Polar diagrams and L/D

Dan Marotta wrote on 9/18/2017 10:01 AM:
Your vario sink rate is an indicated rate, as is the airspeed indicator, so your
calculated glide ratio, /_in the airmass_/ should be a simple calculation. Having
said that, the air is too dynamic to care what your instantaneous glide ratio is
and, like thermals, and investments, past performance is no guarantee of future
performance. It's all "golly, gee-whiz" stuff at the end of the day.

Unless the vario manual declares the calibration is in "indicated" units, I've
always assumed it's calibrated in true rate-of-climb. I recall the old mechanical
(and maybe the thermistor flow sensor varios), flow driven vane-type varios did
read "indicated", but for decades, varios have used pressure sensors and I think
they are calibrated in "actual rate of climb".

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/...anes-2014A.pdf

A man who has one vario knows exactly the airmass movement rate.Â* A man
who has two is never quite sure.

This discussion sounds like the military way:Â* measure with a
micrometer, mark with a grease pencil, cut with an ax.Â* Do you really
believe the current altitude record is accurate to 5 significant
digits?Â* Is that in meters or in feet?Â* I know they claim centimeter
accuracy with GPS, but is it repeatable?Â* How about the thickness of the
line on a barograph, a kink in a pneumatic tube or a spot of sunshine on
the tube?

We went into space mostly with three significant digit accuracy (think
slide rules), why is a glide ratio so important when it's such a
transient thing in an active airmass?Â* I have witnessed a 25:1 glider
(or less) beat a whole gang of 40+:1 gliders.Â* It's the pilot, in the
glider, at that moment, and at that location that makes the performance,
not a number on a graph.

Just my two cents worth.

Dan

On 9/18/2017 9:06 PM, Eric Greenwell wrote:
Dan Marotta wrote on 9/18/2017 10:01 AM:
Your vario sink rate is an indicated rate, as is the airspeed
indicator, so your
calculated glide ratio, /_in the airmass_/ should be a simple
calculation.Â* Having
said that, the air is too dynamic to care what your instantaneous
glide ratio is
and, like thermals, and investments, past performance is no guarantee
of future
performance.Â* It's all "golly, gee-whiz" stuff at the end of the day.

Unless the vario manual declares the calibration is in "indicated"
units, I've always assumed it's calibrated in true rate-of-climb. I
recall the old mechanical (and maybe the thermistor flow sensor
varios), flow driven vane-type varios did read "indicated", but for
decades, varios have used pressure sensors and I think they are
calibrated in "actual rate of climb".


--
Dan, 5J

On Tuesday, September 19, 2017 at 9:13:54 AM UTC-6, Dan Marotta wrote:
A man who has one vario knows exactly the airmass movement rate.Â* A man
who has two is never quite sure.

This discussion sounds like the military way:Â* measure with a
micrometer, mark with a grease pencil, cut with an ax.Â* Do you really
believe the current altitude record is accurate to 5 significant
digits?Â* Is that in meters or in feet?Â* I know they claim centimeter
accuracy with GPS, but is it repeatable?Â* How about the thickness of the
line on a barograph, a kink in a pneumatic tube or a spot of sunshine on
the tube?

We went into space mostly with three significant digit accuracy (think
slide rules), why is a glide ratio so important when it's such a
transient thing in an active airmass?Â* I have witnessed a 25:1 glider
(or less) beat a whole gang of 40+:1 gliders.Â* It's the pilot, in the
glider, at that moment, and at that location that makes the performance,
not a number on a graph.

Just my two cents worth.

Dan

The following recognition was approved at the recent SSA BOD meeting. I do not know if differential GPS was used or available with the GPS flight recorders measurements.

quote
Todd Walter and Duncan Eddy - I hereby nominate Todd Walter and Duncan Eddy for the SSA Exceptional Service Award for their willingness to take their personal time and doing the work which resulted in the Perlan flight recorders (FRs) achieving the first successful certification of high altitude flight recorders.
When a last-minute-type of message came in early summer 2015 from the Airbus-sponsored Perlan project for help to get their FRs certified, a network of people were contacted for assistance. Although several people offered aid, a decision was made to utilize the positive response from Todd Walter, senior research engineer in the Department of Aeronautics and Astronautics at Stanford University, to help by taking on the work immediately. Todd oversaw the operation, setting up an arrangement with Stanford Professor Simone D'Amico to involve his grad student Duncan Eddy who was experienced in operating the GPS simulator.
Considerable effort was needed by Todd and Duncan to find proper connecting cables which were then successfully utilized and testing began. Readings were taken every 5,000' in ascent/descent. However. at 49,000', the run ceased getting readings from the FRs. Both FRs were tried to no avail. Todd searched through the FR documentation and discovered there was an electronic switch in the FR that prevented operation above 15,000 meters. Since operation of the switch on the FR to permit operation above 15,000 meters could not be achieved in the GPS simulator testing lab being utilized at Stanford, the FRs were sent back to the manufacturer in Europe. They reset the switch to permit operation above 15,000 meters and the FRs were sent back to Stanford where runs were successfully completed to above 90,000 feet on both FRs.
The complete evaluation of the FRs was completed in a very short, but intensive work effort on their part, resulting in the issuance of approval for use of that model of FR for high altitude flight verification. The FRs were then shipped to Argentina for use in the Perlan flights of last year. It is believed that this
marked the first time FRs were calibrated for flight above 15,000 meters and that it was done utilizing GPS simulators.

Submitted by Bernald Smith
SSA Honorary Vice Chair
/quote

Frank Whiteley

"Considerable effort was needed by Todd and Duncan to find proper connecting cables..."

- yeah, that's usually the hardest part! :-)