[1.3.1] Ferram Aerospace Research: v0.15.9.1 "Liepmann" 4/2/18

[DaMichel]

The flow at the trailing edge cannot effect the flow at the leading edge, much less the surface area in between, because all of that surface area is no longer there to be effected due to the forward motion vector of the entire plane. Those events happen AFTER the lift. The air doesn't magically travel over the top of the wing at one speed, then massively accelerate around and underneath to catch back up with the already-accelerating plane (engine thrust) in FRONT of the wing to then push it up. At supersonic speeds, this occurs with some actual impact, but not at takeoff speeds.

The body of the wing can affect the flow upstream of the leading edge for sure @subsonic speed. As Ferram4 pointed out somewhere, disturbances, like a wing, cause pressure and density fluctuations which travel in all directions with the speed of sound. Thus you get pressure variations upstream of the wing. The pressure distribution plus inertia mostly drive the flow around. There are viscous forces, too, but as first approximation they can be neglected. Mathematically, this is formulated in the Euler-and Navier-Stokes-Equations. Your probably want to look this up.

[Lutin]

Please watch this:

Not the first 5 minutes, not the first 15 minutes. The whole thing.

[Bakase]

^ Tomato is a fruit isn't it?

Right ok. Well that sucks. I've only been playing a couple of days but I can't go back to stock now knowing that the air resistance model sucks but this is unplayable for me cos I play with mortal kerbals and no reverting. I guess I'll just put this game on hold then until this is sorted.

How can I find out when there's an update and what's included?

Thanks.

You can download the current dev build from the github.

I guess to find out when an update is is to check here and the github! Look at the update log to know what's included.

- - - Updated - - -

Please watch this:

Not the first 5 minutes, not the first 15 minutes. The whole thing.

This'd be useful if he had a common misconception, such as one of those two.

He doesn't, though! He's made a completely new one.

[Red Iron Crown]

Moderation: It would be better to start a thread in the Science Labs to discuss the hows and whys of lift and aerodynamics, this thread is for discussion of the FAR mod itself. Please let the topic of lift drop or continue the conversation in a thread in the appropriate place.

Further, please refrain from making personal attacks against other posters, no matter how wrong you think they are. Argue the post and not the poster.

Thank you.

[Kitspace]

Why do all those misconceptions exist at all?

And what of those does the mod consider here?

[Bakase]

Why do all those misconceptions exist at all?

Because lift is a highly complex principle deriving from a number of factors that it's nigh impossible to fully explain without delving into complex fluid dynamics calculations. As such, most people have been taught a highly simplified version of it that relies on eliminating all but a few factors and hedging the explanations of what gives rise to these things.

[ferram4]

@Jared: You just called me naming all the inter-related parts of the same theory fragmented... why? I see that you haven't bothered to look at them, and that this description:

The flow at the trailing edge cannot effect the flow at the leading edge, much less the surface area in between, because all of that surface area is no longer there to be effected due to the forward motion vector of the entire plane.

Shows that you don't even understand the defining factor of subsonic flow, which is that downstream effects can affect the upstream conditions. That's the whole thing that makes subsonic flow subsonic, as opposed to supersonic flow. If you consider it wrong that someone should be annoyed after the person they're talking to (claiming to ask for answers) simply hasn't bothered to look at any of the stuff that has been provided as answers, then I dearly hope that you come across someone exactly like you in your field. I expect that you will be perfectly understanding when they deliberately ignore everything that has been said to them. I expect that you will be perfectly understanding when they claim that the integral parts of a theory are proof that it is fragmented (seriously, thin airfoil theory starts as incompressible (linear by definition) potential flow, which leads to the standard solutions of source, doublet, and vortex flows (with singularities at their origins, hence the name...), which leads to creating the flow over an airfoil by a distribution of those singularities (hence, singularity distribution method), which then simplifies down to the defining characteristics of thin airfoil theory:

that dCl/dAoA = 2pi per rad

that camber shifts the AoA of zero lift by the factor -1/pi * integral{dz/dx * [cos(theta) - 1] dtheta}, where x = 0.5 * (1 - cos(theta) and z is the height of the camber line

that there is some amount of upwash ahead of the airfoil, and some amount of downwash due to the circulation about the airfoil caused by the vortex distribution

that the entire distribution of lift is built around the fact that the flow must separate at the trailing edge, forcing the pressure gradient about that and the vorticity there to 0

that all of the lift on the airfoil is created by the requirement that the flow separates at the trailing edge, and that in the absence of that, no lift is created

