ATT Aerodynamic Buffs: Ideal boundary layer characteristics at the stall?
So I'm studying for ATPL systems, and have split answers in a question. Any advice on the correct answer and/or the "CASA correct" answer? Here's the question:
In order to delay flow separation on an aerofoil at the stall, the characteristics of the boundary layer should ideally be:
a. laminar due to reduced surface friction b. turbulent due to the higher velocities at the wing surface
Yep. The good old vortex generator applies the concept of energising the laminar layer with " turbulent " air for one of a better word. But if in doubt go C
In order to prevent separation of a boundary layer in the presence of an adverse pressure gradient, the boundary layer must have the highest possible kinetic energy. If a choice is available, the turbulent boundary layer would be preferrable to the laminar boundary layer because the turbulent velocity profile shows higher local velocities next to the surface.
....fascinating no doubt but what's the point of asking such a question in an exam when during yr normal life as an Airline driver you can do nothing about that characteristic of airflow or even know it's happening other than it's end result (stall). Mr Airbus & Mr Boeing have made sure that such aerodynamic forces are relayed to us drivers via the multiple complex stall warning devices etc,reaction by the fright crew should be automatic, it's all about AoA, that's all we need to know/remember!.........weird how the boffins of the aviation world reckon we ought to know it from a purists POV.
But at the end of the day just pass the exam/s then do a memory dump & get on with the actual flying
You're right of course Wally, pilots don't need to know the finer points of wing design in order to fly the aircraft. It's a practical job certainly.
But, perhaps from sentimentality (!) I would not like to work in the industry where pilots really are just bus drivers - that is, they don't know why this aircraft has Type A flaps and that one has Type B flaps, etc. No disrespect to the real bus drivers of course, we all have a job to do. For me, I like to work in a job requiring technical knowledge.
BTW - turbulent FL is best at the stall. High speed flight, friction & drag are important. Low speed flight, they aren't. A gross generalisation that helps with this kind of question.
