Does the Community Want Better Aerodynamics?

[Murph]

Actually, Nao, that's a common misconception. A pressure difference is not in fact what causes lift. It's commonly taught, but it's incorrect -- go on, look it up. I had to, after making the same mistake many times. Lift is created because the curved upper surface deflects air downwards, and by the Second Law of Motion, that results in an upward force on the wing. It works because air clings to the surface of the wing, a bit of an odd quirk of fluid dynamics.

If they did work on pressure difference, stunt planes wouldn't work, since both lower and upper wing surfaces have the same curved surface (so that the plane can fly just as well upside down).

It's actually quite correct that the classic aerofoil shape generates lift via differential pressure, just it's not the only way of designing a wing. Classic non-aerobatic, non-supersonic planes (e.g. big passenger & transport planes) make significant use of it to generate far more lift than mere deflection alone could generate. It's taught by the RAF, amongst other people, and I'm quite inclined to trust their opinion on the matter. Stunt planes and supersonic planes are very much a different case.

[Amram]

im just going to leave this here: A Physical description of Flight, David Anderson(Fermi National Accelerator Laboratory) and Scott Eberhardt(Dept. of Aeronautics and Astronautics, University of Washington)

Take the case of a Cessna 172, which is a popular, high-winged, four-seat airplane.....

....

Using the Popular Description of lift, the wing would develop only about 2% of the needed lift at 65mph(104km/h), which is "slow flight" for this airplane. In fact, the calculations say that the minimum speed for this wing to develop sufficient lift is over 400mph(640km/h)

The Popular description of lift being the Bernoulli principle. You can find that on page 2.

Or if you'd rather a shorter shot at things with much less detail, how about a word from NASA?

Incorrect Lift Theory #1 And look at that, its Bernoulli's principle.

The theory is known as the "equal transit time" or "longer path" theory which states that wings are designed with the upper surface longer than the lower surface, to generate higher velocities on the upper surface because the molecules of gas on the upper surface have to reach the trailing edge at the same time as the molecules on the lower surface. The theory then invokes Bernoulli's equation to explain lower pressure on the upper surface and higher pressure on the lower surface resulting in a lift force. The error in this theory involves the specification of the velocity on the upper surface. In reality, the velocity on the upper surface of a lifting wing is much higher than the velocity which produces an equal transit time. If we know the correct velocity distribution, we can use Bernoulli's equation to get the pressure, then use the pressure to determine the force. But the equal transit velocity is not the correct velocity.

found by following their links to the next page until about 4 pages later, here.

I trust a little reading can settle the Bernoulli debate regarding where the lift in a wing really comes from?

Edited December 24, 2013 by Amram

[Mmmmyum]

Why is there no clear cut answer for where lift comes from? Surely the people at Boeing, Aerospatiale, Airbus, Cessna, Piper, Mooney, etc know how their wings work?

[Murph]

Why is there no clear cut answer for where lift comes from? Surely the people at Boeing, Aerospatiale, Airbus, Cessna, Piper, Mooney, etc know how their wings work?

There is a clear cut answer, it's a combination of pressure differential (dominant in the classic aerofoil), and deflection/downwash. The balance between the two depends on the design choices and intended role of the aircraft, with sub/supersonic being one of the most significant design factors. Air crew and aerospace engineers understand it quite well.

[Superfluous J]

Why is there no clear cut answer for where lift comes from? Surely the people at Boeing, Aerospatiale, Airbus, Cessna, Piper, Mooney, etc know how their wings work?

Because they don't want us, the public to know the real truth: Wings don't actually work. What causes lift is the utter, sheer terror the pilot feels as he or she approaches the end of the runway.

It's true. In 1978 they ran tests by strapping pilots to Player Pianos and accelerating them down the runway. Sure enough, they took off.

(I don't know who I stole that from, and a quick Google search brought up nothing. Sounds like something Douglas Adams would say)

[78stonewobble]

To clarify my yes.

I'd love some more incentive to better design my rockets better and make sure they are aerodynamically effective.

I haven't spend a minute in the spaceplane hangar yet (still new), so for the effect / need there... I'll leave that up to others.

Though I do believe that we could go into infinite detail on "aerodynamics", so it shouldn't be needlessly complicated or "overcomplicated". It should add just an appropriate amount of challenge and realism, but not be a chore that takes away too much fun.

[Nao]

Thanks Amram for the links!

I worked with CFD for a while so i do know how wings work, but i've never been able to explain it well in simple terms. And since most of the "magic" is happening at the top of the wing i've always tried to put emphasis on pressure instead of air deflection as the latter lead to questions like "then why doors aren't good wings". Never thought about using the notion of Conada effect thou , that will help getting people to understand laminar flow.

@5thHorseman ROTFL good one !

[Leatherneck]

@Amramand Murph Thanks for the information.

Like Nao, I too know how wings work, and for me Bernoulli's Principle has always been the simplest explanation of lift. There's a lot less math involved, and the simple diagram usually is enough to satisfy curiosity.

Edited December 24, 2013 by Leatherneck

[astropapi1]

I think the poll speaks for itself. I've always used fairings for the sake of realism, so Iwouldn't mind better aerodynamics.

