From: svoboda@rtsg.mot.com (David Svoboda)
Subject: Re: More R/C Gliding........
Organization: Motorola Inc., Cellular Infrastructure Group
Date: Wed, 22 Jul 1992 23:33:54 GMT

Prolific today, ain't I?  :-)

In article <1992Jul18.214223.1@cc.curtin.edu.au> tmarshall01@cc.curtin.edu.au writes:

|Q:
|THERMALLING!! How does one find a thermal in an R/C plane!!
|I know over trees you can get a bit of up draft...

Tips on thermalling--

1. Look for thermalling birds.  This is a good hint of rising air.  Don't
piss them off.

2. Small, fluffy cumulous clouds indicate better thermalling weather.

3. When flying, watch the airplane closely.  Fly smoothly.  If you see
the airplane bank over of it's own volition (and you didn't get a radio
glitch), that usually means that you have a thermal on the side that the
glider banked away from.

4. If the airplane "wiggles" about the yaw axis, you have crossed a vertical
air transition, and may be in a thermal.

5.  Think of a thermal as a "bubble" of lift, rising from the ground.  Sometimes
you can circle in it, like a bird (if you can place it that well; this is difficult).
Also, the airplane sinks more when you turn.  Sometimes you just work back and 
forth across the region, always turning into the wind.  The thermal moves 
downwind, a little slower than the wind speed.

6. You don't climb with elevator.  Let the thermal do the work.

7. Don't insist on a strong rise.  If you are simply sinking more slowly, you are
gaining something.

8. A thermal is stronger, the higher you find it.  Some thermals extend up many
thousands of feet.  This can be dangerous to your airplane.  On the other hand,
when you get low, land; you probably won't find a thermal down here.

9. Find a "cruise speed" and a "thermal speed" for your particular airplane, and
memorize the elevator trim positions for these.  Cruise speed is usually your
best glide ratio; that is, it's when you cover the most ground horizontally, for
the amount of altitude you are losing.  This is typically pretty fast.  Thermal
speed is your minimum sink rate, usually just a bit faster than stall.

10. Use the cruise speed for searching, and when you find a thermal, bring it back
to thermal speed to stay with it.  Flaps and computer radios are good for this,
but the elevator trim works, too.

11. There are also "downers", usually following thermals.  These are like "inverse"
thermals, which pull your airplane down.  If you find yourself descending faster 
than you expect, don't pull up elevator, push down elevator, accelerate and get 
out of there.

12. Some sailplanes exhibit pitch changes with different rising air rates.  My
Sagitta 900 would consistently pitch down in the presence of a thermal, proportional
with the strength, so I could just hold the fuselage attitude constant and pay
attention to the elevator I was holding to do so, to guage the thermal strength.
Real boomers would require full up elevator!

13. Take a pair of binoculars along.  It really sucks to have to come down just
because the plane is getting too small.

14. You can feel a thermal pass you.  The breeze stops, it's warm and calm for a few
moments, then you feel a cool breeze.  A thermal just walked over you.  The top
extends downwind from where you are standing.

15. If you get the thermal flight of your life, pay attention to how much time you
have on your receiver batteries.  (Ask me how I know this one. :-(  )

			Dave Svoboda, Palatine, IL
Newsgroups: rec.models.rc