physics question about pull ups

On 6/5/2010 2:41 PM, Nine Bravo Ground wrote:
On Jun 5, 2:30 pm, Gary wrote:
On Apr 25, 8:21 am, 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

I don't care what he is referring to. I'm still saying "huh"?
Paul
ZZ

On Jun 5, 3:00*pm, John Cochrane
wrote:
If you aren't referring to dynamic soaring then all I can say is
"huh"?

No, Gary means it. In theory, we can gain a lot by strong pull ups and
pushovers in thermal entries and exits. In fact, in theory, you can
stay up when there is only sink. You push to strong negative g's in
the sink, then strong positive gs when you are out of the sink. Huh?
Think of a basketball; your hand is sink and the ground is still air.
When you push hard negative g's in the sink, the glider exits the sink
with more airspeed than it entered, just like the basketball as it
hits your hand. The opposite happens when you pull hard for the first
second or two after entering lift.

To work, you have to pull hard while the glider is still descending
relative to the surrounding air in the thermal, and ascending relative
to surrounding air in the still air or sink. You only get a second or
two. In my experiments I haven't gotten this to work, though it may
account for some of the aggressive zooming we see in Texas
conditions.

Really, to make it work well, I think we need to surrender pitch
control to a computer that handles pitch based on very fast update
vario and g meter. The optimal pitch control is not a hard problem to
solve. It does take a faster feedback than human -- or at least this
human -- can seem to manage.

Don't laugh. Handing over pitch control to a computer might give the
same performance boost as several meters of span. It would definitely
be worth it, though the occupant might need an iron stomach.

John Cochrane
BB

I was thinking more about this. I can see why as you approach a
beautiful cu you would push over as you enter the downwash around the
thermal then reverse and pull as you get into the lift. The tricky
part for me is that I rely a lot on the G sensation I get from entry
into lift to determine where to stop and circle. If I am pulling a lot
of Gs on top of that it masks the feel of the lift which means I need
other cues to ensure that I don't flail around looking for the core -
such as another glider already racked in tight or a very small cu to
mark the thermal.

On Jun 5, 4:00*pm, John Cochrane
wrote:
If you aren't referring to dynamic soaring then all I can say is
"huh"?

No, Gary means it. In theory, we can gain a lot by strong pull ups and
pushovers in thermal entries and exits. In fact, in theory, you can
stay up when there is only sink. You push to strong negative g's in
the sink, then strong positive gs when you are out of the sink. Huh?
Think of a basketball; your hand is sink and the ground is still air.
When you push hard negative g's in the sink, the glider exits the sink
with more airspeed than it entered, just like the basketball as it
hits your hand. The opposite happens when you pull hard for the first
second or two after entering lift.

To work, you have to pull hard while the glider is still descending
relative to the surrounding air in the thermal, and ascending relative
to surrounding air in the still air or sink. You only get a second or
two. In my experiments I haven't gotten this to work, though it may
account for some of the aggressive zooming we see in Texas
conditions.

Really, to make it work well, I think we need to surrender pitch
control to a computer that handles pitch based on very fast update
vario and g meter. The optimal pitch control is not a hard problem to
solve. It does take a faster feedback than human -- or at least this
human -- can seem to manage.

Don't laugh. Handing over pitch control to a computer might give the
same performance boost as several meters of span. It would definitely
be worth it, though the occupant might need an iron stomach.

John Cochrane
BB

How about somebody writing an "inertial variometer" app for an i-Phone
4 since is has a built-in 6DOF IMU?

On 6/6/2010 7:39 AM, Gary Osoba wrote:

Yes. Your wing is a machine, and the work it performs imparts a
downward flow to the air it moves through. When that downward force is
aligned in a direction that opposes the movement of the air, it gains
energy. The air movement can be from the side, from above, or below-
the most efficient case since this vector opposes gravity. The
transfer of energy from air motion can be increased by manipulating
the inertial field of the glider, and there is an optimal g loading or
unloading for each case. Although physicists define such inertial
forces as "psuedo", the wing does not know this and must develop twice
the lift to sustain 2g flight as 1g flight, three times the lift for
3g flight,etc. The power transferred from the air to the wing
increases linearly with g force increases, while the the losses
associated with the increased g loadings are fractional and therefore
nonlinear, yielding excess power. This excess power can be carried by
the glider into a differential airmass with relative sink by a coupled
acceleration and a portion of it can be transferred to this airmass.
The case of 0g accelerations (freefall) is special in that
theoretically the wing doesn't produce induced drag. Theoretically
only, because the lift distribution will never be perfect- especially
in the unsteady flows which punctuate a soaring environment. In
practice, I have found 0g to be the best target for accelerations
since most of our wing sections are not designed to fly efficiently
upside down and everything is happening so quickly you lose less if
you guess wrong on the strength of the relative downdraft.

