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

ferram4

By ferram4
in KSP1 Mod Releases

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BudgetHedgehog

BudgetHedgehog

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Are there any other ways to slow down. Even if I turn all the engines off, it seems to take a very long time before I slow enough to land safely.

All very good tips so far, but another good one is to dump any un-needed fuel. High mass means high kinetic energy which means it's not going to slow down easy. I find TACFB immensely useful for this and pretty much the only reason I have it installed - dump excess RCS and oxidisor during descent and most of LF as well. Planes slow down pretty easily after that.

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blowfish

blowfish

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How does FAR treat angled body lift? When I build something like this, are the side pods acting as wings or fins?

Body lift is always going to be down if you're flying forward with a positive AoA. It's not dependent on the part's orientation.

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Klingon Admiral

Klingon Admiral

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Am I the only one having real problems with downright ....... control surfaces? The issues with them not properly settling down during ascent are nothing new, and while annoying not very serious, randomly deciding that a 90° roll angle would be pretty cool 300m away from the runway is absolutely game-breaking. Is FAR to blame or did Squad break SAS again? (Possibly the later, I also encountered some weird "ghost"-forces in orbit)

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Wanderfound

Wanderfound

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Am I the only one having real problems with downright ....... control surfaces? The issues with them not properly settling down during ascent are nothing new, and while annoying not very serious, randomly deciding that a 90° roll angle would be pretty cool 300m away from the runway is absolutely game-breaking. Is FAR to blame or did Squad break SAS again? (Possibly the later, I also encountered some weird "ghost"-forces in orbit)

On the latest version of FAR? Double check.

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ferram4

ferram4

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@Wanderfound: They act like non-circular bodies. They don't act like fins or wings at all.

@Forty21112: The 0.24.2-compatible versions of FAR do not function with the new wing parts at all. You would be best served by updating to the latest version of FAR instead of trying to find something "better" among the older, buggier, less-compatible versions.

@Klingon Admiral: Considering that control surfaces only do what you (or SAS or some other control system / autopilot) tells them to do, I'm not sure what problems you're having. I will need logs and reproduction steps for both problems, including exactly what I should find. This means numbers and proof for orbital shenanigans, especially since FAR doesn't even get to the force calculation code if the air density == 0.

@FreeThinker: Nope, and no plans to add them. No idea how to do it easily without causing lots of issues and without adding one more thing that will break when 0.26 comes out.

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Wanderfound

Wanderfound

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@Wanderfound: They act like non-circular bodies. They don't act like fins or wings at all.

:)

Let me put it another way:

Would a vertically rotated lifting fuselage like the sidepods in the earlier screenshot tend to contribute relatively more to yaw stability and less to lift than a horizontal fuselage like the core?

Does the tall and narrow fuselage on this one below have a significant effect on aerodynamic behaviour compared to a conventional flatter equivalent, or is the difference largely cosmetic?

screenshot118_zps0ff3d550.jpg

Edited by Wanderfound
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GabeTeuton

GabeTeuton

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Question, are their any options to pre trim my controls in the editor?

Depending on what you mean by pre trim there may be a way... i'm not sure if while the aircraft is just a .craft file the trim variables will show... but once the aircraft is loaded on the runway, make a quicksave, go edit it with a notepad (i recommend notepad++) and look for "trimpitch", "trimyaw", "trimroll"... all of those are together with pitch, yaw, roll, there you can set it to whatever (max 1, min -1)... The stock trim system is awful, depending on how much time (to the microsec) you are pressing the key, that's the modification it will suffer...

In case you are interested i'm working in an Autopilot that Holds Altitude, yesterday i tested it in a flight to the north pole and worked almost flawlessly, though it has to be tweaked by adjusting the values while in flight, due to the different aircarft settings available... (http://forum.kerbalspaceprogram.com/threads/68089-0-25-kOS-Scriptable-Autopilot-System-v0-14-2-2014-10-08?p=1513717&posted=1#post1513717) that's a modified version by a more advanced user on kOS, make sure you make the correction i noted at the end of the post (the original version i tested is some posts back)... and you'll need kOS mod, it's an amazing mod but it will work with only the Altitude Holder if you can't be bothered in learning the scripting the modder created...

The kOS modders are working in adding the trim feature to kOS, when that happens i may be able to make a more accurate altitude holder, currently depending on the settings you make it will wobble a little up and down increasing or decreasing altitude until the settings you selected reach the "natural" altitude, on that thead there's one or two comments on how to guess the correct (or more accurate) D and U variables, and you can always ask me!

