Accurate plane performace?

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The Speedbyrd :


Yes I have always admired your helpful and intelligent inputs here. Don't
bother replying as I have an excellent killfile :-)


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Sorry, I was indeed sleeping a bit with the weight thing. Too many years
since I had to mess too much with it.

But please notice that I never EVER said that I was saying how to climb the
fastest (either covering the least amount of distance when climbing, nor
gaining altitude as fast as possible, nor reach altitude using as little
fuel as possible). Basically your long statement of how wrong I was is based
on trying to acheive the most efficiant climb - which I never stated it was.
Just like you trid to make it look like I thought a flight model can be
judged from one single messurement. Obviously I never stated that, and
obviously I never meant it, so why comment on it as if I made a mistake?

I can see you might interprete my "maximum lift" statement as "maximum
climb" - it is not how I read it, but I agree - it is a bit "on the edge", I
will give you that.

If you take this into account, along with the fact that I was trying to
explain a simple way of reaching max speed, I still claim my original
information is good enough to reach the ceiling - and that was what this
question was about, the rest you made up.

/Lars

"Lars Møllebjerg" wrote in message
...
But please notice that I never EVER said that I was saying how to climb
the
fastest [...] Basically your long statement of how wrong I was is based
on trying to acheive the most efficiant climb - which I never stated it
was.

No. You said that to climb, one needed to fly at the maximum speed for the
given altitude. This is simply wrong. The maximum speed for any given
altitude will NOT produce a climb.

Just like you trid to make it look like I thought a flight model can be
judged from one single messurement. Obviously I never stated that, and
obviously I never meant it, so why comment on it as if I made a mistake?

I didn't "try to make it look like" anything. You said "this is the
configuration where you should compare it to the real world aircraft to see
how well the model is done". In my reply, I even refrained from saying that
you were flat out wrong. I simply agreed that the "data point" you
described was useful, but pointed out it was not sufficient.

If anything, I gave way more benefit of the doubt than your post deserved.

I can see you might interprete my "maximum lift" statement as "maximum
climb" - it is not how I read it, but I agree - it is a bit "on the edge",
I
will give you that.

The point is that the phrase "maximum lift" is meaningless. You get the
same amount of lift at any airspeed for normal, unaccelerated flight.

If you take this into account, along with the fact that I was trying to
explain a simple way of reaching max speed, I still claim my original
information is good enough to reach the ceiling - and that was what this
question was about, the rest you made up.

"The rest you made up"? Funny. Bottom line: your advice, to fly at maximum
speed, won't allow the airplane to climb at all, never mind reach the
airplane's ceiling.

I understand your desire to save face, but revisionist history just doesn't
cut it on Usenet. Anyone can go back to your previous post to see what you
really said.

Pete

On Mon, 08 Dec 2003 02:32:58 -0600, R wrote:

With the SR-71, I mostly climb with the autopilot. Granted, I
usually set at the default 1,100 fpm climb rate, but I didn't think
that would be too much of a problem for the fastest (known) plane in
the world, a plane that pulls Mach 3.3 at 80,000 feet. At some point
well before 80,000 feet, the autopilot more or less fails, pulling the
nose up into a stall.

Checck WWW for somew real-life SR-71 procedures.

Get her supersonic at 30.000 ft (this means an IAS of about 600
kts...!!!!)... and keep that IAS during a shallow climb. Adjust the
climb rate accordingly - most important is to keep IAS. The higher you
climb, the higher gets your MACH - until you level off at 70.000 ft
with an IAS of abpout 600 kts at Mach 3.x.


Bye
Andreas

On Sun, 7 Dec 2003 at 12:41:21 in message
, Lars Møllebjerg
wrote:

By the way, saying that lift is equal to weight is a bit wierd as the lift
is a force generated, while weight isn't a force, but a number calculated
from the mass and gravity. But I guess it's one of those simplification
making it easier for people to understand.

I presume you are referring to Newton's laws. However if you want to be
pedantic then you are wrong. Weight is a force, Mass isn't. We had a
famous popular scientist who used to ask "how much does a satellite
weigh in orbit?" His answer is zero although its mass remains the same.
Two forces are cancelling out in orbit.

Weight _is_ a force, although it is a restricted case that refers only
to the force that is generated by gravity.

In what way does this 'simplification' make any difference to the
equations? Of course lift only equals weight in steady straight and
level flight.
--
David CL Francis

"David CL Francis" wrote in message
...
Its mass is the same; its weight differs. You are still being confused
between weight and mass.

It is true that its weight differs. It's farther from the Earth's center of
gravity, thus the weight is necessarily less. However, I think what Jeffrey
was trying to point out is that the satellite still does *weigh* something.
And in fact, its weight is almost as great as it would be sitting on the
surface of the Earth.

Weight is the measure that you find if you weigh something on a spring
balance.

