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marchudson 02-14-2012 03:09 PM

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))

Garage Guy 02-14-2012 03:41 PM

Mike,

Quote:

Adding the extension changes the location of the center point of rotation
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:

and the head on the torque wrench is now moving in an arc, not rotation.
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

sstellarv10 02-14-2012 04:10 PM

Now what was for sale?:eek:

Mike S 02-14-2012 04:22 PM

Quote:

Originally Posted by sstellarv10 (Post 629186)
Now what was for sale?:eek:

One each, brain, thoroughly used up.:confused::eek::confused:

M60Marty 02-14-2012 04:23 PM

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

nauga 02-14-2012 04:26 PM

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.

erich weaver 02-14-2012 05:23 PM

Quote:

Originally Posted by nauga (Post 629189)
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.

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

Walt 02-14-2012 06:42 PM

Quote:

Originally Posted by erich weaver (Post 629201)
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

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 :eek:

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.

LifeofReiley 02-14-2012 06:55 PM

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. :D

rvator51 02-14-2012 07:30 PM

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...:D

PerfTech 02-14-2012 07:39 PM

Quote:

Originally Posted by rvator51 (Post 629253)
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...:D

.
EXACTLY!!!!!!!!:D
You got it perfect, Thanks, Allan

nauga 02-14-2012 07:51 PM

Quote:

Originally Posted by rvator51 (Post 629253)
Wouldnt the 3 " extension have the same effect on the 100 ft lbs of torque at the head on all of them?

No, because it's the force you put on the end of the wrench times the distance from the end that generates that torque, it doesn't just magically appear. As the arm gets longer the force to produce 100 lb at the head goes down, and it's this force applied over the total length, wrench plus extension, that produces a torque at the extension end.

gasman 02-14-2012 08:05 PM

There are many publications out there that have printed it wrong I guess. It sure would be easy to prove.
After reading the last 10 pages, the only way I would use this product would be with the wrench at 90 degrees from the adapter..... easy to do with this application.

At least it's not a primer or F/P issue......................:D

Mark Albery 02-14-2012 08:17 PM

Quote:

Originally Posted by rvator51 (Post 629253)
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...:D

WRONG!!!!!!!:D:D

You got it wrong, sorry
It's already been explained correctly a few times.

The nut sees a torque of applied force * distance from handle to nut.
The wrench gauge sees a torque of applied force * distance from handle to drive end of wrench.
So correction is the ratio of those lengths.
Put the crowsfoot at 90 degrees; the lengths are the same so the correction is zero.

schristo@mac.com 02-14-2012 08:19 PM

she's a witch!
 
Many of these posts are pretty humorous, I wonder if I use a large red font if it will have more impact...

It is interesting to see various responses and who makes them; I must be the dumbest guy in the forum; perhaps PI really is 3.

"Who are you, who are so wise in the ways of science?"
http://youtu.be/zrzMhU_4m-g

nauga 02-14-2012 08:23 PM

Quote:

Originally Posted by schristo@mac.com (Post 629272)
"Who are you, who are so wise in the ways of science?"

This new learning amazes me, Schristo. Explain again how sheep's bladders may be employed to prevent earthquakes.

LifeofReiley 02-14-2012 08:30 PM

I bet there are a ton of AN bolts under and over torqued out there... :eek:

Garage Guy 02-14-2012 08:34 PM

Larry, this is great, this is the closest I've seen to someone actually laying out a mathematical argument for a constant conversion factor.

Now my question is, if this is a good argument, why not apply to a torque wrench that reads inch-pounds. Just change foot to inch:

Quote:

Originally Posted by L.Adamson (Post 629135)
Another way of demonstrating.

A inch lb. is the force of 1 lb., 1" perpendicular to the pivot point.

If we take 100 lbs, and set it 1" from the pivot point, then it's 100 in. lbs torque against the pivot point.

If we use a 24" or 36" wrench, we are NOT moving the 100 lbs past the 1" spot on the wrench. It remains at the 1" point. By adding a longer handle, we push with less force, to move that 100 lbs.

