Question of the Day

Since mass is a constant factor on both sides of the equation, it cancels out. Therefore there should theoretically be negligible difference in the pullup altitude gained between the ballasted and unballasted cases.True except for two things:The ballasted glider has more induced dragwhile at the same airspeed as the unballasted oneThe ballasted glider also has a higher stall speedSo the unballasted glider will go higherMark Boyd

Mark.
What about the L/D polar being skewed to the right to the benefit of the
higher
wing loaded vehicle. At VNE the heavier a/p is cleaner and will glide
farther.
If both a/p's pull up together, the cleaner a/p runs out of energy last. It
looks to me like
heavier climbs further.....

Scott


"M B" wrote in message
...
Since mass is a constant factor on both sides of the equation, it
cancels out. Therefore there should theoretically be negligible difference
in the pullup altitude gained between the ballasted and unballasted
cases.True except for two things:The ballasted glider has more induced
dragwhile at the same airspeed as the unballasted oneThe ballasted glider
also has a higher stall speedSo the unballasted glider will go higherMark
Boyd

Indeed you are correct that at high speed the ballasted
Glider 'bleeds' height (not energy) more slowly. That's
why we fly with ballast when we're cruising across
country, flying at higher speeds for longer periods

However if we look at that nice man Mr Johnson's test
flight of the Discus we find that carrying 183lbs of
ballast reduces the sink rate at 100kts from 3.3 m/s
to 2.24m/s.

If we pull up into a 45deg climb our velocity will
reduce at about .7g, i.e about 7m/s/s

So... if we're slowing from 100kts (50 m/s) to 40kts
(20 m/s)this will take about 30/7 seconds (i.e about
4)

Even if our ballasted glider could maintain it's sinkrate
advantage for the whole period we'd gain less than
5 metres.

At 12:36 09 September 2003, Scott Correa wrote:
Shouting is unbecoming a gentleman..................

Somehow I don't think you understood what I said.
Every test I have seen published shows the max L/D
point moving to the right (ie occuring at a higher
speed)
with an increase in wing loading. The sink rate curves
do the same thing. So again I ask, doesn't the heavier
airplane bleed energy more slowly..................

This has nothing to do with starting the engine......

Oh Yeah I also forgot to mention that although you
cannot
create energy, you can add it to the glider by flying
in air
going up faster than you are sinking thru it......................
...

Last time I looked at total energy systems, it read
airspeed
(kinetic energy) and barometric pressure (potential
energy)

Scott



'szd41a' wrote in message
.. .
YOU CANNOT CREATE ENERGY UNLESS YOU FIRE YOUR ENGINE!!!!!!!
'Scott Correa' a écrit dans le message de
...
Mark.
What about the L/D polar being skewed to the right
to the benefit of the
higher
wing loaded vehicle. At VNE the heavier a/p is cleaner
and will glide
farther.
If both a/p's pull up together, the cleaner a/p runs
out of energy last.
It
looks to me like
heavier climbs further.....

Scott


'M B' wrote in message
...
Since mass is a constant factor on both sides of
the equation, it
cancels out. Therefore there should theoretically
be negligible
difference
in the pullup altitude gained between the ballasted
and unballasted
cases.True except for two things:The ballasted glider
has more induced
dragwhile at the same airspeed as the unballasted
oneThe ballasted
glider
also has a higher stall speedSo the unballasted glider
will go
higherMark
Boyd

Hi, this is my first post on this news group, my interest is mainly model
gliders at this stage, but only for financial reasons. I am 18 and education
currently occupys my life.

I was of the understanding that as wing loading increases, best L/D is not
only at a faster speed, but is better then max L/D on an un-balasted glider.
For instance, if you have a glider which has its best glide ratio at 20km/h
(nice and slow) and is aprox 20/1 (nice and crap) - if you add 20kg ballast,
its best glide ratio is acheived at 30km/h and is 30/1
Correct me if I am wrong, it is more then possible.

