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The Great Thrust Vector Debate

Discussion in 'Handguns: Autoloaders' started by 1911Tuner, Aug 18, 2004.

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  1. 1911Tuner

    1911Tuner Moderator Emeritus

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    Okay...here it is. I ask that everyone hold their comments until Mr. Keenan
    has made his counterpoint. This one promises to be interesting, as it has in the past. I fully expect it to be resolved with an agreement to disagree.
    We'll leave it to the readers as to which theory to accept.

    Any attempt to hijack the thread or take it off-topic will be deleted in good humor and fellowship. This is a debate of theories only. If anyone has a topic-related point of interest that may cause either one of us to change our outlook, it's more than welcome as long as it's kept factual and civil.

    Enjoy!
    ___________________________________

    A few years back, I read an article by Jerry Kuhnhausen on how the 1911 pistol really works. It was a good article, with excellent illustrations...but
    when I got to the "Balanced Thrust Vector" part, I couldn't believe that a man as knowledgeable as Kuhnhausen could write that. However...The more I study on it, the more I think that he might have nailed it, and an
    incredible experiment that was done by our own Jim Keenan was what
    got me really thinking about it on a deeper level.

    The gun is recoil operated. No question about it...but what initiates the recoil sequence? The bullet passing through the barrel...or the expansion of the gasses?

    The expanding gasses generate the thrust needed for bullet movement.
    Moreover, that thrust operates in all directions...not just forward. It pushes
    the bullet and the slide equally...and it also generates equal thrust up, down, sideways, and diagonally. All directions.

    The accepted theory is that the slide won't move unless the bullet moves, and that's absolutely true...but the question is why the slide will only move with bullet movement. Is the bullet really generating the recoil impulse...
    or is the bullet merely a launching pad for the gasses...just like the
    breechface of the slide? Two solid objects with an equally applied
    force between them creates Kuhnhausen's Balanced (equal) Thrust vector.

    Jim's experiment entailed threading the muzzle of the barrel and using a steel rod to keep the bullet static with a set screw in the muzzle. When the
    round was fired, the bullet couldn't move at all, and neither did the slide.
    Okay...No bullet movement means no slide movement.

    Looking at it a little closer makes me understand that with the rod against the bullet and a set screw preventing the rod and bullet from moving, it prevented slide movement because the thrust generated by the gasses was transferred directly to the barrel, forcing it forward.

    The barrel is mechanically locked to the slide via the locking lugs, and the slide can't move under those conditions...not because the bullet couldn't move, but because it was locked to the slide under extreme pressure. It's rather like locking your fingers in front of your chest and pulling equally in opposite directions. An isometric lock that won't allow movement UNTIL
    the force becomes UNEQUAL.

    So...The equal thrust is pushing rearward on the slide through the cartridge case at the same time that it's pushing on the bullet that is static in the barrel because of the rod and screw...and you have an isometric lock
    that would be the same as welding the muzzle to a heavy steel block and pulling rearward on the frame of the gun while trying to manually operate the slide.

    Keeping in mind that the bullet is a tight fit in the barrel when the gun is fired normally. The bullet is forced through the barrel under pressure,
    and the barrel is forced forward under this pressure, maintaining the mechanical lockup to the slide...and nothing CAN move UNTIL something
    happens to break the bullet's grip on the barrel.

    When the bullet is pushed out of the case and down the bore, there is no isometric lock between barrel and slide. The thrust pushes backward on the slide at the same time that the bullet is moving, and imparts momentum to the slide which causes the slide and barrel to move rearward together in the same direction, rather than trying to pull them apart.

    The bullet exits the barrel, and breaks the friction between it and the bore,
    which frees up the barrel from its forward thrust. The momentum that was imparted to the slide takes over and completes the recoil cycle by pulling the now-free barrel along with the slide.

    Mr. Keenan? Your counterpoints?
     
    Last edited: Aug 18, 2004
  2. 1911Tuner

    1911Tuner Moderator Emeritus

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    BTT

    Btt with a link to view Kuhnhausen's article. It'll take the illustrations a few minutes to download, so be patient, fer cryin' out loud!:D

    http://www.m1911.org/locking.htm
     
  3. Grump

    Grump Member

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    Simple. Pressure is irrelevant. Movement of mass is. Bullet moves forward, contributes to recoil. Gases move forward, contribute a bit more to recoil.

