physics question about pull ups [Archive]

April 20th 10, 08:56 PM

Interesting problem... Seems like you've defined the concept of
energy height. Energy is height is just how you have described
already...
E= mgh + 0.5mv^2
OR
E = wh + (w / 2g)v^2

The effect of drag on height recovery isn't too bad, but is enough to
matter. In general the shallower the climb and the bigger the speed
change the greater effect drag will have overall.
As an approximation, a glider initiating a 30deg climb from 120kts to
40kts would only take about 8sec (without drag decel, only gravity).
Assuming an average L/D of 24:1 over the entire maneuver the glider
would loose only about 5.6 feet of altitude per second due to drag. So
that means about 45 feet of altitude would be eroded due to drag. Of
course that's just an approximation. I'm sure there's a more correct
way...

The only way I could think to explain the extra height gain with a
heavier glider of the same model is the relationship of L/D vs speed.
For most gliders at a given speed their L/D will be higher with more
weight. Looking at polars you'll see, on average, the ballasted
glider will hold a better L/D at the same speed almost all the way
back to thermalling speed. The difference is small but is enough to
matter. On top of that the heavier glider at the same speed has more
energy height available due to its mass...
www.valleysoaring.net/pk/x-c/polar24c.jpg

One thing I wonder is whether a heavier glider initiating a 1.5g climb
would loose more energy through induced drag than a lighter glider,
assuming the same speed. Since a heaver glider would require more
force (lift) to induce a 1.5g climb then I'd think that would require
a greater angle of attack change thus more induced drag.

Chris Reed[_2_]

April 20th 10, 09:41 PM

wrote:
> The effect of drag on height recovery isn't too bad, but is enough to
> matter.

In a low-performance glider the drag can be extremely significant. In,
say, a K8 or (I'd guess) an I-26, the height gain is very small in
comparison with 40:1 glass.

A pilot flying at the UK Juniors a few years ago described a racing
finish in a K8, producing no more than a 200 ft climb from a 90kt
pull-up. He said that a K8 in this mode was the ultimate efficient
machine "for converting height into noise".

SoaringXCellence

April 20th 10, 11:51 PM

jim archer

April 21st 10, 12:05 AM

On Apr 20, 1:41*pm, Chris Reed > wrote:
> wrote:
> > The effect of drag on height recovery isn't too bad, but is enough to
> > matter. *
>
> In a low-performance glider the drag can be extremely significant. In,
> say, a K8 or (I'd guess) an I-26, the height gain is very small in
> comparison with 40:1 glass.
>
> A pilot flying at the UK Juniors a few years ago described a racing
> finish in a K8, producing no more than a 200 ft climb from a 90kt
> pull-up. He said that a K8 in this mode was the ultimate efficient
> machine "for converting height into noise".

back to the original question...

Maybe I'm missing something, but I think the approach to the problem
is flawed. How does mass "cancel out" if they are different masses?
Total energy is not the same in each case. All things being equal at
the pull up, speed, glider type, etc. a ballasted glider has more mass
and thus more kinetic energy which would result in a higher climbout
compared to a non ballasted glider. I'm not going to attempt to write
the equation because that would be embarrasing for me. But what am I
missing? Even if we start the gliders before the dive at the same
height the result is the same, the heavier glider has more potential
energy and will have a higher climb. Isn't this simple high school
phyics?

Tim Taylor

April 21st 10, 12:49 AM

On Apr 20, 5:05*pm, jim archer > wrote:
> On Apr 20, 1:41*pm, Chris Reed > wrote:
>
> > wrote:
> > > The effect of drag on height recovery isn't too bad, but is enough to
> > > matter. *
>
> > In a low-performance glider the drag can be extremely significant. In,
> > say, a K8 or (I'd guess) an I-26, the height gain is very small in
> > comparison with 40:1 glass.
>
> > A pilot flying at the UK Juniors a few years ago described a racing
> > finish in a K8, producing no more than a 200 ft climb from a 90kt
> > pull-up. He said that a K8 in this mode was the ultimate efficient
> > machine "for converting height into noise".
>
> back to the original question...
>
> Maybe I'm missing something, but I think the approach to the problem
> is flawed. * How does mass "cancel out" if they are different masses?
> Total energy is not the same in each case. *All things being equal at
> the pull up, speed, glider type, etc. a ballasted glider has more mass
> and thus more kinetic energy which would result in a higher climbout
> compared to a non ballasted glider. *I'm not going to attempt to write
> the equation because that would be embarrasing for me. * But what am I
> missing? *Even if we start the gliders before the dive at the same
> height the result is the same, the heavier glider has more potential
> energy and will have a higher climb. *Isn't this simple high school
> phyics?

Actually they are the same mass, that is why a heavier glider does not
go any higher (ignoring drag). A fast glider has more kinetic energy
and a heavier glider has more potential energy at the new altitude.

jim archer

April 21st 10, 02:04 AM

On Apr 20, 4:49*pm, Tim Taylor > wrote:
> On Apr 20, 5:05*pm, jim archer > wrote:
>
>
>
>
>
> > On Apr 20, 1:41*pm, Chris Reed > wrote:
>
> > > wrote:
> > > > The effect of drag on height recovery isn't too bad, but is enough to
> > > > matter. *
>
> > > In a low-performance glider the drag can be extremely significant. In,
> > > say, a K8 or (I'd guess) an I-26, the height gain is very small in
> > > comparison with 40:1 glass.
>
> > > A pilot flying at the UK Juniors a few years ago described a racing
> > > finish in a K8, producing no more than a 200 ft climb from a 90kt
> > > pull-up. He said that a K8 in this mode was the ultimate efficient
> > > machine "for converting height into noise".
>
> > back to the original question...
>
> > Maybe I'm missing something, but I think the approach to the problem
> > is flawed. * How does mass "cancel out" if they are different masses?
> > Total energy is not the same in each case. *All things being equal at
> > the pull up, speed, glider type, etc. a ballasted glider has more mass
> > and thus more kinetic energy which would result in a higher climbout
> > compared to a non ballasted glider. *I'm not going to attempt to write
> > the equation because that would be embarrasing for me. * But what am I
> > missing? *Even if we start the gliders before the dive at the same
> > height the result is the same, the heavier glider has more potential
> > energy and will have a higher climb. *Isn't this simple high school
> > phyics?
>
> Actually they are the same mass, that is why a heavier glider does not
> go any higher (ignoring drag). *A fast glider has more kinetic energy
> and a heavier glider has more potential energy at the new altitude.- Hide quoted text -
>
> - Show quoted text -

Are you saying a ballasted glider and an unballasted glider have the
same mass? Then how does a submarine work? I'm not arguing, I'm
genuinely curious...

