Vern Estes (yes, that Vern Estes) invented the first successful boost glider, that boosted straight up and then would glide back down. It was rear-engine, and ejecting the engine released an elevator tab so it would glide. Those (unaltered) are very marginal performers and also hyper-critical on the CG position because the CG shifts the wrong way at ejection. Losing the engine out of the back most the CG forward, not rearward as you would like. I confirmed that the kit version, the Astron Space Plane, would go unstable if the CG was about .005" behind the recommended position. .005" is well within the tolerance on the engine weight. And it had to be heavy overall, otherwise the CG shift was too much to be overcome by the elevator.
Someone (possibly Larry Renger) came up with the idea of ejecting a pod with a weight in it way up in the nose to overcome this issue, but that was also pretty heavy. Larry used that idea in several pretty neat Estes kits.
The idea to take an HLG and put the engine in the nose was invented by Larry Renger. The first picture isn't exactly his design but a slightly altered kit version of his original SkySlash. It's stable like an arrow on the way up because the engine is by far the heaviest part of the entire thing. Then the engine ejects and that makes it stable in the glide (not to mention the engine ejecting gives it about half the total boost). Larry had one that also actuated an elevator to get around the "death dive" issue from 0-0 gliders - but launched it at Sepulveda basin, and it thermalled out, so he lost the prototype!
Ejecting the engine is not longer permitted in contests (because it comes whistling down as decent speed). Later, someone realized that you could put a hook on the pylon holding the engine, and eject the entire engine pod (with a streamer or parachute) and then its exactly like an HLG in the glide, and legal. That also led to the invention of the "Red Baron", where the streamer or parachute gets caught on the glider and the entire thing flops down ignominiously in a clump.
I *may* have invented the swing-wing BG/RG, or at least I was one of the inventors. Things tend to be invented by multiple people independently around the same time, in this case, the early 70's. I took my original to several contests around then and blew everybody away, who knows what happened afterwards. I figured I could get rid of all that drag on boost by swinging the wing instead, and, I didn't have to take the full load of the 200 mph boost with the deployed wing. It worked and was competitive but is pretty heavy during the glide compared to a pop-pod. It doesn't glide as well but it boosts much higher. The other advantage is that you don't have to worry about boost stability too much. For these little guys (the one below is for 1/2A and A) if it loops into the ground on boost, no real issue, but for a larger one (like a D-E-F) you have an 8 ounce glider looping into the ground at 300 mph, which tends to be frowned upon by the Range Safety Officer.
Later, someone came up with the idea of a separate event for gliding models that *didn't* eject anything, called Rocket Glide or RG. Most of the designs for that were very marginal (because the CG shift effect was mostly gone). The most popular way was to put the wing on a slide and have it be near the tail during boost and then sliding forward during the glide. Others counted on the loss of propellant, and are so marginally stable on boost that This is where the idea really works well and has no real weight penalty in RG. The one below shown stowed and deployed has rubber bands to swing the wings forward, and threads hold the wing stowed. The threads go through a hole and are burned though by the ejection charge, releasing the wings. This one flew a thermal-inhibited 2:55 at the last contest I flew compared to my competitors who had around 30 seconds if they qualified and the majority, who had various failures (like looping in to the ground under power or failed to glide).
This was all very hot stuff until someone invented the Rogallo wing BG, or "flexie" (bottom two pictures). The glider part is the 4th picture. There are three spars with a very light music wire spring spreading them out. The film holds it in shape (in this case, .00025 polyethylene "drop cloth" or "dry cleaner bags" material). This one has spruce spars, but you can make them with balsa, and the total gliding weight can easily be under one gram for a 14" span glider. You fold it up and stuff it in the front of a conventional rocket booster (there's a piston that pushes it out and deploys a streamer). This solves BOTH issues (boost drag and gliding weight) and the performance is astronomically better than any conventional balsa model. The trimming of the glider is *incredibly tricky* and if you don't know the trick, they death dive over and over. My last rocket flight of any kind, in about 2001, was a balsa version, and it did a 40+ minute OOS flight in near dead calm, and I am pretty convinced that there was no thermal, *just a surface Low pressure center* that took it up and to the west very slowly. I stopped after that, figuring there was no way to top that. They made a separate event for this, called flex-wing, FW, or "Flexie" conventional balsa gliders would have a chance.
All of these can be really fun but the performance possible is so high that losing them is about a 50/50 proposition. This is encouraged by the contest rules that generally *don't have any max", just like FF in the 30's. If you set a 2-minute max in Flexie it would be so trivial that everybody would max out, and if you let it rise, they fly out of the field before it becomes non-trivial. I did 35 minute flight in D Dual Eggloft (parachutes) that flew all the way over the city of Livermore, over the Lawrence Livermore laboratory, and into a cow pasture about 8 miles away. With a model I built in the crudest possible manner in about 45 minutes the night before the contest.
Brett