NASA and the flat earth airplane...

Quote from: MicroBeta on March 05, 2018, 07:47:45 AM

Quote from: totallackey on March 05, 2018, 06:07:35 AM

Boy, you people are slacking...

No body has answered the question yet?

Why mention, "constant mass," at all, especially if it is non-existent?

Why mention, "flat, non-rotating," earth if it is non-existent?

All of you are sorry trolls...

Maybe I didn't explain it correctly.  It isn't so much eliminated as it is superimposed on the CG of the aircraft.

Also, you're ignoring the fact that the dynamics aren't any different whether it's on a globe or a flat earth.

So, I ask you.  What does it matter what terminology is used when the actual analytical solution is independent of the shape of the earth?

Mike

You are asking the wrong person.

The person writing the paper saw fit to specifically mention THREE criteria when it came to the model.

1) A plane of CONSTANT MASS!

2) A flat earth!

3) A non-rotating earth!

Evidently, DESPITE YOUR PROTESTS, IT DOES MATTER!

So?  Constant mass.  No need to model the fuel consumption.
Flat earth.  No need to model a curved surface to test the concept.
Non rotating.  No need to model rotation of the earth to test the concept.
Not sure why you are having trouble understanding this.
If the earth were flat they would not have mentioned those things at all.  There would be no need.  The only reason to mention them is because they know the earth is round and rotating and wanted those variables taken out of the model.

Quote from: MicroBeta on March 05, 2018, 07:47:45 AM

Quote from: totallackey on March 05, 2018, 06:07:35 AM

Boy, you people are slacking...

No body has answered the question yet?

Why mention, "constant mass," at all, especially if it is non-existent?

Why mention, "flat, non-rotating," earth if it is non-existent?

All of you are sorry trolls...

Maybe I didn't explain it correctly.  It isn't so much eliminated as it is superimposed on the CG of the aircraft.

Also, you're ignoring the fact that the dynamics aren't any different whether it's on a globe or a flat earth.

So, I ask you.  What does it matter what terminology is used when the actual analytical solution is independent of the shape of the earth?

Mike

You are asking the wrong person.

The person writing the paper saw fit to specifically mention THREE criteria when it came to the model.

1) A plane of CONSTANT MASS!

2) A flat earth!

3) A non-rotating earth!

Evidently, DESPITE YOUR PROTESTS, IT DOES MATTER!

I'm not protesting anything. I'm merely explaining how linear modeling works.   It's a standard engineering concept. You're reading way to much into it.

Mike

Quote from: MicroBeta on March 05, 2018, 07:47:45 AM

Quote from: totallackey on March 05, 2018, 06:07:35 AM

Boy, you people are slacking...

No body has answered the question yet?

Why mention, "constant mass," at all, especially if it is non-existent?

Why mention, "flat, non-rotating," earth if it is non-existent?

All of you are sorry trolls...

Maybe I didn't explain it correctly.  It isn't so much eliminated as it is superimposed on the CG of the aircraft.

Also, you're ignoring the fact that the dynamics aren't any different whether it's on a globe or a flat earth.

So, I ask you.  What does it matter what terminology is used when the actual analytical solution is independent of the shape of the earth?

Mike

You are asking the wrong person.

The person writing the paper saw fit to specifically mention THREE criteria when it came to the model.

1) A plane of CONSTANT MASS!

2) A flat earth!

3) A non-rotating earth!

Of course he did. If someone needed to model an airplane with a rapidly-changing mass, the model described wouldn't be appropriate, and he needs a different model.

For instance, a WWII-era Lancaster bomber could drop a single 22,000-pound bomb. Behavior of an aircraft whose mass suddenly changes by more than 35%, from 30 tons to 19 tons, would probably not be accurately modeled by a model that presumes constant mass. For other phases of a Lancaster's flight, the described model (using appropriate parameters for the mass at the time, of course) probably would be sufficient, since its mass would change so slowly that it could be considered static over a reasonably long period.

Evidently, DESPITE YOUR PROTESTS, IT DOES MATTER!

You're right that it does matter, but no one except you is protesting.

You wouldn't want to use this to model in situations where the mass of the aircraft is rapidly changing, or if the shape and spin of the earth is a consideration. If any of these do apply to your situation, the described model is inadequate (and that's made clear up front), and you need to use a more complete model. If the assumptions are close enough to true that they aren't significant, as they are in many, many cases, the model is sufficient.

Quote from: markjo on March 05, 2018, 07:21:27 AM

Did you miss, or just ignore this post:

Quote from: markjo on March 05, 2018, 06:39:27 AM

I could be wrong, but as near as I can tell, that linear aircraft model is pretty much a computerized equivalent to putting a model airplane into a wind tunnel for testing.  In a wind tunnel, you essentially have a flat, non-rotating earth and a rigid aircraft with a constant mass.

Seriously, just another case of totallakey making much ado about nothing.

I gave it all the respect it has coming...

So you couldn't find anything to disagree with.  Good to know.  Now back to your regularly scheduled trolling.