Paul Remde

April 21st 10, 02:11 AM

Hi,

The K8 example is a good one for this discussion.

I would argue that if the K8 could fly at 150 knots, it could pull up just
as high as a Nimbus 4 that started at 150 knots. But I doubt K8's can fly
at 150 knots. Or, stated another way, any 2 gliders that start at the same
max speed (before the pull-up) and end at the same final (top of the
pull-up) speed will go to very similar heights.

Since the conservation of energy equations use velocity squared, the top
speed has a very large effect on the height gain that is attainable.

It is also true that there is much more drag on the K8 so it would lose a
bit more to friction during the pull up, but I suspect that is minor
difference.

Paul Remde

"Chris Reed" > wrote in message
news:hql3ih$9mv$1@qmul...
> wrote:
>> The effect of drag on height recovery isn't too bad, but is enough to
>> matter.
>
> In a low-performance glider the drag can be extremely significant. In,
> say, a K8 or (I'd guess) an I-26, the height gain is very small in
> comparison with 40:1 glass.
>
> A pilot flying at the UK Juniors a few years ago described a racing finish
> in a K8, producing no more than a 200 ft climb from a 90kt pull-up. He
> said that a K8 in this mode was the ultimate efficient machine "for
> converting height into noise".

Paul Remde

April 21st 10, 02:17 AM

Hi Jim,

It is simple high school physics. Yes the heavier glider has much more
energy, but it also takes much more energy to lift the heavier glider. You
would be much more tired after carrying 100 pounds up a flight of stairs
than you would be after lifting 10 pounds up a flight of stairs. The
physics shows very clearly that the extra speed energy from the higher
weight is exactly cancelled by the extra energy required to raise the
heavier weight.

before pullup after pullup
1/2 mv^2 + mgh = 1/2mv^2 + mgh

As you can see in the equation above you can divide both sides by m and the
equation doesn't change. So the mass of the glider doesn't matter, but the
speeds have a big effect because the velocity is squared.

Paul Remde

"jim archer" > wrote in message
...
On Apr 20, 1:41 pm, Chris Reed > wrote:
> wrote:
> > The effect of drag on height recovery isn't too bad, but is enough to
> > matter.
>
> In a low-performance glider the drag can be extremely significant. In,
> say, a K8 or (I'd guess) an I-26, the height gain is very small in
> comparison with 40:1 glass.
>
> A pilot flying at the UK Juniors a few years ago described a racing
> finish in a K8, producing no more than a 200 ft climb from a 90kt
> pull-up. He said that a K8 in this mode was the ultimate efficient
> machine "for converting height into noise".

back to the original question...

Maybe I'm missing something, but I think the approach to the problem
is flawed. How does mass "cancel out" if they are different masses?
Total energy is not the same in each case. All things being equal at
the pull up, speed, glider type, etc. a ballasted glider has more mass
and thus more kinetic energy which would result in a higher climbout
compared to a non ballasted glider. I'm not going to attempt to write
the equation because that would be embarrasing for me. But what am I
missing? Even if we start the gliders before the dive at the same
height the result is the same, the heavier glider has more potential
energy and will have a higher climb. Isn't this simple high school
phyics?

Bruce Hoult

April 21st 10, 02:28 AM

On Apr 21, 8:41*am, Chris Reed > wrote:
> A pilot flying at the UK Juniors a few years ago described a racing
> finish in a K8, producing no more than a 200 ft climb from a 90kt
> pull-up. He said that a K8 in this mode was the ultimate efficient
> machine "for converting height into noise".

Disregarding drag, the formula to convert speed in knots to the height
in feet with equivalent energy is speed squared, divided by 22.57. It
will take this much height, plus a bit more, to accelerate to that
speed, and on slowing down you will get that much height, less a bit.

For 90 knots this is 359 ft.
At, say, 50 knots, it is 111 feet.

So you'd expect only 248 ft gain even with no drag at all.

jim archer

April 21st 10, 02:35 AM

On Apr 20, 6:17*pm, "Paul Remde" > wrote:
> Hi Jim,
>
> It is simple high school physics. *Yes the heavier glider has much more
> energy, but it also takes much more energy to lift the heavier glider. *You
> would be much more tired after carrying 100 pounds up a flight of stairs
> than you would be after lifting 10 pounds up a flight of stairs. *The
> physics shows very clearly that the extra speed energy from the higher
> weight is exactly cancelled by the extra energy required to raise the
> heavier weight.
>
> before pullup * * * * * *after pullup
> 1/2 mv^2 + mgh *= 1/2mv^2 + mgh
>
> As you can see in the equation above you can divide both sides by m and the
> equation doesn't change. So the mass of the glider doesn't matter, but the
> speeds have a big effect because the velocity is squared.
>
> Paul Remde
>
> "jim archer" > wrote in message
>
> ...
> On Apr 20, 1:41 pm, Chris Reed > wrote:
>
> > wrote:
> > > The effect of drag on height recovery isn't too bad, but is enough to
> > > matter.
>
> > In a low-performance glider the drag can be extremely significant. In,
> > say, a K8 or (I'd guess) an I-26, the height gain is very small in
> > comparison with 40:1 glass.
>
> > A pilot flying at the UK Juniors a few years ago described a racing
> > finish in a K8, producing no more than a 200 ft climb from a 90kt
> > pull-up. He said that a K8 in this mode was the ultimate efficient
> > machine "for converting height into noise".
>
> back to the original question...
>
> Maybe I'm missing something, but I think the approach to the problem
> is flawed. * How does mass "cancel out" if they are different masses?
> Total energy is not the same in each case. *All things being equal at
> the pull up, speed, glider type, etc. a ballasted glider has more mass
> and thus more kinetic energy which would result in a higher climbout
> compared to a non ballasted glider. *I'm not going to attempt to write
> the equation because that would be embarrasing for me. * But what am I
> missing? *Even if we start the gliders before the dive at the same
> height the result is the same, the heavier glider has more potential
> energy and will have a higher climb. *Isn't this simple high school
> phyics?

