WT8WV “Colossus” Air Cannon Antenna Launcher
Folks, this has been a fun and hilarious winter project. Yesterday, when I built this air cannon antenna launcher it was -4 degrees outside and this was a perfect evening project to put together. For years, me and my two ham radio buddies (WR8S Bill Shultz and WV8TG Tom Graf), have enjoyed ARRL Field Day activities and usually used a slingshot and a 3/4 ounce fishing sinker weight and an old Zebco fishing reel (with 20 pound test line) to shoot and suspend our doublet dipole antennas high into the trees. Certainly, the slingshot worked pretty much flawlessly… but… boys will be boys, and the idea of an air cannon / spud launcher / potato gun type system seemed to be a new desire. (Most people, our wives included, wouldn’t trust our 3-man team with a slingshot, let alone a potato gun! But I digress.) Actually, our local ham radio club (Monongalia Wireless Association) had a version of a potato gun antenna launcher, so we decided we needed one of our own… and to make some design modifications in the interest of… “science”… plus our own sadistic pleasures. (Make sure you read below WV8TG’s initial “pressure test” experience.) The following pictures hopefully provide the basic concept and parts we used. Tom and I split the cost of the parts needed to make launchers and each built our own version, but they both are the same basic design with only length dimensions of the air chamber and barrel being the difference.
All parts where sourced from our local Lowes store in their plumbing department, except the Schrader valve which can be purchased at an automotive store. Total cost about $40 but you could make a couple of them as a joint project with a friend and reduce that cost per launcher a bit. I got a small rubber gasket for the outside nipple of the Schrade valve to act as another seal on the exterior of the air chamber. You will need to drill holes for Schrader valve, barrel slug stop and projectile slug caps to attach the screw eyes to attach the fishing line. I used 3 inch PVC for air chamber, 1.25 inch PVC for the barrel and short sections to mate the air chamber, trigger valve and threaded barrel. The projectile slugs were made from 3/4 inch PVC and caps and I filed off the nubs on the caps with a Dremel tool for a smooth fit into the barrel. I used PVC Prep on each joint before applying the glue. When gluing joints together, insert the sections together and twist a quarter turn for a solid adhesion. Let all glue set up for 24 hours before testing air pressure chamber. I will pressurize the chamber inside and let it sit overnight to see if it loses any pressure. It’s too cold right now to take outside in -4 degree temperatures to test, but I will use a bicycle pump with a pressure reading valve, and start at 40 psi… then 50 psi… and then 60 psi for test shots to see how it functions and check for any air pressure leaks. We use 60 psi for our club launcher.
WV8TG (Tom) charged his air chamber (barrel not attached) and let it set overnight to test for chamber air leakage. When he opened the trigger value… there was NO leakage… but there was a sudden LOUD release of 60 psi air gush out of a 30 inch long, 3 inch wide fully charged air chamber. He indicated the compressed air release was… impressive. However, his wife was not impressed… nor was she aware of the scientific test that was taking place. #surprise! #WHOOOOOOOSH #loudwifeexpressions I have no reason to doubt Tom will find his projectile slugs in the next county using his design. The club chamber was 12 inches long versus his 30 inch air chamber. #overkill? I designed my air chamber for 14 inches and will conduct all tests… outside. #potentialmeanwife
Posted on January 4, 2018, in Amateur Radio, Antennas, Digital Modes, DX, Education & Learning, Field Day, Ham Radio, Ham Radio Articles, HF Band, Homebrewing & Kits, Projects, QRP, Radio, Radio Operations, Safety, Station Accessories, Transmitter, Uncategorized and tagged air cannon, air launcher, antenna launcher, Antennas, ARES, ARRL, ARRL Field Day, Bill Shultz, Contesting, dipole antenna, dipole antenna launcher, dipole launcher, ECOMMS, Emergency Preparedness, Field Day, Ham Radio, JOTA, KA8LJO, KB8FIR, Monongalia Wireless Association, NPOTA, potato gun, Projects, QRP, SOTA, Spencer Graham, Spencer W. Graham, Spencer W. Graham II, Tom Graf, W8MWA, Wiring, WR8S, WT8WV, WV8TG. Bookmark the permalink. 2 Comments.
Thanks for the question! The air chamber is about 18 inches long. My reason for that is that a massive air chamber is relatively useless once the projectile / slug exits the barrel… it just goes impressively “whoooooosh” after that until the air chamber reaches equilibrium with the surrounding environment, but no longer has any effect on the slug once it leaves the barrel. I just need the compressed air pressure in the chamber to do work to lob the slug over a tree, not sink a battleship in the next county. Grin.
Excellent question about the “slug”… I actually tested the concept originally without any ballast (sand, dirt, gravel) inside of the slug and it performed “Okay”… however, I quickly found that adding some pea gravel and/or some sand actually did much better for a couple reasons… while not being a physicist or engineer, I surmised that the added weight added a little back-pressure to the slug inside the barrel when the air chamber dumps it’s compressed pressure and then the slug cuts / bucks the wind better on it’s trajectory heading over a tall tree! ALSO… the added weight inside the slug lets the slug take better advantage of gravity coming down through the tree canopy, and it doesn’t get hung-up, nor does the downward falling energy “peter-out” on it’s decent to the ground if it bounces off of foliage and limbs.
I’ve launched many antennas with this design and have never had a problems with it. At the Dayton Hamvention in 2019, I saw a guy in the Flea Market selling a shorter version of an air cannon that used several 90 degree turns of tubing and was asking nearly $100 for them… looked like a baritone / tuba thingy… seemed like extra opportunity for a failure.
The only modification I might make, if I build another one, is that I might add a “T” in the barrel close to, and ahead of, the air chamber trigger section with a short T-Stub to form a bazooka-like handle… maybe 5-6 inches long, and then simply cement it to cap it off… this would help steady the aiming of the barrel, in my opinion… and would need to kinda sorta figure a barrel hand-grip measurement just like a gun stock, so that the air chamber butt-end “rested” somewhere in the shoulder area just like a rifle butt-stock does when you shoulder a rifle.
Couple of questions on your build. How long is that air chamber? About 14″ or so? Do you fill the slugs with anything like shot or are they left hollow?
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