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

[capran]

Is it just me, or does everyone have control issues with FAR? Every time I try it out, things look great for a little while, but then all of a sudden my planes and rockets start doing backflips and somersaults for no good reason and the only cure is to quit and reload. If I remove FAR, things work as they should.

[BudgetHedgehog]

Is it just me, or does everyone have control issues with FAR? Every time I try it out, things look great for a little while, but then all of a sudden my planes and rockets start doing backflips and somersaults for no good reason and the only cure is to quit and reload. If I remove FAR, things work as they should.

That's down to bad design and piloting. If you do what you do in stock with FAR installed, youre going to have a bad time.

[softweir]

What he said - I'm afraid.

FAR tries to represent aerodynamics as realistically as is possible on a home PC. KSP does not! Designs that work in KSP's not-at-all-real drag-and-lift model can be almost guaranteed to fail when using FAR. (Some VERY simple designs may still work.)

Things to look out for:

• You must make certain that Centre of Mass is ahead of Centre of lift. Use those buttons at the bottom of the VAB/SPH screen to see where these are. Do this for each stage, and also try draining tanks to make sure the CoM never moves behind the CoL at any stage during the life of a stage. You may have to do weird things to your payload such as make it launch fuel-and-motors first to help ensure this.
  
• Use fairings around payloads to reduce drag, but keep them as tight to the payload as possible - you may need to redesign payloads so they don't have too many sticky-out-bits.
  
• Make sure you don't have too much control authority. FAR makes them more effective - if they move too far then you will get instability. Right-click on flaps, winglets and canards to use tweeks to reduce their range of movement.
  
• Learn how to do a proper gravity turn. Start a very small turn shortly after the stack gets off the pad, ideally at about 100 to 200 m/s velocity. From then on keep the nose of the rocket pointing near the prograde vector - that is, make sure you aren't trying to fly your rocket sideways, or anything which might look at all near sideways!
  
• Don't overpower your rocket. The first stage should have a thrust to mass ratio of about 1.5 to 1.8 - certainly never above 2.
  
• Give up on asparagus staging, it is unrealistically stable in stock KSP and realistically unstable in FAR. Whackjob need never install this mod!
  

Once you do get the hang of FAR then you should find your rockets need a lot less fuel and engine than you were used to, which could be important savings once we get proper cost-off-the-pad economics in Career Mode!

Edited April 26, 2014 by softweir
Afterthoughts. More afterthoughts, and typos.

[ferram4]

@AndreyATGB: In the real world, the main reasons for changing the height of the wings has to do with non-aerodynamic constraints. The C-5 has its wings mounted high so that its engines have more ground clearance, so it can land on less-than-perfect runways. Most jet airliners have their wings mounted low so they can save weight by combining the structural elements of the wingbox and the main gear into a single structure. However, it does have some interesting effects on aerodynamics (that FAR currently doesn't simulate) due to the way air flows around the fuselage; it causes slightly different angles of attack at the wing root, which leads to different amounts of lift on each wing. This is essentially another contribution to the dihedral effect (like wing dihedral angle and wing sweep); high wings make the plane more stable, low wings make it less stable. However, more stability makes it more prone to respond strongly in roll to sideslipping, so you generally want to keep the dihedral effect in check; too much or too little can always cause problems.

In FAR, often the reason to choose one wing placement over another is to either get more ground clearance, have a good place to mount landing gear, or to control how the plane behaves at higher velocities, where the wing's drag will help contribute to the pitch-stability of the vehicle.

For horizontal tails, those are generally used if you've constructed a high AR, low sweep wing that will lift the plane, but it isn't far enough behind the CoM for any control surfaces on it to be effective. Often for subsonic flight it ends up being more efficient to use a horizontal tail than deal with whatever weird wing-interaction effects occur when you're trying to create positive lift at the front of your wing and negative lift at the back (as is necessary for a stable tailless aircraft). However, at supersonic speeds, having the separate tail can often add more drag to your vehicle, so it's better to go for a single wing there.

@DailyFrankPeter: Sounds like you've got a vehicle that took advantage of some unrealistic behavior. You'll have to redesign it to be more in-line with reality, I'm afraid.

