Kerbal Space Program

Air drag value scales with instantaneous mass. This causes issues with terminal velocity of parts that disobey basic principles of IRL physics.

Effects and recreation of the bug can be done with some detail in following video:
http://www.youtube.com/watch?v=Pgu_FRlXJ8g

Time 13:25 - 22:15

• Same design parts with different masses fall at same speed.
• Same combined components with a fixed lower drag value and higher scaling drag values result in "lighter" assembly falling faster than the "heavy" one.

Recommended fix:
Whatever drag values that need to be assigned to a part, should remain constant through flight. If limitations of systems preclude using surface area and shape constants based on cross sections, then it should be indexed off the dry mass only of any particular part, and not change as it looses mass due to fuel expenditure, etc.

Notes:
Understand drag model is due for overhaul in next couple versions. Listing as bug to document the specific phenomena that should be tested against in new model.