But it seems like you didn't bother to look at any of that. If you're really here to learn, I don't see why you didn't bother. Oh, btw, that fluid sim you used? You might want to try it without the airfoil stalled, since I know that you picked that orientation to deliberately reduce the circulation around the airfoil and create less upwash at the leading edge. And you had massive flow separation even at 0 AoA, which indicates that you set it up with either too low a Reynolds number or too large a cell size. Next time, for your counter-example, you might want to actually set up the sim properly; maybe show the settings that you used as opposed to hiding them, hmm?

@Kitspace: Because teachers fail at explaining things, and then people like Jared muddy things up. Follow that with the fact that we focus on Bernoulli's equation a lot (which is more useful as a tool rather than an explanation) and the fact that no one wants to accept, "they're both correct explanations, just coming from different angles," and you get flamewars on the common correct topics, which keeps people from dealing with equal-transit-time theory and AoA-doesn't-produce-lift theory and mystical-earth-focused-lift theory.

FAR uses the best models that can be run in real-time. In particular, it uses a modified form of lifting line theory, which is a generalization of thin airfoil theory to 3d wings. There are a few modifications to handle sweep, changes in Mach number, and of course, supersonic flow, where the trailing edge really can't affect the leading edge. But otherwise, it uses exactly the theories that I would point Jared to, if he would take a minute to actually read them rather than dismiss them in ways that prove he never bothered to look at them.

[Kitspace]

What kind of airfoil is used for calculations in game?

[damerell]

If it was a simple question, you'd have a simple answer.

Air molecules bounce off the wing. If you tilt the wing so they bounce off downwards, the wing must have exerted a downwards force on them. Hence they exerted an upwards force on the wing. That simple enough?

[Paadwyn]

I have a question...

Something is terribly wrong here, and I could use help to get this back on track.

I just started implementing mods, and I used the suggested FAR and Deadly Re-entry, installed with CKAN and Module Manager and ModularFlightIntegrator, as required. I have some other mods, looking at them, nothing really more than any other people have been using for their games. RemoteTech, RealChutes, TAC FUel Balancer, KW Rocketry...and so forth. I do have a couple that aren't 'standard' for people, KSP Interstellar Extended and all the USI (Tools, Survival, Life Support, Kolonization, Freight, Exploration) Just to give people a hint as to what I'm running.

Now, my issue. I'm not slowing down upon re-entry from orbit. Sure I've seen this post before, and people explaining as to how to do it.

It's not working. In fact, my pod coming in from an AP at 80,000 meters and my PE set at even as low as 5000 meteres. Results in my NOT slowing down, in fact I'm gaining speed. The only time I am slowing down is during my ascent back up to 80,000. In which I gain my speed back up to orbit velocity of approx. 2300m/s when I come back down. It's like the atmosphere is doing NOTHING at all to slow me down, but it sure likes to burn up my craft.

I've watched video's and mimicked their re-entry, to no avail. My mechanics don't even follow close.

So, I've figured out that there must be something terribly wrong. I can't be the one doing this bad, when I'm doing the same thing as others.

In FACT, for more weirdness....I've flown my rocket NOT even on a sub-orbital path, staying below 30K, and I can reach 1800ms, gaining speed as I fall to my inevitable doom.

So...what's wrong people? This is obviously very very wrong.

[Paadwyn]

Ixnay my previous post, I will leave it up there for anybody else to see, as it my help them....but I got it working.

Seems after my frustrations at 2am, I went to bed.

Tried the next day after restarting the game. Bingo.

Worked beautifully. Brought my pod back in from orbit like a champ - except that I had science modules and goo, which made it spin around during re-entry. Everything survived, expect the goo containers, bugger it But that's my issue, one I can easily fix with some design.

Past that, I did like the re-entry. It was going well, chutes deployed, came in at 3.5m/s into the drink.

Yay

Now...I wish I could alter my username, I misspelled it and it bugs me.

[FourGreenFields]

I have a question...

Something is terribly wrong here, and I could use help to get this back on track.

