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

Hi Todd,

You seem to be of the opinion that in the accelerated
part at the start of the pull-up the ballasted glider
has a vast advantage over the un-ballasted one. Have
you any evidence to support this? I would have thought
that the effort required to accelerate the extra ballast
would give the advantage to the light glider at this
point - but yes that's just my opinion.

As far as I'm concerned the overwhelming maths here
is good ol' conservation of energy where speed is traded
for height & the two come out equal.

Yes there's some drag involved but the actual drag
forces are pretty small on modern sailplanes & the
time in which they have to operate is pretty small.


Three questions for you:-

1) How long do you think the pull-up lasts?
2) What sort of difference do you think there is in
the respective sink rates - during the pull, during
the climb & the push over at the top?
3) What sort of difference do you think there is in
the height gained?

Finally I've suggested a couple of times that someone
with a Duo / ASH25 / Nimbus D go & do the tests

At 15:42 18 September 2003, Todd Pattist wrote:
Kevin Neave
wrote:

The heavy glider is indeed losing height more slowly
than the light one at this speed, (But the difference
is only about 1m/s).

Where do you get that number? From the polar measured
at
1G? That's the wrong polar. The glider is not operating
at
1 G for much of the pullup.

This difference is only maintained for the duration
of the pullup (About 4-5 seconds) and will be diminishing
as the speeds drop off.

I regret to say that this analysis is bogus. It just
tells
us what would happen if the gliders flew side by side
for
4-5 seconds. Of course that difference is nominal,
but they
aren't doing that, they are flying at a varying G-load
through the pullup. You can't wave your hands and
ignore
that difference.

So in the end I believe it's too close to call!!

You have no basis other than your opinion. You need
to do
the math or the experiment. You've done neither.

Todd Pattist - 'WH' Ventus C
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