With the addition of the 3" tool, the 1" point (which is used for the "inch" in in/lbs. is now 4". And that's why a fraction is used. 3" & 1" remain as constants.

If I'm following you, now you have a conversion factor of 1/(1+3), or 0.25. That is, if you want a certain torque X in-lbs at the nut, you would set your torque wrench to 0.25 X.

OK so far?

--Paul

LifeofReiley 02-14-2012 08:41 PM

Allan,

New Service Bullet
SB 2012-2-14

For everyone purchasing this wrench, do your own math calculations for torque value. :D

L.Adamson 02-14-2012 09:04 PM

So tell me, wise ones...

A click wrench uses a spring and pawl, which releases when the desired torque setting is hit. This compressed spring is calibrated to match ft/lbs., which is based on one pound of force, at one foot from the pivot point. The one foot is only a measurement of force. The wrench does not have to be a foot long.

How is this spring going to know, if you're grasping the wrench at the exact same spot on the shaft. Does it care? No it doesn't! The force you apply at the handle depending on length, varies. But the spring just doesn't care. It's going to release at the setting it's set to...........which is based on one pound at one foot, for ft/lb settings.

edit: And I'm going to add a 100' extension, pulled by block and tackle, connected to a cement truck.................and the spring still won't care, or notice the difference!!!!
It will just merely click, when it reaches the set point..

L.Adamson

nauga 02-14-2012 09:16 PM

Quote:

Originally Posted by L.Adamson (Post 629290)
It's going to release at the setting it's set to...........which is based on one pound at one foot, for ft/lb settings.

The spring will release when the torque *at the wrench head* reaches the value you have set (assuming the wrench is calibrated). This will be will be consistent regardless of the extension you have attached as long as the setting does not change. The torque at the wrench head will equal the force you've applied times the distance from the point of application of that force to the wrench head.

The torque at the end of the extension, however, doesn't simply scale as a function of torque and distance, it's a function of *force* and distance, the force being the force you've applied and the distance being the distance from the point of application of the force to the end of the extension. It does not matter that the torque in/on the system somewhere in between (say, at the wrench head) is less, the torque at the extension end is a function of total distance (wrench plus extension) times force applied.

Mark Albery 02-14-2012 09:27 PM

The torque on the nut is not being applied at the drive end of the torque wrench. It is being applied by the force on the handle.

If you applied a pure torque to the drive adaptor in the prop wrench (e.g. by using a pneumatic nut driver) you actually wouldn't apply any torque at the nut end of the prop wrench. (Imagine putting a screwdriver handle in the drive hole; it wouldn't matter how long the wrench was, you would just generate a linear force at the other end, not a torque)

I think this debate is a bit like the aircraft on a conveyor belt saga.

L.Adamson 02-14-2012 09:34 PM

Quote:

Originally Posted by nauga (Post 629296)
The spring will release when the torque *at the wrench head* reaches the value you have set (assuming the wrench is calibrated). This will be will be consistent regardless of the extension you have attached as long as the setting does not change. The torque at the wrench head will equal the force you've applied times the distance from the point of application of that force to the wrench head.

The torque at the end of the extension, however, doesn't simply scale as a function of torque and distance, it's a function of *force* and distance, the force being the force you've applied and the distance being the distance from the point of application of the force to the end of the extension. It does not matter that the torque in/on the system somewhere in between (say, at the wrench head) is less, the torque at the extension end is a function of total distance (wrench plus extension) times force applied.

I appreciate the long explanation, but the "spring" has perhaps already clicked........before your potential force and distance ever got there.

Your correct about force and distance in relation to absolute torque. But it has nothing to do with the spring setting. The spring only cares about the correct torque applied to the nut. Not the potential torque that you can add to it, by the force of leverage.

nauga 02-14-2012 09:40 PM

Quote:

Originally Posted by L.Adamson (Post 629301)
The spring only cares about the correct torque applied to the nut.

No, the spring responds to, and is calibrated to, the torque at the wrench head. The torque is different at any other position in the system and is only a function of force and distance from that force to the point in question.

n5lp 02-14-2012 10:05 PM

This would be a really nice place for someone with the proper equipment to set up a demonstration. Easier to do here than with "the downwind turn."

