Re: [Phys-L] Aeroplanes and air temperature

[Carl Mungan <mungan@usna.edu>]

Interesting but complicated. We've got change in drag and lift. We've also
got  to consider whether an animal can metabolically work harder (to flap
their wings) when it's hot out.

I'm pretty sure there is some top temperature limit for any given species
of bird, excluding short emergency flights.

On Wed, Jun 21, 2017 at 2:30 PM, Bill Norwood <bnorwood111@gmail.com> wrote:

> Carl,
> - Is there a temperature above which birds cannot fly when there are no
> updrafts?
> Bill
>
> On Wed, Jun 21, 2017 at 2:27 PM, Carl Mungan <mungan@usna.edu> wrote:
>
> > Are you asking what the top speed is of a plane on an infinitely long
> > flat pavement? Surely reducing air density and hence drag (with all flaps
> > stowed) will help, right?
> >
> > It seems to me that reducing the air density makes it easier to reach a
> > desired speed, but the reduced lift means you need a higher speed. From
> > that point of view, it seems like a tradeoff to me.
> >
> > On Wed, Jun 21, 2017 at 2:22 PM, Bill Norwood via Phys-l <
> > phys-l@mail.phys-l.org> wrote:
> >
> > > Carl,
> > > - At what temperature, safety margin aside, do you think that none of the
> > > planes could fly regardless of runway length?
> > > Bill
> > >
> > > On Wed, Jun 21, 2017 at 2:16 PM, Carl Mungan <mungan@usna.edu> wrote:
> > >
> > > > I'm not so sure. The density is presumably proportional to pressure
> > > divided
> > > > by absolute temperature.
> > > >
> > > > Absolute temperature at 119 F divided by that at 72 F is a bit less
> > > than
> > > > 109%. A 9% effect isn't negligible but isn't going to require a runway
> > > > twice as long or something. Speed squared down the runway is
> > > proportional
> > > > to distance along the runway approximately.
> > > >
> > > > The other thing I'm wondering about is the air pressure. We're changing
> > > > both the number of molecules per square area (perhaps not important
> > > since
> > > > the change doesn't reach all the way up to the top of the atmosphere
> > > but
> > > > only near the surface) and the speed of the molecules (and hence their
> > > > impact speed and frequency). I suppose to zeroth order P is
> > > independent of
> > > > T for an open sample of gas but it isn't obvious to me excluding
> > > > large-scale convective effects.
> > > >
> > > > On Wed, Jun 21, 2017 at 1:55 PM, Bill Norwood via Phys-l <
> > > > phys-l@mail.phys-l.org> wrote:
> > > >
> > > > > Antti,
> > > > > - I find the explanation satisfactory.
> > > > > - Thanks for sharing and asking.
> > > > > Bill Norwood, U of MD at College Park
> > > > >
> > > > > On Wed, Jun 21, 2017 at 12:50 PM, antti.j.savinainen via Phys-l <
> > > > > phys-l@mail.phys-l.org> wrote:
> > > > >
> > > > > > Hi,
> > > > > > there has been recent news on aeroplanes which cannot fly because
> > > the
> > > > air
> > > > > > temperature is too high. Here is one explanation why this is so:
> > > > > > https://www.wired.com/story/phoenix-flights-canceled-heat/
> > > > > > How do you find the explanation?
> > > > > > Regards,
> > > > > > Antti Savinainen, Finland
> > > > > > _______________________________________________
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> > > >
> > > >
> > > > --
> > > > Carl E. Mungan, Professor of Physics  410-293-6680 (O) -3729 (F)
> > > > Naval Academy Stop 9c, 572C Holloway Rd, Annapolis MD 21402-1363
> > > > mailto:mungan@usna.edu     http://usna.edu/Users/physics/mungan/
> > > > _______________________________________________
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> >
> >
> >
> > --
> > Carl E. Mungan, Professor of Physics  410-293-6680 (O) -3729 (F)
> > Naval Academy Stop 9c, 572C Holloway Rd, Annapolis MD 21402-1363
> > mailto:mungan@usna.edu     http://usna.edu/Users/physics/mungan/


-- 
Carl E. Mungan, Professor of Physics  410-293-6680 (O) -3729 (F)
Naval Academy Stop 9c, 572C Holloway Rd, Annapolis MD 21402-1363
mailto:mungan@usna.edu     http://usna.edu/Users/physics/mungan/