In relation to the question, I dont beleive it has much impact.
There are positives and negatives in each case, Personaly I would think at
the same speed, the pullup of a lighter glider would be higher, but at peak
glide ratio speeds a balasted glider would gain more height.
I try to rationalize this by scaling up the flight patern in direct relation
to the flight speed,
If you normaly fly with 20m diameter circles, if you double your speed you
will also double your circle diameter.
If you double your speed you double your height?

Personaly I would like to see the question defined more accuratly.

Regards
Vince

"Scott Correa" wrote in message
...
Shouting is unbecoming a gentleman..................

Somehow I don't think you understood what I said.
Every test I have seen published shows the max L/D
point moving to the right (ie occuring at a higher speed)
with an increase in wing loading. The sink rate curves
do the same thing. So again I ask, doesn't the heavier
airplane bleed energy more slowly..................

This has nothing to do with starting the engine......

Oh Yeah I also forgot to mention that although you cannot
create energy, you can add it to the glider by flying in air
going up faster than you are sinking thru it.........................

Last time I looked at total energy systems, it read airspeed
(kinetic energy) and barometric pressure (potential energy)

Scott



"szd41a" wrote in message
...
YOU CANNOT CREATE ENERGY UNLESS YOU FIRE YOUR ENGINE!!!!!!!
"Scott Correa" a écrit dans le message de
...
Mark.
What about the L/D polar being skewed to the right to the benefit of
the
higher
wing loaded vehicle. At VNE the heavier a/p is cleaner and will glide
farther.
If both a/p's pull up together, the cleaner a/p runs out of energy
last.
It
looks to me like
heavier climbs further.....

Scott


"M B" wrote in message
...
Since mass is a constant factor on both sides of the equation, it
cancels out. Therefore there should theoretically be negligible
difference
in the pullup altitude gained between the ballasted and unballasted
cases.True except for two things:The ballasted glider has more induced
dragwhile at the same airspeed as the unballasted oneThe ballasted
glider
also has a higher stall speedSo the unballasted glider will go
higherMark
Boyd

"Rasman" s comments read:

I was of the understanding that as wing loading increases, best L/D is not
only at a faster speed, but is better then max L/D on an un-balasted glider.
For instance, if you have a glider which has its best glide ratio at 20km/h
(nice and slow) and is aprox 20/1 (nice and crap) - if you add 20kg ballast,
its best glide ratio is acheived at 30km/h and is 30/1
Correct me if I am wrong, it is more then possible.

Errr scratches head - normally the described effect of ballasting is

1) Best L/D stays the same
but
2) At a higher airspeed
and
3) At a higher sink rate

Although we are talking about

Best L/D ~ 42:1 at 55knots at 400kgs
and
Best L/D ~ 42:1 at 60knots at 450kgs

As conservative estimates for my ASW20
--
Tim - ASW20CL "20"

Earlier, "szd41a" wrote:

YOU CANNOT CREATE ENERGY UNLESS YOU FIRE YOUR ENGINE!!!!!!!

Actually, you can't create energy at all, even with an engine. You can
only transform it between different forms.

Bob K.
http://www.hpaircraft.com

The heavier glider will get more altitude.But not very much...If the ballasted glider stalls at exactly 100 knots,it cannot gain any altitude, while the unballastedglider will gain some altitude. Thereforethere is at least one case where the unballastedglider will outclimb the ballasted one.The proposed equations I have seen do not account for this case and must therefore be insufficient.

I REALLY wanted to snipe back with that.
Thanks Bob
Call me at the shop
817-573-2972

Scott Correa
SPEKTR PRODUCTS.

"Bob Kuykendall" wrote in message
om...
Earlier, "szd41a" wrote:

YOU CANNOT CREATE ENERGY UNLESS YOU FIRE YOUR ENGINE!!!!!!!

