Question Aerodynamics- Lift Vector

[Buck Rogers]

Unfotuneately drag is calculated from lift automatically in Vesselbuilder

The starliner may not be top notch but I don't think you'd favour it more if it had 0 lift

 

[Urwumpe]

Unfotuneately drag is calculated from lift automatically in Vesselbuilder

The starliner may not be top notch but I don't think you'd favour it more if it had 0 lift

Then you can't have the lift vector point in a certain direction, if you roll the vessel. The lift vector will roll with it. The typical capsule behaviour.

You could make a rotation projection between horizontal and vertical lift of course, if you pass the bank angle as custom variable to your lift function.

 

[Buck Rogers]

The lift vector will roll with it. The typical capsule behaviour.

but at 0 pitch, 0 AOA (0 yaw) the lift vector shouldn't change?

You could make a rotation projection between horizontal and vertical lift of course, if you pass the bank angle as custom variable to your lift function.

this is what I thought would/should be done for capsules (or any form with 2 symmetries) anyway.

 

[Urwumpe]

but at 0 pitch, 0 AOA (0 yaw) the lift vector shouldn't change?

Depends. Do you have a non-zero lift coefficient at 0° AOA?

this is what I thought would/should be done for capsules (or any form with 2 symmetries) anyway.

Why? The airfoil model rolls with the vessel anyway, the orientation of lift and drag axes of the coordinate system depend on the air velocity vector.

 

[Thunder Chicken]

Unfotuneately drag is calculated from lift automatically in Vesselbuilder

I am unfamiliar with Vesselbuilder innards, but the airfoil functions in Orbiter also can calculate induced drag, which is a direct consequence of lift. If your airfoils are symmetric and your AOA is 0 you shouldn't have induced drag. However, there may also be skin friction / profile drag being calculated as well which would generally be not 0 even at 0 deg. AOA.

but at 0 pitch, 0 AOA (0 yaw) the lift vector shouldn't change?

It doesn't relative to the vessel. If the vessel rotates, the vector will rotate with it as seen from an external viewpoint. From an observer in the vessel that vector does not change.

 

[Buck Rogers]

Bank/roll should have no effect on how much lift is present on a perfectly symetrical capsule.

The issue is due to orbiter's 2 plane airfoil system:

The Airfoil class (CreateAirfoil3, etc.) really expects aerodynamic force to be applied by something that looks like a wing, or a vertical stabilizer. So with your ellipsoid what you want is symmetrical lift and drag that varies with pitch only, but not with roll. The problem is that the Airfoil class is only capable of applying forces in the "lift" and "drag" direction (along a vector that is normal or collinear with the flow over the surface).

This is a problem because "roll" needs to be simulated as a combination of "pitch" and "yaw" (or rather the components projected in to the pitch and yaw direction), this also has the unfortunate effect of making it hard to define aerodynamic behavior near +/-90° yaw and or pitch because of the singularities at those points.

And would be solved with this

AirfoilCoeffFuncEx2, and VESSEL::CreateAirfoil4 which allows you to specify aerodynamic coeffiicient functions as function of: aoa, yaw, and roll at the same time, or as a just a vector function (the vector function may be more useful for lookup functions) .

 

[Thunder Chicken]

Bank/roll should have no effect on how much lift is present on a perfectly symetrical capsule.

The issue is due to orbiter's 2 plane airfoil system:

And would be solved with this

Do you have any information about lift for a football shaped ellipsoid? You may be driving yourself to insanity trying to implement a lift model when there may in fact be little lift.

You need to provide parameters to the airfoil model like lift curve, plan area, aspect ratio, wing efficiency, etc... which are not really descriptive of an ellipsoid. Hacking that model to deliver even just the lift for a non-spinning ellipsoid would require artificially tweaking any or all of those parameters and trying to apply actual ellipse aerodynamics that way will be hard to verify.

I think add_force would be a much saner route for what you are trying to do, as you can dynamically change that force vector as needed, and you can put in custom lift and drag models for ellipsoids and other strange shapes if you can find the relevant data.

