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How Low to Spin??



 
 
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  #21  
Old August 24th 04, 12:43 PM
Chris OCallaghan
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Interesting problem. I would suggest that the primary danger faced by
a competent pilot isn't a spin, but a midair collision. One can choose
to increase speed near the ground. However, a low save requires extra
attention to airspeed control, coordination, and thermal centering.
Myopic focus on a thermal in the high density traffic of a landing
pattern is inappropriate. Pilots entering the pattern depend on others
already in it to act predictably. And once in the pattern, special
attention has to be given to traffic aviodance, since gliderports (and
especially mixed traffic airports) can produce unusual conflicts under
the best of conditions.

I assume your club has a safety officer. If a pilot chooses to thermal
in the pattern, that pilot needs talking too. Part of the discussion
might include the addition of variables during low altitude saves and
their effect on maintaining appropriate safety margins, but the
primary focus should be on the poor judgement that led a pilot to
operate unpredictably (and thereby unsafely) in the landing pattern,
where he may be a danger to others as well as himself.
  #22  
Old August 24th 04, 05:06 PM
scurry
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Ted Wagner wrote:

Thanks Shawn, I'll take a look.

Btw, so say "It's *safe* to say everyone should land (blah blah blah)" is,
well, stating the obvious (kinda like saying "It's safe to stay on the
ground"). The pertinent question is whether it was *unsafe* for me to
continue the turn in the precise circumstances in which I found myself. I
remain open to the possibility that it was not, but in the same spirit,
being over tiger country out of reach of landable points is questionably
unsafe, yet I hear regularly of pilots doing this as a matter of routine,
especially in contests, and if I continue flying contests long enough (and I
hope to be doing them for many years), I will have to take that step many
times myself. I want to err on the side of safety, but at the same time, I
want to be reasonable and competitive.


Was it unsafe? No, not that time. Here you are! Definitely risky though.
Thermalling at low altitude isn't like thermalling aloft. Thermals are
less consolidated and much smaller in area. Wind shear due to ground
features alters the way thermals behave relative to higher up on the
same day, in the same wind. Perspective is different as well. The
ground appears to disappear under the lower wing near the ground (moving
front to back), whereas at altitude it appears from under the lower
wing. If you try to "fix" this picture automatically, you'll keep
finding yourself in a skidding turn every time you scan past the yaw string.
Do most pilots routinely fly over tiger country out of glide of anywhere
landable? I think people talk it up more than they do it. Plus, being
at 19,000 feet (by GPS) over Nevada desert with cloud streets as far as
the eye can see is a different judgment call than being 2000 feet over a
Louisiana swamp with a wisp of a cloud dome up ahead.
The way I'll keep looking at it, is how I was trained. Once I commit to
landing, I'll land. And yes, I can imagine exceptions, but they would
involve the landing option being very very bad anyway (e.g. trees).
Much better not to get into such a situation in the first place.
FWIW its very good you're asking these questions now, and not the next
time you're in lift on downwind.

Shawn
  #24  
Old August 24th 04, 05:27 PM
Bert Willing
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Circling at 400ft while being able to land anywhere doesn't mean unsafe
operations by definition. I frequently start circling over a ridge at less
than half of this altitude. But not always.
Everything depends on experience (with that glider), current training level
(with that glider), personal daily fitness, wind conditions and lift
conditions.
And you have to put the question "is it safe" every single time - but then,
this does hold for every manoeuvre.
You just have to accept that sometimes the answer to this question is "no".

--
Bert Willing

ASW20 "TW"


"scurry" a écrit dans le message de
...
Was it unsafe? No, not that time. Here you are! Definitely risky

though.
Thermalling at low altitude isn't like thermalling aloft. Thermals are
less consolidated and much smaller in area. Wind shear due to ground
features alters the way thermals behave relative to higher up on the
same day, in the same wind. Perspective is different as well. The
ground appears to disappear under the lower wing near the ground (moving
front to back), whereas at altitude it appears from under the lower
wing. If you try to "fix" this picture automatically, you'll keep
finding yourself in a skidding turn every time you scan past the yaw

string.
Do most pilots routinely fly over tiger country out of glide of anywhere
landable? I think people talk it up more than they do it. Plus, being
at 19,000 feet (by GPS) over Nevada desert with cloud streets as far as
the eye can see is a different judgment call than being 2000 feet over a
Louisiana swamp with a wisp of a cloud dome up ahead.
The way I'll keep looking at it, is how I was trained. Once I commit to
landing, I'll land. And yes, I can imagine exceptions, but they would
involve the landing option being very very bad anyway (e.g. trees).
Much better not to get into such a situation in the first place.
FWIW its very good you're asking these questions now, and not the next
time you're in lift on downwind.

Shawn



  #25  
Old August 24th 04, 05:47 PM
Kirk Stant
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(Mark James Boyd) wrote in message news:412a9f4a$1@darkstar...
Ted Wagner wrote:
yaw string straight.


We've had this discussion on RAS before. I'm still
gonna say that yaw string straight doesn't prevent a spin
entry. Spins are when you're stalled and one wing is more
stalled than the other.

One wing is more stalled than the other if one wing
has less AOA/more airspeed than the other. With the yawstring
straight, this is still true in a steep bank, especially
with long wings. It's also true if you're in a slip and
then with a punchy foot coarsely correct it to
center.

The steeper the bank, the higher the stall speed AND
the greater the difference in wing speeds, even with a straight
yaw string.

When I teach rope breaks, I do them at 300 ft and 30-45
degrees of bank, and best L/D for that bank angle.
http://www.stolaf.edu/people/hansonr/soaring/spd2fly/
is a start. I also caution against super rapid roll rates
and coarse use of rudder.

