Thanks for adding real, empirical data to the discussion
Chris.

I think 20-50 feet is less difference than a lot of
us would intuitively have thought initially, but pretty
close to where the analysis has led us collectively
(e.g. no difference in a kinetic energy-to-potential
energy sense, a small difference [15-20 feet] in favor
of the heavier glider due to differences in the unaccelerated
[1G] polar, and an indeterminate difference due to
the G-load losses from the pullup).

Don't forget that in a series of pullups over time,
the heavier glider should steadily gain on the lighter
one just due to the middle effect (i.e. the difference
in L/D at the same speed).

Nice job in getting real data!

9B


At 12:18 29 September 2003, Chris Ocallaghan wrote:
Flew on Sunday in non-stable conditions. David Pixton
flew his Ventus
2b at approx. 800 lbs, and I flew my Ventus 2bx at
1150 lbs. Because
conditions were turbulent, we were unable to do any
smooth air
testing, but during the course of 10 pull ups (entry
100 knots, exit
60 knots) we observed the following:

Wing abreast with about 100 to 150 feet of separation,
pull ups were
either even or slightly better (10 to 20 feet) for
the heavier glider.
Because we were following a cloud street, we were unsure
whether the
apparent parity was actual or lift related. Dave was
selecting the
path, so it is possible that he was better centered
in the lift
street.

I repositioned directly behind Dave (less than 100
feet). With each
pull I was forced to maneuver to avoid him, and would
generally gain
between 10 to 30 feet. On one pull however, I gained
more than 50
additional feet. In each case, I was forced to deploy
spoilers to get
back into position for the next pull. It appeared that
the stronger
the core we pulled in, the more advantage I got. On
a few occasions,
Dave pulled to less than 60 knots, and while this cut
down on my
advantage, I regained it immediately (and then some)
as we returned to
cruising speed.

It is interesting to note that during these tailored
pull ups and
during subsequent street running with freeform pulls,
Dave never
gained on me. I found myself making S turns to keep
from overtaking
him. When at last I took the lead, the overall advantage
to the
heavier glider was apparent and substantial.

We'll try this again in still air, but initial results
indicate that
there is a marked difference in climb during each pull
up. Even at a
conservative 15 feet per pull, a hundered such pulls
during a task
would account for 1500 extra feet, and this doesn't
include the
advantages water offers during the cruising phase of
flight.

So to answer the question, 'is there a difference?'
the answer is
yes... in theory and in practice. Dave commented after
the flight, 'I
need to get back into the habit of putting water in
the wings.'

If I can muster Dave for some early moring flying,
we'll get some more
quantitative results.

OC