required LD versus required MC to make it home ??

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