Polar Analysis from flight logs?

I won't speculate on the results of this type of testing, but, around here
the wind varies considerably with altitude, even with calm conditions
in the morning. When doing performance work I would try to work
crosswind. Wind shear effects are less influential. It is a great
help to take a tape recorder and record every bump and time. A lot of
data gets thrown out.

If you take twenty minutes per point, you'll be spending a lot on tow fees.

Dennis Brown

John Sinclair wrote in message ...
I asked Dick Johnson, why couldn't I fly in calm conditions
(morning) and hold a given airspeed (say 60 knots)
and a given heading (say west) for 10 minutes, then
reverse heading to east (to cancel out any wind) and
then analyze the GPS trace to determine my ships L/D
at 60 knots. We have an accurate distance covered and
fairly accurate altitude lost, so why can't we crunch
the numbers?
Dick said the GPS info wasn't accurate enough. I thought
it was a good idea, but I defer to the master.
JJ

At 03:00 28 December 2004, Bob Gibbons wrote:
On this topic of determining L/D from interthermal
cruising, Dick
Johnson did a fascinating and underappreciated study
in the late
1970's of airmass behavior between thermals. Dick flew
in mostly blue
conditions and simply recoded his height loss versus
distance covered
between thermals. Dick's results are reported in SOARING,
June 1979.

Dick found that, on the average, the airmass between
thermals has an
average sink rate related to the upgoing thermal strength.
The
relationship Dick found was; the airmass sink is approximately
10% of
the lift strength.

I have always felt Dick's study explains why it is
so difficult to fly
cross country (in a blue conditions) with a ship having
an L/D less
than about 30:1. The probability of running into the
next thermal
purely by chance becomes too low as the L/D drops.

For this discussion, I think Dick's study shows the
inadvisability of
trying to deduce flight performance from interthermal
measurements.

Bob

On Mon, 27 Dec 2004 20:43:41 GMT, 'Papa3'
wrote:

Mark,

My first post came across as a bit glib - apologize
for that. But, I
actually put a little thought into that subject recently
while writing some
batch analysis specs for GPS log files. The problem
is that a good glider
pilot will not encounter random vertical motions -
even in cruise flight.
He/she will stack the deck in his favor, seeking out
cloud streets or
connecting the best looking individual Cu. Thus,
you can't just average
out the L/D over time on specific segments (e.g. cruise
flight). What you
can do is deterimine which pilot does the best job
of achieving highest L/D
on a given day. Several of the popular flight analysis
programs do this
already.

I'd certainly be interested in any detailed ideas you
might have.

P3

'Mark Zivley' wrote in message
.com...
Obviously ridge flight would not be conducive, nor
wave, but put enough
data together from cruises during thermal flights
and I bet something
could be put together.

Papa3 wrote:

Mark,

How do you propose to isolate the impact of vertical
air motion? For
instance, I can fly the ridge at 100Kts and maintain
altitude (same for
wave
or cloudstreets). I'm sure Rolladen-Schneider (ahem,
DG) would love to
publish the L/D of my LS8 from the average of my
flights for a season:
'LS8, with a measured L/D of 800:1...'

Cheers,
Erik


'Mark Zivley' wrote in message
m...

We all know what the manufacturer's polars look like,
but what about our
individual planes. Has anyone done any work to develop
a program that
would look at some flight logs and determine what
a particular glider's
actual polar is? At one point Ball was making a vario
system that would
determine the aircraft's polar over time just by flying.

For someone who already had some algorithms for computing
wind from
ground track drift during thermals could take this
info and then be able
to back figure from GPS ground speed what the IAS
was during a
particular phase of the flight. By isolating longer
sections of cruise
flight at varios airspeeds it should be do-able.
Question is, has it
been done.

Mark

extra 'hot' in the address to delay the spammers...