Hypersonic aircraft shatters aviation records | Hacker News Reader

Hypersonic aircraft shatters aviation records

latimes.com

37 pointsilamont34 comments

Speed is not really the issue here: the X-15 was a hell of a lot faster 40 years ago. As usual the media misses the point due to their own ignorance.

There are two news-worthy items here:

1. The ramjet/scramjet engine. (No moving parts)

2. The lack of a test pilot.

This is what makes this test significant.

That and the fact that the speed was sustained for a longer period with this test vehicle than with previous vehicles.

meh. Build a bigger gas-tank. :-)

Not an issue. What makes it fail is the insane erosion it suffers when it rams into air at 2km/s.

Given that we've been launching rockets and missiles into the atmosphere at speeds much faster than Mach 4 for the better part of a century now, I think we've solved that issue as far as practically required. :-)

It all depends on the altitude. If you are using a rocket, you can avoid the friction problem by going out of most of the atmosphere. Do that with an air-breathing engine and it will not function.

As I said, solved as far as practically required, as your comment illustrates.

The viability of the scramjet being actually useful for anything is up for debate. Either you can fly slower with a jet, or leave the atmosphere altogether with a rocket.

Flying at orbital speeds within the atmosphere is of very, very marginal utility, given the number of complexities involved.

Maybe scramjets could be used as auxiliary propulsion for launchers. A pound of oxidizer saved is a pound gained.

More impressive to me is the X-15, which flew faster than the aircraft in this video, had a pilot, and flew in the 1960s. http://en.wikipedia.org/wiki/North_American_X-15#Fastest_fli...

that was a rocket engine though. this is air-breathing.

How many other HN readers built a model X-15?

"With the technology, the military could strike anywhere on planet within an hour or less"

Even at 4000 miles at out it wouldn't it still take up to 3 hours to get anywhere on the planet (24900 mile circumference)?

But we have bases all over the world.

So nowhere on the planet is less than 4000 miles from a US base?

Somehow I expect the answer to that question to be "yes".

And ships are capable of launching missiles and aircraft as well.

Both the US and Russia have had that ability since the 1950's. It's called the ICBM.

The problem is that other countries can't tell whether an ICBM has a conventional warhead or a nuclear one. Russia wouldn't like it if the US launched an ICBM and said, "Trust us, it's just carrying a conventional warhead.. or ten."

Scramjet bombers and cruise missiles would have the same problem.

This is the engine that powers this aircraft: http://en.wikipedia.org/wiki/Scramjet

Right now, it can only operate at high speeds, hence the bomber-based launch.

a scramjet will only _ever_ be able to operate at high speeds. The compression of intake air for combustion is achieved by the forward velocity of the engine itself (the engine has no moving parts) unlike a normal jet engine which uses a fan to compress the intake.

Any scramjet, current or future, will require some combination of other engines in order to accelerate the aircraft to a velocity at which the scramjet becomes self-sustaining (typically 3000+ mph I think).

Edit: needless to say, a stable self-sustaining scramjet is an INSANELY hard fluid dynamics problem.

You could use a conventional jet engine to pump its exhaust into the scramjet intake. It would have less oxygen, but a turbofan engine could compress enough air through the scramjet fast enough. The trick in this is to transition from subsonic flow in the turbofan to full supersonic engine operation.

Looks like an interesting concept.

Putting a conventional jet engine in front of a scramjet defeats any real benefit you derive from having the scramjet there in the first place.

The scramjet's main advantages are cost and efficiency; to accomplish these gains it comes with a myriad of technical problems and hurdles.

The viability of the technology is actually still very much up for debate.

You don't keep the turbofans in front of the scramjet all the time - you use them to give the scramjet enough air to start. As the speed increases, the turbofan engines would eventually cease to operate and could be shut off completely, leaving the scramjet to operate freely.

The turbofans are dead weight when you are cruising at Mach 7 in the upper atmosphere, but are useful for take off and landing.

The SR-71 Blackbird's engines were hybrids; AFAICT they didn't quite use this approach, but instead had a layout where the same engine could function as a conventional jet and a ramjet depending on how fast air was hitting it.

http://en.wikipedia.org/wiki/Pratt_%26_Whitney_J58

Hmmm. The J58 is humongous, but it would be kind of cool to use them to start a scramjet (or, better, use it as the basis of another engine that can function in all three modes).

The SJX6 combustion chamber is not cylindrical and would not fit around a jet engine the way the J58 works in ramjet regime, but I bet many people are thinking about how to do it right now.

A scramjet engine that can take off and land like a more or less ordinary plane (it would certainly not look ordinary) is something very desirable.

Yeah but then the turbo fan is blocking the air intake at high speeds. plus the exhaust of a turbo fan is subsonic, whereas a scramjet intake needs hypersonic intake.

the way to do it is either a) have a short-lived rocket engine to take you to the threshold speed, or b) bootstrap the aircraft using separate turbofan, ramjet and finally scramjet engines.

> plus the exhaust of a turbo fan is subsonic

You could funnel it to increase its speed. I am not a jet-engine expert, much less a ramjet/scramjet one, but the vestigial engineer in me suspects there is some practical solution hiding in this space.

At what point are these things no longer airplanes and just rockets?

"A scramjet is a type of jet engine designed to operate at the speeds of rockets. Its main difference from a rocket is that it collects air from the atmosphere to burn its fuel rather than carrying an oxidizing substance on board. More conventional jets (turbojets, turbofans, and ramjets) share this characteristic but are unsuitable for the high speeds at which scramjets can operate." http://en.wikipedia.org/wiki/Scramjet#Simple_description

So there is a difference between a scramjet and a rocket, beyond the speed that it travels.

When they carry 100% of their own fuel. This one gets oxygen from the atmosphere.

Years ago, on a "hacker-oriented" site, most everyone would've known this automatically through their interest in rockets and sci-fi. Times have changed.

If you carry 100% of your own fuel, you are subject to a nasty Rocket Equation. The fraction of your own weight that can be payload becomes vanishingly small, which can lead to structural and economic problems.

Aha! I was mostly commenting on the wings being useless though (until it slows down)...

Well...not useless, but not really being used to generate any lift.

This plane is a Waverider. It uses its own supersonic shockwave to generate lift.

http://en.wikipedia.org/wiki/Waverider

Make sure to watch the video, it's pretty awesome.

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