Sharing a thermal

"Eric Greenwell" wrote in message
...
Bill Daniels wrote:


Most vario's have a time constant of about 2-3 seconds or more. I put a
bunch of different varios on a test bench last winter and found some
were as
bad as 11 seconds. The average 45 degree bank thermalling turn takes
about
13 - 14 seconds

Yikes! I don't know what you are flying, but it takes my ASH 26 about 27
seconds to make one turn (50 kts IAS, 8000' msl, 8.2 lb/sq ft wing
loading). That's measured from a flight trace. My ASW 20 was a little
quicker, flying at 7.5 lb/sq ft, but nothing like 14 seconds.

Should be 17secs.

Try your flavor.
http://www.soarcsa.org/thinking_page...calculator.htm

Frank Whiteley

Try your flavor.

http://www.soarcsa.org/thinking_page...urn_radius_cal
culator.htm


Frank, the CSA website is truly impressive! Well done to you and your team.
Question though, where is the link to the Thinking Pages section? TIA.

Jim Vincent
N483SZ
illspam

"Jim Vincent" wrote in message
...
Try your flavor.

http://www.soarcsa.org/thinking_page...urn_radius_cal
culator.htm


Frank, the CSA website is truly impressive! Well done to you and your
team.
Question though, where is the link to the Thinking Pages section? TIA.

Jim Vincent
N483SZ
illspam

No such link as it wasn't quite fleshed out. We'll add one though.

Frank

At 8000' 50kts IAS = 58kts TAS, so 27 seconds would
correspond to a 40 degree bank angle. Wing loading
is only relegant to the degree that it affects stall
speed. The only relevant variables for turn radius
are ture airspeed and bank angle - assuming you are
flying in an unaccelerated condition.

Of course you can make a real fast circle if you spin
it...

9B


At 23:30 18 October 2004, F.L. Whiteley wrote:

'Eric Greenwell' wrote in message
...
Bill Daniels wrote:


Most vario's have a time constant of about 2-3 seconds
or more. I put a
bunch of different varios on a test bench last winter
and found some
were as
bad as 11 seconds. The average 45 degree bank thermalling
turn takes
about
13 - 14 seconds

Yikes! I don't know what you are flying, but it takes
my ASH 26 about 27
seconds to make one turn (50 kts IAS, 8000' msl, 8.2
lb/sq ft wing
loading). That's measured from a flight trace. My
ASW 20 was a little
quicker, flying at 7.5 lb/sq ft, but nothing like
14 seconds.

Should be 17secs.

Try your flavor.
http://www.soarcsa.org/thinking_page...adius/turn_rad
ius_calculator.htm

Frank Whiteley

Bill Daniels wrote:

"Eric Greenwell" wrote in message
...


Yikes! I don't know what you are flying, but it takes my ASH 26 about 27
seconds to make one turn (50 kts IAS, 8000' msl, 8.2 lb/sq ft wing
loading). That's measured from a flight trace. My ASW 20 was a little
quicker, flying at 7.5 lb/sq ft, but nothing like 14 seconds.


You might re-check your bank angle and your static port position error. 27
seconds seems too long.

Using Frank's calculator, 55 knots @ 35 degrees gives about the right
diameter and time. I don't know the density altitude that day, but the
speed sounds a little low. The IAS was likely 50 knots, where I usually
thermal when empty.

Looking at a contest flight, the thermal I measured then plugged into
the calculator gave 65 knots @ 40 degrees to get the right diameter and
time (27 seconds). That was a 9800' msl on a warm summer day, so the
speed seems about right; also, I was flying with water.

Next time I thermal, which might be 5 months from now, I'll have to
concentrate on bank angle more and redo the measurements. I generally
find myself flying at steeper bank angles than most pilots, except at
contests with good pilots, where it's about the same. Maybe the
instrument mounting holes on our panels aren't quite at 45 degrees...

