I wish I'd never got into this...

I'd like a bash at this:

Can we get some assumptions out in the open first...

And before I get toasted, I am not being patronising, I just like to get
assumptions clear and out in the open.

1. throughout we stick to one glider type which is, e.g.
i) why? because it would be like comparing apples and oranges otherwise
ii) so, lets assume it is an asw23, or it is a pik20b, or ...
ii) consider two cases: ballasted (= greater mass) and unballasted
iii) otherwise, the configuration of the two gliders is identical except for
the amount of ballast they are carrying

2. potential energy = mass x gravitational acceleration x height, so
i) for a given height the ballasted glider has more potential energy than the
unballasted glider

3. kinetic energy = 1/2 x mass x speed x speed, so
ii) for a given speed the ballasted glider has more kinetic energy than the
unballasted glider

4. total energy = potential energy + kinetic energy
i) from the above we now know that, for a given height and speed, the
ballasted glider has a greater total energy than the unballasted glider

5. from the gliders polar and the basic arithmetic of ballasting we know that,
above a certain speed (i.e. the speed at which the sink rates of both the
ballasted and unballasted gliders are the same), the ballasted glider will be
travelling faster, for a given sink rate (= rate of energy loss), than the
unballasted glider, below that speed the unballasted glider will be losing
energy at a lower rate than the ballasted glider
i) this effect is due to the increase in the wing loading of the glider
ii) the same effect would apply (approximately, because the wing bending
would be somewhat different) to the unballasted glider in accelerated flight
(e.g. during a pull up)
iii) assuming the above, for a given speed the ballasted glider will be
sinking at a lower rate than the unballasted glider (e.g. the rate of energy
loss is lower) - don't believe me? look at the polar

6. provided we stay above that "certain speed" (which is determined by the
wing loading and so will be higher if the wing loading is higher)
i) for a given speed the ballasted glider will always be losing (potential)
energy at a lower rate than the unballasted glider
ii) this will be true regardless of whether the glider is in steady (i.e.
straight line) flight or in accelerated (e.g. turning or pulling up) flight
iii) in fact the difference in the rates of loss will be even greater in
accelerated flight

So far, so good (I hope). Now lets ignore the glide segment and just consider
the pull up and the subsequent zoom.

7. for two real gliders, of the same type, same configuration, one ballasted
more than the other, during the pull up
i) assuming the two gliders start at the same height and the same speed
ii) both gliders increase their wing loading in the same proportion to their
mass during the pull up
iii) I think that, given ii, they will follow the same pull up curve as a
result, but
iv) throughout the maneuvre, the ballasted glider will be losing energy at a
lower rate than the unballasted glider
v) so it should come out of the pull up higher and having lost less energy
than the unballasted glider (i.e. it will start the zoom faster than the
unballasted glider)

8. during the zoom (at zero g), if both gliders started at the same height and
speed
i) both will gain potential energy, and
ii) both will lose kinetic energy, but at a rate proportional to their masses
due to the effect of gravitational acceleration, and so
iii) the gliders would rise to the same height if they were in a vacuum
throughout, but
iv) they are not in a vacuum, they are gliding (probably at a reduced wing
loading), so
v) provided they are flying above that "certain speed", the ballasted glider
will be losing energy at a lower rate than the unballasted glider, and so it
will zoom higher

I admit this is a somewhat qualitative argument, so would someone like to put
figures on it?

Rgds,

Derrick.

Andy,

see my notes earlier in the thread. There's not much penalty for
pulling from high speed so long as you don't go to too quickly to high
AOA (bigger penalty in induced drag). 2g to 30 degrees nose up is
typical. The you ease off to 1g until you start push gently to
attitude at your desired exit speed.

Did your calculations include the losses to friction throughout the
manuever? Your altitude difference seems a little too low. I would
expect about a 20 to 30 foot difference for a pull from 100 knots to
60 knots, ie, a normal "test the strength of the core" pull up.

At any rate, if we get any decent weather, I'll be sure to make some
runs with a lighter glider and tender the real world results.

The original poster was looking for some real world feedback. Right
now all I can offer is that when ridge soaring, if I have water and
another 27/V2 is empty, I'll outpace him by at least 10 knots on a
hundred mile-per-hour day. Roughly 10 to 12 percent more speed at the
same sink rate/drag. A big spoonful of pure, sweet hubris.

Hey Chris,

I used the factory polar to estimate altitude loss
at redline with and without ballast. The difference
over 0.25 nm was 26' (105' - 79'). As you bleed off
airspeed the difference in sink rate declines, so the
actual difference in altitude loss should be less than
25' - maybe more like 15'.

This ignores G-related losses, which should be low
if the Gs are low (i.e. not too radical a pullup).
Of course too gradual a pullup and you don't get maximum
altitude gain because the parasite drag will accumulate.

