Sharing a thermal

I'm at a pretty high sampling rate - 2 seconds I think.
At least my circles look pretty round. I don't know
how SeeYou calculates ground speed, but it stands to
reason that if you only had, say, 2 samples per circle
that might lead to an error - unless SeeYou somehow
assumes a circle through the points (seems doubtful).

The answer is pretty consistent with the bank angles
I thought I was flying based on aligning the diagonal
screws securing my instruments.

9B

At 05:24 20 October 2004, Greg Arnold wrote:
Won't SeeYou underestimate the thermalling speed because
it is
calculating speed based on the straightline distance
between different
points on a circle?


Andy Blackburn wrote:
Actual SeeYou measurements

ASW-27B dry (8.2 lbs/sf)
Altitude 13,000 ft
TAS/IAS: 71/53 mph
Measured radius: ~350 ft
Implied bank angle: 43.5 degrees
Stall speed (calculated): ~51 mph

ASW-27B wet (11.5 lbs/sf) -- prior day
Altitude 13,500 ft
TAS/IAS: 84/61 mph
Measured radius: ~515 ft
Implied bank angle: 42.5 degrees
Stall speed (calculated): ~57 mph

9B

Greg Arnold wrote in message news:0imdd.50323$hj.44614@fed1read07...
Won't SeeYou underestimate the thermalling speed because it is
calculating speed based on the straightline distance between different
points on a circle?

I was unable to duplicate SeeYou's calculations of thermaling speed. I
tried straight line between two points, fitting a circle through three
points, and calculating circumference based on a rough diameter.

I was trying to reconcile indicated airspeed I recalled from the
flight with SeeYou's numbers. But even after correcting for true
airspeed, I was still off. I finally gave up. Does anyone know how
SeeYou calculates speed in a thermal?

Chip Bearden
ASW 24 "JB"

Dnia 10/20/04 5:16 PM, U¿ytkownik Chip Bearden napisa³:

I was trying to reconcile indicated airspeed I recalled from the
flight with SeeYou's numbers. But even after correcting for true
airspeed, I was still off. I finally gave up. Does anyone know how
SeeYou calculates speed in a thermal?
Ground speed (as well as vertival speed) is an average calculated with a
few last readings. Check Options-Flight menu and values named "ground
speed filter" and "vertical speed filter".

--
Wojtus'.net __|__
FidoNet: 2:484/47 `--------o--------'

I fly into it and continue until the trend of the vario reverses to
down, then begin a turn into the lifted wing with between
30-45 degrees of bank. I've tried up to 60 degrees, and have
seen only worse climb from over 45 degrees. This in commonly
4-6 knot thermals.

Less than 30 degrees and I'm not sure I could stay in any of the thermals,
more than 45 and I think the loss of upward lift due to bank angle
exceeds any benefit from a tighter core, at least
in thermals around here.

I also tend to stay in the middle third of the thermal altitude,
so if it tops out at 9000ft agl, I'l stay between 3000-6000 ft agl,
although sometimes a little higher over unlandable or known thermal-free
terrain.

In article ,
Jim Vincent wrote:
Lets have a poll. Tell us how you thermal.

I don't believe in a shallow bank for 180 degrees. The trade off in efficiency
is more than offset by getting out of the sink and into the lift quicker.

Reichman's rules: Increase bank in sink, shallow bank as vario rises, increase
bank in lift. My numbers say min sink is 44 ktws, 30 degree min sink is 49, 45
is 52, and 60 is 63 kts.

If themals are tight and narly, then crank 45-60, decreasing with altitude as
thermals generally widen. Like many here, the screws on the instruments are
the 45 degree indicator (a golden nugget from a CSA instructor). I would
rather increase my airspeed than shallow the bank since the increase in
airspeed effectively increases the turn radius with minimal drag effects and
low time lag.

To me, crankin and bankin to get into the best lift is worth it...plus much
more fun!

Jim Vincent
N483SZ



--

------------+
Mark J. Boyd

Soccer.

Gentlemen play rugby.

junk (RWEpp) wrote in message ...
I like the trash talk, Chris. Did you ever paly basketball?

It's a workable technique, but the logic isn't wholly clear why it's
better than simply steering directly into the core.

Draw a set of concentric circles representing decreasing lift as you
move away from the core. Place your circle slightly off center. While
a widening of the turn puts you in a good position to move gracefully
into the core on the opposite side, it also steers you initially into
weaker lift and keeps you in it for several extra seconds (as your
rate of turn decreases with decreasing bank). Weaker lift, longer
exposure.

Also, as you shallow your bank, the glider opposite will begin to
catch up with you, turning inside, assuming he is not matching your
correction. And in fact, the shallower your turn, the more difficult
it will be to see since your wing blocks more of your view to the
rear, exactly where the other glider will approach you as you widen.

No danger. Simply requires an extra look before steepening into the
core.

If the gradient is strong, it's worth your while to move in quickly,
even if it briefly costs in terms of gliding efficiency. I may be
flying less effeciently, but I'm doing so in stronger lift, and I'll
return to optimum bank sooner, and centered on the core. The stronger
the gradient, the greater the payoff for letting one's impatience
rule.

As for safety, if I'm turning inside the other glider, I'm keeping it
in view. Shallowing your turn puts the other glider in your blind spot
and potentially in a position to keep your from moving gracefully into
the core. If I am breaking the established pattern, I'd much rather
keep others in view than to assume that they've seen me and depend on
them to adjust.

Steeper... gets you to better lift more quickly without traversing
weaker lift first. Shallower... well, I have to admit, it's more
graceful, though not necessarily safer, nor better for maximizing your
climb rate.