you train on being able to understand the relative motion of the silhouette. notice how at the start he's got a contrasting top/bottom, red solid top vs black-and-green echelons on the bottom. I would do something similar, my bottom was purple and big metallic pinstripe panels along the bottom, and my top was blue and yellow in another identifier pattern or something. Panels that are deliberately designed to be difficult to mis-identify.

like I said I'd flown models up to 70mph and it's the same thing which is harder to track for a given distance/speed) although of course nowhere near as extreme a speed. but I'd blast along the available field in like 10-15 seconds during a low dive pass. Then you do a high-speed pullout, go way up, and buzz it again. And that's the plane, those gofasts aren't super fun other than that (they don't even have rudder - see 1:25 in your vid). Actually they would barely take off (note his hi-start/rubberband launcher assist, same timestamp) and we'd handlaunch them. And (again) the speed tends to give them a huge tendency towards harmonic flapping failure so don't dive it too fast!

I flew three of them over the years, the first was a legit balanced build and could get good endurance and fun performance etc. The second we bolted the lower-turn (higher-torque) motor onto (and higher-twist prop etc) and it was such a rocket it flapped during dives. And that tends to destroy the wing foam over time (much cheaper than that guy's fiberglass etc!). Still a lot of fun, and it's beefier than the first one and thus more fun to fly, but you just have to be mindful of how much speed you put on, because you can lose it if it flaps (the elevons cause positive oscillation as the wing bends and torques beyond the point of support). But the extra power is beneficial in climbs etc.

And the third one was a mini model that was explicitly a pocket rocket, and knowing the flapping problem we used extra spars along the wings to reinforce it, it uses the same high-torque 3T motor as the second one but on a much smaller model, along with late-gen sanyo 1950FAUP packs that were rated to 50A and could actually burst to 70A without damage. Thing was an absolute monster but as mentioned, no rudder, so you go up, you go around, you go down, you go fast, you go up... over and over. Still fun though, thing would literally tear into a climb and be high enough in ~6 seconds tops that you wanted to be turning off the climb (lmao). the batteries would absolutely melt the motor if it wants and you run it for too long in a extreme high-thrust/stalled state - the motor is hot after takeoff and I generally would throttle out at pattern height and run for a bit to deliberately cool after launch. It was very controllable yet felt fast and scratched that itch, always a ton of power if you wanted to goof off for something, and the color scheme kept it safe, I am always very serious about that, you don't ever want it to be uncontrollable.

(did a bunch of this with my father and it's one of my fav memories, we learned a bunch about engineering and it made some sick planes)

EPP foam is wild - it's way durable compared to EPS, styrofoam, it's like the heavy duty foam packing material they cut for item packing (bulk HDD shipments etc). buy it cheap, use a foam cutter, etc. And you can fix it with polyurethane glue lol. Worst case you auger in, you shatter your spars, dremel them out, put in new carbon fiber rods (cheap), then pour in more polyurethane foam (mixed with water in a dixie cup), wipe flat after an hour when foaming has slowed. I have augered those three in so many times, all of them.

Sadly I think a lot of that era is coming to an end with drones, the hobby probably isn't going to survive that much longer. Haven't done it in a while but the FAA has taken an interest in airspace that we used to be pretty free to use as long as we kept with the "visual sight" rule.

But yeah that guy's plane is nuts and he'll totally have trained on recognizing which side is up from the light/dark patterns. dude has a little mental gimbal he's flying the plane through and updating it as he tracks the model. It's climbing and dark towards me, roll it and pull up and I'll execute the immelman and then it'll be red and going downwards. And it helps that the radios have a "low rate" mode that allows very slow maneuvers during non-critical phases of flight, and this will help avoid that "the model spun and I lost it" problem. High-rate still often is necessary for brute force especially at launch etc, or during extreme manuevers that want lots of control throw.

still very dangerous to fly like that, I only use that as a secondary regime, if I'm flying the mental gimbal it's to recover the plane and bring it back where I can see it (ideally take note of the lighting angle etc, low and long light near sunset can be particularly dangerous, high-angle daylight is easier). Let alone with something that fast.

Long time ago but I had an aero eng class where we were designing model rocket gliders, team that lands closest to the target wins. same problem, balsa wing on a model rocket tube is super hard to see, the controls were extremely oversensitive (I'd programmed low-rates and high-rates and low was still very sensitive) and the roll rate was absolutely extreme (elevator was ok) but I managed to get it into a known configuration with The Mental Gimbal and nudge it into a glide slope, we actually got some distance versus the other teams before who mostly just lost it and spazzed out into a nosedive. Didn't quite win but I think we came second or third.

edit: a tasty little treat (the design workbook) https://www.mediafire.com/file/39hsny8xc52h6q7/Glider_group....