I just started implementing mods, and I used the suggested FAR and Deadly Re-entry, installed with CKAN and Module Manager and ModularFlightIntegrator, as required. I have some other mods, looking at them, nothing really more than any other people have been using for their games. RemoteTech, RealChutes, TAC FUel Balancer, KW Rocketry...and so forth. I do have a couple that aren't 'standard' for people, KSP Interstellar Extended and all the USI (Tools, Survival, Life Support, Kolonization, Freight, Exploration) Just to give people a hint as to what I'm running.

Now, my issue. I'm not slowing down upon re-entry from orbit. Sure I've seen this post before, and people explaining as to how to do it.

It's not working. In fact, my pod coming in from an AP at 80,000 meters and my PE set at even as low as 5000 meteres. Results in my NOT slowing down, in fact I'm gaining speed. The only time I am slowing down is during my ascent back up to 80,000. In which I gain my speed back up to orbit velocity of approx. 2300m/s when I come back down. It's like the atmosphere is doing NOTHING at all to slow me down, but it sure likes to burn up my craft.

I've watched video's and mimicked their re-entry, to no avail. My mechanics don't even follow close.

So, I've figured out that there must be something terribly wrong. I can't be the one doing this bad, when I'm doing the same thing as others.

In FACT, for more weirdness....I've flown my rocket NOT even on a sub-orbital path, staying below 30K, and I can reach 1800ms, gaining speed as I fall to my inevitable doom.

So...what's wrong people? This is obviously very very wrong.

Looks like already got reported and fixed.

Great mod. One thing is confusing me though. On re-entry as my pod hits the thicker part of the atmosphere below 30,000m it now continues to speed up, instead of slowing down. How come?

@andymc1: Known issue, should be fixed in the dev build, hopefully an updated version soon-ish once I get some other things fixed.

[Paadwyn]

Yeah, I had posted...however it's not showing up, that restarting the game fixed it.

Nice to know it's a known issue, and not just me having some mind numbing issue.

[Red Iron Crown]

Now...I wish I could alter my username, I misspelled it and it bugs me.

Post a request here: http://forum.kerbalspaceprogram.com/threads/122939

[Vegatoxi]

Three times i've tried to deal with FAR after 1.0

And now i can conclude that stock aero >>>...>>> FAR. At least for now.

Most of my crafts, which flies good in stock, completely messed up in FAR.

Russian IL-76 replica. Only craft which fly good enough to not break the keyboard in a rage attack

[spoiler=]

But... when i tried to turn it's just splash into piecies. Lolwhut??!

Russian Su-27 replica. Constantly flips to the back, constantly shakes in flight, almost uncontrollable. In stock aero it can do same what it's real prototype do. I mean supermaneuverability. But in FAR... it's pretty miserable.

---

And last - SR-71 replica, which flies exactly like a brick. Besides it's almost unreal to take-off despite the fact that center of lift matches the center of thrust.

[spoiler=]

In that facts - FAR not makes stock aero better. It makes it worser.

[Svm420]

Three times i've tried to deal with FAR after 1.0

And now i can conclude that stock aero >>>...>>> FAR. At least for now.

Most of my crafts, which flies good in stock, completely messed up in FAR.

Russian IL-76 replica. Only craft which fly good enough to not break the keyboard in a rage attack

[spoiler=]

http://cs625729.vk.me/v625729249/37f9e/UYxAu2G2-z0.jpg

But... when i tried to turn it's just splash into piecies. Lolwhut??!

Russian Su-27 replica. Constantly flips to the back, constantly shakes in flight, almost uncontrollable. In stock aero it can do same what it's real prototype do. I mean supermaneuverability. But in FAR... it's pretty miserable.

http://cs625729.vk.me/v625729249/37fa7/-0nyxddhMFM.jpg

---

http://cs625729.vk.me/v625729249/37fb0/NHx3G2N8PHY.jpg

And last - SR-71 replica, which flies exactly like a brick. Besides it's almost unreal to take-off despite the fact that center of lift matches the center of thrust.

[spoiler=]http://cs625729.vk.me/v625729249/37fb9/YSWDKJREjbo.jpg

In that facts - FAR not makes stock aero better. It makes it worser.

