NDB Holds

Hi,

I'm studying for my IR and having some trouble in calculating the outbound
times. Has anyone got any easy way of calculating the times.

I'm studying for my IR and having some trouble in calculating the outbound
times. Has anyone got any easy way of calculating the times.

What I do in real life is to time the inbound, and then whatever the
error is on the inbound, I apply it to the outbound the opposite way.
It may take a couple of turns to get it right since the relationship is
not linear, but for small wind speeds compared to aircraft speeds, it
seems to work well enough.

Time outbound one minute. Time inbound. Say it's forty seconds.
That's twenty seconds too little, so next time go outbound a minute and
twenty seconds. Time the inbound. Say it's fifty-five seconds. Next
time go outbound another five seconds - that is, go out a minute and
twenty-five seconds. Iterate until happy.

If interested, the actual formula is:
(where v is velocity, t is time, and d is distance)

v = d / t
or
d = v t

The two distances (along the inbound course) will be the same, to first
order, so set them equal.

d = (v1)(t1) = (v2)(t2)

Rewrite v1 as v+w and v2 as v-w (where w is wind speed)
Rewrite t1 as t and t2 as t+d
(where d is the difference between one minute (t1) and the inbound.)

We end up with
(2w)/(v-w) = d

If I didn't mess anything up. (this doesn't take the crosswind's effect
on the half circle sizes into effect).

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.

On 10/27/06 14:35, Alan Burke wrote:
Hi,

I'm studying for my IR and having some trouble in calculating the outbound
times. Has anyone got any easy way of calculating the times.



Alan,

See Jose's answer for the timing. All I wanted to add was that you
should guestimate the crosswind correction before entering the hold,
and apply this on the first leg. Otherwise, the crosswind may really
mess with the timings.

Remember to adjust for the crosswind on the inbound leg as well ;-)

I would have guessed your question would have been more like "how do
you tell when to *begin* timing on the outbound leg".

.... perhaps that's still coming ;-)

I hope that you'll post more about your IR adventures. I sure would like
to read about them and participate in answering questions, etc.

Best Regards,

--
Mark Hansen, PP-ASEL, Instrument Airplane
Cal Aggie Flying Farmers
Sacramento, CA

Mark Hansen wrote:

On 10/27/06 14:35, Alan Burke wrote:

Hi,

I'm studying for my IR and having some trouble in calculating the outbound
times. Has anyone got any easy way of calculating the times.


Keep in mind, as you progress with this, that the "rule" is to not
exceed one minute inbound to the NDB.

Thanks guys for the response. What I suppose I am asking if how do you work
out the times (pre-planning) of the hold. I.e if you know the wind direction
and speed for the hold, I've worked out the single drift and in my notes it
says to work out the timings use 75% of the head / tail wind factor.

This is where I get stuck. How do you work that out??



"Sam Spade" wrote in message
...
Mark Hansen wrote:

On 10/27/06 14:35, Alan Burke wrote:

Hi,

I'm studying for my IR and having some trouble in calculating the
outbound times. Has anyone got any easy way of calculating the times.

Keep in mind, as you progress with this, that the "rule" is to not exceed
one minute inbound to the NDB.

In article ,
"Alan Burke" wrote:

Thanks guys for the response. What I suppose I am asking if how do you work
out the times (pre-planning) of the hold. I.e if you know the wind direction
and speed for the hold, I've worked out the single drift and in my notes it
says to work out the timings use 75% of the head / tail wind factor.

This is where I get stuck. How do you work that out??

Don't try to "work it out". Your primary job is to fly the airplane, not
work out complex geometry problems.

As you're approaching the hold, take a WAG (Wild Assed Guess) at wind
strength. In most common trainers, you'll be holding at about 90 kts. A
really big headwind component on your outbound leg would be 30 kts, making
your outbound groundspeed 60, and your inbound groundspeed 120 (double your
outbound).