 

[francisdrake]

Below are the lift and drag functions I used for the CST-100 capsule. The figures are small indeed, but not zero.

void VLiftCoeff(double aoa, double M, double Re, double *cl, double *cm, double *cd)
{
    static const double step = RAD*30.0;
    static const double istep = 1.0 / step;
    static const int nabsc = 13;
    //    Angle of attack                     -180    -150    -120    -90        -60        -30        0        30     60        90        120        150      180
    static const double CL[nabsc] = { 0, -0.12, -0.1, 0, 0, 0, 0, 0, 0, 0, 0.1, 0.12, 0 };
    static const double CM[nabsc] = { 0, -0.0002, -0.0004, -0.0004, -0.0003, -0.0002, 0, 0.0002, 0.0003, 0.0004, 0.0004, 0.0002, 0 };
    // lift and moment coefficients from -180 to 180 in 30 degree steps.

    aoa += PI;
    int idx = max(0, min(11, (int)(aoa*istep)));
    double d = aoa*istep - idx;
    *cl = CL[idx] + (CL[idx + 1] - CL[idx])*d;
    *cm = (CM[idx] + (CM[idx + 1] - CM[idx])*d) / 10;
    *cd = 0.25 + oapiGetInducedDrag(*cl, 1.27, 0.3);
}

// 2. horizontal lift component (vertical stabiliser and body)

void HLiftCoeff(double beta, double M, double Re, double *cl, double *cm, double *cd)
{
    static const double step = RAD * 30;
    static const double istep = 1.0 / step;
    static const int nabsc = 13;
    static const double CL[nabsc] = { 0, -0.1, -0.1, 0, 0, 0, 0, 0, 0, 0, 0.1, 0.1, 0 };

    beta += PI;
    int idx = max(0, min(11, (int)(beta*istep)));
    double d = beta*istep - idx;
    *cl = CL[idx] + (CL[idx + 1] - CL[idx])*d;
    *cm = 0.0;
    *cd = 0.25 + oapiGetInducedDrag(*cl, 1.27, 0.3);
}

To achieve a capsule-like aerodynamic behavior (flying bottom first), the airfoil attack points are shifted a little above the mass center (z = +0.1 m).
To make it steerable, the capsule has an off-center mass center built in. This is simulated here by shifting the airfoil attack point a little upward (y = +0.01 m). So it does not fly fully with the blunt bottom facing forward, but a little edged upwards. This creates a tiny bit of upward lift, as the heatshield is not fully perpendicular to the flight direction. When the capsule is rolled during reentry, this lift vector follows the capsule orientation and can be used to do some up-down-left-right corrections of the flight path.

    CreateAirfoil(LIFT_VERTICAL, _V(0, 0.01, 0.1), VLiftCoeff, 5.5, 0, 1.27);
    CreateAirfoil(LIFT_HORIZONTAL, _V(0, 0, 0.01), HLiftCoeff, 5.5, 0, 1.27);

 

[Thunder Chicken]

Below are the lift and drag functions I used for the CST-100 capsule. The figures are small indeed, but not zero.

I am aware of this, but this isn't an ellipsoid. Tracking down data for the lift and drag characteristics for ellipsoids should be the first step in figuring out how to program their aerodynamics accurately. In Orbiter you can give a brick the flight characteristics of a sailplane if you give it incorrect inputs. Orbiter can't infer flight characteristics from the mesh. It relies on the add-on developer to do their homework.

 

[Buck Rogers]

Thanks @francisdrake
I have had a look at the Starliner code before, and I'm no proficent coder, but I noticed that induceddrag is being called and AFAIK I don't have access to that with Airfoils in Vesselbuilder (can't define it to AOA), and cd seems to be calculated automatically. And I do seem to be getting too much L/D (Vesselbuilder doesn't have a capsule example and maybe is not ideal for this purpose).

Also I noticed the Hliftcoeff is different, and has no moment coeffs, I would have expected the airfoils to be the same?
VLiftCoeff, 5.5, 0, 1.27)? Are these the initial (max) cl, cm, cd values?

