Sonic booms – Concorde exempt?

[Eric Mc]

Also mentioned earler by me. A number of unmanned projectiles were already achieving supersonic speeds decades ahead of Yeager.

[Asterix]

RizzoTheRat said:

Think of it as the amount of energy it imparts to the air. Virtually all the energy used by the engines is to force it through the air, so anything that reduces fuel use (less weight, less air density, shape, etc) reduce the amount of energy put in to the air, and hence the amplitude of the shock (massive simplification but it gives the gist)

As said, a whip was probably the first man-made supersonic boom, but thunder also a shock wave.

You can also hear the shock wave quite well from bullets, you get the crack of the shock passing before you hear the thump of the weapon that fired it.

The good old 'crack-thump'. IIRC from my Army days, around half a second equated to around 300m away for a standard type of round.

Hence the saying 'you never hear the bullet that kills you'- this obviously assumes instantaneous death.

[Lord Pikey]

Tres Cool

http://www.youtube.com/watch?v=lCw9u_glJNw

edit - repost. sorry chaps

Edited by Lord on Thursday 15th March 14:48

[BliarOut]

I thought she used to fly out of Bahrain on full throttle?

[dr_gn]

Tango13 said:

dr_gn said:

RizzoTheRat said:

dr_gn said:

Depends on the MASS of the object?

Why is mass relevant to over pressure?

Because mass is directly proportional to the amount of lift generated.

So a Concorde completely stripped of all unecessary weight would create a weaker boom than a a Concorde loaded to it's limit, flying under otherwise identical situations?

How does that work?

The intensity of a sonic boom depends on various factors, the aircrafts weight, length, its pitch ie whether it's climbing or diving and the density of the air it's flying through.

OK, so let's say for an 'object' as opposed to an aircraft?

Get rid of lift, and you're left with - let's call it a ballistic object - like a missile or meteorite or something. If two of these hypothetical objects had exactly the same form and speed, but one was half the weight, wouldn't the sonic booms be the same even though due to their different masses, their kinetic energies were totally different?

[Ian Lancs]

kooky guy said:

Surely the SR-71 flew so high that there would be insufficient air to generate a sonic boom...?

And Concorde come to that, once it was up to cruising height...? (60000ft if I recall correctly - and > 70000 for the SR-71)

If there was insufficient air to generate a sonic boom, you'd be a very worried passenger on Concorde - not enough air, means no engine thrust.

[navier_stokes]

The strength of a shock wave depends on velocity of the object, the temperature of the medium it is flying through and the geometry of the object, that's it...

[dr_gn]

navier_stokes said:

The strength of a shock wave depends on velocity of the object, the temperature of the medium it is flying through and the geometry of the object, that's it...

That's what I assumed 2 pages ago, but apparently, for an aircraft you should factor in weight, due to the lift requirements of aircraft of differing weights.

Fundamentally though for an "object" I think it's the three factors you just wrote.

Is there an equation for shock wave strength? If so, does it include mass?

[Hooli]

dr_gn said:

navier_stokes said:

The strength of a shock wave depends on velocity of the object, the temperature of the medium it is flying through and the geometry of the object, that's it...

That's what I assumed 2 pages ago, but apparently, for an aircraft you should factor in weight, due to the lift requirements of aircraft of differing weights.

Fundamentally though for an "object" I think it's the three factors you just wrote.

Is there an equation for shock wave strength? If so, does it include mass?

I think for the aircraft to be producing extra lift then it'll be trimmed slightly nose up compared to when carrying less weight. That higher angle of attack increases the frontal area as the wings aren't horizontal to the flight path.

[daz3210]

Hooli said:

dr_gn said:

navier_stokes said:

The strength of a shock wave depends on velocity of the object, the temperature of the medium it is flying through and the geometry of the object, that's it...

That's what I assumed 2 pages ago, but apparently, for an aircraft you should factor in weight, due to the lift requirements of aircraft of differing weights.

Fundamentally though for an "object" I think it's the three factors you just wrote.

Is there an equation for shock wave strength? If so, does it include mass?

I think for the aircraft to be producing extra lift then it'll be trimmed slightly nose up compared to when carrying less weight. That higher angle of attack increases the frontal area as the wings aren't horizontal to the flight path.

Which alters the geometry yes?

