Blackbird
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Sonic Boom Reduction Techniques

Fri Dec 22, 2006 4:17 am

So, what measures have been thought up to reduce sonic booms so far?

I remember hearing one idea regarding sonic-boom reduction, in which a blunter nose would be used to prevent an underpressure behind the wave and preventing the shocks on the wing-root, and engine pod and pylon to coalesce with the bow-shock and reducing the boom strength. I don't know if I'm interpreting this right, but that sounds like an unpleasantly large amount of drag. (Why not just take an ordinary nose design, put a whole bunch of tiny holes at the front of the nose in key points where the underpressure area would be and shoot a little bit of bleed-air out of the holes? Wouldn't that kill the underpressure?)

Andrea K

[Edited 2006-12-21 20:18:45]
 
N231YE
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RE: Sonic Boom Reduction Techniques

Fri Dec 22, 2006 4:55 am

There was a post on here a while back about a sonic-boom reduction boom (woo-hoo    sorry for any language confusion). Anyways, the boom retracted and extended as needed, altering the sonic-boom and causing a reduction in noise.

EDIT: Found the post, and some pictures
SST - (by Starlionblue Oct 11 2006 in Tech Ops)



[Edited 2006-12-21 20:59:53]
 
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Starlionblue
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RE: Sonic Boom Reduction Techniques

Fri Dec 22, 2006 6:06 am

I read something about anhedral angling the boom out, so that the same amount of noise is distributed over a larger area on the ground. This gives less noise at any given point on the ground.

Or something like that.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Starglider
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RE: Sonic Boom Reduction Techniques

Fri Dec 22, 2006 6:44 am

Quoting Blackbird (Thread starter):
So, what measures have been thought up to reduce sonic booms so far?

Busemann's Biplane:

The top of the upper wing is flat, same goes for the bottom of the lower wing. That allows the airflow to move past with little or no shock.

The lower side of the upper wing and upper side of the lower wing can be compared with a cross section of an inlet ramp. Both have a wedge pointing at each other. It reduces the wave drag by the interference of the shock and expansion waves which generate between the biplane. The wave drag is minimized at the position of that shock wave, which is generated from the leading edge of one half-wedge wing and hits the peak of the other half-wedge wing. These were wind tunnel models where flow analysis was conducted at a Mach number of 2.5. It was confirmed that the generated shock waves almost disappeared by the interference between the two wings. It spreads the residual shocks over much larger footprint. This results in sonic-boom reduction which is almost insignificant on the ground.

The above described model does not generate lift because the outer surfaces are flat. With more research there may be a way to make the lower surface dynamic so that it can generate lift. If it works, the concept could make it's way to a next generation SST. It should be able to reach altitudes where it would not do harm to the stratospheric ozone layer (mainly due to NOx and HOx emissions), meaning altitudes well above 70.000 ft.

Google for the Busemann biplane and find out more.

Regards,
Starglider
 
Blackbird
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RE: Sonic Boom Reduction Techniques

Fri Dec 22, 2006 7:34 am

N231YE,

Haha, I like that idea... So simple and lo-tech and yet so effective


Starlionblue,

Is that the one with the anhedral tips, and dihedral wing with a fairly blunt nose, and a rapidly narrowing tail with minimal pressure changes in between?


Starglider,

I'm not particularly fond of that idea


Andrea K
 
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Starlionblue
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RE: Sonic Boom Reduction Techniques

Fri Dec 22, 2006 7:58 am

Quoting Starglider (Reply 3):
The above described model does not generate lift because the outer surfaces are flat.

Couldn't you just fly with a slight angle of attack and solve that problem? After all, even a flat plane will generate lift if you give it an angle of attack. But presumably that would generate some sort of shockwave at the kilt.

Quoting Blackbird (Reply 4):
Is that the one with the anhedral tips, and dihedral wing with a fairly blunt nose, and a rapidly narrowing tail with minimal pressure changes in between?

I think so.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Blackbird
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RE: Sonic Boom Reduction Techniques

Fri Dec 22, 2006 8:18 am

Starlionblue,

To my knowledge you could fly it at a low angle of attack, but I think there are better ways to get the job done.

I just did a search on google after I read your original message about the anhedral-thing. It sounds very similar to the idea I was talking about earlier, using a fairly blunt nose to produce high pressure behind the wave to avoid coalescing the shockwaves together. The drag levels sound like they'd be a bit higher than desirable at the nose. And the tail, probably would not work particularly well at subsonic speeds. Airflow might be a bit turbulent back there.

