Is there a 'rule' when you should start turning to your next waypoint?

[Simon]

Hi,

I fly mainly Boeing and Airbus.

When I try to follow a flight plan, (either created by me or one that I
picked up on the net), I never seem to be able to turn properly, (either
too late or too soon).

Lets say that I am going from A > B > C, (cruising).

My heading from A > B is 0 degrees and the heading from B > C is 90 degrees.
If I am flying at 300Kts, when should I start my turn?
I aim for a 3 degree minute as a rate of turn, is is too much?

How would a pilot handle such a turn?

My other question is, when I fly from South Africa to London, I never
notice any turns apart for departure and approach.
Is it because the pilot is very good or do they plan their flights to be
mostly a straight line?

Thanks


Simon

[WayPoint]

Hi,

The next waypoint?
Isn't one of me bad enough? :-)

[Tom P]

Post by Simon
Hi,
I fly mainly Boeing and Airbus.
When I try to follow a flight plan, (either created by me or one that I
picked up on the net), I never seem to be able to turn properly, (either
too late or too soon).
Lets say that I am going from A > B > C, (cruising).
My heading from A > B is 0 degrees and the heading from B > C is 90 degrees.
If I am flying at 300Kts, when should I start my turn?
I aim for a 3 degree minute as a rate of turn, is is too much?
How would a pilot handle such a turn?
My other question is, when I fly from South Africa to London, I never
notice any turns apart for departure and approach.
Is it because the pilot is very good or do they plan their flights to be
mostly a straight line?
Thanks
Simon

I believe waypoints can be defined as either fly-over or fly-by.
Fly-over means what it says. Fly-by means you should stay as close as
possible to the straight paths between the waypoints.
The point where you need to start the turn depends on your turn radius,
which depends on the bank angle and the square of the speed.
There are formulae for calculating the turn radius, for example
http://www.flightlearnings.com/radius-of-turn/443/
The formula for 300 knots and 30° bank gives a trun radius of
13845 feet or just over 2 nautical miles.

[WayPoint]

I believe waypoints can be defined as either fly-over or fly-by. Fly-over
means what it says.

I get that a lot.
The good looking chicks just fly-by or fly-over me.

Such is life ....... :-/

[Simon]

Post by Tom P
I believe waypoints can be defined as either fly-over or fly-by.
Fly-over means what it says. Fly-by means you should stay as close as
possible to the straight paths between the waypoints.

You mention fly-over and fly-by, but I think fly-over is not as straight
forward, do you fly-over with the 'from' heading or the 'to' heading?

Because if you fly-over with the 'from' heading then I guess it is
fairly straight forward, but to fly over with the 'to' heading is not as
easy.

Post by Tom P
The point where you need to start the turn depends on your turn radius,
which depends on the bank angle and the square of the speed.
There are formulae for calculating the turn radius, for example
http://www.flightlearnings.com/radius-of-turn/443/
The formula for 300 knots and 30° bank gives a trun radius of
13845 feet or just over 2 nautical miles.

Very interesting read thanks

Simon

[Vic Baron]

Post by Simon

Post by Tom P
I believe waypoints can be defined as either fly-over or fly-by.
Fly-over means what it says. Fly-by means you should stay as close as
possible to the straight paths between the waypoints.

You mention fly-over and fly-by, but I think fly-over is not as straight
forward, do you fly-over with the 'from' heading or the 'to' heading?
Because if you fly-over with the 'from' heading then I guess it is fairly
straight forward, but to fly over with the 'to' heading is not as easy.
Simon

It makes no difference, you fly until the to/from changes. If you're on the
proper radial either to or from, you will be over the facility when it
changes. You could also use DME if available BUT you still have to be on the
radial in order to fly over.

Vic

[boB-copter six]

Post by Vic Baron
It makes no difference, you fly until the to/from changes. If you're on
the proper radial either to or from, you will be over the facility when
it changes. You could also use DME if available BUT you still have to be
on the radial in order to fly over.
Vic

When I flew waypoints it was with an Inertial Navigation System (OH58D)
which was never accurate but on the yearly Instrument Checkrides the
Evaluator would always insert intersections in the flight plan. With
one VOR and one OBS we had to fly the FROM needle while periodically
switching to the second VOR and using the OBS to determine if we had
reached the intersection yet. Once we determined we were over the
intersection (needle swing) we could then make our turn to whichever
navaid was next.

