History Channel, Check it out now, quick! Options

[Aaron]

A wingsuit may not have lift, but 1) I don't care if the craft actually goes up, just that it slows down and 2) thrust is not the same as speed. If I'm going at 100 mph and aim upwards at 30 degrees, I will lose speed faster than I was before, but I will go upwards. This is very basic physics. It may not apply the same way to parachuting, but that's because a parachute isn't a wingsuit.

I'm afraid you'll have to scold your physics teacher. In order for you to go upward, you need a force vector in the upward direction that is greater than the force vector caused by gravity (downward). A glider only generates lift (the upward vector) when it is falling through the air. The lift of a glider is never (ever) greater than the force of gravity. When you tilt a glider upward, its surfaces stop being at the proper angle to generate lift, so you actually lose lift.

To illustrate: I performed the experiment I suggested earlier in this thread.

[ Spoiler ]

I tested the loopty-loop properties by throwing it (providing thrust), and it did a couple loops nicely. I dropped the paper airplane both flat and with nose pointed down. When I dropped it flat, it simply floated downward and forward, like a glider, but did not go upward, loop, or even flip.

When I dropped it nose-down, it looped a lot. It took a lot less time to hit the floor (2s as opposed to 4s with the flat drop). From my angle, it looked like it was gracefully looping and briefly slowing and stalling with each loop, but on the side-view video (yes, I filmed it; it's an experiment, and I'm a geek) it's clear that it took a straight path to the floor, and it was the spin that was speeding up and slowing, not the center of mass.

Conclusion: pointing a glider upwards will not help land it. If it did, you would see it in real glider landings.

[nezumi]

By the Bernoulli principle, the specific job of the wings is to convert forward force into upwards force. By shifting the airfoil, you shift the details of that conversion. I don't know any part of that equation, which is just built on having less air pressure below than above, which requires active acceleration, rather than just velocity, to work.

The paper airplane experiment doesn't compare because you're always looking at a craft with the desired wing shape during acceleration. The question is, how does changing wing shape during unpowered flight alter your ability to gain lift or bleed speed. Since aircraft are capable of landing unpowered (usually under emergency landing conditions), I fail to see how one can argue that you can do it with a plane, but not with a glider. The glider probably needs modifications from the prototype on the show, but that isn't really a showstopper.

[Karoline]

Well, you're actually both sort of wrong.

The squirrel suit doesn't generate lift in the same way as a plane does via having the top and bottom of the wing shaped differently (Which only requires velocity, not acceleration).

You can actually go up in a glider for brief moments, but it requires you to fall more than you went up (Go into a nose dive and pull up, you'll end up higher than your lowest point, but below where you started the dive), but you can generate lift (upward force) in a glider/squirrel suit by tilting so that the wings are pointing up. It'll slow you down (falling), and cost you alot of forward momentum, and is actually how planes and gliders land.

[Aaron]

By the Bernoulli principle, the specific job of the wings is to convert forward force into upwards force. By shifting the airfoil, you shift the details of that conversion. I don't know any part of that equation, which is just built on having less air pressure below than above, which requires active acceleration, rather than just velocity, to work.

I'm no physicist, but I'm a big fan of science. Bernoulli's principle only takes the acceleration due to gravity into account, and then only as potential energy for intrafluid dynamics, not pressure effects. The lift formula doesn't have acceleration at all. See Bernoulli's Principle and lift.

The paper airplane experiment doesn't compare because you're always looking at a craft with the desired wing shape during acceleration. The question is, how does changing wing shape during unpowered flight alter your ability to gain lift or bleed speed. Since aircraft are capable of landing unpowered (usually under emergency landing conditions), I fail to see how one can argue that you can do it with a plane, but not with a glider. The glider probably needs modifications from the prototype on the show, but that isn't really a showstopper.

The problem is that you can increase drag, sure, but in a glider, increased drag means lower airspeed means decreased lift, and now you're plummeting again. The best you can do is decrease your glide ratio, which decreases your forward velocity but increases your downward velocity.

