Re: standard rate turns vs. constant rate turns...

On 04/14/07 19:57, Robert Barker wrote:
I'm trying to figure out the difference between standard rate turns versus
constant rate turns and their relationship to speed.

IIRC, a standard rate turn is 3 degrees per second and turn you 180 degrees
in 1 minute.

That's right. It's also called a 2-minute turn.

The rule of thumb for the bank angle to achieve this is to
divide the airspeed by 10 and add half the resulting answer - i.e., standard
rate at 100kts is about 15 degrees of bank... (So, if that's a standard
rate turn, what's a constant rate one? Something other than 3 degrees a
second?)

Constant rate simply means a turn at a constant rate - whether or not that
rate is the "Standard" rate. In other words, if you turn at 4 degrees per
second, it's a constant rate turn if you maintain the 4 degrees per second
throughout the turn - however it is not a standard rate turn.


But there's an indicator of rate of turn on the turn coordinator that
indicates the standard rate turn.

Actually, the instrument indicates the rate of turn - all turns; not just
standard rate turns.

The mark doesn't move. The turn
indicator is a gyro instrument just like the attitude indicator which also
indicates bank.

Oops: The turn coordinator doesn't indicate bank (at least, not primarily).
It indicates the rate of turn - how quickly your nose is moving from one
heading to the next.

Question: How can the TI always hit the same mark for a
standard rate turn independant of airspeed if, in fact, I'm turning at
different bank angles as indicated on the AI?

I think once you see the difference between bank angle (indicated by the
AI) and rate of turn (indicated by the turn coordinator) you'll answer
this question yourself.

Do a couple mental exercises, playing through a turn with a given bank
angle when the airplane is flying really slow (say 80 knots) and when it
is flying really fast (say 180 knots) and see the difference.

See, in my hood work, I've
only looked at the pitch on the AI, the TI, altitude and compass - never
thought to look at the angle of bank.

Well, if you're trying to fly a standard rate turn, you want to estimate
the angle of bank required to provide the desired turn rate. If you're
getting the desired turn rate, then the bank angle must be pretty close.


OK, next question... If I'm banking at 20 degrees and moving at 100 kts, I
will turn 180 degrees in a given amount of time and radius of turn. If I do
that same 20 degrees of bank at 60 kts, I will turn 180 degrees in a given
amount of time and radius. I know the radius between the 2 turns will be
different. My intuition says that the turn will take the same amount of
time - the radius is bigger but you're doing it faster. But the ROT I noted
above for a standard rate turn woulf seem to indicate otherwise. I know I'm
missing something but seem to be having a brain fart and can't see it. Was
gonna go up and try this out but noticed my solo endorsement was up on
Friday and my CFI won't be back in town till Monday.

Another poster showed the math to answer this question, so I won't go into
it again here. Note that this would be a good use of a simple flight simulator
too. You can try different turns at different speeds and bank angles and see
if they match up with what the books say will happen.



Thanks in advance...






--
Mark Hansen, PP-ASEL, Instrument Airplane, USUA Ultralight Pilot
Cal Aggie Flying Farmers
Sacramento, CA
.

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