Pneumatic Antenna Launching Systems
antennalaunchers.com
antennalaunchers.com
https://m.youtube.com/watch?v=sKEfLm066-4
It’s such a clever idea using the emergent properties of gravity, stiction, and geometry.
A friction saver is a thick strap with two eyelets in it. With the strap placed over a limb, you can then run a thick rope through the eyelets instead of running the rope over the limb, which would otherwise abrade the rope and tree surface.
But how do you get the friction saver up there in the first place? To install, once you have a throw line over a limb you then add the friction saver as a segment to the end of the throw line but with the throw line also threaded into the eyelets of the friction saver. Once the friction saver is over the limb it will stick with a sticktion much stronger than the throw line is stuck to the friction saver.
Getting it back down is another clever trick which relies on one of the eyelets being larger than the other. To understand that (er, or indeed the whole system, as this is quite hard to explain) … watch the video.
https://www.youtube.com/watch?v=dN7wRupZ-AQ
This is meant to be left in the tree long-term, but still removed easily when needed.
Apparently, it launches a lead line over a high tree branch on the end of a tennis ball to hoist up wire for an antenna. PVC potato gun in Stinger form-factor.
I'm curious why they didn't use fishing line considering it's much lighter.
They do:
"In the launcher pictured above a Tennis Ball is propelled by compressed air, towing a fishing line over the tree."
I don't know where you would even get a wire made out of lead. Sounds like that would need to be ordered/made specially.
The only place they mention "lead" is in the context of a lead sinker being attached to the fishing wire. And they reject that approach as not safe enough compared to theirs which is a tennis ball attached to the fishing line.
When you're done with the setup (e.g. field day[1], camping, etc.) you simply cut the anchor and lower your antenna down one end at a time.
[0] https://www.engineeringtoolbox.com/pvc-cpvc-pipes-pressures-...
If you hit a water pipe. with a shovel and break it, and your pipe has a rather high 100 psi of water in it, you will regret it: you will get wet, you’ll have a muddy hole, and you will be sad because you have to repair it.
If you compress air to 100 psi, you are compressing it to a rather small fraction of its original volume. So the change in volume is greater than the entire volume of compressed air and is almost as large as the uncompressed volume, so 100 psi * (change in volume) / 2. 1 cubic foot of air compressed to 100 psi is something like 10 kJ. Beware!
If you winterize your irrigation system with compressed air to 100 psi (terrible idea), and you hit a pipe with a shove while it’s still at 100 psi and break it, you will release a lot of energy.
But systems using hydraulic fluid to carry power have something that keeps it pressurized as it moves: that is, something that can supply power. Often very large amounts of power. (So do water pipes that have some form of supply, of course, but the pressures are much lower.)
So if you pressurize fluid in a pipe, you are storing some energy in the compressed fluid. You may also have a lot of energy stored or power available in some other component of the system.
In any event, the type of injury you’re describing seems like more of a velocity issue. When you allow fluid to escape from a high pressure environment to a low pressure environment through an opening that doesn’t have a whole lot of friction, the stored energy converts to kinetic energy. Some basic physics says that a small volume V of fluid has potential energy PV and mass rho * V. Conservation of energy says that, when that potential energy is gone (the fluid escapes), it has the same energy, but now it’s 1/2 m v^2. You can solve for velocity, which scales like sqrt(P).
(The real story is more complicated. Pressure in fast-moving things is a bit messy due to Bernoulli’s Law, and different disciplines use annoyingly different terminology. Static pressure, total pressure, stagnation pressure, just plain old pressure, oh my!)
Water (or air) jetting out of a hose through a tiny hole at even 100 psi is not likely to inject itself into a person.
Schedule 40 is rated for 400-ish PSI but with epoxy, locktite, and some tape, it can go up to 1200. For repeat use, err on the side of underpressure. There's so many people pushing boundaries in "homegunner" circles, but every time I see someone doing it - with a cheek weld - I get the jibblies. "It's . . your face, dude"
That's close to pre-internet society.
As others point out, the tech and consensus is way different now.
Cheap throw bags on eBay or Aliexpress for instance, no need for sinkers - https://www.aliexpress.com/w/wholesale-throw-bag-Arborist.ht...
The world of confiscated Monkey's Fist's at ports is an interesting one - https://www.portskillsandsafety.co.uk/news/confiscated-monke... You can add it to your dangerous knots list.