Altimeter Setting

On 6/4/2010 4:14 PM, Eric Greenwell wrote:
On 6/1/2010 7:54 AM, Bob Whelan wrote:
On 5/31/2010 8:07 PM, Rolf wrote:
Over the years (30 or so) Caesar Creek Soaring Club has vacillated
with setting the altimeter to zero or MSL. Last year the Board decided
to put the Club ships on an MSL basis (private gliders exempted).
There are however a number of members who are continuing to make it an
issue. I would be interested in your thought and comments.

Wearing my dry humor hat just a bit...

snip
Fast forward to another mountain airport and another time... There I
wuz about to launch from a field at 8149' msl elevation, with a
steenking, howling crosswind of 20+ knots. Naturally, I didn't want to
land right off tow, so I decided I'd tow to 3,000' agl instead of my
normal 2,000'...insurance against broken thermals and getting blown
downwind away from the only landable place for miles around (i.e. the
airport).

I pop off at what my poor overstressed brain said was 3000' agl, known
that instant to be an indicated 10,150' (I rounded up 'for safety's
sake'!), in a decent-feeling upwelling and begin grinding around,
keeping a beady eye on my drift relative to the field. I begin
climbing too, but for some reason I couldn't get comfortable as fast
as I thought my climb rate should be permitting...something about that
lurking ground bugged me. About 500' into my climb I realized it was
because the ground was WAY too close for being 3500' agl. Apparently
my instructor had been right about my 'puny overworked brain' all
those years ago!

Uh, Bob, have you ever tried to set an altimeter to zero when you are at
8149'? Not going to happen - it will still show 1000's of feet when
you've run out of adjustment. Now what do you do? AGL isn't an option,
so you'd have to use MSL (as you did).

Heck, I've never tried to set an altimeter to zero ANYtime/where, except
for my pre-solo flights (@800' msl) before my instructor decided I was
then smart enough to do simple arithmetic in my skull. And except for
the time I couldn't ADD (3,000' to 8,149'), my lack of arithmetic skills
have never been a problem.

Perhaps, perhaps, if you'd used MSL from the start your brain would "do
the math better".

Perhaps indeed...I'm OK with one (aggravating initially, funnier by the
second once I'd climbed away!) bozo error in 1100+ tows. So far as I
know, I'm still 100% on my subtractions!

There is a way around the math problem that's simple:
a simple "dial" on the altimeter marked in 1000's of feet, which can be
rotated to show AGL from any elevation you choose. The 1000's needle
points to your AGL on the "dial".

Before electronic flight computers, I used this "dial" and prayer wheel
when flying XC. I reset the dial to elevation of whatever field I was
currently using as my target.

Sounds like a good tip for the sufficiently needy/motivated - thanks!

Bob W.

P.S. Funnily enough (excuse the shameless pseudo-plug), my memory says
that was the same day 'Wilderness Doug' gained his moniker. It was BLOWing.

Just got back to RAS after a long absence to find this thread. Great
fun!

One more data point:

I learned to fly with CCSC (original poster is CCSC Pres.). Actually
at CCSC's former airport in Richmond, IN. The club gliders and most
private gliders had the altimeters set to AGL (zero). Easier math
(just read, no subtraction required). No radios in club gliders (to
hear warnings or communicate with power aircraft or anyone else). No
Class B or any other type of controlled airspace nearby (no Class B
anywhere in those days). It's Ohio: flat as a board so any airport we
could fly to was within 100' or so of takeoff altitude. Under the
conditions I was flying in--which arguably don't exist anymore--it's
undeniable that the mental load is lighter using AGL. I flew for
years, including cross country and midwestern regional and national
contests using AGL. I can't remember when I switched but it was no big
deal. I'd already had to do it a few times at wave camps, etc., and
just decided it was time to make the change. For some years even after
I switched to MSL, before each contest flight I would set the
altitmeter to zero, write down the altimeter setting, then reset it to
MSL. On final glide, I would reset it to AGL to make the mental math
easier with my cardboard "prayer wheel" final glider computer. I need
4200' to get home, the altimeter says 4800', so I'm in good shape.
Again, no subtraction required: just read the altimeter and compare to
the calculator.

There may still be situations where AGL works fine. Yeah, it's
probably better to start off doing it "right" with MSL, but we don't
start students off with spins or advanced thermaling techniques. We
begin with the easier stuff and move on gradually. This month marks
the 45th anniversary of my first lesson. I like to think I was no less
a "real pilot" for those years I flew with the altimeter set to AGL.

Chip Bearden
ASW 24 "JB"
USA