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Exploding Tree
Why spend time cutting trees with a chainsaw when you can use the stick-of-dynamite-in-the-tree? | |
The title says it all, but I will elaborate a bit.
This whole idea of alternate methods of cutting trees came to me last night when I was watching a Dicovery Channel show on deep-forest loggers...I think that's what they were talking about because I had the sound off- it was late and the family was
asleep. Anyway, I flipped channels and there was the Tactical 2 Practical show showing military stuff turned civilian. Went to sleep and the next day I had this brilliant idea- why not use a small power drill to drill a hole at the bottom of a tree, stick a piece of dynamite in it, drill a few more trees, grab the remote and kaboom? I haven't conducted any deep thinking on this, but I imagine it to be way faster than spending time cutting trees with chainsaws. The dynamite could be a problem, but I am sure we could find ways around it...
I also watched a show on Nature that same night and another thought crossed my mind- we could use woodpeckers to cut trees thus saving a bundle in time and gas for the chainsaws, but I like my dynamite idea much better. Besides, the birds would eventually get organized and setup a union or something...
[link]
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I have dreams like this... |
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when I don't know my other from my general... |
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A friend and I tried doing this years ago. We only used half a stick of dynamite, which was all we could get. Our technique was to duct tape it to the tree, light fuse, run. It didn't work as well as we had hoped, it must have been one tough tree. The tree still stands to this day. |
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There is an art to falling trees that could not be easily duplicated with dynamite. How to avoid the fence, house, and powerlines? An experienced tree cutter can do it. |
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[Laughs Last], I'm guessing the reason your duct tape approach didn't work is because the explosive wasn't contained and the pressure wave was lost to the open air. Using a faster, shattering explosive, or just a lot more dynamite may have worked. (Where's [quarterbaker] when you need him?) |
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Using explosives to drop trees certainly isn't uncommon. As [UB] notes, detcord has been and is still used to fell swaths of trees. In addition to the detcord diameter, the number of windings about each tree is used to adjust the charge. |
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Though detcord is not dynamite (it's usually an even higher explosive called PETN) I think explosive timbercutting is a practice that is widely-known-to-exist. So, [mfd removed to retain quarterbaker's marvelous explanation]. |
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That's a quiz question that I would have gotten wrong. I would have thought the limit was the speed of sound (in cordtex). |
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Me too. In fact I still think so. If it's gonna manage to detonate at that speed, there must be some interesting physics going on. For example, is it possible that the shockwave compresses the material, increases its density and hence increases the speed of sound in the material? |
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Just off google, cordtex detonates at 6000 metres per second, superflex at 8500metres per second, PETN at 8400 metres per second. That's a good bit slower than 75 miles a second (120000 metres per second) - where did you get your figures from [UB]? |
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Isn't detonating at faster than the shock
wave what defines a 'high explosive'? So
if cordtex is a HE, speed of sound may
not be relevant. That said, UB's figures
sound a little speedy. |
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A loop of Cordtex would be quite effective at removing heads, if the tree idea doesn’t work. |
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If you can see the flash and the tree falling but haven't heard the explosion yet, does it make a sound? |
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Seems I have been summoned. |
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Detcord has been used to cut trees. It has also been used to cut many other materials, such as the removal of a huge expensive propellor from the drive shaft of a sunken ship, for recovery operations. |
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The physics and chemistry of explosions really is interesting. The detonation speeds listed by AWL look about right from my recollection. |
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There are 2 "shock waves" to consider: the wave going through the explosive material (i.e., the propagation wave, which defines and hence moves at the detonation speed) and the shock wave propagated through the surrounding medium (air or water, for example). The design of shaped charges takes into account these different propagation rates/ energies to precisely control the direction, concentration, and dispersion of force. [In the math/geometry, it becomes markedly similar to optics]. Shaped charges could quite easily be more precise than any chainsawing maniac at making a tree fall in a particular manner. |
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There are 2 rough classes of explosion - detonation and deflagration. Generally, deflagration occurs as a propagation of a chemical reaction (i.e., burning), such as seen when a fuel ignites. Detonation occurs as a propagation of a percussive wave through the material at a rate faster than can be accounted for by chemical reaction alone. Roughly speaking, any material such as PETN can "go off" either high-order (detonation) or low-order (deflagration), depending primarily on density and confinement (oh, and also somewhat dependent upon how it is initiated*). In the high-order detonation, the energy propagates as a wave through the material, essentially fracturing chemical bonds, making the constituents available for immediate reaction. This propagation wave travels faster than the purely chemical reaction can. This distinction between high-order and low-order, detonation and deflagration, isn't always precise. But to conclude, AWL's listed speeds are somewhat misleading, since there are controllable variables that can affect detonation velocity. Explosives designers usually have reference graphs for different materials, showing the speed/density relationship (which assumes some amount of confinement). |
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Long-winded, and not too informative perhaps. Sorry. I no longer have access to the reference materials required to be more exact in my explanation. |
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As others have mentioned, this is baked. |
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But explosives are fun stuff, as long as you don't have to make a living at it. |
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[*Method of initiation does matter -- there are some materials that, were you to take a match to it, would burn fast and hot but certainly not explode, whereas the same material in the same configuration would most definitely explode if initiated with, say, another explosive device. This dual-nature also has some design possibilities.] |
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[qb] Thanks for all that. I took a look at the [AWOL]'s figures and was puzzled by how PETN is given a detonation velocity of > 8000m/s, but cordtex (which is "just" a thin tube filled with PETN) detonates a couple of thousand metres per slower. Any thoughts?
Recently visited Royal Armouries Explosion! museum at Gosport, and was surprised that "past sell-by-date" cordite was simply burned in the open. |
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hey qb. you got there before me! |
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Thank you, QB for the great explanation. I learned from it. |
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I should try this username invocation thing more often. |
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"In the math/geometry, it becomes markedly similar to optics" |
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So, is this why optical-grade milling machines are used for shaping the charges for nuclear weapons--both the fissile material and HE? |
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[bristolz] A good read on the subject is "At work in the fields of the bomb" - the accuracies and the timing are phenominal. Excellent photos too. Who'd've thought styrofoam could be used to focus, well, anything really? |
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If I said any more I'd soon have a nice friendly "conversation" . . . somewhere . . . |
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I also really enjoyed [QB]'s explosives primer. |
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