speed record set by scramjet - fair?

Peter,

You apparently never took high school physics. Look up Newton's first
law of motion, the law of inertia. The scramjet only had to provide
enough power to overcome the friction of air to continue at Mach 9.5
forever or until it hit something, like the earth. 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. And that is all that
the scramjet did.

Yes, if you towed a Yugo behind a Porsche, and released it at 150 mph,
it would continue at 150 mph if there were no friction of air and
road. But it could not accelerate to 180 because the means of
propulsion depend on that same friction, unlike a jet plane, which
does not use the friction, but only has to overcome it.

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

As to the media, yes I know the media gets almost everything wrong.
But the speed record claim was the topic of my post, not whether there
was a significant accomplishment in running a scramjet in an aircraft
going Mach 10.

-- Don French

I never said it wasn't a successful test, but the only thing touted in
the media was the speed it achieved and the world record it set for
speed

Who cares what the media says? If you know anything about aviation, you
know as well as the rest of us that the media does a pretty poor job of
getting facts straight, especially for technical issues like this one.

and attributed that speed to the scramjet, not the rocket.
That was just wrong. The speed was almost entirely a result of the
rocket's velocity and had nothing to do with the scramjet.

Todd already pointed out the fallacy of that statement. The fact that the
scramjet *accelerated* to the maximum speed clearly shows that the scramjet
is, in fact, the *entire* source of the speed. It produced enough thrust to
maintain Mach 10.

Your statement is like saying that if you towed a Y*go behind a Porsche and
got it up to 150 mph, that you'd be able to then simply disconnect from the
Porsche and still maintain 150 mph in the Y*go. That's simply not true. A
vehicle that can accelerate to Mach 10 from *any* speed and maintain that
speed is capable, all by itself, of that speed. It's just plain incorrect
to claim that "only the last Mach was due to the scramjet" (or however you'd
like to word it).

Seriously,
they could have dropped a Piper cub off that rocket and it could have
maintained Mach 9 for hundreds of miles.

Hundreds? I doubt it. But more importantly, it would NOT have accelerated
to Mach 10.

Should it get the world's
speed record for prop-driven planes?

In your example, the Piper Cub at no point *maintained* a record-breaking
speed.

I think not. And I think that
giving the X-43A a worlds speed record is just as fraudulent.

Well, I'm sorry your incomplete grasp of the facts makes you think that.
Fortunately, those who have a say in the matter have a better understanding
of the situation.

Pete

"Jay Masino" wrote in message news:419c904b$0

The excitement is about the technology. I think the press is making a
bigger thing about the "record" than NASA really cares about. The ability
to run a jet engine, at close to Mach 10, without bringing along an
oxygen tank, is the REAL achievement.

Exactly. All they care about is the proof of concept, although I'd be
surprised if it hasn't already been done out there. (Kinda like Cassini.)

-c

(Don French) wrote:

Peter,

You apparently never took high school physics.
Pot calling the kettle black?

Look up Newton's first
law of motion, the law of inertia. The scramjet only had to provide
enough power to overcome the friction of air to continue at Mach 9.5
forever or until it hit something, like the earth.
Odd use of the word "only". Like "only" 850-odd times as much power as
it takes to fly at Mach 1. Or does the velocity cubed relationship not
apply for air friction in supersonic flight?

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. And that is all that
the scramjet did.
BZZZT! It takes a little more power (how much more determines how
rapid the acceleration will be) to accelerate from 0 to Mach0.5 than
it takes to maintain Mach 0.5. It takes a little more power to
accelerate from 9.5 to 10 than it takes to maintain 10. And using the
cube rule, it takes 8000 times as much power to maintain mach 10 as it
does to maintain mach 0.5.

Yes, if you towed a Yugo behind a Porsche, and released it at 150 mph,
it would continue at 150 mph if there were no friction of air and
road. But it could not accelerate to 180 because the means of
propulsion depend on that same friction,
No. It has the means of friction (it's tires are on the road, at least
in this thought experiment; I'd hate to think about it in real
lifeg), just not enough power to overcome drag at 150, much less to
accelerate from that point.

unlike a jet plane, which
does not use the friction, but only has to overcome it.

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


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"Don French" wrote in message
om...
You apparently never took high school physics.

Right back at ya'.

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

The law of inertia has nothing to do with this.

The scramjet only had to provide
enough power to overcome the friction of air to continue at Mach 9.5
forever or until it hit something, like the earth.

In aircraft, that power is everything. Inertia provides very little support
to flight, and especially for light aircraft (like those we fly) and for
extremely fast aircraft (like the scramjet equipped test vehicle). And the
power required is the same whether you start at 0 mph or Mach 9.

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.

And that is all that the scramjet did.

"All". Yes, you continue to demonstrate your lack of knowledge on this
point.

Yes, if you towed a Yugo behind a Porsche, and released it at 150 mph,
it would continue at 150 mph if there were no friction of air and
road.

