physics question about pull ups

On Jun 5, 3:07*pm, Gary Osoba wrote:
On Jun 5, 2:41*pm, Nine Bravo Ground wrote:





On Jun 5, 2:30*pm, Gary Osoba wrote:

On Apr 25, 8:21*am, Andy wrote:

As an aside - the strong G-effect on induced drag is the main reason
why you should try to avoid hardpullupsinto thermals - you give away
a bunch of altitude.

9B

Yes, if you both accelerated and are now pulling up in a constant
velocity of transportation field. But by mentioning the thermal, this
is not likely. With discontinuous fluid fields, coupled pullups and
pushovers which are properly timed within a shifting frame of
reference have the potential to gain much more energy than is ever
lost to induced and friction drag- dry or fully loaded. The fully
loaded case has more potential in typical soaring environments because
more time is available to apply the technique and the events can be
further apart.

For most gliders, the optimized multiplier is so substantial that you
run out of positive g maneuvering envelope (based on JAR standards)
with a mere 2-3 knots of lift.

Best Regards,

Gary Osoba

If you mean dynamic soaring then the airmass velocity gradient needs
to be horizontal, not vertical as is the case with thermals - plus the
magnitude of the gradient in a thermal is way too low to be useful,
even if it were in the correct orientation.

If you aren't referring to dynamic soaring then all I can say is
"huh"?

9B

9B:

The physics apply in all directions, but the potential is greatest
with positive vertical velocity gradient since that vector directly
opposes gravity- *and that's our job if we're going to stay up. The
reason the horizontal gradients are more readily recognized is that
they are often sustainable in a cycle, witness the Albatross. However,
I'm not wanting to argue about it. I know the physics and the math and
have been using them effectively for about 15 years now.

Best Regards,
Gary Osoba

Got it - sounds a bit uncomfortable since moving the velocity vector
around in the vertical axis takes a lot more aggressiveness then
horizontally. I assume it also helps to know where the boundaries of
the gradients are before you reach them. If you miss you just mush and
lose altitude fro all the induced drag.

It's the exact opposite technique from what I see and hear from most
top racing pilots who advise flying slower than McCready theory and
maintaining laminar flow over the wing with only modest maneuvering.
How do you decide when to use which technique when you are cruising
along at 15,000 feet and 85 knots and run into a 6 knot thermal?

9B

On Jun 6, 10:06*am, Andy wrote:

Got it - sounds a bit uncomfortable since moving the velocity vector
around in the vertical axis takes a lot more aggressiveness then
horizontally. I assume it also helps to know where the boundaries of
the gradients are before you reach them. If you miss you just mush and
lose altitude fro all the induced drag.

Yes, as you have properly shown in the still air case- only now the
penalties are even higher than in still air.


It's the exact opposite technique from what I see and hear from most
top racing pilots who advise flying slower than McCready theory and
maintaining laminar flow over the wing with only modest maneuvering.
How do you decide when to use which technique when you are cruising
along at 15,000 feet and 85 knots and run into a 6 knot thermal?

9B

Well. that's the trick, isn't it? I would say that if you're at
15,000', full of water, but only going 85 knots, it must be pretty
spotty overall and would recommend sticking to the conventional
approach. For one thing, you only have a little over a second of
deceleration time at that speed. When the conditions allow, it is much
better to have more maneuvering time through higher velocities.
However, it has also been shown that chasing MacCready through a
thermal will usually yield poorer results than stick-fixed excursions
(Braunschweig Tech. University, 1982). Chasing any of this with the
vario is futile due to lag times.

In any event, much of this does run counter to the normal "racing"
protocol. E.g., Moffat's final turn at the top of a climb when it is
tightened and you accelerate across the thermal core before exiting.
Exactly opposite to the best total energy/dynamic maneuvering
scenario, apart from tightening the turn in order to be right at the
center of the core for the straight line flight.

I only entered a contest once as an individual, and chose to fly it
without a computer (or even a speed ring). I did effectively use these
techniques, and lateral dynamic maneuvering as well.

Best Regards,

Gary Osoba

However, it has also been shown that chasing MacCready through a
thermal will usually yield poorer results than stick-fixed excursions
(Braunschweig Tech. University, 1982). Chasing any of this with the
vario is futile due to lag times.

