speed record set by scramjet - fair?

Look up Newton's first law of motion, the law of inertia.

The law of inertia has nothing to do with this.

The law of inertia has nothing to do with this? It has everything to
do with it. It is usually stated thusly: An object at rest tends to
stay at rest and an object in motion tends to stay in motion with the
same speed and in the same direction unless acted upon by an
unbalanced force.

In this case, if you dropped anything at all out of that rocket at
Mach 9.5, it would contine to move at Mach 9.5 forever unless acted
upon. The jet would never have to fire its engines and it would
maintain Mach 9.5 if it weren't for the effect of air friction, the
unbalanced force. In a vacuum, the thrust required to accelerate from
Mach 0.5 to 1.0 is exactly the same force required to accelerate from
Mach 9.5 to Mach 10.0.


To accererate the
jet from Mach 9.5 to Mach 10 takes exactly the same amount of power as
accerating from 0 mph to Mach 0.5, not very much.

You are absolutely wrong on this point. The drag at Mach 9.5 is vastly
larger than the drag at 0 mph, and as such requires vastly greater amounts
of power to accomplish any acceleration. Nearly all of the power invested
is used to overcome drag, not inertia.

I see part of the problem. You, like many non-technical people, think
that inertia is only something to overcome. Inertia is as much about
the difficulty in slowing something down as it speeding something up.
I understand why you were confused about that, though, because in
common non-technical usage, the word is almost only used to mean hard
to get going, not hard to stop. But it is also inertia that keeps
objects moving.

For what it is worth, there isn't a lot of air at 100,000 feet. If I
am not mistaken, the density of air at 100,000 feet is 1/400 the air
density at 5000 feet. It is pretty thin, so that also has to be taken
into consideration when evaluating the accomplishment.



But there IS friction. In this scenario, the friction dominates the physics
completely. Your frictionless scenario is completely irrelevant.

The frictionless scenario is the starting point for understanding the
problem. Once you undersand that the plane would fly at the rocket's
speed without an engine if there were no air resistance, you can limit
the problem to analyzing the power it takes to overcome friction.
However, I admit that I did not know the velocity cubed rule. I don't
think it is basic high school physics like the first law of motion is,
but I didn't know it. I was under the impression that the relationship
between velocity and drag was linear. I never studied fluid dynamics
and made a wrong assumption. My bad. That made my comparison between
accelerating from 0.5 to 1.0 versus 9.5 to 10.0 incorrect. It makes
the achievement of the scramjet more impressive than I thought.
Thanks for educating me.


i.

This is elementary physics, a subject that it seems fewer and fewer
people have a grasp of these days.

Yes, you are demonstrating that quite well.

Well, I wasn't trying to personalize my statement and I don't think
you really needed to either. My statement is in fact true. Less and
less people have a grasp of physics these days. In point of fact, I
have a very old bachelor's degree in physical chemistry, which is not
physics per se, but I did study mechanics, if not fluid dynamics.

-- Don French


Pete

Look up Newton's first law of motion, the law of inertia.

The law of inertia has nothing to do with this.

The law of inertia has nothing to do with this? It has everything to
do with it. It is usually stated thusly: An object at rest tends to
stay at rest and an object in motion tends to stay in motion with the
same speed and in the same direction unless acted upon by an
unbalanced force.

In this case, if you dropped anything at all out of that rocket at
Mach 9.5, it would contine to move at Mach 9.5 forever unless acted
upon. The jet would never have to fire its engines and it would
maintain Mach 9.5 if it weren't for the effect of air friction, the
unbalanced force. In a vacuum, the thrust required to accelerate from
Mach 0.5 to 1.0 is exactly the same force required to accelerate from
Mach 9.5 to Mach 10.0.


To accererate the
jet from Mach 9.5 to Mach 10 takes exactly the same amount of power as
accerating from 0 mph to Mach 0.5, not very much.

You are absolutely wrong on this point. The drag at Mach 9.5 is vastly
larger than the drag at 0 mph, and as such requires vastly greater amounts
of power to accomplish any acceleration. Nearly all of the power invested
is used to overcome drag, not inertia.

