Phantom Forces and a Big Black Box, Capsule Aerodynamic Misery

[Beale]

I was wondering if anybody can offer insight on aerodynamics configs on Capsule + Parachute + Heatshield combinations? I am having a lot of issue getting a capsule to orient correctly.

The three parts.

 The re-entry vehicle is a parachute, capsule and heatshield.

Without any config offsets:
Capsule enters window forward, surfing on the heatshield and cooking the crew.

With config offets:
It is a bit more well-behaved, but there are weird lifts in directions during re-entry (you can see also the capsule is tilting for some reason). 

The configs:

Parachute

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PART
{

name = Alnair_Parachute_1
module = Part
author = Tantares

MODEL
{
   model = Tantares/Parts/VA/VA_Parachute_1
}
scale = 1.0
rescaleFactor = 1.0

node_stack_bottom = 0.0, -0.05, 0.0, 0.0, -1.0, 0.0, 1
node_stack_top    = 0.0,  0.05, 0.0, 0.0, 1.0, 0.0, 1

bulkheadProfiles = size0

attachRules = 1,0,1,1,0

sound_parachute_open = activate
sound_parachute_single = deploy

TechRequired = survivability
entryCost = 2000
cost = 600

category     = Utility
subcategory  = 0
title        = A-V2K Return Parachute
manufacturer = Tantares Space Technologies
description  = 

tags = 0.9375

mass = 0.1

dragModelType  = default
angularDrag    = 3
crashTolerance = 10
maxTemp        = 2000
fuelCrossFeed = False
bodyLiftMultiplier = 0

stageOffset = 1
childStageOffset = 1

MODULE
{
      name = ModuleParachute
    semiDeployedAnimation = Alnair_Parachute_1_Semi
    fullyDeployedAnimation = Alnair_Parachute_1_Full
    invertCanopy = false
    autoCutSpeed = 0.5
    capName = Cap1
    canopyName = Canopy1
    stowedDrag = 0.22
    semiDeployedDrag = 1
    fullyDeployedDrag = 500
    minAirPressureToOpen = 0.38
    deployAltitude = 500
    deploymentSpeed = 1
    semiDeploymentSpeed = 0.5    
}

MODULE
{
    name = ModuleDecouple
    isOmniDecoupler = false
    ejectionForce = 250
}

    MODULE
    {
        name = ModuleDragModifier
        dragCubeName = SEMIDEPLOYED
        dragModifier = 0.67
    }
    MODULE
    {
        name = ModuleDragModifier
        dragCubeName = DEPLOYED
        dragModifier = 25
    }

}

Capsule

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PART
{

name = Alnair_Crew_1
module = Part
author = Tantares

MODEL
{
   model = Tantares/Parts/VA/VA_Crew_1
}
scale = 1.0
rescaleFactor = 1.0

node_stack_bottom = 0.0, -0.43125, 0.0, 0.0, -1.0, 0.0, 1
node_stack_top    = 0.0,  0.43125, 0.0, 0.0, 1.0, 0.0, 0

bulkheadProfiles = size1.5, size0.5

CoPOffset = 0.0,  0.43125,  0.0
CoMOffset = 0.0, -0.215625, 0.0

attachRules = 1,0,1,1,0

TechRequired = flightControl
entryCost = 3500
cost = 1000

category     = Pods
subcategory  = 0
title        = A-LK1 Capsule
manufacturer = Tantares Space Technologies
description  = The LK1 represents the vision of a slightly more sophisticated crew capsule, through frosted glass.

