Ground/Air Nautical Miles

I have never really seen the terms used with light aircraft flight
planning (G.A), only with heavy aircraft flight planning. Whats the
difference between GNM and ANM?

"M.Lopresti" wrote in message
...
I have never really seen the terms used with light aircraft flight
planning (G.A), only with heavy aircraft flight planning. Whats the
difference between GNM and ANM?


A trip of 100 nm over the ground, in an hour, if into a 10 knot direct
headwind, would be a trip of 110 nm relative to still air. For logical
range calculations, the ANM concept is necessary.

John Lowry
Flight Physics

On Wed, 3 Nov 2004 at 12:33:39 in message
.net, John T Lowry
wrote:
A trip of 100 nm over the ground, in an hour, if into a 10 knot direct
headwind, would be a trip of 110 nm relative to still air.

Are you sure about that?

Aircraft flying at 200k effective speed over the ground 190 knots
agreed?
Time taken = 100/190 = 0.5263157 hours
Effective distance at 200k TAS is 200*0.5263157 = 105 .26 nm

try a very low flight speed of 50k

Effective speed 50 -10 = 40k
Time take = 100/40 = 2.5 hours
effective distance = 50*2.5 = 125 nm

Try 1000k
effective speed over ground 990k
time taken = 100/990 = 0.10101010hours
effective distance = 1000*0.1010101 = 101.1nm

If you imagine that the headwind is the same as the aircraft speed than
it makes no progress at all and covers an infinite distance through the
air to cover that 100nm.
--
David CL Francis

Divide by zero error! A division by zero is undefined, so I think
John's statement is correct. Even if you take the limit as the
effective speed goes to zero, the result is infinity, which is also,
theoretically, an undefineable number since it leads to inherent
contradictions in the strict sense. If we were to take ANM as a strict
mathematical concept, then I fear we would be laughed at. But
practically speaking, you're never going to have an effective ground
speed of 0 in an airplane.

On Thu, 4 Nov 2004 at 18:23:24 in message
. com, Raul Ruiz
wrote:
Divide by zero error! A division by zero is undefined, so I think
John's statement is correct. Even if you take the limit as the
effective speed goes to zero, the result is infinity, which is also,
theoretically, an undefineable number since it leads to inherent
contradictions in the strict sense. If we were to take ANM as a strict
mathematical concept, then I fear we would be laughed at. But
practically speaking, you're never going to have an effective ground
speed of 0 in an airplane.

That does not answer the fact that the original statement by John
appears to me to be wrong.

What is wrong with my calculations? I am perfectly willing to hear
corrections or that I was wrong.

A divide by zero error is a *computing* error that computers cannot
easily handle. There is nothing mathematically wrong with a result of
infinity.

In this case it merely represents the obvious fact that if you head into
a wind of the same strength as your cruising speed you will not get
anywhere. There is no contradiction in a result of infinity per se. Some
practical problems break down at that point. This one doesn't. The
meaning of infinity in this case is perfectly clear.

Finally a division of a real number by zero is *not* undefined, the
answer is unequivocally infinity. Zero divided by zero is undefined.

I await John's response.
--
David CL Francis

On Fri, 05 Nov 2004 15:33:21 GMT, David CL Francis
wrote:

On Thu, 4 Nov 2004 at 18:23:24 in message
.com, Raul Ruiz
wrote:
Divide by zero error! A division by zero is undefined, so I think
John's statement is correct. Even if you take the limit as the
effective speed goes to zero, the result is infinity, which is also,
theoretically, an undefineable number since it leads to inherent
contradictions in the strict sense. If we were to take ANM as a strict
mathematical concept, then I fear we would be laughed at. But
practically speaking, you're never going to have an effective ground
speed of 0 in an airplane.

That does not answer the fact that the original statement by John
appears to me to be wrong.

What is wrong with my calculations? I am perfectly willing to hear
corrections or that I was wrong.

A divide by zero error is a *computing* error that computers cannot
easily handle. There is nothing mathematically wrong with a result of
infinity.