I see part of the problem. You, like many non-technical people, think
that inertia is only something to overcome. Inertia is as much about
the difficulty in slowing something down as it speeding something up.
I understand why you were confused about that, though, because in
common non-technical usage, the word is almost only used to mean hard
to get going, not hard to stop. But it is also inertia that keeps
objects moving.

For what it is worth, there isn't a lot of air at 100,000 feet. If I
am not mistaken, the density of air at 100,000 feet is 1/400 the air
density at 5000 feet. It is pretty thin, so that also has to be taken
into consideration when evaluating the accomplishment.



But there IS friction. In this scenario, the friction dominates the physics
completely. Your frictionless scenario is completely irrelevant.

The frictionless scenario is the starting point for understanding the
problem. Once you undersand that the plane would fly at the rocket's
speed without an engine if there were no air resistance, you can limit
the problem to analyzing the power it takes to overcome friction.
However, I admit that I did not know the velocity cubed rule. I don't
think it is basic high school physics like the first law of motion is,
but I didn't know it. I was under the impression that the relationship
between velocity and drag was linear. I never studied fluid dynamics
and made a wrong assumption. My bad. That made my comparison between
accelerating from 0.5 to 1.0 versus 9.5 to 10.0 incorrect. It makes
the achievement of the scramjet more impressive than I thought.
Thanks for educating me.


i.

This is elementary physics, a subject that it seems fewer and fewer
people have a grasp of these days.

Yes, you are demonstrating that quite well.

Well, I wasn't trying to personalize my statement and I don't think
you really needed to either. My statement is in fact true. Less and
less people have a grasp of physics these days. In point of fact, I
have a very old bachelor's degree in physical chemistry, which is not
physics per se, but I did study mechanics, if not fluid dynamics.

-- Don French


Pete

"Don French" wrote in message
om...
The law of inertia has nothing to do with this? It has everything to
do with it.

No, it doesn't. Inertia is a very tiny component of the overall physics
problem.

[...]
In this case, if you dropped anything at all out of that rocket at
Mach 9.5, it would contine to move at Mach 9.5 forever unless acted
upon.

There IS something acting upon it. Air resistance, which is VERY
significant at that speed, even with the relatively low air density.

The jet would never have to fire its engines and it would
maintain Mach 9.5 if it weren't for the effect of air friction, the
unbalanced force.

So you DO understand that there is air friction. Amazing.

In a vacuum, the thrust required to accelerate from
Mach 0.5 to 1.0 is exactly the same force required to accelerate from
Mach 9.5 to Mach 10.0.

We are not talking about a situation in a vacuum.

I see part of the problem.

No, you don't.

You, like many non-technical people, think
that inertia is only something to overcome.

What an odd statement. Inertia is simply inertia. It's not defined by what
one does to it.

Inertia is as much about
the difficulty in slowing something down as it speeding something up.

Is not speeding something up a matter of "overcoming inertia"?

For what it is worth, there isn't a lot of air at 100,000 feet. If I
am not mistaken, the density of air at 100,000 feet is 1/400 the air
density at 5000 feet.

I don't have the exact density numbers in front of me, but you are certainly
mistaken about your method of calculating the air density at that altitude,
as well as your assumption as to just how significant drag is at that speed
and altitude.

The frictionless scenario is the starting point for understanding the
problem.

Unfortunately, you don't seem to be able to get past that starting point.

Once you undersand that the plane would fly at the rocket's
speed without an engine if there were no air resistance, you can limit
the problem to analyzing the power it takes to overcome friction.

I already understand that, and have been trying to point out all along that
the issue is "the power it takes to overcome friction". How nice of you to
finally show up at this party.

[...] It makes
the achievement of the scramjet more impressive than I thought.
Thanks for educating me.

You are quite amusing. You spend the better part of a post insinuating that
I don't know my physics, and then bury a "mea culpa" in the middle,
admitting that all along you did not have your facts straight. That's rich.

Well, I wasn't trying to personalize my statement

Of course you were...you started out accusing me of never having taken high
school physics. It doesn't get much more personal than that.

and I don't think you really needed to either.

