Welcome to the Slashdot Beta site -- learn more here. Use the link in the footer or click here to return to the Classic version of Slashdot.

Thank you!

Before you choose to head back to the Classic look of the site, we'd appreciate it if you share your thoughts on the Beta; your feedback is what drives our ongoing development.

Beta is different and we value you taking the time to try it out. Please take a look at the changes we've made in Beta and  learn more about it. Thanks for reading, and for making the site better!

NASA Prototype Plane Scheduled To Attempt Mach 5+

timothy posted about 13 years ago | from the faster-than-a-speeding-mozilla dept.

Technology 381

Logic Bomb writes: "Mach 5 -- 5 times the speed of sound, or 5000 mph -- is a speed that so far has eluded jet-powered aircraft (the existing record for a production craft is about mach 2.1). NASA, however, has high hopes for its latest attempt, the X-43A. Using a booster rocket, the prototype will be accelerated to mach 5, at which point its engine will be scooping enough oxygen to power the craft at those speeds on its own. Hopefully, it will fly at speeds up to almost mach 7 for 10-15 seconds before shutting off and plunging into the Pacific. An article from the Los Angeles Times has more details." Not to be confused with the X-33 and X-34 projects.

cancel ×
This is a preview of your comment

No Comment Title Entered

Anonymous Coward 1 minute ago

No Comment Entered


Aurora (1)

Anonymous Coward | about 13 years ago | (#300623)

Yeah, right.

Aurora, a Mach 5+ plane, has been flying for years. The public just hasn't been told yet. Just like it was with the F117 Stealth bomber.

Mach 5 (1)

Anonymous Coward | about 13 years ago | (#300624)

Speed Racer was able to get to the Mach 5!

MiG 25 (2)

Wyatt Earp (1029) | about 13 years ago | (#300629)

I recall reading the fastest a MiG 25 was clocked by the west were MiG-25 recon birds flying out of Syria and chased by Israel F-4s. I'd read that they were clocked at Mach 2.7.

The MiG-25 was designed not to fight the F-15, but to intercept the XB-70 bomber, which was a Mach 3+ high altitude delta wing bomber, like a nasty Concorde with nukes. The XB-70 was canned and then development started on the B-1B, but the MiG-25 continued. The F-15 was actually designed to beat the MiG-25...not the other way around.

Old timers may remember the SR-71 (2)

heroine (1220) | about 13 years ago | (#300631)

Maybe I'm too old to be reading slashdot but the SR-71 achieved mach 3 and used the same "scooping enough oxygen to power the craft at those speeds on its own". They called it a ramjet. Reinventing the wheel is yet another fine use of our 39% tax bracket that the Clintons invented.

Re:Mach 2.1 the record? - NOT (2)

jCaT (1320) | about 13 years ago | (#300632)

Actually, the SR71 uses a hybrid turbojet/ramjet engine. At low speeds the engine acts like a standard turbojet; as speeds rise the engine begins to act more like a ramjet. Here [wvi.com] is some good info and pictures.

Here [aviation-history.com] are a couple good pictures of ramjet and scramjet engines. A scramjet is just a form of ramjet that only works above mach 1.

Concorde almost goes mach 2.1!... (2)

Malc (1751) | about 13 years ago | (#300640)

Concorde can fly at mach 2.01. That's almost the mach 2.1 mentioned above, and it's a *commercial passenger airliner*. I find it rather hard to believe that the military aircraft in production don't go much faster! People need to get their facts straight before spouting off technical details and trying to sound clever.

http://www.concordesst.com/performance.html [concordesst.com]

Matrix - Bulletspeed (2)

unsung (10704) | about 13 years ago | (#300654)

Is this really of any use? We all know that anything that moves this fast will be in extreme slow motion.:).

Concrete evidence of the Aurora? (4)

Christopher Thomas (11717) | about 13 years ago | (#300657)

For quite a while there have been persistent rumours of a US military aircraft that flies at Mach 5 using liquid methane as a fuel. That would nix the "first aircraft to travel at this speed" claim.

Are there actual records of the US craft's existence, or does it remained a rumour?

Mach 5 != 5000 mph (1)

nathanm (12287) | about 13 years ago | (#300660)

The speed of sound is approx 720 mph at sea level, and reduces with altitude.

Re:SR-71 (5)

nathanm (12287) | about 13 years ago | (#300661)

The SR-71's top speed record was Mach 3.24, which is still the record for air breathing propulsion powered aircraft. (Of course there've been plenty of rumors of top secret planes even faster.)

The F-15 can fly Mach 2.5 at high altitude, & many current fighter aircraft can fly Mach 2.1.

The X-15 (which was rocket powered) reached speeds of over Mach 7, which was the fastest human piloted aircraft ever. The space shuttle reaches Mach 25 (~17,000 mph) in order to reach orbit.

Mach 1 != 1000mph (4)

Julius X (14690) | about 13 years ago | (#300670)

Logic Bomb seems to be under the impression that The speed of sound is 1000mph. It's more like 730-750mph last time I checked.... Mach 7 is 5000 mph, not Mach 5.

