Effect of Subsidence on Night Flying

[Ravi]

Hey Guys,

I was just wondering; would anybody be able to give me detailed
information on the effects of atmospheric subsidence during night
flying in terms of aerodynamic and engine considerations?

I would also appreciate it if someone could provide me with links
and detailed explanations of the said phenomenon.

[Matt Barrow]

"Ravi" > wrote in message
oups.com...
> Hey Guys,
>
> I was just wondering; would anybody be able to give me detailed
> information on the effects of atmospheric subsidence during night
> flying in terms of aerodynamic and engine considerations?
>
> I would also appreciate it if someone could provide me with links
> and detailed explanations of the said phenomenon.

http://www.google.com

[Paul Tomblin]

In a previous article, "Matt Barrow" > said:
>"Ravi" > wrote in message
oups.com...
>> I was just wondering; would anybody be able to give me detailed
>> information on the effects of atmospheric subsidence during night
>> flying in terms of aerodynamic and engine considerations?
>
>http://www.google.com

I think you mean:
http://www.just****inggoogleit.com/search.pl?query=atmospheric+subsidence


--
Paul Tomblin > http://xcski.com/blogs/pt/
As convenient as it is for information to come to us, libraries do have a
valuable side effect: they force all of the smart people to come together in
one place where they can interact with one another. -- Neal Stephenson

[Gig 601XL Builder]

"Paul Tomblin" > wrote in message
...
> I think you mean:
> http://www.just****inggoogleit.com/search.pl?query=atmospheric+subsidence


THat is one of the greatest things I have seen on the internet ever.

[Peter Duniho]

"Ravi" > wrote in message
oups.com...
> I was just wondering; would anybody be able to give me detailed
> information on the effects of atmospheric subsidence during night
> flying in terms of aerodynamic and engine considerations?

As funny as Paul's reply is, I doubt you'll find anything specific to your
question there. I'm still looking for a good explanation of what exactly
"atmospheric subsidence" actually is.

Assuming the dictionary definition is appropriate, there would be little, if
any, affect of atmospheric subsidence during night flying in terms of
aerodynamic and engine considerations. It might affects density altitude,
but since you can determine that directly, and since there are many other
factors that would affect that in a MUCH more significant way, atmospheric
subsidence is irrelevant from a practical standpoint.

Hope that helps.

Pete

[Bob Gardner]

I agree. Not worth spending a single brain cell on.

Bob Gardner

"Peter Duniho" > wrote in message
...
> "Ravi" > wrote in message
> oups.com...
>> I was just wondering; would anybody be able to give me detailed
>> information on the effects of atmospheric subsidence during night
>> flying in terms of aerodynamic and engine considerations?
>
> As funny as Paul's reply is, I doubt you'll find anything specific to your
> question there. I'm still looking for a good explanation of what exactly
> "atmospheric subsidence" actually is.
>
> Assuming the dictionary definition is appropriate, there would be little,
> if any, affect of atmospheric subsidence during night flying in terms of
> aerodynamic and engine considerations. It might affects density altitude,
> but since you can determine that directly, and since there are many other
> factors that would affect that in a MUCH more significant way, atmospheric
> subsidence is irrelevant from a practical standpoint.
>
> Hope that helps.
>
> Pete
>

[private]

Unless we are talking about low canyon flying, rising terrain, or a small or
obstructed or sloping airstrip affected by mountain leaside or solar
subsidence or catabatic flow, particularly if off a glacier.

