Re: [Phys-L] Aeroplanes and air temperature

[brian whatcott <betwys1@sbcglobal.net>]

Airline operations, and to some extent light-plane pilots,  do not deal 
in limiting  air temperatures, but rather maximum weight for the 
density-altitude and runway length available.
 A sea plane unconstrained by takeoff length and required angle of 
climb would still have some minimum weight limit  at which level flight 
could be maintained and so it is possible to say that the prevailing 
density altitude must certainly be lower than this limit (ignoring 
ground-effect which provides a measure of extra lift at half wing span 
above the surface ). For light aircraft, the decreasing power available 
limits their 'service ceiling' (>=150fpm rate of climb) to the low or 
mid teens of altitude unless turbo/superchargers or normalizers are 
used. For commercial airliners, the confluence of limiting Mach Number 
and Stall Speed sets the highest altitude of operation. (in the 30s to 
50s of thousands of feet.)
(As far as I know - the Spruce Goose made only one trial flight at low 
altitude, so not much data available).
Brian W

On 6/21/2017 3:10 PM, Bill Norwood via Phys-l wrote:
> Anybody got any idea, given practical considerations, what the maximum
> take-off temperature would have been for the spruce goose?
>
> Bill N
>
> On Wed, Jun 21, 2017 at 3:59 PM, brian whatcott <betwys1@sbcglobal.net>
> wrote:
>
> > I find this explanation is what I would call a physicist-style approach.
> > Talking about air molecules....    Better to say that the ground elevation
> > / altitude that an airplane cares about at takeoff is the density altitude
> > - which increases with air temperature.
> > Increased density altitude requires higher ground speed in order to have
> > lift balance weight at takeoff, which in turn demands longer runways or
> > higher power to weight. Civil airliners are operated so as to have enough
> > 'balanced' runway length left to brake to a halt from takeoff speed, which
> > further constrains hot and high operations.
> >
> > Brian W
> >
> >
> >
> > On 6/21/2017 11:50 AM, antti.j.savinainen via Phys-l 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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