hemispherical crusing rule

got into a discussion at the old watering hole tonight about the base
altitude of the hemispherical cruising altitude( you know, 3000 agl). but
the question came up what do you do in mountainous terrain where the ground
elevation can change thousands of feet in just a few miles. how do you
determine the lowest cruising altitude in conformance with the
hemispherical cruising altitude when the ground elevation is always changing
by thousands of feet?


tony zambon
grumman 9941L

If I'm crossing a number of ridges (large ones out here) I get to a
comfortable altitude above the highest ridge for the cross country, select
the proper hemispheric and stay there. If I'm parallel, flying up the
valley, I select the proper hemispheric and stay to the right. Most flying
is above the 3000ft AGL of the valley floor.

If I'm below 3000ft AGL, I might as well be nap-o-the-earth because of all
the ridge lines I have to climb and it don't matter, yes, most "ridges" out
here are higher than 3000ft above the valley floor. Plus now with spring and
summer approaching, if I'm that low, it serves me right to get beat up with
the low level turbulence from thermal activity.

BT

"tony zambon" wrote in message
m...
got into a discussion at the old watering hole tonight about the base
altitude of the hemispherical cruising altitude( you know, 3000 agl). but
the question came up what do you do in mountainous terrain where the
ground
elevation can change thousands of feet in just a few miles. how do you
determine the lowest cruising altitude in conformance with the
hemispherical cruising altitude when the ground elevation is always
changing
by thousands of feet?


tony zambon
grumman 9941L

"tony zambon" wrote in message
m...
[...] how do you
determine the lowest cruising altitude in conformance with the
hemispherical cruising altitude when the ground elevation is always
changing
by thousands of feet?

I'm not sure I understand the question. The rule applies only about 3000'
AGL. If terrain rises placing you below 3000' AGL, then the rule doesn't
matter. If the terrain drops placing you above 3000' AGL, then the rule is
the same as it is everywhere else.

Why would you ever need to "determine the lowest cruising altitude in
conformance with the hemispherical cruising altitude"? Or if you prefer,
what's so hard about doing so?

What you actually need to do is pick a cruising altitude that puts you at an
appropriate altitude above all obstacles, and then do your best to make it
conform the hemispheric rule (you may be limited by oxygen requirements or
climb performance, and this may be true even for the purpose of simply
clearing all obstacles).

Pete

"Peter Duniho" wrote in message
...
I'm not sure I understand the question. The rule applies only about 3000'
AGL.

That should, of course, read "only above 3000' AGL". Sorry...

On Tue, 13 Apr 2004 02:50:42 GMT, "tony zambon"
wrote:

got into a discussion at the old watering hole tonight about the base
altitude of the hemispherical cruising altitude( you know, 3000 agl). but
the question came up what do you do in mountainous terrain where the ground
elevation can change thousands of feet in just a few miles. how do you
determine the lowest cruising altitude in conformance with the
hemispherical cruising altitude when the ground elevation is always changing
by thousands of feet?

If you are flying is such a fashion as to stay under 3000 feet agl
that must make for quite a ride in the mountains:-))

Basically if you are high enough to use the rule over the high spots,
there is no need to worry about the low spots.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com




tony zambon
grumman 9941L

Roger Halstead wrote:


If you are flying is such a fashion as to stay under 3000 feet agl
that must make for quite a ride in the mountains:-))

It ain't no fun if all the ground is always below you.

Roger Halstead wrote in message . ..

If you are flying is such a fashion as to stay under 3000 feet agl
that must make for quite a ride in the mountains:-))


Some of my favorite mountain flying is done below the ridgelines.
That's where all of the good airports are.

I can spend a week flying around the Idaho backcountry without ever
having to think about the hemispherical rule :-) And yes, it is quite
a ride!

John Galban=====N4BQ (PA28-180)