Much of this is counterintuitive. For example, here's something
presented in a 2001 lecture on the subject. It is stated as
exclusionary to emphasize how flight through a discontinuous
atmosphere can up-end long held conventions.

"For any body of mass moving through or in contact with a medium that
is not uniform, the most efficient path(s) for a given power input
will never be defined by a straight line or a constant speed." -
Osoba's Theorem of Dynamic Locomotion

The concise statement of this is "...never be defined by a constant
velocity..." since velocity incorporates both speed and direction but
most pilots don't understand the term that way.

Best Regards,

Gary Osoba

Can someone explain that first part? Is it really obvious? Seems
critical to the theory and I don't get it. Seems like when the wing
imparts a downward force on the air and displaces it, work is done on
the air. While the forces should be equal and opposite, the work is not.
In fact, energy is conserved. So the energy came out of the wing and
into the air. The wing doesn't know the air is moving relative to the
earth or anything else. And the air doesn't know its moving either. Its
wafting along at a nice steady pace (convenient inertial reference
frame) when the wing comes along and shoves it. The harder you push and
more air you displace, the more energy is transferred out of the wing
and into the air. Where does the energy into the wing come from?

Its not because the wing accelerates up due to the increased lift force.
The lift force generated by the wing is normal to its path through the
local air. Always. So that force curves the flight path. And by
definition, no work is done by a force normal to the displacement. But
the increased lift does increase the drag force, which works opposite
the direction of motion (negative work, which transfers energy to the
air). How does aggressive vertical maneuvering help?

Seems like dribbling a flat basketball. The bounce is kind of lossy.

But plenty of smart people see that it works, so I'm missing something?

I suppose dynamic soaring on the edge of a thermal might work. Looping
at the edge, diving in the core, pulling up vertical in the sink would
increase airspeed on each side of the cycle. But that requires pulling
in sink and pushing (pulling the top of the loop is more efficient) in
the lift. Hard to believe that is more efficient than normal thermalling
at adding energy. And its the opposite of this theory. But the
horizontal version works spectacularly well for the RC dynamic soaring
guys (record is well over 400 mph!) although they do not use the
turnaround high g turns to gain energy and they also do not pull at the
gradient, but go directly for the airspeed increase on both sides of the
cycle.

I'm skeptical. There are plenty of good reasons to pull hard once in
awhile. But its a necessary evil used only when it really pays off to
put the glider exactly where you want it right now.

-Dave Leonard

Looking forward to the Parowan experiment next week. I'll be the control
case, cruising sedately along like grandma on her way to church on Sunday...

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 7, 6:51*pm, ZL wrote:
On 6/6/2010 7:39 AM, Gary Osoba wrote:





Yes. Your wing is a machine, and the work it performs imparts a
downward flow to the air it moves through. When that downward force is
aligned in a direction that opposes the movement of the air, it gains
energy. The air movement can be from the side, from above, or below-
the most efficient case since this vector opposes gravity. The
transfer of energy from air motion can be increased by manipulating
the inertial field of the glider, and there is an optimal g loading or
unloading for each case. Although physicists define such inertial
forces as "psuedo", the wing does not know this and must develop twice
the lift to sustain 2g flight as 1g flight, three times the lift for
3g flight,etc. The power transferred from the air to the wing
increases linearly with g force increases, while the the losses
associated with the increased g loadings are fractional and therefore
nonlinear, yielding excess power. This excess power can be carried by
the glider into a differential airmass with relative sink by a coupled
acceleration and a portion of it can be transferred to this airmass.
The case of 0g accelerations (freefall) is special in that
theoretically the wing doesn't produce induced drag. Theoretically
only, because the lift distribution will never be perfect- especially
in the unsteady flows which punctuate a soaring environment. In
practice, I have found 0g to be the best target for accelerations
since most of our wing sections are not designed to fly efficiently
upside down and everything is happening so quickly you lose less if
you guess wrong on the strength of the relative downdraft.