As for climbing, gliders don't accelerate without a downward component vector. If we could change a glider's wing to generate a stronger lift than gravity, we'd be able to fly anywhere in the world without power. As cool as that might be, it would be adding energy into a system, not transferring it, and so violate the laws of thermodynamics (first and second, I think).

Gliders can fly upward, but only with thrust supplied by an outside source (there is a different name for gliders with internal sources of thrust) or by generating enough airspeed, usually by shedding altitude for speed (with no net gain -- pesky laws of thermodynamics again). I found an example of a glider that takes off with a winch launch, climbing with the thrust provided by the pull of the winch. However, after the winch releases (you can see it in the video), the pilot keeps trying to climb and ... well, you can see it in the vid.

[Aaron]

Well, you're actually both sort of wrong.

The squirrel suit doesn't generate lift in the same way as a plane does via having the top and bottom of the wing shaped differently (Which only requires velocity, not acceleration).

I believe you'll find that these two articles by a manufacturer of wingsuits disagree with this assertion. As a bonus, the first article discusses landing a wingsuit without a parachute.

[Smokeskin]

Well, you're actually both sort of wrong.

The squirrel suit doesn't generate lift in the same way as a plane does via having the top and bottom of the wing shaped differently (Which only requires velocity, not acceleration).

Of course squirrel suit generates lift like a plane, by having lower pressure on top than below. This is caused by the different shape that causes air to flow faster on top than below.

What other mechanism could be responsible?

You can actually go up in a glider for brief moments, but it requires you to fall more than you went up (Go into a nose dive and pull up, you'll end up higher than your lowest point, but below where you started the dive), but you can generate lift (upward force) in a glider/squirrel suit by tilting so that the wings are pointing up. It'll slow you down (falling), and cost you alot of forward momentum, and is actually how planes and gliders land.

Are you sure about that? Since lift is generated by air going over the wing, by tilting upwards, you would lose lift. When you flare a parachute, you lose lift, but reduce forward speed. Do it too early, and you land hard. I think that's the same with gliders, when you're at very low altitude, your concern is to brake. Planes have flaps that increases lift at low speeds, so they can land slower without stalling - they don't have the luxury of flexible human legs that can absorb impact.

[KarmaInferno]

Since we're talking about wingsuits having no inherent thrust capacity, I thought this would be appropriate:

http://www.youtube.com/watch?v=eS2rjcVcaqQ





-karma

[Karoline]

I believe you'll find that these two articles by a manufacturer of wingsuits disagree with this assertion. As a bonus, the first article discusses landing a wingsuit without a parachute.

Hmm, weird, the design didn't really look like it would act like a foil, so I figured it relied on simple increased air resistance to decrease terminal velocity.

Are you sure about that? Since lift is generated by air going over the wing, by tilting upwards, you would lose lift. When you flare a parachute, you lose lift, but reduce forward speed. Do it too early, and you land hard. I think that's the same with gliders, when you're at very low altitude, your concern is to brake. Planes have flaps that increases lift at low speeds, so they can land slower without stalling - they don't have the luxury of flexible human legs that can absorb impact.

Yeah, but it is going to be a temporary thing. If you want, make a paper airplane and make some flaps on it. Throw it and see if it doesn't do a loop that sends it flying upwards for a bit. That would be the same as if you went into a dive and then pulled up. If you throw well it can even do multiple loops which will further prove that a gliding object can go up, if only for short periods of time.

I don't know how good the suits are, but I'd imagine that if you were skilled (and suicidal) you could glide till you are close to your target, then dive and pull up near the ground to create as much lift as possible. If you can go up then the fall would only be the same as whatever high you stalled out from (Maybe a bit less thanks to extra air resistance), and if you just reduce your falling speed, then you'll be hitting the ground alot softer. It would require a great deal of skill and nerve though, as you'd likely have to dive bomb to within a few dozen meters of the ground before pulling up to make it work properly, and if you wait too long then you face plant into the ground at max speed.

[nezumi]

You can actually go up in a glider for brief moments, but it requires you to fall more than you went up (Go into a nose dive and pull up, you'll end up higher than your lowest point, but below where you started the dive), but you can generate lift (upward force) in a glider/squirrel suit by tilting so that the wings are pointing up. It'll slow you down (falling), and cost you alot of forward momentum, and is actually how planes and gliders land.

