General Question More AOA results in less Drag??

[Swisslady]

Orbiter 2016; Reentry with Delta-Glider or Atlantis Shuttle;

AOA increase from 00 towards 30 degrees --> Drag also Increases, so far so good, but,
AOA increase from 30 towards 90 degrees --> Drag decreases.... :idk:

Thanks for any Confirmation or Explanation.

 

[n122vu]

Drag is also a by-product of lift, so perhaps even though there is drag due to AoA, the amount of drag being contributed as said by-product decreases as the wings contribute less lift, making the total amount of drag less?

 

[Urwumpe]

Orbiter 2016; Reentry with Delta-Glider or Atlantis Shuttle;

AOA increase from 00 towards 30 degrees --> Drag also Increases, so far so good, but,
AOA increase from 30 towards 90 degrees --> Drag decreases.... :idk:

Thanks for any Confirmation or Explanation.

Yes, can happen that way, even in the real world.

EDIT: Yes, it seems to be uncommon for typical airfoils to see drag decrease before 90°, but remember, that the aircraft only rarely consists of the wing alone.

 

[RisingFury]

Yes, can happen that way, even in the real world.

EDIT: Yes, it seems to be uncommon for typical airfoils to see drag decrease before 90°, but remember, that the aircraft only rarely consists of the wing alone.

No, the DG's aerodynamics model - and in general the aerodynamics models in Orbiter - need some serious work. Yes, lift contributes to drag, but at 90° AOA we're talking about exposing the entire surface area of the glider to the air stream and having it act as a blunt projectile.

Just the way aerodynamics is implemented in code is already a bit weird.

Maybe now that we have a giant leap forward with terrain, a more comprehensive atmospheric model could be brought to Orbiter?

 

[Urwumpe]

Maybe now that we have a giant leap forward with terrain, a more comprehensive atmospheric model could be brought to Orbiter?

That is the matter of the aerodynamic solver of Orbiter, right now it uses classic lift functions and is rather poorly suited for more complex aerodynamics.

And of course a matter of the add-ons to provide better aerodynamics.

BUT: AFAIR, there are really vehicles that have maximum drag already before 90°, especially conical shapes.

 

[RisingFury]

And of course a matter of the add-ons to provide better aerodynamics.

Which explains the terrible state of aerodynamics in Orbiter. We need a more comprehensive model that "every man for himself".

BUT: AFAIR, there are really vehicles that have maximum drag already before 90°, especially conical shapes.

Yes, sure, but I'd be much more comfortable claiming that the Space Shuttle is a better approximation for a Delta Glider than a conical shape.

 

[Urwumpe]

Yes, sure, but I'd be much more comfortable claiming that the Space Shuttle is a better approximation for a Delta Glider than a conical shape.

I am pretty sure, aerodynamically, the DG is unique. :lol:

But how could you help people get better aerodynamics? Even with what is possible with Orbiter, you still need to span between "unrealistic aerodynamics with desired results" and "realistic aerodynamics with realistic results".

 

[RisingFury]

I am pretty sure, aerodynamically, the DG is unique. :lol:

But how could you help people get better aerodynamics? Even with what is possible with Orbiter, you still need to span between "unrealistic aerodynamics with desired results" and "realistic aerodynamics with realistic results".

You have to assume that the general addon developer doesn't know much about aerodynamics, so a suite of tools need to be developed to aid creation of aerodynamics, which included a general "Orbiter aerodynamics for dummies"

There would be two advantages to this:
1.) It would raise the quality of aerodynamics. I don't expect fully realistic results, but in general Orbiter craft have too little drag and too much lift.
2.) It would unify how vessels handle given what their properties are. We currently have several vessels that are very similar, but handle wildly differently.

The Orbiter aerodynamics model is currently so simplistic that it only takes into account horizontal and vertical surfaces, but reality is so much more complicated, from V tails, to dihedrals and anhedrals...

There's also no turbulence in Orbiter and stalls are very disappointing. I've tried many times to make planes tip stall and it's very difficult or impossible. Generally the nose just drops and nothing unexpected happens. DGIV is so stable that if you cut engines after takeoff for a few seconds, but maintain pitch up along with RCS, you end up with a powered backflip low over the runway. In a realistic scenario, at high AOA the vessel would lose stability and tumble before crashing...

While at it, a stress model could be implemented as well, to estimate the stresses the vessels is experiencing. And yes, that can be done in addons... but it could be done so much better in the core when every addon could make use of it.

 

[Urwumpe]

While at it, a stress model could be implemented as well, to estimate the stresses the vessels is experiencing. And yes, that can be done in addons... but it could be done so much better in the core when every addon could make use of it.

Well, I see such things to be more an issue of the add-on framework. Orbiter API is just the core, and we still have a good demand for middleware. For example, calculating the aerodynamic forces would be easily possible in any thinkable real-time model inside the add-on DLL, if there is a stable way to get the aerodynamic forces properly into Orbiter. Like adding a force to a vessel with a flag "Lift force" on it, so it is also properly displayed in the planetarium mode for teaching and debugging, or could also be properly recorded by other add-ons.