The mph speeds are correct as stated, but all of the mach speeds are off. The SR-71 does go 2100mph, but thats nearly Mach 3, not Mach 2.1. And the new craft in question which will go 5000mph is Mach 7, not 5.

Just nitpicking here folks, but someone should clarify this....

-Julius X

Re:mach5 != 5000mph (1)

jamesneal (15488) | about 13 years ago | (#300673)

Right, the speed of sound is approximately .2miles /second.

.2*3600 =~ 720mph.
5000/720 = 6.9 times the speed of sound.

Seeing as the plane "will fly at speeds up to almost mach 7", I think this is a case of a confused submitter.

Self-contradictory military mind (2)

PeterM from Berkeley (15510) | about 13 years ago | (#300674)

Interesting, an example of the self-contradictory military mind.

1) They want a bomber flying at mach 5 which will be "too fast to shoot down".

2) They want a missile defense system capable of destroying both theater and ballistic missiles.

Is it just me, or is this another proof of the
oxymoron "Military Intelligence"?

Also (1)

Pope (17780) | about 13 years ago | (#300676)

not to be confused with the X-11 [x.org] project.


Freedom is Slavery! Ignorance is Strength! Monopolies offer Choice!

Re:Self-contradictory military mind (2)

dillon_rinker (17944) | about 13 years ago | (#300677)

I have no background in aerospace (IANAAE), but I am perfectly willing to believe that a human piloted vehicle moving at mach 5 is too fast to shoot down. Rapid, small changes in velocity (speed & direction) can make its flight path unpredictable; the human pilot can correct for the navigational errors introduced thereby and still get to the target. Since you don't know where it's going to be, you can't shoot it down. And if you shoot at where it is, you'll be shooting at air (unless you're firing a laser).

Ballistic missiles move in a completely predictable path. It's easy (theoretically) to watch them for a second or two, produce a complete model of its ballistic path, and shoot at where it will be.

I see no contradiction. I still don't think anti-projectile defense systems will be effective until energy weapons are used.

Re:Old timers may remember the SR-71 (5)

nyet (19118) | about 13 years ago | (#300680)

Ya what a WASTE of time to fly real fast! Its a shame we throw away money on stuff like that! I mean, who wants to go gallavanting around really fast! And in the AIR too! WHAT MADNESS! If God intended us to fly he'd have given us wings! If God intended us to go faster than 20mph he'd have given us turboprop thighs!

I, for one am OFFENDED that we are wasting money on fruitless projects like flying fast. It would be better spend on expanding the west wing of my 8 bendroom mansion, or paying some immigrant to scrape barnacles off my yacht.

Re:Self-contradictory military mind: Not Really... (1)

Salgak1 (20136) | about 13 years ago | (#300683)

Several points.

  • Different parts of the military want different things. Contrary to popular thought, the military, heck, even the individual services, are NOT monolithic, especially in thought....
  • At Mach 5 +, a plane IS a missile
  • The real-eye opener on air defense is what has REALLY shot down the most aircraft. And the answer is. . . Guns. Not missiles. And at Mach 5 plus, all you have to do is NICK the jet, and it WILL explode quite memorably. The problem of getting a round, of whatever caliber, to the altitude and vicinity of the target jet will be a major problem, but not insoluble...

Re:Hate to be the pilot. (1)

sohp (22984) | about 13 years ago | (#300701)

I heard that Shrubya is looking for a Chinese pilot to make the flight.

Re:mach5 != 5000mph (1)

Pahroza (24427) | about 13 years ago | (#300703)

This already exists. As a matter of fact it goes from 90 to 0 in less than a second. Any car as a matter of fact can do that, if run into a steel reinforced brick wall.

mach5 != 5000mph (2)

tongue (30814) | about 13 years ago | (#300717)

I thought the speed of sound was roughly 730 mph? That would make mach 5 ~ 3600 mph. Somebody correct me if i'm wrong

RTFM! (2)

Rocketboy (32971) | about 13 years ago | (#300721)

But the ramjet cannot power an aircraft past Mach 5. That requires a scramjet, in which gases can flow at supersonic speeds.

You'd look a bit less silly if you actually read the article before commenting...

Re:Concrete evidence of the Aurora? (2)

Rocketboy (32971) | about 13 years ago | (#300722)

My wife would say that if the gov'ment is letting us see a mach 7-10 aircraft then obviously the military has something much better...

My favourite quote (2)

p3d0 (42270) | about 13 years ago | (#300725)

The first flight of the unmanned X-43A is expected to last about 10 seconds--covering about 14 miles...
Holy living fsck. You know, if this thing went about four times faster, it would be in low-earth orbit.
Patrick Doyle

Friction with air is not a problem? (1)

caffeineboy (44704) | about 13 years ago | (#300726)

From the artice itself:

Aviation: Craft may reach 5,000 mph on May flight. L.A. to N.Y. would take 30 minutes, but cargo, military more likely uses

Yes.. Unfortunately, slightly short of the miraculous 30 min NY to LA, all of the cargo fell into the ocean. 15 seconds into the flight in fact...