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

But it could not accelerate to 180 because the means of
propulsion depend on that same friction, unlike a jet plane, which
does not use the friction, but only has to overcome it.

Again, your frictionless scenario is completely irrelevant.

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.

Pete

The significance of all this is that it is an air breathing engine -
not one (like a rocket for example) that also has to bring its
oxidizer along. Yes, it takes a lot of speed to get it in positive
thrust territory, but it accelerated beyond that point to an even
higher speed. The engine is very simple in its construction and has
no primary moving parts - other than a large fuel pump.

There are more than a few details though to be ironed out before Tokyo
will be an hour away...........

The X-prize is different. They did what was required to win the
prize, which was get someone into space and return. Well, maybe the
scramjet did what was required to set the world's speed record too,
but it fails to impress since it wasn't the jet's engine that got it
going that fast. The jet only contributed the last few pounds of
thrust required to defeat air friction to keep it going at that speed
and maybe a few more to accelerate a half Mach or so.

I did a calculation that makes some assumptions that may or may not be
completely accurate. I am neither an aeronautical engineer or a fluid
dynamics expert, but I still made a go at trying to compute how
difficult it was for the scramjet to accelerate from Mach 9.5 to Mach
10.

Newton's first law of motion tells us that a plane released from a
rocket at Mach 10 will, in the absence of air friction, continue at
that speed indefinitely (or until it encounters another object, like
the Earth), and never have to turn on its engines to do so. The
scramjet only has to have enough power to overcome what little air
friction there is at 100,000 feet to maintain its release speed. The
question is how much air friction is there at Mach 10 at 100,000 feet.

Since I don't know how to compute the actual frictional effects at
that speed and altitude, it occured to me that maybe I can at least
compute the ratio between overcoming friction at that speed and
altitude and at say, Mach 1 at 5000 feet. That would provide a way of
making a comparison that makes sense to me.

My first assumption is that for the same air density, the friction is
directly proportional to the speed of the aircraft. If that is true,
the scramjet has to exert 10 times as much thrust to overcome friction
than a jet flying at Mach 1 for the same air density.

But the scramjet is flying at 20 times the altitude of the other jet,
and the air density is much lower up there. My second assumption is
that air resistance is directly proportional to air pressure. If this
is true, I can compute the relative ease of overcoming the friction by
simply computing relative air pressures. Air pressure decreases with
the square of the distance from Earth. So the difference between the
air pressure at 5000 feet and 100,000 feet is 1/20 squared, or 1/400.
And since air pressure and air density are proportional, there is
1/400 times as much air per cubic centimeter at 100,000 feet than
there is at 5,000 feet.

So, if all my assumptions are correct, then it is about 40 (400/10)
times as easy to maintain Mach 10 at 100,000 feet as it is to maintain
Mach 1 at 5000 feet. My final assumption is that this also means that
it takes about 1/40 the thrust to accelate from Mach 9.5 to Mach 10 at
100,000 feet as it does to accelerate from Mach Mach 1.0 to Mach 1.5
at 5000 feet. And if that is true, then it is also true that it takes
exactly the same amount of thrust to go from Mach 9.5 to Mach 10 at
100,000 feet as it takes to go from Mach 1 to Mach 1 plus 1/40 of a
half Mach. 1/40 of a half Mach is about 10 miles an hour increase in
speed.

Therefore, according to my calculations, if the scramjet accelerated
from Mach 9.5 to Mach 10, it took about as much thrust as for a jet
flying at Mach 1 at 5000 feet to increase its speed by 10 miles per
hour.

Like I said, I am neither an aeronautical engineer nor a fluid
dynamics expert, so consider the source. If there is an aeronautical
engineer or a fluid dynamics expert out there who can point out the
errors in these calculations, please do. Just leave out the flames,
OK? At least I made an attempt at reasoning through the problem and
realize my limitations.


-- Don French





Regardless, it seems to me that the rocket's speed has to be
subtracted from the jet's speed to arrive at the actual jet speed when
you talk about the world's record for speed of a jet plane.

Hmm. Would you say the same for Yeager and the X-1, it having been dropped
from the belly of another aircraft, or is your particular question related
just to the rocket?

Would this same sort of criteria apply to the X-prize given that Space Ship
One was given a lift to an intermediate altitide?

Interesting.
-c

"Jay Honeck" wrote in message news:03Umd.45151$V41.23702@attbi_s52...
Regardless, it seems to me that the rocket's speed has to be
subtracted from the jet's speed to arrive at the actual jet speed when
you talk about the world's record for speed of a jet plane.

On a deeper level, I find the enthusiasm about this scramjet flight to be,
in many ways, pathetic.

I mean, c'mon -- we're talking about an unmanned, rocket-assisted, 10 second
flight here -- which is somehow trumped up to be some sort of a huge success
for NASA? Worse, they're claming that they've "beaten the speed record set
by the X-15 some 40 years ago..."