[dr_gn]

daz3210 said:

Hooli said:

dr_gn said:

navier_stokes said:

The strength of a shock wave depends on velocity of the object, the temperature of the medium it is flying through and the geometry of the object, that's it...

That's what I assumed 2 pages ago, but apparently, for an aircraft you should factor in weight, due to the lift requirements of aircraft of differing weights.

Fundamentally though for an "object" I think it's the three factors you just wrote.

Is there an equation for shock wave strength? If so, does it include mass?

I think for the aircraft to be producing extra lift then it'll be trimmed slightly nose up compared to when carrying less weight. That higher angle of attack increases the frontal area as the wings aren't horizontal to the flight path.

Which alters the geometry yes?

Effectively, I think so.

So I'd argue that fundamentally (or maybe theoretically), mass has no effect at all on the magnitude of a sonic boom, but practically it does, because it has the knock-on effect of altering form.

I'd assume that if there was an equation defining the magnitude, mass wouldn't be in there.

[RizzoTheRat]

That would be my interpretation too. And I'm certainly not going to argue aerodynamics with someone who's username is Navier Stokes!

[Dr Jekyll]

I'd certainly assume that the Thrust SSC bang wasn't affected by mass.

[Zad]

Not actually Concorde: http://www.youtube.com/watch?v=TYEtQGLzvkI

Still makes me go a bit weak at the knees though.

[Hooli]

daz3210 said:

Hooli said:

dr_gn said:

navier_stokes said:

The strength of a shock wave depends on velocity of the object, the temperature of the medium it is flying through and the geometry of the object, that's it...

That's what I assumed 2 pages ago, but apparently, for an aircraft you should factor in weight, due to the lift requirements of aircraft of differing weights.

Fundamentally though for an "object" I think it's the three factors you just wrote.

Is there an equation for shock wave strength? If so, does it include mass?

I think for the aircraft to be producing extra lift then it'll be trimmed slightly nose up compared to when carrying less weight. That higher angle of attack increases the frontal area as the wings aren't horizontal to the flight path.

Which alters the geometry yes?

I missed that bit in your post, yes I'd agree.

[Le TVR]

Sorry, missed the discussion as I've been away.

For a flying object as opposed to a balistic object the mass is directly related to overpressure.
To fly, the mass of air deflected by the flying surfaces is directly proportional to the mass of the object being sustained in flight. The mass of the deflected air is proportional to the the size of shock wave created hence the overpressure.

I'll try and find my lecture notes on hypersonics when I'm back home for the formulae.

[crofty1984]

RizzoTheRat said:

Because mass is directly proportional to the amount of lift generated.

Is it? The amount of lift required, yes.

[navier_stokes]

dr_gn said:

navier_stokes said:

The strength of a shock wave depends on velocity of the object, the temperature of the medium it is flying through and the geometry of the object, that's it...

That's what I assumed 2 pages ago, but apparently, for an aircraft you should factor in weight, due to the lift requirements of aircraft of differing weights.

Fundamentally though for an "object" I think it's the three factors you just wrote.

Is there an equation for shock wave strength? If so, does it include mass?

There is an equation for the pressure difference across a shock (which effectively gives you the strength) and it does not include mass!

In general, an aircraft with higher wing loadings will produce stronger shocks due to higher pre-shock Mach numbers - but this is a generalisation as the pre-shock mach number will be highly dependent on the wing geometry. I.e. lift is not directly related to the shock strength, but they do often go hand-in-hand.

[Le TVR]

navier_stokes said:

There is an equation for the pressure difference across a shock (which effectively gives you the strength) and it does not include mass!

http://www.nasa.gov/centers/dryden/news/FactSheets/FS-016-DFRC.html

[navier_stokes]

Le TVR said:

navier_stokes said:

There is an equation for the pressure difference across a shock (which effectively gives you the strength) and it does not include mass!

http://www.nasa.gov/centers/dryden/news/FactSheets/FS-016-DFRC.html

As has been discussed, mass is irrelevant. Only additional lift, which is required as a bi-product of increased weight, is proportional to shock intensity.

If you have two identical wings flying through the same medium - one made of lead and the other of aluminium, the resulting aerodynamics, and thus shock structure would be identical (ignoring surface finish and aeroelastic effects).

Edited by navier_stokes on Tuesday 20th March 21:09