    *THAT'S* why my 125-gr reloads with a 20.5 gr load of WW296 going 1350+ fps kick just as hard as 140-gr loads using 10 gr of (Yikes-what powder was it???) something else going about the same speed.

    The internal ballistics term is "recoil ejecta." It's just physics. There's a tiny bit of gas-thrust recoil after the bullet leaves, but that is also a function of the gas mass and the gas velocity.
    Well, you can get the same lockup that's never unlocked by taking a slide assembly, suspending it on strings, then snapping some means to get the firing pin up to ignition speed. Pressure stays the same and all that, the bullet will go forward, but allowing both the barrel and the slide to recoil together without any resistance to the barrel (the link connected to the frame), the thing stays locked tight. Gas pressure is irrelvant. The only "forward" thrust on the barrel is bullet friction in the bore, and any measurement of that force from slugging barrels will undoubtedly prove far less than 18,000+ psi times 1/2 times .45 times 3.14146....
     
  4. Darkside

    Darkside Member

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    Question.....Since the bullet wasn't allowed to move, the gasses of the combustable solid powder couldn't expand and burn properly. Could the powder have just set there and smoldered until compleatly burned up? The powder wouldn't have reached anything near full preasure if this happened.

    I have wondered about this????

    Darkside
     
  5. Grump

    Grump Member

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    Darkside, it's actually quite the opposite. Nitrocellulose/nitroglycerine in a burning situation burns faster under higher pressure. Even in the roomy .45 ACP case, I would have expected such a closed-breech experiment *with a normal powder charge* to blow the chamber steel, or at least the casehead.
     
  6. 1911Tuner

    1911Tuner Moderator Emeritus

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    Barrel on a String?

    Grump said:

    Pressure stays the same and all that, the bullet will go forward, but allowing both the barrel and the slide to recoil together without any resistance to the barrel (the link connected to the frame),
    __________________

    Flawed theory. The thrust works equally in all directions. If the bullet and slide/barrel assembly were of equal mass, they would be propelled at the same rate of acceleration in opposite directions. The barrel is forced to unlock from the slide by the link after the barrel has traveled rearward for the distance required to get the slidestop pin out from under the lug. Until that happens, the link can pull until it snaps, and it won't unlock the barrel. The slide and barrel suspended on a string would remain locked on ignition because of the equal thrust in both directions. There is no link attached to the frame to force the barrel to change its rearward direction to a downward direction.

    Suspend a firecracker in the geographic center between two tin cans.
    When it explodes, both cans will be propelled equally in opposite directions, assuming instantaneous ingition of the firecracker rather than a progressive burn from one end to the other.

    So...Does the barrel recoil and push on the slide...or does the slide recoil and pull on the barrel? Chicken or egg...Chicken or egg...
     
  7. pauli

    pauli Member

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    for every action, there is an equal and opposite reaction.

    for every pressure propelled bullet, there is a pressure propelled casing (and, in this case, a breechface and all the rest).

    of course, there are still expanding gasses exerting pressure on the casing after the bullet leaves the barrel... albeit briefly.

    an interesting experiment would be to yank the bullet from the chambered round in a manner duplicating the velocity pattern of a real fired round.
     
  8. 1911Tuner

    1911Tuner Moderator Emeritus

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    Equal and Opposite

    pauli! Yes!

    A theoretical experiment for everybody to consider :

    IF...you could attach a cable to the bullet and yank it through the bore at
    the same rate of acceleration as it would have when it's PUSHED through the bore by the expanding gasses WITHOUT the benefit of those gasses
    exerting thrust in both directions...would the slide and barrel move backward? I don't think so. I believe that the barrel would be pulled
    forward until the bullet exited, and that the slide wouldn't move.
     
  9. Tamara

    Tamara Senior Member

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    B.

    That's why they call it "boltface (or breechface) thrust." :)

    (Even guns with fixed barrels get that slide moving rearward just fine, like the NGC(?) gas-delayed conversions of the 1911 that have the bbl fixed in place. :cool: )
     
  10. Ktulu

    Ktulu Member

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    Right on!