So, that's pretty much an upper limit, and gives you your first WAG: with a
really honking headwind outbound, fly the outbound leg for 2 minutes.
Estimate down from the with a moderate headwind outbound, try 1.5
minutes. With little or no wind, try 1 minute. With a moderate tailwind
outbound, try 50 seconds, and with a really honking tailwind outbound, try
40 seconds. If you're trying to get things any more accurate than that,
you're doing way too much work.

It's better to fly your first outbound leg a little bit long rather than a
little bit short. If you under-estimate how long to fly outbound, by the
time you complete your inbound turn, you can be almost on top of the NDB
and not have enough time to re-intercept the inbound bearing before you
reach station passage. When that happens, you tend to just keep getting
more and more confused and lost.

But, the real way to do NBD holds is to tear that piece of crap ADF out of
the panel and train in a GPS-equipped airplane. If your school doesn't
have GPS in their trainers, find another school.

Alan,

my notes it
says to work out the timings use 75% of the head / tail wind factor.


Hmm. Why not 100 percent? The way I would do it is to figure out the
percentage the head/tail wind is of my IAS (TAS, if you want to get
precise). Then, I would correct 1 minute by that percentage. From your
notes, your supposed to take 75 percent of that percentage.

In reality, this takes way too much brain power away from controlling
the aircraft. Make intelligent guesses. E.g. your holding speed is 90
knots, your wind component is an estimated 10 knots, so you try a 10
seconds correction.

--
Thomas Borchert (EDDH)

Thomas Borchert wrote:
Alan,


my notes it
says to work out the timings use 75% of the head / tail wind factor.



Hmm. Why not 100 percent? The way I would do it is to figure out the
percentage the head/tail wind is of my IAS (TAS, if you want to get
precise). Then, I would correct 1 minute by that percentage. From your
notes, your supposed to take 75 percent of that percentage.

In reality, this takes way too much brain power away from controlling
the aircraft. Make intelligent guesses. E.g. your holding speed is 90
knots, your wind component is an estimated 10 knots, so you try a 10
seconds correction.


At 90 knots it all is just b.s. to try to placate some anal instructor
or check airperson. The holding pattern protected airspace is designed
for a jet aircraft.

At 90 knots it all is just b.s. to try to placate some anal instructor or check airperson. The holding pattern protected airspace is designed for a jet aircraft.

I wouldn't go that far. We are also building good habits and attitudes
for the future. One day we may be flying jet aircraft, who knows? The
attitudes you start out with are likely to be the attitudes you end up
with, and the skills you learn from day one are the ones that come back
to you in an emergency.

However, yes, there is plenty of room in the hold for a spam can.

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.

On 10/28/06 08:24, Sam Spade wrote:
Thomas Borchert wrote:
Alan,


my notes it
says to work out the timings use 75% of the head / tail wind factor.



Hmm. Why not 100 percent? The way I would do it is to figure out the
percentage the head/tail wind is of my IAS (TAS, if you want to get
precise). Then, I would correct 1 minute by that percentage. From your
notes, your supposed to take 75 percent of that percentage.

In reality, this takes way too much brain power away from controlling
the aircraft. Make intelligent guesses. E.g. your holding speed is 90
knots, your wind component is an estimated 10 knots, so you try a 10
seconds correction.


At 90 knots it all is just b.s. to try to placate some anal instructor
or check airperson. The holding pattern protected airspace is designed
for a jet aircraft.

Exactly. I think if you show the inspector that you:

1. consider the crosswind when taking a guess at your outbound and
inbound headings;
2. consider the head/tail wind when taking a guess at your initial
outbound timing;
3. make a reasonable adjustment to your second outbound timing after
seeing what your first inbound leg time was.

he will be impressed.

Note that in all three cases, all that will matter is that you make
the correction in the right direction; the *amount* of the correction
won't matter to them.

I know that during training, I would like to go around the holds over
and over, making minor corrections to try to get the time and heading
to work out perfectly - my instructor would just get bored and make
us move on ;-)


--
Mark Hansen, PP-ASEL, Instrument Airplane
Cal Aggie Flying Farmers
Sacramento, CA