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

[jrc <jrccea@bellsouth.net>]

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.