I think this view of "weight" is what's tripping you up. The satellite in
freefall would appear to weigh nothing if weighed on a weighing scale that
is also in freefall with the satellite. However, that doesn't mean that the
satellite weighs nothing. In fact, if it weren't for its weight, it would
fly off at a tangent to its orbit.

The satellite's weight is what keeps it in orbit. It's just not true that
the satellite weighs zero in orbit. It's my impression that this is what
Jeffrey was saying in his post.

Mass is a measure of the total quantity of matter in an object. If you
are floating in deep space in free fall, then you cannot detect any
weight.

Detecting weight and the existence of weight are two different things.
Consider the folks riding the "Vomit Comet", the jet used to create freefall
conditions without going into orbit. The occupants of the aircraft during
its parabolic flight cannot detect their weight. However, it is their very
weight that keeps them accelerating toward the planet, as it always does
during the non-parablic phases of flight or even while standing on solid
ground.

However the _mass_ is the same and if a force (perhaps from a
rocket motor} is applied then the acceleration depends on the force
exerted by the rocket and the mass of the object.

I'm not sure what this has to do with the so-called "weightless satellite".

Some of the confusion arises because in the imperial system of units
there is no obvious distinction in the measurement of them.

I'm not sure that explains your confusion regarding whether a satellite in
orbit is weightless or not.

For ordinary everyday, stuck on the surface of earth, people the
distinction is subtle. To engineers, physicists and applied
mathematicians the distinction is essential.

Which is why it's odd you seem to think that a satellite in orbit is
weightless. It's not.

Pete

Peter Duniho wrote:

[confused stuff on weight snipped]

Sorry, but you are confusing mass and weight. There is no such thing as
weight. Weight is a nebulous term that non-physicists use to describe
gravitational attraction between two bodies, or so it seems to me.

A body has mass and velocity; that's all it has, it doesn't have weight. No
reflection on PD, since we all did different things at school, but this is
plain-vanilla high-school physics.

A satellite has no weight in orbit; it has mass and velocity (and therefore
momentum). The reason it doesn't fly off on a tangent is because of the
gravitational attraction between the mass of the Earth and the mass of the
satellite, exactly counter-balancing the satellite's momentum which would
act to keep it going in a straight line.

Similarly, in the Vomit Comet it is not weight that is attracting the people
towards the ground, it is the gravitational attraction between the mass of
the Earth and the mass of the people.

--
Nick

On Sun, 14 Dec 2003 at 13:08:32 in message
, Peter Duniho
wrote:
"David CL Francis" wrote in message
...
Its mass is the same; its weight differs. You are still being confused
between weight and mass.

It is true that its weight differs. It's farther from the Earth's center of
gravity, thus the weight is necessarily less. However, I think what Jeffrey
was trying to point out is that the satellite still does *weigh* something.
And in fact, its weight is almost as great as it would be sitting on the
surface of the Earth.

That is mass you are talking about. I defined weight earlier. But why
'almost' in your world?

Weight is the measure that you find if you weigh something on a spring
balance.

I think this view of "weight" is what's tripping you up. The satellite in
freefall would appear to weigh nothing if weighed on a weighing scale that
is also in freefall with the satellite. However, that doesn't mean that the
satellite weighs nothing. In fact, if it weren't for its weight, it would
fly off at a tangent to its orbit.


It is not a 'view' it is definition to help to try and help you
understand the difference between force and mass. I am not the list bit
'tripped up'.

The satellite's weight is what keeps it in orbit. It's just not true that
the satellite weighs zero in orbit. It's my impression that this is what
Jeffrey was saying in his post.

Once more, it is the satellite's MASS that keeps it in orbit and the
MASS of the earth..

Mass is a measure of the total quantity of matter in an object. If you
are floating in deep space in free fall, then you cannot detect any
weight.

Detecting weight and the existence of weight are two different things.
Consider the folks riding the "Vomit Comet", the jet used to create freefall
conditions without going into orbit. The occupants of the aircraft during
its parabolic flight cannot detect their weight. However, it is their very
weight that keeps them accelerating toward the planet, as it always does
during the non-parablic phases of flight or even while standing on solid
ground.

You are talking mass again. Weight is a force, Mass is the _quantity_ of
material in an object.

However the _mass_ is the same and if a force (perhaps from a
rocket motor} is applied then the acceleration depends on the force
exerted by the rocket and the mass of the object.

I'm not sure what this has to do with the so-called "weightless satellite".


Some of the confusion arises because in the imperial system of units
there is no obvious distinction in the measurement of them.

I'm not sure that explains your confusion regarding whether a satellite in
orbit is weightless or not.

For the last time - I am not confused.

For ordinary everyday, stuck on the surface of earth, people the
distinction is subtle. To engineers, physicists and applied
mathematicians the distinction is essential.