I understand now what you mean, the mass is the same at the bottom and
top for each glider and therefore the climb is the same height if
velocity is the same. Interesting. Why does it feel like you climb
so much higher with ballast?

JJ Sinclair

April 21st 10, 02:03 PM

On Apr 20, 6:35*pm, jim archer > wrote:
> On Apr 20, 6:17*pm, "Paul Remde" > wrote:
>
>
>
>
>
> > Hi Jim,
>
> > It is simple high school physics. *Yes the heavier glider has much more
> > energy, but it also takes much more energy to lift the heavier glider. *You
> > would be much more tired after carrying 100 pounds up a flight of stairs
> > than you would be after lifting 10 pounds up a flight of stairs. *The
> > physics shows very clearly that the extra speed energy from the higher
> > weight is exactly cancelled by the extra energy required to raise the
> > heavier weight.
>
> > before pullup * * * * * *after pullup
> > 1/2 mv^2 + mgh *= 1/2mv^2 + mgh
>
> > As you can see in the equation above you can divide both sides by m and the
> > equation doesn't change. So the mass of the glider doesn't matter, but the
> > speeds have a big effect because the velocity is squared.
>
> > Paul Remde
>
> > "jim archer" > wrote in message
>
> ...
> > On Apr 20, 1:41 pm, Chris Reed > wrote:
>
> > > wrote:
> > > > The effect of drag on height recovery isn't too bad, but is enough to
> > > > matter.
>
> > > In a low-performance glider the drag can be extremely significant. In,
> > > say, a K8 or (I'd guess) an I-26, the height gain is very small in
> > > comparison with 40:1 glass.
>
> > > A pilot flying at the UK Juniors a few years ago described a racing
> > > finish in a K8, producing no more than a 200 ft climb from a 90kt
> > > pull-up. He said that a K8 in this mode was the ultimate efficient
> > > machine "for converting height into noise".
>
> > back to the original question...
>
> > Maybe I'm missing something, but I think the approach to the problem
> > is flawed. * How does mass "cancel out" if they are different masses?
> > Total energy is not the same in each case. *All things being equal at
> > the pull up, speed, glider type, etc. a ballasted glider has more mass
> > and thus more kinetic energy which would result in a higher climbout
> > compared to a non ballasted glider. *I'm not going to attempt to write
> > the equation because that would be embarrasing for me. * But what am I
> > missing? *Even if we start the gliders before the dive at the same
> > height the result is the same, the heavier glider has more potential
> > energy and will have a higher climb. *Isn't this simple high school
> > phyics?
>
> I understand now what you mean, the mass is the same at the bottom and
> top for each glider and therefore the climb is the same height if
> velocity is the same. *Interesting. *Why does it feel like you climb
> so much higher with ballast?- Hide quoted text -
>
> - Show quoted text -

Most of us would be dumping our water ballast as we climbed, does that
make the ship gain more altitude? This is an old argument and I have
always believed the heavier ship gains more altitude.
JJ

CoggFly

April 21st 10, 06:52 PM

I don't have time right now to run the numbers, but am interested and
will probably do that this evening... But looking at the Nimbus vs.
K8 examples, The sink rates need to be factored in. If they both
start 50 feet above the ground, and initiate the same degree pull up,
as the speed bleeds off they gain potential energy. If they start at
100 kts and the K8 sink rate at 100 kts is 900 fpm, and the nimbus is
600 fpm(not the actual numbers, just for an idea) then during that
time at 100 kts the nimbus loss is less than the K8. So, for that
moment when both are at 90 kts, if the K8 is losing 850 fpm and the
Nimbus 500 fpm, the K8 is still losing more. factor this in with the
theoretical no drag equations and you should be able to see the
difference. If from 100 kts they should reach 1000 ft, then you
subtract whatever you get from integrating the sink rates, the nimbus
might have lost 250 ft leaving it at 800 ft agl while the K8 might
lose 600 ft and ending its pull up at 450 ft. The polars need to be
integrated into the equation in order to get the actual differences.
The same would go for a given sailplane wet vs. dry. As the polar is
shifted to the right when wet, the sink rate changes. The wet
sialplane, through the speeds in the range of the pull up would be
losing less than the same sailplane dry over the same speed range.

Darryl Ramm

April 21st 10, 07:11 PM

On Apr 21, 6:03*am, JJ Sinclair > wrote:
> On Apr 20, 6:35*pm, jim archer > wrote:
>
>
>
> > On Apr 20, 6:17*pm, "Paul Remde" > wrote:
>
> > > Hi Jim,
>
> > > It is simple high school physics. *Yes the heavier glider has much more
> > > energy, but it also takes much more energy to lift the heavier glider.. *You
> > > would be much more tired after carrying 100 pounds up a flight of stairs
> > > than you would be after lifting 10 pounds up a flight of stairs. *The
> > > physics shows very clearly that the extra speed energy from the higher
> > > weight is exactly cancelled by the extra energy required to raise the
> > > heavier weight.
>
> > > before pullup * * * * * *after pullup
> > > 1/2 mv^2 + mgh *= 1/2mv^2 + mgh
>
> > > As you can see in the equation above you can divide both sides by m and the
> > > equation doesn't change. So the mass of the glider doesn't matter, but the
> > > speeds have a big effect because the velocity is squared.
>
> > > Paul Remde
>
> > > "jim archer" > wrote in message
>
> > ....
> > > On Apr 20, 1:41 pm, Chris Reed > wrote:
>
> > > > wrote:
> > > > > The effect of drag on height recovery isn't too bad, but is enough to
> > > > > matter.
>
> > > > In a low-performance glider the drag can be extremely significant. In,
> > > > say, a K8 or (I'd guess) an I-26, the height gain is very small in
> > > > comparison with 40:1 glass.
>
> > > > A pilot flying at the UK Juniors a few years ago described a racing
> > > > finish in a K8, producing no more than a 200 ft climb from a 90kt
> > > > pull-up. He said that a K8 in this mode was the ultimate efficient
> > > > machine "for converting height into noise".
>
> > > back to the original question...
>
> > > Maybe I'm missing something, but I think the approach to the problem
> > > is flawed. * How does mass "cancel out" if they are different masses?
> > > Total energy is not the same in each case. *All things being equal at
> > > the pull up, speed, glider type, etc. a ballasted glider has more mass
> > > and thus more kinetic energy which would result in a higher climbout
> > > compared to a non ballasted glider. *I'm not going to attempt to write
> > > the equation because that would be embarrasing for me. * But what am I
> > > missing? *Even if we start the gliders before the dive at the same
> > > height the result is the same, the heavier glider has more potential
> > > energy and will have a higher climb. *Isn't this simple high school
> > > phyics?
>
> > I understand now what you mean, the mass is the same at the bottom and
> > top for each glider and therefore the climb is the same height if
> > velocity is the same. *Interesting. *Why does it feel like you climb
> > so much higher with ballast?- Hide quoted text -
>
> > - Show quoted text -
>
> Most of us would be dumping our water ballast as we climbed, does that
> make the ship gain more altitude? This is an old argument and I have
> always believed the heavier ship gains more altitude.
> JJ

