Lift/Drag attack point, flipping ships, and other SC3 issues!

[Epsilon]

Heh. Of course, I get this -after- I'd set the flight parameters aside...

In any case, the help -is- appreciated, and a 'confirmation' of that certainly gives me a direction in which to point. For the moment, my problem is texturing.

But it's working! Kinda. It ain't gonna be that pretty, but it should work well enough. Since that seems to be my thing, question for you modellers/textureres out there! Does Orbiter have issues applying different textures to different parts of the same object? I think it does... Of course, since I didn't see anything specific pertaining to it in the forums, I ask anyway, just to make sure I'm not missing something.

 

[ar81]

See http://www.mh-aerotools.de/airfoils/

 

[Albinon]

Greeting folks, form a posting newbie. I have been playing with orbiter for a few years now and been making my own DLLs. I decided to challange my self (not that hard) and try to build a capsule rentry body based on the CEV. I can figure aircraft CoG/CoP OK, but this little puppy has me licked. I tried looking at NASA docs and it seems there is no easy way to calculate. They seem to do it right up to time of reentry. Using legacy SetLiftCoeffFunc, I get somewhat close but it still doesn't move right. My design is CAP_CS = {12.67,12.68,21.75}, CAP_PMI = {2.78,2.80,3.38}, CAP_EMPTY_MASS = 7891, Radius of 2.72 (after scaling down to Orbiter) and a height if 3.52 (1.76 +/- of origin in Meshwizard). I tried using ShuttleA_PL from ShuttleA MkII to create an Airfoil. I had to rotate X-Axis -90 on the ShuttleA_PL MomentCoeff. Once chute is deployed, the craft spins and whips. Using center of mass didn't work and setting CG at -Z anywhere did not make a difference. Any easyway to calculate CG with out having to hunt and pick?

 

[Albinon]

Got an answer

I went to the able and capable people at Apollo NAASP. Seems my SetCW was inverted and I needed to rotate my SetCrossSections Y +90. They also provided a CreateAirfoil and CoeffFunc. My original CG calcs were close and I needed to define my Aerodynamics and orientation to Orbiter standards. All I have to do now is play with a few SetCrossSections parameters and tickle the CG slightly since I am burning too much RCS fuel during reentry to keep "heads down" orientation and the landing Velo is a bit high.

 

[MajorTom]

Some great stuff in this thread, folks!

Dr. Martin,

Thanks for this great program and environment!

Epsilon,

Based on some of your earlier posts here, it seems to me you might be interested in reading about the Von Karman Line. (Paragraph 2 is particularly interesting, it seems to describe your earlier issue with using control surfaces at high altitudes, such as 45 km...)

It seems to me that the region between 30 and 130 km altitude is really a "dead zone" for air and spacecraft, good only for re-entry. Try to orbit below 130 km, and I'm sure your spacecraft will be coming down within a few hours. And it's extremely hard to fly above 30 km with an aircraft.

Albinon,

I'd love to learn from you how you coded your lift and drag work for capsules. There has been some really good work done by the Apollo teams here, and also Francisdrake's CEV really seems to have excellent re-entry abilities, with enough lift to do "skip" reentry. I'm working now on enhancing the SoyuzTMA add on and would like very much to add such capability to the new dll.

The trick, as I understand it, is to have your center of mass be slightly off-center, so your craft generates lift during re-entry when it assumes its natural position, without having to use any RCS fuel. But if you've got too much lift, you can zero it by rolling 90 degrees, or reverse it by rolling 180 degrees about your roll axis, which takes very little fuel. Just like real Apollo.

However, I'm a real newbie at coding dll's. Anyone who is willing to work with me will probably have to answer a lot of dumb coding questions!

Happy Holidays to all...

 

[Albinon]

Got some details

Some great stuff in this thread, folks!

The trick, as I understand it, is to have your center of mass be slightly off-center, so your craft generates lift during re-entry when it assumes its natural position, without having to use any RCS fuel. But if you've got too much lift, you can zero it by rolling 90 degrees, or reverse it by rolling 180 degrees about your roll axis, which takes very little fuel. Just like real Apollo.

The attached file has the basic minimum. The capsule heght should not be more than 3.62 and diameter more than 5.5. You will have to fiddle with the CreateAirfoil location reference a little, not more than .01 increments until your craft stabilizes. I found that the Y location just about fit. The Z location will control the AoA nicely.

 

[ar81]

For reference only
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