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

"Scott Correa" wrote in message ...
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.

Let's continue a bit with physics and math:

I solved the equation of motion for an ascending flight path of a
constant angle with the following parameters:

mass of the glider = 325 and 525kg (= 750 and 1160 lbs)
drag coefficient = 0.015 (constant with velocity)
wing area = 10.5 m^2
start velocity = 185 km/h (100kt)
final velocity = 110 km/h (60kt)

density of air = 1 kg/m^3
gravit.acceleration= 10 m/s^2

I did not account for the initial rotation from normal glide path into
the ascending flight path and I did not account for the subsequent
rotation back into normal glide.

Results for an ascending constant glide path angle of 10°
for the 325kg glider compared to the 525kg glider:

The heavier glider can go up with an angle of 10.8° in order
deaccelerate in the same time (9s).

Both gliders reach the final velocity after 380m flight path.

The 325kg glider climbs to 65m,
however the heavier 525kg glider reaches 70m.

The reason for this is, that the second deaccelarating term in the
equation of motion is: drag/mass, when resolved to acceleration; hence
deaccelaration due to drag is less for the heavier glider.
Robert has already given a vivid explanation for it.

This result (altitude difference=5m=16ft) is less than the observed
altitude difference for the two Venti
(where is the discussion thread ?).

Ewald

Great Math! But I think we are baseing this on the
wrong constant. All of these base the constant on airspeed.
I am not a mathematition (I can't even spell it) but
if we base it on sink rate it should be alot more
obvious. After all thats exactly why we carry water
ballast in the first place, to increase speed for the
same amount of altitude loss right? So if your going
10 knots faster in the ballasted glider and at the
same sink rate as the unballasted glider. You will
gain more in pullup, right?

Cliff


At 21:00 07 October 2003, Ewald Bombelka wrote:

"
http://www.tux.org/~milgram/papers/alds_auvsi2003.pdf

This paper was referred to me by an aerodynamics
professional/glider pilot. I hope he won't mind if I post
this limited excerpt from his email to me:

"I notice you carrying the torch for good physics on r.a.s.,
more power to you. But don't fret over it (especially not on
r.a.s.), since as you've noted you have to look at the
energy losses to see any difference, and no analysis can
answer this without incorporating some kind of trajectory
analysis. That would have to include some kind of
representation of the glider's long-period longitudinal
dynamics (a.k.a. phugoid dynamics), and a way to optimize
the pullup for each given weight. Plus you have to decide
what the rules are (pullup from same airspeed, pullup from
weight-appropriate MacCready speed, etc.).

Todd Pattist - "WH" Ventus C
(Remove DONTSPAMME from address to email reply.)

We can appreciate that very intelligent view on the question. In no ways, it
denies the fact that in our system, no energy is created, so ultimaly we
will have to balance the conservation of energy theorem. This is simple:
kinetic energy, potential energy and drag. Not matter what trajectory you
will choose, you will have to balance the equations even if you use phugoid
dynamics. There are no rule here for trajectory, just go for max height!!!
We did the maths, and we look at our total energy probe (i.e vario), we
notice we're trashing energy in a pull-up (if the probe is well calibrated),
otherwise in still air, nothing is gained.
This is going way further than I expected!!! We had all kinds of comments,
this one from a mathematician CFI who conclude that ballasted will go twice
as high, another from an outsider power pilot who candidly state that he
noticed that pull-ups with a load (passengers) were more demanding (we all
know that power pilots are no physicians ;-)... and that soaring is an art
that defy laws of physics) and all kind of rewritten equations that give
a substantial advantage to the ballasted. Don,t get me wrong, we are talking
one hundred feet difference on an avergage 300'+ pull-up!!!!! Now, that is a
lot of drag!!!!
We sill expect a probant mathematical proof, or a reality check in still
air.
BQ