@capran: What softweir said. You appear to be suffering from the standard effects of changing the rules of the game but trying to use strategies that only work using the old rules. As an example, this would be as if you were playing chess and you had changed the rules so that pawns couldn't be promoted, but then in the end-game you race to get your pawns to the end of the board to promote all of them to queens. Consider how much of your earlier piloting and design is focused around dealing with stock "aerodynamics" and then adjust to account for new aerodynamics.

[Fraz86]

I'm writing a ModuleManager file to provide FAR support for Porkjet's wings, and I have a config question. Two of Porkjet's control surfaces are angled, as seen here (bottom right):

I'm wondering how FAR handles non-zero MidChordSweep and TaperRatio other than 1 for parts that are "nonSideAttach = 1". In plain English, I'm curious if/how the plugin knows which end of the control surface is the "root chord" versus the "tip chord" when, unlike wings, the root chord is not the attachment site. Does it even matter? Should I just pretend the parts are flat across the back?

[phoenix_ca]

[*]Don't overpower your rocket. The first stage should have a thrust to mass ratio of about 1.5 to 1.8 - certainly never above 2.

Probably the most useful point in that whole post, I think. Even if you built quasi-realistic rockets in stock KSP, super-powered rockets with immense (i.e. insane) TWR would be just fine. In FAR, things get wacky, fast. Slower, steady progression is far better. Thank goodness SRBs are tweakable. (I remember those days when docking was a twinkle in Minmus' craters and SRBs were truly Kerbal. I'm not actually fond of those days. At all.)

[ferram4]

@Fraz86: FAR should handle those just fine, since the parts will be flipped across symmetry, so the sweep line should flip as well. Calculate the sweep angle and taper ratio as if it were any of the other wing parts, FAR will account for thins properly.

[ferram4]

And version 0.13.2 is out, with lots of fun things, such as aerodynamically-caused structural failures. A few other tweaks, and more options set up through ConfigNodes (like Deadly Reentry does) for easy integration with other mods.

More info the changelog.

For those unaware of what aerodynamically-caused structural failures entail, this is your rocket 30 degrees off prograde at Mach 1.2:

May your launches be interesting.

[ayana]

how good that I don't flip my rockets, much

[brusura]

Nice update, just had my control surface ripped off during a landing

I have a question, does this:

Reduced supersonic and transonic drag to somewhat more reasonable levels

means that I should go faster with less drag? Before the patch I was able to go up to 34.000 m at around 1900 m/s now I start to lose speed at 24.000 m at 1500 m/s ( I am using a look a like skylon craft )

[smunisto]

I'm writing a ModuleManager file to provide FAR support for Porkjet's wings, and I have a config question. Two of Porkjet's control surfaces are angled, as seen here (bottom right):

I'm wondering how FAR handles non-zero MidChordSweep and TaperRatio other than 1 for parts that are "nonSideAttach = 1". In plain English, I'm curious if/how the plugin knows which end of the control surface is the "root chord" versus the "tip chord" when, unlike wings, the root chord is not the attachment site. Does it even matter? Should I just pretend the parts are flat across the back?

Wondering if you are making FAR configs for his structural, fuel tanks and command modules?

[Fraz86]

Wondering if you are making FAR configs for his structural, fuel tanks and command modules?

Yes, see below:

@PART[mk2Cockpit_Standard]
{
	@module = Part
	!dragCoeff = DELETE
	!deflectionLiftCoeff = DELETE
}
@PART[mk2Cockpit_Inline]
{
	@module = Part
	!dragCoeff = DELETE
	!deflectionLiftCoeff = DELETE
}
@PART[mk2CrewCabin]
{
	@module = Part
	!dragCoeff = DELETE
	!deflectionLiftCoeff = DELETE
}
@PART[mk2_1m_Adapter]
{
	@module = Part
	!dragCoeff = DELETE
	!deflectionLiftCoeff = DELETE
}
@PART[mk2_1m_AdapterLong]
{
	@module = Part
	!dragCoeff = DELETE
	!deflectionLiftCoeff = DELETE
}
@PART[mk2_1m_Bicoupler]
{
	@module = Part
	!dragCoeff = DELETE
	!deflectionLiftCoeff = DELETE
}
@PART[mk2FuselageL_long]
{
	@module = Part
	!dragCoeff = DELETE
	!deflectionLiftCoeff = DELETE
}
@PART[mk2Fuselage_LFO]
{
	@module = Part
	!dragCoeff = DELETE
	!deflectionLiftCoeff = DELETE
}
@PART[mk2CargoBayS]
{
	@module = Part
	!dragCoeff = DELETE
	!deflectionLiftCoeff = DELETE
}
@PART[mk2CargoBayL]
{
	@module = Part
	!dragCoeff = DELETE
	!deflectionLiftCoeff = DELETE
}
@PART[deltaWingX]
{
	@module = Part
	@maximum_drag = 0
	@minimum_drag = 0
	@angularDrag = 0
	@dragCoeff = 0
	@deflectionLiftCoeff = 0
	MODULE
	{
		name = FARWingAerodynamicModel
		MAC = 2.16 //Mean chord length in meters
		e = 0.75 //Drag per lift, lower equals more drag
		MidChordSweep = 26 //Angle of line from mid root chord to mid tip chord
		b_2 = 3.76 //Root to tip in meters
		TaperRatio = 0.08 //Ratio of tip chord to root chord
	}
}
@PART[structuralWing1]
{
	@module = Part
	@maximum_drag = 0
	@minimum_drag = 0
	@angularDrag = 0
	@dragCoeff = 0
	@deflectionLiftCoeff = 0
	MODULE
	{
		name = FARWingAerodynamicModel
		MAC = 2.16 //Mean chord length in meters
		e = 0.75 //Drag per lift, lower equals more drag
		MidChordSweep = 44 //Angle of line from mid root chord to mid tip chord
		b_2 = 1.88 //Root to tip in meters
		TaperRatio = 0.08 //Ratio of tip chord to root chord
	}
}
@PART[wingStrake]
{
	@module = Part
	@maximum_drag = 0
	@minimum_drag = 0
	@angularDrag = 0
	@dragCoeff = 0
	@deflectionLiftCoeff = 0
	MODULE
	{
		name = FARWingAerodynamicModel
		MAC = 2.16 //Mean chord length in meters
		e = 0.75 //Drag per lift, lower equals more drag
		MidChordSweep = 62 //Angle of line from mid root chord to mid tip chord
		b_2 = 0.94 //Root to tip in meters
		TaperRatio = 0.08 //Ratio of tip chord to root chord
	}
}
@PART[structuralWing2]
{
	@module = Part
	@maximum_drag = 0
	@minimum_drag = 0
	@angularDrag = 0
	@dragCoeff = 0
	@deflectionLiftCoeff = 0
	MODULE
	{
		name = FARWingAerodynamicModel
		MAC = 1.16 //Mean chord length in meters
		e = 0.75 //Drag per lift, lower equals more drag
		MidChordSweep = 13 //Angle of line from mid root chord to mid tip chord
		b_2 = 3.76 //Root to tip in meters
		TaperRatio = 0.16 //Ratio of tip chord to root chord
	}
}
@PART[wingConnector1]
{
	@module = Part
	@maximum_drag = 0
	@minimum_drag = 0
	@angularDrag = 0
	@dragCoeff = 0
	@deflectionLiftCoeff = 0
	MODULE
	{
		name = FARWingAerodynamicModel
		MAC = 4 //Mean chord length in meters
		e = 0.75 //Drag per lift, lower equals more drag
		MidChordSweep = 0 //Angle of line from mid root chord to mid tip chord
		b_2 = 1.88 //Root to tip in meters
		TaperRatio = 1 //Ratio of tip chord to root chord
	}
}
@PART[wingConnector2]
{
	@module = Part
	@maximum_drag = 0
	@minimum_drag = 0
	@angularDrag = 0
	@dragCoeff = 0
	@deflectionLiftCoeff = 0
	MODULE
	{
		name = FARWingAerodynamicModel
		MAC = 2 //Mean chord length in meters
		e = 0.75 //Drag per lift, lower equals more drag
		MidChordSweep = 0 //Angle of line from mid root chord to mid tip chord
		b_2 = 3.76 //Root to tip in meters
		TaperRatio = 1 //Ratio of tip chord to root chord
	}
}
@PART[elevon1]
{
	@module = Part
	@maximum_drag = 0
	@minimum_drag = 0
	@angularDrag = 0
	@dragCoeff = 0
	@deflectionLiftCoeff = 0
	@ctrlSurfaceRange = 0
	@ctrlSurfaceArea = 0
	MODULE
	{
		name = FARControllableSurface
		MAC = 0.5
		e = 0.9
		nonSideAttach = 1
		maxdeflect = 20
		MidChordSweep = 0
		b_2 = 1.8
		TaperRatio = 1
	}
}
@PART[elevon2]
{
	@module = Part
	@maximum_drag = 0
	@minimum_drag = 0
	@angularDrag = 0
	@dragCoeff = 0
	@deflectionLiftCoeff = 0
	@ctrlSurfaceRange = 0
	@ctrlSurfaceArea = 0
	MODULE
	{
		name = FARControllableSurface
		MAC = 0.62
		e = 0.9
		nonSideAttach = 1
		maxdeflect = 20
		MidChordSweep = -4
		b_2 = 1.8
		TaperRatio = 0.67
	}
}
@PART[elevon3]
{
	@module = Part
	@maximum_drag = 0
	@minimum_drag = 0
	@angularDrag = 0
	@dragCoeff = 0
	@deflectionLiftCoeff = 0
	@ctrlSurfaceRange = 0
	@ctrlSurfaceArea = 0
	MODULE
	{
		name = FARControllableSurface
		MAC = 0.86
		e = 0.9
		nonSideAttach = 1
		maxdeflect = 20
		MidChordSweep = -4
		b_2 = 1.8
		TaperRatio = 0.75
	}
}