Brantel 02-15-2012 05:46 AM

The formulas that all of you are getting stuck on are only for simple levers and pivots.

Torque wrenches when you include the indicating mechanizm are complex machines not simple levers.

The key is the calibrated indicating method of the torque being applied. If you take a typical high quality aircraft torque wrench and set it to click at 100ft pounds and pull it on a nut in stock configuration, it should click when there is 100ft pounds on the nut. How much you have to pull is based on how long the wrench handle is. Remember the clicker is calibrated to a certain torque on the nut driver shaft.

Now take the same wrench and add a 3 ft extension to the handle. Pull the handle till the clicker clicks.....You still get 100ft pounds at the nut as long as you stop pulling when the clicker clicks. The amount you have to pull is reduced because of the longer handle. The calibrated clicker still clicks at 100ft lbs at the nut driver shaft.

If you take all the indicating mechanizms away and use a spring scale on the end of a simple lever, all of these textbook formulas work just fine with including the lever length.

gstone 02-15-2012 05:55 AM

Well said Brian...
 
"If you take all the indicating mechanizms away and use a spring scale on the end of a simple lever, all of these textbook formulas work just fine with including the lever length."

I will add that if the attachment was welded on to the torque wrench then the over-all length would matter but it is not, the torque is all measured and applied to the attachmnet at a point 3 inches from the nut and this gives the additional leverage that must be compensated for.....

mkraus01 02-15-2012 06:47 AM

Not to ruin the fun, but I think it's way past time for the moderators to move this out of the classifieds section. I asked a question last week (on page 2) as to whether this works on a MT prop and there was so much talk about how to torque a prop that no one answered my question that could actually turn into a sale....

We are on page 11 now, and nothing in the last 8 pages has anything to do with the classifieds. Let's move this to the proper list.

And I'm still hoping someone can answer my question on whether this works on an MT 3 bladed RV-10 prop? The web site mentions Hartzell....

Thanks
-Mike Kraus
RV-10 Flying

Sam Buchanan 02-15-2012 06:56 AM

Quote:

Originally Posted by mkraus01 (Post 629358)
Not to ruin the fun, but I think it's way past time for the moderators to move this out of the classifieds section. I asked a question last week (on page 2) as to whether this works on a MT prop and there was so much talk about how to torque a prop that no one answered my question that could actually turn into a sale....

We are on page 11 now, and nothing in the last 8 pages has anything to do with the classifieds. Let's move this to the proper list.

And I'm still hoping someone can answer my question on whether this works on an MT 3 bladed RV-10 prop? The web site mentions Hartzell....

Thanks
-Mike Kraus
RV-10 Flying

Nawwww, let's leave it in classifieds so it will be deleted in a couple of weeks. :D

Walt 02-15-2012 07:08 AM

Quote:

Originally Posted by Brantel (Post 629348)
The formulas that all of you are getting stuck on are only for simple levers and pivots.

If you take all the indicating mechanizms away and use a spring scale on the end of a simple lever, all of these textbook formulas work just fine with including the lever length.

I guess Hartzell in wrong too... have a look at page 3-6 of the Hartzell manual.

http://www.hartzellprop.com/public_dl.php?id=4

Again, the .8 factor is ONLY for a 1 ft torque wrench, for any other length you need to do the math for your wrench.

L.Adamson 02-15-2012 07:41 AM

Quote:

Originally Posted by Walt (Post 629365)
I guess Hartzell in wrong too... have a look at page 3-6 of the Hartzell manual.

http://www.hartzellprop.com/public_dl.php?id=4

Again, the .8 factor is ONLY for a 1 ft torque wrench, for any other length you need to do the math for your wrench.

Hartzell is saying exactly what Allan, myself, and some others are saying.

How many torque wrenches, that you would be using on a prop.........are just one foot long? I doubt there are any!

That one foot figure has to do with 12" meaning a foot pound. That's the distance that torque values are measured from. The drawing isn't even close to being scale.