Nope dumping the water loses you energy proportional to the mass of
the water, that energy no longer lifts that weight of water higher. In
the simple potential/kinetic energy model there is no effect.

AS stated by others I expect the perceived benefit of extra weight is
due to you more likely to be flying faster if ballasted and therefore
get a higher zoom climb.

Darryl

[email protected]

April 22nd 10, 01:47 AM

On Apr 21, 11:11*am, Darryl Ramm > wrote:
> On Apr 21, 6:03*am, JJ Sinclair > wrote:
>
>
>
> > On Apr 20, 6:35*pm, jim archer > wrote:
>
> > > On Apr 20, 6:17*pm, "Paul Remde" > wrote:
>
> > > > Hi Jim,
>
> > > > It is simple high school physics. *Yes the heavier glider has much more
> > > > energy, but it also takes much more energy to lift the heavier glider. *You
> > > > would be much more tired after carrying 100 pounds up a flight of stairs
> > > > than you would be after lifting 10 pounds up a flight of stairs. *The
> > > > physics shows very clearly that the extra speed energy from the higher
> > > > weight is exactly cancelled by the extra energy required to raise the
> > > > heavier weight.
>
> > > > before pullup * * * * * *after pullup
> > > > 1/2 mv^2 + mgh *= 1/2mv^2 + mgh
>
> > > > As you can see in the equation above you can divide both sides by m and the
> > > > equation doesn't change. So the mass of the glider doesn't matter, but the
> > > > speeds have a big effect because the velocity is squared.
>
> > > > Paul Remde
>
> > > > "jim archer" > wrote in message
>
> > > ...
> > > > On Apr 20, 1:41 pm, Chris Reed > wrote:
>
> > > > > wrote:
> > > > > > The effect of drag on height recovery isn't too bad, but is enough to
> > > > > > matter.
>
> > > > > In a low-performance glider the drag can be extremely significant.. In,
> > > > > say, a K8 or (I'd guess) an I-26, the height gain is very small in
> > > > > comparison with 40:1 glass.
>
> > > > > A pilot flying at the UK Juniors a few years ago described a racing
> > > > > finish in a K8, producing no more than a 200 ft climb from a 90kt
> > > > > pull-up. He said that a K8 in this mode was the ultimate efficient
> > > > > machine "for converting height into noise".
>
> > > > back to the original question...
>
> > > > Maybe I'm missing something, but I think the approach to the problem
> > > > is flawed. * How does mass "cancel out" if they are different masses?
> > > > Total energy is not the same in each case. *All things being equal at
> > > > the pull up, speed, glider type, etc. a ballasted glider has more mass
> > > > and thus more kinetic energy which would result in a higher climbout
> > > > compared to a non ballasted glider. *I'm not going to attempt to write
> > > > the equation because that would be embarrasing for me. * But what am I
> > > > missing? *Even if we start the gliders before the dive at the same
> > > > height the result is the same, the heavier glider has more potential
> > > > energy and will have a higher climb. *Isn't this simple high school
> > > > phyics?
>
> > > I understand now what you mean, the mass is the same at the bottom and
> > > top for each glider and therefore the climb is the same height if
> > > velocity is the same. *Interesting. *Why does it feel like you climb
> > > so much higher with ballast?- Hide quoted text -
>
> > > - Show quoted text -
>
> > Most of us would be dumping our water ballast as we climbed, does that
> > make the ship gain more altitude? This is an old argument and I have
> > always believed the heavier ship gains more altitude.
> > JJ
>
> Nope dumping the water loses you energy proportional to the mass of
> the water, that energy no longer lifts that weight of water higher. In
> the simple potential/kinetic energy model there is no effect.
>
> AS stated by others I expect the perceived benefit of extra weight is
> due to you more likely to be flying faster if ballasted and therefore
> get a higher zoom climb.
>
> Darryl

Just fly the damn thing...

Best explanation I ever heard was the heavier roller coaster car goes
further up the next hill than the lighter one.

