David Cartwright wrote:
"Greg" wrote in message
ups.com...

The turn co-ordinator is your primary measure of bank, for a couple of
reasons. First, the compass doesn't measure bank angle - it just shows what
direction you're pointing in - whereas the TC does show the degree to which
you're banked. Second, and most importantly, because of the way it's put
together, the compass doesn't turn steadily, and so it'd be wrong to fool
yourself into thinking that the faster the compass was moving, the more
you're banked.

In a full panel your primary bank is, of course, your heading indicator
in straight flight. Yet it also does not indicate bank angle.

Have a go one day and you'll see. Take someone competent with you to look
out of the window, get to a safe place and height, make sure your DI's set
correctly, and do a rate-one turn through 720 degrees or more (go around as
much as you like, in fact). In the northern hemisphere at least, you'll note
that when the DI goes through 090 or 270, the compass stands a fair chance
of agreeing with the DI. As you go through north, though, the compass will
under-read, and as you go through south, it'll over-read. The only time you
can rely on the compass is when going in a straight line - which is why you
always check and adjust your DI when flying in a straight line.

Actually the compass is very predicatable in a standard rate turn and
its effect is well known and commonly taught to students as "compass
turns" as described in the FAA publication I posted earlier.


Hence if you want to do a partial-panel turn in IMC, you fly straight and
check the compass, then do a rate-one turn (the turn co-ordinator shows you
the bank angle) for the required number of seconds - three degrees per
second for a rate-one turn, of course.

You are describing "timed turns". That is a different technique than
"compass turns". Both are commonly taught to instrument students in the
U.S. and both result in very exact heading changes when understood.
Both are very difficult in turb though.

-Robert, CFII