Slashdot Mirror
Supersonic Flight Without The Sonic Boom
fname writes "Here's a story from Spaceflight Now about a new test aircraft that can travel at supersonic speeds without triggering a sonic boom. The technology works by modifying the shape of the plane. Although it's been believed to be possible for a long time, this is the first actual flight test, barring black box projects I suppose."
It just modifies it so it isn't as annoying. (Spreading the force over a larger area.)
Very useful, yes, but you would still hear it going overhead. (Though I suppose the 'boom' fades as you move away from the plane, and this could speed that up...)
'Sensible' is a curse word.
I would really like more infomation on this, that article was incredibly short and left me with many questions. Mostly, how are the shock waves being broken up, and how would it affect the drag (ie, would it be a better design for watercraft also?)
But then again, it is a government project, can't expect much in the way of information.
___________
"Build a man a fire warm him for a day, set a man on fire and warm him for the rest of his life."
Uhh...no. Your story is refuted by the fact that the Russian program (which would have suffered none of the enivronmental concerns of the Boeing and Concorde efforts) failed as well, despite being hugely helped by data stolen from the Concorde's testing. The Russian SST died when their test plane crashed horribly at the Paris Air Show. Despite the Russian air fleet's total lack of interest in passenger safety, the Air Ministry decided to kill the project.
The big barrier to SST success has always been economics. It's incredibly expensive to fly faster than sound. Boeing had a quite successful SST program, but cancelled it when it became clear that SSTs would not be economical. Concorde never made money for either of its parent airlines, despite the incredibly expensive tickets for the flights for which it made any sense at all.
Sonic booms can be a helluva lot more than just "loud" or "annoying." They can implode outbuildings, knock shit off shelves, break windows... and toss around house trailers like a blast from a hurricane.
would it be a better design for watercraft also?
Judging from the picture, the design borrows heavily from that of watercraft. The bottom of the aircraft has been modified to the point that it resembles the hull of a boat of personal watercraft.
I suspect that it works very similarly to the way that planing hulls(no pun intended) work. Just as a boat's hull spreads its wake outwards from the sides of the hull, this aircraft design likely spreads the aircraft's wake out to the sides more than straight down. This would reduce the pressure wave below the aircraft. I am confident that if the sonic boom was measured from the side on the same plane with the aircrafts altitude the sonic boom would be the same as normal and possibly more intense.
Getting 1/4 of the MPG per passenger compared to a subsonic plane also had something to do with it. The extra cost for fuel alone is going to double the price of most airline tickets.
That means you're in a niche market, which reduces the number of customers and impacts economy of scale. This increases maintenence costs and R&D and manufacturing overhead to very high levels. That's how you get $10,000 one-way fares across the Atlantic on the Concorde.
To compound the problem, most domestic flights just aren't that long. If you take a 1500-mile trip that needs a connection (as many do with the hub-and-spoke system), it can easily take you 9 hours to get from your home to your destination address, and only about 3 of those hours is in the air. An SST would cut that trip down to 7-1/2 or 8 hours at the cost of 4X the fuel usage. It just doesn't make any sense on the vast majority of flights.
Which is why there are sub-sonic bullets in the black ops arsenal.
The future of ultra fast transit isn't in airplanes gliding along, masking their sonic wake. It's with things like multi stage trans-orbital aircraft. A plane could take off using standard jets until it got to the maximum height the jets could support. Then switch over to SCRAM jets and break for the outer atmosphere. Even the prototype SCRAM jets today are capable of flying at many multiples of mach. It just takes the energy to get a plane beyond mach 2 (or so) to begin with. If you stay at the edge of the atmosphere, the very low pressures create little drag compared to today's cruising altitudes. Also, the higher you are, the faster you must go in order to create that critical pressure point. You don't need to totally leave the atmosphere; in fact it's easier that you don't. You won't have nearly as much heat to deal with as reentry, and you won't have to add rockets or thrusters to maneuver in low orbit. Imagine flying form New York to Tokyo so fast that food service isn't needed.
now under special conditions the sound waves all pile up making one giant pressure sheer, the shock front.
to the extent that you can disperse the shock front then the boom is indeed disperesed. You have not however eliminated the energy dumped into the air. But the "boom" is gone.
that's what this article is saying I beleive.
The really cool part of this is that its like to old adage about genius taking many steps. first everyone believes that something cannot be done. then some fool shows it might be not be impossible. then a scientist shows it is theoretically possible, and finally some engineer shows how to do it. Then it seems obvious
now that we have crossed the threshold of knowing that its possible to break the sound barrier without a sonic boom we can now get on with wondering if maybe the remaining waves could be modified in other ways, like directing all the sonic energy up and not down, minimizing it or maximally dispersing it. its now on the table.
It reminds me of discovery of negaitve index of refraction or of "optical bullets". At a certain optical power density the plasma of electrons stripped from air creates a non-linear lens that focuses a light beam in both time and space down to a stable optical pulse that neither diffracts nor diverges for macroscopic distances (hundred of meters till it runs out of energy). Now that is pretty weird since if you ask anyone who knows anything about light they will tell you that the two most fundamental proerties of waves propagation in media are dispersion and diffraction. Thus optical bullets are a form of electormagnetic farfield propagation that is not like a light wave. Negative index of refraction destroys another myth that light cant be focused smaller than a wavelength without non-linear methods.
so now we have yet another wave propagation myth falling, that when the speed of an aobject passes the wave speed in the media that a shock front is created.
just to go off on wacky extrapolation for a moment, I will point out that there is a close connection between the idea of a shock front and the idea that faster than light travel is impossible. Perhaps we can disperse that "light cone" and bend time some day.
Some drink at the fountain of knowledge. Others just gargle.
On the contrary, my guess is these low-noise jets will be even bigger gas guzzlers than normal supersonic jets, for three reasons.
1 - Fuel efficiency wasn't mentioned in the article. If it were better, I figure they'd be bragging about it.
2 - Apparantly the main advancement that they did was to have the air heat up near the nose of the aircraft, to make a smooth pressure gradient. Now that heating must come from friction, which takes energy (quite a bit when the air is rushing by at Mach 2).
3 - Current aircraft are designed with loads of computer aerodynamics modelling, with the main design goal being low drag (ie., high fuel efficiency), so if reducing the sonic boom reduced drag, it already would have been discovered and implemented long ago. In subsonic aircraft, design improvements of 0.01% are fairly typical and worth going after, as this is a very mature field of engineering.
I guess we can forget about those 4 hour NYC to Tokyo flights for the time being.
A month ago a F4 went supersonic in 11000m height in the area i live. Actually, it traveled 200km west to east through north bavaria.
I can tell you "boom" is a light understatement...
I grew up near an infantry test area and im quite used to RPG explosions in the distance ect.
I was standing near an open window and could feel the pressure. It was like back in the army if someone detonated a practice handgranate and your earplugs filter out the high frequency noise.
I read in the paper the next day that hundereds of people called the police believing there was some kind of bombing...
HI O WISE PRINCE. WHT TOOK U SO DAM LONG?
This is simply the most amazing thing I have ever seen. A bunch of civi's were on a naval ship when a hotshot pilot buzzed the ship at supersonic speed. One of them happened to get some amazing video of the pressure wave.
There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order. Starting now.
I just noticed something with the nose.. it looks a LOT like the front of a boat. that's probably how it disperses sound waves.. I'm probably wrong, but it looks that way.