Take it easy on the poor media. The election is over and they are
desperate for something to talk about.
--
Gene Seibel
Space Ship One - http://pad39a.com/gene/ss1.html
Because I fly, I envy no one - except Mike Melvill.

Peter Duniho wrote:
Don French wrote:

... and attributed that speed to the scramjet, not the rocket.
That was just wrong. The speed was almost entirely a result of the
rocket's velocity and had nothing to do with the scramjet.

Todd already pointed out the fallacy of that statement. The fact that the
scramjet *accelerated* to the maximum speed clearly shows that the scramjet
is, in fact, the *entire* source of the speed. It produced enough thrust
to maintain Mach 10.

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".

If that were *truly* the case, there would have been no rocket and not
thundering great bomber involved.

What the flight *does* demonstrate is that once *other means* have been
used to get the aeroplane to the scramjet's working speed range *then*
the scramjet can accelerate further and maintain Mach 10 while its fuel
lasts.

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.

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
--
Freedom. It seemed like a good idea at the time.
for Email, make the obvious change in the address.

(Don French) wrote:

The X-prize is different. They did what was required to win the
prize, which was get someone into space and return. Well, maybe the
scramjet did what was required to set the world's speed record too,
but it fails to impress since it wasn't the jet's engine that got it
going that fast. The jet only contributed the last few pounds of
thrust required to defeat air friction to keep it going at that speed
and maybe a few more to accelerate a half Mach or so.

I did a calculation that makes some assumptions that may or may not be
completely accurate. I am neither an aeronautical engineer or a fluid
dynamics expert, but I still made a go at trying to compute how
difficult it was for the scramjet to accelerate from Mach 9.5 to Mach
10.

Newton's first law of motion tells us that a plane released from a
rocket at Mach 10 will, in the absence of air friction, continue at
that speed indefinitely (or until it encounters another object, like
the Earth), and never have to turn on its engines to do so. The
scramjet only has to have enough power to overcome what little air
friction there is at 100,000 feet to maintain its release speed. The
question is how much air friction is there at Mach 10 at 100,000 feet.

Since I don't know how to compute the actual frictional effects at
that speed and altitude, it occured to me that maybe I can at least
compute the ratio between overcoming friction at that speed and
altitude and at say, Mach 1 at 5000 feet. That would provide a way of
making a comparison that makes sense to me.

My first assumption is that for the same air density, the friction is
directly proportional to the speed of the aircraft.
Bad assumption. I think that drag is proportional to the square of
speed.

If that is true,
the scramjet has to exert 10 times as much thrust to overcome friction
than a jet flying at Mach 1 for the same air density.
100 times if it is square.

But the scramjet is flying at 20 times the altitude of the other jet,
and the air density is much lower up there. My second assumption is
that air resistance is directly proportional to air pressure.
Intuitively that "feels" right. But I don't trust my intuition on
things like this.

If this
is true, I can compute the relative ease of overcoming the friction by
simply computing relative air pressures. Air pressure decreases with
the square of the distance from Earth.
Another assumption I would question. Please tell me you do not believe
that the air in New Orleans at 22'MSL is 57,000 time more dense and
higher pressured than the air in Denver!!!!

So the difference between the
air pressure at 5000 feet and 100,000 feet is 1/20 squared, or 1/400.
And since air pressure and air density are proportional, there is
1/400 times as much air per cubic centimeter at 100,000 feet than
there is at 5,000 feet.

So, if all my assumptions are correct, then it is about 40 (400/10)
times as easy to maintain Mach 10 at 100,000 feet as it is to maintain
Mach 1 at 5000 feet.
Highly suspect assumptions, even with sound reasoning, lead to highly
suspect conclusions.

My final assumption is that this also means that
it takes about 1/40 the thrust to accelate from Mach 9.5 to Mach 10 at
100,000 feet as it does to accelerate from Mach Mach 1.0 to Mach 1.5
at 5000 feet. And if that is true, then it is also true that it takes
exactly the same amount of thrust to go from Mach 9.5 to Mach 10 at
100,000 feet as it takes to go from Mach 1 to Mach 1 plus 1/40 of a
half Mach. 1/40 of a half Mach is about 10 miles an hour increase in
speed.
And you were complaining about the demise of physics education? g

Therefore, according to my calculations, if the scramjet accelerated
from Mach 9.5 to Mach 10, it took about as much thrust as for a jet
flying at Mach 1 at 5000 feet to increase its speed by 10 miles per
hour.

Like I said, I am neither an aeronautical engineer nor a fluid
dynamics expert
Glad you pointed that out!

, so consider the source. If there is an aeronautical
engineer or a fluid dynamics expert out there who can point out the
errors in these calculations, please do.
I'm neither.

Just leave out the flames,
OK? At least I made an attempt at reasoning through the problem and
realize my limitations.

Okay. Sorry for the sarcasm that crept in. But hopefully you see where
the assumptions look suspect to this layman.
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