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.

No sonic boom?

[93 Escort Wagon]

Where's the fun in that? Seriously, when I was a kid living near an air force base, I thought the sonic booms were the coolest thing ever.

Re:No sonic boom?

[jamstar7]

One of the problems with the Concorde was, they weren't allowed to fly at supersonic speeds across the US because of the booms. So, supersonic London to LA was flat out of the question. From what I understand, a lot of other countries followed suit, outlawing supersonic flights in their airspaces. Without the speed advantage, the Concorde was a low passenger fuel hog that turned into a hanger queen and eventually got grounded and decommissioned. Fix the sonic boom problem, get fuel economy as a bonus, and we just might see the Concorde II in our lifetimes. LA to Melbourne in under 14 hours? COOL!!!

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.

Romulans?

[gstoddart]

Is it me, or does that look like a Romulan War Bird? :-P

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:Solving the worng problem

[Chuckstar]

Concorde flight time from JFK to Heathrow was closer to 3 hours. And among a very wealthy (or expense accounted) class it was very popular (just not quite popular enough).

But remember that the biggest impediment to the success of Concorde might have really been that it only made sense to fly JFK Heathrow and JFK de Gaulle. Because of this, few planes were built, eliminating any economies of scale of building or even maintaining them. Also eliminating the possibility of follow-on models -- as it is often the subsequent models where the manufacturer finally gets it "right".

The reason this is announcement is a big deal, therefore, is that it potentially fixes Concorde's achilles heel -- that it was only allowed to go full speed over water, and didn't have the range to go over water any further than NY to Europe. This plane could fly over land, and have a longer range -- opening the possibility of many more city-pairs, many more sales, therefore economies of scale.

Having said that, barring a magic bullet like "engineers figure out sure-fire way to make a Mach-2 passenger jet at only 50% higher cost per passenger mile with limited up-front development risk", you are correct that no one is going to spec billions to see if they can make the thing work. Concorde was cool, but a financial boondoggle for Britain and France. Boeing thought about making a (relatively) efficient Mach-0.95 jet, but at the cost of a dramatic departure from traditional airliner design. They decided the risk was too great and went with the more traditionally-shaped 787.

We're stuck at Mach-0.85 until another government decides to underwrite the development costs. There's just too much risk for a private corporation to take on. They could spend billions and have it just not work.

The one possibility for this tech, however, is for a really high-end private jet. A guy like Burt Rutan might be able to put together a skunk-works-style prototype of the thing, and then sell copies at a few hundred million a piece. At that price, could probably sell a half-dozen around the world.

(Note: current passenger jets can reach top speeds above Mach-0.9, but typical cruising speed is right around Mach-0.85.)

Re:The problem.

[Chuckstar]

The MIT team is not using an adaptive wing. As described by Icyfire0573 above "...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."

There is a team in Japan that is using an adaptive wing. Depending on exactly how the Japanese team's wing adapts, that could be an impediment to use in a commercial airliner. Thinking about current airliner designs, the wing surface shape is modified by flaps and slats, but the core load bearing structures of the wings (spars and the connection points to the airframe) remain fixed. I would be wary of a swing-wing design for commercial air, for instance, but something similar to flaps/slats would theoretically be no more of a safety risk than today's (incredibly safe) designs.

In addition to safety, there is also the simple fact that fewer moving parts would be cheaper to build and maintain.

Sub-supersonic speeds?

[damburger]

At sub-supersonic speeds, a Busemann Biplane doesn't produce sufficient lift under acceleration, undergoing considerable drag.

Well, that is all well and good - but what happens at super-subsupersonic speeds?

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:The problem.

[element-o.p.]

With a zero degree angle of attack your aircraft with any amount of thrust will fall...

Are you sure about that? I think you confused "angle of attack" with "coefficient of lift."

There are airfoil designs (basically, any asymmetric airfoil) that will produce lift at an AoA of zero degrees. If lift is non-zero, then the only question is how fast does an aircraft need to be going to generate enough lift to overcome weight at a zero-degree angle of attack?

Also, just to be pedantic, the balancing act is between lift, weight, thrust and drag. Lift is related to AoA so I'll concede that you basically covered that force, but you completely neglected to mention drag above.