Article on glide strategy

In addition to considering the probability of a landout, you have to take into consideration the consequences of one. If your final glide is over a landscape of neatly mowed large fields, the consequences of a landout are trivial and you can push closer to the theoretical limits. As Cliff says, many western sites have very poor options and carrying extra height, perhaps even more than mathematically indicated, might be wise.

I once got very very low over Zion National Park in Utah and have carried higher safety margins ever since!

Mike

On Mar 7, 12:08*pm, Mike the Strike wrote:
In addition to considering the probability of a landout, you have to take into consideration the consequences of one. *If your final glide is over a landscape of neatly mowed large fields, the consequences of a landout are trivial and you can push closer to the theoretical limits. *As Cliff says, many western sites have very poor options and carrying extra height, perhaps even more than mathematically indicated, might be wise.

I once got very very low over Zion National Park in Utah and have carried higher safety margins ever since!

Mike

Exactly. In the paper analysis, you adjust the "probability of not
making it" parameter according to the consequences of a landout. The
profile to follow over mowed fields, where the costs are inconvenience
or contest points, is very different than the profile to follow over
Zion. They're both square roots but the Zion profile is much higher up
-- in the range of MacCready settings you may never have used before.

That's one of the big points. We get used to Mc 3 or so glides and
that they almost always work out. Over Zion, that experience is not
good enough. To an earlier comment that experience trumps analysis,
well, you don't want to be the guy that learns about how often Mc 1
glides work out by experience!

John

On Wednesday, March 7, 2012 11:34:23 AM UTC-8, John Cochrane wrote:
On Mar 7, 12:08*pm, Mike the Strike wrote:
In addition to considering the probability of a landout, you have to take into consideration the consequences of one. *If your final glide is over a landscape of neatly mowed large fields, the consequences of a landout are trivial and you can push closer to the theoretical limits. *As Cliff says, many western sites have very poor options and carrying extra height, perhaps even more than mathematically indicated, might be wise.

I once got very very low over Zion National Park in Utah and have carried higher safety margins ever since!

Mike

Exactly. In the paper analysis, you adjust the "probability of not
making it" parameter according to the consequences of a landout. The
profile to follow over mowed fields, where the costs are inconvenience
or contest points, is very different than the profile to follow over
Zion. They're both square roots but the Zion profile is much higher up
-- in the range of MacCready settings you may never have used before.

That's one of the big points. We get used to Mc 3 or so glides and
that they almost always work out. Over Zion, that experience is not
good enough. To an earlier comment that experience trumps analysis,
well, you don't want to be the guy that learns about how often Mc 1
glides work out by experience!

John

Excellent article and excellent thread.
John, I am curious to hear your opinion about using higher MC vs degrading the polar (aka bug factor) for safety as some do instead or in addition.

Ramy

Excellent article and excellent thread.
John, I am curious to hear your opinion about using higher MC vs degrading the polar (aka bug factor) for safety as some do instead or in addition.

Ramy

I don't think using the bugs setting to calculate glides in real time
is that helpful. I never know what percent bugs means.

I do think it would be useful if our instrument makers could allow us
to input lift or sink. I'd like to input, "MacCready 3, 500 foot
reserve, and 100 fpm sink." Or when doing a final glide in Uvalde,
"MacCready 3, 500 foot reserve, and 100 fpm lift." (Clearnav has a few
emails from me on this!)

This simply shifts the polar curve up and down by the given lift and
sink, and would be easy for them to program.

For contest final glides, by keeping track of average netto in the
last few legs you could have an idea of lift/sink to be expected on
final glide, and then bump up / be cautious accordingly.

For safety reasons this would be very educational. You'd see directly
just how disastrous small bits of extra sink can be on your
glideslope. I also think many pilots would find it easier to take the
advice "assume 200 fpm sink all the way to your safest landing" than
they would to take the advice "input Mc 10 into your glide computer."
The former sounds reasonable, the latter outlandish based on cross-
country experience, yet they are the same thing.

Good point -- I'll add this to the article.

John

Super interesting. Thankyou!

Still important, but perhaps for a separate thread, is a strategy for escaping from a line of sink rather than just dealing with the mathematical consequences.

As I noted earlier, lift and sink lines are frequently aligned and knowledge of the relative heading of the glider along or across these lines would give the pilot useful information for an avoidance strategy.

You can see the forecast predictions of any such lift/sink lines on the RASP Boundary Layer Up/Down Motion or the equivalent HRRR field "Mean Layer Vertical Velocity".

Changing your final glide heading from a line of sink into a line of lift might have more benefit than accepting the inevitable and dialing up doom on your flight computer!

Mike

On Mar 8, 9:55*am, Mike the Strike wrote:
Still important, but perhaps for a separate thread, is a strategy for escaping from a line of sink rather than just dealing with the mathematical consequences.

As I noted earlier, lift and sink lines are frequently aligned and knowledge of the relative heading of the glider along or across these lines would give the pilot useful information for an avoidance strategy.

You can see the forecast predictions of any such lift/sink lines on the RASP Boundary Layer Up/Down Motion or the equivalent HRRR field "Mean Layer Vertical Velocity".

Changing your final glide heading from a line of sink into a line of lift might have more benefit than accepting the inevitable and dialing up doom on your flight computer!

Mike

Yes. In rivers of blue sink, I often just head 90 degrees off course
and wait.

Put another way, though, you have to use a much higher glide slope
(MacCready value + reserve) for safety spots that are upwind/downwind
or aligned with lift/sink streets than for safety spots that are
crosswind or not so aligned. The airports are where they are, so going
crosswind isn't always an option.

John Cochrane