L.Adamson


P.S.--- the extensions, crows foot, or whatever, are required, because you can't just place a torque wrench directly over the prop nuts. There is a flange in the way.
As Hartzell says, if the extension is at 90 degrees, just use the normal reading.

L.Adamson 02-15-2012 07:58 AM

Since so many here, are ignoring the mechanical aspects of a torque wrench, as Brantel mentioned.....

We'll just all go out, and take an ordinary wrench & stick 100 lbs of dumbbell weights at the 12" mark, or 50 lbs. at the 24" mark. If the 3" extension is used, we'll put only 80 lbs. at the 12" mark. Note: It doesn't matter how long your wrench actually is. It's those 12", 24" or any calculated mark in between that matters. Figure in a bit of weight, for the shaft, too.

If using an actual torque wrench, then ignore the above...

L.Adamson

JonJay 02-15-2012 08:11 AM

Quote:

Originally Posted by L.Adamson (Post 629375)
Hartzell is saying exactly what Allan, myself, and some others are saying.

How many torque wrenches, that you would be using on a prop.........are just one foot long? I doubt there are any!

Not to take away from your comments because you are correct, but the torque wrench I use from my neighbor is exactly 12", so they do exist. I will try to get the brand from him as it is perfect for the job with a 3" extension (yes, you need to do the math) The formula's from Hartzell, and every manual I have ever seen are correct. Not sure why anybody would argue what should be considered common knowledge.

L.Adamson 02-15-2012 08:23 AM

Quote:

Originally Posted by JonJay (Post 629385)
Not to take away from your comments because you are correct, but the torque wrench I use from my neighbor is exactly 12", so they do exist. I will try to get the brand from him as it is perfect for the job with a 3" extension (yes, you need to do the math) The formula's from Hartzell, and every manual I have ever seen are correct. Not sure why anybody would argue what should be considered common knowledge.

Is that wrench for inch pounds only? A wrench that's capable of 50 to 150 ft/lbs., would be a tough one to use, at only 12" long.

ccsmith51 02-15-2012 08:24 AM

It seems that this whole discussion is about whether the 0.8 multiplier with a 3" extension is universal for any torque wrench. I propose it is not.

Let's use the Hartzell formula:

(actual torque required) X (torque wrench length) / (torque wrench length) + (length of adapter) = Torque wrench reading to achieve required actual
torque

Example 1:

Actual torque required- 100 ft-lbs
Torque wrench length- 12" (1.0')
Length of adapter- 3" (0.25')

Formula: (100 ft-lbs x 1 ft) / (1 ft + 0.25 ft) = 100 ft-lbs / 1.25 ft = 80 lbs torque wrench reading

Example 2:

Actual torque required- 100 ft-lbs
Torque wrench length- 18" (1.5')
Length of adapter- 3" (0.25')

Formula: (100 ft-lbs x 1.5 ft) / (1.5 ft + 0.25 ft) = 150 ft-lbs / 1.75 ft = 85.71 lbs torque wrench reading

So, using the math that has been shown before seems to indicate that a 0.80 factor is only valid when the torque wrench is 1' long...

There is a relatively easy way to confirm or debunk the 0.8 universal multiplier theory. Three beam type torque wrenches (of at least two different lengths) and some adapters are required.

Take one torque wrench and clamp the shaft in a vise such that a torque applied to the end can give a reading (the captured wrench). Using an adapter attach the second torque wrench (the free wrench) to the captured wrench. Press the free wrench to 100 ft-lbs. The captured wrench should also read 100 ft-lbs.

Do the same test with the third wrench, of a different length. Again, both readings should be the same, as both wrenches, regardless of their length, are calibrated to read the same torque at the head.

Now, do the same test with the 3" extension.

If at 100 ft-lbs on the captured wrench, both free wrenches read the same, then the 0.8 multiplier is proven.

If at 100 ft-lbs on the captured wrench, both free wrenches read different, then the 0.8 multiplier is busted.

Hey, maybe we could get Kari from MythBusters involved!! :)

JonJay 02-15-2012 08:34 AM

Quote:

Originally Posted by L.Adamson (Post 629387)
Is that wrench for inch pounds only? A wrench that's capable of 50 to 150 ft/lbs., would be a tough one to use, at only 12" long.

