GPS 430 or 480?

Sandy Trevor wrote in message
snip

One more really neat featu it sizes holding patterns based on your
ground speed so you'll do 1 minute legs if you just follow the line!
--Sandy, Worthington OH

Actually it does more than that. Using it in a stiff wind last week, I
found that it appears to take note of either your ground speed
variation in the turns or your outbound versus inbound ground track
and if it finds a difference, it assumes that your holding pattern
needs wind correction. Then it actually *draws* a holding pattern with
sides that are not parallel, just as you would fly in a crosswind.
This can have a downside in that if you vary your speed or track for
some other reason, it would draw an incorrect pattern.

Lee Elson wrote:
Sandy Trevor wrote in message
snip

One more really neat featu it sizes holding patterns based on your
ground speed so you'll do 1 minute legs if you just follow the line!
--Sandy, Worthington OH


Actually it does more than that. Using it in a stiff wind last week, I
found that it appears to take note of either your ground speed
variation in the turns or your outbound versus inbound ground track
and if it finds a difference, it assumes that your holding pattern
needs wind correction. Then it actually *draws* a holding pattern with
sides that are not parallel, just as you would fly in a crosswind.
This can have a downside in that if you vary your speed or track for
some other reason, it would draw an incorrect pattern.

Aha! Very interesting. There was an earlier thread about this and I never did
understand how this works. If anyone has any more detail, I'm interested in
learning about it. My partners and I are considering the GNS-480.

Dave

I'm confused I guess. Doesn't the holding pattern outline as drawn represent
the desired track for the aircraft to fly over the ground? Clearly the
heading of the aircraft will change to compensate for a crosswind but why
does the desired track change?

Doug

"Dave Butler" wrote in message
...
Lee Elson wrote:
Sandy Trevor wrote in message snip

One more really neat featu it sizes holding patterns based on your
ground speed so you'll do 1 minute legs if you just follow the line!
--Sandy, Worthington OH


Actually it does more than that. Using it in a stiff wind last week, I
found that it appears to take note of either your ground speed
variation in the turns or your outbound versus inbound ground track
and if it finds a difference, it assumes that your holding pattern
needs wind correction. Then it actually *draws* a holding pattern with
sides that are not parallel, just as you would fly in a crosswind.
This can have a downside in that if you vary your speed or track for
some other reason, it would draw an incorrect pattern.

Aha! Very interesting. There was an earlier thread about this and I never
did understand how this works. If anyone has any more detail, I'm
interested in learning about it. My partners and I are considering the
GNS-480.

Dave

Doug Easton wrote:
I'm confused I guess. Doesn't the holding pattern outline as drawn represent
the desired track for the aircraft to fly over the ground? Clearly the
heading of the aircraft will change to compensate for a crosswind but why
does the desired track change?

Don't feel bad, you're not the only one who has never been taught this. If the
wind is blowing across the inbound course, one of your turns will be upwind and
the other will be downwind. If the inbound and outbound courses are parallel and
you make standard rate turns, the radius of your turn (as observed from ground)
will be greater on the downwind turn and smaller on your upwind turn, and you'll
undershoot on the upwind turn and overshoot on the downwind turn. In order to
avoid undershoot and overshoot on the turns, you need to make the inbound and
outbound tracks closer together at the end where you turn upwind, and farther
apart at the end where you turn downwind.

If you follow the rules-of-thumb about multiplying the inbound course correction
by 2 or 3 on the outbound leg, this happens automatically. The holding pattern
is really more-or-less egg-shaped, and you roll out of your standard rate turn
right on the desired course. You shouldn't be trying to make the outbound course
parallel the inbound.

If you wanted to make the outbound parallel the inbound, you would make your
outbound course correction equal to the inbound course correction.

Dave


Doug

"Dave Butler" wrote in message
...

Lee Elson wrote:

Sandy Trevor wrote in message snip

One more really neat featu it sizes holding patterns based on your
ground speed so you'll do 1 minute legs if you just follow the line!
--Sandy, Worthington OH


Actually it does more than that. Using it in a stiff wind last week, I
found that it appears to take note of either your ground speed
variation in the turns or your outbound versus inbound ground track
and if it finds a difference, it assumes that your holding pattern
needs wind correction. Then it actually *draws* a holding pattern with
sides that are not parallel, just as you would fly in a crosswind.
This can have a downside in that if you vary your speed or track for
some other reason, it would draw an incorrect pattern.

Aha! Very interesting. There was an earlier thread about this and I never
did understand how this works. If anyone has any more detail, I'm
interested in learning about it. My partners and I are considering the
GNS-480.

Dave






--
Dave Butler, software engineer 919-392-4367

Dave Butler wrote to Doug Easton, "... you're not the only one who has never
been taught [that in a crosswind the inbound and outbound legs of a holding
pattern are not parallel]."

I figured this out when I wrote a simple holding pattern simulator and
played with it. My instructor hadn't been taught it either and was amazed by
the result.

Jon

Doug Easton wrote:
I'm confused I guess. Doesn't the holding pattern outline as drawn represent
the desired track for the aircraft to fly over the ground? Clearly the
heading of the aircraft will change to compensate for a crosswind but why
does the desired track change?

Certainly, you can track any straight line on the ground simply by
appling the correct wind correction angle. But that only covers the
inbound and outbound legs.

If you want to fly a circular arc over the ground (i.e. the inbound
and outbound turns) with any wind, you need to be continuously
changing the rate of turn, and thus the bank angle, as you progress
through the turn. If you want to fly constant bank, standard-rate
turns (as we were all taught to do), it is IMPOSSIBLE to fly an exact
racetrack pattern in anything other than calm air.

The general rule of thumb is to double (or triple, depending on the
authority you read) the inbound WCA on the outbound leg. You end up
flying some blob-shaped track instead of a nice neat racetrack, but at
least you stay on the protected side of the inbound course.