This is what I was working with before

EMPTY_MASS = 1117
VSIZE = 4
PMI = 1.2 1.2 1.85
CSECTIONS = 5.3 5.3 14.85
GRAVITYGDAMP = 0
ROTDRAG = 0.05 0.05 0.01

;<-------------------------AIRFOILS DEFINITIONS------------------------->
 
AIRFOIL_0_ID = 0
AIRFOIL_0_NAME = V_Airfoil_0
AIRFOIL_0_ORIENTATION = 0
AIRFOIL_0_REF = 0 0 0.03
AIRFOIL_0_C = 3.7
AIRFOIL_0_S = 14.85
AIRFOIL_0_A = 1
AIRFOIL_0_POINT_0_AOA = -180
AIRFOIL_0_POINT_0_CL = 0
AIRFOIL_0_POINT_0_CM = 0
AIRFOIL_0_POINT_1_AOA = -118
AIRFOIL_0_POINT_1_CL = -0.7
AIRFOIL_0_POINT_1_CM = -0.004
AIRFOIL_0_POINT_2_AOA = -95
AIRFOIL_0_POINT_2_CL = -0.1
AIRFOIL_0_POINT_2_CM = 0
AIRFOIL_0_POINT_3_AOA = -85
AIRFOIL_0_POINT_3_CL = 0.01
AIRFOIL_0_POINT_3_CM = 0
AIRFOIL_0_POINT_4_AOA = -30
AIRFOIL_0_POINT_4_CL = 0.1
AIRFOIL_0_POINT_4_CM = 0.001
AIRFOIL_0_POINT_5_AOA = 0
AIRFOIL_0_POINT_5_CL = 0
AIRFOIL_0_POINT_5_CM = 0
AIRFOIL_0_POINT_6_AOA = 30
AIRFOIL_0_POINT_6_CL = -0.1
AIRFOIL_0_POINT_6_CM = -0.001
AIRFOIL_0_POINT_7_AOA = 85
AIRFOIL_0_POINT_7_CL = -0.01
AIRFOIL_0_POINT_7_CM = 0
AIRFOIL_0_POINT_8_AOA = 95
AIRFOIL_0_POINT_8_CL = 0.1
AIRFOIL_0_POINT_8_CM = 0
AIRFOIL_0_POINT_9_AOA = 118
AIRFOIL_0_POINT_9_CL = 0.7
AIRFOIL_0_POINT_9_CM = 0.004
AIRFOIL_0_POINT_10_AOA = 180
AIRFOIL_0_POINT_10_CL = 0
AIRFOIL_0_POINT_10_CM = 0
 
AIRFOIL_1_ID = 1
AIRFOIL_1_NAME = H_Airfoil_1
AIRFOIL_1_ORIENTATION = 1
AIRFOIL_1_REF = 0 0 0.03
AIRFOIL_1_C = 3.7
AIRFOIL_1_S = 14.85
AIRFOIL_1_A = 1
AIRFOIL_1_POINT_0_AOA = -180
AIRFOIL_1_POINT_0_CL = 0
AIRFOIL_1_POINT_0_CM = 0
AIRFOIL_1_POINT_1_AOA = -118
AIRFOIL_1_POINT_1_CL = -0.7
AIRFOIL_1_POINT_1_CM = -0.004
AIRFOIL_1_POINT_2_AOA = -95
AIRFOIL_1_POINT_2_CL = -0.1
AIRFOIL_1_POINT_2_CM = 0
AIRFOIL_1_POINT_3_AOA = -85
AIRFOIL_1_POINT_3_CL = 0.01
AIRFOIL_1_POINT_3_CM = 0
AIRFOIL_1_POINT_4_AOA = -30
AIRFOIL_1_POINT_4_CL = 0.1
AIRFOIL_1_POINT_4_CM = 0.001
AIRFOIL_1_POINT_5_AOA = 0
AIRFOIL_1_POINT_5_CL = 0
AIRFOIL_1_POINT_5_CM = 0
AIRFOIL_1_POINT_6_AOA = 30
AIRFOIL_1_POINT_6_CL = -0.1
AIRFOIL_1_POINT_6_CM = -0.001
AIRFOIL_1_POINT_7_AOA = 85
AIRFOIL_1_POINT_7_CL = -0.01
AIRFOIL_1_POINT_7_CM = 0
AIRFOIL_1_POINT_8_AOA = 95
AIRFOIL_1_POINT_8_CL = 0.1
AIRFOIL_1_POINT_8_CM = 0
AIRFOIL_1_POINT_9_AOA = 118
AIRFOIL_1_POINT_9_CL = 0.7
AIRFOIL_1_POINT_9_CM = 0.004
AIRFOIL_1_POINT_10_AOA = 180
AIRFOIL_1_POINT_10_CL = 0
AIRFOIL_1_POINT_10_CM = 0

but I didn't have a Y offset
I'll add a Y component and remove the moments
To add to the confusion I don't think AerobrakeMFD likes retrograde vessels so I've stopped using that for reference.
Thanks for the inspiration, I'll give it another go and see if I can get something usable with VB together
@Thunder Chicken
I appreciate your input but your suggestions (admitedly an interesting topic) go past the subject at hand. Again sorry for any confusion, as I've said it's simply about airfoils (in VB) for a capsule.

 

[Luke Reichelt]

Thanks @francisdrake
I have had a look at the Starliner code before, and I'm no proficent coder, but I noticed that induceddrag is being called and AFAIK I don't have access to that with Airfoils in Vesselbuilder (can't define it to AOA), and cd seems to be calculated automatically. And I do seem to be getting too much L/D (Vesselbuilder doesn't have a capsule example and maybe is not ideal for this purpose).

Also I noticed the Hliftcoeff is different, and has no moment coeffs, I would have expected the airfoils to be the same?
VLiftCoeff, 5.5, 0, 1.27)? Are these the initial (max) cl, cm, cd values?

This is what I was working with before

EMPTY_MASS = 1117
VSIZE = 4
PMI = 1.2 1.2 1.85
CSECTIONS = 5.3 5.3 14.85
GRAVITYGDAMP = 0
ROTDRAG = 0.05 0.05 0.01

;<-------------------------AIRFOILS DEFINITIONS------------------------->
 
AIRFOIL_0_ID = 0
AIRFOIL_0_NAME = V_Airfoil_0
AIRFOIL_0_ORIENTATION = 0
AIRFOIL_0_REF = 0 0 0.03
AIRFOIL_0_C = 3.7
AIRFOIL_0_S = 14.85
AIRFOIL_0_A = 1
AIRFOIL_0_POINT_0_AOA = -180
AIRFOIL_0_POINT_0_CL = 0
AIRFOIL_0_POINT_0_CM = 0
AIRFOIL_0_POINT_1_AOA = -118
AIRFOIL_0_POINT_1_CL = -0.7
AIRFOIL_0_POINT_1_CM = -0.004
AIRFOIL_0_POINT_2_AOA = -95
AIRFOIL_0_POINT_2_CL = -0.1
AIRFOIL_0_POINT_2_CM = 0
AIRFOIL_0_POINT_3_AOA = -85
AIRFOIL_0_POINT_3_CL = 0.01
AIRFOIL_0_POINT_3_CM = 0
AIRFOIL_0_POINT_4_AOA = -30
AIRFOIL_0_POINT_4_CL = 0.1
AIRFOIL_0_POINT_4_CM = 0.001
AIRFOIL_0_POINT_5_AOA = 0
AIRFOIL_0_POINT_5_CL = 0
AIRFOIL_0_POINT_5_CM = 0
AIRFOIL_0_POINT_6_AOA = 30
AIRFOIL_0_POINT_6_CL = -0.1
AIRFOIL_0_POINT_6_CM = -0.001
AIRFOIL_0_POINT_7_AOA = 85
AIRFOIL_0_POINT_7_CL = -0.01
AIRFOIL_0_POINT_7_CM = 0
AIRFOIL_0_POINT_8_AOA = 95
AIRFOIL_0_POINT_8_CL = 0.1
AIRFOIL_0_POINT_8_CM = 0
AIRFOIL_0_POINT_9_AOA = 118
AIRFOIL_0_POINT_9_CL = 0.7
AIRFOIL_0_POINT_9_CM = 0.004
AIRFOIL_0_POINT_10_AOA = 180
AIRFOIL_0_POINT_10_CL = 0
AIRFOIL_0_POINT_10_CM = 0
 
AIRFOIL_1_ID = 1
AIRFOIL_1_NAME = H_Airfoil_1
AIRFOIL_1_ORIENTATION = 1
AIRFOIL_1_REF = 0 0 0.03
AIRFOIL_1_C = 3.7
AIRFOIL_1_S = 14.85
AIRFOIL_1_A = 1
AIRFOIL_1_POINT_0_AOA = -180
AIRFOIL_1_POINT_0_CL = 0
AIRFOIL_1_POINT_0_CM = 0
AIRFOIL_1_POINT_1_AOA = -118
AIRFOIL_1_POINT_1_CL = -0.7
AIRFOIL_1_POINT_1_CM = -0.004
AIRFOIL_1_POINT_2_AOA = -95
AIRFOIL_1_POINT_2_CL = -0.1
AIRFOIL_1_POINT_2_CM = 0
AIRFOIL_1_POINT_3_AOA = -85
AIRFOIL_1_POINT_3_CL = 0.01
AIRFOIL_1_POINT_3_CM = 0
AIRFOIL_1_POINT_4_AOA = -30
AIRFOIL_1_POINT_4_CL = 0.1
AIRFOIL_1_POINT_4_CM = 0.001
AIRFOIL_1_POINT_5_AOA = 0
AIRFOIL_1_POINT_5_CL = 0
AIRFOIL_1_POINT_5_CM = 0
AIRFOIL_1_POINT_6_AOA = 30
AIRFOIL_1_POINT_6_CL = -0.1
AIRFOIL_1_POINT_6_CM = -0.001
AIRFOIL_1_POINT_7_AOA = 85
AIRFOIL_1_POINT_7_CL = -0.01
AIRFOIL_1_POINT_7_CM = 0
AIRFOIL_1_POINT_8_AOA = 95
AIRFOIL_1_POINT_8_CL = 0.1
AIRFOIL_1_POINT_8_CM = 0
AIRFOIL_1_POINT_9_AOA = 118
AIRFOIL_1_POINT_9_CL = 0.7
AIRFOIL_1_POINT_9_CM = 0.004
AIRFOIL_1_POINT_10_AOA = 180
AIRFOIL_1_POINT_10_CL = 0
AIRFOIL_1_POINT_10_CM = 0

but I didn't have a Y offset
I'll add a Y component and remove the moments
To add to the confusion I don't think AerobrakeMFD likes retrograde vessels so I've stopped using that for reference.
Thanks for the inspiration, I'll give it another go and see if I can get something usable with VB together
@Thunder Chicken
I appreciate your input but your suggestions (admitedly an interesting topic) go past the subject at hand. Again sorry for any confusion, as I've said it's simply about airfoils (in VB) for a capsule.

Looking good so far, but you still haven't replied to any of my inquiries regarding those Shadow vessels.

 

[francisdrake]

Also I noticed the Hliftcoeff is different, and has no moment coeffs

You are right! There should be moments both for X and Y lift.
The reason why I never missed it, could be that the capsule is not steered like an aircraft. It does not have active rudders, but flies (a little bit) in the direction of the offset mass center. The steering is done by rolling the capsule around with the RCS roll thrusters.

The capsule steering is perfect with BrianJ's CrewDragon2022. The source code included in the OrbiterSDK samples folder.
When using the Auto Reentry it will roll the capsule a lot during reentry to adjust the reentry path and drop it into the sea within line of sight to the target.

 

[Buck Rogers]

Looking good so far, but you still haven't replied to any of my inquiries regarding those Shadow vessels.

I have, but repeating the question doesn't change the answer. Again, when I have something I will post in the relevant thread. It hasn't been forgotten
Currently still stuck on Airfoils and progress is minimal, help appreciated.