Quote from: MicroBeta on March 05, 2018, 07:47:45 AM

Quote from: totallackey on March 05, 2018, 06:07:35 AM

Boy, you people are slacking...

No body has answered the question yet?

Why mention, "constant mass," at all, especially if it is non-existent?

Why mention, "flat, non-rotating," earth if it is non-existent?

All of you are sorry trolls...

Maybe I didn't explain it correctly.  It isn't so much eliminated as it is superimposed on the CG of the aircraft.

Also, you're ignoring the fact that the dynamics aren't any different whether it's on a globe or a flat earth.

So, I ask you.  What does it matter what terminology is used when the actual analytical solution is independent of the shape of the earth?

Mike

You are asking the wrong person.

The person writing the paper saw fit to specifically mention THREE criteria when it came to the model.

1) A plane of CONSTANT MASS!

2) A flat earth!

3) A non-rotating earth!

Evidently, DESPITE YOUR PROTESTS, IT DOES MATTER!

You still didn't understand the answer?
Or you don't like it and it is hard to swallow?
Let me try to sugar-coat it for you:

1. To simplify behavior of the plane on "sample distances" (short distances), it is ignored the loss of mass by burning fuel off.
The "constant mass" can be set as single parameter and get equations lower number of varibles.
When the final set of the solutions is produced, they can just plug in diverent values for 'constant mass' and test in the whole range.

2. On "sample distances" (short distances), engineer can simplify further by approximation with straight path.
Planes don't always follow great circles, they curve up, down, lef, right, ...
Predictions have to include them from all directions later.

3. Non-rottaing Earth assumes no Coriolis, no centrifugal, no Eotvos or other effects, for final simplification.
Mentioned effects act one way if you go east, another if you go west, differently if you go north and differently if go south.
Since the final product will be under those effects in all directions, they will be calculated later.

So, tell us again:
"Why would they insist on 'constant mass airplane' if it doesn't exist" ?
We all know that airplane burns fuel and loses mass during flight.

Have you guys seen this?

Totally lacking I think you are being incredibly unreasonable about this whole thing. You have been given answers about the questions you keep repeating. Almost every post you make is essentially making a claim not backed up by any proof, claiming you still haven't been given the answers your looking for, and somewhere in the post insult someone. But aside from the actually reasoning behind why NASA would ignore those variables in a report, you need to look behind the logic of it. Why would they, after claiming since their formation that the world is in fact round, suddenly in a report, leave a very vague sentence proof that they in fact do know that the world is flat and have been lying about it. Then immediately after return to their original position. There is no sane reason for them to do that. Honestly it sounds about as sane as a group of people forming out of mid air to claim that well proven science is a lie and all proof has been faked by our government and every scientist is lying in a massive conspiracy, and also there are aliens I guess as well, and it sounds a bit different when each member claims what it is, and also gravity isn't actually real.

Does reading this make you realize how Preposterous it sounds, you can believe what you want, god knows I can't change your view, but think logically about the theoretical situation you are creating with this claim. A claim entirely based off a few added or missing variables that is very logically accounted for.

The person writing the paper saw fit to specifically mention THREE criteria when it came to the model.
1) A plane of CONSTANT MASS!
2) A flat earth!
3) A non-rotating earth!

Evidently, DESPITE YOUR PROTESTS, IT DOES MATTER!

Yes. I'll agree that for a completely accurate long-term simulation that these three factors matter.
But in the early design stages, there is a distinct advantage in a simpler model that can run far more rapidly on slower computers.

The NASA paper quoted in the following is an older and more detailed reference to the same simplification.

Yes, it's a simplification that is reasonably accurate:

• the mass of the aircraft is changing relatively slowly,
• the Globe is locally nearly flat and
• the Globe rotates very slowly at only at about 0.0007 rpm.

These simplifications allow much faster simulations, especially on slower computers and are quite adequate in many cases.

You might read, learn and inwardly digest, A STANDARD KINEMATIC MODEL FOR FLIGHT ANALYSIS SIMULATION AT NASA-AMES, NASA CR-2497, by Richard E. McFarland.
That should convince even a Total Lackey that NASA really does understand that the earth is really a Globe rotating at an angular rate, 7.2685X10^-3 rad/sec.

That document contains:

• in the list of symbols:
  Quote

  τ_i     vehicle’s longitude on a non-rotating earth, rad
  ω_e      earth’s angular rate, 7.2685X10^-3 rad/sec
• on page 13:
  Quote

  The rate of change in longitude over a rotating earth is equal to the inertial rate of change due to translation about the Z_E axis, minus the earth’s rate itself (derivative of 2.1) such that (2.13) may be rewritten
• and on page 21:
  Quote

  Equations (5.5) through (5.8) are “flat-earth” approximations which are only valid in the vicinity of the runway.

So I do believe that NASA fully understands that the earth is a rotating Globe.

Now I'm no Aeronautical Engineer, but I am a retired Electrical Engineer and in that models of circuits with many different levels of simplification are commonly used.
In many cases, a non-linear dc design might be performed to find the "operating points" of all the active devices and then a linear ac design for say frequency or transient response.