If the intersection was made up of a VOR and an ADF we were in heaven.
Fly the FROM arrow until the NDB needle indicated we were over the
intersection then turn to where-ever.
--
____^____
===========================
boB Copter Six
Central Texas KGRK
DCA 1720 QB Norfolk
===========================
____<>____
<>

|¯ |¯| |¯| ¯|¯ |¯ |¯| |¯
|_ |_| |¯ | |¯ |¯\ |¯|
¯ ¯

[Simon]

Post by Vic Baron
It makes no difference, you fly until the to/from changes. If you're on
the proper radial either to or from, you will be over the facility when
it changes. You could also use DME if available BUT you still have to be
on the radial in order to fly over.

Yes, it does make a difference, I was not taking about to/from VOR I was
talking about to/from waypoints.

If I am going from A > C via B and I want to 'fly-over' B then, do I fly
over B with the heading A > B or the heading B > C.

Flying over with the heading A > B is straight forward, (Turn toward C
as soon as you fly over B), but flying over with the heading C is a lot
more complicated.

Hope this makes more sense.

Simon

[Mxsmanic]

Post by Simon
If I am going from A > C via B and I want to 'fly-over' B then, do I fly
over B with the heading A > B or the heading B > C.

You fly over B with the A > B heading, then make your turn.

A fly-over waypoint does not allow a turn until the waypoint is overflown. A
fly-by waypoint allows for a turn that anticipates the course change and may
begin before the waypoint is reached.

See the FAA Instrument Procedures Handbook for details; it discusses the
difference at several points, with illustrations.

[Simon]

If I am going from A> C via B and I want to 'fly-over' B then, do I fly
over B with the heading A> B or the heading B> C.

You fly over B with the A> B heading, then make your turn.
A fly-over waypoint does not allow a turn until the waypoint is overflown. A
fly-by waypoint allows for a turn that anticipates the course change and may
begin before the waypoint is reached.

I did not know that. Thanks

See the FAA Instrument Procedures Handbook for details; it discusses the
difference at several points, with illustrations.

I just did a quick search online and I see that it is available.
I'll have a read to see what it says.

Many thanks

Regards,

Simon

[Mxsmanic]

Post by Simon
I just did a quick search online and I see that it is available.
I'll have a read to see what it says.

There's a bunch of literature available for free download from the FAA Web
site ... enough to give yourself a complete ground school course.

[Matthias Ruckenbauer]

Post by Simon
Hi,
I fly mainly Boeing and Airbus.
When I try to follow a flight plan, (either created by me or one that
I picked up on the net), I never seem to be able to turn properly,
(either too late or too soon).
Lets say that I am going from A > B > C, (cruising).
My heading from A > B is 0 degrees and the heading from B > C is 90
degrees. If I am flying at 300Kts, when should I start my turn? I aim
for a 3 degree minute as a rate of turn, is is too much?
How would a pilot handle such a turn?

I wouldn't know, because I am no pilot, so I derived the formula for
myself now.
I assume now, that you have a "fly-by" waypoint, such as a VOR, where
you come from one radial and change to another without ever over the VOR
itself.
The distance before this waypoint, where you have to begin to turn will
depend on three things:
1) your groundspeed (GS),
2) the turning angle (alpha) and
3) your rate of turn.
The third one is not really a variable, because you are supposed to make
standard ('2 minute'; 2°/second) turns and thus it is a function of the
groundspeed. Tom already posted a link to a calculator for the radius of
such a turn.
This is leaving us only groundspeed and turning angle as input.
The *exact* formula for the distance is

x(nm)=GS(kt)/(60*pi)*tan(alpha/2)

For your example with 300kt an 90° turning angle you get
300/(60*pi)*tan(90/2) = 1.59nm.

I assumed the groundspeed to be in kt and alpha in degrees.
This is not very handy if you have no calculator.
For turning angles below 60° you can get a rough estimate using:

x(nm)~[(GS/1000)*5-10%]*(alpha/90)

above that you would have to correct by 10% for 80° and +20% for 90°
(estimate inbetween this values).

For your example with 300kt and 90* turning angle you get thus
[(300/1000)*5*0.9]*90/90*1.2 =
= [1.5*0.9]*1*1.2 = 1.62nm
which is slightly overestimated (which is a good thing, *never*
underestimate distances you need for anything!).

