Question: Standard rate turns, constant rate turns, and airspeed

"Robert Barker" wrote:

Working on getting my PPL and 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. 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?)

A standard rate turn is a specific KIND of constant rate turn. It's a
constant rate turn whose rate happens to be 3 degrees per second.

Ask your instructor to show you a chandelle or a lazy eight -- those are
maneuvers from the commercial checkride which are NOT constant rate; the
rate of turn changes throughout the maneuver. Be warned, your instructor
may be hesitant to show you these because the last time he did them is
probably the day he took his commercial checkride and he's forgotten how to
do them :-)

But there's an indicator of rate of turn on the turn coordinator that
indicates the standard rate turn. The mark doesn't move. The turn
indicator is a gyro instrument just like the attitude indicator which also
indicates bank. 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?

Because the TC isn't an ATTITUDE gyro, it's a RATE gyro. Actually, a
modern TC is designed to measure a mix of roll (bank) rate and yaw (turn)
rate. There's a lot of clever engineering that went into designing how
these little wonders work.

The TC responds to bank/roll and to turn rate.

As for the effect of speed on rate of turn, ask the baseball
pitcher about whether he would have missed the building had
he slowed down and then banked steeply?

The rate of turn decreases and the radius increases with
increased air speed (TAS) and the radius is 4 times greater
if you double the speed, so it is lost cause, unless you
have the power of an F16, you can't maintain a turn at an
85° bank in level flight.

Typical autopilot systems just do a 25° bank angle and let
the rate work itself out.


"Roy Smith" wrote in message
...
| "Robert Barker" wrote:
|
| Working on getting my PPL and 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. 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?)
|
| A standard rate turn is a specific KIND of constant rate
turn. It's a
| constant rate turn whose rate happens to be 3 degrees per
second.
|
| Ask your instructor to show you a chandelle or a lazy
eight -- those are
| maneuvers from the commercial checkride which are NOT
constant rate; the
| rate of turn changes throughout the maneuver. Be warned,
your instructor
| may be hesitant to show you these because the last time he
did them is
| probably the day he took his commercial checkride and he's
forgotten how to
| do them :-)
|
| But there's an indicator of rate of turn on the turn
coordinator that
| indicates the standard rate turn. The mark doesn't
move. The turn
| indicator is a gyro instrument just like the attitude
indicator which also
| indicates bank. 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?
|
| Because the TC isn't an ATTITUDE gyro, it's a RATE gyro.
Actually, a
| modern TC is designed to measure a mix of roll (bank) rate
and yaw (turn)
| rate. There's a lot of clever engineering that went into
designing how
| these little wonders work.

Jim,

Typical autopilot systems just do a 25° bank angle and let
the rate work itself out.


Uhm, with the proliferation of rate-based AP systems (both from S-TEC
and King), that statement simply doesn't hold true anymore for GA
aircraft. It may have been true way back (can't imagine it, really,
though, 25 degrees seems very steep), but it certainly isn't any
longer. The S-Tecs (at least the 50) do 90 percent of standard rate,
the King KAP 140 is similar.

--
Thomas Borchert (EDDH)

"Thomas Borchert" wrote in message
...
Jim,

Typical autopilot systems just do a 25° bank angle and let
the rate work itself out.


Uhm, with the proliferation of rate-based AP systems (both from S-TEC
and King), that statement simply doesn't hold true anymore for GA
aircraft. It may have been true way back (can't imagine it, really,
though, 25 degrees seems very steep), but it certainly isn't any
longer. The S-Tecs (at least the 50) do 90 percent of standard rate,
the King KAP 140 is similar.

--
Thomas Borchert (EDDH)


Thanks to everyone who replied! Grabbed some coffee and my calculator this
morning and ran thru some numbers... It seems obvios now, but not sure what
I was basing my "intuition" on...