And that's the point - if our suit is gliding, it's because it's already done the fall part to get up speed. Now you still have the option of tilting upwards again. You can't get back to your starting point, but that was never the goal.

I'm no physicist, but I'm a big fan of science. Bernoulli's principle only takes the acceleration due to gravity into account, and then only as potential energy for intrafluid dynamics, not pressure effects. The lift formula doesn't have acceleration at all. See Bernoulli's Principle and lift.

I think you're agreeing with me here, yes?

The problem is that you can increase drag, sure, but in a glider, increased drag means lower airspeed means decreased lift, and now you're plummeting again. The best you can do is decrease your glide ratio, which decreases your forward velocity but increases your downward velocity.

You get lift as a function of airspeed, but also as a function of the curvature of the wing (a flatter wing generates less lift than a curved one, for instance). Altering the curvature does sacrifice speed, but it should increase lift from curvature more than it loses lift from speed loss - as long as you don't hit stall speed. Once you hit stall speed, you fail to generate lift at all, obviously.

[quote]
As for climbing, gliders don't accelerate without a downward component vector. If we could change a glider's wing to generate a stronger lift than gravity, we'd be able to fly

[nezumi]

Double post.

[nezumi]

Post frenzy!

[Karoline]

And that's the point - if our suit is gliding, it's because it's already done the fall part to get up speed. Now you still have the option of tilting upwards again. You can't get back to your starting point, but that was never the goal.

TP for the win (IMG:style_emoticons/default/nyahnyah.gif)
Yeah, never said you could get back to your original point, just that you could temporarily generate enough lift to go upwards, but it will never get you higher than your starting point.

As for climbing, gliders don't accelerate without a downward component vector. If we could change a glider's wing to generate a stronger lift than gravity, we'd be able to fly

But we can generate a stronger lift than gravity, we just can't sustain it for more than a few moments. Like I said, go make a paper airplane with flaps and throw it hard. It'll do loops. It'll even go above where you originally threw it from, but that is because you start it at a higher velocity than it can obtain just gliding (Without dive bombing).

Got to read what I'm writing carefully. I'm not saying a glider can fly, simply that it can, for a short time, generate enough lift to go upwards, and it is easily provable if you have a piece of paper and several feet in which to throw a paper airplane (And, I guess, working arms).

[Aaron]

And that's the point - if our suit is gliding, it's because it's already done the fall part to get up speed. Now you still have the option of tilting upwards again. You can't get back to your starting point, but that was never the goal.

When you're talking about a wingsuit, you're talking about something that is incapable of level flight, much less actually climbing. The best wingsuit in the world has a glide ratio of 2.5 or maybe 3. Hang gliders are more like 18 or 19, and they can't climb steeply and loop by stalling.

I think you're agreeing with me here, yes?

I don't think so. You seemed to be saying that lift was generated by acceleration. I'm saying it's velocity [edit: more accurately airspeed]. They're two different things.

You get lift as a function of airspeed, but also as a function of the curvature of the wing (a flatter wing generates less lift than a curved one, for instance). Altering the curvature does sacrifice speed, but it should increase lift from curvature more than it loses lift from speed loss - as long as you don't hit stall speed. Once you hit stall speed, you fail to generate lift at all, obviously.

That's why I provided links to documents talking about the high stall speed of wingsuits. You did read them, right? In case you didn't, I'll summarize: wingsuits have a minimum air speed that varies according to the body it's wrapped around, but according to the calculations provided in those articles the average stall speed is probably around 57.7 mph (92.8 kph, 25.8 m/s). More for an ork, less for an elf.

[nezumi]

When you're talking about a wingsuit, you're talking about something that is incapable of level flight, much less actually climbing. The best wingsuit in the world has a glide ratio of 2.5 or maybe 3. Hang gliders are more like 18 or 19, and they can't climb steeply and loop by stalling.