Just my .02

"Bob Gardner" > wrote in message
...
> I agree. Not worth spending a single brain cell on.
>
> Bob Gardner
>
> "Peter Duniho" > wrote in message
> ...
> > "Ravi" > wrote in message
> > oups.com...
> >> I was just wondering; would anybody be able to give me detailed
> >> information on the effects of atmospheric subsidence during night
> >> flying in terms of aerodynamic and engine considerations?
> >
> > As funny as Paul's reply is, I doubt you'll find anything specific to
your
> > question there. I'm still looking for a good explanation of what
exactly
> > "atmospheric subsidence" actually is.
> >
> > Assuming the dictionary definition is appropriate, there would be
little,
> > if any, affect of atmospheric subsidence during night flying in terms of
> > aerodynamic and engine considerations. It might affects density
altitude,
> > but since you can determine that directly, and since there are many
other
> > factors that would affect that in a MUCH more significant way,
atmospheric
> > subsidence is irrelevant from a practical standpoint.
> >
> > Hope that helps.
> >
> > Pete
> >
>
>

[Matt Barrow]

"Paul Tomblin" > wrote in message
...
> In a previous article, "Matt Barrow" > said:
> >"Ravi" > wrote in message
> oups.com...
> >> I was just wondering; would anybody be able to give me detailed
> >> information on the effects of atmospheric subsidence during night
> >> flying in terms of aerodynamic and engine considerations?
> >
> >http://www.google.com
>
> I think you mean:
> http://www.just****inggoogleit.com/search.pl?query=atmospheric+subsidence
>
BIG :~)

[tony roberts]

You'd do all that stuff at night?
I ain't flying with you :)

Tony

--

Tony Roberts
PP-ASEL
VFR OTT
Night
Cessna 172H C-GICE


> Unless we are talking about low canyon flying, rising terrain, or a small or
> obstructed or sloping airstrip affected by mountain leaside or solar
> subsidence or catabatic flow, particularly if off a glacier.
>

[private]

Hello Tony,

The weather is not aware of the definition of legal night and begins its
process of night time cooling and ciculation long before dark.

IMHO summertime catabatic evening downslope flow can be expected on the
eastern slope of any of the Rockies. Lots of destinations with lights will
tempt a late takeoff for a night flight across foothills/praire or down the
middle of your interior valley. Late in the day the slope in the shade will
be cooling, and cold air from the higher ground and glaciers to the west,
combined with the prevailing westerlies may result in large areas of sinking
air that can surprise those who think the density altitude has improved
because the sun is low in the sky. The sinking air will be warmed somewhat
by compression and the density altitude may not be much better than earlier
in the day. Combine an airport on the wrong side of the valley, with a
loaded aircraft and some rising ground and we have another failure to climb
situation.

I seem to recall a thread about the best side of a mountain valley to fly
and this would be the classic trap when flying the eastern slope/western
side of our valleys late in the day. If you have lots of altitude and power
to burn it will be smooth, but not the best place to be low and heavy, and
any turn away from terrain will likely be downwind.

Just my .02 YMMV


"tony roberts" > wrote in message
news:nospam-9F1FC6.21063024062005@shawnews...
> You'd do all that stuff at night?
> I ain't flying with you :)
>
> Tony
>
> --
>
> Tony Roberts
> PP-ASEL
> VFR OTT
> Night
> Cessna 172H C-GICE
>
>
> > Unless we are talking about low canyon flying, rising terrain, or a
small or
> > obstructed or sloping airstrip affected by mountain leaside or solar
> > subsidence or catabatic flow, particularly if off a glacier.
> >

[Peter Duniho]

"private" > wrote in message
news:3Q6ve.1795956$6l.1699114@pd7tw2no...
> [snip]

None of what you wrote suggests that atmospheric subsidence would have any
significant effect on the aerodynamics or engine of an airplane.

It is true that there are variety of atmospheric effects related to
nightfall. But they don't change the way the airplane flies, not in a way
that requires even knowing about atmospheric subsidence, never mind
understanding it.

