Towards Silent Supersonic Planes

Roland Piquepaille writes "There is no longer a single commercial supersonic airplane since the retirement of the Concorde last year. And even during its years of glory, the Concorde was not a commercial success, mainly because it was not allowed to cruise at supersonic speed over land. Why? Because of the sonic 'boom' which arises when you break the sound barrier. Now, a joint program between NASA, the military and the aerospace industry wants to remove, or at least reduce, this sonic boom, by changing the shape of supersonic planes. It seems to work. After a 'nose job' on a Northrop Grumman F-5E, about a third of the pressure released when breaking the sound barrier has already been suppressed. This overview contains more details. It also includes a photograph of the modified Northrop Grumman F-5Ea aircraft flying off the wing of the F-15B research testbed aircraft. [Note: Previous results were reported here by Slashdot in last September.]"

Comments

Re:Directing the sound?

[FrYGuY101]

Nope. The Boom is omnidirectional. In fact, the downward part of the wave is aided by the increasing atmospheric pressure.

PopSci...

[PeaceTank]

There was a smaller article like this in Popular Science a while back, and since I am very interested in planes and aerospace, it now is on my wall. I'll type it down for you guys, I'ts actually very interesting...

All Zoom, No Boom
Teaching an F-5E Tiger how to tiptoes.

There's nothing more dramatic than a supersonic jet streaking overhead; and nothing more annoying than the bone-rattling sonic boom it leaves behind. The boom really consists of two bangs caused by the N-wave in the planes wake, with rapid pressure rises corresponding to the nose and tail. Northrop-Grumman hopes that by tailoring a F-5E Tiger with a longer nose an modified tail, and tinkering wiht its body and wngs, the boom can be transformed into a smooth, inaudible hump. Engineers got the idea from research that goes back to the 1970's. Today's computers, which make it possible to model airflows up to 200 yards from a plane, were required to put the theories into practice. Tests being next august. --Written by Bill Sweetman.

I don't know exactly when it was published, but it shows that this is really no new idea. On an interesting side-note, my uncle worked for McDonald Douglas before they were bought out by Boeing, and actually was a systems engineer for the Coherent Readar systems for the F-5F. When I told him about this he thought it was one of the coolest things he'd ever heard.

~I was playing poker with tarot cards the other night. I got a full house and that same night five people died. True story.

Supercruising also important

[Zergwyn]

The goal of suppressing and/or absorbing the sonic boom has been around for a long time now, and I have seen a number of different attempts at doing it, most without particularly good levels of success. But at least for a commercial aircraft, another very important consideration is fuel costs. People who follow the aviation industry should remember the recent airliner choice of the new Boeing 7E7 over their Sonic Cruiser concept, because the 7E7 is much more efficient, which therefore translates to lower fuel costs.

Most supersonic aircraft require afterburners in order to go faster then sound, and afterburners are incredibly voracious consumers of fuel. I think that one of the other very important innovations is the "Supercruise" ability, seen on aircraft like the F-22 Raptor. This allows the aircraft to maintain supersonic speed for extended periods of time in a low power setting, and this in turn is just as vital for cheap, commercially viable flights. I hope that advances in sonic boom suppression will also work well with the necessary designs for supercruising, and that we may all be able to take advantage of such flights within the next 2-3 decades. If both aren't taken into account, and designers come up with plans that make for an either-or choice, it could mean supersonic planes will still be relegated to the relatively wealthy.

that is an opfor plane

[Nf1nk]

That plane is used for training purposes to be the agressor, it looks like one of the Navy OpFor planes from Palomar. The us military uses mocked up soviet equipment, or sometimes even real soviet equipment to train against.

Re:Looking at the picture

[PD]

The bottom left photo is not a F-20. There were just 1 or 2 made, and they are owned by Northrop, not the Navy.

The F-5 in the lower left is owned by the Navy. The reason that it has the Red Star painted on it is that it's an agressor plane used by the Top Gun dogfighting school.

not the sonic boom

[blitz487]

The reason the Concorde was an economic failure was not the sonic boom - it was a failure because of the enormous fuel consumption per passenger, as well as the enormous maintenance costs per passenger. This was true even though the airlines purchased the Concordes for $1 apiece, and there was no purchase cost to amortize.

Re:I've always wondered...

[FrYGuY101]

It's created constantly by supersonic flight. It's a byproduct of the air pressure in front of the plane being extremely high, steadily decreasing as you head back to the tail, and a sharp rise behind the tail when the pressure snaps back to normal.