Which is why it's odd you seem to think that a satellite in orbit is
weightless. It's not.

I give up. Get a book on physics or applied mechanics. Perhaps someone
else might be able to help. You seem to be stuck with your preconceived
idea as to what weight and mass are, or to put it another way as to what
a force and a mass are.

If I mention that force is a vector quantity (weight is a force) and
that mass is a scalar quantity, I suppose that will mean nothing to you?

A quote from an A level physics book:
~~~~~~begin quote~~~~~~~~~~
The weight of a body is the force of gravity acting on it towards the
centre of the earth. Weight is thus a _force_ , not to be confused with
mass which is independent of the presence or absence of the earth.
~~~~~~~~~~~~~end quote~~~~~

The Gravitational force F between two particles of masses m1 and m2 , a
distance r apart ,is given by;

F=(G*m1*m2)/r^2 where G is the Gravitational constant.
--
David CL Francis

"David CL Francis" wrote in message
...
That is mass you are talking about. I defined weight earlier. But why
'almost' in your world?

That is not mass I'm talking about. It's weight, and the reason it's
"almost" the same as on the ground is that weight depends both on the masses
of the two objects being considered as well as the distance between them.
Weight decreases with the square of the distance.

It is not a 'view' it is definition to help to try and help you
understand the difference between force and mass. I am not the list bit
'tripped up'.

So you say.

The satellite's weight is what keeps it in orbit. It's just not true
that
the satellite weighs zero in orbit. It's my impression that this is what
Jeffrey was saying in his post.

Once more, it is the satellite's MASS that keeps it in orbit and the
MASS of the earth..

The mass only keeps it in orbit inasmuch as mass near another mass causes a
force. This force is weight, and the satellite in orbit has this force
called weight. Without the weight, the satellite would fly off in a
straight line. The acceleration due to weight is the only thing that allows
the satellite to follow a curved path.

[...] However, it is their very
weight that keeps them accelerating toward the planet, as it always does
during the non-parablic phases of flight or even while standing on solid
ground.

You are talking mass again. Weight is a force, Mass is the _quantity_ of
material in an object.

No, I'm talking weight. Mass is not a force. The acceleration toward Earth
is caused by a force. What force? Weight.

For the last time - I am not confused.

Yes, you keep saying that. And yet...

I give up. Get a book on physics or applied mechanics. Perhaps someone
else might be able to help. You seem to be stuck with your preconceived
idea as to what weight and mass are, or to put it another way as to what
a force and a mass are.

So you say. And yet, that's not really the problem here.

If I mention that force is a vector quantity (weight is a force) and
that mass is a scalar quantity, I suppose that will mean nothing to you?

I know the difference between a vector and a scalar. So?

A quote from an A level physics book:
~~~~~~begin quote~~~~~~~~~~
The weight of a body is the force of gravity acting on it towards the
centre of the earth. Weight is thus a _force_ , not to be confused with
mass which is independent of the presence or absence of the earth.
~~~~~~~~~~~~~end quote~~~~~

How does that contradict my statement that the satellite in orbit DOES have
weight? The satellite in orbit is affected by the force of gravity acting
on it towards the center of the Earth. Your quote defines this as "weight".
By your own quote, the satellite DOES have weight.

The Gravitational force F between two particles of masses m1 and m2 , a
distance r apart ,is given by;

F=(G*m1*m2)/r^2 where G is the Gravitational constant.

I am quite aware of that. You'll notice that this gravitational force is
the same as weight. You'll also notice that nowhere in that equation is
there any term that would differentiate between a satellite in orbit and a
satellite sitting motionless at the same distance from the planet. Both
satellites wind up with the same "F", and that "F" is their weight.

So, please...I'd love to hear you try to explain again why it is the
satellite in orbit has no weight.

Pete

On Mon, 15 Dec 2003 at 17:52:06 in message
, Peter Duniho

wrote:

No, I'm talking weight. Mass is not a force. The acceleration toward Earth
is caused by a force. What force? Weight.

A large amount of quote is not necessary here. The object in orbit or in
any trajectory around a massive object is in free fall. The path of the
object caused by gravitational attraction means that there is no force
measurable on the object (If you happened to be part of it.) If we want
to be very precise then you might detect the gravitational gradient
across the object if it had significant dimensions. Otherwise, except by
external observations, you would be unable to detect acceleration to
provide 'weight'.

No one denies the force of gravity except in the sense that other
theories claim that the effect of a large mass is to distort space.

I see now at last what you are talking about, but to call the force of
gravity 'weight' seems curious to me. Weight cannot be detected except
when a body is not in free fall. So in orbit an object has no weight.
Gravity enables 'weight' on objects that are on the surface of a body to
be measured. Astronauts cannot weigh things in orbit.
--
David CL Francis