Pete

[private]

"Peter Duniho" > wrote in message
...
> "private" > wrote in message
> news:3Q6ve.1795956$6l.1699114@pd7tw2no...
> > [snip]
>
> None of what you wrote suggests that atmospheric subsidence would have any
> significant effect on the aerodynamics or engine of an airplane.
>
> It is true that there are variety of atmospheric effects related to
> nightfall. But they don't change the way the airplane flies, not in a way
> that requires even knowing about atmospheric subsidence, never mind
> understanding it.
>
> Pete

Hello Pete,

I agree that subsidence does not change aircraft aerodynamics, and does not
have a significant effect on engine power. What it does do is change the
way an aircraft performs. Rising air adds to an aircraft's climb rate,
sinking air subtracts from it. There will be small changes in maximum level
cruise speed and aircraft attitude with respect to horizon when flying in
descending air.

IMHO it is better to have unrequired knowledge than to be in ignorance when
that knowledge is needed. My main instructor always maintained that you can
never have too much weather knowledge.

There is some discussion of subsidence and katabatic and glacier fed
downslope winds in this excellent BC weather manual from Navcan. There is
also discussion of coastal diurnal and wintertime outflows.
http://www.navcanada.ca/ContentDefinitionFiles/publications/lak/bc/BC31E-V.P
DF
Note chapter 2 Aviation Weather Hazards, page 28 provides discussion of
glacier winds and notes local wind speeds to >80 knots and notes that these
winds may be magnified by terrain funneling and comments that they may be
pulsing in a kind of reverse thermal. I would submit that this subsidence
is substantial and hardly "irrelevant from a practical standpoint."

This subsidence can add to the reduction of performance due to density
altitude and is often a factor in failure to climb after takeoff or
inability to out climb rising terrain and has contributed to lots of
crumpled aluminum in the mountains.

Just my .02

[Bob Gardner]

Not to beat this dead horse any deader, but folks who learn to fly where
this knowledge is important, such as Canada, Alaska, New Zealand, etc, get
it as part of their training. I'm chauvinist enough to think that the
majority of participants in this ng do not fly in those areas, and thus a
general question to the group won't get many enlightened responses. I
learned to fly in Southeast Alaska, and never heard the word subsidence
mentioned.

Bob Gardner

"private" > wrote in message
news:5kgve.1798330$6l.939730@pd7tw2no...
>
> "Peter Duniho" > wrote in message
> ...
>> "private" > wrote in message
>> news:3Q6ve.1795956$6l.1699114@pd7tw2no...
>> > [snip]
>>
>> None of what you wrote suggests that atmospheric subsidence would have
>> any
>> significant effect on the aerodynamics or engine of an airplane.
>>
>> It is true that there are variety of atmospheric effects related to
>> nightfall. But they don't change the way the airplane flies, not in a
>> way
>> that requires even knowing about atmospheric subsidence, never mind
>> understanding it.
>>
>> Pete
>
> Hello Pete,
>
> I agree that subsidence does not change aircraft aerodynamics, and does
> not
> have a significant effect on engine power. What it does do is change the
> way an aircraft performs. Rising air adds to an aircraft's climb rate,
> sinking air subtracts from it. There will be small changes in maximum
> level
> cruise speed and aircraft attitude with respect to horizon when flying in
> descending air.
>
> IMHO it is better to have unrequired knowledge than to be in ignorance
> when
> that knowledge is needed. My main instructor always maintained that you
> can
> never have too much weather knowledge.
>
> There is some discussion of subsidence and katabatic and glacier fed
> downslope winds in this excellent BC weather manual from Navcan. There is
> also discussion of coastal diurnal and wintertime outflows.
> http://www.navcanada.ca/ContentDefinitionFiles/publications/lak/bc/BC31E-V.P
> DF
> Note chapter 2 Aviation Weather Hazards, page 28 provides discussion of
> glacier winds and notes local wind speeds to >80 knots and notes that
> these
> winds may be magnified by terrain funneling and comments that they may be
> pulsing in a kind of reverse thermal. I would submit that this subsidence
> is substantial and hardly "irrelevant from a practical standpoint."
>
> This subsidence can add to the reduction of performance due to density
> altitude and is often a factor in failure to climb after takeoff or
> inability to out climb rising terrain and has contributed to lots of
> crumpled aluminum in the mountains.
>
> Just my .02
>
>
>
>