End of Season Sunset Warning for SSA-OLC Participants

Mike,

It is a Schreder HP-14 kit built sailplane designed in 1966. Dick Schreder
won the US Nationals with serial number 1 in 1967.
http://www.soaridaho.com/Schreder/HP-14/N4736G.htm

Wayne
HP-14 N990 "6F"
http://www.soaridaho.com/Schreder/N990_Borah_Mt.JPG
http://www.soaridaho.com/Schreder



"Mike Schumann" wrote in message
ink.net...
What kind of glider is that?

Mike Schumann

"jb92563" wrote in message
oups.com...
I can think of one way to make a glider more visible with an intensity
equal to the sun and draws absolutley NO POWER and requires NO WIRING

Check this out!

http://www.soaridaho.com/Schreder/HP...LH/N14LH_2.jpg

In truth the power it requires is in the buffing, but the results are
incredible.

The polish to get this is called Nuvite and costs a lot but with
outstanding results http://www.perfectpolish.com/

I have been through this process twice. One certified,
one experimental.

Check your glider's operating limitations. If it is
a certified glider (not experimental), it is probably
placarded against night flying. The only way to change
that is to place it in experimental category. It will
still require an STC (or 337/ field approval, if you
can get one). Whelen lights have been put on everything
from airliners to fighters, yet it requires a totally
new STC for installation on a new make/model. I douby
Whelen is interested in this tiny market segment.

If it is experimental, your ops limits probably state
'Day VFR only, unless equipped according to 91.205'.
They probably also require you to notify FSDO of any
major alterations. Adding lights is a major alteration.

LEDs are very bright, but also very directional. To
meet the angle, color requirements is fairly difficult.
Whelen does make LED wingtip lights, but they are
fairly expensive. You will also need at least two
strobes, and the power supplies to go with them. LEDs
won't currently meet the requirements for strobes.

Unless your motorglider (Stemme, Katana, Ximango) came
factory equipped, or unless someone is paying you to
fly at night, probably more trouble than it's worth.

Bob C.


At 21:00 15 September 2006, Wayne Paul wrote:
Mike,

It is a Schreder HP-14 kit built sailplane designed
in 1966. Dick Schreder
won the US Nationals with serial number 1 in 1967.
http://www.soaridaho.com/Schreder/HP-14/N4736G.htm

Wayne
HP-14 N990 '6F'
http://www.soaridaho.com/Schreder/N990_Borah_Mt.JPG
http://www.soaridaho.com/Schreder



'Mike Schumann' wrote in message
link.net...
What kind of glider is that?

Mike Schumann

'jb92563' wrote in message
oups.com...
I can think of one way to make a glider more visible
with an intensity
equal to the sun and draws absolutley NO POWER and
requires NO WIRING

Check this out!

http://www.soaridaho.com/Schreder/HP...LH/N14LH_2.jpg

In truth the power it requires is in the buffing,
but the results are
incredible.

The polish to get this is called Nuvite and costs
a lot but with
outstanding results http://www.perfectpolish.com/

Mike the Strike wrote:
"GC flight logs contain a GPS time stamp which is the most exact time
standard readily available. So, violations of this requirement are
quite plain to see in these logs."

Unfortunately, sunset doesn't come with a GPS timestamp, so I'm afraid
this isn't as easy as you make it sound.

Yes, I know there are standard tables of sunset times, but these make
assumptions that may not be exactly correct and at a given location
actual sunset may differ from the calculated one by many minutes.
(Ask any local physicist./astronomer).

I am both of those and I assure you that the time of sunset is well-
defined and readily predicted for any location to a tiny fraction of
a second.

You may have difficulty observing the position of the sun. Like,
it might be cloudy, there might be a mountain in the way, or
you might be indoors. But that is not relevent.

Any regulatory requirement should (and I daresay will) be based
on that well-defined time, or the equally well-defined times of civil,
nautical, or astronomical twilight.

http://en.wikipedia.org/wiki/Astronomical_twilight
http://aa.usno.navy.mil/faq/docs/RST_defs.html#top

Obviously you may be safer flying a few minutes after sunset in
a clear sky than a few minutes before sunset in a cloudy sky.
But that is a practical consideration.

You are correct that these definitions are based on certain
assumptions, but the point is that a rule that says you are
supposed to be on the ground by sunset, the end of civil
twilight, or whatever, should be a rule that uses the defined
time, not some local observation. That gives you a clear,
unambiguous requirement.

--

FF

A minor clarification:

wrote:
I am both of those and I assure you that the time of sunset is well-
defined and readily predicted for any location to a tiny fraction of
a second.

Well, not exactly to the second. Even the USNO only reports sunset time
to the nearest minute (see the "Accuracy of rise/set computations"
section in the link below). And their calculator only accepts Lat/Lon
to the nearest 1/10th of a dagree. So the error in the calculations are
+/- a minute or more. This is a technical point, but it is important to
remember that all measurements have some error.