Al

Brian Whatcott

April 22nd 10, 06:25 PM

wrote:
> On Apr 21, 11:11 am, Darryl Ramm > wrote:
>> On Apr 21, 6:03 am, JJ Sinclair > wrote:
>>
>>
>>
>>> On Apr 20, 6:35 pm, jim archer > wrote:
>>>> On Apr 20, 6:17 pm, "Paul Remde" > wrote:
>>>>> Hi Jim,
>>>>> It is simple high school physics. Yes the heavier glider has much more
>>>>> energy, but it also takes much more energy to lift the heavier glider. You
>>>>> would be much more tired after carrying 100 pounds up a flight of stairs
>>>>> than you would be after lifting 10 pounds up a flight of stairs. The
>>>>> physics shows very clearly that the extra speed energy from the higher
>>>>> weight is exactly cancelled by the extra energy required to raise the
>>>>> heavier weight.
>>>>> before pullup after pullup
>>>>> 1/2 mv^2 + mgh = 1/2mv^2 + mgh
>>>>> As you can see in the equation above you can divide both sides by m and the
>>>>> equation doesn't change. So the mass of the glider doesn't matter, but the
>>>>> speeds have a big effect because the velocity is squared.
>>>>> Paul Remde
>>>>> "jim archer" > wrote in message
>>>>> ...
>>>>> On Apr 20, 1:41 pm, Chris Reed > wrote:
>>>>>> wrote:
>>>>>>> The effect of drag on height recovery isn't too bad, but is enough to
>>>>>>> matter.
>>>>>> In a low-performance glider the drag can be extremely significant. In,
>>>>>> say, a K8 or (I'd guess) an I-26, the height gain is very small in
>>>>>> comparison with 40:1 glass.
>>>>>> A pilot flying at the UK Juniors a few years ago described a racing
>>>>>> finish in a K8, producing no more than a 200 ft climb from a 90kt
>>>>>> pull-up. He said that a K8 in this mode was the ultimate efficient
>>>>>> machine "for converting height into noise".
>>>>> back to the original question...
>>>>> Maybe I'm missing something, but I think the approach to the problem
>>>>> is flawed. How does mass "cancel out" if they are different masses?
>>>>> Total energy is not the same in each case. All things being equal at
>>>>> the pull up, speed, glider type, etc. a ballasted glider has more mass
>>>>> and thus more kinetic energy which would result in a higher climbout
>>>>> compared to a non ballasted glider. I'm not going to attempt to write
>>>>> the equation because that would be embarrasing for me. But what am I
>>>>> missing? Even if we start the gliders before the dive at the same
>>>>> height the result is the same, the heavier glider has more potential
>>>>> energy and will have a higher climb. Isn't this simple high school
>>>>> phyics?
>>>> I understand now what you mean, the mass is the same at the bottom and
>>>> top for each glider and therefore the climb is the same height if
>>>> velocity is the same. Interesting. Why does it feel like you climb
>>>> so much higher with ballast?- Hide quoted text -
>>>> - Show quoted text -
>>> Most of us would be dumping our water ballast as we climbed, does that
>>> make the ship gain more altitude? This is an old argument and I have
>>> always believed the heavier ship gains more altitude.
>>> JJ
>> Nope dumping the water loses you energy proportional to the mass of
>> the water, that energy no longer lifts that weight of water higher. In
>> the simple potential/kinetic energy model there is no effect.
>>
>> AS stated by others I expect the perceived benefit of extra weight is
>> due to you more likely to be flying faster if ballasted and therefore
>> get a higher zoom climb.
>>
>> Darryl
>
> Just fly the damn thing...
>
> Best explanation I ever heard was the heavier roller coaster car goes
> further up the next hill than the lighter one.
>
> Al
>
>
Which reminds me....the Boy Scouts' soap box derby needs cars on the TOP
weight limit (and with weight preferably as far back as possible to
maximize potential energy...)

Brian W

Mark Jardini

April 22nd 10, 09:54 PM

Dumping water will give you a little F=ma acceleration upwards. Like a
very anemic rocket.

The heavier roller coaster goes higher by overcoming drag forces
better, ie friction is a smaller % of total force in play.

On a frictionless track, in a vaccum, a feather and a brick accelerate
the same.

Andy[_1_]

April 23rd 10, 04:58 PM

On Apr 22, 1:54*pm, Mark Jardini > wrote:
> Dumping water will give you a little F=ma acceleration upwards. Like a
> very anemic rocket.

Seems unlikely. If I pour water out of a jug, the jug is not forced
upwards.

The force in a rocket comes from the fact that the exhaust gas is
being pushed out of the nozzle, not just from the fact it is pouring
out of the nozzle. Thre is no internal force or presure ejecting the
water from a glider and, if there was, the vector would be about 90
deg to the direction required for useful thrust.

Andy

Brian Whatcott

April 23rd 10, 05:56 PM

Andy wrote:
> On Apr 22, 1:54 pm, Mark Jardini > wrote:
>> Dumping water will give you a little F=ma acceleration upwards. Like a
>> very anemic rocket.
>
> Seems unlikely. If I pour water out of a jug, the jug is not forced
> upwards.
>
> The force in a rocket comes from the fact that the exhaust gas is
> being pushed out of the nozzle, not just from the fact it is pouring
> out of the nozzle. Thre is no internal force or presure ejecting the
> water from a glider and, if there was, the vector would be about 90
> deg to the direction required for useful thrust.
>
> Andy

Though I'm with you on the explanation, you open an interesting line of
speculation.
It has stayed with me that a nozzle into an evacuated bottle can develop
a sonic efflux.
It has stayed with me that your average throw-away crinkly plastic soda
bottle can handle 50 psi on up.

It's also true that the bigger the bottle the lower the limit pressure.
But here's the thought: a low pressure pump into the water tank with an
efficient nozzle and you might have somewhat usable temporary thrust.....

Brian W

brianDG303[_2_]

April 23rd 10, 06:10 PM

On Apr 23, 9:56*am, brian whatcott > wrote:
> Andy wrote:
> > On Apr 22, 1:54 pm, Mark Jardini > wrote:
> >> Dumping water will give you a little F=ma acceleration upwards. Like a
> >> very anemic rocket.
>
> > Seems unlikely. *If I pour water out of a jug, the jug is not forced
> > upwards.
>
> > The force in a rocket comes from the fact that the exhaust gas is
> > being pushed out of the nozzle, not just from the fact it is pouring
> > out of the nozzle. *Thre is no internal force or presure *ejecting the
> > water from a glider and, if there was, the *vector would be about 90
> > deg to the direction required for useful thrust.
>
> > Andy
>
> Though I'm with you on the explanation, you open an interesting line of
> speculation.
> It has stayed with me that a nozzle into an evacuated bottle can develop
> a sonic efflux.
> It has stayed with me that your average throw-away crinkly plastic soda
> bottle can handle 50 psi on up.
>
> It's also true that the bigger the bottle the lower the limit pressure.
> But here's the thought: a low pressure pump into the water tank with an
> efficient nozzle and you might have somewhat usable temporary thrust.....
>
> Brian W

I think I see where we are going with this. Replace the water with
diet coke and add a mentos injection system. (youtube/diet coke
mentos). A low save system that works every time.

