Energy management

Am I right that the reasoning behind the high speed low height dash is that it
takes one of the variables out of the risk equation?

You arrive at a point where you have the finish line made with some spare
energy, but not a lot.
If you fly the conservative approach at height you have an equal chance of
finding lift and/or sink over that last stretch.
Do this and there is uncertainty about the air you will fly through right up to
the finish line.

If you get right down into the stable layer right above the ground, the only
thing you have to worry about is running out of airspeed, height and ideas
simultaneously... But you did calculate this accurately with your flight
computer so not having to worry about vertical airmass movement is an advantage.
You can also fly above the rough air speed - you can be reasonably sure there
will be no significant vertical gusts under 50-100 feet AGL.

Finishing higher is safer for a number of reasons:
It presents a better view of the airfield, and other aircraft. (Less surprises,
better planning)
You can use the MK1 eyeball to confirm what your computer(s) are saying about
reaching the landing point.
If - for some reason you experience a malfunction, you have a little more time
to sort it out.
If - for some reason someone else does something unexpected, you have alternatives.
You have the luxury of slowing down and getting your mind out of race and into
landing gear - with time for a reasonable, predictable circuit so other people
know exactly what you are doing.

All the time based advantages in safety equate to points forfeited.

The personal level of risk accepted in the interests of winning is very
personal. Those making these low fast approaches presumably believe that it
improves their competitive position. But it helps to remember that you can't
race in a broken glider, or with a broken body.



Ian Cant wrote:
Thankyou, KF and all others. Am I correct to summarize
that there is a handful [or two, or maybe three handfuls]
of points to be lost by finishing low but with enough
surplus energy to pull up into a pattern rather than
finishing with minimum safe energy at any altitude;
that a safety margin should be carried right down to
the final few moments; that a straight-in and land
[either a rolling finish or after minimum-permitted
altitude finish] tactic on the remaining runway ahead
is the most 'efficient' provided it incurs no penalty;
and the balance between points grasped and safety and
showmanship is entirely at each pilot's discretion
?

Thanks again for the education,

Ian




At 22:42 16 February 2007, Hl Falbaum wrote:

'Ian Cant' wrote in message
...

The perennial contest finish argument is always entertaining.
May I, as an ignorant bystander, ask a related question
without being strafed too much ? If a finisher has
the energy for a fast low pass and then pullup to
a
safe pattern, how much time along the course was spent
to acquire that energy to be dissipated after the
task
is over ? Seems to me that there must be some points
loss involved, even if it's small. Except of course
for someone who is sure he has won by a large margin
and will get his 1000 - but even then, there is a
points
gain for all the other competitors.

Ian


It appears that nobody has answered Ian's actual question
(imagine that?)

The height gained in the pullup is equivalent to the
total energy excess and
the 'efficiency' of the glider in the conversion. Figure
90% for an open
classser, and about 85% for a current 15m ship (yeah,
it's a W.A.G.) so if
the glider gets 600' on the pullup and has 85% efficiency,
he had 705' of
total energy excess. If the last thermal was 4kt, then
it took 1.76 min
extra to climb. If points are about 8/ min, then it
cost about 14 points! If
running a street it gets a lot more complex as the
streets are not uniform.

It is seldom so simple, as, unless the air is dying
ahead, one must have the
power of prophecy to tell what is really going to happen.

Hartley Falbaum
DG800B 'KF' USA

"Bruce Greef" wrote in message
...
Am I right that the reasoning behind the high speed low height dash is
that it takes one of the variables out of the risk equation?

You arrive at a point where you have the finish line made with some spare
energy, but not a lot.

In the USA the Sailplane Racing Association , and in Canada, the Candian
Advanced Soaring websites have excellent discussions on the subject
http://sailplane-racing.org/Articles...llustrated.pdf
http://www.sac.ca/cas/techniques/techniques.html

Books by Reichmann, Piggott, Welch & Irving explain the problem fully.

Modern flight computers can give you Total Energy corrected differential
final glide height. This means that at any time, the computer can tell you
how high above your "safety height" you would be when you reach the finish,
if you slowed to best glide speed-MacCready Zero, or in some computers, if
you slow to the set MacCready speed.

So you follow your MacCready directed speed until you see that you have the
field made--no doubt about it--. Either you see the airport at a comfortable
angle below your glidepath, or the computer says you are a good margin above
your safety height (500-1000 ft) that you have set-and you are just a few
miles (4-6) out. From that point you go to "visual" and burn as much height
as you think safe, while your computer tells you if you are gaining or
losing on the differential. If you set, say 500 in, and the differential
goes to zero, it means you can make it up to 500 if you slow down. Of
course--don't trust your life to this!

In general, a pull up from 120 kt to 60 kt recovers about only 450 ft. So
don't plan on a low 50 ft pass at anything less or you won't like what could
happen. If you are just crawling in, or walking at, say 80-90 kt, plan a
rolling finish, but announce it because you will be landing against the flow
of traffic! Better would be a high pattern---in the USA you lose points for
a rolling finish.

At any rate---These few points may make the difference between 1st and 3rd,
or between 21st and 22nd, but who cares? Nobody will remember if you won or
came in third that day, but they will remember a long time if you do
something stupid.

Hartley Falbaum
DG800B "KF" USA
850 points on a really good day!