    EDITED TO ADD: Great thread!
     
  11. 1911Tuner

    1911Tuner Moderator Emeritus

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    Boltface Thrust

    Tamara! YEEESSS!!!!! Exactimundo! There is a thrust vector
    that imposes both against the base of the bullet and on the breechface
    through the case head.

    Where's Keenan at? :scrutiny:
     
  12. JAREDSHS

    JAREDSHS Member

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    way too much spare time on our hands here!!!lol
     
  13. Grump

    Grump Member

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    Hold it!!! Pressure = Thrust???

    Don't think so. Rocket engines got pressure out the wazoo, in all directions, inside. But the thrust is only in the direction opposite the outgoing gas jet. As the bullet accelerates down the bore, thrust is generated in only one direction, although pressure is directed everywhere. The only forward thrust on the barrel is what the bullet imparts from friction drag...and that must be far less than the recoil impulse going in the opposite direction. Recoil impulse before unlocking is transferred from the slide to the barrel through the lockin surfaces.

    So, my bottom line is that I see no NET forward thrust on the barrel because the recoil impulse caused by powder plus bullet accelerating far exceed the forward friction drag. That gas pressure going forward only "pushes" the barrel to the extent and limit of the drag.

    Consider this experiment--hang a barrel with chambered round by strings. Heat the primer until it lights. See what happens. If the case can resist blowing out or rupturing long enough to get the bullet very far down-bore (maybe 3/4 an inch?), then you will have rearward recoil. If the case blows and the bullet stays put, the accelerating case and gases will give "forward" recoil.
     
  14. 1911Tuner

    1911Tuner Moderator Emeritus

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    Jet Propulsion

    Uh...Grump. I ain't a rocket scientist, so i can't explain jet propulsion to any degree of accuracy. The "thrust" that I speak of is against
    the bolt face and the base of the bullet equally...as well as up, down, sideways, etc. The pressure of the expanding gasses creates that thrust
    between the two solid objects..The vector. Each one is the launching pad
    for the other, and each one resists movement as a function of its own
    different mass....thus the difference in acceleration from a standstill.

    An experiment that can be don to illustrate the theory.

    Find a short length of PVC pipe and a rubber ball that will fit the ID
    fairly snugly. Punch a hole in the ball and attach a 100-foot cord.
    Tie the cord to the bumber of a car and have a friend accelerate the car
    until the slack comes out of the cord and pulls the ball out of the pipe.

    Will the pipe "kick" while the ball is still inside it? No. You'll have to hang on tight to keep the pipe from being yanked out of your hands. You'll
    move rearward only after the ball has exited, and only because of your resistance to the forward movement of the pipe. Rather like playing tug of war with somebody who suddenly lets go of the rope.
     
  15. Jim Watson

    Jim Watson Member

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    Ever seen a Schwartzlose blow-forward pistol?

    The breechface is a solid part of the receiver, the barrel is free to move forward against a spring. Fire the shot, the bullet goes forward, dragging the barrel forward with it by friction. The bullet departs the muzzle and the recoil spring drives the barrel backwards, scooping a fresh round out of the magazine. Recoil is said to be very heavy, as .32s go.

    Carbine Williams designed a rifle with forward moving barrel. It, too, was said to be a hard kicker because you were moving both barrel and bullet forward at the shot, so the receiver and butt had to move backward all the harder. I 'spect it did a good deal of jumping around as the barrel returned.

    Newton's Law sez that momentum must be conserved, with equal and opposite reactions. He doesn't say how.

    Put a rod down the barrel of a 1911. Push against the breechface. The barrel and slide move rearward to unlock and separate from the force just like in firing where the force on the casehead (force = pressure x area) drives the slide back and the bullet forward. Opposing forces to the handle of the rod and the butt of the gun balance out. Momentum transfer is miniscule because you are not pushing that rod very fast.

    In firing, pressure drives the bullet forward so the same pressure pushes the slide rearward to balance the momentum. Cause and effect. Can't separate them.
     