How many G's is this thing expected to pull in accelerating to Mach 7?

Also, wasn't the big problem with anything that is trying to go this fast within the atmosphere friction? They haven't found anything that won't melt at the temperatures that would be generated by speeds that fast. With the exception of missiles or maybe some type of millitary aircraft with consumable heat shields, wouldn't this be silly?

Re:mach5 != 5000mph (1)

wmoore (45078) | about 13 years ago | (#300727)

ahh, no, you're wrong. The speed of sound does not vary with density. The exact formula is a=SQRT(gamma*R*T) where gamma and R are constants for a particular gas. So, the higher you go, the lower the speed of sound is actually ... And yes, I am an aerospace engineer.

Think of the sonic boom (4)

anticypher (48312) | about 13 years ago | (#300734)

New York to Los Angeles in a half hour. Wow.

In completely unrelated news:

Every window from New Jersey to Nevada was broken today, which officials are at a loss to explain. It appears to have been a sharp earthquake which rattled houses and businesses across the country. Seismologists have reported that every one of their seismographs recorded a large spike, possibly a new type of fault slippage previously unknown.

Officials at UnitedSpace were unavailable for comment.

the AC

Re:mach5 != 5000mph (1)

qmrf (52837) | about 13 years ago | (#300738)

Actually, the speed of sound varies with local conditions:

The speed of sound a is defined as (gamma * R * T)^.5, where gamma is the ratio of specific heats (1.4 for air at reasonable temperatures), R is the gas constant (universal gas constant divided by molecular weight; 287 J/kg-K for air), and T is the local temperature. At standard atmospheric temperature and pressure (STP), a = 346 m/s. Mach 5 = 5 * a, or roughly 3700 mph at STP.

One consequence of this is that you can travel at a higher mach number while going the same speed if the local temperature is lower. As you go up to higher altitudes, temperature decreases, so the sound of speed decreases. For air-breathing vehicles, though, this can cause a problem, because local pressure also decreases significantly with altitude...*trails off in an irrelevant tangent*

IANAL...but I am an aerospace engineer...

Re:mach5 != 5000mph (1)

qmrf (52837) | about 13 years ago | (#300739)

Almost right...Speed of sound varies with temperature (see my post down a little ways). If you assume constant pressure, then yes, speed of sound varies with density (ideal gas law: pv = RT). But density decreases with altitude, and thus so does sound speed. Mach 5 is about 3700 mph at STP; as you go up, this would *decrease*, not increase.

Re:Mach 5 != 5000 mph (1)

qmrf (52837) | about 13 years ago | (#300740)

And now we *know* you're not one. Or, if you are, you're perhaps an EE. I know *I* don't want you designing airplanes. Get yourself a fluid dynamics text if you don't believe me.

Re:Why This Is Important but Won't Replace Shuttle (1)

qmrf (52837) | about 13 years ago | (#300741)

As a more direct reason why this won't replace the shuttle, it's still an air-breathing engine. And there's no air to breath where the shuttle goes.

Re:Better use of tax dollars (1)

qmrf (52837) | about 13 years ago | (#300742)

Hey, there are plenty of engineers who *do* get off on those things. The problem is that the people with money get off more on things which go fast and blow up things, thus allowing them to keep other people from getting money.

Re:mach5 != 5000mph (3)

jovlinger (55075) | about 13 years ago | (#300746)

So the claims of the space shuttle reaching Mach25 aren't that impressive? Does that mean that while in orbit it is effectively orbiting at Mach infinity (as sound has zero propagation speed in space...)?

For some reason I thought Mach was defined as the speed of sound at such a presure and humidity, analogously to c, which is constant, vs the Speed Of Light, which varies.

OT sig ref: I hate, you milk man dan!

Re:Hate to be the pilot. (1)

QID (60884) | about 13 years ago | (#300750)

What makes you think it's going to be piloted? Most of these really experimental things are remote-controlled.

Just read the damn article. (1)

eg0n (62511) | about 13 years ago | (#300751)

"If all goes according to plan, the X-43A should reach a speed of Mach 7, or about 5,000 mph, breaking the record for both air-breathing and rocket-powered airplanes, surpassing even the Mach 6 record set by the rocket-powered X-15 in 1967." They never once mention mach 5 in the article and they even say that the record is mach 6 by a rockey-powered X-15. Read the actual article not just the stupid mistake on /.

Mach 2.1 the record? - NOT (1)

fnj (64210) | about 13 years ago | (#300752)

the existing record for a production [jet] craft is about mach 2.1).

Eh? Hello??? The SR-71 speed is more like Mach 3.0 - SUSTAINED - with many fleet hours at that kind of speed. It was a jet (turbojet).

The X-43A is a RAMjet, which is another kettle of fish.

