Setting altimeters with no radio

"Jim Macklin" wrote in message
...
they give altitude, accurate to within a few feet. just set
the altimeter to read the same. then you know adjusted
pressure. considering the legal requirements, it is
perfectly adequate.

First of all, no they don't give altitude accurate to within a few feet.
Secondly, they give a completely different kind of altitude measurement than
the altimeter provides. Even if the GPS were accurate to within feet for
altitude, setting your altimeter to the GPS displayed altitude would not be
the same as having the current, local altimeter setting.

Pete

"Jim Macklin" wrote in message
...
GPS, even a $100 hikers model will solve the problem. But I
just say, look at the ground, you can judge 1,000 feet
pretty well and you only need to apply the hemisphere rule
above 3,000 AGL.


On the other hand, we always tell airport noise complainers that it is very
hard to accurately judge aircraft distances, such as whether the plane is
500 feet or 1000 feet high.

I think we can judge 1000' from the air better than somebody on the ground
because we spend a lot of time in the pattern at 1000' agl. We gt used to
the perspective and can verify it with our altimeters.

mike

"Super Dave" wrote in message
ink.net...

"Jim Macklin" wrote in message
...
GPS, even a $100 hikers model will solve the problem. But I
just say, look at the ground, you can judge 1,000 feet
pretty well and you only need to apply the hemisphere rule
above 3,000 AGL.


On the other hand, we always tell airport noise complainers that it is
very
hard to accurately judge aircraft distances, such as whether the plane is
500 feet or 1000 feet high.

right
"mike regish" wrote in message
news |I think we can judge 1000' from the air better than
somebody on the ground
| because we spend a lot of time in the pattern at 1000'
agl. We gt used to
| the perspective and can verify it with our altimeters.
|
| mike
|
| "Super Dave" wrote in message
|
ink.net...
|
| "Jim Macklin"
wrote in message
| ...
| GPS, even a $100 hikers model will solve the problem.
But I
| just say, look at the ground, you can judge 1,000 feet
| pretty well and you only need to apply the hemisphere
rule
| above 3,000 AGL.
|
|
| On the other hand, we always tell airport noise
complainers that it is
| very
| hard to accurately judge aircraft distances, such as
whether the plane is
| 500 feet or 1000 feet high.
|
|
|
|

On Sun, 12 Nov 2006 06:43:31 -0500, mike regish wrote:
I think we can judge 1000' from the air better than somebody on the
ground because we spend a lot of time in the pattern at 1000' agl. We gt
used to the perspective and can verify it with our altimeters.

Plus, there is also the issue of we have more to took at to get a
reference on... People on the ground are trying to judge distance by
looking at a single object that is relatively rather small... Nothing to
really compare it to... On the other hand, if we are above water with no
surrounding terrain or boats, I would suspect that we might have a bit
more difficulty judging altitude...

Looking down you're eye sees details of known sizes, roads,
cars and houses. It is also able to see angles and
relations on the surface. Judging altitude from the air is
fairly easy. I always require my pre-solo students to fly
the traffic pattern [dual] with all the instruments covered.
I have them tell me their altitude and speed and then
uncover the instruments. They are always within 100 feet of
the correct altitude.

On the other hand, looking up, there are no references to
judge height. Is it a full size B52 or a model, is it 2
miles away or 25, the human eye /brain needs reference
points. But a trained observer is taught how to get those
references, such as the size of the airplane, the relation
of their thumb at arms length and the object, etc.



"Super Dave" wrote in message
ink.net...
|
| "Jim Macklin" wrote
in message
| ...
| GPS, even a $100 hikers model will solve the problem.
But I
| just say, look at the ground, you can judge 1,000 feet
| pretty well and you only need to apply the hemisphere
rule
| above 3,000 AGL.
|
|
| On the other hand, we always tell airport noise
complainers that it is very
| hard to accurately judge aircraft distances, such as
whether the plane is
| 500 feet or 1000 feet high.
|
|

"Jim Macklin" writes:

GPS, even a $100 hikers model will solve the problem. But I
just say, look at the ground, you can judge 1,000 feet
pretty well and you only need to apply the hemisphere rule
above 3,000 AGL.

GPS is far less accurate than an altimeter, and I don't think the
regulations say "if you have no radio, use GPS."

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Recently, Mxsmanic posted:

"Jim Macklin" writes:

GPS, even a $100 hikers model will solve the problem. But I
just say, look at the ground, you can judge 1,000 feet
pretty well and you only need to apply the hemisphere rule
above 3,000 AGL.

GPS is far less accurate than an altimeter, and I don't think the
regulations say "if you have no radio, use GPS."

I'm not sure why you think that "GPS is far less accurate than an
altimiter...", as an altimeter only need be accurate to 75' to be legal.
GPS can do much better than that, and are unaffected by barometric
pressure; the result is a potential source of problems that require pilots
to fly by the altimeter, not the GPS. None of this has anything to do
with regulations, of course.

To answer your original question, the prudent pilot will take the
barometric pressure of their destination into consideration during
preflight planning, and adjust the altimeter accordingly. Most of the
time, the pressure won't change all that drastically at the destination in
the time it takes to fly 100 miles, and non-radio VFR pilots aren't likely
to fly in weather where the pressure is changing too rapidly.

Neil

agreed
"Neil Gould" wrote in message
m...
| Recently, Mxsmanic posted:
|
| "Jim Macklin"
writes:
|
| GPS, even a $100 hikers model will solve the problem.
But I
| just say, look at the ground, you can judge 1,000 feet
| pretty well and you only need to apply the hemisphere
rule
| above 3,000 AGL.
|
| GPS is far less accurate than an altimeter, and I don't
think the
| regulations say "if you have no radio, use GPS."
|
| I'm not sure why you think that "GPS is far less accurate
than an
| altimiter...", as an altimeter only need be accurate to
75' to be legal.
| GPS can do much better than that, and are unaffected by
barometric
| pressure; the result is a potential source of problems
that require pilots
| to fly by the altimeter, not the GPS. None of this has
anything to do
| with regulations, of course.
|
| To answer your original question, the prudent pilot will
take the
| barometric pressure of their destination into
consideration during
| preflight planning, and adjust the altimeter accordingly.
Most of the
| time, the pressure won't change all that drastically at
the destination in
| the time it takes to fly 100 miles, and non-radio VFR
pilots aren't likely
| to fly in weather where the pressure is changing too
rapidly.
|
| Neil
|
|
|

Neil Gould writes:

I'm not sure why you think that "GPS is far less accurate than an
altimiter..." ...

Because I studied GPS for a long time and was using it before anyone
else knew what it was, and I know how badly it measures altitude. GPS
was designed to accurately measure longitude and latitude; at best, it
gives only a rough estimate of altitude (ships and troops, the
original users of GPS, don't need to know their altitudes).

... as an altimeter only need be accurate to 75' to be legal.

GPS is routinely off by hundreds of feet.

GPS can do much better than that ...

No, it cannot ... not vertically. It's actually much worse.

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