But, what I was getting around to saying is your comment -

The average 45 degree bank thermalling turn takes about
13 - 14 seconds

may be true for you, but not most pilots, based on my observations in
sport and contest flying, where 22+ seconds is typical. Maybe you meant
your average turn?


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Eric Greenwell
Washington State
USA

"Eric Greenwell" wrote in message
...

But, what I was getting around to saying is your comment -

The average 45 degree bank thermalling turn takes about
13 - 14 seconds

may be true for you, but not most pilots, based on my observations in
sport and contest flying, where 22+ seconds is typical. Maybe you meant
your average turn?


Nope, I meant my standard thermalling turn in the Nimbus is 14 seconds, 45
degrees and 45 MPH. If the core is small, I'll tighten up to a 60 degree
bank and 48mph. Ballast will, of course, bump those numbers up a little.

Eric, I think your turns are way too shallow and fast to make use of the
strong cores.

Bill Daniels

Wow, I really appreciate all the comments on thermalling. It is
amazing how much thought and calculations go into this sport although
not all agree on the solution. Reminds me of all the advice I got on
take-off. It was all good but also different.

It would seem logical if you are in a close circle with another glider
that reducing the bank angle is the safer technique. That said if you
are not in danger of conflict then increasing the bank angle seems to
follow what I was taught and what I have read.

The last flight of this year I tried water and that brought out a lot
of flaws in my termalling technique. Controlling speed and flying
through thermals were a problem. It was like learning all over again,
although when I looked at the trace after the flight I was impressed
with my average speed. I think using smoother and less abrupt changes
is something I need to work on and some of the techniques mentioned
here seem to enforce that.

But, what I was getting around to saying is your comment -

The average 45 degree bank thermalling turn takes about
13 - 14 seconds

may be true for you, but not most pilots, based on my observations in
sport and contest flying, where 22+ seconds is typical. Maybe you meant
your average turn?


Nope, I meant my standard thermalling turn in the Nimbus is 14 seconds, 45
degrees and 45 MPH. If the core is small, I'll tighten up to a 60 degree
bank and 48mph. Ballast will, of course, bump those numbers up a little.

Eric, I think your turns are way too shallow and fast to make use of the
strong cores.

Bill Daniels

Eric &Bill
If a stall speed of a glider is 36 kt at a wing loading of 6 lb/sq/ft in a
45 deg.
it will be about 44 kt and at a 60 deg bank it will 50kt.
With a loading of 9lb/sq/ft the stall speed will be 44kt at a 45 deg bank it
will be 53kt and at a 60 deg bank it will be 61 kt.
I do not know what your respective wing loading are but both of you could be
right. It is more beneficial to turn tighter with a lighter wing loading ,
then it is
with a heavier wing loading.
Regards
Udo

Udo Rumpf wrote:


Eric, I think your turns are way too shallow and fast to make use of the
strong cores.

Bill Daniels

You might be right, but I'm not routinely outclimbed by other pilots
wherever I fly, even by US World team members, so experience suggests
I'm not too far off the mark. I do try tighter banking occasionally, and
sometimes it helps, but it usually not, so the 40 degree bank is what I
normally end up using.

Perhaps you are circling more tightly than needed, your thermals are
much smaller than the ones I encounter, or as Udo suggests, it's the
wing loading difference. Or all items...

It would be interesting to look at the circling times of good contest
pilots using contest flight files, or perhaps the OLC files. Circle time
(our primary parameter in the discussion) and circle diameter can be
obtained directly from the flight trace, the true airspeed can be
determined by noting the highest and lowest ground speeds during the
circle and taking the average. These can be plugged into Frank's web
calculator to get the bank angle.


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Eric Greenwell
Washington State
USA

Eric Greenwell wrote:

Udo Rumpf wrote:


Eric, I think your turns are way too shallow and fast to make use of the
strong cores.

Bill Daniels

Ooops! The above was written by Bill, not Udo, as I accidentally replied
to the wrong posting.

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Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA