Hi,
many thanks for the input. I'm sure many folks here have a much better grasp of aerodynamic simulations than I do!
However, it still seems intuitively right (not always a good guide, I know) that for a capsule where the effective aerodynamic surface is oriented in the XY vessel plane, it should be possible to specifiy a simulated aerofoil in that orientation, and have Orbiter handle the lift and drag calculations in a similar manner to the current aerofoils (thus reducing/eliminating the need for workarounds - see
@indy91 post above).
What if you could define them by a normal vector or an alignment matrix?
That would certainly be sufficient, but might be more complex than a simple 3rd option of XY plane, but more flexible from a user point-of-view.
This airfoil direction was omitted on purpose. By definition lift is the aerodynamic force perpendicular to the relative wind direction, so defining an airfoil orthogonal to the direction of flight is kind of a weird idea.
The lift would be perpendicular to relative wind direction, and in the plane of relative wind direction and the normal to the aerofoil surface.
I think its only weird if you're thinking about it terms of Shuttle type vessels.
Could you model a blunt capsule as an airfoil? Sure, I guess, maybe, but it would be a perpetually stalled airfoil with a nearly 90° angle of attack
That sounds about right to me, for a capsule!
developing hardly any lift in the Z direction with all of the drag expressed as profile drag.
I'm not sure why lift would be in the Z direction? (see my definition of lift vector above).
Maybe not much lift - that would depend on how you specify the lift in the LiftCoefficient function, though.
Profile drag is one of my concerns - for current ZX plane aerofoil, profile drag increases as AoA increases from 0.
But for a capsule with an aerofoil in XY plane, profile drag should
decrease as AoA increases from 0 (surely?).
I think most people intuit that drag is the major force acting on the vehicle in that direction, and calculating a single drag force based on relative wind is far simpler than additionally calculating lift coefficients and forces that are always around zero.
I naively imagine calculating drag/lift for an XY plane aerofoil is not much more work than for the current orientations?
As you mention, the current models allow both the drag and lateral lift forces for bodies like capsules, so there would be nothing gained by doing this except adding confusion.
Except that folks like Indy91 and myself are having to find workarounds to make things come out right in the sim.
But I can live with that
Well, as I say, I have very little clue as to the optimal simulation of aerodynamics!
I'm very happy to leave it to you folks who generously give your time to develop Orbiter
It was just something that comes to my mind everytime I start making capsule reentry stuff.
Thanks,
BrianJ