As I think of Gary's maneuvers, they are more characterized by sharp
pull ups and pushovers when lift changes, as opposed to classic
"chasing the needle" which we know doesn't work. I suspect that when
we get this right, G and airspeed will be a much more important input
than varios. We're trying to pull when we get the increased G from
entering a thermal, "bouncing" off the change in vertical speed, and
vice versa. Similarly, the time when this works is during the rush of
positive airspeed as you enter a vertical gust.

The instrument or pitch controller that gets this right may be
essentially one that tells us what the G reading is subtracting the
effects of controls -- a "total energy g meter" if you will. Then you
can pull when "total energy" g is positive and push when it's
negative, subtracting the "stick g"


In any event, much of this does run counter to the normal "racing"
protocol. E.g., Moffat's final turn at the top of a climb when it is
tightened and you accelerate across the thermal core before exiting.
Exactly opposite to the best total energy/dynamic maneuvering
scenario, apart from tightening the turn in order to be right at the
center of the core for the straight line flight.

Moffat's technique was great in the 70s, but most pilots don't use it
now. Especially in wind or under clouds, there is often not sink
surrounding a thermal, but a long stretch of buoyant air. They didn't
know that in the 70s because they didn't have netto or speed to fly
varios, so when they sped up to 90 knots they were in fact sinking
like stones. Most of the time the key to thermal exit is to leave
gently in such a way as to milk the surrounding up air while cruising
relatively slowly for a few miles

John Cochrane

On Jun 6, 1:14*pm, John Cochrane
wrote:
However, it has also been shown that chasing MacCready through a
thermal will usually yield poorer results than stick-fixed excursions
(Braunschweig Tech. University, 1982). Chasing any of this with the
vario is futile due to lag times.

As I think of Gary's maneuvers, they are more characterized by sharp
pull ups and pushovers when lift changes, as opposed to classic
"chasing the needle" which we know doesn't work. I suspect that when
we get this right, G and airspeed will be a much more important input
than varios. We're trying to pull when we get the increased G from
entering a thermal, "bouncing" off the change in vertical speed, and
vice versa. Similarly, the time when this works is during the rush of
positive airspeed as you enter a vertical gust.

The instrument or pitch controller that gets this right may be
essentially one that tells us what the G reading is subtracting the
effects of controls -- a "total energy g meter" if you will. Then you
can pull when "total energy" g is positive and push when it's
negative, subtracting the "stick g"



In any event, much of this does run counter to the normal "racing"
protocol. E.g., Moffat's final turn at the top of a climb when it is
tightened and you accelerate across the thermal core before exiting.
Exactly opposite to the best total energy/dynamic maneuvering
scenario, apart from tightening the turn in order to be right at the
center of the core for the straight line flight.

Moffat's technique was great in the 70s, but most pilots don't use it
now. Especially in wind or under clouds, there is often not sink
surrounding a thermal, but a long stretch of buoyant air. They didn't
know that in the 70s because they didn't have netto or speed to fly
varios, so when they sped up to 90 knots they were in fact sinking
like stones. Most of the time the key to thermal exit is to leave
gently in such a way as to milk the surrounding up air while cruising
relatively slowly for a few miles

John Cochrane


Okay, this is going to totally mess up my next contest.

I admit that I substantially rely on Gs to decide whether to turn in
lift - the vario only tells you if you made a good choice 1/4 turn
later. I honestly don't find that many thermals with a very strong
gradient, so I am wondering how much benefit I'll get from the extra
push and pull, especially if the optimal strategy emphasizes search
range over theoretical McCready optimum cruise speed.

As to flying 85 knots - that's pretty common for me when I am dry -
maybe 95 knots wet on a good day. If the thermals are closely placed
and consistent and the lift band is deep enough I'll bump it up,
otherwise I like the extra search range.

9B

On Jun 7, 5:42*am, Gary Osoba wrote:
In any event, much of this does run counter to the normal "racing"
protocol. E.g., Moffat's final turn at the top of a climb when it is
tightened and you accelerate across the thermal core before exiting.

I've never understood how you are supposed to do that. I'm *already*
circling as tightly as I can at the speed I'm flying!

