Newbie question: staying calmly behind glider tug

One way of putting this into practical effect is, assuming the glider
gets out of position to one side:

1. Level the wings and hold your current position.

2. Start to move the glider back behind the tug in the lateral dimension
only (e.g. if you're out to the left, start to move right, but if you're
also low don't try to climb at the same time).

3. Immediately it starts to move, bring the wings level again.

4. Repeat 2 and 3 until you're behind the tug.

This worked for me when I was learning. Initially the glider moves a
long way each time, but you soon learn to anticipate and stop the
movement quicker. Once you can do this, you can start moving the glider
back into position in just two goes - one large movement and a final
correcting movement - and eventually in one go.

The same technique can work for height displacement.


Tom wrote:
In control system jargon we would say that you have more than unity
gain at 180 degrees of phase shift. What that means in English is that
by the time you recognize you need to make a correction your corrective
action is too much. So you make another corrective action to fix the
problem the first action, using even more control input. This results
in an even larger deviation in the opposite direction. And so it
goes...

Add to this that you have three control surfaces that you are
manipulating (you may feel like they are manipulating you!).

The phase shift part means you are late in recognizing you need to make
an adjustment.

Try making more timely (reduce the phase shift), but smaller
adjustments (reduce the gain). Remember, once you get a large mass in
motion (such as a turn to bring the glider back to center line) it
can't stop immediately, so you have to anticipate stopping it with
control action in the opposite direction.

Start out by towing in the morning before thermal activity starts - it
is much easier to maintain position in calm air.

Don't worry: with practice you will get comfortable with towing.

Good luck!

Tom Seim

This is a good example of "turning down the gain". When we tune control
systems we generally don't crank the gain up to the max and then reduce
it until the system becomes stable. We do the opposite: start with low
(zero) gain and gradually increase it until the system becomes
unstable.

Part of the confusion is that there are times when large control
movements are required (rolling into a steep bank turn) and times when
they aren't (flying straight and level). The student needs to be
clearly told, and told again and again, when each is appropriate.