To be honest, a normal nose with a tiny amount of bleed air sounds more efficient than blunting the nose. You'd blow some forward, some up, and use some small holes to skim of any excessively turbulent areas. You'd only need a little bit of bleed-air for this to work and it would blank the underpressure behind the shock. And the holes would absorb some turbulent results.

However, the telescoping nose idea would be the simplest, and easiest idea to work.


Andrea K
 
GAIsweetGAI
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RE: Sonic Boom Reduction Techniques

Fri Dec 22, 2006 8:44 am

Another concept that somewhat worked is this:



A modified US Navy F-5.
"There is an art, or rather a knack to flying. The knack lies in learning how to throw yourself at the ground and miss."
 
N231YE
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RE: Sonic Boom Reduction Techniques

Fri Dec 22, 2006 8:47 am

Quoting GAIsweetGAI (Reply 7):
Another concept that somewhat worked is this:

I forgot about that. Thanks for mentioning it.

Quoting Blackbird (Reply 4):
N231YE,

Haha, I like that idea... So simple and lo-tech and yet so effective

Pinocchio!

[Edited 2006-12-22 00:49:08]
 
Starglider
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RE: Sonic Boom Reduction Techniques

Fri Dec 22, 2006 9:42 am

Quoting Starlionblue (Reply 5):
Couldn't you just fly with a slight angle of attack and solve that problem? After all, even a flat plane will generate lift if you give it an angle of attack. But presumably that would generate some sort of shockwave at the kilt.

Yes, the configuration would only work at zero alpha and at a specific Mach number. Any deviation in angle of attack would generate a shock wave. A more complex problem with the Busemann biplane is that it has poor performance at subsonic speeds. Any movable surface on such a configuration to handle the low speed area of the envelope could generate negative effects, disturbances, at cruising speed.

Another option that has been tested is to mimic a Busemann biplane by using a single wing with a nozzle shaped underside, together with an under-wing planar jet of engine compressor air. At cruising speed the under wing high speed jet of air, mimicking to some extent the lower wing of the Busemann biplane, is then used to deflect the downward propagating shock wave produced at the leading edge of the wing. This jet reflection system is also intended to recover energy lost to dissipation in the shock. In this case most but not all of the bow shock will be deflected by the jet. Some of the shock would exit through the jet but considerably weakened and the sonic-boom may still be insignificant on the ground. At lower speeds the wing can function as a conventional wing with the jet of air under the wing switched off.

Quoting Blackbird (Reply 4):
I'm not particularly fond of that idea

But in theory it does suppress a sonic-boom. Putting it into practice is a bit tougher. Solving problems is what puts fun into engineering.  stirthepot 
 
Blackbird
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RE: Sonic Boom Reduction Techniques

Fri Dec 22, 2006 11:42 am

Yeah, but I figure to make such a design (Busemann wing) work, it would require a lot of work. Lots of variable geometry to provide effective sonic boom nullification across the whole speed-range and to provide low-speed handling. Too much of a pain.

All the other ideas sound far more practical and easier to pull off.

Andrea K
 
Starglider
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RE: Sonic Boom Reduction Techniques

Fri Dec 22, 2006 9:50 pm

Quoting Blackbird (Reply 10):
Too much of a pain.

New explorations will always endure some pain . . . We explore things . . "not because they are easy but because they are hard" . . to quote John F. Kennedy, 1962.

And to add to that . . . don't try to make complicated things simple or make simple things complicated. They are what they are for a reason.

Supersonic aerodynamics are complicated.

If the Busemann biplane concept would ever work this is what it might look like:

Big version: Width: 500 Height: 375 File size: 27kb


Regards.
Starglider
 
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Starlionblue
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RE: Sonic Boom Reduction Techniques

Sat Dec 23, 2006 1:30 am

Quoting Starglider (Reply 11):

New explorations will always endure some pain . . . We explore things . . "not because they are easy but because they are hard" . . to quote John F. Kennedy, 1962.

And to add to that . . . don't try to make complicated things simple or make simple things complicated. They are what they are for a reason.

Supersonic aerodynamics are complicated.

If the Busemann biplane concept would ever work this is what it might look like:

My feelings exactly. In 10 years, we might have smart metals that can morph at the nano level without mechanics. Hang on a minute, we already have those in the lab...
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Blackbird
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RE: Sonic Boom Reduction Techniques

Sat Dec 23, 2006 5:15 am

The Busemann biplane is definetly a fascinating idea. I won't deny it.
 
Starglider
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RE: Sonic Boom Reduction Techniques

Tue Dec 26, 2006 11:56 am

Quoting Starlionblue (Reply 12):
My feelings exactly. In 10 years, we might have smart metals that can morph at the nano level without mechanics. Hang on a minute, we already have those in the lab...