Probably there is a better rule of thumb for this somehwere, but this
should work.

Regards

Matthias

[Simon]

Post by Matthias Ruckenbauer
I wouldn't know, because I am no pilot, so I derived the formula for
myself now.
I assume now, that you have a "fly-by" waypoint, such as a VOR, where
you come from one radial and change to another without ever over the VOR
itself.
The distance before this waypoint, where you have to begin to turn will
1) your groundspeed (GS),
2) the turning angle (alpha) and
3) your rate of turn.

Ok,

Post by Matthias Ruckenbauer
The third one is not really a variable, because you are supposed to make
standard ('2 minute'; 2°/second) turns and thus it is a function of the
groundspeed. Tom already posted a link to a calculator for the radius of
such a turn.
This is leaving us only groundspeed and turning angle as input.
The *exact* formula for the distance is
x(nm)=GS(kt)/(60*pi)*tan(alpha/2)
For your example with 300kt an 90° turning angle you get
300/(60*pi)*tan(90/2) = 1.59nm.

So, assuming a perfect speed/rate of turn, I should start 1.59nm before
the waypoint my turn?

Post by Matthias Ruckenbauer
I assumed the groundspeed to be in kt and alpha in degrees.
This is not very handy if you have no calculator.
x(nm)~[(GS/1000)*5-10%]*(alpha/90)

I would still need a calculator for that :)

Post by Matthias Ruckenbauer
above that you would have to correct by 10% for 80° and +20% for 90°
(estimate inbetween this values).
For your example with 300kt and 90* turning angle you get thus
[(300/1000)*5*0.9]*90/90*1.2 =
= [1.5*0.9]*1*1.2 = 1.62nm

I would still need a calculator for that :)

Post by Matthias Ruckenbauer
which is slightly overestimated (which is a good thing, *never*
underestimate distances you need for anything!).

Many thanks for the tips, very interesting.

Simon

[Matthias Ruckenbauer]

Post by Simon

Post by Matthias Ruckenbauer
x(nm)=GS(kt)/(60*pi)*tan(alpha/2)
For your example with 300kt an 90° turning angle you get
300/(60*pi)*tan(90/2) = 1.59nm.

So, assuming a perfect speed/rate of turn, I should start 1.59nm
before the waypoint my turn?

Yes, exactly.

Post by Simon

Post by Matthias Ruckenbauer
x(nm)~[(GS/1000)*5-10%]*(alpha/90)

I would still need a calculator for that :)

Post by Matthias Ruckenbauer
For your example with 300kt and 90* turning angle you get thus
[(300/1000)*5*0.9]*90/90*1.2 = = [1.5*0.9]*1*1.2 = 1.62nm

I would still need a calculator for that :)

Well, you *could* practice before flying. ;-)
And it might be better to calculate these things during the
flight-planning. Then you can make a small table with three groundspeeds
for each turn and roughly interpolate between these values.

Post by Simon
Many thanks for the tips, very interesting.

You are very welcome. It was fun for me figuring out - I fly (simulated)
uncontrolled VFR most of the time and do my navigation only very
roughly, so I had not needed that before.

Regards

Matthias

[Simon]

Post by Matthias Ruckenbauer
You are very welcome. It was fun for me figuring out - I fly (simulated)
uncontrolled VFR most of the time and do my navigation only very
roughly, so I had not needed that before.

Thanks,

I was wondering if you, or someone else, has some insight my other
question as well.

" ...when I fly from South Africa to London, I never notice any turns
apart for departure and approach.
Is it because the pilot is very good or do they plan their flights to be
mostly a straight line?"

Thanks

Simon

[Matthias Ruckenbauer]

Post by Simon
I was wondering if you, or someone else, has some insight my other
question as well.
" ...when I fly from South Africa to London, I never notice any turns
apart for departure and approach. Is it because the pilot is very
good or do they plan their flights to be mostly a straight line?"

That's something I don't know, sorry.

Regards

Matthias

[Mxsmanic]

Post by Simon
" ...when I fly from South Africa to London, I never notice any turns
apart for departure and approach.
Is it because the pilot is very good or do they plan their flights to be
mostly a straight line?"

You won't notice them unless they are uncoordinated or you are looking out the
window. In a coordinated turn, it feels like you are climbing and then
descending; there is no sensation of turning. You may have felt as though you
were going up or down at certain points when in fact you were turning.