On Apr 1, 9:15*am, "Wayne Paul" wrote:
I like Mike Borgelt's approach. *Collect the data for your glider during a couple test flight and enter the data into his free software to determine the quadratic equation A, B, and C values.http://www.borgeltinstruments.com/so...ies.html#Polar

"Mike" wrote in ...

Paul,

Actually I entered the data in your conversion spreadsheet as a
Cambridge Polar File and then posted the resulting See You data
points.

Using the best L/D and speed and the 2 meter sink rate at speed, when
I checked the resulting generated polar, it was pretty close to the
Johnson measured polar. Close enough that I would fly with it.

Best L/D was actually measured at 36.8 @ 92 kph and the 2 meter sink
speed @ 148kph. Test weight was 315.2 kg.

On Apr 1, 6:13 am, "Paul Remde" wrote:

Hi Mike,

Those numbers look like they may be correct. Hopefully, when you enter
those numbers into SeeYou Mobile, it displays the correct glide ratio and
other data.

If you send me the 3 airspeed and sink rate pairs (with the lowest speed one
at the best L/D speed). I would be glad to put them onto my Polars web
site. I will also need to know the wing loading at which the numbers were
obtained.

Best Regards,

Paul Remde

"Mike" wrote in message

...
On Mar 31, 9:50 pm, Randy wrote:

Mike,
I do not understand what to enter on the SeeYou Mobile
Polar setting page. There are six available boxes.
Name Sgs 1-35
Min Load - 6.38
Stall Speed - 43 mph
a -
b -
c -

I do not know what goes in a, b, c boxes.
Even when I look at the polars for my own
glider, I do not understand what the numbers
mean.

If I entered the data correctly into Paul's spreadsheet, and the
conversion from a cambridge file to a See you file is correct, the
data supplied by Dick Johnson's actual test polar at his weight is ...

a= 2.1
b= -4.4
c= 3.2



I just want to point out that if you have SeeYou Mobile you probably
have SeeYou and then all you need are sink numbers at three reasonably
spaced speeds and SeeYou (the desktop program not SeeYou Mobile) can
create the polar itself from these.

For sake of argument lots lock in on a fixed set of numbers and see
what the a,b,c parameters for SeeYou Mobile turn out to be.

Lets use the sink measurments of....

Airspeed Sink
53kts 1.42kts
82kts 3.50kts
109kts 7.58kts

Assume these measurements made at a weight of 685lb and a wing area of
103.8 ft2 (from wikipedia) gives a wing loading "as flown" of 6.60lb/
ft2. The wing loading is not needed to calculate the a b c parameters
but it does affect how they scale at other weights. In SeeYou and
SeeYou Mobile the "minimum weight" is a bit of a misnomer - it is
really the weight as flown that gives the sink numbers we are using. I
think this leads to some common mistakes. By just working with wing-
loading SeeYou and SeeYou Mobile easily scales the polar for different
wing loadings.

So now in SeeYou (not SeeYou Mobile) go to ToolsPolar and click the
"Add" button. SeeYou will create a new polar with Glider Type called
"default".

Change the Glide Type field to "SGS 1-35" or whatever you want.

In the minimum load field type "6.60lb/f2" -- Enter exactly what is
between the quotation marks. SeeYou is smart and will let you mix and
match different units you want in all these fields and just entering
the right unit names after the numeric values.

In the stall speed field type "37kts" (but stall speed does not get
used to calculate the a, b, c parameters.).

In the 1) row type "53kts" in the first field and "1.42kts" (not
"-1.42kts" and not "1.42" - since SeeYou may assume different units).
Then in the 2) row fields type "82kts" and "3.5kts" and in the 3)
row type "109kts" and "7.58kts"

As you enter these data pairs the Polar dialog box calculates the a,
b and c polar coefficients as

a 2.12491
b -3.3237
c 1.94564

(extra silly precision shown to show exactly what I get).

And Andy I should have made it clearer that the a, b, c coefficients
assume speed in km/h and sink in m/s but the convention here is to
scale the speed in km/h divided by 100 to get more convenient
coefficients.

Paul Remde's polar calculating spreadsheets in the "Polar Adjustment
and Conversion Spreadsheets" section at http://www.cumulus-soaring.com/polars.htm
will do these same calculations and have the benefit of showing nice
graphs etc. But I wanted to point out SeeYou can do a lot itself. The
SeeYou polar UI us a bit confusing at first until you realize you can
enter the units with the numbers.

Darryl