  16. RJ357

    RJ357 Member

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    When the bullet is immobilized in the barrel, the forward and rearward forces are equal and opposite and cancel. There is no net force in either direction. In that case, the high pressure gas exerts a force on the breechface and through the slide, the barrel. The gas also exerts an equal force against the bullet base, and against the barrel which it is locked to. Nothing moves. A similar situation exists in a cylinder of high pressure gas. The cylinder doesn't move either.

    While it is true that the bullet needs to move forward in order for recoil to exist, that is not the direct cause of the recoil. Back to the cylinder of high pressure gas, it just sits there, as the pressure is equal in all directions. Now we take a hammer and knock the valve off of the cylinder. It takes off like a rocket. This is not due to the gases pushing against the air. The cylinder would do the same thing in the vacuum of outer space. The cylinder moves because the pressure against the non-valve end is greater than the pressure at the valve end, where there is now nothing to push against.

    The barrel (and slide) recoils backward normal firing because there is more force in the rearward direction. The forward force is only applied to the barrel through the friction of the bullet in the barrel. Imagine a precisely fitting bullet with a gastight and frictionless fit. You can see that there would be virtually no force against the barrel in the forward direction. Now increase the friction of the bullet and barrel a little. The barrel will be dragged forward a little and the recoil will be reduced a little. The bullet will also be slowed down a little. As you increase the friction, the forward force on the barrel increases, the recoil decreases, and the bullet slows even more. Increase the friction enough, and the bullet stops, the barrel tries to move forward as much as it tries to move backward and goes nowhere.
     
  17. RJ357

    RJ357 Member

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    If you use an independent means of preventing the bullet from moving forward, like a rod extending into the barrel and attached to the wall, you will find a rather large amount of recoil, as you might imagine. What's important above with the immobilized bullet, is that the bullet is being held in place by the barrel, or something attached to the barrel.

    It is not the forward movement of the bullet that's important, but the fact that is is free to move in relation to the barrel.
     
  18. baker

    baker Member

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    The "jet" of hot gases propels the slide backwards, opposite the thrust of the jet. It is "directed" out of the barrel in one direction, and moving the slide backward is the equal and opposite reaction.

    Also, the mass of the bullet is contained in the gun, and pushing it out will cause recoil and slide movement.

    In the vacuum of space, it is the lost mass of the rapidly burning fuel that propels a rocket forward.

    The "bullet pulled by a wire" analogy isn't applicable.

    Think both/and, instead of either/or for causing the slide to move.
     
  19. RJ357

    RJ357 Member

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    Incorrect.
    The pressure of the gases against the front of the rocket motor is what pushes it forward. There is a lack of opposing force in the rear of the motor where it is open.
     
  20. 1911Tuner

    1911Tuner Moderator Emeritus

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    Balance

    Jim Watson said:

    In firing, pressure drives the bullet forward so the same pressure pushes the slide rearward to balance the momentum. Cause and effect. Can't separate them.

    Precisely!
    _______________

    RJ357 said:
    When the bullet is immobilized in the barrel, the forward and rearward forces are equal and opposite and cancel. There is no net force in either direction.

    And:
    While it is true that the bullet NEEDS to move forward in order for recoil to exist, that is NOT the direct cause of the recoil.

    Exactly! The "Thrust Vector" pushing equally in both directions is the cause of bullet AND slide movement...Recoil!
    ________________

    My theory...and mine alone...is split between these two questions:

    Does the barrel push the slide through the locking lugs and hood...or
    does the thrust exerted on the breechface move the slide, causing the slide to pull the barrel along with it?

    AND...If it's due to the barrel pushing the slide, does it occur at the interface between locking lugs on the barrel and in the slide...or is it a function of the expanded case in the chamber exerting the force against the breechface and pulling the barrel along with it (the expanded case)
    ...or is it a combination of the two. I lean toward the theory of the barrel pushing the slide, with the resulting momentum imparted to the slide causing it to continue after the barrel has unlocked. Why? Look no further than the short gas piston of the little M-1 Carbine. A very short, quick movement carries the slide and bolt assembly through the entire cycle...
    Momentum. Ditto for the M-14 rifle, though the piston moves farther than in the War Baby.

    This one's rollin'! More theories! Make me doubt mine!


