Re: Dewpoint & Night VFR
Posted: Mon Jan 09, 2017 9:41 pm
[quote]Why is the dewpoint spread important?[/quote]
It determines the cloud layer/ceiling, which
you probably want to stay under, VFR.
[quote]What causes the dewpoint spread to decrease?[/quote]
Temperature decrease (sun goes down) or
source of moisture can cause the dewpoint
to increase.
[quote]What's a visual telltale that you have dewpoint spread problems?[/quote]
One that scares the shit out of me, is moisture
falling (generally from an inversion) and I see a
scattered cloud layer developing below. It can
easily become a solid layer.
[quote]What can happen when the dewpoint spread drops to zero?[/quote]
WOXOF. But not necessarily. Some mornings,
you will see the temp and dewpoint the same
(very common with clear skies) and no cloud
forms. As soon as the sun hits the earth and
warms it up, you're good. With a solid layer,
the sun bounces off the top of the layer and
it can persist into the day. You need a hole
for the sun to peek through, and burn it open
with an increasing dewpoint spread.
[quote]What is the minimum dewpoint spread for night VFR? Why?[/quote]
3 degrees C for 1000 AGL for dry adiabatic
lapse rate. But watch the trend of the dewpoint
closely.
[quote]What can go wrong during a night VFR takeoff?
What techniques and exercises can improve this?[/quote]
The so-called exotic "Black Hole" effect, which
causes us old guys to snort.
As a takeoff technique, get on the AI ASAP with wings
level and 10 degrees nose up. No turns until 500 AGL.
As a training exercise, learn to do a 0/0 takeoff. They
used to teach them in the military (probably don't any
more).
[quote]What can go wrong during a night VFR landing?
What techniques and exercises can improve this?[/quote]
Low-timer are fooled by illusions and have difficulty
judging their height at night. They are already prone
to pitch PIO's and this makes it almost a certainty,
which is terribly hard on the nose gear. Wiping it off
is quite routine. See photo above.
Learn to do a "glassy water" landing. No sawing away
at the control column. Set a pitch attitude and a power
setting that results in a gentle descent and let the
aircraft enter ground effect and flare on it's own.
Learn to land without the aircraft landing light. Learn
to land without any lights at the airport. All of these
will improve your night landings, as will simply more
of them, so you get used to the illusions.
Learn to do a 0/0 instrument landing. Builds character,
it will save your life some day.
After a while, you won't give a shit - day or night, it's
all the same. Aircraft has no eyes, it cannot tell the
difference.
It determines the cloud layer/ceiling, which
you probably want to stay under, VFR.
[quote]What causes the dewpoint spread to decrease?[/quote]
Temperature decrease (sun goes down) or
source of moisture can cause the dewpoint
to increase.
[quote]What's a visual telltale that you have dewpoint spread problems?[/quote]
One that scares the shit out of me, is moisture
falling (generally from an inversion) and I see a
scattered cloud layer developing below. It can
easily become a solid layer.
[quote]What can happen when the dewpoint spread drops to zero?[/quote]
WOXOF. But not necessarily. Some mornings,
you will see the temp and dewpoint the same
(very common with clear skies) and no cloud
forms. As soon as the sun hits the earth and
warms it up, you're good. With a solid layer,
the sun bounces off the top of the layer and
it can persist into the day. You need a hole
for the sun to peek through, and burn it open
with an increasing dewpoint spread.
[quote]What is the minimum dewpoint spread for night VFR? Why?[/quote]
3 degrees C for 1000 AGL for dry adiabatic
lapse rate. But watch the trend of the dewpoint
closely.
[quote]What can go wrong during a night VFR takeoff?
What techniques and exercises can improve this?[/quote]
The so-called exotic "Black Hole" effect, which
causes us old guys to snort.
As a takeoff technique, get on the AI ASAP with wings
level and 10 degrees nose up. No turns until 500 AGL.
As a training exercise, learn to do a 0/0 takeoff. They
used to teach them in the military (probably don't any
more).
[quote]What can go wrong during a night VFR landing?
What techniques and exercises can improve this?[/quote]
Low-timer are fooled by illusions and have difficulty
judging their height at night. They are already prone
to pitch PIO's and this makes it almost a certainty,
which is terribly hard on the nose gear. Wiping it off
is quite routine. See photo above.
Learn to do a "glassy water" landing. No sawing away
at the control column. Set a pitch attitude and a power
setting that results in a gentle descent and let the
aircraft enter ground effect and flare on it's own.
Learn to land without the aircraft landing light. Learn
to land without any lights at the airport. All of these
will improve your night landings, as will simply more
of them, so you get used to the illusions.
Learn to do a 0/0 instrument landing. Builds character,
it will save your life some day.
After a while, you won't give a shit - day or night, it's
all the same. Aircraft has no eyes, it cannot tell the
difference.