Brian Whatcott

April 23rd 10, 06:11 PM

brianDG303 wrote:
> On Apr 23, 9:56 am, brian whatcott > wrote:
>> Andy wrote:
>>> On Apr 22, 1:54 pm, Mark Jardini > wrote:
>>>> Dumping water will give you a little F=ma acceleration upwards. Like a
>>>> very anemic rocket.
>>> Seems unlikely. If I pour water out of a jug, the jug is not forced
>>> upwards.
>>> The force in a rocket comes from the fact that the exhaust gas is
>>> being pushed out of the nozzle, not just from the fact it is pouring
>>> out of the nozzle. Thre is no internal force or presure ejecting the
>>> water from a glider and, if there was, the vector would be about 90
>>> deg to the direction required for useful thrust.
>>> Andy
>> Though I'm with you on the explanation, you open an interesting line of
>> speculation.
>> It has stayed with me that a nozzle into an evacuated bottle can develop
>> a sonic efflux.
>> It has stayed with me that your average throw-away crinkly plastic soda
>> bottle can handle 50 psi on up.
>>
>> It's also true that the bigger the bottle the lower the limit pressure.
>> But here's the thought: a low pressure pump into the water tank with an
>> efficient nozzle and you might have somewhat usable temporary thrust.....
>>
>> Brian W
>
> I think I see where we are going with this. Replace the water with
> diet coke and add a mentos injection system. (youtube/diet coke
> mentos). A low save system that works every time.

Durn it! You were WAY ahead of me! :-)

Brian W

Andy[_10_]

April 24th 10, 05:27 PM

On Apr 20, 4:24*am, "Paul Remde" > wrote:
> Hi John,
>
> You are correct. *The physics equations show that you will get the same
> height regardless of the weight of the glider.
>
> However, I think it is true that a heavier glider will have a slightly
> higher pull-up. *I don't think the difference is very much though. *Both
> gliders will have similar frictional losses and losses due to inefficiencies
> during the pull-up.
>
> Paul Remde
>
> "John Rivers" > wrote in message
>
> ...
>
>
>
> >I was trying to work out the expected height gain from a pull up
> > Experienced glider pilots say you will get a better pull up with a
> > heavier glider / water etc.
> > But I can't see this from my (probably incomplete) equations:
>
> > total energy = potential energy + kinetic energy
>
> > total energy before pull up = total energy after pull up
>
> > m * g * h0 + m * pow(v0, 2) * 0.5 == m * g * h1 + m * pow(v1, 2) * 0.5
>
> > with h0 v0 being height and speed before pull up
> > and h1 v1 being height and speed after pull up
>
> > mass cancels out of this equation
>
> > I think I need to include momentum in there somehow?

The kinetic to potential energy balance yields no difference as has
been pointed out. There are small drag differences that give some
advantage to a heavier glider since it has a higher L/D at any given
speed. Back of the envelope polar math says the difference in sink
rate at 150 knots with full ballast versus dry is about 100 feet per
mile (for a modern glider). At 100 knots it's about 50 feet per mile.
I'd estimate a typical pullup consumes about a quarter mile. Without
taking the time to integrate the declining sink rate difference over
the entire pullup, I'd guess the overall difference in altitude gain
would be around 20 feet. This ignores any differences in secondary
energy losses associated with pulling G's to make the pullup happen.
My intuition tells me that this would favor the lighter glider
slightly because it takes more energy to change the vector of a
heavier sailplane - how much I don't know except to say that the
harder the pullup the greater the drag losses.

All in all it's a barely measurable difference. I suspect the reason
people feel like they get a bigger pullup full of water is that they
are generally carrying more speed at the beginning of the pullup when
they are full of water.

9B

Bruce Hoult

April 25th 10, 08:57 AM

On Apr 25, 4:27*am, Andy > wrote:
> The kinetic to potential energy balance yields no difference as has
> been pointed out. There are small drag differences that give some
> advantage to a heavier glider since it has a higher L/D at any given
> speed. *Back of the envelope polar math says the difference in sink
> rate at 150 knots with full ballast versus dry is about 100 feet per
> mile (for a modern glider). At 100 knots it's about 50 feet per mile.
> I'd estimate a typical pullup consumes about a quarter mile. Without
> taking the time to integrate the declining sink rate difference over
> the entire pullup, I'd guess the overall difference in altitude gain
> would be around 20 feet.

I agree.

> This ignores any differences in secondary
> energy losses associated with pulling G's to make the pullup happen.
> My intuition tells me that this would favor the lighter glider
> slightly because it takes more energy to change the vector of a
> heavier sailplane - how much I don't know except to say that the
> harder the pullup the greater the drag losses.

No, for sure not if the heavier glider doesn't pull so hard that it
goes above the angle of attack for max L/D.

Supposing that the speed for best L/D full of ballast (in level
flight) is 75 knots, at 150 knots you'll have to pull (150/75)^2 = 4
Gs before you get to the max L/D angle of attack. (and the
unballasted guy with a best L/D at 60 knots would have to pull 6.25
Gs)

If both gliders pull the same number of Gs at 150 knots then the
ballasted one will lose a lower percentage of its energy unless they
both pull over 4 Gs.

They are probably equally efficient at around 5 Gs. And the lighter
glider is for sure more efficient at 6.25 Gs -- the ballasted guy is
getting close to stalling by that point.

> All in all it's a barely measurable difference. I suspect the reason
> people feel like they get a bigger pullup full of water is that they
> are generally carrying more speed at the beginning of the pullup when
> they are full of water.

Yes, probably, and the smaller loses while cruising along the runway.