In this case it merely represents the obvious fact that if you head into
a wind of the same strength as your cruising speed you will not get
anywhere. There is no contradiction in a result of infinity per se. Some
practical problems break down at that point. This one doesn't. The
meaning of infinity in this case is perfectly clear.

Finally a division of a real number by zero is *not* undefined, the
answer is unequivocally infinity. Zero divided by zero is undefined.

I await John's response.

I cant believe that you are asking this.
you always use the airspeed corrected for wind to determin time
enroute so that you can then determin the actual fuel consumed for the
leg.
John's response was correct.
Stealth Pilot

Brush up on your math...
http://www.math.utah.edu/~alfeld/math/0by0.html

David CL Francis wrote in message ...
On Wed, 3 Nov 2004 at 12:33:39 in message
.net, John T Lowry
wrote:
A trip of 100 nm over the ground, in an hour, if into a 10 knot direct
headwind, would be a trip of 110 nm relative to still air.

Are you sure about that?

Aircraft flying at 200k effective speed over the ground 190 knots
agreed?
Time taken = 100/190 = 0.5263157 hours
Effective distance at 200k TAS is 200*0.5263157 = 105 .26 nm

What you say confirms what John T Lowry said. He said that if you
spend an hour taking that 100nm (measured on the ground) trip into
a 10nm headwind, you add 10nm to your total air distance travelled.
Your calculations show that if you spend approximately one-half
hour going into that headwind, you'll add approximately one half
that distance, or about 5 nm.

Actually, John's original statement could have been generalized to
say that a trip of X nm over the ground in an hour, if into a 10 knot
direct headwind, would be a trip of X+10 nm relative to still air.

It could be further generalized to say that a trip of X nm over the
ground in T hours, into a Y knot headwind, will be a trip of X + T*Y
nm relative to still air. Using your numbers, we get X=100, T=.526,
Y=10, X + T*Y = 105.26nm effective distance, just as you claim.

--Rich

David CL Francis wrote in message ...
On Wed, 3 Nov 2004 at 12:33:39 in message
.net, John T Lowry
wrote:
A trip of 100 nm over the ground, in an hour, if into a 10 knot direct
headwind, would be a trip of 110 nm relative to still air.

Are you sure about that?
Aircraft flying at 200k effective speed over the ground 190 knots
agreed?
Time taken = 100/190 = 0.5263157 hours
Effective distance at 200k TAS is 200*0.5263157 = 105 .26 nm

I'm no expert, but I think you misread and overanalyzed his statement
grin.

He said the 100nm trip was actually made in 1 hour while into a 10kt
headwind. Therefore the effective speed was 110kts, and the effective
distance (which is the point of ANM) was 110nm in that 1 hour.

ANM is sometimes used to compute the theoretical range of an aircraft.
For example, you fly a prototype jumbo jet from NYC to Paris, and it
took X thousand pounds of fuel. But after you add in the headwind x
time, then you can figure out the total ANM that it it went, and thus
compute its range or fuel usage/nm.

Kev

On Fri, 5 Nov 2004 at 14:40:51 in message
, Kevin Darling
wrote:
David CL Francis wrote in message
...
On Wed, 3 Nov 2004 at 12:33:39 in message
.net, John T Lowry
wrote:
A trip of 100 nm over the ground, in an hour, if into a 10 knot direct
headwind, would be a trip of 110 nm relative to still air.

Are you sure about that?
Aircraft flying at 200k effective speed over the ground 190 knots
agreed?
Time taken = 100/190 = 0.5263157 hours
Effective distance at 200k TAS is 200*0.5263157 = 105 .26 nm

I'm no expert, but I think you misread and overanalyzed his statement
grin.

Your right - I did. See other posts.

He said the 100nm trip was actually made in 1 hour while into a 10kt
headwind. Therefore the effective speed was 110kts, and the effective
distance (which is the point of ANM) was 110nm in that 1 hour.

ANM is sometimes used to compute the theoretical range of an aircraft.
For example, you fly a prototype jumbo jet from NYC to Paris, and it
took X thousand pounds of fuel. But after you add in the headwind x
time, then you can figure out the total ANM that it it went, and thus
compute its range or fuel usage/nm.

That makes sense.
--
David CL Francis