Re: [Phys-L] Aeroplanes and air temperature

[Carl Mungan <mungan@usna.edu>]

I didn't see the comments until you told me to look at them. They make a
good point that the engines will also have a hard time providing
acceleration (along the runway) when the air is thin.

On Wed, Jun 21, 2017 at 2:26 PM, Stefan Jeglinski <jeglin@4pi.com> wrote:

> Based on the article's comments, it seems like there might be
> contributions from flight rules as well, some but not all of which may be
> physics based? I'm sure JD will be able to correct the discussion on all
> counts!
>
> One of the comments also refers to the NASA resources on lift. I found
> that to be a good read.
>
> Stefan Jeglinski
>
> > On Jun 21, 2017, at 11:16 AM, 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
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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/