Scratching
MIKE BROOKS
does anyone have tips about thermalling when
at ,say, 1000 feet (and sweating)?
Prior to pattern entry at my home field, I can
usually find some 0-sink to 1/2-knot lift to
work for a while, but I can never sustain it
well enough to make the save and climb out.
Being blown downwind takes on added significance
while trying to keep the field in sight.
Hints? -- Or do I just need to "thermal better"
down low? BTW -- my personal cutoff at this time
is 1100' AGL -- I'm not looking to thermal into the
ground, just practice low saves.
Mike Brooks
bro...@imsl.com
Kevin Ford
>In addition to the existing thermalling thread,
>does anyone have tips about thermalling when
>at ,say, 1000 feet (and sweating)?
>Being blown downwind takes on added significance
>while trying to keep the field in sight.
>Hints? -- Or do I just need to "thermal better"
>down low? BTW -- my personal cutoff at this time
>is 1100' AGL -- I'm not looking to thermal into the
>ground, just practice low saves.
Here in the Midwest we get a lot of practice in scratching. I have had
three saves at 500' AGL this season (2 of them in one cross-country
flight). Thermals down below 1000' tend to be smaller and more
turbulent than they are at higher altitudes. For this reason and the
fact that you are fairly close to the ground, I like to fly about 5 mph
faster than optimum thermalling speed. One of the thermals that saved
me was causing "jumps" of 10 mph in my airspeed. Get lots of practice
near your home airport before trying this on a cross-country.
One of the harder parts of scratching is judging whether a bump you feel
is a bona-fide thermal that you can stay in or a "teaser" before you
initiate a turn. I like to have 2-3 seconds of good lift before
turning. A couple of other rules that I use for scratching below 1000'
on a cross-country are
1) have a good landing field very close by
2) abandon the thermal if I don't get lift all the way around the
first turn (or any turn thereafter if I'm still below 1000').
Everyone should have there own personal cutoff altitude, below which you
are committed to land, regardless of what lift you encounter.
Happy scratching!
Kevin Ford
fo...@symcom.math.uiuc.edu
Bruce...@bbs.actrix.gen.nz
> In addition to the existing thermalling thread,
> does anyone have tips about thermalling when
> at ,say, 1000 feet (and sweating)?
>
> Prior to pattern entry at my home field, I can
> usually find some 0-sink to 1/2-knot lift to
> work for a while, but I can never sustain it
> well enough to make the save and climb out.
>
> down low? BTW -- my personal cutoff at this time
> is 1100' AGL -- I'm not looking to thermal into the
> ground, just practice low saves.
Yeah, I usually find the best thermals of the day while on base leg
for landing :-(
I've just started flying for the season (it's early spring here in New
Zealand) -- actually the last two weeks are essentially my first
gliding in about five years -- and the lift isn't all that good yet.
This last Wednesday was a windless blue day and a very pleasant day to
be on the field, but by the time I got into the air at 3:30 pm it was
dying. I managed to do 39 minutes in the Blanik from a 2500 ft tow, but
I don't think I gained any height at any stage during the flight -- just
slowed the descent to 20 or 30 fpm in various very weak thermals. The
one exception to the "no climb" claim I just made is that at 1100 ft,
getting close to the circuit, I found a little lift. About five
minutes of scratching got me to 1200 ft, but two minutes later I was
back down to 1100 ft again and gave it away...
The good news is that after two dual flights -- a brief and very rough
flight two weeks ago in rotor conditions and a flight of stalls,
incipient spins, steep turns and a simulated field landing this week
-- I've been cleared to get out of the Blanik into the K6 next time.
Hopefully that will be this week.
--
Bruce...@bbs.actrix.gen.nz Twisted pair: +64 4 477 2116
BIX: brucehoult Last Resort: PO Box 4145 Wellington, NZ
"Cray's producing a 500 MIPS personal computer with 256MB RAM and 8 GB
hard disk that fits in your pocket!" "Great! Is it PC compatible?"
Rich Carr
> told me that exactly *twice* he has thermaled up in the blue to the
> condensation level and had a cumulus start to form all around him -- i.e.
> he was indeed at the very top of the bubble. This is possible if the thermal
> follows the torroidal bubble model, the sailplane is well centered in the
> core and the core rate of rise exceeds the overall rate of rise by more
> than the sink rate of the sailplane. Pretty neat.
> --
> Evan Ludeman
> astroatc!lud...@spool.cs.wisc.edu
I've had this happen to me at least once. The sky was perhaps 1/10
scattered cumulus. I was climbing in a blue thermal about 1500 feet
below the predominant cloudbase when wisps began to form around me. I
widened my circle to stay in the clear and watched the wisps form a small
cloud. It only lasted a few minutes before dissipating again.
I think there are other explanations than the bubble model. In this
case, I think the thermal just happened to be moister than the rest of
the thermals, as evidenced by the lower level of condensation.
Rich Carr