You may have difficulty observing the position of the sun. Like,
it might be cloudy, there might be a mountain in the way, or
you might be indoors. But that is not relevent.

You are correct that the time of actual sunset is moot, since nobody
regularly observes and records this. The only relevant time is the
official prediction. This prediction is normally in the pilot's favor,
since the sun sets earlier than predicted at high surface elevation and
high temperature due to recuced refraction in the less dense air.

Any regulatory requirement should (and I daresay will) be based
on that well-defined time, or the equally well-defined times of civil,
nautical, or astronomical twilight.

http://en.wikipedia.org/wiki/Astronomical_twilight
http://aa.usno.navy.mil/faq/docs/RST_defs.html#top

Obviously you may be safer flying a few minutes after sunset in
a clear sky than a few minutes before sunset in a cloudy sky.
But that is a practical consideration.

You are correct that these definitions are based on certain
assumptions, but the point is that a rule that says you are
supposed to be on the ground by sunset, the end of civil
twilight, or whatever, should be a rule that uses the defined
time, not some local observation. That gives you a clear,
unambiguous requirement.

--

FF

Doug Haluza wrote:
A minor clarification:

wrote:
I am both of those and I assure you that the time of sunset is well-
defined and readily predicted for any location to a tiny fraction of
a second.

Well, not exactly to the second. Even the USNO only reports sunset time
to the nearest minute (see the "Accuracy of rise/set computations"
section in the link below). And their calculator only accepts Lat/Lon
to the nearest 1/10th of a dagree. So the error in the calculations are
+/- a minute or more. This is a technical point, but it is important to
remember that all measurements have some error.

True it is not possible to predict when the sun would be
observed tangent below the horizon, with an accuracy of
better than a minute or so. But that's a silly way to define
sunset in the first place. If the atmospheric conditions
(e.g. clouds) made make the sun unobservable, you wouldn't
say there was no sunset that day. (Though the sun would
still be observable outside of the visible spectrum)

If the "time of sunset" is _defined_ based on nominal atmospheric
conditions that moots the issue, just like defining the horizon
to be 90.8333 degrees from zenith moots the issue of the local
topography.

Those conditions can be defined as accurately as one wants.

Similarly, uncertainty in your lattitute, longitude and elevation
may also be mooted. You may be uncertain as to where
YOU are, but the estimation of the time of sunset for an arbitrary
location (which therefor you can define with arbitrary accuracy)
is uncertain only due to the variablity in the motions of the earth,
uncertainty and variablility in the orbital parameters of the Earth,
and uncertainty and variability in the apparent size of the sun.

Actually, since Universal Time is _defined_ by the orientation
of the Earth and not by atomic time, the time of sunset is
only affected by variabilty in the motions of the Earth because
they affect the place on the horizon where the sun is tangent.
That is why we have leap seconds from time to time, to
keep international atomic time and universal time in agreement
(coordinated) to within one second, though there has been
debate about discontinuing that practice.

Those leap-seconds are pretty important in orbit determination,
which gets us back to something of potential interest to glider
pilots. A GPS satellite moves moves more than a mile in one
second.

--

FF

Fred:

You should really check your facts before posting twaddle!

Clearly I should have said to ask any physicist or astronomer who is
conversant with atmospheric refraction, which you clearly are not.
Because of variations in refraction, sunset (the time when the limb of
the sun becomes invisible to an observer) may vary by several minutes
from that calculated by the accepted formula. This formula assumes a
constant refraction that is unlikely to be exact for any specific place
or time.


Mike

(also a physicist and astronomer - and who knows a sunset when I see
one!)



I am both of those and I assure you that the time of sunset is well-
defined and readily predicted for any location to a tiny fraction of
a second.

You may have difficulty observing the position of the sun. Like,
it might be cloudy, there might be a mountain in the way, or
you might be indoors. But that is not relevent.

Any regulatory requirement should (and I daresay will) be based
on that well-defined time, or the equally well-defined times of civil,
nautical, or astronomical twilight.

http://en.wikipedia.org/wiki/Astronomical_twilight
http://aa.usno.navy.mil/faq/docs/RST_defs.html#top

Obviously you may be safer flying a few minutes after sunset in
a clear sky than a few minutes before sunset in a cloudy sky.
But that is a practical consideration.

You are correct that these definitions are based on certain
assumptions, but the point is that a rule that says you are
supposed to be on the ground by sunset, the end of civil
twilight, or whatever, should be a rule that uses the defined
time, not some local observation. That gives you a clear,
unambiguous requirement.

--

FF

Mike the Strike wrote:
Fred:

You should really check your facts before posting twaddle!