tags = 1.875 0.9375 ?VA Alnair

mass = 1.275

dragModelType  = default
maximum_drag   = 0.20
minimum_drag   = 0.15
angularDrag    = 2
crashTolerance = 20

maxTemp             = 3400
skinMaxTemp         = 3400
heatConductivity    = 0.1
thermalMassModifier = 1.0

vesselType = Ship

CrewCapacity = 3

INTERNAL
{
  name = Alnair_Crew_1_Interior
}

MODULE
{
    name = ModuleCommand
    minimumCrew = 1
}

MODULE
{
    name = ModuleSAS
}

MODULE
{
    name = ModuleReactionWheel
    
    PitchTorque = 1.5
    YawTorque = 1.5
    RollTorque = 1.5
    
    RESOURCE
    {
        name = ElectricCharge
        rate = 0.075
    }
}

MODULE
{
    name = ModuleScienceExperiment    
    
    experimentID = crewReport
    
    experimentActionName = Crew Report
    resetActionName = Discard Crew Report
    reviewActionName = Review Report
    
    useStaging = False    
    useActionGroups = True
    hideUIwhenUnavailable = True    
    rerunnable = True
    
    xmitDataScalar = 1.0
}

MODULE
{
    name = ModuleScienceContainer
    
    reviewActionName = Review Stored Data
    storeActionName = Store Experiments
    evaOnlyStorage = True
    storageRange = 2.0
}

RESOURCE
{
    name = ElectricCharge
    amount = 100
    maxAmount = 100
}

RESOURCE
{
    name = MonoPropellant
    amount = 30
    maxAmount = 30
}

MODULE
{
    name = ModuleAnimateGeneric
    animationName = Alnair_Crew_1_Light
    actionGUIName = Toggle Lights
    startEventGUIName = Lights On
    endEventGUIName = Lights Off
}

}

Heatshield

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PART
{

name = Alnair_Heatshield_1
module = Part
author = Tantares

MODEL
{
   model = Tantares/Parts/VA/VA_Heatshield_1
}
scale = 1.0
rescaleFactor = 1.0

node_stack_bottom = 0.0, -0.11375, 0.0, 0.0, -1.0, 0.0, 1
node_stack_top    = 0.0,  0.11375, 0.0, 0.0, 1.0, 0.0, 1

    CoPOffset = 0.0,  0.11375, 0.0
    CoLOffset = 0.0, -0.11375, 0.0

bulkheadProfiles = size1.5

attachRules = 1,0,1,1,0

sound_vent_large = decouple

TechRequired = survivability
entryCost = 900
cost = 900

category     = Thermal
subcategory  = 0
title        = A-LK1 Heatshield
manufacturer = Tantares Space Technologies
description  = 

tags = 1.875 ?VA Alnair heatshield 

mass = 0.15

dragModelType  = default
maximum_drag   = 0.20
minimum_drag   = 0.20
angularDrag    = 2
crashTolerance = 20

maxTemp             = 3400
skinMaxTemp         = 3400
heatConductivity    = 0.1
thermalMassModifier = 1.0

stageOffset = 1
childStageOffset = 1

MODULE
{
    name = ModuleJettison
    jettisonName = Alnair_Heatshield_1_Fairing
    bottomNodeName = bottom
    isFairing = True
    jettisonedObjectMass = 0.5
    jettisonForce = 15
    jettisonDirection = 0 0 1
    stagingEnabled = False
    checkBottomNode = True
}

MODULE
{
    name = ModuleDecouple
    ejectionForce = 100
    isOmniDecoupler = true
    menuName = Jettison Heat Shield
    stagingEnabled = False
    stagingEnableText = HS Jettison Not Staged
    stagingDisableText = HS Jettison Staged
}

MODULE
{
        name = ModuleAblator
        ablativeResource = Ablator
        lossExp = -7500
        lossConst = 0.1
        pyrolysisLossFactor = 6000
        reentryConductivity = 0.01
        ablationTempThresh = 500
}

RESOURCE
{
        name = Ablator
        amount = 300
        maxAmount = 300
}    

}

 

[Nansuchao]

IRL usually capsules has and offset CoM, to better handle the vertical speed in the high atmosphere. If you want the easy way, just move the CoM of your capsule near the bottom, centered on the main axis.