Re:Mach 2.1 the record? - NOT (1)

fnj (64210) | about 13 years ago | (#300753)

Duh. A Supersonic Combustion Ramjet is a kind of Ramjet, as its name makes plain.

Splash... (4)

brogdon (65526) | about 13 years ago | (#300756)

"Hopefully, it will fly at speeds up to almost mach 7 for 10-15 seconds before shutting off and plunging into the Pacific"

Fortunately the seat cushions can be used as a floatation device.


SR-71 (2)

wowbagger (69688) | about 13 years ago | (#300758)

Sorry, but the SR-71 is a jet powered aircraft that has routinely exceeded Mach 2.1. Even F-15's have exceeded that speed.

As for Mach 5+.... no aircraft that anybody has admitted to has gone that fast.

Stupid units: Foot, pound, ton, mach (4)

MobyDisk (75490) | about 13 years ago | (#300764)

Why do we use Mach as a measurement of speed when it varies with altitude? No one would ever use a measurement of length that varied with what country you were in? Hmmm... I'll make a measurement called "Schnach" which is 1 meter in Australia, but is 3 inches in the US. Brilliant idea, eh?

And if you read the fscking article.... (2)

Nexx (75873) | about 13 years ago | (#300765)

You'd know that the other poster is not talking about the SR-71, but is talking about the now-scrapped space-plane project. *plonk*

Re:mach5 != 5000mph (1)

diablovision (83618) | about 13 years ago | (#300772)

Perhaps they meant feet per second? FPS is often used in ballistics and the reference yardstick is that the speed of sound is roughly 1000fps. It's really around 1070fps under average temperature/humidity/pressure.

Re:mach5 != 5000mph (1)

Gryffin (86893) | about 13 years ago | (#300778)

Whoops, you're right, my mistake... it goes *down with altitude. Guess that shows how long I've been outta the business...

Re:Old timers may remember the SR-71 (1)

Gryffin (86893) | about 13 years ago | (#300779)

Nope, it was a conventional turbojet.

The biggest problem with a turbojet is that it won't work at supersonic speeds. If the shock wave hits the compressor, things stop working fast.

So how do planes fly faster than sound? Well, their inlets are designed to slow the intake air down to subsonic speeds before it gets to the compressor. Above mach 2 or so, you need complex variable-geometry inlets that allow in very little air, then allow it to expand in volume to slow it down.

Problem is, the faster you go, the harder it gets to slow the air down *and* deliver enough to the engine to generate sufficient thrust to maintain airspeed. The practical limit seems to be between Mach 3.5 to Mach 4.0.

Ramjets don't have compressors, and so they aren't limited to the subsonic regime; in fact, they work very efficiently at supersonic speeds. So theoretically, you could push a ramjet up to Mach 5, Mach 7, who knows? But a ramjet designed for supersonic speed doesn't work at subsonic speed, hence the rocket booster mentioned in the article.

Re:SR-71 (2)

Gryffin (86893) | about 13 years ago | (#300783)

The SR-71 has been clocked at a little over Mach 3. Most folks in the business believe it'll go faster.

Rumor has it that no pilot yet has been brave enough to actually put the pedal all the way to the metal. The airframe itself probably limits it to about Mach 3.5 or 3.6; at that point, the shock cone is swept back to where it hits the wing tips, which is a Very Bad Thing.

If I recall correctly, the F-15C tops out at about Mach 2.8, which is pretty impressive for a conventional turbine engine. The former Soviet Union went to great lengths to beat that, the result of which was the MiG-25, which reached Mach 3, but only by using an enormous afterburner that sucked fuel like crazy, limiting such speeds to short bursts.

Re:mach5 != 5000mph (4)

Gryffin (86893) | about 13 years ago | (#300784)

Actually, if memory serves, Mach 1.0 at mean sea level and mean atmospheric conditions is about 714 MPH at sea level.

However, the speed of sound varies proportionally to the density of the medium, in this case, air. So at higher temperatures, and higher altitudes, the speed of sound increases. At the sort of near-space altitudes at which this thing will probably operate, Mach 5 is close to 5000 MPH.

Re:Been there, done that.... (1)

wannabe (90895) | about 13 years ago | (#300794)

Not to mention the X-15.

I don't quite have the stats, but someone should be easily able to look them up.

Speed of sound not 1000 mph (1)

donaldm314 (96425) | about 13 years ago | (#300797)

It depends on temperature and the medium through which the sound is travelling.

In air at sea level, sound travels around 740mph.

Re:Mach 1 != 1000mph (2)

bmajik (96670) | about 13 years ago | (#300798)

To nitpick _you_ some..

I dont buy for a minute that the SR 71 only goes mach 3. What a bunch of crap :) The X-15 (rocket plane) went Mach 6 back in the 50-60s. The MiG-25 FoxBat (similar to F15) does mach 2.5+ (probably more like mach 3). The F-15 does mach 2+. The 16 does mach 2+ on a single engine.

You're telling me the SR-71 only beats these run of the mill jet aircraft by a few hundred miles per hour ?

