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I have noticed some wingsuits start flying faster than others.
What are the qualities of a wingsuit which causes faster starts besides the ability of the pilot ?

I do believe it has a lot to do with the pilot.

A lighter jumper will have a slower Terminal so would take off quicker, but so will a bigger suit.

Some people like to dive more on exit to gain extra speed to turn it into forward movement/lift.
If you notice, a guy might take off quicker then another guy who just drops below him, but the guy that drops below eventually shoots forward past him because he gained more speed and converted it into forward movement.
Another factor, Suits can have a larger tail giving a steeper angle of attack to produce more speed naturally.

Something like that

Big surface + thick profile = lower stall speed
so, can start to fly faster.

examples :
Apache : big surface, but thin profile = must fly faster, so start later.
xBird : big surface and thick profile = lower stall speed, can start to fly earlier.
Prodigy : small surface but you can run like hell and save your ass

Assuming the pilot is perfect, the wing suit has to exceed the stall speed to start flying. Larger wings, and often lower performance wings, will start flying sooner. A very high performance wing should take longer to start flying, if all else is equal.

Depends heavily on what your opinon of a "high performance" wing is

Yes. And unfortunately there are lots of different ways to measure wing performance.

Are we talking about more lift at a certain airspeed? More maximum lift at the optimum airspeed? A lower stall speed? A higher maximum airspeed?

Without defining our terms, it's hard to really discuss much.

For non motorized flying stuff, performance is often glide ratio (if not always, but sometime sink rate can be the shit)
For gliders, paragliders, hangglider ... Better glide ratio is achieved by thiner profiles, and faster wings.(and higher aspect ratio too, but not easy with a wingsuit and small arms )
So in this way, for a wingsuit, high performance often mean slowest start ...

Profile is really important in stall speed, that's why an apache with a bigger surface than a x as a slower start.

ive barely been WS skydiving, and im not approaching base WS probably ever, but i must ask, what is the reasoning behind the delay in opening the legwing after exit?
is this simply to throw you into a bit of a dive after a couple seconds to gain speed to plane out with?

forgive me for my most basic question

I think you risk going head down if you open the legs too soon. You delay the legs with the arms spread till you feel the lift, then open your legs. Could also be just to get some belly speed without having to dive.

I see 2 main reasons :
Angle control Spreading you leg slowly help you controlling your angle while speed increase and your wing start flying.

Stability issue. If you use full surface at low speed, you can stall the wingsuit. If you stall with legs and arms open, and not symmetric, you risk some brutal stall, flat spin, side sliding and other funny things

But, like with a pantz, if you start with the right angle straight away (not flat!) you can use full power from beginning of jump. Just need to do it right.


My 0.000000002 cents

Good jumps and happy end of the world year everybody

This statement does not make sense to me. It might be a language thing, or maybe we have different reference models.

Wingsuits fly because there's a fluid (air) that is exerting a force on a surface (the presented suit). We have lift, which is a component of this force, and drag which is another component. The amount of lift divided by the amount of drag at any given point gives us the L/D ratio at that time.

Stall speed is the speed that has a correlation to the angle of attack at which a flying wing no longer flies. I do not see what it has to do with how fast a suit starts to fly, but then maybe my reference model is not the same as yours.

The size of the presented surface, the pressurization time of the suit, and the air speed are the factors which determine how fast it will take for a suit to start flying, the way I see it.

For comparisons between suits and/or pilots, it is important to look at the L/D curve. e.g. a suit which is poorly pressurized will have a higher drag component, thus (all other things being equal) have worse glide. It would be nice to separate the suit from the pilot when looking at the L/D curve, but I'm afraid it's pretty difficult to do so.

I'm not saying that I am right in my explanation, but I do feel a discussion of our models and thought patterns are in order. It's not magic that makes a suit fly, after all, and the science behind it is important if we want to be anything more than consumers. And it's not about wing suits. It's about physics, about truths eternal :)

I'm not a wingsuit pilot and I don't have any degrees, so take this under consideration while reading anything that I write, but don't dismiss anything because of those two facts either.

Steeper as in higher AoA? Angle of attack is the angle between the chord line of the jumper/suit/flying meatball and the vector of the force exerted by the oncoming fluid (/relative wind). I think you mean a higher angle between the chord and the gravity vector. But then again, too high and it would not be favourable either.

Wings with lower stall speed create more lift at low air speed. So you don't have to increase the angle to start moving forward. And they accept more angle too before stalling (i don't know the English words to describe the angle compare to ground, and the angle compare to air flow, witch is the interesting one)

Wings with thin profile don't create much lift at low air speed, so what you can try is to increase the angle (more "flat") to create some lift at low speed, and here comes the troubles, you stall the wing ...

I'm not sure i explain it well, English is not my mother language ...

Edit : fixed the quote

MontBlanc typed:

i don't know the English words to describe the angle
compare to ground, and the angle compare to air
flow, witch is the interesting one

Is the word "Relative" ?

Sebcat typed:

It might be a language thing...

