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I'm aware that under zero power it is a glider, but there are gliders that sustain flight and have enough lift to climb etc (Edit: this is not always true. See below answers for why). So, would it not be an interesting idea to make a wingsuit that you can use to climb and not just fall?

With longer wings could it be done? Or maybe a longer airfoil?

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    $\begingroup$ Yes, it's called a hang glider. $\endgroup$ – GdD May 11 '18 at 9:10
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    $\begingroup$ Many years ago, a friend of mine used to joke that people flying hang-gliders would eventually invent the glider. Looking at the rigid wings and all the electronics you see these days, he was not far from the truth. $\endgroup$ – Martin Argerami May 11 '18 at 14:21
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    $\begingroup$ Obligatory mention of the fictional "wingsuit" which used lighter than air gas to inflate the suit enough, supposedly, to enable a sort of flight. dc.wikia.com/wiki/Max_Bine_(Earth-Four) $\endgroup$ – nijineko May 11 '18 at 16:23
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    $\begingroup$ Given sufficient lifting air, anything can sustain flight. The only trick is finding a location with enough lift -- perhaps near a tornado? ;) $\endgroup$ – Jeremy Friesner May 12 '18 at 2:06
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There are very small jets that for hype-related reasons are called wingsuits. As current jet technology (and propeller technology) is easily capable of producing (from a human-portable frame) enough thrust to lift itself and a human-sized load, there is no obstacle to creating a true powered wingsuit. The reaction surfaces are very small in relation to the combined mass and necessary speed, so it will not be a swooping-soaring kind of flight, and more ballistic — unless you opt for vectored thrust, which is cheating.

EDIT: I just realized you were asking about unpowered flight. The glide ratio on a wingsuit is much too bad for that: you'd need hurricane-strength updrafts. A normal glider has about 500kg of total mass, and <20m wingspan for a glide ratio of about 40:1, which is just enough to soar in good thermals. To get that on a wingsuit (which might weigh, with occupant, 100kg) you'd need about a 5 meter wingspan (but this does not take into account that the Reynolds numbers start working against you as you scale down - Andean condors are 15kg @ 3m wingspan!). This might be achievable with tensairity or some other lightweight wing concept. You'd need something to take the brunt of the lifting force for you, while retaining the intuitive grasp on the lifting surfaces you get in a wingsuit. Should be doable, but I guess the engineering on something like that is too expensive to have been done by enthusiasts.

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    $\begingroup$ What kind of Reynolds number effect do you have in mind at these scales? Do you belive the skin friction / form drag ratio is significantly larger for a human size object than for a glider aircraft sízed object? $\endgroup$ – Vladimir F May 11 '18 at 7:02
  • $\begingroup$ What you need to effectively gain altitude in thermals is a low sink rate. A good L/D is what you need between thermals so that you can find the next thermal before running out of altitude, but it's not a requirement for gaining lift. If you're willing and able to stay in a thermal for the entire flight, then you just need a low sink rate. $\endgroup$ – Wayne Conrad May 11 '18 at 18:10
  • $\begingroup$ That said, I'll bet that wingsuits have unfavorable sink rates for thermalling. $\endgroup$ – Wayne Conrad May 11 '18 at 18:17
  • $\begingroup$ @VladimirF : A human is about 5 times shorter than a glider, and certainly not faster (in the glider-wingsuit), so the Reynolds number would be about five times lower, so we're very near the 150 000 that separates the two regimes of airflow. WayneConrad : while max L/D and min sinkrate are not reached at the same velocity, planes with a good L/D and planes with a low sinkrate are usually very similar (glider often take on water to finagle the specifics of L/R vs. sinkrate, but they stay the same aerodynamically. $\endgroup$ – bukwyrm May 11 '18 at 18:51
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    $\begingroup$ I don't think the chord length of the wing is that different. The length of the tail is irrelevant. $\endgroup$ – Vladimir F May 11 '18 at 20:22
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I'm aware that under zero power it is a glider, but there are gliders that sustain flight and have enough lift to climb etc.