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GabeTeuton

GabeTeuton

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Posted (edited)

@ferram4 i need to ask you a few questions on how some of the values in your mod are calculated, in order to replicate them for my autopilot system, should i ask here or do you prefer a PM? (in the case you are willing to answer me of course)...

Also if anyone else knows how this mod works I'm all ears, and i have 2 simpler question...

-what's the math behind the Air Density and Altitude (in other words how can I relate X altitude with Y Air Density, as shown in the far gui while in flight?

-the speed the static analysis show, is surface speed, angular momentum, or angular velocity?

TIA

(all those questions are in regards to FAR, not NEAR, just in case...)

Edited by GabeTeuton
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GabeTeuton

GabeTeuton

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density = pressure / (R_air * temperature_absolute). Kerbin uses Earth's atmosphere's gas constants in FAR.

awesome, now is there a chart of pressure/altitude or a way to calculate the pressure at said altitude? and what is R_air? (same as pressure, is there a chart for temperature/altitude or a calculation i can do? (this questions are related to the fact that what i'm trying to do is going to be based on the desired altitude of flight, so i need to calculate the AoA at the desired altitude and speed, i need to word everything in terms of altitude and speed pre selected by the user..

and so far the other question i have for ferram4 is (and I think this is the most important question): is there a way to calculate what AoA will give me said pitch (pitch as a number between -1 and 1)?

Thank you for you help NathanKell!

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Corovaneer

Corovaneer

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Something that I can't really put my finger on, but maybe someone else noticed it too - "new" 0.25 wings behave in a much more unpredictable way than "old" wings, especially the new swept-rectangle wing. Having two wings of comparable area and sweep made from new wing, and from old curvy swept wing will produce two radically different aircraft - with former much more likely to stall and tip over to the front and side and into spiral, and latter easily making combat turns with rudder firmly pressed down.

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NathanKell

NathanKell

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pressure at any given height is given either by

e^(-height_in_km / planet_scaleHeight) [ if CelestialBody.legacyAtmosphere is true ] OR

the evaluation of CelestialBody.pressureCurve for that height in km [ if CelestialBody.legacyAtmosphere is false]

Temperature is given by evaluating CelestialBody.temperatureCurve at the given height

The gas constants for Kerbin's atmosphere are given in FAR's atmosphere data cfg. IIRC R is 287.06 or so.

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GabeTeuton

GabeTeuton

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Posted (edited)
pressure at any given height is given either by

e^(-height_in_km / planet_scaleHeight) [ if CelestialBody.legacyAtmosphere is true ] OR

the evaluation of CelestialBody.pressureCurve for that height in km [ if CelestialBody.legacyAtmosphere is false]

Temperature is given by evaluating CelestialBody.temperatureCurve at the given height

The gas constants for Kerbin's atmosphere are given in FAR's atmosphere data cfg. IIRC R is 287.06 or so.

Okay... Found this under FARAeroData.cfg=

//Kerbin

BodyAtmosphericData

{

index = 1

specHeatRatio = 1.4

gasMolecularWeight = 28.96

}

So e is constant and easy...//-heightinkm is the desire altitude i'm guessing...//planet_ScaleHeight i have no idea what that is, or where to find it...// After Wanderfound suggestion (THANK YOU), i can now calculate air density at any height, should it be=

Air Density (5km) = e^(-5/5) = 0.3678794411714423 right?

This still stands as unknown if someone can explain further=

Temperature is giving by evaluating? (evaluating like apply the pressure curve function for kerbin???) (english is not my native language) If so, where do i find that function? (i'm saying function 'cause that's the translation for spanish if i'm understanding correctly, a function like "f(x) = 2x + 1", so evaluating 4 would be "f(4) = 2*4 +1=9", though i don't know which "function" is CelestialBody.temperaturecurve

gas constants is what? and what do i use it for?, i know it should be 28.96, according to FARAeroData.cfg, right?

I'm sorry that i didn't get half of what you said... please keep in mind that i'm not a modder, i know nothing about actual coding, and i don't know much about specific aerodynamics... the code i'm writing is for kOS, which actual "code" was made for people like me, with no previous knowledge on programing...

Thank you once again, and i hope you don't find my ignorance bothering...

Edited by GabeTeuton
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NathanKell

NathanKell

Posted
Posted (edited)

KSP, stock, considers density linearly related to pressure. FAR, however, will calculate density based off pressure, temperature, and gas laws. So that post is correct for stock KSP but not for FAR.

The problem is that using FAR's approach, you need to know the temperature at a given height, and unlike pressure, temperature is not set by formula but by interpolating from a table of height-temperature keys (and not linearly, either). This is why I was talking about using code to get what the temperature would be, since you can only get at Squad's data ingame (unless you write a plugin to dump it).