Richard[_9_]

April 25th 10, 03:10 PM

On Apr 25, 12:57*am, Bruce Hoult > wrote:
> On Apr 25, 4:27*am, Andy > wrote:
>
> > The kinetic to potential energy balance yields no difference as has
> > been pointed out. There are small drag differences that give some
> > advantage to a heavier glider since it has a higher L/D at any given
> > speed. *Back of the envelope polar math says the difference in sink
> > rate at 150 knots with full ballast versus dry is about 100 feet per
> > mile (for a modern glider). At 100 knots it's about 50 feet per mile.
> > I'd estimate a typical pullup consumes about a quarter mile. Without
> > taking the time to integrate the declining sink rate difference over
> > the entire pullup, I'd guess the overall difference in altitude gain
> > would be around 20 feet.
>
> I agree.
>
> > This ignores any differences in secondary
> > energy losses associated with pulling G's to make the pullup happen.
> > My intuition tells me that this would favor the lighter glider
> > slightly because it takes more energy to change the vector of a
> > heavier sailplane - how much I don't know except to say that the
> > harder the pullup the greater the drag losses.
>
> No, for sure not if the heavier glider doesn't pull so hard that it
> goes above the angle of attack for max L/D.
>
> Supposing that the speed for best L/D full of ballast (in level
> flight) is 75 knots, at 150 knots you'll have to pull (150/75)^2 = 4
> Gs before you get to the max L/D angle of attack. *(and the
> unballasted guy with a best L/D at 60 knots would have to pull 6.25
> Gs)
>
> If both gliders pull the same number of Gs at 150 knots then the
> ballasted one will lose a lower percentage of its energy unless they
> both pull over 4 Gs.
>
> They are probably equally efficient at around 5 Gs. And the lighter
> glider is for sure more efficient at 6.25 Gs -- the ballasted guy is
> getting close to stalling by that point.
>
> > All in all it's a barely measurable difference. I suspect the reason
> > people feel like they get a bigger pullup full of water is that they
> > are generally carrying more speed at the beginning of the pullup when
> > they are full of water.
>
> Yes, probably, and the smaller loses while cruising along the runway.

More calculation opportunities for the phyisics groupies.

Which glider gets you to the same altitude faster assuming the same
speed. Ballasted or non ballasted?

Andy[_10_]

April 25th 10, 04:21 PM

On Apr 25, 12:57*am, Bruce Hoult > wrote:
>
>
> > On Apr 25, 4:27*am, Andy > wrote:
>
> > > The kinetic to potential energy balance yields no difference as has
> > > been pointed out. There are small drag differences that give some
> > > advantage to a heavier glider since it has a higher L/D at any given
> > > speed. *Back of the envelope polar math says the difference in sink
> > > rate at 150 knots with full ballast versus dry is about 100 feet per
> > > mile (for a modern glider). At 100 knots it's about 50 feet per mile.
> > > I'd estimate a typical pullup consumes about a quarter mile. Without
> > > taking the time to integrate the declining sink rate difference over
> > > the entire pullup, I'd guess the overall difference in altitude gain
> > > would be around 20 feet.
>
> > I agree.
>
> > > This ignores any differences in secondary
> > > energy losses associated with pulling G's to make the pullup happen.
> > > My intuition tells me that this would favor the lighter glider
> > > slightly because it takes more energy to change the vector of a
> > > heavier sailplane - how much I don't know except to say that the
> > > harder the pullup the greater the drag losses.
>
> > No, for sure not if the heavier glider doesn't pull so hard that it
> > goes above the angle of attack for max L/D.
>
> > Supposing that the speed for best L/D full of ballast (in level
> > flight) is 75 knots, at 150 knots you'll have to pull (150/75)^2 = 4
> > Gs before you get to the max L/D angle of attack. *(and the
> > unballasted guy with a best L/D at 60 knots would have to pull 6.25
> > Gs)
>
> > If both gliders pull the same number of Gs at 150 knots then the
> > ballasted one will lose a lower percentage of its energy unless they
> > both pull over 4 Gs.
>
> > They are probably equally efficient at around 5 Gs. And the lighter
> > glider is for sure more efficient at 6.25 Gs -- the ballasted guy is
> > getting close to stalling by that point.
>
> > > All in all it's a barely measurable difference. I suspect the reason
> > > people feel like they get a bigger pullup full of water is that they
> > > are generally carrying more speed at the beginning of the pullup when
> > > they are full of water.
>
> > Yes, probably, and the smaller loses while cruising along the runway.

I'm not totally sure about this but here's my logic (been a while
since engineering school). If you assume the ballasted and unballasted
gliders fly the same profile then they need to pull the same number of
Gs to execute the pullup. We've already accounted for the steady-
flight L/D effects in the initial calculation so all we need here is
how much energy is lost in pulling the same number of Gs to initiate
the climb. It's the same glider except for the ballast so the form
drag is the same which means we only have to account for the
difference in induced drag. The formula for that is:

D=(kL^2) / (.5pV^2S(pi)AR)

At the start of the pullup all these variables are the same except for
L which equals the weight of the glider times the G's being pulled. If
the heavier glider is 1.5 times as heavy the induced drag is 9 times
as great at 2 Gs. Keep in mind that at redline the induced drag term
overall is small because the speed is high, but still the advantage
should go to the lighter glider for the G-losses part. If you
calculate the L/D in accelerated flight you still end up with a weight
times Gs term in the denominator. I haven't done the math fully
through with real numbers, but that's how the formula looks to me.

Bruce's comment generated one additional thought. The energy balance
calculation we all did assumes the ballasted and unballasted gliders
both start at the same speed (redline) and end up at the same speed.
However, the ballasted glider has a higher stall speed, min sink speed
and best L/D speed - in my case by around 10 knots. If both gliders
pull up to their respective best L/D speeds the unballasted glider
gets about 65 feet higher due to being able to turn that last 10 knots
into altitude. Of course if both gliders went ballistic and did a
hammerhead stall at the top you wouldn't get this difference - but I'm
assuming typically you'd pull up to the same margin above stall speed,
which translates to a slower speed for the lighter glider.

So, by my new calculation the unballasted glider has a slight
advantage. It loses 20 feet to the ballasted glider due to L/D
effects, but gains 65 feet by being able to top out at a lower speed
and gains an unspecified amount (probably small) from G effects on
induced drag at the start of the pullup.

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

9B

John Rivers

May 6th 10, 02:27 PM

I was considering two identical gliders - one with water ballast - one
without
both flying at the same speed - and both pulling up to the same speed

The only relevant differences I can see are:

- ratio of drag to mass
- slightly different attitude

I believe gliders that take water are optimised for ballast
(so that they have the minimum profile drag for the required angle of
attack at best glide)

Larry Goddard

May 6th 10, 02:41 PM

Of course, if they are flying the same speed, then they are at different
places on their respective polars to begin with.

