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Re: Archie a non-flyer? (was:Re: origin of bats/reply 2 to TMK)



I agree with Mike, but have inserted a couple of extra comments.
JimC

----- Original Message ----- From: "Michael Habib" <mhabib5@jhmi.edu>
To: <rmtakata@gmail.com>
Cc: <dinosaur@usc.edu>
Sent: Tuesday, June 24, 2008 6:03 PM
Subject: Re: Archie a non-flyer? (was:Re: origin of bats/reply 2 to TMK)



The trick is the scale of the turbulence in the flow: a turbulent boundary layer will tend to stay attached to the wing surface (which is helpful), while massive flutter causes separation of the flow from the wing

Though massive flutter will cause seperation, turbulent seperation also occurs in the absence of flutter and and flutter isn't usually present in the turbulent seperated area (though it can be). A symmetric feather can resist flutter by simply having a relatively more massive shaft (which was the reason that I said that it would increase the biological cost of the moult).


and associated large-scale turbulent wakes (and thus a sudden loss of lift and the ground rushing up rather quickly to offer its salutations).

Again, large-scale turbulent wakes can be associated with flutter, but that is not always the case. Flutter occurs when the aeroelastic number falls below the aeroelastic limit. BTW, when the wing stalls, the lift doesn't go to zero, but it is substantially reduced. Reminds me of an old saying about airplanes, "If you want to climb, pull the stick back. If you want to descend, pull the stick back even more".


The camber of the wing cross section increases effective angle of attack, actually.

Depending upon the airfoil section, for a given angle of attack, it typically increases the lift coefficient by about 0.2 or 0.3. Most airplanes with cambered wings cruise at a slightly negative angle of attack and see positive angles of attack only when climbing or in tight turns.


More importantly, the tapered shape forces a stagnation point at the trailing edge,

At increasing angles of attack, that stagnation line moves forward. Note that this is not the same stagnation line that is seen near the leading edge of the airfoil.