I doubt it, your written English is excellent

In French, the word is "Incidence", and look like the English name is really close : incidence angle
(Oder Einfallswinkel vielleicht ?)

Well, stall speed _is_ a given angle of attack for a specific aircraft. It's the definition of stall speed. Airspeed does not determine when a stall occurs, only AoA. The only reason we speak of stall speed is that it's easy for a pilot to look at his airspeed indicator and see if he's in a stall or not, or if he's getting close to one, because the AoA also determines his airspeed.

As long as a falling object displaces air at an angle from the direction of the relative wind, it's going to generate lift. Now, it's also going to generate drag, and the sum of these vectors are your glide. High AoA is a high lift, high drag configuration e.g. and that's why we flare our canopies.

If you want your suit to start to fly early, you want to clear something. In order to do so, you must have high glide early on. So we want to have as much lift as possible, with the least amount of drag possible. The suit that will start to fly the fastest must have the highest L/D ratio, all other things being equal. Which they're not. It's possible to have a poor L/D ratio early in the jump because your suit is creating a lot of drag, due to e.g. pressurization issues. A small suit with relatively big and well placed inlets will pressurize faster, but it will not be able to generate as much lift as a bigger suit, thus having a lower L/D ratio overall. But it might still start to fly sooner.

So after three seconds, suit/jumper configuration A might have a glide ratio of 2, but that's about as good as it's going to get for the duration of this jump. Meanwhile, suit/jumper configuration B might have a glide ratio of 1.8 after three seconds, but his L/D will still improve and at 4 seconds it might be up at 3.

So the question might not only be about which suit starts to fly the fastest, but also which suit will start to fly the fastest relative to its overall performance? The fastest increase in glide in time from launch to "terminal"? Imagine the curve where you have the L/D ratio on the Y axis and time on the X axis. A function of time that determines your L/D. I guess the question is, what can this curve look like? Will it be linear? Which factor can I look for in a suit that will probably yield a certain L/D over time curve?

The L/D ratio of a wingsuit is very complex. You can not calculate it, you have to do empirical testing, and then you have to rely on the "all other things being equal". Or you can assume things, because sometimes you just know that a prodigy will not outperform a V4, until the day you see someone who's a really shitty or a really good pilot, but these generalizations are often times good enough, because we can determine if the performance we see from the shitty pilot is because of the pilot himself just by looking at him flying, and then we can discard that data. Problem is, we might have a bias.

I think AoA will be the major factor in determining the L/D over time curve. So it really is up to the jumper. But that's my personal, non-scientific view.

It's not really applicable to liken a wingsuit to a traditional, rigid, cambered airfoil. There's no laminar flow over the wings of a wingsuit for example. I would say that you are correct though from observations, but I still don't know why that is. It's not some mystery to mankind, it's just that I don't have the math background to figure it out for myself and there's not a lot of information to look for.

Again, I'm just relating my understanding here and it might be wrong. But having had discussions about lift and drag with skydivers who think "lift" is about being "light in a formation/floaty", I just want someone to step up and either put forth a valid reason of why I'm wrong and explain it to me so that I understand, or confirm my views.

You are correct that a wing will stall at higher speed with a high enough angle of attack, if the wing is already at a speed that generates lift. Air speed, and AoA both determine a stall. Airspeed also determines if a wing stalls, because, if there is not enough air flowing over and under a wing at a high enough rate (air speed) it will not generate a pressure differential to create lift... At a low enough air speed - the angle at which the wing stalls will be 0 - Stall Speed.
The term I think that applies to your definition is the "Critical angle of attack"." A wing can stall at any airspeed or any attitude, but will always stall at the same critical angle of attack". As I said before, that angle will be zero, if the speed is slow enough.

What you are describing in regards to a no-lift situation is not a stall. And to use that as the definition as to when a suit starts to fly would be like saying "a suit starts to fly when it generates lift", so "it starts to fly when it starts to fly". And there's more factors than airspeed there.

You can consider lift to be a function of AoA. Same rate, same wing, etc. Initially, when the AoA increases, so will lift. At some point though, lift will start to decrease as the AoA is increased. This is the critical AoA. A stall is simply what occurs when you pass the critical AoA. If you're above that angle, lift decreases, AoA increases further and airspeed drops as a result. This is the relationship between airspeed and AoA.

A stall is only about AoA. By definition.

Damn dudes, just jump off the cliff and fly the damn suit...this isn't rocket science, its Wingsuit BASE ;)

i like what you just said =)

What are you a noob? ;)

Yes, you are correct. I was not clear on the definition. This is what I was getting at,
"Stall Speed" - "Stalls depend only on angle of attack, not airspeed. Because a correlation with airspeed exists, however, a "stall speed" is usually used in practice. It is the speed below which the airplane cannot create enough lift to sustain its weight in 1g flight"

Airspeed and angle would be the primary factors in a wingsuit starting to fly. The speed and angle depending on the wingsuit.

Having your shoulders and leading ledge pointed in the direction of the relative wind and a stable position with out rotation, lead to faster starts in my experience. That start time is different with each suit and the jumper.