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

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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