A friend of mine (W9SQ, Hi Peter!) mentioned that he was looking for a way to hold up a beam when he goes bicycle-portable. Design constraints: at least 15' when erected, not more than 5' when stowed. Relatively lightweight (this is on a bicycle, not a pickup truck), yet should be able to support an 8 pound beam.
This is the type of project that I love... how to whip something together, quickly and cheaply, that will work well.
So far, I've come up with the following:
The beam could be clamped to the top, or an adapter could be fit to it for ready connection to the top section.
There will probably be a tent spike or similar to hold the bottom in place (we don't want it to walk away!), and 3 or 4 guy ropes around the outside (I'm thinking polyester braid, maybe .25" or .375") to hold it down (and consequently, up).
Immediate problem: .75" PVC is flexible (almost downright FLOPPY). Putting a 10 pound weight on the top will make it flex if there's any kind of wind. 1" Aluminum tubing is approximately the same diameter, and much more rigid... but also 6-8 times more expensive and less durable overall (it can be crushed, folded, dented, etc.... PVC is less likely to crush, as it's a thicker wall, however it may crack and split when subjected to abuse).
A possible fix would be to use .75" aluminum tubing on the inside of a length of .75" PVC. This would add rigidity. How to get it inside? One could bore the inside of the PVC slightly larger (messy) or use ice or dry ice (or liquid nitrogen, but that's a touch harder to come by) to cool the aluminum, shrinking it slightly, and then quickly shoving it inside the PVC... when it expands, it should form a very tight fit, and add lots of rigidity.
A different possible fix would be to use 1" PVC as the top section. 1" PVC should just barely fit inside 1.25" PVC, and so either a reducing fitting could be used at the top, or the top could be "split" (2 slits in the side, allowing the tube to be compressed) and used with a hose clamp. Use of a hose clamp requires that TOOLS be used to assemble the mast, which may be a detriment. This possibility would require a different size Schedule 80 floor flange for use as a guy ring.
Provision for Armstrong Beamswinger: about 3.5' or 4' up from bottom of bottom section, add a reducing Tee (2" to 1"). This will allow adding a lever at a convenient height to allow swinging the beam. This does not add a convenient pivot point at the bottom, however: this could be done with a 2" PVC cap, center drilled, and a a 2.5" or 3" long .25" bolt could be added (nut on the "outside" or bottom of the cap) to serve as an anchor. This may put wear on the turf underneath the mast, however, as the mast is likely to rotate the endcap and bolt as well when the mast is turned. There should probably be some sort of anti-slip provision at each reducing section (perhaps a notch in the smaller tube, and a bolt or peg in the reducing adapter).
The 1" floor flange / guy ring will need to be (slightly!) enlarged in the middle, otherwise it should provide a decent slip to allow use of the Armstrong Beamswinger. This will ride just above the 1.25" to .75" transition, with the flat side of the flange up.
Problems with the PVC: it's big and heavy. It's cheap and versatile, however. Aluminum is much more expensive, but also lighter in weight and harder to work.
Cost breakdown (I've estimated a bit high, but close, to our local building supplier's prices):
The cost of the aluminum tubing may be able to be saved by using two guy rings, one near the top of the .75" section, and one at the base of the .75" section. This should keep the top section from flexing TOO much, but I have no idea how much load a .75" Schedule 40 PVC pipe can bear... it may be better to reinforce it.
An alternative reinforcement method, not investigated yet, would be to use a length of allthread rod down the middle of the .75" section, probably .25" allthread. Spacer (standard flat) washers should be used at 1 foot intervals down the middle, to minimize flexing. Capping on either end could use a larger diameter washer. All spacer washers would have a nut on either side, and the end washers on the outside only. .25" Flat washers seem to just fit inside .75" SCH 40, and .3125" washers don't, so they could be used as spacers and ends. The uninvestigated part is will this impart enough rigidity to help things, or would it just be adding weight. The aluminum weighs less, but will be harder to install and will cost more.
This hasn't been built... yet. Maybe tomorrow, maybe next week.