On Aug 24, 9:32*pm, Ramy wrote:
On Aug 24, 5:16*pm, Darryl Ramm wrote:





On Aug 24, 5:06*pm, Ramy wrote:

On Aug 24, 2:54*pm, mattm wrote:

On Aug 24, 4:44*pm, Ramy wrote:

On Aug 24, 1:11*pm, mattm wrote:

Reichmann points out that MC 1 is a better setting if you are in
desparation mode, because you give up only a little glide distance
but you get to sample more air in a given time.

Are you sure about that? MC=0 will give you more time and more air to
sample (beeing the best L/D speed) than MC=1. I always use MC=0 when I
switch to survival mode unless I am also battling significant head
wind.

Ramy

Yes, it's true. *It's on the last page of this paper:http://www.dragonnorth.com/djpresent...training_for_c...

"A lot of pilots flew and fly unnecessarily low average
speeds when they get low, because they are anxious
and fly with a zero setting. They don’t know that with a
setting at 1 knot they have almost the same glide angle
and lose much less average speed in case they recover
and complete the task."

In my plane (ASW-19) MC=0 speed is 53kts, and L/D is 38:1.
MC=1 speed is 61kts, and L/D is 35:1. *Granted my sink rate
is about 30fpm faster, but I'll have almost 20% greater range to find
that thermal I need to get back up again.

-- Matt

Matt I'm afraid you missunderstood Reichmann comment. He claimed that
you will lose less average speed with MC1 which is true. But you will
not gain 20% greater range. On the contrary, Your search range will
always be less if you fly faster than MC=0 (unless you have
significant head wind which requires flying faster than best L/D).
Bottom line, as other pointed out, it all depends on your goal. If you
are flying contest, in which every second counts, then flying correct
MC is important. If you fly for OLC or distance, like I believe the
majority of XC flights are, and your main objection is to make it back
home at the end of the day (as the subject lline says), than fly *MC 0
when you are in survival mode or starting your final glide.

Ramy

But, but, but, (and I think I can hear John Cochrane pounding his head
on his desk in Chicago...) when about to go on final glide and you are
in that last thermal you know what the theoretical final glide Mc
should be. And by all means factor in safety margins but if you have a
climb significantly over your Mc="0" value then keep climbing and bump
the Mc appropriately to match that climb. I mean why not? I know
sometimes pilots like to float past the home airport and stretch a few
more OLC miles then turn back. Personally the call of that cold beer
makes me want to fly that final glide as fast as possible.

What is really annoying about arguing with Ramy on this point (which I
think I've done before) is no matter what I can argue on paper I have
no hope of keeping up with him in practice.

Sigh

Darryl- Hide quoted text -

- Show quoted text -

Funny, I guess I can fly better than I can explain myself :-)
All I am trying to say about the final glide is that if you are not
competing (or competing against the sun as in my case sometimes) the
exact speed you fly on your final glide wouldn't matter much. And
instead of dialing MC according to your last climb to determine when
to leave the thermal and then ignore this MC on your glide if you want
to ensure you get back home even with no lift, just degrade your polar
instead, climb as high as you feel comfortable, then fly as fast as
you can without loosing glide. Simple. Of course while on course and
high crank up the MC as high as you dare, just make sure you stay in
the desired lift band.
But honestly, I don't understand how many of you fly XC safely if you
don't degrade your polar. How do you determine you are within safe
glide from airports at any point in time? using your published polar
and a safety altitude margin? Good luck if you hit any sink or head
wind on the way unless you use a big altitude margin which will
significantly hurt your decision down lower. The suggestion to use bug
factor to degrade your polar is basically an implementation of the
common rule of thumb to use 50%-75% of your published polar to
determine arrival altitude.

Ramy

Hi Ramy,

I know you are an OLC stud. Nevertheless I will take a crack at
spanning the gap between you and Mr. Cochrane - who is a competition
strategy stud.

There are two potential objectives in calculating how to look for and
manage the last climb leading to final glide: 1) maximize the
probability of getting home when time is not a factor, and 2)
maximizing expected speed (and hence expected contest points) adjusted
for probability of landing out. In the first case, if you are low and
desperate you pull back to best L/D and fly in the direction of the
most likely lift, even if it means backtracking on course. In the
second case you are trading off your best estimate of probability of
landing out against speed, with the tradeoff in contests dictated by
the ratio of speed points to distance points. Reichmann's point here
is quite relevant - a 1.0 McCready keeps up progress toward the goal
and dilutes your total speed less quickly than Mc = 0, which trades
landout probability for speed at a suboptimal rate - that is, you gain
expected finish points less quickly than you lose speed points - all
probability adjusted. The stronger the lift the more you want to fly a
little faster while searching to make sure that you don't give up
speed points.

As to the final glide itself (and I understand the unique issues
associated with returning to an elevated airport like Truckee, where
you need to set up the final glide quite far out with little chance to
recover if you miss low). The basic issue here is how to balance the
glide margin - how much should be based on glide angle margin and how
much should be based on finish height margin? There are two potential
estimation errors you need to deal with: 1) error associated with mis-
estimating the actual glide angle you can achieve at any given glide
speed and 2) errors associated with short-term losses in altitude from
sink enroute. Ideally you can account for 1) by managing your glide
speed to make sure your achieved glide angle is shallower than needed.
You can do this in one of two ways. First you can artificially steepen
up the glide angle at any given speed through manipulating the polar,
or you can set the Mc for higher than the speed you actually fly (or
some combination of the two). The basic objective under both
approaches is to ensure you gain a bit on the glide rather than losing
a bit. The problem with using bugs and flying with a zero Mc is that
you fly too slow to optimize speed and you tend to leave strong final
thermals too soon.

As to issue 2), the issue to keep in mind is the risk of hitting a
line of sink and losing your glide. As John points out, this risk
goes up as you get closer to home because you get progressively lower
and have a declining chance of being able to find a saving climb after
a sink street. This is why the better strategy when there is a lot of
uncertainty about lift/sink on the way home is to add finish altitude
rather than steepen the glide - steepening the glide give you a margin
that decrements to zero feet as you approach the finish whereas
altitude margin doesn't. This says that you are better off adding
finish height than steepening the glide angle as a glide angle margin
goes away as you get closer to home. It also argues for leaving the
final thermal at with a Mc setting that is a bit higher than you
actual climb rate, then setting speed-to-fly a bit slower so yo gain
on the glide going home.

I will observe that in my experience the first glider to leave the
thermal gets home first. I have left thermals before getting to the
the height indicated by the Mc setting and won by a couple of minutes
and have stuck with 10-knot thermals only to be unable to catch
gliders leaving before me. It has never worked any other way. This
must mean that either pilots are able to "bump up' the final glide on
the way home, or that final thermal isn't as strong as I think. In
either case it means I generally stay with my final climb too long.

9B

Hope that helps,

9B