Unless all you're doing is increasing the bank angle while maintaining
the same elevator setting, which will make you turn in a bit more and
enter a dive.

On 6/6/2010 7:29 PM, Bruce Hoult wrote:
On Jun 7, 5:42 am, Gary wrote:

In any event, much of this does run counter to the normal "racing"
protocol. E.g., Moffat's final turn at the top of a climb when it is
tightened and you accelerate across the thermal core before exiting.

I've never understood how you are supposed to do that. I'm *already*
circling as tightly as I can at the speed I'm flying!

Do you mean you are flying close to stalling? My glider, and many
others, climb better if flown about 5 knots above stall, so I can always
tighten my turn if I need to reposition my circle, or take evasive
action if another glider gets too close.

--
Eric Greenwell - Washington State, USA (netto to net to email me)

On Jun 7, 7:20*pm, Eric Greenwell wrote:
On 6/6/2010 7:29 PM, Bruce Hoult wrote: On Jun 7, 5:42 am, Gary *wrote:

In any event, much of this does run counter to the normal "racing"
protocol. E.g., Moffat's final turn at the top of a climb when it is
tightened and you accelerate across the thermal core before exiting.

I've never understood how you are supposed to do that. I'm *already*
circling as tightly as I can at the speed I'm flying!

Do you mean you are flying close to stalling? My glider, and many
others, climb better if flown about 5 knots above stall, so I can always
tighten my turn if I need to reposition my circle, or take evasive
action if another glider gets too close.

--
Eric Greenwell - Washington State, USA (netto to net to email me)

After doing the math on sink rate versus bank angle I realized that
there is a reason why I am always 50-100 feet lower than everyone else
- I always circle at 45 degrees of bank. In fact you should bank as
shallow as possible while staying in the strong lift. Between 30
degrees of bank and 45 degrees the sink rate goes up a lot so you best
be sure that the core is really so small that you need to give up the
extra sink rate to circle tight.

On the tightening up to go through the core, even if your are racked
up tight you can usually bank and yank even tighter if you are willing
to accept a little downward acceleration since you won't be able to
produce enough lift to maintain steady flight. This may in fact be
exactly what you are looking to do if you believe there is a REALLY
strong core and strong sink beyond the edge of the lift. Your sink
rate will go up to a couple of knots, so the core needs to be worth
the extra inefficiency and you have to want to accelerate to scoot
through the sink, otherwise it's all a waste of energy. I don't
generally do it as I more often find widespread lift at the top of a
climb.

9B

On Jun 8, 2:20*pm, Eric Greenwell wrote:
On 6/6/2010 7:29 PM, Bruce Hoult wrote: On Jun 7, 5:42 am, Gary *wrote:

In any event, much of this does run counter to the normal "racing"
protocol. E.g., Moffat's final turn at the top of a climb when it is
tightened and you accelerate across the thermal core before exiting.

I've never understood how you are supposed to do that. I'm *already*
circling as tightly as I can at the speed I'm flying!

Do you mean you are flying close to stalling? My glider, and many
others, climb better if flown about 5 knots above stall, so I can always
tighten my turn if I need to reposition my circle, or take evasive
action if another glider gets too close.

Of course I'm a similar amount over the stall speed, and can tighten a
little, but nowhere near the halving of the radius that would be
required to go through the center of the existing circle.

Flying at 45 knots with a 40 knot stall speed (at that G loading) only
gives you scope to increase the lift by 25%, not the 100% needed.

OTOH it's true that if you've only got a 30 degree bank angle then
rolling to 90 degrees bank without changing the AoA will halve the
initial turn radius (before you plummet and speed up). From a 45
degree bank you can only decrease the radius to 70% in this way. Maybe
it's enough.

Hmm. Rolling from 30 degrees to 60 degrees will decrease the turn
radius to 58% (pretty close to 50), but still leave half a G worth of
vertical lift. Or rolling from 30 degrees to 53 and also pulling 25%
more G would halve the turn radius while only accelerating downward at
0.25 G.

Yeah, maybe it's doable. But it will have to be good lift in there and
no one just ahead of and below you in the thermal (blind spot!) to hit
on the way out!