Help estimating altitude without altimeter?

On Oct 26, 3:51*am, tstock wrote:
Hi, as a beginner I am still a little rough at this. *I've done 3
successful patterns with no altimeter, but today I failed one
miserably with my instructor. * There were two issues which threw me
off. 1) *we towed higher than the past attempts, and 2) instead of
entering the pattern at a familiar entry point, he had me circle
directly over the airport which made judging the angle a bit
difficult.

While we did eventually land safely, I failed miserably at setting up
the first pattern (way too high) and was forced to land on the
opposite runway (which left me way too low). *A little scary but a
good learning experience... one I do not care to repeat anytime soon.

I know I should be looking for the landing strip to be about 30
degrees below the horizon. *But how can I do this when circling
directly over the field looking down at it?

I made a second attempt and moved my circle so that the outermost edge
of the circle was where I would enter the downwind.. I succeeded this
time. *Unfortunately we also only towed to 1500' AGL which left me
with a much smaller chance of messing things up... so I can't say I am
completely confident despite the success.

Are there any easy methods for estimating the angle from the horizon?
For example a fist at arms length is 10 degrees, but obviously I can't
hold my first at arms length through the canopy. * The method I've
used is to wait until my aim point aligns with the outer most edge of
the air brakes. *To measure 45 degrees I look directly over the top of
my shoulder... *is there a better method?

Thanks
-tom

Don't get hung up on the ' 30 degree' rule. Its a rough guide for
beginners to get them into the right ball park. The actual perspective
will vary depending on the performance of your glider. From any given
height the angle by which you assess the pattern in a Ka8 will be
steeper than in an ASH25. You have to make the judgements no matter
what your orientation to the airstrip so peering at your shoulder or
airbrake won't work. You must be able to make the assessments, as it
were, out of the side of your eye whilst flying the plane and looking
out for traffic so focusing short and agonising about angles is
potentially dangerous.

In the UK we put far more emphasis on 'whether it looks right' which
entails practise from all sorts of positions and heights. In that
respect your comment "one I do not care to repeat anytime soon" is
against your interests for it's only by having another go soon will
you learn. You need to get some right to achieve the 'Ahaa!' and some
wrong to give your brain the database needed to make good judgements.
The job of the guy in the back is to engineer all that safely. His is
to 'take you to peer over the edge of the abyss without falling in' to
quote one of our most respected national coaches.

Of course you can't judge your pattern from over the airfield. Your
general height judgement, unaided by altimeters, needs to be
sufficient to tell you it's time to move away to the position from
where you will start the circuit and use different judgements of
perspective to effect it. Darryl says that in his post. If you always
fly from the same place and do the same circuits you are at risk of
getting habituated on secondary fixed references and not exercising
the necessary judgement skills to land out in a pasture. If possible
set yourself targets of landing within pre-set boundaries on
different parts of the airfield so you keep sharp.

Given the luxury of sufficient height (which is usually denied by the
pilot himself attempting to soar too long and not being disciplined
enough to enter circuit mode in good time) you should ensure you are
outside (and usually up-wind) of the intended pattern so that you can
see it all. As circuits are roughly rectangular the high key point
wants to be as far from the centre line of your final line as you
would like you base leg to be long. Choose a ground feature under the
high key and lurk by it, still outside the pattern until the
perspective looks right - then set off on downwind.
Learn to ignore the altimeter. Monitor the ASI assiduously and pay
attention to the vario. And lookout, lookout, lookout.

Peter