Is the highly optimized high subsonic cruise airfoil less safe for higher AOA flight? [duplicate]

An examination of the 737 airliner wing profile and that of a blue whale leads to the question of whether the high Reynolds number subsonic cruising airfoil and the low speed, high AOA airfoil are compatible.

Supercritical airfoils are designed for efficient cruising flight, relying on bottom lift and minimizing acceleration of air over the top to avoid creating drag producing transsonic shock waves.

The blue whale is designed to cruise efficiently over thousands of miles, through a viscous, non-compressible fluid (water). Their shape includes a rounded, sloping lower fore and a flatter top, very similar to a supercritical airfoil! Applying thrust to this shape would provide "lift" simply by directing water "down" (or pushing the whale "up").

Reynolds Number = Velocity×Chord/Kinematic Viscosity

Reynolds Number 20th century Type VII U Boat (submarine): speed: 4 meters/second chord length: 70 meters. Kinematic viscosity (sea water): 1.04 × 10e-6

      4 × 70/1.04 × 10e-6 = 269 million


Reynolds number Blue Whale: speed: 5 meters/second, chord length: 30 meters Kinematic viscosity (sea water): 1.04 × 10e-6

      5 × 30/1.04 × 10e-6  = 144 million


Reynolds number Supercritical Airfoil (approximate): speed 300 meters/second, Chord length: 4 meters Kinematic Viscosity (air): 1.46 × 10e-5

    300 × 4/1.46 × 10e-5 =     82 million


Reynolds Number Cessna 172 Airfoil : speed 30 meters/second Chord length: 2 meters Kinematic Viscosity (air): 1.46 × 10e-5

   30 × 2/1.46 × 10e-5 =         4 million


Reynolds Number Albatross (bird) airfoil: speed 10 meters/second Chord length: 0.2 meters Kinematic Viscosity (air): 1.46 × 10e-5

  10 x 0.2/1.46 x 10e-5 =        140,000


We can see the supercritical wing is more in the range of the blue whale!

When pitched up to a higher AOA, this shape would be a very poor wing in the classic Bernoulli sense, as the significantly contributing top lift would be lost at a lower AOA than a top rounded airfoil, behaving much more like a flat plate (see polars).

There are accounts of airline pilots extending their slats at higher speeds for better performance (and getting into trouble for doing so).

So, for modern designers, would it not be important to consider a more robust low speed system that could be left on (in varying degrees) at higher speeds (V maximum flaps and slats extended airspeed) to help avoid stalling?

This could create a wider safety margin for the climb-out and landing phases of flight. Hard earned efficiency gains in cruising flight (from the supercritical wing) would be kept, when they are fully retracted, but only at safe speed and AOA conditions (for example, above 10,000 feet or at cruising flight level).

• I think whales benefit a lot from their size, alas buoyancy is negligible in heavier-than-air flight. Apart from that distraction (whales don't stall), it's a good question. – ymb1 Sep 27 '19 at 15:42
• Blue whales and their like, minke and sei, are amoung the fastest of the whales. They could not be caught by sailing ships. If only buoyant, they would be fully symmetrical (like blimps). Look again at their profile, and please give me a Reynolds number of a 35 meter blue whale swimming through water at 20 knots. My guess is they are both bouyant and partially lifting (like some modern airships) – Robert DiGiovanni Sep 27 '19 at 16:00
• If that's the case, how do they deal with their lousy aspect ratio? It can be a good question for Physics.SE or Biology.SE. Their shape is so (and they flap up/down not left/right like fish) because of their mammalian vertebral column. IMO the question will be better if we forget about whales here. – ymb1 Sep 27 '19 at 16:08
• I think the whole "whales" thing is clouding your question and will get people off-topic. Whales use other "lift devices" than just the fins (like air in the lungs) so I don't think you can do an apples-for-apples comparison here on the other lift devices. Plus whales don't travel at trans-sonic speeds, even if they are fast. – Ron Beyer Sep 27 '19 at 16:10
• @ymb1 The underbelly fairing of the Pilatus PC-24 in another question got me thinking. – Robert DiGiovanni Sep 27 '19 at 16:38