Okay, but that's a limitation of the technology as it stands. We have 50 years to improve it, thanks to smart materials and yes, short-burn rockets and such. I find the argument that the suit now can't land safely, and therefore in 2050 it can't land safely dubious (and that was my original point). But regardless, our goal still isn't technically to go up - it's to hit a given target at a speed slow enough to land. Aiming up is a good way to bleed off airspeed because it increases forward drag, while slowing your actual descent. The question is simply, can we make a suit that can use this method in order to land safely (using 2050 technology).

I don't think so. You seemed to be saying that lift was generated by acceleration. I'm saying it's velocity [edit: more accurately airspeed]. They're two different things.

I think you must be responding to someone else there. I never said that - in fact, I was arguing specifically against it, saying unpowered craft can go up.

That's why I provided links to documents talking about the high stall speed of wingsuits. You did read them, right? In case you didn't, I'll summarize: wingsuits have a minimum air speed that varies according to the body it's wrapped around, but according to the calculations provided in those articles the average stall speed is probably around 57.7 mph (92.8 kph, 25.8 m/s). More for an ork, less for an elf.

But that's okay, if we're only stalling for a few moments. Let's say we're coming in at 60 mph. We pull up and create enough drag to decelerate say 20 mph/s (which is fast, but not deadly fast). We start dropping, but the standard rate of 9.8 m/s^2 doesn't apply, because we still have the airfoil decreasing our rate of descent. Any physicist should be able to calculate the point at which our forward motion + descent is at its lowest point, and aim to put down then.

Combine that with a targeting computer to do the calculations for you, smart materials that let out fabric as necessary or turn rigid or soft or into particular shapes, secondary chutes and short-burn rockets and the idea of landing on a small, pre-selected point seem quite achievable.

[Aaron]

Okay, but that's a limitation of the technology as it stands. We have 50 years to improve it, thanks to smart materials and yes, short-burn rockets and such. I find the argument that the suit now can't land safely, and therefore in 2050 it can't land safely dubious (and that was my original point). But regardless, our goal still isn't technically to go up - it's to hit a given target at a speed slow enough to land. Aiming up is a good way to bleed off airspeed because it increases forward drag, while slowing your actual descent. The question is simply, can we make a suit that can use this method in order to land safely (using 2050 technology).

Sure, there's an advance in technology, but we'll be using the same physics. Aiming up doesn't bleed off airspeed in a wingsuit, because it ain't got enough wing. It's also not a way to generate lift, since the airfoils are pointed the wrong direction. The best you can get is a wing load situation, like a parachute only not as good. It's in the documents I linked, but I'm done summarizing links; read it or argue from ignorance.

Combine that with a targeting computer to do the calculations for you, smart materials that let out fabric as necessary or turn rigid or soft or into particular shapes, secondary chutes and short-burn rockets and the idea of landing on a small, pre-selected point seem quite achievable.

Again, it's about wingload. There's only so much you can do with the wing you have. To do what you propose, you need more wing. Maybe that means a complicated system of braces and expanding fabric, but then you have a hang glider (a la the Shadowrun video game), not a wing suit. There's another way of getting the right wing load that would be far cheaper, easier, more reliable, and less prone to failure or hacking: a parachute.

[Smokeskin]

Hmm, weird, the design didn't really look like it would act like a foil, so I figured it relied on simple increased air resistance to decrease terminal velocity.

Air resistance? Seriously? It only looks to about double your surface area.

Yeah, but it is going to be a temporary thing. If you want, make a paper airplane and make some flaps on it. Throw it and see if it doesn't do a loop that sends it flying upwards for a bit. That would be the same as if you went into a dive and then pulled up. If you throw well it can even do multiple loops which will further prove that a gliding object can go up, if only for short periods of time.

You can't really compare a wingsuit to a paper airplane. A wingsuit has over 10lbs per sq feet of wingload. A paper airplane has what, 1/10 sq foot surface area? So if you put a 1 lbs weight on that paper plane (use some of that weight to reinforce the wings), then you have a proper balance between lift, air resistance and gravity. Then try your flaps experiment.

By the way, no one said that a gliding object can't ever go up. It can dive to build speed enough to have sufficient lift to momentarily go upwards. Wingsuits can't generate enough lift to do that though.