Needed to? No...probably not. Still, it seemed quite appropriate in
context (and still does).

My statement is in fact true. Less and
less people have a grasp of physics these days.

I don't dispute that claim. I think it's ironic coming from you though.

In point of fact, I
have a very old bachelor's degree in physical chemistry, which is not
physics per se, but I did study mechanics, if not fluid dynamics.

And so? Are you trying to say that you should have known better? I'm a bit
lost as to what your point in describing your studies is.

Pete

Hi all,
(this discussion is getting rather circular)

Recently, Don French posted:
(largely snipped)

[...] In a vacuum, the thrust required to accelerate from
Mach 0.5 to 1.0 is exactly the same force required to accelerate from
Mach 9.5 to Mach 10.0.

The problem, of course, is that scramjets don't operate in a vacuum.

For what it is worth, there isn't a lot of air at 100,000 feet.

Then, what, exactly is the scramjet "breathing", and what, exactly, is
heating the leading edges of the surfaces to 2600°? Seems to be quite a
lot of air to me.

I really don't understand why aviators would rather diminish the
accomplishment than come to an understanding of it.

Neil

(Don French) wrote:


Look up Newton's first law of motion, the law of inertia.

The law of inertia has nothing to do with this.
He probably should have more accurately said that the effect of
inertia is an insignificant factor in this. You are right that it has
something to do with it.

The law of inertia has nothing to do with this? It has everything to
do with it. It is usually stated thusly: An object at rest tends to
stay at rest and an object in motion tends to stay in motion with the
same speed and in the same direction unless acted upon by an
unbalanced force.

In this case, if you dropped anything at all out of that rocket at
Mach 9.5, it would contine to move at Mach 9.5 forever unless acted
upon.
Which happens immediately due to the HUGE drag.

The jet would never have to fire its engines and it would
maintain Mach 9.5 if it weren't for the effect of air friction, the
unbalanced force.
Big "if"

In a vacuum, the thrust required to accelerate from
Mach 0.5 to 1.0 is exactly the same force required to accelerate from
Mach 9.5 to Mach 10.0.
True. Not very relevant, but true.


To accererate the
jet from Mach 9.5 to Mach 10 takes exactly the same amount of power as
accerating from 0 mph to Mach 0.5, not very much.

You are absolutely wrong on this point. The drag at Mach 9.5 is vastly
larger than the drag at 0 mph, and as such requires vastly greater amounts
of power to accomplish any acceleration. Nearly all of the power invested
is used to overcome drag, not inertia.

I see part of the problem. You, like many non-technical people, think
that inertia is only something to overcome. Inertia is as much about
the difficulty in slowing something down as it speeding something up.
I understand why you were confused about that, though, because in
common non-technical usage, the word is almost only used to mean hard
to get going, not hard to stop. But it is also inertia that keeps
objects moving.
LOL! I think you are out of your depth in this discussion. And your
trying to paint others as "non-techincal" is laughable.


For what it is worth, there isn't a lot of air at 100,000 feet. If I
am not mistaken, the density of air at 100,000 feet is 1/400 the air
density at 5000 feet. It is pretty thin, so that also has to be taken
into consideration when evaluating the accomplishment.

I don't know the amount, but yes, it is pretty thin. But drag is still
HUGE. Did you read Todd's post about how much it heated the tail
surfaces at Mach 7? That takes a huge amount of energy.


But there IS friction. In this scenario, the friction dominates the physics
completely. Your frictionless scenario is completely irrelevant.

The frictionless scenario is the starting point for understanding the
problem. Once you undersand that the plane would fly at the rocket's
speed without an engine if there were no air resistance, you can limit
the problem to analyzing the power it takes to overcome friction.
However, I admit that I did not know the velocity cubed rule. I don't
think it is basic high school physics like the first law of motion is,
but I didn't know it. I was under the impression that the relationship
between velocity and drag was linear. I never studied fluid dynamics
and made a wrong assumption. My bad. That made my comparison between
accelerating from 0.5 to 1.0 versus 9.5 to 10.0 incorrect. It makes
the achievement of the scramjet more impressive than I thought.
Thanks for educating me.


i.