[sagirfahmid3]

I also vote for better aerodynamics! At the moment, I am using FAR mod, and Ferram did an AMAZING job with it. I love it.

In some ways, the game is made harder, but in other ways, easier. Getting to orbit now is much more realistic.

Honestly, it shouldn't take 4 Rockomax orange tanks with Mainsail engines to get just a Rockomax 1/2 grey tank into orbit--that is highly unrealistic. With far, it takes me only 2 tanks with Mainsails + 1/4th tank with Skipper to get into orbit. Much more realistic.

You also have to worry about your planes and rockets ripping apart due to drag and G-forces using FAR, and I absolutely love that challenge.

[CoolBeer]

In some ways, the game is made harder, but in other ways, easier. Getting to orbit now is much more realistic.

Honestly, it shouldn't take 4 Rockomax orange tanks with Mainsail engines to get just a Rockomax 1/2 grey tank into orbit--that is highly unrealistic. With far, it takes me only 2 tanks with Mainsails + 1/4th tank with Skipper to get into orbit. Much more realistic.

Sorry, but this is wrong.

If you want realistic(and I define "realism" as "the way things are in the real world") you would have the payload be roughly 3% of your rocket, if you mange 4% you would have an extremely good rocket. (If you want to verify this, look at what spaceX manages and look at what Apollo managed).

-Kolbjørn

[TYRT]

I only want multi-core and x64 support. You will feel like You're playing minecraft on a high-end computer. Really, I think.

[luckyhendrix]

Why is there no clear cut answer for where lift comes from? Surely the people at Boeing, Aerospatiale, Airbus, Cessna, Piper, Mooney, etc know how their wings work?

There is a clear explanation for lift. But to explain it, it is needed to understand advanced mathematical concepts , like for instance : controls volumes, surface and volume integrals , divergence and rotational, complex harmonics functions, etc ...

So this is why there are simplified explanation used to expose the theory to the public but often a lot of details and even sometimes "trueness" is lost in the process.

See, I'm an student in aeronautical engineering in my last year now, and of course,I've seen how lift is created , but I could not explain it with out starting with a few hours long lessons on fluids mechanics, that only people with already a strong mathematical background would understand.

There is a clear cut answer, it's a combination of pressure differential (dominant in the classic aerofoil), and deflection/downwash. The balance between the two depends on the design choices and intended role of the aircraft, with sub/supersonic being one of the most significant design factors. Air crew and aerospace engineers understand it quite well.

You should note that those two effect are not independent actually, both are consequence of the conservation of momentum in the fluid, and that fluid can not slide on a surface (the speed of the fluid particle in contact with the wing is zero) .

Edited December 26, 2013 by luckyhendrix

[LameLefty]

There is a clear explanation for lift. But to explain it, it is needed to understand advanced mathematical concepts , like for instance : controls volumes, surface and volume integrals , divergence and rotational, complex harmonics functions, etc ...

That's entirely untrue; I have a bachelor of science in aerospace and mechanical engineering and was the aerodynamics engineer for our senior design project. Those concepts are necessary if you're going to computationally model lift, but to analyze, understand and make us of it? Complete rubbish. Hardly anyone in mainstream aerospace design even thought about lift in those terms until the 70's/early 80's when supercomputer computational capacity got good enough to do detailed CFD. Before then it was all Bernoulli, wind tunnel and experimental flight tests, and LOTS of iteration.

In fact, NACA (the predecessor organization to NASA) did so much experimental work on wing and airfoil design that they published volumes of "standard airfoils" with all the standard coefficients tabulated out. Aircraft designers routinely picked a basic airfoil from the catalog and designed their aircraft around it.

[Psycix]

Sorry, but this is wrong.

If you want realistic(and I define "realism" as "the way things are in the real world") you would have the payload be roughly 3% of your rocket, if you mange 4% you would have an extremely good rocket. (If you want to verify this, look at what spaceX manages and look at what Apollo managed).

-Kolbjørn

But these rockets achieve 10,000 m/s delta-V instead of 4500 m/s, so payload fraction is diminished accordingly.

[luckyhendrix]

That's entirely untrue; I have a bachelor of science in aerospace and mechanical engineering and was the aerodynamics engineer for our senior design project. Those concepts are necessary if you're going to computationally model lift, but to analyze, understand and make us of it? Complete rubbish. Hardly anyone in mainstream aerospace design even thought about lift in those terms until the 70's/early 80's when supercomputer computational capacity got good enough to do detailed CFD. Before then it was all Bernoulli, wind tunnel and experimental flight tests, and LOTS of iteration.

In fact, NACA (the predecessor organization to NASA) did so much experimental work on wing and airfoil design that they published volumes of "standard airfoils" with all the standard coefficients tabulated out. Aircraft designers routinely picked a basic airfoil from the catalog and designed their aircraft around it.

yes , you are right, to design an airplane you don't need to know that ,you just use correlations, curve fittings and numerical resolution N-S equations ... But, to answer the question "why is there lift ?" Ideally you need to go trough some analytical development, looking at a CFD simulations doesn't give much insight.

