Heat Shield Occlusion?

[Kelderek]

What is the shape of the slipstream of hot air diverted around your vessel when you use a heat shield? Please forgive this *very* crude paint drawing:

I can think of 3 different ways this might work:

1. In this option the air would flow out in a parabolic shape. You could conceivably have parts radially attached further away from your heat shield that are wider than the diameter of the shield itself as long as it's far enough behind it.

2. In this option the air flows straight back along the prograde-retrograde axis. Any parts outside the diameter of the shield would likely get blown off.

3. In this option the air flows inward and parts inside the diameter of the shield, but too far behind might overheat.

4. Other shapes?

I think this might be useful to know for placing heat shields on things other than the usual command pods. Does anyone know how this works in the new aero system?

[Xannari Ferrows]

It depends on your velocity. To put it in a basic way, you start off in diagram one, and move towards diagram two. The process is logarithmic, and the air stream will never quite reach perpendicularity with the heat shield, but it gets closer as you move faster.

The closer it gets to perpendicular, the more you are affected by drag forces.

Basically diagram one is the most correct, but it's more or less and average. This could be illustrated on a graph as well.

[Kelderek]

So does this mean that diagram 3 would never happen? If I use a 2.5m heat shield and further back I have some parts attached to a 1.25m core then they should be safe? Or is there still some dangerous drag present? I guess this idea of shapes wouldn't be exclusive to using heat shields, I'm thinking of streamlining designs in general with respect to atmospheric drag.

[Xannari Ferrows]

Any cross sections of your structure present in flight will produce drag. Whatever is behind a heat shield should be fine whenever you're moving prograde. Deviating from that will expose the other parts, but it will also divert your trajectory to whatever direction desired based on the properties of your lift.

If only aerodynamic heat shields existed...