Originally published at: https://boingboing.net/2021/01/22/watch-a-motor-less-rc-plane-set-a-new-speed-record.html
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Someone who is a physicist (ETA: Or is part of the 95% of the adult population who knows more about this sort of thing than I do. Actual physicist not strictly required, but would be nice), please:
- Doesn’t the turning shed speed in some way?
- Would it be possible to hit Mach 1 with a motor-less RC vehicle, given normative conditions like this?
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Didn’t have a chance to watch all the way to the end of the video but I do NOT wanna be the guy who has to attempt catching that thing at the end of the flight.
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Given the fact that it gently plops back down on the ground when it’s done, you should’ve probably at least watched the end. 
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I’ve seen the future, and it’s now.
BTW: How’d land that thing?
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I don’t know how the wings stay on that thing, it looks as if it should be torn to bits.
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Turning always involves drag which reduces speed.
I doubt you could hit Mach 1. Falling rocks don’t even move that fast, but the sound barrier seems to have been broken during the second world war by fighter/bombers who started really high and pointed the nose down.
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RC Aircraft dork here…The plane accelerates because of the technique called ‘dynamic soaring’. Essentially, they are flying into a windy patch of air to accelerate then into a calmer patch of air to whip it around back into the direction of the wind. In this video, it’s jumping into a really windy bit of air above the hillside to accelerate. It then ducks down into the calm patch of air created by the hillside blocking the wind to complete the turn while facing less headwind. Each loop into and out of the wind acts to accelerate the plane a bit more.
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Landing: Skilled flying by the RC pilot got the plane (on the very edge of losing lift) through the headwind as would sea gulls hovering over fish at sea on a windy day. Plane control surfaces have nothing on birds’ wings and tails, but they get the job done. 
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Your rock example is more about terminal velocity and drag than anything else. Terminal velocity for a human is about 120mph if falling in a belly first skydiving stance but it is nearly 200mph of falling feet first primarialy because of the difference in drag.
Like the WWII planes you highlighted that could reach mach 1 in a dive at full throttle, if enough energy is propelling these sailplanes and the drag is low enough, they could theoretically get to mach 1.
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If you dived into lift, then I could believe it, because its a bit like a sailboat moving much faster than the wind which drives it. The glider would turn the upwards thrust of the wind into horizontal thrust.
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Ok so it was perhaps just me … but that video was unwatchable. What was all the jerking back and forth on an empty bit of sky? (Well, it might as well have been empty for all the use it was - a very occasional infinitesimally small flash at one end of the violent whip pan.)
Watch a plane set a new record? Nah. This was not that.
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Run the video in full screen on a large display. It’s definitely not great video, but considering it’s amateur video of a model plane circling at over 500 MPH in winds of up to 65 MPH, I’m impressed they managed to track the thing at all.
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I did. Didn’t really improve matters, I’m afraid.
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Not just you. A bit of description in the post about the plane looping around and around to build speed would definitely have helped orient those of us not familiar with this corner of the hobby world.
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Was legit disappointed that there was no camera on the plane. Maybe that would have messed with the weight - but would have been a way cooler video
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I did - and it helped. wow! amazing capture by whoever was holding the camera and WOW amazing rc pilot! it would been kinda fun to see it auger into the hillside at the end…
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I, too, look forward to commercial engine-less passenger aviation… we just need to scale this up!
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I really wonder what the G forces were on that plane. They must have been crazy high doing such tight circles at over 500mph
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In case anyone else needs one:
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