The capsule steering is perfect with BrianJ's CrewDragon2022. The source code included in the OrbiterSDK samples folder.

Still working through the code and API but there's still a lot I haven't figured out, for example the crew dragon has 4 airfoils, 2 designated neg?

 

[Thunder Chicken]

You are right! There should be moments both for X and Y lift.

Moments calculated from the moment coefficients are a correction to account for the fact that the center of lift on an airfoil generally can move as a function of angle of attack. Lift is generally calculated and assumed to act at a fixed quarter chord location on the airfoil (25% of the chord length from the leading edge). For many conventional airfoils that's pretty close, and the moment is used to correct for the small differences.

Typically you need these moment coefficients for the main airfoils as they will affect pitching forces significantly, but on stabilizers and control surfaces those moments are generally minor - the lever arm of a fuselage to the tail control surfaces is much longer and has a much bigger effect.

 

[Luke Reichelt]

I have, but repeating the question doesn't change the answer. Again, when I have something I will post in the relevant thread. It hasn't been forgotten
Currently still stuck on Airfoils and progress is minimal, help appreciated.

I'm sorry, I didn't mean to be rude. I just wanted to know your progress, that's all.

Indeed, lately I've been rather busy catching up with Trekkie on my Star Trek systems. At the moment, he's on a business trip and hopes to resume work on the various vessels and structures required for said systems.

 

[BrianJ]

Still working through the code and API but there's still a lot I haven't figured out, for example the crew dragon has 4 airfoils, 2 designated neg?

Hi,
my knowledge of aerodynamics is sketchy at best, I would hesitate to copy mine - you might be better off finding your own way. I usually start off coding something "reasonable" that "should work", then find I have to hack it to make it behave more like "real life". But I thought I might mention a couple of things that might be useful...
1. The "Lift vector" display in Orbiter only shows the "vertical lift" aerofoil force.
2. "Neg" lift designation - so named because the lift goes the opposite way to the way to a typical aeroplane.
(for a capsule travelling in -Z direction, blunt heatshield first)
3. CrewDragon has 4 airfoils, 2 are for parachutes (they have a "positive lift" profile for stability)
4. My most succesful Mars EDL capsule was "TGO" add-on (conforms to nominal EDL profile quite well, it has two 0-lift airfoils for drag, only airfoil size and ref.point are modified for parachute deploy) - code is in "tgo_edl_capsule.cpp".

It's been a long time since I used anything like spacecraft.dll (or now VesselBuilder) to try and make an EDL capsule - I seem to remember having to do some "work-arounds" for parachute deploy, etc.

Good luck!
BrianJ

 

[Buck Rogers]

Moments calculated from the moment coefficients are a correction to account for the fact that the center of lift on an airfoil generally can move as a function of angle of attack...

Thanks, this is very helpful, moments are a bit of a mystery and I'm still trying to make rhyme or reason from the examples.

center of lift on an airfoil generally can move

Moments are either positive or negative, should I visualise this as a horizontal correction Z+ of the original center of lift position (in m.)?
Generally in the examples I've seen so far they are negative if the lift is negative, and I presume they influence points of stability across the AOA range, but testing so far has been only partially successful.

I'm sorry, I didn't mean to be rude. I just wanted to know your progress, that's all.

Indeed, lately I've been rather busy catching up with Trekkie on my Star Trek systems. At the moment, he's on a business trip and hopes to resume work on the various vessels and structures required for said systems.

No problem. Hope, time willing, to make some progress soon.
Glad to hear you guys are still working on them, look forward to news! You use predominantly Orbiter2016, do you use Orolux with your planetery tex? and what program do you use to make them?

Hi,
my knowledge of aerodynamics is sketchy at best, I would hesitate to copy mine - you might be better off finding your own way. I usually start off coding something "reasonable" that "should work", then find I have to hack it to make it behave more like "real life". But I thought I might mention a couple of things that might be useful...

Good luck!
BrianJ

Thanks, really appreciate the input, hearing how other developers have handeled similar issues is very helpful.