Bullshit :)

If you buy the discovery channel folklore about the SR-71 (i do :) then it doesn't add up. Pilots wear _spacesuits_. The thing has an operating altitude of 100,000+ feet. Pilots heat their pre-packaged meals by putting the pouch against the cockpit glass. The thing uses special exotic motors and special exotic fuel. (i think its called JP7. Its not flammable. You can apparently fling lit matches into it and they go out. etc etc)

The plane stretches a significant length during flight from heat expansion. its panels and seams are made to expand so much during flight that it _leaks fuel_ when its cold and on the ground. It takes it _several states_ to make a banked turn when flying over the US.

All this bullshit for a couple hundred extra MPH ?

I dont think so :)

Hmmmm... (4)

zpengo (99887) | about 13 years ago | (#300800)

Using a booster rocket, the prototype will be accelerated to mach 5, at which point the pilot's face will be torn from his skull. Hopefully, the plane will fly at speeds up to almost mach 7 for 10-15 seconds before getting hit by a Chinese hotdog pilot.

The problem is (1)

skwog (101252) | about 13 years ago | (#300803)

more about building strong enough air frames that can properly stretch and continue to act as load carrying structures. The SR-71's wing span stretched by more than a foot at cruising speeds nearing Mach 3. (and yes top speed was 3+)

And how do you store enough fuel? The SR-71 was forced to take off with 1/4 tank of fuel due to weight restrictions. It then had less then 5 minutes to find and hook up with a refueling aircraft, when it would completely top off it's tanks.

Another considerations is the human factor of both pilot skill and physical endurance to manage such a craft. At just Mach 3, a deviance of 1 or 2 degrees from flight plan will put you off course by a mile in about 1 second (literally).

An SR-71 required a minimum of 45 minutes of cool-down time after landing before any anything could be touched or any panels or outlets could be opened.

The SR-71 program discontinued for only one reason. Cost. Go figure.

Hypersonic Cruise Missiles? (1)

Mr Krinkle (112489) | about 13 years ago | (#300808)

That was what caught my attention. Now the real question is was that the reporters attempt at trolling to get the attention of everyone? "Oh my God China can kill us faster than we can kill them"(It wouldnt matter we would still have time to blow up the entire world if something ended in nukes) Or was their sort of a space race we did it first type approach? If it is the latter then cool and he should have developed that more. The former he should have been edited. my .02$

Re:mach5 != 5000mph (1)

VultureMN (116540) | about 13 years ago | (#300813)

Speed of sound goes UP if things are denser.
Speed of sound goes DOWN if things are less dense.

12ft aircraft (3)

mr_gerbik (122036) | about 13 years ago | (#300819)

"a 12-foot experimental airplane is scheduled to make its maiden flight next month, flying over the Pacific Ocean at more than 5,000 mph."

Nothing like spending billions of dollars on something that can send two midgets across the pacific in record time.


Mach Numbers and Engines (5)

smannell (157236) | about 13 years ago | (#300843)

Although the author seems to be confused about the value of Mach 1, some of the responses aren't much more informed. Mach 1 is the speed of sound, which varies greatly depending on the density of the air. At sea level it is usually around 730 mph or so. So it is difficult to say what Mach number the blackbird achieved when it was flying 2,100 mph. You'd have to know the density altitude for the flight. Also, a scramjet engine is not quite the same as a ramjet. The idea is the same, but since air is highly compressible, it behaves differently at different speeds. There are basically four areas of flow: subsonic, transonic, supersonic, and hypersonic. What holds true for supersonic flow is not necessarily true for hypersonic flow. The divisions between these areas of flow depends on the Mach number of the fluid, which is why speeds are rated in Mach numbers and not mph or km/s. So, a different design is required for hypersonic flow compared to supersonic flow. Hope this clears some things up.

Re:Hmm... (2)

JCMay (158033) | about 13 years ago | (#300845)

You forget that the men that least want to go to war are those that actually have to fight it. They don't want advanced weapons so that they can kill more people faster. They want advanced weapons so that they can scare the enemy enough such that the said weapons are never used.

Talk to a soldier or two. Career types are best. They don't want war.

Re:Old timers may remember the SR-71 (1)

finchman (166628) | about 13 years ago | (#300853)

The sr-71 had a conventional turbine engine with a radical mosecone on the engines to adjust the supersonic shockwave in the engine for greater compression of the air moving through it.

Re:Concrete evidence of the Aurora? (5)

SquadBoy (167263) | about 13 years ago | (#300854)

This link (http://www.abovetopsecret.com/aurora.html) has some good background info for those of you who don't know much about the Aurora. Although I can't find links just now. There are several pictures of the "donuts-on-a-rope" contrail and also I heard on TLC a few years ago a story about evidence for sonic booms over the Pacific for which the Aurora is the only really good explanation. So in short yes I do think the government has things that none of us know about. From the fact that this is public knowledge and NASA is doing it we can assume that Mach 5 is nice and slow at this point. :)

closer... (1)

b0r1s (170449) | about 13 years ago | (#300860)

Everything's fine... except your ideal gas law... where you left out a seemingly meaningless term (at least in this example) ...

pv = nRt, where p = pressure, v = volume, n = number of moles of substance, R = universal constant, t = temperature.