Edited April 27, 2014 by Fraz86

[ferram4]

@brusura: Upgraded from FAR v0.12.5.2? Then you were taking advantage of a bugged config for the turbojet engine. But otherwise zero-lift drag at transonic and supersonic speeds is lower, so you don't need as much thrust at those speeds. This doesn't help you if your engines stop producing thrust because their combustion chambers are overheating.

[ayana]

well that was fun, sadly it the aerodynamic failure seemed to invite the Kraken. I tore a rocket up in the low atmosphere, safely got the crew pod out of it and landed, but couldn't recover or revert.

[brusura]

nope ferram4 I have update from v0.13.1 and thanks for the aerodynamic explanation

I was going to record a video to show the isse but the quality is very awful, the craft file is in my signature, dunno if you need some log everything seems to work fine just I am not getting the same speed as before ( sorry I am an aerodyamic noob )

[ferram4]

@ayana: I'll need a copy of the output_log.txt then. I haven't seen this issue in my game, what other mods are you running?

@brusura: Oh, your ship is using the RAPIER. Yeah, those got nerfed back to where the turbojet is now. There was no reason to ever use the turbojet over the RAPIER, so I toned down the RAPIER to compensate.

[brusura]

Ah! So it is an intended feature oh well... ok then

[MAKC]

Should we still change the config.xml values for RSS? If so, maybe include them in the OP?

[BudgetHedgehog]

So with this aerodynamic-induced destruction, watching deorbited lifter stages is a whole load of fun! Thanks ferram!

[illectro]

For those unaware of what aerodynamically-caused structural failures entail, this is your rocket 30 degrees off prograde at Mach 1.2:

So is this doing something beyond generating different aerodaynamic forces on each part?

[AndreyATGB]

About the aerodynamic failures, the option in the space center doesn't seem to do anything. I disabled it and parts still break. I didn't try a game restart though.

About the failures as well, is it normal for a plane going 150 or so m/s on the runaway to instantly lose its control surfaces when I pitch up to take off? Every time if I hold S, the thing lifts off the ground and the control surfaces on the wings proceed to explode within 1-2 seconds.

[smunisto]

Same thing. I am trying to use procedural wings, but the procedural control surfaces break each time.

[AndreyATGB]

Same thing. I am trying to use procedural wings, but the procedural control surfaces break each time.

Stock ones do the same thing for me.

[theSpeare]

"Option to switch on / off various debug data about FAR drag model applied to particular parts"

Where is this? I opened up the FAR menu in SC and all I see are:

- Display Aero Forces

- Display Coefficients

- Display Shielding

- Spline Stuff

- Aero destruction

[AndreyATGB]

"Option to switch on / off various debug data about FAR drag model applied to particular parts"

Where is this? I opened up the FAR menu in SC and all I see are:

- Display Aero Forces

- Display Coefficients

- Display Shielding

- Spline Stuff

- Aero destruction

Aero forces - likely lift and drag values when right clicking parts.

Coefficients - what happened in 0.13.0. You see Cd, Cm and all that for parts when you right click them.

Shielding - toggles isShielded: true/false

I don't know what the calculation does.

Aero destruction is supposed to disable dynamic pressure from destroying your vessel but it doesn't seem to work.