Did we decide if ballasted pullups are higher????????

OK, here we go, just to exite trolls, believers, non-believers, math
fereaks, the lot:

Off course wet pullups go higher. In the end, a pullup is conversion from
kinetic energy (speed) to potential energy (altitude). Soaring is all about
trading one of these for the other.
Picture two identical gliders (please, no Discus/Duo Discus (sorry, couldn't
resist)) both at 100 feet, 250 Km/h. Their kinetic energy is derived from
their speed (equal in this setup) and mass. So the heavy one has the most
kinetic energy. -Which one can then obtain the highest potential energy ?
Elementary, my dear Watson.

Happy soaring,
Lars Peder

Replace the obvious by a dot to respond via e-mail




"Scott Correa" skrev i en meddelelse
...
OK people, what was the verdict.
I'm sure some logger equipped pullups were made.
Who wins?? Wet or dry.
I still think wet pullups go higher, but I can't prove it.

Scott.

In article ,
"Lars Peder Hansen" wrote:

OK, here we go, just to exite trolls, believers, non-believers, math
fereaks, the lot:

Off course wet pullups go higher. In the end, a pullup is conversion from
kinetic energy (speed) to potential energy (altitude). Soaring is all about
trading one of these for the other.
Picture two identical gliders (please, no Discus/Duo Discus (sorry, couldn't
resist)) both at 100 feet, 250 Km/h. Their kinetic energy is derived from
their speed (equal in this setup) and mass. So the heavy one has the most
kinetic energy. -Which one can then obtain the highest potential energy ?

Except that potential energy is proportional to both altitude *and* mass.

IOW, double the mass, and you double the kinetic energy at a given
speed, but you also double the potential energy of the change in
altitude.

Elementary, my dear Watson.

If you think about it a moment, the correct answer is "Elementary, my
dear Galileo" (think dropping balls of different masses, and then
reversing the experiment).



Happy soaring,
Lars Peder

Replace the obvious by a dot to respond via e-mail




"Scott Correa" skrev i en meddelelse
...
OK people, what was the verdict.
I'm sure some logger equipped pullups were made.
Who wins?? Wet or dry.
I still think wet pullups go higher, but I can't prove it.

Scott.





--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."

On Thu, 25 Sep 2003 13:38:01 -0500, "Scott Correa"
wrote:

OK people, what was the verdict.
I'm sure some logger equipped pullups were made.
Who wins?? Wet or dry.
I still think wet pullups go higher, but I can't prove it.

What Alan, Mike and m said. Strictly from a potential/kinetic energy
standpoint, it's a wash. Not APPROXIMATELY a wash --- EXACTLY a wash.
However, there at least two more factors.

First, the wet ship has to pitch up to a higher angle of attack as it
starts the pullup, in order to achieve a given upward acceleration.
This will extract a penalty in the form of energy removed by induced
drag.

Once the change of direction is completed, both pilots can reduce
their angle of attack to the zero-lift point, giving an ascending
parabola which will maximize the altitude reached. In this condition
the only drag is parasite drag, which will be the same for both ships;
consequently the wet ship has an edge here because its larger mass
will decelerate less for a given drag force.

So the answer to the question depends on which of these effects is
larger. It shouldn't be hard to settle with an empirical test: just
have two ships pull up simultaneously in line-abreast formation.

rj

Lars Peder Hansen wrote:
OK, here we go, just to exite trolls, believers, non-believers, math
fereaks, the lot:

OK I'll bite

Off course wet pullups go higher.....

Picture two identical gliders (please, no Discus/Duo Discus (sorry, couldn't
resist)) both at 100 feet, 250 Km/h. Their kinetic energy is derived from
their speed (equal in this setup) and mass. So the heavy one has the most
kinetic energy. -Which one can then obtain the highest potential energy ?
Elementary, my dear Watson.

Happy soaring,
Lars Peder

The heavier one does have more energy. Then again, it
requires more energy to lift a heavier object. And the
additional work required to lift a heavier object to the
same height as a lighter one is directly proportional to the
difference in mass.

--

Peter D. Brown
http://home.gci.net/~pdb/
http://groups.yahoo.com/group/akmtnsoaring/

"Mike Borgelt" wrote
Dear God!

Didn't anyone pay attention to physics lessons in high school?

Actually, I skipped a lot of physics & math lessons in high school, to go
soaring with a friend from my class. ( I guess you figured that out by now
;-)
We had a math teacher who eventually figured out the connection between blue
skies with cumulus, and the two of us being absent from class. One day he
called the gliderport, just to let us know what chapters to read for next
week. -I was the unlucky one who picked up the phone...