Larry

"John Rivers" > wrote in message
:

> I was considering two identical gliders - one with water ballast - one
> without
> both flying at the same speed - and both pulling up to the same speed
>
> The only relevant differences I can see are:
>
> - ratio of drag to mass
> - slightly different attitude
>
> I believe gliders that take water are optimised for ballast
> (so that they have the minimum profile drag for the required angle of
> attack at best glide)

Gary Osoba[_3_]

June 5th 10, 10:30 PM

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

Nine Bravo Ground

June 5th 10, 10:41 PM

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

John Cochrane

June 5th 10, 11:00 PM

>
> 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

Gary Osoba[_3_]

June 5th 10, 11:07 PM

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

Gary Osoba[_3_]

June 5th 10, 11:08 PM

On Jun 5, 3:00*pm, John Cochrane >
wrote:

> 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

Hi John:

Precisely what Taras Keceniuck, Paul MacCready and I were doing in a
DARPA funded study when Paul passed away.

Best Regards,
Gary Osoba

John Cochrane

June 5th 10, 11:33 PM

>
> Hi John:
>
> Precisely what Taras Keceniuck, Paul MacCready and I were doing in a
> DARPA funded study when Paul passed away.
>
> Best Regards,
> Gary Osoba

Is the study finished and any publication done? I want the pitch
controller for the worlds!
John Cochrane

Gary Osoba[_3_]

June 5th 10, 11:45 PM

On Jun 5, 3:33*pm, John Cochrane >
wrote:
> > Hi John:
>
> > Precisely what Taras Keceniuck, Paul MacCready and I were doing in a
> > DARPA funded study when Paul passed away.
>
> > Best Regards,
> > Gary Osoba
>
> Is the study finished and any publication done? I want the pitch
> controller for the worlds!
> John Cochrane

Let's go private, John.

-Gary

Jim Logajan

June 6th 10, 12:08 AM

John Cochrane > wrote:
> 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.

I _think_ I get what you are saying: you basically propose extracting the
kinetic energy that is available due to the different fluid speeds. It
doesn't matter which direction the fluid streams flow - merely that one
part of the fluid is moving relative to another part and you can move your
aircraft from one to the other.

We're so used to getting energy out of upward fluid flows that we overlook
the fact that in a fundamental sense it doesn't matter (to a first
approximation) which direction the stream is going.

So what you all seem to be saying is that there is energy available for
extraction in wind shear, sinks, and thermals. If the whole mass of fluid
is moving then you are out of luck because you need a difference in fluid
speeds - with the exception that upward flows always make energy available
due to conversion of the fluid kinetic energy to gravitational potential
energy. (Hence the "first approximation" caveat.)

Is all that about right?

Bruce Hoult

June 6th 10, 03:54 AM

On Jun 6, 10:33*am, John Cochrane >
wrote:
> > Hi John:
>
> > Precisely what Taras Keceniuck, Paul MacCready and I were doing in a
> > DARPA funded study when Paul passed away.
>
> > Best Regards,
> > Gary Osoba
>
> Is the study finished and any publication done? I want the pitch
> controller for the worlds!

Hmm. Come to think of it, I don't recall seeing anything in the rules
that prevent use of an autopilot.

Do you even have to have a human on board?

Brian Whatcott

June 6th 10, 04:15 AM

John Cochrane wrote:
>> Hi John:
>>
>> Precisely what Taras Keceniuck, Paul MacCready and I were doing in a
>> DARPA funded study when Paul passed away.
>>
>> Best Regards,
>> Gary Osoba
>
> Is the study finished and any publication done? I want the pitch
> controller for the worlds!
> John Cochrane

Hmmm..I see the ArduIMU runs about $300. That might make a suitable
start on it?

Brian W

Gary Osoba[_3_]

June 6th 10, 02:39 PM

On Jun 5, 4:08*pm, Jim Logajan > wrote:
> John Cochrane > wrote:
> > 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.
>
> I _think_ I get what you are saying: you basically propose extracting the
> kinetic energy that is available due to the different fluid speeds. It
> doesn't matter which direction the fluid streams flow - merely that one
> part of the fluid is moving relative to another part and you can move your
> aircraft from one to the other.
>
> We're so used to getting energy out of upward fluid flows that we overlook
> the fact that in a fundamental sense it doesn't matter (to a first
> approximation) which direction the stream is going.
>
> So what you all seem to be saying is that there is energy available for
> extraction in wind shear, sinks, and thermals. If the whole mass of fluid
> is moving then you are out of luck because you need a difference in fluid
> speeds - with the exception that upward flows always make energy available
> due to conversion of the fluid kinetic energy to gravitational potential
> energy. (Hence the "first approximation" caveat.)
>
> Is all that about right?

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

Brian Whatcott

June 6th 10, 05:34 PM

Gary Osoba wrote:
/snip/
> "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
/snip/
> Gary Osoba
>

Darn! I was following along nicely with this note, until I got to the
conjunction of a heading which included the word "physics"
and a person citing his own name for a physics construct.

That's usually a warning about the level of information....

:-)

Brian W

Andy[_10_]

June 6th 10, 06:06 PM

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

Gary Osoba[_3_]

June 6th 10, 06:42 PM

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

John Cochrane

June 6th 10, 09:14 PM

> 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

Bruce Hoult

June 7th 10, 03:29 AM

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.

Andy[_10_]

June 7th 10, 07:47 AM

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

June 7th 10, 02:35 PM

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

Andy[_10_]

June 7th 10, 08:54 PM

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.

bildan

June 7th 10, 10:45 PM

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?

June 8th 10, 02:51 AM

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...

Eric Greenwell

June 8th 10, 03:20 AM

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)

Andy[_10_]

June 8th 10, 07:20 AM

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

Andy[_10_]

June 8th 10, 09:42 AM

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

Bruce Hoult

June 8th 10, 10:18 AM

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.

Bruce Hoult

June 8th 10, 10:37 AM

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!

Gary Osoba[_3_]

June 10th 10, 12:21 PM

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