Futuristic Biplane Design Eliminates Sonic Boom

Zothecula writes "A throwback to early 20th century aviation may hold the key to eliminating the sonic boom — at least according to researchers at MIT and Stanford University. Strongly reminiscent of biplanes still in use today, the researcher's concept supersonic aircraft introduces a second wing which, it is claimed, cancels the shockwaves generated by objects near or beyond the sound barrier."

Comments

Re:The problem.

[Icyfire0573]

I read the article, so I know that they fixed that by taking the old design which had no lift, ran it through a ton of simulations and found a design which has the lift necessary to fix this. It's not like people never discover new things.

Solving the worng problem

[TrumpetPower!]

Sure, sonic booms are (more than just) annoying, but that's not why we're highly unlikely to ever see supersonic commercial flight again.

The problem is that supersonic flight requires too damned much fuel for too little gain. Airlines are struggling to make a profit with today's already-fast airliners as fuel costs skyrocket. Cutting a six-hour flight (with a hour of "secure" groping before takeoff and another hour each to get to and from the airport) to a four-hour flight (with the same groping and pre- and post-travel times) just isn't that big of a deal. And it's especially not worth more than double the expense.

Figure out a way to move just as many people at a time with existing infrastructure with half the fuel, even if it means adding 50% to the travel time, and then the airline industry might get excited.

But this thing just ain't gonna take off.

Sorry.

b&

Re:The problem.

[pittance]

The Busemann biplane came up when we did supersonic aero in University back in '98 or '99 and it was always stated to be an impractical wing design because, at the supersonic zero boom/zero wave drag condition, it couldn't produce lift; this doesn't stop it being useful for other things like shells etc. where you don't mind zero supersonic lift if you can get low drag

The diagrams in the article seem to look like that condition in supersonic flow where the "inner" surfaces interfere favourably with each other to cancel wave drag and have the upper and lower surfaces with no incidence to the flow so they produce no shock waves.

Supersonically it should still produce lift quite happily if you angle it so there is incidence to the flow but I think that it should then produce wave drag and booms... For example I can't see from the article how, in a lifting condition, the shock wave from the compression of the supersonic flow on the undersurface (which produces the compression & higher pressure that helps lift the wing) could be cancelled out without having another wing underneath that; then you have the same problem with the undersurface of that wing & then you're in a "it's wings all the way down" problem.

Conventional 'low boom' solutions (like the Gulfstream/NASA "quiet spike") all tend to shape the nose of the aircraft to reduce the suddenness of the pressure increase across the shock wave but they aren't able to eliminate it...

It could be that they've found a case where they can get low wave drag/boom while still producing some lift and also getting decent subsonic lift/drag - that would be really interesting...

Re:No sonic boom?

[element-o.p.]

And of course the shock-wave itself causes some major control issues as you pass through the barrier itself, at least as I understand it, as well as creating a huge amount of drag. That is a large reason they had so much trouble breaking the barrier in the first place: the planes would lose control as they passed through it and crash.

Yep. There were two big problems with control. The first was that as you move from subsonic to supersonic, the center of lift would move. The aircraft was balanced for controllability at subsonic flows, but when you passed from subsonic to supersonic, the aircraft became unstable and would either crash or break up. The second problem was that the control systems were easily manipulated by the pilot at subsonic speeds, but the shock wave created at the control surface hinge was too great for a human to overcome -- pilots literally weren't strong enough to push the control surfaces against the shock wave until engineers developed all-flying tail surfaces (stabilators rather than elevators). Overcoming drag was basically just a problem of developing a powerful enough engine.

Re:No sonic boom?

[AmiMoJo]

Actually the banning of sonic booms was more political than based on reality. Boeing had pretty much given up on their supersonic passenger aircraft and the French/British design looked set to rule the long distance market.

Concord was still an impressive aircraft, cutting flight times to the US down to five hours. Unfortunately it cost a lot to design, build and run, but had it not been effectively banned from many parts of the world those costs would certainly have come down with volume and improvements to the technology. Instead the supersonic passenger jet market was killed before it really started.

We have been promised radically new aircraft designs for decades but they never seem to come. In many ways Concord was the last big step forwards, everything after that was just a refinement of existing technology.