6 ms·

I think there's (at least) one important factor this leaves out. Drag doesn't care what direction you're moving: it will slow you to about 120 mph regardless of

I think there's (at least) one important factor this leaves out. Drag doesn't care what direction you're moving: it will slow you to about 120 mph regardless of whether you're going straight down or at an angle. This implies that you want to control your horizontal velocity not just to decide where you land, but also to build up as much horizontal velocity as possible. If you can get yourself going at a moderate angle, you can significantly decrease your vertical velocity, which is by far the most dangerous part of a freefall! The most important thing about approaching at an angle is not to tumble. This strategy would work best if you could slide down or along a loose surface like snow or small gravel, ideally down a hill. This basic strategy is why high speed skiers (who are moving at least 120 mph) can survive crashes.

oska 7y ago
Stuntman Garry Connery demonstrated the efficacy of what you're describing when he jumped from a helicopter at 2,400 feet (730 metres) and steered himself using a wingsuit onto a runway of vertically stacked cardboard boxes. [1] [1] https://www.youtube.com/watch?v=DEP8juRSBRo https://www.youtube.com/watch?v=DEP8juRSBRo > At approximately 200 feet (61 m) over the landing strip, he changed the configuration of his wingsuit so as to decrease the gliding and vertical (falling) components of his velocity to 50 mph (80 km/h) and 15 mph (24 km/h) respectively. [2] [2] https://en.wikipedia.org/wiki/Gary_Connery#World's_first_wingsuit_landing_without_a_parachute https://en.wikipedia.org/wiki/Gary_Connery#World's_first_win...
- bscphil 7y ago
  Yep! 15 mph falling is survivable. His total velocity was 52.2 mph on impact - if all that had been straight into the ground it's doubtful that even the thick layer of cardboard boxes would have prevented injury. Without a wingsuit you're not going to get ratios that good, but every bit helps, and if you can hit a sloped surface with any accuracy your survival chances go up significantly.
  - thom 7y ago
    I guess this is an argument for always having a towel with you.
Pinckney 7y ago
Wikipedia claims glide ratios of 1:1 with efficient tracking. You'll still hit with a 90mph vertical speed, and I suspect you will compromise your ability to land on a soft point target. Myself, I think landing head-first sounds like the best plan.
RSZC 7y ago
Hmmm...former skydiver here, not sure your point is accurate. I don't understand why increasing your forward momentum from tracking would decrease your fall rate. I think your assumption that drag will slow you to 120mph is inaccurate - for example, if you fall heads-down your terminal velocity is instead up to ~180mph. Similarly, I'd expect that if you track in a direction your velocity could increase above 120mph while not lowering the speed at which you approach the ground. Apologies - my physics knowledge and terminology is very limited, but do have some practical experience in the area :)
- bscphil 7y ago
  You might have to spend your last 10 seconds or so in an orientation that maximizes drag, so as to take advantage of the horizontal velocity you've built up. I'm familiar with the physics angle, but not the skydiving one. :-) I think to know this accurately we'd have to look at some kind of simulation.
- nkoren 7y ago
  The trick is that while you can't actually decrease the total amount of energy in your fall, you can get some of that energy to work in your favour. Think about when you flare a parachute, shortly before landing. What you're doing is trading forward momentum for vertical lift, softening your landing. The more forward momentum you have prior to a flare, the more lift you can get out of it. This is why you see experienced / foolhardy skydivers doing "hook turns" to maximise their forward velocity immediately before landing. (Of course if you just stayed in the flare position continously, you'd have no forward momentum to trade, and would therefore lose lift entirely, producing the opposite of the intended effect.) Anyhow, yeah, I doubt that tracking alone would help with survivability. My hunch is that you'd be trading 10mph of vertical momentum for about 40mph of horizontal momentum. Doesn't sound like a good trade. Although maybe -- just maybe -- you could execute a "body flare", whereby you kick your legs forward at exactly the right moment, to kill that forward momentum and trade it for lift. That might actually work (a bit)! But it sounds like an extraordinarily difficult manouevre. You'd certainly never get it right on the first try. Which of course is as many tries as you'll ever get.
1_person 7y ago
Lift generated in the vertical direction is probably a factor worth considering here as well. If you are able to build up a significant velocity in horizontal direction, you might in the final moments before landing be able to shift posture to an aerodynamic form which converts your horizontal motion to a force in the positive vertical direction with a drag force in the negative horizontal direction, reducing both your horizontal and vertical velocity for a brief period. The notion reminds me of how helicopters land in the event of an engine failure, a regime of flight called autorotation. After engine failure the main rotor begins to be driven by the airflow. It is set to maximize drag, impart a horizontal velocity (I think? I am not a helicopter pilot, this is not helicopter landing advice), and primarily maintain rotational inertia -- more like a glider with a spinning wing than a rock falling from the sky as one might assume. In the moments before landing the rotor angle of attack is increased, and the rotational inertia is converted to brief surge of lift allowing the helicopter to touch down practically as normal. The question becomes, what posture should one assume to maximize lift to drag ratio? It seems like something edge on, with the body in a flying wing formation essentially, could come pretty close to offering enough lift to make survival feasible if you could somehow manage to transition to that orientation through what appear to be aerodynamically unstable configurations which would oppose that. And the side-on orientation does not seem like a good posture for the actual impact, so you'd need to quickly shift back to the "shock absorption" posture and if the flying wing orientation had the intended effect you would not have much airflow to maneuver with so it would presumably have to be something more like a zero-g change of attitude (https://youtu.be/960CsCgI6Jg?t=105 https://youtu.be/960CsCgI6Jg?t=105). I'll be sure to give it a try if I ever end up falling out of an airplane and let everyone know how it goes, though.