I found it very easy to use for the 60-70 ft lbs on my prop with a 3" extension. I will find out the brand and what the top end is, but yes, at 150 lbs with no extension it would take some grunt.

jpharrell 02-15-2012 08:47 AM

My 2 cents
 
Wow, I just picked up on this thread and have not been involved in the flurry of opinions up to this point. Seeing the chaos I hesitated to chime in but after considering that this could have safety of flight implications for some relying on the information they get here I decided to weigh in. We all bring different strengths to the discussion on this forum. There is a lot I don?t know but I do have a master's degree in mechanical engineering, so whatever that is worth, here are the key points I would offer:

1) A torque wrench is designed to accurately measure and set torque at the head of the torque wrench. To that extent, it does not matter if the handle is 12 inches or 24 inches; whether you apply the force at the end of the handle or in the middle of the handle. The wrench "clicks" when the torque applied at the head reaches the set value.

2) If an extension (or crows foot) is attached the torque applied at the wrench head will be different than the torque applied at the end of the extension unless the extension is turned 90 degrees to the axis of the wrench handle such that the moment arm for the applied force is the same for the extension as it is for the wrench head.

3) If you use an extension on a torque wrench rotate it 90 degrees to the wrench axis and you will be fine. Set the wrench to the same torque value you would without the extension and the same torque will be applied at the bolt head on the extension.

4) If you must use an extension straight in line with the handle of a torque wrench you should be very careful. The torque applied to the bolt will be greater than the value you set on the torque wrench and the correction factor depends on both the length of the extension and the moment arm of the force application. It is not just the length of the torque wrench handle that counts, it is also dependent on where you apply the force on the handle. The correction formula is

C = L / (E + L)

If the extension length E is 3 inches and the distance from the wrench head to the point on the handle where you apply the force (L) is 12 inches then the correction factor is 0.8. But realize it is not always simply 0.8 for a 3 inch extension. Notice I said ?the point where you apply the force?. Using an extension this way makes the true torque applied to the bolt dependent on your ?technique?. Not so when a torque wrench is used without any kind of extension.

I happen to work in aerospace where we build spacecraft and other aerospace equipment and we follow these guidelines in torquing fasteners. As a rule we avoid using extensions or crows feet whenever possible. If we have use an extension we turn the extension 90 degrees to the torque wrench handle. If we can?t do that, we are very careful to calculate the correction factor accurately based on the specific wrench and the force application technique.

I hope this helps.:)

L.Adamson 02-15-2012 08:57 AM

Quote:

Originally Posted by ccsmith51 (Post 629389)
So, using the math that has been shown before seems to indicate that a 0.80 factor is only valid when the torque wrench is 1' long...

Okay.............

Start looking through catalogs, and look for torque wrenches in the 100 ft/lb. category...............and see how many you'll find at just 12" long. I've looked all morning, and found none. That .80 factor applies to 12" (1') as it relates to ft/lb torque. Since the measurement of torque that we're using to set the prop nuts is in ft/lbs, then it all makes sense.

L.Adamson 02-15-2012 09:03 AM

Quote:

Originally Posted by jpharrell (Post 629392)
I happen to work in aerospace where we build spacecraft and other aerospace equipment and we follow these guidelines in torquing fasteners. As a rule we avoid using extensions or crows feet whenever possible. If we have use an extension we turn the extension 90 degrees to the torque wrench handle. If we can?t do that, we are very careful to calculate the correction factor accurately based on the specific wrench and the force application technique.

I'll assume, you won't be torquing too many Hartzell props, where and extension or crows foot, is a must. :)

Radomir 02-15-2012 09:38 AM

No amount of math and physics will "fix" this -- some just don't get it and it's more important to believe than to learn.

Either way, for those "wrenchers" -- RTFM for your torque wrench and follow instructions in it.. Once you realize you were wrong all along, you have an option of creating your own torque wrench that works the way you describe it.. you WILL make a lot of money selling those. Heck, I'll buy one.. cause all the torque wrenches I own work the same way Hartzell, McCauley, AC 43.13, and every other publication written says...


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