Re:mach5 != 5000mph (5)

ChrisCampbell47 (181542) | about 13 years ago | (#300872)

However, the speed of sound varies proportionally to the density of the medium, in this case, air. So at higher temperatures, and higher altitudes, the speed of sound increases.

Nope, you're wrong too. Speed of sound decreases with increasing altitude (less dense air).


  • http://www.grc.nasa.gov/WWW/K-12/airplane/atmosi .h tml
  • http://www.grc.nasa.gov/WWW/K-12/airplane/sound. ht ml
for the basic information and a cool little demonstrator app. However, even at high altitude, the SOS doesn't change much (-14% is "not much" to me). Now, speed of sound through solid rock, THAT'S fast!

One source of confusion is that SOS is about 1100 feet per sec or about 750 miles per hour. People often get the numbers and units swapped.

- Chris

P.S. Wow, I actually used my Aerospace Engineering degree today!

P.P.S. SR-71 has gone to Mach 3 according to public knowledge, but it's widely expected that it went MUCH faster. Hell, most fighter jets can push Mach 2.0, and the SR-71's design point is Speed At All Costs.

Mach 5 != 5000mph (1)

milkmandan9 (190569) | about 13 years ago | (#300877)

Whoa there, cowboy.

Mach 5 is roughly 3800mph at sea level.

But the article gets it right...Mach 7 at several thousand feet is quite close to 5000mph.

Although technically, Mach 5 == 5000mph for compressed (>1atm) air, but you'll be hard pressed (no pun intended) to find enough of that to fly a plane in.

Re:mach5 != 5000mph (2)

milkmandan9 (190569) | about 13 years ago | (#300878)

Mach 1 is fairly close to 714mph at sea level.

And the speed of sound varies inversely proportionally to the compressability of the medium, which in turn varies inversely proportionally to the density and pressure. So you got that right; the speed of sound is proportional to the density of the medium.

But the last part of your argument is backwards; at higher altitudes, the density of air decreases and so does the speed of sound.

I also remember reading somewhere that the speed of sound at 30,000 feet is close to 630mph.

Re:mach5 != 5000mph (1)

Highlordexecutioner (203297) | about 13 years ago | (#300890)

As a base speed that is correct, but temperature and air density can alter that. On average I think it is around 730mph-750mph or so.

Re:mach5 != 5000mph (1)

Gehenna_Gehenna (207096) | about 13 years ago | (#300895)

Mach 5?

When are they going to invent something REALLY usefull, like a car that goes from 90 to 55 in .5 seconds....

Just a thought

Re:mach5 != 5000mph (1)

Gehenna_Gehenna (207096) | about 13 years ago | (#300896)

Of course, but slamming into a steel reinforced brick wall doesn't prevent me from getting a traffic ticket.

....then again, it may prevent me from paying taxes......reading Katz articles...maybe a good idea...

Re:Mach 1 != 1000mph (1)

Fujisawa Sensei (207127) | about 13 years ago | (#300897)

Where are my moderator points when I need them.:)

But seriously I believe that the equation can be reduced to a function of T . When you figure in the ideal gas law PV=nRT, air density is actually a function of Pressure which also is a function of height, so you can eliminate both height and pressure leaving only function of T.

Could sombody post the actual equation for determining mach?

Re:Old timers may remember the SR-71 (1)

bpowell423 (208542) | about 13 years ago | (#300899)

The difference (the only one! :) between a ram jet and a scram jet is that in a ram jet, the incoming air is slowed to sub-sonic before combustion. In the scram jet, the fuel is mixed with air at super-sonic speeds and ignited. Hence the "Super-sonic Combusion" part of the name. Right now they're apparently using a rocket to get up to Mach 5 or so and then kicking in the SCRAM jet. I wonder if they'll eventually use a RAM jet to get up to Mach 3 or so and then kick in the SCRAM jet? That'd eliminate the rocket engine altogether.

Re:Why This Is Important but Won't Replace Shuttle (2)

TOTKChief (210168) | about 13 years ago | (#300901)

Go back and read the article. The idea is to have rockets power the craft to scramjet speed, use the scramjets until oxygen consumption is minimal [probably 100,000 feet, but then I don't have good scramjet data here in my office], and then use rockets again to boost to orbit. So that's their goal in this, although I wonder how they would want to land it, either...

Your memory semi-fails you! (3)

TOTKChief (210168) | about 13 years ago | (#300909)

Quoth NASA [nasa.gov] :
The SR-71 was designed and built by the Lockheed Skunk Works, now the Lockheed Martin Skunk Works. SR-71s are powered by two Pratt and Whitney J-58 axial-flow turbojets with afterburners, each producing 32,500 pounds of thrust. Studies have shown that less than 20 percent of the total thrust used to fly at Mach 3 is produced by the basic engine itself. The balance of the total thrust is produced by the unique design of the engine inlet and "moveable spike" system at the front of the engine nacelles and by the ejector nozzles at the exhaust which burn air compressed in the engine bypass system.