Happy soaring, and safe pullups to exactly the same altitude no matter what
mass you fly at,
Lars Peder

I'm not sure I follow your reasoning about the heavy
glider having the advantage in the 2G case.

In normal flight at high speed we have relatively little
induced drag, and the major component of our total
drag is profile.
With it's higher reserve of energy the heavy glider
gains the benefit 'cos even though the induced drag
is higher it's a small proportion of the total.

If we now start to pull G the induced drag for both
gliders goes up, it now becomes a more significant
proportion of the total for each glider so surely the
advantage of the heavy glider is reduced?

(And I notice that you have admitted you're in the
'Heavy Glider Wins' camp) :-)



At 21:06 26 September 2003, Todd Pattist wrote:

The advantage of the heavy glider (in terms of lost
altitude) remains throughout the increased G-load portion
of
the pullup. Think of the two gliders suddenly doubling
their
weight (2G pullup). The ballasted glider would have
a lower
sink rate in the 2G case for the same reason that it
has a
lower sink rate in the 1G case.

In article ,
Kevin Neave k
wrote:

I'm not sure I follow your reasoning about the heavy
glider having the advantage in the 2G case.

In normal flight at high speed we have relatively little
induced drag, and the major component of our total
drag is profile.
With it's higher reserve of energy the heavy glider
gains the benefit 'cos even though the induced drag
is higher it's a small proportion of the total.

If we now start to pull G the induced drag for both
gliders goes up, it now becomes a more significant
proportion of the total for each glider so surely the
advantage of the heavy glider is reduced?

But how hard are you pulling?

Minimum drag (min sink) for the dry glider is probably at around 50
knots, so to get the same AOA at 110 knots you have to pull well over
4G. Min sink for the wet glider might be -- what -- 55 knots? So
you're still talking 4G at 110 knots to get that AOA.

If you're only pulling 2 or 3 G then you'll be above best L/D speed as
well.

The heavy glider still clearly has an advantage.

-- Bruce

Drag is the thing here...
My ASW24, being lighter than, say, a ASK-21, will get 200mts (600ft) from a
high speed pull up. The ASK will get 100 to 130mts.
A Blanik will get much less.
A ballasted ASW-24 gets more from the pull up than I do unballasted.
In our kind of flying drag is everything! Why an ASK-13 flyes less than
a -21, a -24, a -25 and so on? How can we explain such large differences in
performance? Drag is reduced for the newer gliders.
You are all right with the math, and in the total energy equations mass is
nonrelevant as it is a constant. But you're all disregarding the effect of
drag and you cannot do that! That is the reason why all the fancy math
you're doing does not match with our real life experience. And if a
theorical reasoning does not match with reality, then it's obvious that the
theory is somewhere wrong.
So please if you want to get into math please do account drag and fluid
mechanics into it. If you simplify it so much, it will be inaccurate enought
to be false.
Ballasted gliders will go higer because of the increased mass, more
penetration and more energy for the same aerodinamic drag.

"Bruce Hoult" escribió en el mensaje
...
In article ,
Kevin Neave k
wrote:

Lots of maths snipped...

The original post way, way, way back specified 100kts
& 100kgs ballast.

Why will none of the 'Heavy Glider Wins' contingent
actually give any numbers as to what they think the
advantage here is?

At 09:24 29 September 2003, Jose M. Alvarez wrote:
Drag is the thing here...
My ASW24, being lighter than, say, a ASK-21, will get
200mts (600ft) from a
high speed pull up.

And how much EXACTLY will it get from 100kts?

A ballasted ASW-24 gets more from the pull up than
I do unballasted.

How much ballast EXACTLY are we talking about here?
And EXACTLY how much extra height do you think you'd
gain in a pull up from 100kts.

You are all right with the math, and in the total energy
equations mass is
nonrelevant as it is a constant. But you're all disregarding
the effect of
drag and you cannot do that!

And you're disregarding TIME, there's simply not enough
time in which the slight difference in performance
of the ballasted/unballasted glider has to operate.


That is the reason why all the fancy math
you're doing does not match with our real life experience.
And if a theorical reasoning does not match with reality,
then it's obvious that the theory is somewhere wrong.

I think you're confusing 'perception' with reality
here

So please if you want to get into math please do account
drag and fluid mechanics into it. If you simplify it
so much, it will be inaccurate enought to be false.

My analysis, including drag, but with some approximations
(All in favour of the heavy glider) is on the way


Ballasted gliders will go higer because of the increased
mass, more penetration and more energy for the same
aerodinamic drag.


Ballasted Gliders average higher cross country speeds,
finish faster, and with the pilot feeling better about
life! That's why the perception is that ballasted gliders
gain more in the pull-up!!!