[nezumi]

Ok, I'm going to take this personally for a moment.

See, but now you're changing arguments (or at least not presenting the same argument Smokeskin did earlier). When I brought up the idea, people were complaining that no, gliding objects can't go up, you can only do that with powered thrust.

Now, if you argument is that the wingsuit specifically can't do this because the surface area of the wings is too small to generate significant lift OR breaking power, then just state that plainly.

[Karoline]

Ok, I'm going to take this personally for a moment.

See, but now you're changing arguments (or at least not presenting the same argument Smokeskin did earlier). When I brought up the idea, people were complaining that no, gliding objects can't go up, you can only do that with powered thrust.

Now, if you argument is that the wingsuit specifically can't do this because the surface area of the wings is too small to generate significant lift OR breaking power, then just state that plainly, but don't insult my knowledge of physics.

edit: And Aaron did say gliders can't go up - in post #51. You yourself implied it in post #50. And Aaron again in #42.)

I got the same impression as you Nezumi. Sudden shift from 'impossible to generate enough lift to go up' to 'can't do it with a squirrel suit specifically'

[Aaron]

I'll bite. Sure, I was wrong about gliders climbing in all instances. I failed to account for aerobatic flight in my arguments. However, I think we all agree that while aerobatic flight is climbing instantaneously, a glider doesn't get to keep the altitude for very long without an updraft. Doing a wingover by diving doesn't help land a glider unless you can dip underground when you do it. Has there been a suggestion that aerobatic-type flight should be considered for landing procedures?

My failure to be comprehensive about an aircraft we were not actually discussing doesn't negate all of my points, though, and certainly not about wingsuits. None of these point have been addressed or refuted (or even mentioned when the poking started in #67).

And I've never insulted nezumi's knowledge of physics. I may have insinuated that his or her physics teacher needs some scolding, but unless I am mistaken, his or her description of Bernoulli's principle and airfoil mechanics were mistaken, and have not been refuted on that point. I've engaged nezumi's arguments, not him or her personally, offering substantive sources from knowledgeable third parties. I did suggest that he or she may be arguing from ignorance (which may have crossed the line and if so I apologize), but his or her arguments were refuted directly by the material I linked prior to his or her post.

I've refrained from listing the individual fallacies in the arguments of other posters, and I see no reason why I should start. I certainly try to refrain from piling on.

I think that sorts things. Any other issues that we should have taken to private messages, or shall we continue talking about wingsuits?

[Karoline]

I'll bite. Sure, I was wrong about gliders climbing in all instances. I failed to account for aerobatic flight in my arguments. However, I think we all agree that while aerobatic flight is climbing instantaneously, a glider doesn't get to keep the altitude for very long without an updraft. Doing a wingover by diving doesn't help land a glider unless you can dip underground when you do it. Has there been a suggestion that aerobatic-type flight should be considered for landing procedures?

Yeah, aerobatic-type flight is exactly what I was suggesting, and even detailed doing a dive bomb to within a few dozen meters of the ground, then pulling up, almost skimming the ground before getting enough lift to go up several meters, killing all forward momentum in doing so, and then falling back down the however many meters of height you got. Not something doable today, because even a 2-3 meter fall can be dangerous, and you couldn't skim that close safely, but with good hydraulic system and some specialized software to tell you when to pull up, you could maybe get it to to where you are only falling about 10m or so, which is within the ability of the hydraulics to absorb.

What I don't know is if wing/squirrel suits can actually manage a maneuver like this or not, but I do know that a glider and even (edit: paper) airplanes can.

And I stated in almost every one of my posts that the height gained followed the laws of physics (indirectly), as it couldn't bring you higher than the highest point you started at, but simply higher than the lowest point of your dive.

So yeah, I was just noting that I too saw a sudden shift of 'cannot happen' to 'cannot happen with a wing suit', the latter of which may be valid. I really don't know enough about the physics involved to say for sure. I would however imagine that such a maneuver could at least bring you to a near stop as far as falling is concerned while bleeding off all your forward speed, thus allowing you to land safely with hydraulic systems and nerves of steel at getting so close to the ground in a dive bomb.