    EDIT to Add:

    baker said:

    Think both/and, instead of either/or for causing the slide to move.

    Hmmmm... I think I like that one too. Nothing is everything, but everything is something.

    Good point!
     
  21. R.H. Lee

    R.H. Lee Member

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    ACK! Yer givin' me a headache.

    For every action, there is an equal and opposite reaction. The bullet leaves the case due to expanding gasses, and heads down the bore. The case, which is expanded inside the chamber, moves backwards (the opposite way), pushing against the breechface, taking the slide along with it. By the time the case has contracted, it has already dumped it's energy into the slide.
     
  22. RJ357

    RJ357 Member

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    There would be a combination of effects. The force is back against the breechface through the case head. It is also back against the barrel through the friction of the case walls and chamber. And it is also forward against the barrel through the friction between bullet and bore. I cannot say, though, how much each contributes. The case friction and bullet friction are in opposite directions with a net force in one or the other direction. I am going to guess that the case wall friction is greater, due to the pressure being applied outward against it. This outward radial pressure is not present in the bullet except through an attempted mushrooming of the bullet base. But again, just a guess.
    Even if the slide and barrel received equal force impulses (rearward), the barrel would attempt to accelerate faster than the slide because of lower mass. That would add support to the "barrel pushing the slide theory".
     
  23. baker

    baker Member

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    OK, I could be wrong, but it WAS what I was taught in public school. :) (That the mass of the fuel leaving the rocket at a high rate of speed causes an equal and opposite reaction, propelling the rocket forward, especially in space, where there are no other gases to push against.)

    Actually, I still think I'm right :)

    http://science.howstuffworks.com/rocket1.htm

    "A rocket engine is throwing mass in one direction and benefiting from the reaction that occurs in the other direction as a result."

    See the link. It actually uses a shotgun as an example
     
  24. RJ357

    RJ357 Member

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    The reason I don't like to explain it that way is because it expresses it in the form of a law but it really doesn't explain why. In the case of the shotgun example, the question still remains as to why the shotgun recoils. If you look carefully at what is happening inside the chamber, you will find one single thing that explains why the shotgun moves rearward: pressure against the breechface.

    You are quite correct about action and reaction.

    (Just edited this in)

    If you look even more closely, at the molecular level, what you will see are gas molecules transferring energy (momentum) to the molecules of the breechface by collision. And it is this alone that produces the force.
     
  25. Grump

    Grump Member

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    As long as the barrel and slide are locked up, they are one unit for the sake of recoil. Just like a muzzleloading rifle barrel. You *can* unlock them while the bullet is in the barrel and pressure is way up, but you can't do it using a tilting-link mechanism like a pistol. The inertia of getting the parts moving is too slow.

    The "stretch forward" thrust vector to the separate barrel cannot be the sum total average chamber pressure at bullet base at any instant, because the pressure is being released in the direction of bullet travel. I'm sure we're looking at bullet drag, maybe plus a factor for its inertial resistance to acceleration. Intuitively, somewhere between the middle and the last third of any instantaneous powder chamber volume (breechface to base of bullet), there may even be an area where the gas pressure starts pulling the barrel back--there are gas dynamics going on, not a static situation. For sure, a major component of barrel recoil is caused by the slide pulling it back.

    That ain't no stinkin' equal force vector.
    Remember, the barrel and slide are connected by the locking lugs.
    I don't see what you're pointing out as a flaw. I've fired a Luger "cannon" (top end) without its frame, and the rear/breechface part of the assembly is much nearer to the same mass as the barrel, compared to a .45 barrel/slide assembly's vastly different masses. It recoils as a unit, and any forward thrust vector to the barrel is greatly overcome by the breech end pulling the whole shebang back in recoil.

    Pressure is in the powder area an omnidirectional force, work is mass being moved, and thrust is a directional force caused by Newton's law of acceleration??. We may be playing too fast and loose with terms, and missing each others' points...

    Bum barrels split longways, not in an annular ring of failure. The forward "stretch" force on a barrel cannot be the same as radial force, because the bullet is releasing the pressure with a relatively small friction drag in the forward direction.

    We may be agreeing more than we think...
     
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