This is elementary physics, a subject that it seems fewer and fewer
people have a grasp of these days.

Yes, you are demonstrating that quite well.

Well, I wasn't trying to personalize my statement and I don't think
you really needed to either. My statement is in fact true. Less and
less people have a grasp of physics these days. In point of fact, I
have a very old bachelor's degree in physical chemistry, which is not
physics per se, but I did study mechanics, if not fluid dynamics.

-- Don French


Pete

--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

Don't you think that the air is "acting upon" the vehicle? Air resistance
is heating the vehicle to temperatures greater than those in a jet engine.

Mike
MU-2

"Don French" wrote in message
om...

Look up Newton's first law of motion, the law of inertia.

The law of inertia has nothing to do with this.

The law of inertia has nothing to do with this? It has everything to
do with it. It is usually stated thusly: An object at rest tends to
stay at rest and an object in motion tends to stay in motion with the
same speed and in the same direction unless acted upon by an
unbalanced force.

In this case, if you dropped anything at all out of that rocket at
Mach 9.5, it would contine to move at Mach 9.5 forever unless acted
upon. The jet would never have to fire its engines and it would
maintain Mach 9.5 if it weren't for the effect of air friction, the
unbalanced force. In a vacuum, the thrust required to accelerate from
Mach 0.5 to 1.0 is exactly the same force required to accelerate from
Mach 9.5 to Mach 10.0.


To accererate the
jet from Mach 9.5 to Mach 10 takes exactly the same amount of power as
accerating from 0 mph to Mach 0.5, not very much.

You are absolutely wrong on this point. The drag at Mach 9.5 is vastly
larger than the drag at 0 mph, and as such requires vastly greater
amounts
of power to accomplish any acceleration. Nearly all of the power
invested
is used to overcome drag, not inertia.

I see part of the problem. You, like many non-technical people, think
that inertia is only something to overcome. Inertia is as much about
the difficulty in slowing something down as it speeding something up.
I understand why you were confused about that, though, because in
common non-technical usage, the word is almost only used to mean hard
to get going, not hard to stop. But it is also inertia that keeps
objects moving.

For what it is worth, there isn't a lot of air at 100,000 feet. If I
am not mistaken, the density of air at 100,000 feet is 1/400 the air
density at 5000 feet. It is pretty thin, so that also has to be taken
into consideration when evaluating the accomplishment.



But there IS friction. In this scenario, the friction dominates the
physics
completely. Your frictionless scenario is completely irrelevant.

The frictionless scenario is the starting point for understanding the
problem. Once you undersand that the plane would fly at the rocket's
speed without an engine if there were no air resistance, you can limit
the problem to analyzing the power it takes to overcome friction.
However, I admit that I did not know the velocity cubed rule. I don't
think it is basic high school physics like the first law of motion is,
but I didn't know it. I was under the impression that the relationship
between velocity and drag was linear. I never studied fluid dynamics
and made a wrong assumption. My bad. That made my comparison between
accelerating from 0.5 to 1.0 versus 9.5 to 10.0 incorrect. It makes
the achievement of the scramjet more impressive than I thought.
Thanks for educating me.


i.

This is elementary physics, a subject that it seems fewer and fewer
people have a grasp of these days.

Yes, you are demonstrating that quite well.

Well, I wasn't trying to personalize my statement and I don't think
you really needed to either. My statement is in fact true. Less and
less people have a grasp of physics these days. In point of fact, I
have a very old bachelor's degree in physical chemistry, which is not
physics per se, but I did study mechanics, if not fluid dynamics.

-- Don French


Pete

On Fri, 19 Nov 2004 at 22:53:26 in message
, alexy
wrote:
Jose wrote:

My first assumption is that for the same air density, the friction is
directly proportional to the speed of the aircraft.

Nope. To oversimplify, it goes as the cube at subsonic speeds. Once
supersonic other terms enter the equation. So at Mach 10 the scramjet
would
have to exert more than 1000 times the thrust as for Mach 1 at the
same altitude. And a scramjet can't run from a standing stop.

