primary flight instruments on partial panel

"Greg" wrote in message
ups.com...
In primary and supporting method of attitude instrument flying, which
do you consider the primary instrument for bank in the partial panel
situation (loss of both attitude indicator and heading indicator)?
Turn coordinator or magnetic compass?

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.

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.

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 then level out, give the compass
a few seconds to stop wiggling, and then adjust your heading if you're a
little bit out. I seem to recall in the IMC rating test you have to get to
within five or ten degrees of the desired heading with one initial turn and
one "fine tune" adjustment - which is generally pretty achievable.

David C

"David Cartwright" wrote in message
...
"Greg" wrote in message
ups.com...
In primary and supporting method of attitude instrument flying, which
do you consider the primary instrument for bank in the partial panel
situation (loss of both attitude indicator and heading indicator)?
Turn coordinator or magnetic compass?

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.

The turn coordinator shows direction and rate of turn but no bank angle.
You can do a skidding standard rate turn with the wings level by applying
rudder in one direction and opposite aileron to keep the wings level. In a
coordinated turn it does somewhat show bank angle but the faster your
airspeed the more bank angle is required to achieve standard rate.

I agree with using the TC over the compass if it is avalable. Following is a
quote out of the Wikipedia, for what it's worth:
"Aircraft compass turns are used in an aircraft when other directional
instruments, such as the directional gyro or turn coordinator, have failed."
http://en.wikipedia.org/wiki/Aircraft_compass_turns


Allen

whereas the TC does show the degree to which
you're banked.

The TC does not show bank. It shows rate of turn, and has a temporary
indication of bank intended to "lead" the turn indication. If you slip
or skid, the TC will shortly indicate "straight" (non turning) flight.
Even though you are banked, you are going straight.

Nonetheless, it's what I would use as primary, if I only had that and
the whiskey compass.

Jose
--
The monkey turns the crank and thinks he's making the music.
for Email, make the obvious change in the address.

"Jose" wrote in message
t...
whereas the TC does show the degree to which you're banked.

The TC does not show bank. It shows rate of turn, and has a temporary
indication of bank intended to "lead" the turn indication. If you slip or
skid, the TC will shortly indicate "straight" (non turning) flight. Even
though you are banked, you are going straight.

Nonetheless, it's what I would use as primary, if I only had that and the
whiskey compass.

Yup. The crucial point is that the inclinometer tells you about slipping or
skidding. So if it's centered, then the TC indeed tells you whether you're
banked or level.

--Gary

In article ,
"Gary Drescher" wrote:
"Jose" wrote in message
t...

Nonetheless, it's what I would use as primary, if I only had that and the
whiskey compass.

Yup. The crucial point is that the inclinometer tells you about slipping or
skidding. So if it's centered, then the TC indeed tells you whether you're
banked or level.

--Gary

Just two weeks ago I had the wonderful experience of a real live vacuum
failure in the middle of clouds over a 200' ceiling. TC with
inclinometer to keep the wings level and GPS for navigation got me
safely down with help from ATC. I'd check the whiskey compass about once
a minute to make sure nothing was lying to me.

I always practice partial panel approaches without the GPS, but when it
happened in real life I was very happy to have it as a workload reducer.

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

On 25 Aug 2006 09:20:56 -0700, "Robert M. Gary"
wrote:


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.


Most of you guys are far better qualified as I only have an IMC
rating. This is less demanding and only valid in the UK. Only 15 hours
training are required so to keep things simple I was told to use the
second VOR dial as a reminder of present heading by setting heading at
the top of the dial. When you make a turn you don't need any maths but
look where you need to be on the VOR dial and convert it visually to a
clock face. If for example you need to turn 120° right that's 20 past
on a clock therefore double and time 40 seconds.

Timing is simply bank into a rate one turn and visually add 40 seconds
to the clock hand (or could use a timer). The only calculation needed
is to double the interpreted time. Hopefully I'll only have to use it
when renewing the rating every couple of years.

As has already been mentioned the easier way is to use the ADF needle.