[KarmaInferno]

So, no comment about the link I posted?

I would hazard a guess that strapping jet turbines to your legs might alter the flight characteristics of a wingsuit.

(IMG:style_emoticons/default/smile.gif)

The flight shown in the video is about 30 seconds of level flight. Later iterations of the system have allowed up to two minutes of sustained level flight.

Could one use the additional thrust to create enough of a stall force to make a difference in landing without the parachute?



-karma

[Daylen]

Yeah, History Channel and Discovery are basically the only channels I watch. HC in particular tends to provide really cool ideas for SR.

but then how do you catch Successful Farming Machinery show? http://www.rfdtv.com/shows/SuccessfulFarmingMach.asp

[Smokeskin]

Ok, I'm going to take this personally for a moment.

See, but now you're changing arguments (or at least not presenting the same argument Smokeskin did earlier).

I am Smokeskin...

[Smokeskin]

Now, if you argument is that the wingsuit specifically can't do this because the surface area of the wings is too small to generate significant lift OR breaking power, then just state that plainly, but don't insult my knowledge of physics.

You yourself implied it in post #50.

I never said that nothing without trust couldn't go upwards. In the earlier post I said that

Exchanging speed for altitude: A wingsuit doesn't have thrust and doesn't have the lift. You're never going to be going upwards in one of these things.

That's pretty specific.

You then said that pointing upwards made you go upwards, which you claimed was very basic physics, but is frankly nonsense so I responded:

Your velocity vector doesn't change with facing. What does change is the forces that work on you from airflow, and that can change your velocity. Since you are not able to generate lift (ie the upward component of the forces from airflow) of a larger magnitude than gravity, you are not able to generate any acceleration in an upwards direction - so you have no way of going upwards.

I don't know how you reached the conclusion that you'd go upwards by changing facing. Do you think that changing your facing will change the direction of movement in the same way?

I have a very hard time seeing how the bolded part with "you" could be anything but wingsuit - obviously there are lots of things that can generate lift larger than gravity. Airplanes for example (they generally don't move upwards by pointing thrust down, but by going fast enough to generate sufficient lif).

I explained precisely how the physics of lift work. I don't understand how you can think that is an insult to your knowledge of physics.

I also didn't understand what you meant about changing facing changing your direction of movement, and asked you to explain it.

[nezumi]

I feel like I've made this mess, so perhaps I can help straighten some of it out (IMG:style_emoticons/default/nyahnyah.gif)

Smokeskin - most of my last post was in response to Aaron (except for the bit under the edit tag - which I included only in specific response to your comment). Yes, realizing now that the bit about gliders is a completely different discussion, and one that I started because at least I understand how gliders work (but not so much parachutes), your comments make more sense and I understand your point. It might be possible with a wing-suit - if the wingsuit had enough lift area to actually overcome its descent. So that was the source of my confusion there; I was entertaining two separate lines of discussion about two separate devices simultaneously.

Aaron - I do apologize. I did take your physics comment a little personally, because you seem to know what you're talking about, and I came away feeling like if I don't even understand how lift works well, boy am I dumb. So definitely a level of confusion and frustration and a lot of misreading on my part.

So there's my public apology for losing my patience and embarassing myself in public. *sigh*

I'll edit out the reference to posts, since that was specifically aimed at Smokeskin's comment, and I think that's been answered, and edit out the accidental triple post I just noticed.


On the topic at hand - alright, a wingsuit has insufficient wing area to generate lift greater than the fall of gravity. Still, this suit seems awfully convenient - it has a tiny foot print (both when deployed and when in use, physically and on sensors), looks to offer excellent mobility, and requires no heavy fuel or magic to use. So it definitely seems like it can be useful, but that use is limited by it requiring a long landing pad to stop on.

How else might you make landing possible? Perhaps permitting a body-hugging parachute attached at the hands and feet that turns you sort of into a squirrel biplane (or triplane)? A standard parachute? A tail hook? This feels like it should be an almost trivial question to answer, so I'm wondering what I'm missing.