Busted IFR Checkride

On Fri, 23 Apr 2004 20:54:39 -0400, Roy Smith wrote:

How does it know what the wind is?

My club has the CNX-80 in four of our planes now. It's a cool radio,
but there is certainly a learning curve. I've got about 25 hours behind
box now, and havn't learned everything there is to know about it yet.

I don't know that it knows the winds. But it knows the ground track and
ground speed. It probably assumes a constant airspeed and makes
computations that way. It was interesting seeing the *shape* of the
holding pattern (as drawn on the screen) change.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

On 24 Apr 2004 16:09:14 GMT, Stan Gosnell wrote:

Matt Whiting wrote in
:

Seems like it would have to have an internal compass or some other
source of heading information to do this trick.

It has to know your heading and airspeed. Knowing this, calculating the
wind is trivial. Most boxes require the pilot to input this information,
because the normal airspeed and heading indicators don't have electric
output. With new glass cockpits, this information becomes available to the
boxes.

There's no input for either. I'd guess for holding patterns it's able to
make computations based on known GS and track; and probably it assumes a
constant airspeed.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

On Fri, 23 Apr 2004 22:54:16 -0400, Matt Whiting
wrote:

That is definitely cheating! :-)

And no apologies!!


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

"Ron Rosenfeld" wrote in message =
...
On Fri, 23 Apr 2004 20:54:39 -0400, Roy Smith wrote:
=20
How does it know what the wind is?

My club has the CNX-80 in four of our planes now. It's a cool radio, =

but there is certainly a learning curve. I've got about 25 hours =
behind=20
box now, and havn't learned everything there is to know about it yet.
=20
I don't know that it knows the winds. But it knows the ground track =
and
ground speed. It probably assumes a constant airspeed and makes
computations that way. It was interesting seeing the *shape* of the
holding pattern (as drawn on the screen) change.
=20
=20
Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

The Windows simulator for the CNX80 also changes the shape
of the hold if you alter its simulated speed during the hold.
Is that reasonably faithful to what you noticed in flight?
---JRC---

Andrew Sarangan wrote

OK, now I'm confused. If you triple the correction, wouldn't the inbound
turn be less than standard rate? What am I missing here?

Well...ignoring the turns for the moment, using the same drift
correction for the outbound leg as used on the inbound leg (with
an opposite sign of course) would result in parallel tracks. This
is one times the inbound drift (1x). Now, for a one minute pattern,
there are two standard rate turns, each requiring one minute to
complete. The distance blown off during each of the turns is the
same as one would be blown off during one of the one minute strait
legs, requiring an ammount of drift correction on the outbound leg
for each of the turns equal to the ammount used for the one minute
strait leg. All adds up to be three times (3x) the inbound drift
correction.

Yes, even the old AC 61-27C, Instrument Flying Handbook had it wrong.

Bob Moore

Bob Moore wrote

Well...Now after spell checking.."amount and straight"

Bob Moore

In article ,
Bob Moore wrote:

Andrew Sarangan wrote

OK, now I'm confused. If you triple the correction, wouldn't the inbound
turn be less than standard rate? What am I missing here?

Well...ignoring the turns for the moment, using the same drift
correction for the outbound leg as used on the inbound leg (with
an opposite sign of course) would result in parallel tracks. This
is one times the inbound drift (1x). Now, for a one minute pattern,
there are two standard rate turns, each requiring one minute to
complete. The distance blown off during each of the turns is the
same as one would be blown off during one of the one minute strait
legs, requiring an ammount of drift correction on the outbound leg
for each of the turns equal to the ammount used for the one minute
strait leg. All adds up to be three times (3x) the inbound drift
correction.

Yes, even the old AC 61-27C, Instrument Flying Handbook had it wrong.

Bob Moore

The only problem with that is it assumes that tripling the wind
correction angle triples the drift correction. For small angles, that's
a reasonable approximation (it's saying that sin(x) = x), but it falls
apart for big ones.

In a 90 kt spam can, a direct 25 kt crosswind requires a 15 degree WCA
inbound, which would mean a 45 degree WCA angle outbound. You don't
often see a 25 kt crosswind on the runway, but it's not uncommon at 3000
AGL where you might be holding. A jet holding at 180 kts will need half
the WCA you do at 90 kts.

So, yes, triple is better than double, but even better in a slow
airplane is asking the controller for longer legs! 2 minute legs will
let you fly double the inbound WCA on the outbound leg, and 3 minute
legs will make it even easier. Even easier than that is to ask for 5 or
even 10 DME legs, assuming you're so equipped (gotta love GPS).

On Sat, 24 Apr 2004 18:13:32 GMT, "John R. Copeland"
wrote:

The Windows simulator for the CNX80 also changes the shape
of the hold if you alter its simulated speed during the hold.
Is that reasonably faithful to what you noticed in flight?

I've not done that with the simulator. One of these days I'll have to play
with it. In flight, I also occasionally received messages as to what
outbound course to turn to. For example, the outbound course track was
146°, but I would get a message to turn to 154°.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

In article ,
Ron Rosenfeld wrote:

On Sat, 24 Apr 2004 18:13:32 GMT, "John R. Copeland"
wrote:

The Windows simulator for the CNX80 also changes the shape
of the hold if you alter its simulated speed during the hold.
Is that reasonably faithful to what you noticed in flight?

I've not done that with the simulator. One of these days I'll have to play
with it. In flight, I also occasionally received messages as to what
outbound course to turn to. For example, the outbound course track was
146°, but I would get a message to turn to 154°.

Outbound course or outbound heading?

Roy Smith wrote:

My club has the CNX-80 in four of our planes now. It's a cool radio,
but there is certainly a learning curve. I've got about 25 hours behind
box now, and havn't learned everything there is to know about it yet.

Nice club. Where's this, again?

- Andrew