Here is a cross-section with movable leading and trailing edges for low-speed handling, perhaps to be made out of morphing metals.


Big version: Width: 500 Height: 301 File size: 14kb


Quoting Blackbird (Reply 13):
The Busemann biplane is definetly a fascinating idea. I won't deny it.

It sure is. Here are a few wind tunnel shots showing the shock-waves at different speeds:


Big version: Width: 400 Height: 272 File size: 14kb
Big version: Width: 350 Height: 222 File size: 8kb
Big version: Width: 350 Height: 230 File size: 7kb
 
Blackbird
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RE: Sonic Boom Reduction Techniques

Wed Dec 27, 2006 2:46 am

If you have a curved structure on the bottom part of the Busemann Biplane to produce lift, you'll get a shockwave.

To be honest, running huge amounts of electricity through the nose part of the plane seems a hell of a lot simpler to get the same results. They current levels could be varied across various parts of the nose and could reduce the strength of the shockwaves. Of course, there'd be a risk of fatal electrocution for personnel on the ground, unless it's turned off.

And my previous creative little idea of running some hot bleed air just behind the shockwave and then skimming off any turbulent result further aft, I'm not sure if it would produce any less drag than using a blunter nose! (Any ideas on this one?)

Andrea K
 
Starglider
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RE: Sonic Boom Reduction Techniques

Wed Dec 27, 2006 5:48 am

Quoting Blackbird (Reply 15):
If you have a curved structure on the bottom part of the Busemann Biplane to produce lift, you'll get a shockwave.

You are correct. Assuming your comment refers to the sectional drawing with the dimensions, i should have written: high lift devices for subsonic speeds because that is what the drawing represents.

Quoting Blackbird (Reply 15):
To be honest, running huge amounts of electricity through the nose part of the plane seems a hell of a lot simpler to get the same results. They current levels could be varied across various parts of the nose and could reduce the strength of the shockwaves. Of course, there'd be a risk of fatal electrocution for personnel on the ground, unless it's turned off.

Reading your words i suppose you mean using electricity to alter the leading and trailing edges as an alternative to morphing? Please explain how that would work. Let me guess, using electricity like in magnetism whereby the upper- and lower surface wing leading- and trailing-edges are attracted to each other by an electric current?

To prevent electrocution one could wire the system via the weight-on-wheel switches. Armed to switch off at touch-down like current lift-dumpers are armed to extend. Electrical current is then switched off which bleeds off lift with the wing surfaces returning to their flat state. Essentially acting as a lift-dumper. With the vehicle on jacks, other measures would have to be taken like pulling c/b's and huge warning signs when the system needed to be activated for adjustment or testing. For take-offs however, the system must be selected to create lift. That would need a system which, when in take-off mode, overrides the weight-on-wheel circuit.

Quoting Blackbird (Reply 15):
And my previous creative little idea of running some hot bleed air just behind the shockwave and then skimming off any turbulent result further aft, I'm not sure if it would produce any less drag than using a blunter nose! (Any ideas on this one?)

I understand your idea. I will look into this a bit further as it may or may not have some resemblance to something i mention in another thread i've started titled "SST Emissions and Noise". There i describe an issue regarding base pressure increase (drag reduction) at a flattened after body (boat-tail) using bleed air flow extracted from an air inlet induction system which is ejected at the flattened after-body into the wake of the aircraft's aft shock-wave. I will post my reply to your question later.

Regards,
Starglider

[Edited 2006-12-26 21:49:02]
 
Blackbird
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RE: Sonic Boom Reduction Techniques

Wed Dec 27, 2006 7:51 am

Starglider,

When I mentioned the electric-field generation idea, I did not mean it to be misenterpreted as magnetically attracting the upper and lower wings of a busemann plane. I meant using an electrical field on the leading edge of the nose of a run of the mill pointy-nosed, delta monoplane configuration. The electrical field produces plasma, and could provide a number of useful effects, including reducing the strength of sonic booms.

Andrea K
 
Starglider
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RE: Sonic Boom Reduction Techniques

Wed Dec 27, 2006 11:03 pm

Quoting Blackbird (Reply 15):
And my previous creative little idea of running some hot bleed air just behind the shockwave and then skimming off any turbulent result further aft, I'm not sure if it would produce any less drag than using a blunter nose! (Any ideas on this one?)

Perhaps this is of help:

http://www.smithinst.ac.uk/Projects/ESGI40/ESGI40-VRC/Report

On the website above you can download a report "ShockFree" which deals with a bleed-air jet, modelled by two vortex sheets enclosing a region of uniform high speed flow. It deals with the interaction between the jet and an incident shock breaking down ito two successive interactions.

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