Looking for a math wiz!

d&tm schrieb:

if you know HDG ( ie where you are pointing), GS and TAS then there is only
1 possibility for the wind speed and direction.

Actually, there are two.

But the question was a different one. It has already been answered
pretty well, all what remains is to do the dirty work and shuffling some
formulas.

Stefan

Terry - thanks for the reply, but heading is not known.

Stefan - we need to be able to plug these known values into a formula
and kick out a result. Assuming the original responder was on the
right track, I still don't know what to do with his suggestion. Any
ideas on that? I'm not lazy, this just went over my head a long time
ago. :-)


Chad Speer
PP-ASEL, IA
ATCS, Kansas City ARTCC



On Dec 16, 4:13 pm, Stefan wrote:
d&tm schrieb:

if you know HDG ( ie where you are pointing), GS and TAS then there is only
1 possibility for the wind speed and direction.Actually, there are two.

But the question was a different one. It has already been answered
pretty well, all what remains is to do the dirty work and shuffling some
formulas.

Stefan

Stefan wrote:
d&tm schrieb:

if you know HDG ( ie where you are pointing), GS and TAS then there is only
1 possibility for the wind speed and direction.

Actually, there are two.

Eh? Not to sidetrack the thread too much, but how could there be two
wind answers?

For example on the E-6B, to solve this, you'd set TRACK up, grommet
over GS, and then look for where your TAS arc meets your drift
correction angle (HDG-TRACK). The vector back to the grommet is the
single direction and speed for the wind.

Thanks, Kev

Kev schrieb:

Eh? Not to sidetrack the thread too much, but how could there be two
wind answers?

Mathematically: There are always two square roots which solve the
equation: A positive and a negative.

Physically: If you only know GS, TAS and HDG, then you don't know
whether the wind blows from the let or from the right. (If you also know
the track, then of course there's only one solution.)

Stefan

"Stefan" wrote in message
...
Kev schrieb:

Eh? Not to sidetrack the thread too much, but how could there be two
wind answers?

Mathematically: There are always two square roots which solve the
equation: A positive and a negative.

Physically: If you only know GS, TAS and HDG, then you don't know
whether the wind blows from the let or from the right. (If you also know
the track, then of course there's only one solution.)

Of course you are correct, I meant to include Track in the knowns, (
afterall if you dont know the track whether you are the pilot or the ATC you
are really in trouble.)
terry

"Stefan" wrote in message
...
Mathematically: There are always two square roots which solve the
equation: A positive and a negative.

Physically: If you only know GS, TAS and HDG, then you don't know
whether the wind blows from the let or from the right.

While that statement is true, it doesn't cover all the possibilities.
We're talking about the case of a single aircraft? We know its HDG,
GS, TAS, but nothing else? That's only three of the six wind triangle
variables. We must know at least four to get an exact answer. With
only three knowns, there are a whole range of possible answers, since
we don't know what the wind correction angle is without knowing a CRS.

For example, for the following HDG, TAS and GS:

HDG 0
TAS 120
GS 100

All the following CRS, WD an WS are valid solutions, plus many more
in-between:

CRS WD WS
=== === ===
310 054 095
330 056 060
350 039 028
000 000 020 CRS=HDG
010 321 028
030 304 060
050 306 095

I think you were visualizing a triangle, and thought of the two obvious
solutions. But there are a lot more. Again, use the E6B method and
you'll see that any drift angle along the TAS arc contains a valid WS
and WD answer.

Regards, Kev

Kev schrieb:

I think you were visualizing a triangle, and thought of the two obvious
solutions. But there are a lot more.

Frankly, I didn't contemplate very much and just posted the obvious.

Stefan

Chad,

I think that some clarification of the use might help. I can imagine two
scenarios:

1) enroute - in this case, you know the track and ground speed from radar.
You have the filed TAS. You have no idea of the crab angle or heading. This
sounds like the information you presented in your question. However,
enroute, who cares what the wind correction is. I am having trouble
imagining how this would help a controller - in training or not.

2) terminal - in this case, you still know the track and ground speed from
radar. However, now the filed TAS is probably no longer valid since it is
probably at a lower altitude than filed and used to compute the TAS. The
plane may also be under speed constraints. On the other hand, the controller
may be vectoring so now you have an assigned heading and maybe even an
assigned speed. You also have the pressure for the area and the TAS can be
computed from that and radar data. If this were an automated computation, it
could be done on every plane that was given an assigned speed (or even IAS
queried from the pilot) and an assigned heading (or even queried from the
pilot). Now maybe not every plane can provide all of the data but certainly
some could. Enough to update the calculated wind periodically.

Scenario 2 seems to me the one that would make knowledge of the wind most
desirable. It is also the scenario that could provide additional data and
certainly provides different data than what was posed in your question.

What say you?

--
-------------------------------
Travis
Lake N3094P
PWK

Travis wrote:
*****
I think that some clarification of the use might help. I can imagine
two scenarios:

1) enroute - in this case, you know the track and ground speed from
radar. You have the filed TAS. You have no idea of the crab angle or
heading. This sounds like the information you presented in your
question. However, enroute, who cares what the wind correction is. I am
having trouble imagining how this would help a controller - in training
or not.
*****

This is for enroute training, Travis. It is not the crab angle we are
after, but the winds aloft. If we could pull the actual (or even just
forecast) winds aloft into this system, we'd be set. Unfortunately,
I'm told that data cannot be used for this purpose. I don't know if it
is inaccessible or if there is a contractual reason we can't get to it.
The bottom line is that we have only radar data to estimate the winds.

I see no other way of estimating the winds with this data. I hope that
this eventually provides us a workable solution. I've seen too many
trainees make bad decisions because they didn't consider the effects of
the wind to discount the usefulness of this information. A fair number
of operational errors occur because controllers don't use the wind to
their advantage.

By the way, my wife fell in love with Chicago on our trip last weekend,
so I'll be in your neck of the woods much more often. Atlantic
Aviation at Midway made us feel very welcome. :-)


Chad Speer
PP-ASEL, IA
ATCS, Kansas City ARTCC

"Stefan" wrote in message
...
d&tm schrieb:

if you know HDG ( ie where you are pointing), GS and TAS then there is
only
1 possibility for the wind speed and direction.

Actually, there are two.

I give up, can you please explain how there can be 2 ?