This is why there are two booms from each aircraft. The first one from the pressure wave preceding the plane, and the second from the posterior wave.

Re:Looking at the picture

[YrWrstNtmr]

Riiiight...

Top right - F-15
Center - Modified F-5
Bottom left - Standard F-5, painted in TigerShark livery.

The F-20 is just slightly different frm the F-5, as evidenced by the extra bulk around the tail root.

This particular F-15B from NASA has a different nose. More pointed than a line model. That is why you were confused.

Re:I've always wondered...

[billcopc]

The sonic boom is constant. It is because the sound source is travelling than the sound itself, thus the wave doesn't have a chance to decay before it is regenerated by the travelling object. The individual waves add up to form the sonic boom.

When a jet flies by, you would hear two booms: one at the front when the nose pierces the air, and another at the rear when the air fills the void behind the aircraft (in theory its polarity would be opposite that of the first).

Read about it here: Doppler Shift

Re:Wrong

[ishmaelflood]

Possibly, however you said " it was a failure because of the enormous fuel consumption per passenger,"

I took a few minutes to demonstrate that the cost of fuel was not, in itself, an especially large component of the running cost of the aircraft.

ALso, BA's accounts show that the Concorde operation was profitable prior to the crash.

Re:I've always wondered...

[FrYGuY101]

Actually, if you'll notice in those pictures, there is one massive burst, with several minor ones on places that you pointed out, mainly the canopy and wings.

The main boom is the one I was describing, and as far as I can tell, it was accurate. At least the Wikipedia seems to agree with me:

In smooth flight, the shock wave starts at the nose of the aircraft and ends at the tail. There is a sudden rise in pressure at the nose, decreasing steadily to a negative pressure at the tail, where it suddenly returns to normal. This "overpressure profile" is known as the N-wave due to its shape. We experience the "boom" when there is a sudden rise in pressure, so the N-wave causes two booms, one when the initial pressure rise from the nose hits, and another when the tail passes and the pressure suddenly returns to normal. This leads to a distinctive "double boom" from supersonic aircraft.

Re:Here are the Concorde problems:

[plusser]

There are a number of additional reason why Concorde was not a commercial success and was withdrawn from service:-

1) The wings were virtually hand made. This was because at the time of manufacture CNC machines had not been really developed. As a consequence when the linings were put in the fuel tanks on the BA aircraft after the Paris crash, they found the shape of the fuel tanks on each aircraft were completely different. The TU144 (Concordski) had less complicated wings, due to the use of Canards on the front of the aircraft.

2) Concorde could only just make JFK from Paris. If the wind were in the wrong direction, the plane couldn't fly. The proposed (but never built) B version of Concorde could have flown Supersonic from Germany to JFK, and could have reached a number of other destinations from London.

3) The Avionics on Concorde needed to be replaced for the aircraft to continue in service past 2004. I know this as the company I work for built the engine controllers, which were the first controller to have full digital control (RB211 engines on the 747 didn't get this until the 1980's). Needless to say the work was cancelled.

4) After the Paris crash, the work carried out on the aircraft meant that the Air France Concorde could not operate fully loaded with 100 passengers. I believe as Air France could then no longer operate the aircraft economically, therefore withdrew their service. This also made the BA service unviable. Due to political reasons the aircraft were not sold to another air carrier that were prepared to continue operating the aircraft (Virgin Atlantic).

To date Concorde is one of only 2 aircraft with supercruise capability (flying above Mach 1 without afterburn); the other is the F22. It has flown more hours supersonically than all the other supersonic planes in the world.

I spoke to Sir Richard Branson (Owner of Virgin Atlantic) live on BBC TV the day before Concorde was withdrawn from service. I asked him when he expected the replacement for Concorde to enter service, and he replied "not for another 30 to 40 years". I would hope that the developments into reducing supersonic noise and jet engine fuel economy would allow the development of a large passenger jet within the next 15 to 20 years, but that depends on the airline market for such an aircraft. A small supersonic business jet capable of reaching mach 1.4 may be in service in as little as 3 to 4 years, especially as Concorde is no longer in service.

Concorde will end up in history as the aircraft equivalent of the SS Great Eastern; a large Brunel ship that was built some 50 years ahead of its time. It too was never a commercial success, and was scrapped 30 years after entering service. No ship of the size of Great Eastern was built under the SS Titanic era of the early 20th century.