GordonP
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Re: Stone shifting 4
Sep 07, 2003, 12:02
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If I can think of a way to anchor the tie rope to the bottom of the stone we can tension it with a Spanish Windlass, if we do need to reduce the tension as the stone moves then it will be easy.
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GordonP
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Re: Stone shifting 4
Sep 07, 2003, 12:24
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OK fixed the anchorage problem, tie a rope belt round the stone at a piont that will be just below ground level when the stone is upright. Pass ropes from the belt under the stone and back to the belt. 4000 years later there will be no trace of the ropes.
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Steve Gray
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Re: Stone shifting 4
Sep 07, 2003, 12:46
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If we are going to use a Spanish windlass, why not use it to pull the stone up? I take your point about anchoring it to the bottom of the stone. That thought had occurred to me. I wondered whether small channels could be left in the base of the hole for two ropes to be laid in and then covered over with chalk rubble to protect them from the impact of the stone dropping. The ends of the rope could be tied to a log laid across the hole on the far side of the stone. Mind you, I don't know if we would be able to remove the ropes afterwards and I'm sure the archaeos won't have found any rope remnants in the holes.
The snag with the idea is that the tower is not far from the hole, so the ropes would have to go up at a fairly steep angle. This increases the required tension in the ropes to considerably more than the 7 tons being exerted on the stone. Used in conjunction with diagonal props, however, we could probably arrange that the props take the bulk of the leverage load and the ropes serve only to prevent the props from rising.
Each time you need a new fulcrum log you could insert it so that it bears on the previous one, perhaps with a little rope lashing to stop it from slipping upwards. This way the previous fulcrum logs would become the platform for the men placing the levers.
I'll try to find the time to do some calculation of forces for both methods. Whichever method we use, the forces and distance are much less for 80 degrees than they are for 70 degrees, but we might be constraied by the angle of the hole. On the BBC picture that you have on your website the angle looks more like 50 degrees!
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GordonP
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Re: Stone shifting 4
Sep 07, 2003, 13:23
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Don't fancy pulling the stone up with a windlass, they can be lethal if you tension them a lot.
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GordonP
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Re: Stone shifting 4
Sep 07, 2003, 13:34
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According to the paper "Science and Stonehenge" the angle is 70 degrees, in the experiment the sledge fell between the ramp and the stone increasing this angle.
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Steve Gray
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Re: Stone shifting 4
Sep 07, 2003, 14:20
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Some quick calculations on the weighted rope.
Initially the gearing is so high that the rope has to sag under the weight of the stone. As it does, the gearing reduces. Eventually a point will be reached where the tension in the rope balances the weight, or the weight reaches the ground first (in which case its work is done).
To get some idea of the numbers involved, I calculated a case where the rope has sagged to the point where the weight is just about to touch the ground and that all the forces are then in balance. With a monolith sticking 24 feet out of the ground and a rope 100 feet long, the gearing is about 2.5:1. It starts much higher than this when the rope is almost straight, so the monolith cannot resist the initial pull. We would therefore need a weight of about 3 tons (allowing for the fact that the rope is not pulling perpendicular to the monolith).
If we can raise a 40 ton stone to a height of 16 feet, it should be easy-peasy to raise a 3 ton stone 10 feet in the air. I estimate that we'd need to do it twice to get the stone to vertical from 70 degrees.
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GordonP
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Re: Stone shifting 4
Sep 07, 2003, 17:35
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Looking good, let me get this straight, you've got a rope going from the top of the stone to the top of an "A" frame, with a 3 ton weight hanging in the middle. So the pull on the "A" frame is equal to the pull on the sarsen. It will take some anchoring.
I'm still thinking about levering from the tower, if we do the initial levering with the levers starting at an angle of 45 degrees (instead of vertical or 70 degrees to be more accurate) then the levers will be at 90 degrees to the diagonal bracing logs creating downward pressure on the tower. That way we'll need less anchorage on the tower.
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GordonP
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Re: Stone shifting 4
Sep 07, 2003, 17:38
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At 35 degrees it will be even better and the levers will still work.
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Steve Gray
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Re: Stone shifting 4
Sep 07, 2003, 19:58
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No, the rope just goes straight to the ground, no A-frame. Since the monolith is 24 feet high, the centre of the rope will be 12 feet off the ground. We need about 7 tons of tension in the rope, so we need a big stone on the ground to act as an anchor. The lintel might do, epecially if we had some stakes in front of it to stop it from being dragged along. Hey, could this explain some of the mysterious post holes?
Your reduction of the lever angle WILL reduce the side load on the tower. If we have diagonal bracing poles going from the (first) fulcrum to the ground, the ideal angle for the levers would be at right angles to these braces. The angle of the braces will depend on their length and the height of the tower. If the tower is 24 feet and the braces are 34 feet, the angle will be 45 degrees. You could therefore have your levers starting at 45 degrees and the lever load would be transmitted directly down the brace. As the angle reduced, some of the load would be transfered to the tower as a vertical load, which it is well able to withstand. This would, of course, reduce the overall throw of the levers, but I guess we don't care too much about that.
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goffik
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Re: Stone shifting 4
Sep 07, 2003, 20:09
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Sorry - not very funny am I? :o(
I'll just... go... shall I?
*snif!*
G
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