3. CrewDragon has 4 airfoils, 2 are for parachutes (they have a "positive lift" profile for stability)

I "presumed" that the parachutes were only variable drag elements (My C++ is not the best- my coding days are long ago)

4. My most succesful Mars EDL capsule was "TGO" add-on (conforms to nominal EDL profile quite well, it has two 0-lift airfoils for drag, only airfoil size and ref.point are modified for parachute deploy) - code is in "tgo_edl_capsule.cpp".

Mars is where it's happening so that sounds ideal, it should be in many ways very comparable, so only drag and 0 lift (0 CM), I'll play with the numbers a bit more and see if I can get better results.
thanks again for the motivation.

 

[Luke Reichelt]

You use predominantly Orbiter2016, do you use Orolux with your planetery tex? and what program do you use to make them?

Unfortunately, I'm still using Orbiter 2010, and I don't have Orulex installed, so I'm not really sure what I can do there. Regarding the textures, I use the Photoshop plugin LunarCell for Star Trek planets, but only them, as I want them to have a unique look. For planets from other fictional universes (Babylon 5, Star Wars, Blake's 7, et cetera), I use whatever textures I can find online, including from the Celestia Motherlode.

 

[Thunder Chicken]

Moments are either positive or negative, should I visualise this as a horizontal correction Z+ of the original center of lift position (in m.)?

The moments are calculated as the lift force times the horizontal shift of the center of lift in the Z direction. The moment is a torque about the X-axis of the airfoil. If the center of lift moves forward of the quarter chord position, you get a moment that wants to pitch the airfoil upward. If that point moves aft of the quarter chord position you get a downward pitching moment.

Generally in the examples I've seen so far they are negative if the lift is negative,

The idea of negative lift is just taking an airfoil and inverting it so its lift force is downwards instead of upwards. The sign of the moment coefficient shouldn't be related to that - it's a property of the airfoil. You can define the lift, drag, and moment characteristics of an airfoil as a function of AOA, and then use that one definition for airfoils in different orientations.

and I presume they influence points of stability across the AOA range, but testing so far has been only partially successful.

For the main lifting surfaces moments will affect pitching stability on the axes they are defined. You should make some effort to get good data that is continuous from +180 to -180 degrees AOA. If there are any step changes to any airfoil property you're going to have stability problems.

Again, if you are trying to model capsule lifting forces using airfoil models, you really are abusing the model and using it where it was never intended to be used. Many aspects of airfoils like aspect ratio, efficiency, etc.. simply have no analogs in blunt bodies like capsules. You might get something to work, but all you'll ever be able to do is tweak numbers until it seems to fly right in your opinion. It'll never fly with accurate characteristics of a capsule.

 

[Buck Rogers]

Unfortunately, I'm still using Orbiter 2010, and I don't have Orulex installed

Sorry, I meant Orbiter2010! I was interested how your textures work with the 3D generation. AFAIK this is still the easiest way to have 3D landscapes for alien worlds in Orbiter, I think someone tried to make Kerbin for Orbiter2016 but sadly gave up, at some point I'd really like to make one, but without some procedual element I'm not sure how to create enough detailed data.

Regarding the textures, I use the Photoshop plugin LunarCell for Star Trek planets, but only them, as I want them to have a unique look. For planets from other fictional universes (Babylon 5, Star Wars, Blake's 7, et cetera), I use whatever textures I can find online, including from the Celestia Motherlode.

What software do you use to convert to Orbiter? TileEdit?

The sign of the moment coefficient shouldn't be related

This what I initially thought, looking for patterns can be misleading.

Again, if you are trying to model capsule lifting forces using airfoil models, you really are abusing the model and using it where it was never intended to be used. Many aspects of airfoils like aspect ratio, efficiency, etc.. simply have no analogs in blunt bodies like capsules. You might get something to work, but all you'll ever be able to do is tweak numbers until it seems to fly right in your opinion. It'll never fly with accurate characteristics of a capsule.

I guess the new Airfoil function will make making capsules easier/more accurate in the next Orbiter release. If I can tweak it so under nominal conditions it follows the historic flight path I'll be happy, just need the time for all the testing.