This statement is a bit incorrect. Gliders don't climb like aircraft as they are constantly falling to the ground unless they catch a thermal, wave lift or ridge lift, in which case they can ride the updraft to gain altitude. In theory, a wingsuit could do that if you could maneuver to stay in the thermal but wingsuits are not maneuverable like a glider and tend not to have nearly the glide ratio of a glider so they sink far faster than a thermal could cary them up.

There is an interesting discussion on it here.

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    $\begingroup$ Oh I see. I guess I misinterpreted what someone said on this forum. Thanks for clearing that up. $\endgroup$ – TrapAlcubierreDrive May 10 '18 at 22:51
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    $\begingroup$ An unsuited human can ride an updraft too. At least if that updraft is from a transport aircraft propeller under a floor grating... $\endgroup$ – Chris Stratton May 10 '18 at 23:51
  • $\begingroup$ I thouugth it was much about fall rate than glide ratio. Best glide ratio is generally achieved at a greater speed than lowest fall rate. $\endgroup$ – Manu H May 11 '18 at 6:12
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    $\begingroup$ "wingsuits are not nearly as maneuverable" i strongly disagree on this one $\endgroup$ – thibaut noah May 11 '18 at 15:00
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As an ex-hang-glider pilot...

Two other answers have covered the basic concept of gliding - namely that you're constantly descending, and to stay aloft you need to be in air that's rising faster than you're descending. Early hang gliders and paragliders had no problems staying up in normal ridge lift with glide ratios of 7ish:1. Before that, they were just an exercise in top-to-bottom "sled rides".

EDIT TO ADD EVIDENCE: According to Geoff Broom, the first hang-glider flown in Britain in 1971 had a glide ratio of about 3:1 in flat air, or 5:1 in ground effect from flying close to the hill, and this was strictly limited to top-to-bottom flights. By 1972, pilots on Broom's gliders were starting to manage sustained soaring flights in ridge lift. The Skyhook Mk3 hang-glider plans recommend learning on a hill with a 5:1 slope, requiring the glider to have at least this glide ratio or better.

In more exceptional weather conditions, of course, you can get away with worse glide ratio; in fact you may want to. Most hill pilots (myself included) have had the experience of the wind picking up during their flight and having to pull on full speed (essentially a dive) in order to get back down to the ground against the rising air. So it's theoretically possible for a wingsuit to stay up in those kind of conditions.

And in the most extreme cases, it may simply be impossible to get down. I've read of paraglider pilots caught in the updraft from a cumulonimbus formation, where they have literally pulled their canopy in around themselves and were still going up, because the cu-nim updraft was stronger than gravity.

What other answers haven't covered though is that you also need to be able to land. If you can't flare to a landing below running speed, then you have problems! Typically a hang-glider has a stall speed of 15-25mph, and from that speed can be flared to near-stationary on landing. A wingsuit flies at around 60mph, and cannot be flared in anything like the same way. A good wingsuit pilot probably could stay aloft on a ridge in high winds, but he'd need to pop a chute to land - and parachutes and high winds are not a healthy combination.

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Because the glide descent ratio of a wingsuit is around 2:1 vs a well designed sailplane exceeds 40:1. This very gradual descent rate allows the sailplane to take advantage of normal, commonly encountered thermals in the atmosphere and gain altitude when in them. Thermals do alter the rate of descent for a wingsuit as well but is generally not powerful enough to allow the jumper to gain altitude.

It is theoretically possible for a wingsuit rider to ride powerful thermals or strong updrafts such as those encountered in the mature stage of a severe thunderstorm. However the dangers associated with flying in violent weather like that deter any attempts.