The moveable spike does add a lot of the thrust. But what's being discussed is a scramjet, and as such, it gets all its air without compression. The ramjet is a compromise between the scramjet and the turbojet, really. Also, the ramjet has realistic speed limits, because there is some compression needed to fly, and the craft can't make it to scramjet operational speeds with air-breathing engines.

I'd rant further, but I sold back my propulsion texts when I realized I was going into the church business. Oh well.


Re:Mach 1 != 1000mph (3)

TOTKChief (210168) | about 13 years ago | (#300910)

Actually, a [the speed of sound] varies with altitude, as temperature and density have an effect on the speed of sound. You can go supersonic, technically, simply by holding speed but changing altitude.

Most Mach references are to sea level a of 340 m/s.


Why This Is Important but Won't Replace Shuttle (5)

TOTKChief (210168) | about 13 years ago | (#300912)

This is important aerospace research, and if you read the article, it's pretty easy to see why. The ability to fly at such speeds for intercontinental, oceanic flights is of great societal benefit. Speed of transport will make this work commercially.

The military aspects are a bit more challenging, though. If you're going to build a bomber so fast it can't be shot down, fine--but then you have to either slow down the craft so that the munitions can exit the slipstream, or you have to come up with some design that will allow you to drop iron at high speeds--such as the Valkyrie, which dropped munitions out the tail.

Either is a huge design problem. If you slow the craft down, you have to design a craft that performs at all speed ranges with in-theater fidelity. If you kick the munitions out of the back, you have to compensate for the mass changes with aerodynamics, because you change the center of gravity all the way through the release profile, and you better hold the craft steady during release, lest you hit the bomb on the way out. "Somebody set us up the bomb," indeed!

But this won't replace STS. Yes, a scramjet is nice. Yes, this is similar to rocket-based combined cycle. But we could more cheaply build a reliable, two-stage system to get into orbit. Mass fractions are all you have to look at to wonder why Single Stage To Orbit [SSTO] is some perverted NASA priority. As a NASA sub, I know they don't live in reality, but damn...

But this is, for once, a positive example of your tax dollars at work.


Re:Old timers may remember the SR-71 (1)

damiangerous (218679) | about 13 years ago | (#300922)

the SR-71 achieved mach 3 and used the same "scooping enough oxygen to power the craft at those speeds on its own". They called it a ramjet.

And if you'd read the article you would see that this is a scramjet, an improvement that is directly based on, yet overcomes some limitations of, ramjet technology.

Reinventing the wheel

Only if you consider the 8008 processor (or 8086, 8088, 80186, 286, etc)to be "reinventing the wheel." After all, once we had the 4004, who needed a better microprocessor?

Re:Stupid units: Foot, pound, ton, mach (1)

damiangerous (218679) | about 13 years ago | (#300923)

No one would ever use a measurement of length that varied with what country you were in?

I'll bet someone did. After all, we have the gallon, which measures 4.545 liters in the Commonwealth countries and 3.785 liters in the US. Or how about counting? You know how much a billion is? Well, maybe not. It's 10^12 in the Commonwealth countries and 10^9 in the US. (They call 10^9 a milliard).

Every system of measurement everywhere is arbitrary to some extent. Even the metric system (a meter is the distance light travels in 1/299,792,458th of a second? Umm, ok) has changed a few times in the past few centuries or so.

I think the article needs to be re-looked at (1)

ilsie (227381) | about 13 years ago | (#300929)

Mach 5 is the speed that the scramjet needs to kick in. When this happens, the plane will theoretically accelerate to Mach 7. It says right there in the article that the current record is Mach 6, set in 1967, not Mach 2.1, which is only about 1500 mph, depending.

Re:Old timers may remember the SR-71 (1)

Baba Abhui (246789) | about 13 years ago | (#300941)

Actually, the SR-71 used turbine jets, not ram jets. They were augmented with some extremely large afterburners and some very clever intake design, however. All in all, a really remarkable piece of engineering.

Re:mach5 != 5000mph (1)

Baba Abhui (246789) | about 13 years ago | (#300942)

The speed of sound does vary with the medium. But if it varies proportionally with the density of the medium, then surely you mean it gets *slower* at higher altitudes and temperatures.

I thought that was part of the reason those high-flying spook planes (SR-71, The XB-70 Valkyrie, etc) post such impressive Mach numbers. At those altitudes, sound goes slower - so a speed that might be Mach 2.9 at sea level *is* Mach 3+ at altitude.

Not to be confused with... (1)

traphicone (251726) | about 13 years ago | (#300945)

the X-33 and X-34 projects....

Also, of course, not to be confused with the X10 [x10.com] , which is a whole different kind of fun altogether. :D.

