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yuri_base

The Great Confusion

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Yo!

There is a big confusion that gets repeated over and over again, and that is taking the concepts of powered flight and applying them to nonpowered gliding flight. The result is - wrong conclusions and delusions.

First of all, the force diagram for powered and nonpowered flight is totally different. In powered flight, there are 4 forces: weight W, lift L, drag D, and thrust T. In level powered flight, these forces form a simple "+" shape: weight down, lift straight up, drag horizontal and pointing back, thrust horizontal and pointing forward. The sum of these 4 vectors is zero in sustained flight:

W + L + D + T = 0

or simply

L = W
D = T

If you know L/D for given trim, you can easily calculate thrust required for level flight:

T = D = W/(L/D)

Or vice-versa: if you know thrust during level flight, you know L/D:

L/D = W/T

In nonpowered flight, there are 3 forces: weight W, lift L, and drag D. In gliding nonpowered flight, these forces form a simple right triangle shape: weight down, lift pointing at an angle up and forward, drag pointing at an angle up and back. The sum of these 3 vectors is zero in sustained flight:

W + L + D = 0

or by Pythagorean theorem

W^2 = L^2 + D^2

since L and D vectors are perpendicular to each other and weight is triangle's hypotenuse. If you know L/D, you can easily calculate lift and drag:

L = W*(L/D)/sqrt(1 + (L/D)^2)
D = W/sqrt(1 + (L/D)^2)

(these are simply that Pythagorean theorem rewritten in terms of L/D)

Do the equations for powered and nonpowered flight look similar? Since you're sleeping, I'll answer for you: no. Totally different animals.

Secondly, the design goals are vastly different.

Airplanes need to take up a certain load, transport it from A to B as fast as possible with as little fuel as possible, and take off and land at slowest speed possible. Airplane can have cruise speed of 500kts and landing speed of 175kts. Now, we know that dynamic pressure is proportional to speed squared. So at 175kts the dynamic pressure is only 12% of that of at 500kts. How does it generate as much lift at only 12% of dynamic pressure as at 100%? To achieve this feat, big airplanes use several methods. First, the simplest one, is to increase angle of attack, which increases the coefficient of lift. But it may not be enough of a measure for such wide range, so it extends the flaps (increases surface area), increases the coefficient of lift by modifying the camber of the wing, and uses high-lift devices (various appendages that increase coefficient of lift), slats, and even lift from the fuselage. Everything is put in line to land that two hundred ton monster!

From the formula for level flight T = D = W/(L/D) we see that the higher L/D, the less thrust is needed for cruise level flight. That's why in level cruise flight, the trim is streamlined as much as possible: flaps are flush with the wing, high-lift devices and other "stuff" are hidden as much as possible, the fuselage is horizontal (in-line with the airflow for minimum footprint). On landing, all those lift generating technologies are used to bring the big bird home safely. On take off and landing, they only care about generating as much lift as possible from limited airspeed, and for that they sacrifice L/D, the trust needed increases, but they simply crank up the engine to overcome the increased drag! Slow landing speed is achieved by increasing power to overcome the increased drag.

Back to wingsuits. In high-performance suits, we look for only one number: L/D. There's only one person on Earth thinking about taking off in wingsuit and just a few thinking about landing one, but for the rest of us - straight L/D people, that is, not the extra gay flocking crowd ;) - it's sustained flight at maximum possible L/D that's of interest. As you can see now - if you're not sleeping yet - none of the "technologies" used in airplanes to generate lift at the expense of increased drag - is useful for our purpose.

High-lift devices - not useful. Poor L/D.

Extending flaps - not useful. Poor L/D.

Slats - not useful. Poor L/D.

Any "cool developments" in powered aircraft should be taken through the prism of L/D: do they increase L/D or both L and D at the expense of lower L/D to achieve other goals?

Using Concorde as an example when talking about wingsuits = nonsense. Let Concorde engineers have their problems and us - our problems.