Much of this is counterintuitive. For example, here's something
presented in a 2001 lecture on the subject. It is stated as
exclusionary to emphasize how flight through a discontinuous
atmosphere can up-end long held conventions.

"For any body of mass moving through or in contact with a medium that
is not uniform, the most efficient path(s) for a given power input
will never be defined by a straight line or a constant speed." -
Osoba's Theorem of Dynamic Locomotion

The concise statement of this is "...never be defined by a constant
velocity..." since velocity incorporates both speed and direction but
most pilots don't understand the term that way.

Best Regards,

Gary Osoba

Can someone explain that first part? Is it really obvious? Seems
critical to the theory and I don't get it. Seems like when the wing
imparts a downward force on the air and displaces it, work is done on
the air. While the forces should be equal and opposite, the work is not.
In fact, energy is conserved. So the energy came out of the wing and
into the air. The wing doesn't know the air is moving relative to the
earth or anything else. And the air doesn't know its moving either. Its
wafting along at a nice steady pace (convenient inertial reference
frame) when the wing comes along and shoves it. The harder you push and
more air you displace, the more energy is transferred out of the wing
and into the air. Where does the energy into the wing come from?

Its not because the wing accelerates up due to the increased lift force.
The lift force generated by the wing is normal to its path through the
local air. Always. So that force curves the flight path. And by
definition, no work is done by a force normal to the displacement. But
the increased lift does increase the drag force, which works opposite
the direction of motion (negative work, which transfers energy to the
air). How does aggressive vertical maneuvering help?

Seems like dribbling a flat basketball. The bounce is kind of lossy.

But plenty of smart people see that it works, so I'm missing something?

I suppose dynamic soaring on the edge of a thermal might work. Looping
at the edge, diving in the core, pulling up vertical in the sink would
increase airspeed on each side of the cycle. But that requires pulling
in sink and pushing (pulling the top of the loop is more efficient) in
the lift. Hard to believe that is more efficient than normal thermalling
at adding energy. And its the opposite of this theory. But the
horizontal version works spectacularly well for the RC dynamic soaring
guys (record is well over 400 mph!) although they do not use the
turnaround high g turns to gain energy and they also do not pull at the
gradient, but go directly for the airspeed increase on both sides of the
cycle.

I'm skeptical. There are plenty of good reasons to pull hard once in
awhile. But its a necessary evil used only when it really pays off to
put the glider exactly where you want it right now.

-Dave Leonard

Looking forward to the Parowan experiment next week. I'll be the control
case, cruising sedately along like grandma on her way to church on Sunday....

If dynamic soaring works because of the additional energy gained from
transitioning between two inertial frames that have a horizontal
velocity gradient between them I can accept the possibility that this
may also be true for transitions through vertical velocity fields,
though the aerodynamics and physics are a bit beyond what I have the
time, skill or energy to do on my own. Here is the thought experiment
I ran through. You are flying at 100 knots in still when you run into
a 10 knot thermal. Since the glider can't instantaneously change
decent rate or pitch attitude due to it's inertia the first thing that
happens is you experience an increase in angle of attack of maybe 5
degrees. If I'm pulling enough G's when I hit the lift the change in
flow field will cause the wing to stall, or exceed the max G-load of
the airframe. If I pull max Gs as I decelerate AND transition to the
vertical air movement inside the thermal I can see how I gain
potential energy that is greater than a still air pullup alone but I
don't yet see why I'd gain more energy than for pullup plus the
vertical air movement while I'm pulling up.

That's where I get lost.

9B

9B

On Jun 8, 9:45*am, bildan wrote:
How about somebody writing an "inertial variometer" app for an i-Phone
4 since is has a built-in 6DOF IMU?

The thought (and a lot of other applications) crossed my mind while
watching the presentation.

I have no idea how much drift there is. Will have to experiment.

The accelerometer in all iPhones/iPod Touchs is good enough to give a
pretty accurate position still after integrating for 30 seconds or so
-- see the various car quarter mile timing apps out there, which match
up well against expensive purpose-built equipment.

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!

