Releases

[Tad Eareckson]

Nah, that's one thing that really left an impression on me way back in school whenever the hell it was that we were introduced to the concept of coefficient of friction.

When you're dragging a timber across the ground it doesn't make any difference whatsoever whether it's flat or standing on an edge. Exactly the same effort either way.

Likewise - if you ignore the improved mechanical advantage of holding the pin rotated back a full 180 degrees - it doesn't matter if the barrel is perfectly matched such that the entire length of the pin shaft is in contact with the fully closed barrel or the barrel's a wee bit wide such that just the tip is in contact. Same pull.

And with the full length of the shaft in contact, it wouldn't get progressively easier to pull the barrel back. Same effort for the last couple of millimeters of retraction as for the first.

[Steve Davy]

Likewise - if you ignore the improved mechanical advantage of holding the pin rotated back a full 180 degrees - it doesn't matter if the barrel is perfectly matched such that the entire length of the pin shaft is in contact with the fully closed barrel or the barrel's a wee bit wide such that just the tip is in contact. Same pull.

That makes sense.

And with the full length of the shaft in contact, it wouldn't get progressively easier to pull the barrel back. Same effort for the last couple of millimeters of retraction as for the first.

In my original post today I almost asked if the pull force was linear. Now you have stated it is not, let me see if I can figure out why.

[Steve Davy]

In a system where the barrel and pin remain parallel throughout the release the pin cannot get more parallel.

In a system where the barrel and pin start out non-parallel the pin can get more parallel as the barrel is pulled aft.

Assuming that the pin getting more parallel to the barrel causes the pin to be closer to 180 degrees.

Best guess, The red line is engaging the pin below the pin's dead center and exerting a force on the system such that the pin is allowed or caused to rotate closer to 180 as the barrel is pulled aft.

[Tad Eareckson]

In a system where the barrel and pin remain parallel throughout the release the pin cannot get more parallel.

Right. And now that I look at some photos...

http://www.flickr.com/photos/aerotowrelease/8311348069/

http://www.flickr.com/photos/aerotowrelease/8312399698/

http://www.flickr.com/photos/aerotowrelease/8322228469/


...and think a bit...

The red line / bridle / bridle link is spreading the pin and base apart, that force is pushing against the inside of the barrel at its front end so...
- the base inside the barrel and pin shaft are pretty damn parallel - to each other and the barrel; and
- as the barrel's retracted back from the point of the spreading the pull actually WILL get a bit easier.

In a system where the barrel and pin start out non-parallel the pin can get more parallel as the barrel is pulled aft.

Yeah but...

That second photo is a bit confusing. With the barrel almost fully retracted the pin is now LESS parallel to the barrel, more angled up from eye to tip.

My best shot at an explanation...

The bridle link is being engaged by some line on the bottom and a rigid structure on the top, the barrel downwind is rigid, and there's some asymmetrical, offset, torque stuff going on - you can see the deflection in the third photo. And as the barrel is retracted the pin shaft is freed and the pin is allowed to deflect down (from tip to eye).

Assuming that the pin getting more parallel to the barrel causes the pin to be closer to 180 degrees.

Less, it seems. This real world stuff can be a real pain in the ass sometimes.

Best guess, The red line is engaging the pin below the pin's dead center and exerting a force on the system such that the pin is allowed or caused to rotate closer to 180 as the barrel is pulled aft.

- Yeah, the bridle link can't be dead center on the pin 'cause that's where the shaft is.
- There's a war between the pin and the base and the pin's got an edge 'cause it's a rigid structure and the base isn't.

Practically speaking though, all we have to worry about (fortunately) is that we:
- can blow seven hundred pounds towline with a seventeen pound pull; and
- have even more reason to use a short barrel on a remote setup like Joe Street's.

[Tad Eareckson]

Steve Davy - 2012/04/14 21:08:33 UTC

In my original post today I almost asked if the pull force was linear. Now you have stated it is not, let me see if I can figure out why.

Spoiler Alert

If you're still working on this puzzle and wanna do it yourself read no further.

Otherwise - and for future reference or anyone else...

In the previous post I discussed a bunch of troublesome real world issues I hadn't thought out before. But in terms of pounds they're all pretty negligible and not worth worrying about.

The main issues are the:

-a) coefficients of friction between the aluminum barrel and:
- - Dacron leechline base; and
- - stainless steel pin; and

-b) force with which the base and pin are pushing out on the inside of the barrel wall (equal and opposite and dependent upon the loading and mechanical advantage of the mechanism).

And the contact surface areas are totally irrelevant - you don't need to know anything about them.

And, again, practically speaking, you really don't need to worry about any of that either. Once you get that barrel moving - be it a nice straight pin job or some bent pin piece of crap from Bobby, Malcolm, Matt, or Davis; hand pulled or remote; leechline or cable lanyard - it's gonna keep moving until it clears the pin (unless you throw an overstrength spring into the equation).

[Steve Davy]

we can blow seven hundred pounds towline with a seventeen pound pull;

To find the load on a barrel on the secondary.
700 lbs. Towline divided by 2 = 350. Multiply by 1.15 = 402.5. Divide by 2 = 201.25.

To find the load to actuation, divide 201.25 by 17 = 11.83.

Did I do that right?

[Tad Eareckson]

1. I wouldn't put 700 on the glider two point. 650 loads the primary release to 374 and that's about as high as I ever wanna go. Let's back it off to 600.

2. Otherwise you're good until you get down to 17. My test average for the shoulder mounted barrels is 20.38 and for the remote (two point) 16.41. So you'd be pulling 9.9 pounds.

3. But you REALLY don't wanna know that 'cause you don't EVER wanna be pulling a secondary while you're still connected at the top.

[Steve Davy]

Just so I am certain, when you refer to load/actuation that is always direct load - correct?

[Tad Eareckson]

Yeah, whenever I talk about a mechanism it's gonna be direct - and before I jack things up with pulleys.

[deltaman]

mouth release in action:

http://www.youtube.com/watch?v=Uu1MPb2zfxA