Sgs 1-35 Polars for SeeYou Mobile

On Apr 1, 7:19*am, Andy wrote:
On Apr 1, 6:13*am, AGL wrote:



On Mar 31, 10:14*pm, Randy wrote:

A friend of mine has a Schweizer 1-35 and we need to find the
correct polar numbers to put into his SeeYou Mobile program.

Check which of the three models of 1-35 it is. * Numbers for a "C"
that doesn't retract are different. There are very clear graphs of the
polars updated in 2002 in the latest Flight Manual. * There are not
too many "A" models, so I'm not sure about that one since the Flight
Manual doesn't specify differences in the polar. *Seehttp://members.goldengate.net/~tmrent/soar/docs/135/types135.htm

I use the following numbers are for a "regular" 1-35 with a
retractable wheel. The numbers are good for final glides from 5 nm
out, dry @ 685# * * (We have low cloud bases here) * I use
"SoarPilot," but a polar is a polar. *Your mileage may vary given the
wide range of wing finishes I've seen on 1-35's.

53 kts *-1.42 kts
82 kts -3.5 kts
109 kts -7.58

Be careful with that "stall speed" number. *It can vary from 30 kts to
56 kts, depending on model, flap settings, and ballast. *Check page 10
of the Flight Manual.

ms

Wow - be careful what you put into your glide calculator. You have a
lot riding on it, like your butt.

First of all, units matter. SeeYou accepts as settings a variety of
units for airspeed and vertical speed. The manual doesn't appear to
say this explicitly, but I believe you need to enter coefficients for
the polar derived from the same system of units you specify in
SeeYou's settings.

Second, a,b and c are the coefficients of a quadratic curve that is a
best fit for the glider polar. *You generate this quadratic by picking
three points off the polar - preferably for speeds that you typically
fly. Best L/D, medium cruise, fast cruise, for example. Pick speeds
for no water ballast - the computer can figure out the ballast
effects. The three pairs of speeds, plugged into the generic quadratic
formula y=ax^2+bx+c will give you three equations with three unknowns,
which you can solve using high school algebra. I suspect this is what
Paul's spreadsheet does.

If you are using knots as the units for airspeed and vertical speed
then the above pairs of polar coordinates yield:

a * * * -0.0014
b * * * 0.1197
c * * * -3.7796

This gives a polar with a best L/D of 37 at 52 knots, an L/D of 25 at
80 knots and an L/D of 17 at 100 knots.

You should check the calculations and figures yourself to ensure they
are correct as I have not looked at a polar directly and it's your
friend's but that will end up short of the airfield on final glide if
there are errors in the data or the math.

Hope that helps,

9B

While the units of sink and speed matter the convention is to use the
a, b, c quadratic coefficients with sink in m/s and speed in km/h.
Changing the units that SeeYou Mobile or SeeYou uses won't change the
values of a, b or c that you need to enter.

The Polar dialog in SeeYou (not SeeYou Mobile) has a little calculator
built in where you can enter sink vs. speed numbers and derive a, b, c
coefficients or visa versa. There the sink/speed numbers are dependent
on the display units selected but SeeYou must be internally converting
to standard units to calculate the a, b, c. Andrej can kick me if I'm
wrong.

Paul's spreadheet is very handy.

Darryl




Darryl

On Apr 1, 11:40*am, Darryl Ramm wrote:
On Apr 1, 7:19*am, Andy wrote:





On Apr 1, 6:13*am, AGL wrote:

On Mar 31, 10:14*pm, Randy wrote:

A friend of mine has a Schweizer 1-35 and we need to find the
correct polar numbers to put into his SeeYou Mobile program.

Check which of the three models of 1-35 it is. * Numbers for a "C"
that doesn't retract are different. There are very clear graphs of the
polars updated in 2002 in the latest Flight Manual. * There are not
too many "A" models, so I'm not sure about that one since the Flight
Manual doesn't specify differences in the polar. *Seehttp://members..goldengate.net/~tmrent/soar/docs/135/types135.htm

I use the following numbers are for a "regular" 1-35 with a
retractable wheel. The numbers are good for final glides from 5 nm
out, dry @ 685# * * (We have low cloud bases here) * I use
"SoarPilot," but a polar is a polar. *Your mileage may vary given the
wide range of wing finishes I've seen on 1-35's.

53 kts *-1.42 kts
82 kts -3.5 kts
109 kts -7.58

Be careful with that "stall speed" number. *It can vary from 30 kts to
56 kts, depending on model, flap settings, and ballast. *Check page 10
of the Flight Manual.

ms

Wow - be careful what you put into your glide calculator. You have a
lot riding on it, like your butt.

First of all, units matter. SeeYou accepts as settings a variety of
units for airspeed and vertical speed. The manual doesn't appear to
say this explicitly, but I believe you need to enter coefficients for
the polar derived from the same system of units you specify in
SeeYou's settings.

Second, a,b and c are the coefficients of a quadratic curve that is a
best fit for the glider polar. *You generate this quadratic by picking
three points off the polar - preferably for speeds that you typically
fly. Best L/D, medium cruise, fast cruise, for example. Pick speeds
for no water ballast - the computer can figure out the ballast
effects. The three pairs of speeds, plugged into the generic quadratic
formula y=ax^2+bx+c will give you three equations with three unknowns,
which you can solve using high school algebra. I suspect this is what
Paul's spreadsheet does.

If you are using knots as the units for airspeed and vertical speed
then the above pairs of polar coordinates yield:

a * * * -0.0014
b * * * 0.1197
c * * * -3.7796

This gives a polar with a best L/D of 37 at 52 knots, an L/D of 25 at
80 knots and an L/D of 17 at 100 knots.

You should check the calculations and figures yourself to ensure they
are correct as I have not looked at a polar directly and it's your
friend's but that will end up short of the airfield on final glide if
there are errors in the data or the math.

Hope that helps,

9B

While the units of sink and speed matter the convention is to use the
a, b, c quadratic coefficients with sink in m/s and speed in km/h.
Changing the units that SeeYou Mobile or SeeYou uses won't change the
values of a, b or c that you need to enter.

The Polar dialog in SeeYou (not SeeYou Mobile) has a little calculator
built in where you can enter sink vs. speed numbers and derive a, b, c
coefficients or visa versa. There the sink/speed numbers are dependent
on the display units selected but SeeYou must be internally converting
to standard units to calculate the a, b, c. Andrej can kick me if I'm
wrong.

Paul's spreadheet is very handy.

Darryl

Darryl

Good catch Darryl.

On that basis I believe the values a

a -0.00015
b 0.0125
c -0.5905

Of course it's RAS so you should do your own math.

9B