oska 7y ago

Stuntman Garry Connery demonstrated the efficacy of what you're describing when he jumped from a helicopter at 2,400 feet (730 metres) and steered himself using a wingsuit onto a runway of vertically stacked cardboard boxes. [1] [1] https://www.youtube.com/watch?v=DEP8juRSBRo https://www.youtube.com/watch?v=DEP8juRSBRo > At approximately 200 feet (61 m) over the landing strip, he changed the configuration of his wingsuit so as to decrease the gliding and vertical (falling) components of his velocity to 50 mph (80 km/h) and 15 mph (24 km/h) respectively. [2] [2] https://en.wikipedia.org/wiki/Gary_Connery#World's_first_wingsuit_landing_without_a_parachute https://en.wikipedia.org/wiki/Gary_Connery#World's_first_win...

bscphil 7y ago
Yep! 15 mph falling is survivable. His total velocity was 52.2 mph on impact - if all that had been straight into the ground it's doubtful that even the thick layer of cardboard boxes would have prevented injury. Without a wingsuit you're not going to get ratios that good, but every bit helps, and if you can hit a sloped surface with any accuracy your survival chances go up significantly.
- thom 7y ago
  I guess this is an argument for always having a towel with you.

Pinckney 7y ago

Wikipedia claims glide ratios of 1:1 with efficient tracking. You'll still hit with a 90mph vertical speed, and I suspect you will compromise your ability to land on a soft point target. Myself, I think landing head-first sounds like the best plan.

RSZC 7y ago

Hmmm...former skydiver here, not sure your point is accurate. I don't understand why increasing your forward momentum from tracking would decrease your fall rate. I think your assumption that drag will slow you to 120mph is inaccurate - for example, if you fall heads-down your terminal velocity is instead up to ~180mph. Similarly, I'd expect that if you track in a direction your velocity could increase above 120mph while not lowering the speed at which you approach the ground. Apologies - my physics knowledge and terminology is very limited, but do have some practical experience in the area :)

bscphil 7y ago
You might have to spend your last 10 seconds or so in an orientation that maximizes drag, so as to take advantage of the horizontal velocity you've built up. I'm familiar with the physics angle, but not the skydiving one. :-) I think to know this accurately we'd have to look at some kind of simulation.
nkoren 7y ago
The trick is that while you can't actually decrease the total amount of energy in your fall, you can get some of that energy to work in your favour. Think about when you flare a parachute, shortly before landing. What you're doing is trading forward momentum for vertical lift, softening your landing. The more forward momentum you have prior to a flare, the more lift you can get out of it. This is why you see experienced / foolhardy skydivers doing "hook turns" to maximise their forward velocity immediately before landing. (Of course if you just stayed in the flare position continously, you'd have no forward momentum to trade, and would therefore lose lift entirely, producing the opposite of the intended effect.) Anyhow, yeah, I doubt that tracking alone would help with survivability. My hunch is that you'd be trading 10mph of vertical momentum for about 40mph of horizontal momentum. Doesn't sound like a good trade. Although maybe -- just maybe -- you could execute a "body flare", whereby you kick your legs forward at exactly the right moment, to kill that forward momentum and trade it for lift. That might actually work (a bit)! But it sounds like an extraordinarily difficult manouevre. You'd certainly never get it right on the first try. Which of course is as many tries as you'll ever get.

1_person 7y ago

Lift generated in the vertical direction is probably a factor worth considering here as well. If you are able to build up a significant velocity in horizontal direction, you might in the final moments before landing be able to shift posture to an aerodynamic form which converts your horizontal motion to a force in the positive vertical direction with a drag force in the negative horizontal direction, reducing both your horizontal and vertical velocity for a brief period. The notion reminds me of how helicopters land in the event of an engine failure, a regime of flight called autorotation. After engine failure the main rotor begins to be driven by the airflow. It is set to maximize drag, impart a horizontal velocity (I think? I am not a helicopter pilot, this is not helicopter landing advice), and primarily maintain rotational inertia -- more like a glider with a spinning wing than a rock falling from the sky as one might assume. In the moments before landing the rotor angle of attack is increased, and the rotational inertia is converted to brief surge of lift allowing the helicopter to touch down practically as normal. The question becomes, what posture should one assume to maximize lift to drag ratio? It seems like something edge on, with the body in a flying wing formation essentially, could come pretty close to offering enough lift to make survival feasible if you could somehow manage to transition to that orientation through what appear to be aerodynamically unstable configurations which would oppose that. And the side-on orientation does not seem like a good posture for the actual impact, so you'd need to quickly shift back to the "shock absorption" posture and if the flying wing orientation had the intended effect you would not have much airflow to maneuver with so it would presumably have to be something more like a zero-g change of attitude (https://youtu.be/960CsCgI6Jg?t=105 https://youtu.be/960CsCgI6Jg?t=105). I'll be sure to give it a try if I ever end up falling out of an airplane and let everyone know how it goes, though.