Very good discussion, very good test of theories and images used personally while assessing these mechanics. Think it would make a dynamic chat..........
i'd like to say that i'm glad noone was hurt by the tree landing 90* from target and/or ressultant forces from this tension on spar, or line snapping, branches over someone's head breaking free on that control line behind the spar going to other tree. Or, spar not moving quick enough and poor cutter taking out more hinge.....
i think that this would turn, cuz it to me is a self tightening rig, favouring the higher pressure side for spin to. For exactly (oooops here goes, never thought i'd say this.......) for the reasons that JP says, if the control line pull is not center, it will pull off center. It will create this pull from the weight, speed, and hitched length of the spar- here enormously scheduled forces.
To counter that spin (best is to realize what ya got and not resisti it too much)a kerf dutchman or block/step dutchman ( a dutchman being an early interuption in face to cause pushing off, either of these dutchys would push off away from the line pull is put on the same side as it) can throw/punch away from this pull on that same side of the face, as too tapered hinge pulls to the other side (away from twist) can help correct the balance of pulls to target; as well; as fibre in that extreme opposite to side line pressure, position presents the most leveraged opposition to twist to the opposite side. Taking Dutchmnan push (which takes speed...), and taapered hinge pull, you might be able to balance that force with offside line pull, if line is given enough 'finesse' (proper slack at proper time); but chances are probably against. Dutch face interuptions and tapered hinge are both passive force (though diagonal to each other)strategies, that use some of the available force; but you have to throw that force into the dutchman. Each force will only work as long as it is tensioned on arc of hinge, hinge is logically the best to fight that full arc, then adding more strategies, IMLHO.
This would be synonomous to felling thru trees pushing the same way from the front that line is pulling from the back( or simiraiily dangerous vine pulls), i think the hinge taper will fight either longer on the arc of hinging than other strategies. Making it in my mind best for especially interuptions (tree branches to side front, line pull from opposite side rear being same analysis as direction and constantcy once spar is committed is same, only varied in force of each.)
Another balancing strategy (to target, against line's offside pull) would be a block on back side of the spar, with balanced angles of rear, low pull from the legs of line, one anchored, one friction device, for 2/1 of balanced pull on spar. But paying out line fast enough as to not bind or pull too much is already a problem, this would increase with less load on friction device. i guess that would be the self equalizing version of comradski Stumper's idea, just set at equal rear angles.
i think the pull line, pulls to target, and control line should allow freedom of movement before 1:30 to force stronger hinge, then start lending support definitely by 2:30; if you care to take that danger(using rear line). If during this phase (before 1:30-2:30)the control line pulls against the pull line, the hinge will form weaker, you need the control line barely checking the pull, and the hinge taking the stress to make hinge strong for rest of journey on arc of delivery. After that
If this was moving up on same axis, or down from 3 to 6:00, i would say it invokes hinge pocket pressure to help, but here the pressure comes off; not on, not because it isn't available, but the resistance to it is lower, to give effect.
Alternatively,if needing to drop across the drive (i think that 'porcelan' is more fragile than sand..., grass can take any strategy drive can; sounds like insurance liabilty deal).
So i would choose lower force, deflecting delivery to forgiving ground in compounding factors to my favour. To stack the level of help, higher than that of the test, while lowering the pressure of the challenger's force.
i would try to get Center of Balance of spar to reach across the road, and provide a 'rock pile' of laarge logs to make a pivot (to keep stump end high) and carry stump end away from tree as all falling force is sliding forward on roch pile.....
And/or 3' high tightly packed matresses of brush or rimless tires etc., for (anything that crushes dissipates force) on drive. No, log, no half-azz wimpy piles, real purposefull mattress to scale of real wood!
And/or logs on grass (not on root, that could push hole in drive from underneath if hit right!) to bridge spar across drive, on stout logs on either side, and spread out force to lawn.
And/or mechanical 'fuse' bridges on lawn. =2parallel logs (to each other and spar's lay) with 3rd log bridged across, facecut up, partial backcut from bottom. Hit facecut with spar. If it takes 1500# to break it, that is 1500# subtracted from the falling force. If there are 4 sets broken, that removes a matching 3 tons from the force of the spar.
And/or let green branches stay high, form own 'matress', perhaps go up and mechaniclaly fuse to make sure and not dig in lawn, use their leverage of pull to induce stronger hinge......
And/or Delivering to the side of pull and not directly to lean, forms a fight, any of which force the tree employs in, reducing the finite amount of force delivered. So lay to the side, as not to feed straight into the pull of that ol'mutha gravity, a part of force is direction.
In fact, IMLHO, it is the first part of force, to commit which way the Mass x Speed is to be placed. So if a machine has to fight an imbalance, it must do so constantly and use up force that could be utilized elsewhere.
i too beleive in wide hinges, for when the faces meet, game over; the machine must decide wether to shear, sieze or break.
Definitely i would draw down the spar slowly, with high leverage powered by 3 men on 3-5/1 or GRCS and slow backcut to wide face. i'd have line guided over laying in V trench at top tied to back side, for highest leveraged position, and straghtest pull.
In this way the hinge is forced stronger, total drop is reduced, as well as speed; all at the same time; these reductions scheduled into sideways to lean onto forgiving aforementioned 'structures' can add up to supports needed, with less force to begin with; withoout that higher risk procedure{DAN
GER!!}. IMLHO.
This is like the self tightening rigs i use on limbs. It is also with rope fibre, what i try to explain to do with slanted hinge using wood fibre at base, rather than rope fibre high. Both are passively powered, fibred restriction, that self tightens and controls by being placed on the highest leveraged position to be self powered by the motion (180* from), and that power is placed at a high leverage position on the load. The farther the arc of the hitchpoint goes from rear support (arc) the more leveraged tightening too. In these examinations, length just becomes leveraged positions for support, pivot and C.o.B.
Or Something like that!
:alien: