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

[Robert Barker]

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?)

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? 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.

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.

Thanks in advance...

[Jose]

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

Yes. (At least for piston powered planes. Jets may use half that IIRC)

> So [...] what's a constant rate one?

Any turn at a constant rate of angular change. A standard rate turn is
an example of a constant rate turn. A half standard rate turn is another.

> the turn indicator is a gyro instrument
> just like the attitude indicator which also
> indicates bank.

It is a gyro instrument, yes, but it isn't "just like the attitude
indicator". Don't let the display confuse you. The gyro is set at an
angle, and when the airplane turns, a force develops between the
airplane and the fixed axis of the gyro. This turns an indicator. The
gyro =will= be dragged unwillingly around the turn, complaining the
whole while. (This "complaint" is the turn indication :)

By choosing the angle carefully, one can also have the =rate= of change
of bank be incorporated into the indication, providing a more rapid
response, at the expense of purity of indication.

And for your last question, yes, for that reason the standard rate turn
will indicate the same no matter what the speed and bank angle, because
the gyro is not responding to bank angle. It is responding to the
rapidity of change of nose direction.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

[Roy Smith]

"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 Macklin]

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.

[Thomas Borchert]

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)

[Robert Barker]

"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...