Existing record is Mach 2.1? (1)

typical geek (261980) | about 13 years ago | (#300949)

Logic Bomb writes: "Mach 5 -- 5 times the speed of sound, or 5000 mph -- is a speed that so far has eluded jet-powered aircraft (the existing record for a production craft is about mach 2.1).

Umm, while the Blackbird (SR-71)'s top speed is classified, most knowledgeable folk put it between Mach 3.1 and Mach 3.3.

Also, there are always those fun tales off liquid hydrogen tanks at Lockheed, and C5's loading strnagely shaped waveriders.

Hmm... (1)

Sarcasmooo! (267601) | about 13 years ago | (#300958)

The military's vision calls for a bomber that would be too fast to shoot down.
Someone needs to head up to Washington DC with a bag full of copies of Tribes 2 and Half-Life. That way the warmongers can have a harmless outlet for their pent-up aggression, and the civilized world can stop worrying and wondering, which pissing contestant will dream up the most efficient means of mass-murdering the opponent's population.

That's fast enough.... (1)

DragonPup (302885) | about 13 years ago | (#300963)

That's fast enough to make Speed Racer jealous!

But seriously, don't aircraft going at those speeds do more environmental damage? I think I heard something about that in high school....


About time... (1)

Roarkk (303058) | about 13 years ago | (#300964)

Does this hold hope for SSTO development? Single Stage to Orbit is the next step from here....

Re:Mach 1 != 1000mph (1)

WolfDeusEx (310788) | about 13 years ago | (#300973)

Maybe he ment to write mach 2 + 1. Or maybe not. Anyway does this realy matter. Most compaines know that customers are not willing to pay loads of money just to get somewere realy fast. That is why concord is a flop. So what is this tech going to be used for.

Nasa wasting money. Thank god I British.

Re:Hate to be the pilot. (2)

sonofevil (316367) | about 13 years ago | (#300978)

Either it's deisgned to operate without a pilot, or the plan has the untimely death of the pilot factored in, since the vehicle will "plunge into the pacific" to end its flight...

Better use of tax dollars (1)

hal9000(jr) (316943) | about 13 years ago | (#300981)

Ok, this is an interesting exercise and I am all for the forwarding of science. Looks more like anohter manifestation of short guy syndrome.

Too bad engineers don't get the same woody from trying to do something truly challenging like exploring the ocean, building oceanic habitats, or finding ways to use renewable resources more efficently.

Or (heaven forbid), they find alternative fuels.

Re:Self-contradictory military mind (1)

Chakat (320875) | about 13 years ago | (#300985)

Different divisions. One builds offense, one builds defense. One side gets the advantage, one counters, lather, rinse, repeat.

Hate to be the pilot. (1)

silent_poop (320948) | about 13 years ago | (#300986)

"Using a booster rocket, the prototype will be accelerated to mach 5, at which point" ...it's pilot will be ripped to shreds.


Re:Hate to be the pilot. (1)

silent_poop (320948) | about 13 years ago | (#300987)

I don't know, whenever I think of the testing of experimental aircraft I picture Chuck Yager attempting to reach supersonic speeds back in the '40s.


What's the point? (1)

silent_poop (320948) | about 13 years ago | (#300989)

What is the point in building a plane that travels so fast that it's only means of stopping itself is to plunge into the ocean?


In a related story: (3)

Magumbo (414471) | about 13 years ago | (#300997)

(Associated Press) Boston, MA -- James Kilts, CEO of The Gillette Company, announced today at a press conference the aggressive rollout of a new line of razors to succeed the popular Mach 3 series.

"We at Gillette want our products to be cutting edge," Kilts said, "Absolutely at the bleeding edge of technology."

The product name has yet to be announced, but Kilts claims, "They will have 5 or more blades."


Don't land in China (1)

B.Assturd (416078) | about 13 years ago | (#301000)

... but seriously, what is the point of all of this? Don't feed me that baloney about technology, spacemen and iron heros. The Cold War is over, folks. Let's turn our attention to the real issues at hand: I can't name any right now. This is my worst troll ever. I'm sorry.

Re:Hate to be the pilot. (1)

jvance (416133) | about 13 years ago | (#301001)

> ...its pilot will be ripped to shreds.

Just like all the X-15 [nasa.gov] pilots, right?

The X-15 regularly exceeded Mach 6. It just didn't have a scramjet (as far as we know.)
Load More Comments
Slashdot Account

Need an Account?

Forgot your password?

Don't worry, we never post anything without your permission.

Submission Text Formatting Tips

We support a small subset of HTML, namely these tags:

  • b
  • i
  • p
  • br
  • a
  • ol
  • ul
  • li
  • dl
  • dt
  • dd
  • em
  • strong
  • tt
  • blockquote
  • div
  • quote
  • ecode

"ecode" can be used for code snippets, for example:

<ecode>    while(1) { do_something(); } </ecode>
Sign up for Slashdot Newsletters
Create a Slashdot Account