Apologies for my lack of clarity before. Put another way, while pressure is calculable via a scale height exponential decay equation*, density (which is not the same thing) is not, or at least is not in FAR.

*only holds true if you're on a planet whose atmospheric pressure is set in the legacy manner. All planets with atmospheres in RSS, by contrast, use pressure curves.

Edited by NathanKell
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GabeTeuton

GabeTeuton

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KSP, stock, considers density linearly related to pressure. FAR, however, will calculate density based off pressure, temperature, and gas laws. So that post is correct for stock KSP but not for FAR.

The problem is that using FAR's approach, you need to know the temperature at a given height, and unlike pressure, temperature is not set by formula but by interpolating from a table of height-temperature keys (and not linearly, either). This is why I was talking about using code to get what the temperature would be, since you can only get at Squad's data ingame (unless you write a plugin to dump it).

Apologies for my lack of clarity before. Put another way, while pressure is calculable via a scale height exponential decay equation*, density (which is not the same thing) is not, or at least is not in FAR.

*only holds true if you're on a planet whose atmospheric pressure is set in the legacy manner. All planets with atmospheres in RSS, by contrast, use pressure curves.

Thanks for the clarification, so in other words i won't be able to calculate what i need unless i learn how to "really" code and make a plugin to get that number i need, right? This value i was trying to calculate it to make the user of the autopilot select an altitude and get the air density calculated, so the script can later calculate the level flight AoA, now if under FAR i can't calculate the air density, how can i make FAR stability analysis calculate the AoA needed for level flight for a X altitude?? I mean when i do the analysis for SSTO's, as you guys told me i use 0.5, 0.04 and 0.01, mmmmm i believe i'm confused, is air density what i need to calculate the AoA? the inputs for that chart are "temperature", "air density", and "speed (in mach)"...

Speed is selected by user, temperature and air density are related to height, how do i tell the user of the autopilot to input under FAR's chart X temperature and X air density if the want a cruise altitude of 5km?, as an example.

I'll go a little further here and may be find a work around... provided i need AoA for level flight for my autopilot... i need just that so i can achieve that AoA during the flight and maintain altitude... instead of making my script calculate it i can just use the FAR stability data and make the script use that AoA provided there, and set the altitude and speed inside FAR's editor... so that solves the problem in a less sofisticated way... but it works nonetheless... the next problem is going to be to translate the pitch (which goes from -1 to 1) into a usable data, in other words the AoA for said pitch, now is there a way to calculate that?

I'm confident enough to say that the pitch value will change by the amount of elevons you have, the design of them, and the position in the plane as well, but rather than tweaking it until it gets there (which my current script kind of does) i would like to be able, if possible, to calculate that exact pitch number, is it possible?

And last but not least, i just don't remember this haha... but does far show the current AoA? it does right? under flight data? (i believe it is, so to save time i'll go ask the kOS devs if that value is gettable, if it's not, then there it comes the previous question, is it possible to calculate it, if it's not, then hmmmmmmm... will have to think a work around!

Thank you once again for the support, i have been receiving so much support from the kOS thread, and from this thread that i do need to make this happen! I will end up with a altitude holder that holds the exact desired altitude!

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slumpie

slumpie

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Posted (edited)

Does this mod fix the "infiniglide" bug with stock control surfaces?

Yep! Deflecting control surfaces with FAR will increase the drag of your vehicle, not speed it up. Magic turbines, flapping probes, and other infinite-motion vehicles are not possible with FAR installed.

I'm sorry ferram, but this is not correct.

The craft that exploited it has about 330 parts, but by far the most are wings and struts (it must be rigid to withstand 15+g loads at 500m/s just 100m above ground...).

Oh and it's not even my craft, it was made by a guy who thought it would never fly with FAR... I just removed the engines and a few other things, that's it.

  • It can as example glide from ground up to 10000 meters (It could go higher) without losing speed, ... no wait... with gaining speed. Simply by flying in a spiral with constant pitch input.
  • It can fly an infinite number of loopings directly above the ground, without ever coming close to low speeds, again just by holding the s key.
  • It can fly loopings at mach speeds directly above ground and break the terminal velocity by about the factor 2.
  • It falls up to 100m/s faster than the terminal velocity would allow (even at low altitudes)...
  • SAS is NOT needed, but somehow makes it even worse...

Shocking: That thing weights between 25 and 45 tons! Depending on how much ballast I use.

EDIT: I think I should upload a video...

EDIT: Derp...

Edited by slumpie
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