9B





At 23:00 15 September 2003, Chris Ocallaghan wrote:
Andy,

see my notes earlier in the thread. There's not much
penalty for
pulling from high speed so long as you don't go to
too quickly to high
AOA (bigger penalty in induced drag). 2g to 30 degrees
nose up is
typical. The you ease off to 1g until you start push
gently to
attitude at your desired exit speed.

Did your calculations include the losses to friction
throughout the
manuever? Your altitude difference seems a little too
low. I would
expect about a 20 to 30 foot difference for a pull
from 100 knots to
60 knots, ie, a normal 'test the strength of the core'
pull up.

At any rate, if we get any decent weather, I'll be
sure to make some
runs with a lighter glider and tender the real world
results.

The original poster was looking for some real world
feedback. Right
now all I can offer is that when ridge soaring, if
I have water and
another 27/V2 is empty, I'll outpace him by at least
10 knots on a
hundred mile-per-hour day. Roughly 10 to 12 percent
more speed at the
same sink rate/drag. A big spoonful of pure, sweet
hubris.

I'm sorry Kate but maths beats 'Feminine Logic' every
time.

If two gliders start at the same height & speed & accelerate
to the same speed then they'll lose pretty much the
same height & follow the same trajectory.

And before anyone else brings up golf balls & ping-pong
balls may I remind people that your average sphere
is a much much draggier shape than your average sailplane,
and the ratio of masses is way way way greater than
the ratio for a glider with / without ballast

At 00:18 16 September 2003, Glider Kate wrote:
Boys

You seem to be forgeting one or two things!!!

If two identical sailplanes with identical weight pilots
but with sailplane a) carrying water ballast and b)
dry. Set off in still air, side by side at the same
speed, say 45 knots and accelerate at the same rate,
to a new identical speed, say 100knots.

By the time they reach the new speed, sailplane a)
will accelerate faster and travel further and lose
more height than glider b).

No need for maths just a bit of feminine logic

Bye...............

Kate

And you miss the point, if I am on a final glide I don't care what height I
started from, what I am interested in is how fast I can make the glide to
the goal. The height I can pull up to determines how low I dare go near the
goal bearing in mind that I want to pull to a safe height for my approach
and landing. The point is that the ballasted glider will not only get there
faster, it will also pull up higher = ballasted glider wins.

Rgds,

Derrick.

Well, at least we've got everyone on the same theme now. It's the
drag. Why don't you guys in Phoenix do a little testing and we'll do
the same here at M-ASA. I think we all agree that the heavier glider
has a significant drag advantage at high speed, and will gain
additional altitude. But how much, exactly?

It's worth noting that the heavier glider has more energy
stored kinetically and potentially. Whatever the difference
in height is, it's due to drag, and heavier glider needs to
give up less altitude for any given amount of energy
required to overcome drag.

Since Newton was hit by the apple, it is very unfortunate that everywhere on
this universe, any system trying to carry a load away from the center of the
planet will have to work harder than one travelling light. This is intuitive
enough. I wonder what is catching here. For any ten feet of height, the
heavy system will have to work more than the light system. True, our
ballasted glider has more money in the bank at the start, but it will have
to spend more on the way up. I hope that money comparaison will help. There
is no way around this fact. Travelling towards the center of the planet is
another ball game. The reason that for a given angle of glide, the heavy
will go faster is that the weight being larger, it's component parrallel to
the direction of travel is bigger. That simple. This is the motor. Drag is
"induced". it is not running the show.!!
Hope this help.
Bravo Quebec

inclined ramp. There are two things slowing them and
limiting the height they coast to, gravity and drag.
Gravity has the same effect on both. Drag is higher on the
heavy glider, but it has more kinetic energy, so the higher
drag has less proportional effect on the distance up that
ramp that the glider will travel.

Todd
Please admitt that the heavy has a bigger job to do. You just need more
energy to carry a heavy load up. Please stop denying that, or the buildings
around us will start to soar ;-))))
Bravo quebec

(Chris OCallaghan) wrote in message om...
Well, at least we've got everyone on the same theme now. It's the
drag. Why don't you guys in Phoenix do a little testing and we'll do
the same here at M-ASA. I think we all agree that the heavier glider
has a significant drag advantage at high speed, and will gain
additional altitude. But how much, exactly?


So far I have not seen anyone consider the fact that, at the same
(high) speed, the unballasted glider has a significantly higher sink
rate at the start of the pull up. The initial conditions are not the
same.


Andy (GY)

While Udo doesn't state the numerical value of the difference, I bet it's
only 30-40 ft.

That makes sense, considering the expected 3-400' delta h. So this would be
a tie, and quite satisfying, considering that everybody I know in the
soaring world, including H. Reichman ;-)), believes that the ballasted
glider would go noticebely higher. I never tested it, but along with anybody
that did a little maths, I could not force-fit the extra ballasted height
into the equations. The debate is still on, and we deeply wish that someone
could run a "scientific" test. This is fun!!!
Bravo Quebec