:-)

OK Folks here we go with the maths, including that
old chesnut drag, and before any of you start to pick
nits I'm going to use kilograms as a unit of 'Force'
to avoid confusing our American friends who seem to
use pounds as both a unit of mass and force.
But I'm assuming that the analysis I'm doing here is
for our own planet earth where G is about 9.8m/s/s
and the difference in Gravitational field between the
start and end of the pull up is negligible.

Let's start with a Glider weighing 300kgs with a stall
speed of 38kts (19m/s), and a best L/D of 40:1 at 60kts.
If we now add 100kgs of ballast all the numbers are
multiplied by sqrt(4/3) so we have a stall speed of
44kts (22m/s) and a best L/D of 40:1 at 69kts

Now I believe that at Best L/D the Profile and Induced
drag are equal (And I'm sure someone will correct me
if I'm wrong).
So for our light glider at 60kts we have a total 'drag'
of 7.5kgs (300/40) which means that we have Induced
= Profile = 3.5kgs

I also believe that Induced Drag goes down with the
square of the speed (i.e 1/Vsquared) (Again I'm sure
I'll be corrected!) and that profile goes up with the
square of the speed.

Induced drag is also proportional to wing loading so
our Heavy Glider will always have 4/3 the induced drag
of the light one.

So going back to our light glider...

At 100kts our induced 'drag' is now (60/100) * (60/100)
* 3.75 = 1.35kgs
And our profile is (100/60) * (100/60) * 3.75 = 10.41kgs.
Total 'drag' = 11.76kgs

Assuming that adding the ballast doesn't alter the
shape of our glider too much then for the heavy glider

Induced = 1.35*4/3 = 1.8kgs
Profile = 10.41kgs
Total = 12.21kgs.

Now we're ready to pull up & I'll make a few assumptions
here.
1) That we're not going to pull up to below the stall
speed of either glider. This is a reasonable assumption,
pulling up to an airspeed of 0kts followed by a spin
recovery and return to normal flight almost certainly
hands the 'advantage' to the light glider (It'll hit
the ground less hard!!)

2) We're going to pull up into a 45deg climb & maintain
a straight line up to our recovery speed. This is not
a ballistic trajectory 'cos in order to maintain this
straight course the wings will have to generate some
lift and so will upset my next assumption, which is...

3) We can ignore changes drag!! This is a pretty big
assumption but here goes... At the same level of 'G'
the induced drag is propotional to the wing loading
i.e the heavy glider will have 4/3 times the induced
drag. However the 'Energy Fuel Tank' of the heavy glider
also has 4/3 as much as the Light one so I think the
two effects cancel out
(And once again I'm sure someone out there will correct
me!). Secondly, as the speed drops off our profile
drag will also be reduced with the square of our speed,
in some ways this makes up for ignoring the increasing
induced drag required to maintain our straight 45deg
climb.
Thirdly, making these assumptions about drag gives
a slight advantage to the heavy glider. And Lastly
it makes the maths simpler!!

So here we go...

Both gliders start to pull 2G. The induced drag for
each is doubled (i.e goes to 2.7kgs for the light,
3.6 for the heavy) but since the change is not significant
compared to the total I'm ignoring it!

And we start to climb (I'm assuming that the time taken
to transition from level flight to 45deg climb is small
so any transient effects in our 2G pull won't be significant)

The retarding force for the light glider is now 300kgs
* 1/sqrt(2) due to gravity plus the 11.76kgs due to
drag = 212.13 + 11.76 = 223.89kgs
So our deceleration will be 223.89/300 * 9.8 = 7.31
m/s/s

For the heavy glider we have 400 * 1/sqrt(2) for gravity
plus 12.21kgs due to drag = 295.05kgs
So our deceleration will be 295.05/400 * 9.8 = 7.23
m/s/s

Now finally we're going to continue up our 45deg climb
to our respective stall speeds, all of which is done
at Newtonian rather than Einsteinian speeds

So V*V = U*U - 2*a*s :- where V is final velocity,
U is initial, A is acceleration and s is distance travelled.

So ((U*U) - (V*V)) / (2*a) = s

For the light glider

V=19m/s, U=50m/s, a=7.31m/s/s

((50 * 50) - (19 * 19)) / (2 * 7.31) = 146.31 metres.
So Our height gained = 1/sqrt(2) * 146.31 = 103.46m

For the heavy glider

V=22m/s, U=50m/s, a=7.23m/s/s

((50 * 50) - (22 * 22)) / (2 * 7.23) = 139.24 metres
!! Height gained = 98.46 metres !!

------------------------------------------------------------------
---------------------------

OK, So there's some assumptions in the above, but I
think all of them were made in favour of the heavy
glider.

But I say once again, for a pull up from 100kts with
100kgs of ballast, 'It's too close to call'...

Over to you Todd

:-))