Mach 6 Test Aircraft Set For Trials

coondoggie writes "The aspiration that jets may someday fly at over six times the speed of sound took a very real step toward reality recently, as the US Air Force said it successfully married the test aircraft, known as the X-51A WaveRider, to a B-52 in preparation for a Dec. 2 flight test. The X-51A flight tests are intended to demonstrate that the engines can achieve their desired speed without disintegrating. While the X-51 looks like a large rocket now, its applications could change the way aircraft or spaceships are designed, fly into space, support reconnaissance missions and handle long-distance flight operations. At the heart of the test is the aircraft's air-breathing hypersonic scramjet system."

Comments

Rockets vs Scramjets

[sanman2]

Rocket supporters say that it's better to clear the atmosphere asap, and accelerate cleanly in a frictionless environment. Scramjet supporters say it's better to accelerate inside the atmosphere as much as possible to exploit its available oxygen, rather than carrying it as extra weight.

Which costs more energy - carrying the extra O2, or overcoming the friction from having to accelerate in an atmosphere? Which imposes more design compromises?

Which would be more economical in the long run? Bear in mind that there are 2 kinds of people that need to achieve very high velocities -- astronauts trying to make orbit and intercontinental travelers trying to get to the other side of the world.

Re:Rockets vs Scramjets

[HiThere]

It's worth remembering that Mach numbers are dependent on the current speed of sound.

If a scramjet can reach over 7 miles/second in the very upper stratosphere, then the scramjet would clearly win....at least if it didn't need the same G forces as the rocket. And particularly if it could carry a sizable cargo. (I.e., anything better than an Apollo capsule, but the larger the better.)

A scramjet might make an admirable second stage for a rocket, but then you need a first stage to get it up to speed. Note that these first two stages are airplanes, and are expected to be built to be re-useable.

There's a bit of a question as to how feasible this is, however, given that this little test plane requires a B-52 to launch it.

Re:Hmmm...

[Z00L00K]

The biggest problem for general use is to achieve speeds above about Mach 3.5.

This was roughly the maximum speed for the SR-71 and the problem was the friction heat from the air. And the SR-71 had a hull of Titanium. The Concorde did achieve about Mach 2 and had a hull from Aluminum. So for commercial use it's probably not practical to exceed the speed of the Concorde. What has to be done for commercial use is to get a more economic version and a version that has a less annoying sound bang.

But there is a use for faster vessels and that is to decrease the amount of fuel needed for putting a vessel into orbit by using the air in the atmosphere. And other uses are of course military use allowing for rapid strikes from long distance.

Titanium may well get cheaper

[PeterM from Berkeley]

Recent advances in the production of titanium may bring this metal into wide use in airframes. And everything else.

Re:Not for aircraft.

[maeka]

When calling the Concorde (or any other aircraft) "too expensive to create, manufacture, and maintain." on needs to take into account the ticket price the market will bear.
Since the Concorde was not designed with a range suitable for flying the Pacific routes, it was forced to try to make up it's high costs on the much tighter margins of the Atlantic routes. Had it been able to fly the higher margin Pacific routes it is quite possible it would not have been too expensive to be sustainable - even at the same (or slightly higher) cost basis.

Re:Not for aircraft.

[moosesocks]

The concorde was profitable in its last years (not extremely profitable, but it made money, which is more than most airlines can currently say).

In the end, its operators decided it wasn't worth maintaining/refurbishing the planes, scrapped the program, and wouldn't let competitors purchase the unused aircraft. Richard Branson allegedly made several serious offers for the planes, all of which were rejected. Numerous allegations have been made that the grounding of the Concorde fleet was a result of a conspiracy between Airbus and the airlines (unsubstantiated, but certainly plausible, especially in light of their refusal to sell the craft to other carriers at a time when the company was losing money)

In short, we got lazy and stupid.

Cool but...

[Brad1138]

What ever happened to the Aurora?

It's no concorde

[Errol backfiring]

It's no Concorde in any sense. The Concorde was created to make an efficient aircraft, not a fast one. This is the history I learned in college:

Jet engines are more economical the faster you get. Too bad the air friction (drag) gets worse the faster you get. For subsonic aircraft with single flow engines, the optimum lies just a bit below the speed of sound. As there were only single-flow jet engines at that time, the Concorde was created to try to shift the optimum to above the speed of sound. They succeeded in that.

But then, the multi-flow jet engine was invented. Instead of blowing the air out even faster, a more powerful jet engine could now mount an extra turbine that drove an extra flow of air, thereby spreading the power over more air, that was accelerated less. Bummer. Now the Concorde was just a fancy fast-flying airliner.