Hysteresis, or Why sometimes you barely move forward

[Tonto 1]

[sarcasm]No, it's airspeed - cos I measured it on a GPS!

And we all know that the GPS is the holy grail of flight, and that every aircraft ever built was designed with ONLY GPS info.[/sarcasm]

t

It's the year of the Pig.

[yuri_base 1]

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To get out from behind the power curve, you have to add more power (for acceleration) and reduce the pitch angle to get the plane flying faster. Well, in a glider (wingsuit), your only option is to nose down and turn your altitude into airspeed to get back to the desired flight regime.

I noticed this "stall entrapment" mostly occurs after flat turns. So far, it happened just a few times - a couple of times on balloon jumps (light winds, not affecting groundspeed much), once in BASE (after flat 135 degree turn; no wind), and a couple of times on plane jumps (very poor glide in maxed out position, thinking, must be strong headwind, flat-turning 180 and still having very poor glide, like 1.0).

We need to understand the nature of the glide destroyers - more predictable stall entrapment for one and unpredictable flutter for two - to efficiently fight them. Poor glide sometimes is just not healthy.

Yuri

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[The111 1]

Oooooh, so it's airspeed because you measured it while in the air. Now I get it.

/also sarcasm...

www.WingsuitPhotos.com

[phoenixlpr 0]

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[sarcasm]No, it's airspeed - cos I measured it on a GPS!Laugh

And we all know that the GPS is the holy grail of flight, and that every aircraft ever built was designed with ONLY GPS info.Angelic[/sarcasm]

Look, he has a hammer, so everything started to look like nails....

We don't have to measure everything like your happiness in flight.

So how about finding some feasible tool for comparing flight performance?

We can use GPS, because they are commercially available and affordable.

I don't think that would be so hard to make a set of sensors for recording airspeed and temperature in flight.

[Tonto 1]

Too many variables.

We weigh a different amount on every jump. We jump through differnent air on every jump.

I watch soccer players who get paid millions try and put a ball in the same place each time and fail. What makes you think we can begin to be constant?

We are different on each jump. There are no constants. You have no need to measure my joy.

Just fly.

t

It's the year of the Pig.

[KrisFlyZ 0]

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I noticed this "stall entrapment" mostly occurs after flat turns. So far, it happened just a few times - a couple of times on balloon jumps (light winds, not affecting groundspeed much), once in BASE (after flat 135 degree turn; no wind), and a couple of times on plane jumps (very poor glide in maxed out position, thinking, must be strong headwind, flat-turning 180 and still having very poor glide, like 1.0).

We need to understand the nature of the glide destroyers - more predictable stall entrapment for one and unpredictable flutter for two - to efficiently fight them. Poor glide sometimes is just not healthy.

Yuri

Dude...

Turns screw up glide and there is nothing we can do about it. We do not have direct yaw control...so we have to use the roll control to induce a turn.


Anyway, its not the turn that kills the glide and there is no 'trap'...quit thinking up excuses and think of solutions . I have included examples of maintaining speed thru the turn but there have been instances when the speed falls. IMO, this is due to the pitch angle changing. If you are disciplined enough...you can maintain speed thru the turn. Maintaining glide through a turn is not possible.

Kris.

[The111 1]

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I watch soccer players who get paid millions try and put a ball in the same place each time and fail.

You just put into words something I've been trying to say for a long time...

www.WingsuitPhotos.com

[Pendragon 1]

If that dotted yellow line in the 2nd was your flight, then you were definitely outside the 1.5nm radius permitted and playing with the jumbos inside London airspace.

BTW - it is possible to make coordinated turns on any unpowered wing.

Speaking of which, do I care?

--
BASE #1182
Muff #3573
PFI #52; UK WSI #13

[phoenixlpr 0]

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I watch soccer players who get paid millions try and put a ball in the same place each time and fail. What makes you think we can begin to be constant?

We don't want to have constant reading, do we?

We might able to fly better if we could have some realtime feedback.

Think about those days when altimeter was not available, just a stopwatch! Has it made a big impact on our sport?

[base283 0]

Oh, Is that why you landed in the trees?
take care,
space

[Tonto 1]

You're losing something in the language.

t

It's the year of the Pig.

[yuri_base 1]

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A pitot reading will only give you a reading when pointing into the airflow. It will only tell you how fast you are going through the air, not true airspeed (unless you have a static reading too) to be a little more accurate, you need mulitple pitot probes and a flight management computer.

Now we're talking! Now, that's the collective brainpower of creative individuals sharing their passion!

So if we have a pitot tube with two pressure sensors measuring dynamic and static pressure, we know absolute airspeed V and vertical speed Vy. Then we know the horizontal speed, too: Vx = sqrt(V^2-Vy^2). So we have an L/D meter: L/D=Vx/Vy.

This will be a much more accurate L/D meter and provide instant feedback to the flyer e.g. via beeps, like vario.

The pitot tube will need to be mounted on a weathervane to point into the airflow. Maybe this is what's on the head of the Gibolin guy. But it seems they don't want to share.

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[piisfish 140]

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The pitot tube will need to be mounted on a weathervane to point into the airflow. Maybe this is what's on the head of the Gibolin guy. But it seems they don't want to share.

If you can read french there is some stuff on his blog : http://gibolin.bleublog.ch article number 4 (but feel free to visit the rest), in french...... AND in english

scissors beat paper, paper beat rock, rock beat wingsuit - KarlM

[ryoder 1,590]

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Birds don't know all this shit. That's why they fly well.

