at 22.57 inches (1.88feet) = a torque of 70.56 FT-LBS
Adding a 3" extension to the equation. 37.23LBS x 25.57 inches (2.13feet) = 80 FT-LBS
Tim can't just multiply torque required by .8 and plug that into his torque wrench. His torque wrench manual values line up with the extension formula.
Wrench torque = Torque Spec * (Wrench length / (Wrench length + extension length))
__________________
Marc Hudson
Houston
RV-7 Sold
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02-14-2012, 03:41 PM
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Join Date: Mar 2008
Location: San Diego
Posts: 457
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Mike,
Quote:
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Adding the extension changes the location of the center point of rotation
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With the extension, now there are two center points of rotation, one at the torque wrench head, the other at the nut. This whole discussion is about the multiplier that relates the torques applied around these two axes.
Quote:
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and the head on the torque wrench is now moving in an arc, not rotation.
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Well if we're measuring static torque, nothing is moving at all, but you are getting at a key point. The head on the torque wrench has both a torque moment around the head axis, and is applying a force perpendicular to the extension wrench arm. The torque wrench is directly measuring the first of these (that's what torque wrenches do) and is not measuring the second one directly at all. (But you can compute the second one if you know the torque wrench and extension wrench lengths.) I think a big part of the confusion is folks confusing the two.
--Paul
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02-14-2012, 04:10 PM
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Join Date: Feb 2009
Location: Southbridge,MA
Posts: 193
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Now what was for sale? 
__________________
Steve Stella
#40654 Finishing
N521RV reserved
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02-14-2012, 04:22 PM
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Senior Curmudgeon
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 15,420
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Quote:
Originally Posted by sstellarv10
Now what was for sale? 
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One each, brain, thoroughly used up.   
__________________
Mike Starkey
VAF 909
Rv-10, N210LM.
Flying as of 12/4/2010
Phase 1 done, 2/4/2011 
Sold after 240+ wonderful hours of flight.
"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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02-14-2012, 04:23 PM
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Join Date: May 2008
Location: Payson, AZ
Posts: 47
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Question
In the video the wrench appears to be made of 2 thinner pieces based on the appearance. is it? Or is it one piece with a line around it? Thanks Marty
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02-14-2012, 04:26 PM
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Join Date: Jan 2007
Location: AOTP
Posts: 192
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This is supposed to be a prop wrench, how 'bout a prop service bulletin for reference?
http://www.mccauley.textron.com/sb227B.pdf, see the last page.
__________________
Nauga
2004 RV-4
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02-14-2012, 05:23 PM
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Join Date: Aug 2006
Location: santa barbara, CA
Posts: 1,682
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Quote:
Originally Posted by nauga
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To save everyone the trouble of an extra click, the McCauley Service Bulletin above says that when using a torque wrench with an extension:
dial reading = torque wrench length (ft) x desired torque (ft lbs) / [torque wrench length + extension length (ft)]
Clearly this falls into "the 0.8 multiplier is not a constant" camp. Im back to not knowing what to think. Could this SB really be wrong?
erich
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02-14-2012, 06:42 PM
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Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,687
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Quote:
Originally Posted by erich weaver
To save everyone the trouble of an extra click, the McCauley Service Bulletin above says that when using a torque wrench with an extension:
dial reading = torque wrench length (ft) x desired torque (ft lbs) / [torque wrench length + extension length (ft)]
Clearly this falls into "the 0.8 multiplier is not a constant" camp. Im back to not knowing what to think. Could this SB really be wrong?
erich
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OMG... this is the same thing that AC 43-13 says, could it actually be that all these documents have been wrong all these years and remarkably the brilliant minds on VAF have finally discovered the truth
As I said before, show me the math and I'll be a believer, but I still haven't seen it.
All ft pound wrenches are not 1 ft long which is what this "theory" is based on. If every torque wrench was 1 ft long then Allen would be right, end of story.
__________________
Walt Aronow, DFW, TX (52F)
EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 1700+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154
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02-14-2012, 06:55 PM
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Join Date: Jan 2005
Location: Round Rock, TX
Posts: 3,778
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Allan,
Looks like the Retail Price of your wrench has gone up... include a 12" 3/8" drive Snap On high quality torque wrench in the wrench kit and then nobody will have the need to do the math. 
__________________
Reiley
Retired N622DR - Serial #V7A1467
VAF# 671
Repeat Offender / Race 007
Friend of the RV-1
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02-14-2012, 07:30 PM
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Join Date: Jan 2005
Location: Peoria, AZ
Posts: 1,053
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Take 3 torque wrenchs, one 1 ft long one 2 ft long and ine 3 ft long. All are calibrated for 100 ft lbs torque.
So even though they are different lengths, they all put exactly the same 100 ft lbs of torque at the head.
So all three torque wrenches put exactly 100 ft lbs of torque at the head and then you add the exact same 3 " extension to them. Wouldnt the 3 " extension have the same effect on the 100 ft lbs of torque at the head on all of them?
Just saying... 
__________________
Regards,
Thomas Velvick
Goodyear, AZ (KGYR)
2020 Donation sent.
N53KT RV-6a finished 2018, Flying
N7053L RV-4 Wife's RV
N56KT RV-4 Finishing
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