And you can't answer to the question "why is there lift ?" without at least knowing what a Boundary layer is, or how these create vorticity in the flow,

and how this vorticity can be directly linked to a force. All these notion making use of the concepts I listed earlier.

Edited December 27, 2013 by luckyhendrix

[Beowolf]

NACA (the predecessor organization to NASA) did so much experimental work on wing and airfoil design that they published volumes of "standard airfoils" with all the standard coefficients tabulated out. Aircraft designers routinely picked a basic airfoil from the catalog and designed their aircraft around it.

I miss my old Cherokee-140 and it's NACA 659-415 Hershey Bar wing so very much!

The angle-of-attack I could get after I added vortex-generators to the leading edge defied belief. Short-field takeoff literally became: Accelerate to 45 mph, pop flaps to 20-degrees, yank the wheel clear back into my belly button until we'd cleared the trees, then lower the nose into a normal cruise-climb.

The flaps were controlled by a big lever between the seats that looked like a parking brake handle. Electric flaps took several seconds to deploy, but I could change my flaps in a fraction of a second. The VGs enhanced flap effectiveness hugely, to the point where I could essentially turn low-speed lift on and off like a light switch and with practice, I could plant the wheels within a foot of my target almost every time. The newer tapered wings on the Archers/Tomahawks were generally safer and more comfortable to fly, but tended to float in ground-effect hundreds of feet down the runway bleeding off speed.

Here's to you, N7044R. The 550 hours we spent flying together were some of the best times of my life! I just now realized that sweet girl turned 50 last September. I hope she's enjoying her new life, and is properly appreciated by whoever flies her today.

--------

Sorry about the off-topic stuff. Here's the KSP part:

I'd love better aerodynamics for rockets, particularly a drag penalty for big, unstreamlined payloads without fairings. But I don't particularly care about the planes. I doubt I've spent over an hour in SPH since it was introduced. Flight sims depress me.

Flying a light plane is a whole-body experience. I probably got nearly as much flight data from my buttocks as I did from the airspeed indicator, and considerably more than that from the feel of the wheel in my hands. Even a $500 PFC flightsim yoke feels nothing at all like the real thing, and I can't get immersed and believe I'm really flying. It's a bummer.

[Dante80]

Here is a nice video from the KerbalKon that shows the current aerodynamics placeholder.

I don't know about you, but I find FAR...eh..far more enjoyable for the game. Its a nice preview on how Squad could change the current placeholder in the future.

A better aerodynamic system can ONLY do good for the game. C:

[RuBisCO]

Question: does "better" aerodynamics translate into a need for shrouds and heatsheilds?

[Dante80]

Well, if re-entry ever becomes something more than a graphical effect, then heatshields would be handy if you like your Kerbals rare and not..well done. Have in mind that the stock capsules look that they already have heatshields at their bottom. I think Squad has said that re-entry heat is a planned feature.

Regarding shrouds/cones/fairings, I don't really think that it would be compulsory to use them, but having them would make your rocket more efficient. It just makes sense, drag according to mass only is a stopgap that produces more problems than it solves..

[Eric S]

Question: does "better" aerodynamics translate into a need for shrouds and heatsheilds?

Yes and No.

Well, if re-entry ever becomes something more than a graphical effect, then heatshields would be handy if you like your Kerbals rare and not..well done. Have in mind that the stock capsules look that they already have heatshields at their bottom. I think Squad has said that re-entry heat is a planned feature.

Harvester has said in the past that he wants reentry heat not to require heat shields. Before anyone gets upset about that not being realistic, keep in mind that we're reentering Kerbin's atmosphere at about a third the speed that you would enter Earth's atmosphere, so reentry heat would be much less an issue. You'll probably still need to pay attention to your more delicate parts, but you won't need dedicated heat shields. Then again, the devs may change their minds and go with full heat shields, or ditch the idea of reentry heat.

[Guest]

Well, I think that the pool speaks for itself. KSP needs a better aerodynamic system, IMO as realistic as possible. Ideally, it'd use a Procedural Wings-like approach to making wings (because in a detailed simulation, they need to be tailored to the plane) and simulate airflow over the wings like X-Plane (it can be done with reasonable computer tasking, as X-Plane proves). Remember that aerodynamics are simulated only for active vessel and immediate neighborhood, usually meaning a single airplane/rocket.

Mind you, there are many physical constants that could be changed to make this more or less forgiving, for gameplay reasons. Kerbin is a fictional planet, so it's always going to be easier to fly on it.

[Dooz]

Nooooo.. when i tried farram it messed up all my rockets and made them not able to make orbit

But still better aerodynamics would be neat

[Wahgineer]

Its probably because you didn't have any fairings over your payloads, no nose cones, or tried using asparagus staging right off the bat (asparagus staging is aerodynamically unsound). If you cover your payloads, make tall, spindly rockets, and use nose cones, getting into orbit should be easier, since the atmosphere is much thinner when you use FAR.

[Bloodbunny]

Seeing as how the very first mod I always install when going to a new version is FAR, I voted yes