[Beale]

  On 4/24/2017 at 6:45 PM, Nansuchao said:

IRL usually capsules has and offset CoM, to better handle the vertical speed in the high atmosphere. If you want the easy way, just move the CoM of your capsule near the bottom, centered on the main axis.

Expand  

Already in place:

CoMOffset = 0.0, -0.215625, 0.0

Still problems  

[linuxgurugamer]

But where is that in relation to the model?

Can you show a pic of it in the editor with the com shown?

[Beale]

  On 4/24/2017 at 7:35 PM, linuxgurugamer said:

But where is that in relation to the model?

Can you show a pic of it in the editor with the com shown?

Expand  

The model origins are centred exactly, so the relation is from the exact centre of the model:

I have the parts here on GitHub, by the way.

Edited April 24, 2017 by Beale

[linuxgurugamer]

Drop the CoM of the capsule to just above the bottom of it. It's still too high.

[Beale]

  On 4/24/2017 at 7:55 PM, linuxgurugamer said:

Drop the CoM of the capsule to just above the bottom of it. It's still too high.

Expand  

Is that appropriate to real-life capsules, they do not have the CoM at the very bottom do they?

I would consider it more of a hack than a real fix if that's not the case.
 

Edited April 24, 2017 by Beale

[linuxgurugamer]

Not really.

Look at this picture:  https://www.hq.nasa.gov/alsj/CSM06_Command_Module_Overview_pp39-52.pdf

You can see that most everything is below the astronauts, which lowers the CoM

[Beale]

  On 4/24/2017 at 7:58 PM, linuxgurugamer said:

Not really.

Look at this picture:  https://www.hq.nasa.gov/alsj/CSM06_Command_Module_Overview_pp39-52.pdf

You can see that most everything is below the astronauts, which lowers the CoM

Expand  

Need something more concrete than that, my CoM is already lowered, only 20cm from the absolute bottom of the capsule.

I thank you for the help, but I think this is barking up the wrong tree, maybe.

The stock capsules show something very different:

 

[Beale]

Example of weird tilt induced on my Capsule, vs. Stock.

Only change here, I have added a CoL offset to the capsule:

CoLOffset = 0.0, -0.215625, 0.0

Something is really strange...

[SpannerMonkey(smce)]

Hi i note that the stock capsule also uses

	CoPOffset = 0.0, 0.6, 0.0

which effectively moves the aerodynamic pressure  up the capsule(i think I'm correct here)  which looks like it gives the desirable lawn dart effect.  (Are you clearing the part database too after every test?, as moved com col cos etc change the drag cube (does with ships at least) , you could be getting odd results if not)

[Beale]

  On 4/24/2017 at 8:57 PM, SpannerMonkey(smce) said:

Hi i note that the stock capsule also uses

	CoPOffset = 0.0, 0.6, 0.0

which effectively moves the aerodynamic pressure  up the capsule(i think I'm correct here)  which looks like it gives the desirable lawn dart effect.  (Are you clearing the part database too after every test?, as moved com col cos etc change the drag cube (does with ships at least) , you could be getting odd results if not)

Expand  

I do currently have the CoP set on both the capsule and heatshield (at, or just above, the top node of the part). See configs in OP.
Clearing partDatabase in-between games, btw  

@Pak Has noticed if you look at the pic above, something is happening with the drag and lift unusual, compared to the stock capsule.

Edited April 24, 2017 by Beale

[Stone Blue]

@Beale I see you have CoM and CoL using the same exact offset... Are you sure that should be?..  Maybe offsetting the CoL off-center, opposite the side that is "tilting" the wrong way, may compensate?...or maybe just moving one to slightly ABOVE the other, on-center, may work?

Edited April 25, 2017 by Stone Blue

[hraban]

Hi Beale,

I had the same problems a few weeks ago and it helps to set the CoM to the lower end of the capsule and the CoP to the top of the capsule. As reference: MK1-2 Command Pod, here is the CoM ~ 0.35m above the lower model edge, but the CoP is set to 0.6m above the CoM.