Those have design flaws that are very obvious if you even took the time to learn to build properly. I would love to see the graphs which are what matter not the pretty lines though they still matter just not as much. Also take your craft to the FAR craft thread to get help building right.

[Vegatoxi]

Those have design flaws that are very obvious if you even took the time to learn to build properly. I would love to see the graphs which are what matter not the pretty lines though they still matter just not as much. Also take your craft to the FAR craft thread to get help building right.

FAR positioned as real life aero. But in real life SR-71 flies prefect. As Su-27 to, even with supermaneuvers.

If you're right - real SR-71 cant fly. Lol.

But i take your advice, mb i'm not enough understand some things in FAR logic.

[Iskierka]

SR-71 doesn't actually "fly perfect", it's a very limited airframe. But, that does not mean you got the balance or shape correct at all, and aircraft are highly sensitive to even small changes. Just visibly looking, I can tell your vertical tails are too vertical, too far forward, and too long, and your wings are too narrow if you were trying to make a replica. But these things aren't necessarily your problems, and you definitely should go look up advice on how to build aircraft if you want to make something that works in FAR.

As for stock supermanoeuvrability, that's because stock aero doesn't model even basic things like stall that old FAR did, making very extreme-performance designs very easy. Extreme performance is possible in FAR, if to a slightly lesser extent, but requires much better design.

[Ryds]

[Vegatoxi]

Explain?

[Gamer217]

Completely stumped on why this NASA style orbiter is not working (Career, mostly stock with some tweakscale). During reentry the shuttle is fine till 50,000-45,000 the it snaps upward pointing towards space and spins wildly.

[futrtrubl]

Completely stumped on why this NASA style orbiter is not working (Career, mostly stock with some tweakscale). During reentry the shuttle is fine till 50,000-45,000 the it snaps upward pointing towards space and spins wildly.

http://images.akamai.steamusercontent.com/ugc/30745266801604881/94A0EBE230A6D35D6061474E9B348CFE597C3C06/

Better to ask that in http://forum.kerbalspaceprogram.com/threads/121176-Official-FAR-Craft-Repository

They will also need more information, at the very minimum the various graphs.

[ferram4]

@Vegatoxi: Point by point:

1) The IL-76 is an airliner, correct? Pulling absurd manuevers in an overloaded airliner will cause the wings to come off. You should probably post the wing area of your replica and its mass and then compare it to the real thing; I suspect that you will find that your "replica" is about 20-30 tonnes overweight.

2) Many problems with this Su-27 replica. For one, of course it flips back, you put the main gear in front of the CoM; if the gear is in the correct position, then all this proves is that you put the CoM in the wrong position. For two, your vertical tails actually look a little too small, which will cause yaw instability. For three, the cockpit / nose section looks like it's about 2m too short. For four, you have no leading edge extensions along the forward fuselage.

This doesn't appear to be an Su-27 replica. This seems to be a lot closer to a traditional early jet fighter, which will certainly lack supermanueverable capabilities. Should be rather fast, but very brick-like. And remember, supermanueverability is really only possible at Mach < 0.7. Higher than that leads to either disintegration or changes in flight characteristics making the plane more statically stable. Also, remember to check that it isn't overloaded with fuel.

3) I dunno how you managed to screw this up, but unless the entire thing is chock-full of fuel, that'll fly just fine. I've built plenty of SR-71s, and they've always behaved just as you'd expect; accelerate well, take off well, slightly unstable, tend to go sideways above Mach 3.5.

I think your designs are overloaded or aren't close enough to the real designs to function properly.

[plausse]

In Hollywood films they often use modified planes to act as other planes they can't get hold of for whatever reason. Making something that looks vaguely like a spitfire doesn't make it fly like a spitfire (although admittedly it will look cool and maybe share some aerodynamics).

Not trying to be arrogant, but when I build a far plane I focus more on niche - and borrow solutions from real life planes. Fact is some things are hard /tedious in ksp, and some things easier than real life. Say a certain supersonic airliner, but without the extending canards. Still looks the same... But now with a lift off speed from the fifth circle of inferno.

[smunisto]

I, on the other hand, am kinda pissed that I only produce craft which strongly resemble real world ones.

This is mostly due to my limited knowledge about how to actually use the tools provided with FAR. Or the limited time I have to play which results in even more limited time to read the kindly provided help and tooltips by Ferram within the game.