On Jun 7, 6:51*pm, ZL wrote:
On 6/6/2010 7:39 AM, Gary Osoba wrote:





Yes. Your wing is a machine, and the work it performs imparts a
downward flow to the air it moves through. When that downward force is
aligned in a direction that opposes the movement of the air, it gains
energy. The air movement can be from the side, from above, or below-
the most efficient case since this vector opposes gravity. The
transfer of energy from air motion can be increased by manipulating
the inertial field of the glider, and there is an optimal g loading or
unloading for each case. Although physicists define such inertial
forces as "psuedo", the wing does not know this and must develop twice
the lift to sustain 2g flight as 1g flight, three times the lift for
3g flight,etc. The power transferred from the air to the wing
increases linearly with g force increases, while the the losses
associated with the increased g loadings are fractional and therefore
nonlinear, yielding excess power. This excess power can be carried by
the glider into a differential airmass with relative sink by a coupled
acceleration and a portion of it can be transferred to this airmass.
The case of 0g accelerations (freefall) is special in that
theoretically the wing doesn't produce induced drag. Theoretically
only, because the lift distribution will never be perfect- especially
in the unsteady flows which punctuate a soaring environment. In
practice, I have found 0g to be the best target for accelerations
since most of our wing sections are not designed to fly efficiently
upside down and everything is happening so quickly you lose less if
you guess wrong on the strength of the relative downdraft.

Much of this is counterintuitive. For example, here's something
presented in a 2001 lecture on the subject. It is stated as
exclusionary to emphasize how flight through a discontinuous
atmosphere can up-end long held conventions.

"For any body of mass moving through or in contact with a medium that
is not uniform, the most efficient path(s) for a given power input
will never be defined by a straight line or a constant speed." -
Osoba's Theorem of Dynamic Locomotion

The concise statement of this is "...never be defined by a constant
velocity..." since velocity incorporates both speed and direction but
most pilots don't understand the term that way.

Best Regards,

Gary Osoba

Can someone explain that first part? Is it really obvious? Seems
critical to the theory and I don't get it. Seems like when the wing
imparts a downward force on the air and displaces it, work is done on
the air. While the forces should be equal and opposite, the work is not.
In fact, energy is conserved. So the energy came out of the wing and
into the air. The wing doesn't know the air is moving relative to the
earth or anything else. And the air doesn't know its moving either. Its
wafting along at a nice steady pace (convenient inertial reference
frame) when the wing comes along and shoves it. The harder you push and
more air you displace, the more energy is transferred out of the wing
and into the air. Where does the energy into the wing come from?

Its not because the wing accelerates up due to the increased lift force.
The lift force generated by the wing is normal to its path through the
local air. Always. So that force curves the flight path. And by
definition, no work is done by a force normal to the displacement. But
the increased lift does increase the drag force, which works opposite
the direction of motion (negative work, which transfers energy to the
air). How does aggressive vertical maneuvering help?

Seems like dribbling a flat basketball. The bounce is kind of lossy.

But plenty of smart people see that it works, so I'm missing something?

I suppose dynamic soaring on the edge of a thermal might work. Looping
at the edge, diving in the core, pulling up vertical in the sink would
increase airspeed on each side of the cycle. But that requires pulling
in sink and pushing (pulling the top of the loop is more efficient) in
the lift. Hard to believe that is more efficient than normal thermalling
at adding energy. And its the opposite of this theory. But the
horizontal version works spectacularly well for the RC dynamic soaring
guys (record is well over 400 mph!) although they do not use the
turnaround high g turns to gain energy and they also do not pull at the
gradient, but go directly for the airspeed increase on both sides of the
cycle.

I'm skeptical. There are plenty of good reasons to pull hard once in
awhile. But its a necessary evil used only when it really pays off to
put the glider exactly where you want it right now.

-Dave Leonard

Looking forward to the Parowan experiment next week. I'll be the control
case, cruising sedately along like grandma on her way to church on Sunday....

Hello Dave:

I haven't been very active on ras for several years now- could you or
other posters suggest a preferred way to share graphics by going to
some other site? I have some useful vector diagrams, math, and flight
testing results that could be shared easily. Also, if we had an ftp
site I could share some ppt files from lectures on the subject that
also have some useful info.

I see that you have been flying a 27 for awhile- I'll bet you're
enjoying that! What a wonderful design.

Best Regards,

Gary Osoba