Jose
Jose, hopefully someone will correct me if I'm wrong, but the drag
(and the thrust needed to overcome it) increase with the square of
velocity. It is the power needed that increases with v^3.

Perhaps it is time to insert the simple fundamental equation of
aerodynamic drag.

Drag = 0.5 * (air density)* ( a representative area - commonly wing
area )*(velocity squared)*( a 'constant that depends mostly on shape)

If using pounds divide the result by 'g': 32.2 ft/(second squared) for
an answer in pounds.

The speed of sound in air is proportional to the square root of the
absolute temperature of the air. Thus in the standard atmosphere the
speed of sound falls from 1,117 ft/sec at sea level to 968.5 ft sec at
36,000 ft. Above that it is constant up to around 80,000 ft when it
starts to rise again up to about 175,000 ft when it starts to fall
again!.

So the original simple calculation is wrong. It is more complex than I
have said as drag also depends on Mach number and a number called
Reynolds Number.

Altitude ft Speed of sound density
S.L. 1,117 ft/second 0.076475 lb/(cubic foot)
50,000 ft 968.5 ft/second 0.011642
100,000 ft 1003.2 ft/second 0.0010332

E&OE (' Errors And Omissions Excepted. That means I hope it's right but
I don't guarantee it! Check the tables yourself.)

I apologise that this is not metric units.
--
David CL Francis

Peter Duniho wrote:
Well, a) for an "air-breathing engine", Mach 10 *is* a pretty amazing speed
record to break, and b) I really don't get your interpretation of the web
page you've pointed us to.
They mention the speed here and there, but the press release announcing the
successful flight concentrates almost entirely on the technology, and
certainly the technology is not given short shrift compared to the speed
anywhere else that I can find on that site.
Maybe you could quote exact language on that site that illustrates your
interpretation? Please don't forget to explain how the language negates all
the other mentions of the technology.

In addition, these press releases are released by NASA public relations
people. The scientists and engineers working on the project are probably
more concerned with the advancement of the technology.

--- Jay


--
__!__
Jay and Teresa Masino ___(_)___
http://www2.ari.net/jmasino ! ! !
http://www.oceancityairport.com
http://www.oc-adolfos.com

Peter Duniho wrote:
Robert Briggs wrote:

Peter, your grasp of the physics of the matter seems to be substantially
better than Don's (not that that is difficult), but I don't buy the bit
about "the scramjet [being] the *entire* source of the speed".

Todd's interpretation of my statement was exactly correct. This particular
scramjet had limited fuel available, and all scramjets have the limitation
that they only operate in supersonic flight. These limitations forced the
use of a bomber and support rocket. But the thrust generated *exceeded*
that provided by the rocket, which is why the scramjet was able to
accelerate after being released from the rocket.

Right.

The flight is a *proof-of-concept* for something which would require at
least one non-scramjet engine type to make a self-contained system.

Yes, it has always been understood that a scramjet by itself is not very
useful, since it can't be used from a standing start.

Agreed.

I simply think that your wording about "the scramjet [being] the
*entire* source of the speed", rather than its being "sufficiently
powerful to complete the acceleration to Mach 10" (or something to that
effect) is a tad loose.

"Robert Briggs" wrote in message
...
[...]
I simply think that your wording about "the scramjet [being] the
*entire* source of the speed", rather than its being "sufficiently
powerful to complete the acceleration to Mach 10" (or something to that
effect) is a tad loose.

It is the entire source of the speed. Had the scramjet not been operating
when it disconnected from the rocket, it would have quickly slowed to
subsonic speed and of course would eventually have come to a complete stop.
The speed of the rocket simply ensured proper operation of the scramjet
engine...in the end, it's contribution to the final speed of the scramjet
vehicle is irrelevant.

An engine sufficiently powerful to accelerate the test vehicle from Mach 9
to Mach 10 is sufficiently powerful to accelerate the test vehicle from 0
mph to Mach 10. There's nothing loose about that statement at all, and it's
perfectly correct. The rocket used to launch the scramjet has nothing to do
with how powerful the scramjet is, or its final speed. Only the scramjet
itself does.

Pete