Actually, you can't create energy at all, even with an engine. You can
only transform it between different forms.

Bob K.
http://www.hpaircraft.com

It will gain more height with ballast. The
kinetic energy is defined as 1/2*m*v squared.
[...]
The potential energy is m*g*h,
[...]
So for example, if a gldier weighs twice as much, it will
gain twice the height, or at least I think so!

Again, take out the constants. Both aircraft have the same velocity at the
beginning, 100Kts. Assume, for the sake of argument, that they have the same
velocity at the end, say 30 kts (I know the heavier one will stall first, but
in a vertical pull up, the wing loading is zero, so the stall speed would be
very close).

SO at the beginning, the delta in kinetic energy for two ships travelling the
same speed is only proportional to the mass. Since the heavier one weighs more,
it has more kinetic energy. At the end of the pull up, when all the kinetic
is converted to potential, take out the constants again (g), and the only
remaining variable is h. h is proportionally more for the heavier ship. And,
as I said before, this is not accounting for drag.

P.S. I f'in hate calcusus. R dR d theta double dot!
Jim Vincent
CFIG
N483SZ

Scott
Please accept my apology for shouting
Of course everyone knows that a glider cimbing in a thermal is gaining
potential energy.
Evryone knows that a ballasted glider will will trade potential energy to
kinetic energy at a faster rate than a dry glider.
No matter how we look at it, we will have to repect the law of conversation
of energy.
My problem was set in still air, maybe i should have made this clear. So,
you have to balance the total energy at the start of the climb with the
total energy at the end of the climg. I am going to be rude again, THERE IS
NO WAY AROUND THAT. That is what I meant with the big letters.
I solved the equation without taking drag into account, my feeling is that
it has little effect ( both glider will be affected by drag, but we will
need to cut down H a bit).
Going down towards the center of the earth ballasted is one thing, going
away from it is another ball game.
You will need the extra enrgy to lift the extra weight and it will be traded
from the extra kinetic enrrgy you had at the start.
For simplcity, if you set start point at H=0, all you have a start is
kinetic energy and there is much more stored in the heavy glider. Then you
solve for potential energy at the end, knowing your final speed, and you
find height achieved.
Then there is drag.....
Then there are conflicting reports from pilots who don't care about maths,
but have the right stuff....
This is fun, isn't it.:-))))
Réjean


"Scott Correa" a écrit dans le message de
...
Shouting is unbecoming a gentleman..................

Somehow I don't think you understood what I said.
Every test I have seen published shows the max L/D
point moving to the right (ie occuring at a higher speed)
with an increase in wing loading. The sink rate curves
do the same thing. So again I ask, doesn't the heavier
airplane bleed energy more slowly..................

This has nothing to do with starting the engine......

Oh Yeah I also forgot to mention that although you cannot
create energy, you can add it to the glider by flying in air
going up faster than you are sinking thru it.........................

Last time I looked at total energy systems, it read airspeed
(kinetic energy) and barometric pressure (potential energy)

Scott



"szd41a" wrote in message
...
YOU CANNOT CREATE ENERGY UNLESS YOU FIRE YOUR ENGINE!!!!!!!
"Scott Correa" a écrit dans le message de
...
Mark.
What about the L/D polar being skewed to the right to the benefit of
the
higher
wing loaded vehicle. At VNE the heavier a/p is cleaner and will glide
farther.
If both a/p's pull up together, the cleaner a/p runs out of energy
last.
It
looks to me like
heavier climbs further.....

Scott


"M B" wrote in message
...
Since mass is a constant factor on both sides of the equation, it
cancels out. Therefore there should theoretically be negligible
difference
in the pullup altitude gained between the ballasted and unballasted
cases.True except for two things:The ballasted glider has more induced
dragwhile at the same airspeed as the unballasted oneThe ballasted
glider
also has a higher stall speedSo the unballasted glider will go
higherMark
Boyd