All the numbers and spreadsheets in the world don't make you fly.

t

Birds learned to fly efficiently through the trial and error of natural selection. Engineers prefer to get something done correctly in this generation, rather than hope some later generation perfects it, so they adopted math.

"There are only three things of value: younger women, faster airplanes, and bigger crocodiles" - Arthur Jones.

[yuri_base 1]

That's THE SPIRIT!!!
"Selling new wingsuits is not my point. What I want is to create. I could work with a brand or with any sponsor. To keep developping my project with "proper tools" (a good sewing machine, studies in a windtunnel, proper materials and not second hand ones, more time to create...) is my next goal. I would like to reach the technical and physiological limits of the free human flight, and allow the "birdmen" to fly always further..."

Thanks for sharing!

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[pchapman 279]

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So, you can "max out" and your body is at "usual maxed out" pitch of 10 degrees below the horizon, and yet in one case you fly like a bird [....], while in the other case - same body position, same pitch - you fall like a brick [....].

To put it all another way, you are pointing out how it is easy to confuse pitch angle with angle of attack.

It is difficult (particularly for the novice) to have a feeling for the angle of attack of the relative wind, so we naturally tend to use our pitch angle relative to the horizon as a reference, without always realizing what the AoA is.

A "good body angle" isn't useful if it isn't matched to an appropriate glide path.

All this can indeed be an issue after turns, where (without experience) one tends to forget one doesn't automatically and instantly fly fast in the direction one points. Even if one has the ability to yaw 180 degrees in an instant, that won't necessarily change one's velocity vector at all.

[VectorBoy 0]

There is no value, no price, no data worthy of the personal feelings my flights generate.

t

[pchapman 279]

YuriBase's posts get a little intimidating and occasionally overenthusiastic on the mathematics.

But be that as it may, Yuri's math here looks right. I especially liked the convenient analytical solution to Vx and Vy which didn't require sine's and cos's (which I went through to confirm the numbers -- looks like it's all set up for sea level, 80kg as the assumptions). Where did you get those equations, or did you derive them, Yuri?

The shape of the curves depend heavily on the inputs for lift and drag curves. Without debating exactly what they should look like for a wingsuited jumper, they look reasonable as a starting point -- based on the tested characteristics of a simple airfoil, with L/D kept down to an assumed maximum.

In the example given, Yuri allows a good low angle of attack lift coefficient (like a 'real wing' pre-stall) that creates a big lump in the L/D curve, which in turns creates the big squiggles in some of the other graphs -- So that at the same body angle one might be in flight at either high or low glide ratio.

If one has a much smoother L/D curve, perhaps for a person tracking without a wingsuit, one doesn't get those effects. (I once did similar graphs, for that situation.)

As Yuri says, this all assumes that a jumper can trim at any angle of attack, with a zero pitching moment. Without that assumption, it just means that they might have to 'skip' certain areas on the graph because they can't consistently hold a certain angle of attack, at least with whatever body shape gives the assumed lift & drag curves.

[Tonto 1]

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Birds learned to fly efficiently through the trial and error of natural selection. Engineers prefer to get something done correctly in this generation, rather than hope some later generation perfects it, so they adopted math.

So... if math has always been there... why do aircraft keep getting better?

t

It's the year of the Pig.

[VectorBoy 0]

So... if math has always been there... why do aircraft keep getting better?

t

[Tonto 1]

But we are skin and bone. No better construction tech. No better materials.

t

It's the year of the Pig.

[piisfish 140]

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But we are skin and bone. No better construction tech. No better materials.

please read Gibolin's blog (link above), apparently Ikea chairs can help you fly better

scissors beat paper, paper beat rock, rock beat wingsuit - KarlM

[Costyn 1]

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Turns screw up glide and there is nothing we can do about it. We do not have direct yaw control...so we have to use the roll control to induce a turn.


Anyway, its not the turn that kills the glide and there is no 'trap'...quit thinking up excuses and think of solutions . I have included examples of maintaining speed thru the turn but there have been instances when the speed falls. IMO, this is due to the pitch angle changing. If you are disciplined enough...you can maintain speed thru the turn. Maintaining glide through a turn is not possible.

Kris.

I dunno man, I've seen Loic do some pretty damn flat turns on video. Of course, he's not doing optimal flight when he's skirting the cliff-sides, but still, those turns look pretty flat.

Costyn van Dongen - http://www.flylikebrick.com/ - World Wide Wingsuit News

[yuri_base 1]

I agree with your thoughts. You explained in plain English what I'm trying to explain with squiggles.

You can easily derive the equations if you write the components of forces:

Fx = L*sin(A) - D*cos(A) = 0
Fy = M*g - L*cos(A) - D*sin(A) = 0

(L = lift, D = drag, A = glide angle, M = mass)

and then replace sin and cos by

sin(A) = Vy/V
cos(A) = Vx/V

and lift and drag by

L = (1/2)*Cl*ro*S*V^2
D = (1/2)*Cd*ro*S*V^2

where ro is the density of air, S is the surface area of wingsuit. ro, S, and M end up being wrapped in an empirical constant K:

K = sqrt(2*M*g/(ro*S))

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[KrisFlyZ 0]

Where did the numbers for Cl and Cd come from?

Kris.