I'm open to thoughts on this. I didn't do the math to
see how MUCH the factor affects spins (somebody else did and
came up with 3 degrees diff or so for 50 deg and 18m wings),
but it sure surprised me.

Now when I do spins in the L-13, I do them from string centered
flight, and sure enough it always spins in the direction of the
steep bank, and in a hurry too...

P.S. Of course this assumes the rigging is right. If
flaps are lower on one side than the other, hey man, there's
yet another factor...



I disagree with your conclusion about steep bank angles. It is
usually a lot harder to spin from a steep turn, and a lot easier to
recover from an incipient spin, for a simple reason (see Piggott for
more details): a properly flown steep turn is flown at a
significantly higher speed, and the elevator is limited, making it
harder to reach stalling angle of attack, and much easier to reduce
the angle of attack if needed due to the higher speed.

You mention in an earlier post about making shallow, fast turns during
a low save. Why shallow? If the thermal is narrow, you usually need
to be steep (and fast) to stay in the (probably a bit turbulent) core.
A shallow turn is asking for the classic base-to-final spin entry,
unless you fly so fast that any climb is more luck than skill!

Methinks your power background is showing (all those shallow turns!).
Even though I also have a power past going way back, I now find my
glider bias showing when I fly a stinkpot; I find myself whipping into
nice 45 to 60 degree banks, scaring the daylights out of my power-only
friends...

Kirk
  #26  
Old August 24th 04, 07:42 PM
Eric Greenwell
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Ted Wagner wrote:

Thanks Shawn, I'll take a look.

Btw, so say "It's *safe* to say everyone should land (blah blah blah)" is,
well, stating the obvious (kinda like saying "It's safe to stay on the
ground"). The pertinent question is whether it was *unsafe* for me to
continue the turn in the precise circumstances in which I found myself. I
remain open to the possibility that it was not, but in the same spirit,
being over tiger country out of reach of landable points is questionably
unsafe, yet I hear regularly of pilots doing this as a matter of routine,
especially in contests,


We must know entirely different groups of pilots, because I sure don't
hear pilots talking about this, unless it starts out "Boy, did I screw
up today...". The story often ends with "... so I ended up ground
looping (or "scaring myself sh--less", "hitting the fence", "breaking
the tail", etc)".

and if I continue flying contests long enough (and I
hope to be doing them for many years), I will have to take that step many
times myself.


No, you certainly don't have to. Pilot's choice, you know. It some areas
in some conditions, the lift can be so reliable that you can actually
count on it, but if done regularly, you will find the times when you
misjudge the weather.

I want to err on the side of safety, but at the same time, I
want to be reasonable and competitive.


Take a look at the flight traces from the top pilots. See if they are
really taking these chances. The ones I've flown with didn't seem to
take these kinds of chances. I think the philosophy for many of them is
"there is always another day and another contest, and if you break your
glider, you won't even win this day or this contest".

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

  #27  
Old August 24th 04, 07:56 PM
Mark James Boyd
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scurry wrote:
wrote:

scurry wrote:

Ridge flying is practised currently *much* closer to the ridge than that, in
fact so close than not touching some tree is the real problem.


Carl Herold has stated he no longer does ridge soaring because
he finds it too dangerous. On the other hand, he has so many other
forms of lift available in the Sierras, I suspect this isn't
a problem

If you land with pine needles in your ailerons, you are
too close...
--

------------+
Mark Boyd
Avenal, California, USA
  #28  
Old August 24th 04, 08:00 PM
Mark James Boyd
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scurry wrote:
Ted Wagner wrote:

Thanks Shawn, I'll take a look.

Was it unsafe? No, not that time. Here you are! Definitely risky though.
Thermalling at low altitude isn't like thermalling aloft. Thermals are
less consolidated and much smaller in area. Wind shear due to ground
features alters the way thermals behave relative to higher up on the
same day, in the same wind. Perspective is different as well. The
ground appears to disappear under the lower wing near the ground (moving
front to back), whereas at altitude it appears from under the lower
wing. If you try to "fix" this picture automatically, you'll keep
finding yourself in a skidding turn every time you scan past the yaw string.


An excellent point. I've found myself more than once skidding
because of wind creating an illusion close to the ground. The
only way I've found to counter it is being aware of the wind, and
using slow roll rates and shallow banks close to the ground (so I don't
need much rudder anyway).
--

------------+
Mark Boyd
Avenal, California, USA
  #29  
Old August 24th 04, 08:25 PM
Marc Ramsey
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Mark James Boyd wrote:
An excellent point. I've found myself more than once skidding
because of wind creating an illusion close to the ground. The
only way I've found to counter it is being aware of the wind, and
using slow roll rates and shallow banks close to the ground (so I don't
need much rudder anyway).


*Listen* to what Kirk (and others) have said about this. The last thing
you want to do when thermalling down low is use a shallow bank angle.
It is just too easy to lose track of what you are doing, and end up a
bit too slow in a skidding turn. It is far safer to be in a properly
coordinated turn with a 40 to 50 degree bank angle. Every glider I've
ever flown gives a much better warning of impending departure in a tight
turn, plus the visual (nose above horizon) and physical (G forces
slacking off) cues are much more pronounced.

Marc
  #30  
Old August 24th 04, 08:34 PM
BMacLean
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I fly with the same group as you Ted and I wonder where you get the idea
that it is "routine" to fly with no landing options, even in hardcore
competition. I don't believe this to be the case and I agree with Eric. I
have found that when a pilot is relating a story of some scary situation
they got themselves into and I ask them where they would have landed, 99% of
the time they have an answer.

Barb


 




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