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  • $\begingroup$ Cross country competition gliders like the Nimbus 4T with a 26.5 meter wingspan have glide ratios of 60:1. $\endgroup$ – rcgldr May 11 '18 at 8:05
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    $\begingroup$ A favorable glide ratio is not needed for gaining lift. What's needed for gaining lift is a suitably low sink rate. But I think a wingsuit probably has a lousy sink rate. $\endgroup$ – Wayne Conrad May 11 '18 at 18:19
  • $\begingroup$ @WayneConrad Minimum sink is indeed the issue, but the only way to get a low sink rate with a low glide ratio is to go slowly, and wingsuits do not fly slowly. Fair-weather thermal soaring with a 2:1 glide ratio would require an airspeed around 10 knots. $\endgroup$ – sdenham May 12 '18 at 16:37
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This has a good example at the 2:15 mark. The glider has plenty of control for a landing. He is close enough but has to maintain a speed that is WAY TO FAST to land.

shows an example of a wingsuit jumper entering a plane, notice the speeds and angle of the plane.

Basically there just isn't enough lift generating surfaces to go slow enough to land.

Same is true for a climb. You just need more lift generating surface then is available. That said, it could work, in an insanely strong updraft, but it probably wouldn't be very much fun.

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The human body isn't strong enough to sustain flight in a wingsuit, without adding structural elements to make the wing independent of the human body.

Current wingsuits have wings that are too small for level flight. To get more wing area, you need to make the wings longer. But this increases the force exerted on the wing. In a wingsuit, the user has to push his arms and legs down to counteract the upward force exerted by the airfoil. For a wing that allows level flight, the user has to push down with a force equal to his own weight. Even strong athletes have trouble doing this for more than a minute or so.

You'd have to add two spars across the wing that take most of the load. The spars would be attached to the user's torso and transmit the forces without requiring the user to keep his muscles tensed up. The wing would then allow the user to use his arms as control surfaces. I've never seen a wingsuit design like this though.

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  • $\begingroup$ Thanks for the info. I guess that's why the guys with the jet suits have wings attached to them not as a part of them. $\endgroup$ – TrapAlcubierreDrive May 12 '18 at 7:18
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A regular skydiver in a track (the same body configuration as a ski jumper) has an L/D of about .5 to 1. Wingsuits improve the L/D to 1 to 1, which means a jumper weighing 200 lbs is generating about 200 lbs of drag at his gliding speed. Just to maintain level flight he'd need 200 lbs of thrust from a power source.

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  • $\begingroup$ So 200 lbs of thrust for 200 lbs of drag. Why is it that number? Is it always how it works out that the drag force equals the thrust required? $\endgroup$ – TrapAlcubierreDrive May 12 '18 at 7:19
  • $\begingroup$ If the total lifting force in steady state flight is equal to the all up weight, and knowing the L/D ratio, then drag is the product of the L/D ratio applied to all up weight. A sailplane with an L/D of 40, with an all up weight of 700 lbs, when flying at its max L/D speed will have total drag of 1/40th of its all up weight, or 17.5 pounds of drag. 17.5 pounds of thrust would be required to maintain level flight. A wing suit with an L/D of 1:1 will require the same thrust as the all up weight to maintain level flight. $\endgroup$ – John K May 13 '18 at 15:15
  • $\begingroup$ There was a guy with a wingsuit that installed a Jet Cat micro turbojet on each foot and it looked like he was in level flight but I don't think those engines made quite enough thrust and I suspect he was still descending but gently. $\endgroup$ – John K May 13 '18 at 15:18
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The wing surface area is too small to support the weight of the human pilot. Wings that small simply can not generate enough lift to sustain unpowered flight.

Below is the engineering "lift equation" you seek.

enter image description here

Here is the NASA article that describes how lift works in detail.

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    $\begingroup$ If you have enough power, it doesn't matter how small the wings are. Without power, a wing or lifting body, no matter how small, can still glide at some angle less than straight down. A bare human body in a track position still has an L/D of .5 and can attain 60 mph horizontal speed at terminal velocity. This is one of the major risks in skydiving relative work, running into each other while tracking. The issue is how steep the glide, or how much thrust is required to fly level if there is an engine. $\endgroup$ – John K May 13 '18 at 15:25

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