Using supersonic planes as an example when talking about wingsuits = nonsense. Supersonic - and powered at that! - aerodynamics is completely different from way-subsonic glide of wingsuits. Fuggedaboutid!

Discussing wing profiles of various - subsonic or supersonic - powered aircraft as example for wingsuits = nonsense. Wing profiles for powered aircraft are chosen based on given design criteria - payload, speed, landing/takeoff characteristics. If they need to sacrifice L/D to meet these criteria - they will without blinking their eye. In trash can you go!

Mentioning that powered aircraft use their fuselages to create more lift as an example for wingsuits = nonsense. Those supersonic jets strive for every inch of lifting surface to land on an air-carrier deck at ridiculously low speed compared to their supersonic cruise speed. Pure insanity!

Etc. etc. etc. etc.

Let's make 2008 special by thinking before we say something! Let's be a little bit smarter than in 2007. Remember, it's the Year of the Great Wingsuit Revolution, so don't relax! ;)

Yuri
Android+Wear/iOS/Windows apps:
L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP
iOS only: L/D Magic
Windows only: WS Studio

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The thing about this sport... it's about flying. Not talking.



Neeeeh....talking hapens in person...seeing someone face to face....just writing about it is way more fun...

For all we know Yuri doesnt even jump and is a 180 kg fat bastard who lives in his mothers basement and has never seen a women up closeB|

But he rocks at his math though! Bet he could outfly you by at least twice the distance if it came down to a writing contest!B|
JC
FlyLikeBrick
I'm an Athlete?

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All the yawns and jokes aside. Although it is a bit boring to read...the theory is sound and I agree that powered flight and non-powered flight are much different.

Comparing wingsuit flight to powered flight doesn't work.

Although comparing wingsuit flight to any rigid aircraft may be just as useless. We are venturing into unknown territory. We must proceed with R&D that is related to wingsuit dynamics. R&D that hasn't been done in the aircraft design world.
WSI-6 / PFI-55
The Brothers Gray Wingsuit Academy
http://www.myspace.com/cgwingsuitpilot
http://www.myspace.com/thebrothersgray

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For all we know Yuri doesnt even jump and is a 180 kg fat bastard who lives in his mothers basement and has never seen a women up closeB|




I'm pretty sure that he was, until his recent banning there,
Heavy trolling the commodore 64 forums. And now that he is banned there he can commit 100% of his focus here.

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All the yawns and jokes aside. Although it is a bit boring to read...the theory is sound and I agree that powered flight and non-powered flight are much different.


I second that.

Quote

Comparing wingsuit flight to powered flight doesn't work.

Although comparing wingsuit flight to any rigid aircraft may be just as useless. We are venturing into unknown territory. We must proceed with R&D that is related to wingsuit dynamics. R&D that hasn't been done in the aircraft design world.


I'm not sure reinventing the wheel is useful. We may have use for some of the existing stuff.

Meanwhile, Jarno ribbing Yuri makes my day every time.
Johan.
I am. I think.

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Yo!

[snip]

From the formula for level flight T = D = W/(L/D) we see that the higher L/D, the less thrust is needed for cruise level flight. That's why in level cruise flight, the trim is streamlined as much as possible: flaps are flush with the wing, high-lift devices and other "stuff" are hidden as much as possible, the fuselage is horizontal (in-line with the airflow for minimum footprint).

[snip]

Back to wingsuits. In high-performance suits, we look for only one number: L/D. .. it's sustained flight at maximum possible L/D that's of interest.

[snip]

Yuri


And then the man started to expound on the flaws of high lift gadgets from powered craft when applied to gliding craft (us, that is).

That's where he lost me - going off on a tangent. Keep on track Yuri - streamline the trim, rig the angle of incidence, stop eating and hollow out your bones.
Johan.
I am. I think.

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For all we know Yuri doesnt even jump and is a 180 kg fat bastard who lives in his mothers basement and has never seen a women up closeB|



Not that there's anything wrong with being a 180 kg fat bastard... ;)

-Blind
"If you end up in an alligator's jaws, naked, you probably did something to deserve it."

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