Clearly I should have said to ask any physicist or astronomer who is
conversant with atmospheric refraction, which you clearly are not.
Because of variations in refraction, sunset (the time when the limb of
the sun becomes invisible to an observer) may vary by several minutes
from that calculated by the accepted formula. This formula assumes a
constant refraction that is unlikely to be exact for any specific place
or time.


Mike

This is like the advice from the old joke about the guys who get lost
in a balloon, then ask someone on the ground where they are, and the
person on the ground tells them they are up in the air in a balloon.
The joke is that the person on the ground must be a lawyer, beacuse his
answer was technicaly correct, but totally useless.

Same goes for actual sunset. Unless you are on a ship at sea, you won't
have a clear level horizon to observe actual sunset. So the refraction
issue is moot. And if you wait until you observe actual sunset in
flight, the sun will have already set on the ground.

The predicted sunset time is the only thing relevant for flight
planning.

Mike the Strike wrote:
Fred:

You should really check your facts before posting twaddle!

Clearly I should have said to ask any physicist or astronomer who is
conversant with atmospheric refraction, which you clearly are not.
Because of variations in refraction, sunset (the time when the limb of
the sun becomes invisible to an observer) may vary by several minutes
from that calculated by the accepted formula. This formula assumes a
constant refraction that is unlikely to be exact for any specific place
or time.


The issue is not atmospheric refraction.

The issue is not the definition of sunset.

The issue is the defintion of _time_ of sunset.

If the "time of sunset' is defined by a mathematical model,
then the time of sunset is independent of the actual atmospheric
conditions and therefor does not vary with them.

That was my point, and I am sorry that I was unclear.

The issue at hand was what time should be used to determine
if a pilot has landed befor sunset. OP's complaint was that
'time of sunset' was highly uncertain. My point is that it is
only highly uncertain if you use an entirely impractical
definiton of 'time of sunset'.

As an astronomer who knows a sunset when he sees one,
how do you know the sun has set when the sky is overcast?

--

FF

Fred:

Sorry, but I still disagree.

The time of sunset is the point at which the limb of the sun disappears
to an observer. This is an exact legal definition.

I don't think you'd get far in a court of law if a dozen eyewitnesees
said the sun was still visible but you said your mathematical equation
predicted that it had set!

For convenience, we use a mathematical model that uses a constant term
to correct for atmospheric refraction and you can look up those times
in published tables. However, the correction is approximate and
subject to error.

I merely suggested that since the actual time of sunset was not known,
we should allow folks some slack if they land close to sunset to allow
for this error.

The same goes for pressure altitude, by the way.

Mike

Overcast? What's that - I live in Arizona!


The issue is not atmospheric refraction.

The issue is not the definition of sunset.

The issue is the defintion of _time_ of sunset.

If the "time of sunset' is defined by a mathematical model,
then the time of sunset is independent of the actual atmospheric
conditions and therefor does not vary with them.

That was my point, and I am sorry that I was unclear.

The issue at hand was what time should be used to determine
if a pilot has landed befor sunset. OP's complaint was that
'time of sunset' was highly uncertain. My point is that it is
only highly uncertain if you use an entirely impractical
definiton of 'time of sunset'.

As an astronomer who knows a sunset when he sees one,
how do you know the sun has set when the sky is overcast?

--

FF

Mike the Strike wrote:
Fred:

Sorry, but I still disagree.

The time of sunset is the point at which the limb of the sun disappears
to an observer. This is an exact legal definition.

I don't think you'd get far in a court of law if a dozen eyewitnesees
said the sun was still visible but you said your mathematical equation
predicted that it had set!

Probably not, even if the law specified that the legal defintion of
sunset was that estimated by the exact legal model. But mens
rea isn' t really at issue here, is it?


For convenience, we use a mathematical model that uses a constant term
to correct for atmospheric refraction and you can look up those times
in published tables. However, the correction is approximate and
subject to error.

I merely suggested that since the actual time of sunset was not known,
we should allow folks some slack if they land close to sunset to allow
for this error.

My suggestion for dealing with the ambiguity of the actual time of
sunset is to not use the actual time of sunset. Use the putative
time of sunset, as calculated by a standard formula for the
published lattitude and longitude of the airfield in question instead.
That eliminates the ambiguity. All the pilot needs is to plan
ahead by looking up the putative time of sunset for the various
airfields and an decent clock. If he has a GPS receiver, he
has an extremely accurate clock.

Do you suppose the FAA has addressed this issue?

Allowing them some slack is fine, but does not address the problem.
When does the grace period begin and when does it end?
I'm not addressing the issue of what should be done about
those who land after the deadline, whatever it would be. Only
the practical issue of what to base that deadline on. If you
base it on the 'actual' time of sunset, no one knows what
that deadline is, not in advance, nor even after the fact.

As for what is fair and what is not, IMHO the more objective,
precise, and predicable a rule is, the more fair it is regardless
of how arbitrary it is.

--

FF