speed record set by scramjet - fair?

(Don French) wrote in message . com...
Seriously,
they could have dropped a Piper cub off that rocket and it could have
maintained Mach 9 for hundreds of miles.

I know you started that sentence with the word "seriously", but you
can't be serious. A Piper Cub would instantly disintegrate at Mach 9,
assuming you were somehow able to protect it from the blast of
(relatively thin) air while you accellerated to that speed. It
certainly doubt that even the pieces would "maintain" Mach 9 long
enough to travel hundreds of miles. I'm pretty sure that they would
travel hundreds of miles, though.

John Galban=====N4BQ (PA28-180)

"Todd Pattist" wrote

It takes a lot more than "a few pounds of thrust" to fly at
Mach 10.

The temperature of the leading edge of the tail was 2600
degrees F on the Mach 7 flight. They rebuilt flight
surfaces to get to 10.

Indeed. Air friction heating a tail surface to 2600 degrees, sounds like
LOTS more than "a few pounds of thrust" would be needed to overcome
friction.
--
Jim in NC


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In article , alexy wrote:
(Don French) wrote:

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

On the contrary, it would seem that he did attend highschool physics,
got a C, and stopped there. :-)


Morris (considering the sperical cow)

"Robert Briggs" wrote in message
...
[...]
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.

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.

Had the scramjet had that thrust available from 0 mph, and had it had enough
fuel for the flight, it would have just as easily accelerated to Mach 10
from 0 mph as it did from Mach 9.

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.

Yes, it does demonstrate that. Having a functional scramjet is a pretty
huge accomplishment.

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. The shuttle is not
very useful without its booster rockets, but that doesn't take away from the
engineering accomplishments of the shuttle itself.

Pete

NASA's site prominently mentions the speed record and the technology
hardly at all. Read all about it:

http://www.nasa.gov/missions/research/x43-main.html

(Jay Masino) wrote in message ...
Jay Honeck wrote:
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..."


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. There will undoubtedly be many
more unmanned test flights before a manned flight is attempted with this
engine.

--- Jay

"Don French" wrote in message
om...
NASA's site prominently mentions the speed record and the technology
hardly at all. Read all about it:

http://www.nasa.gov/missions/research/x43-main.html

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.

Pete

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

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

Like waiting for a rippin' wind right down the runway to get the engine
started!

Mike
MU-2

Are you sure that you are really not an aeronautical engineer? Are you a
high school graduate?

Mike
MU-2

"Don French" wrote in message
om...
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

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.

Yep. Misread it. But still far from linear.

Jose
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