physics question about pull ups

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?

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.

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...

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".

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?

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.

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?

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

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.

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