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Sonic Boom/Pressure Wave Question

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posted on Mar, 12 2006 @ 11:48 AM
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I have been taught that a Sonic Boom consists of a pressure wave of compressed air molecules moving away from leading edges of an aircraft. I need to know two things about this, if you guys wouldn't mind.

How fast does this pressure wave move away from the aircraft? (I think its the speed of sound)

And What would happen if you directed this pressure wave into the intakes of the aircraft? Would it give a sudden boost in thrust as the molecules compress themselves more in the engine, or tear it off?




posted on Mar, 12 2006 @ 11:51 AM
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Originally posted by Darkpr0
How fast does this pressure wave move away from the aircraft? (I think its the speed of sound)

And What would happen if you directed this pressure wave into the intakes of the aircraft? Would it give a sudden boost in thrust as the molecules compress themselves more in the engine, or tear it off?


www.pbs.org...

hope this clears it up.

Justin



posted on Mar, 12 2006 @ 04:04 PM
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Originally posted by Darkpr0

And What would happen if you directed this pressure wave into the intakes of the aircraft? Would it give a sudden boost in thrust as the molecules compress themselves more in the engine, or tear it off?


Don't want to direct the wave anywhere near the engines - it would unbalance the fan/compressor face with bad bad results.



posted on Mar, 12 2006 @ 05:16 PM
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Originally posted by Darkpr0

And What would happen if you directed this pressure wave into the intakes of the aircraft? Would it give a sudden boost in thrust as the molecules compress themselves more in the engine, or tear it off?


jet engines slow supersonic air down before it is compressed for combustion, like on the concord or military jets





A ramjet has no moving parts and achieves compression of intake air by the forward speed of the air vehicle. Air entering the intake of a supersonic aircraft is slowed by aerodynamic diffusion created by the inlet and diffuser to velocities comparable to those in a turbojet augmentor. The expansion of hot gases after fuel injection and combustion accelerates the exhaust air to a velocity higher than that at the inlet and creates positive push.







Scramjet is an acronym for Supersonic Combustion Ramjet. The scramjet differs from the ramjet in that combustion takes place at supersonic air velocities through the engine. It is mechanically simple, but vastly more complex aerodynamically than a jet engine. Hydrogen is normally the fuel used.



posted on Mar, 13 2006 @ 06:42 AM
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Originally posted by bigx01
jet engines slow supersonic air down before it is compressed for combustion, like on the concord or military jets


Yes, but I think he means the mach cone pressure wave coming from the nose of the aircraft - which is kept well clear of the engine air intakes.

[edit on 13-3-2006 by kilcoo316]



posted on Mar, 13 2006 @ 07:35 AM
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The reason that the intake of an engine compresses the air is to force it to slow down. If the air was to hit the compressor blades at mach 1 they would shatter and blow the engine apart. That's why if you look at the engine of the SR-71 is has the moveable cone in the intake.



posted on Mar, 13 2006 @ 09:38 AM
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Originally posted by Zaphod58
The reason that the intake of an engine compresses the air is to force it to slow down. If the air was to hit the compressor blades at mach 1 they would shatter and blow the engine apart. That's why if you look at the engine of the SR-71 is has the moveable cone in the intake.


That wouldn't shatter the blade in itself. Sure turbofan blade tips run at local speeds higher than the speed of sound - hence buzzsaw noise.

But the nose pressure wave on the fan face would cause very local and very large force variations on the fan blades, which would unbalance the bearings and may also make the blade fail. For sure it would cause the compressor to stall or surge.



posted on Mar, 13 2006 @ 11:48 PM
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I see. This complicates matters. Is there any way to widen the mach cone pressure wave's effect? Diffuse it somehow?Or redirect it before it hits the fan blades?



posted on Mar, 14 2006 @ 06:55 AM
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Originally posted by Darkpr0
I see. This complicates matters. Is there any way to widen the mach cone pressure wave's effect? Diffuse it somehow?Or redirect it before it hits the fan blades?


Its quite simple really - place the air intakes far enough back on the plane that the shock cone is upstream of it.

From memory, I think the eqn for a shock cone is M = 1/(sin[alpha])

where:
alpha = shock cone angle
M = flight Mach number

Its pretty much this equation that tells you the SR-71 Blackbird's max speed is around Mach 3.3 or so [simply look at the wing planform, and measure the angle from the aircraft nose to the most forward point on the wing or engine inlet.



posted on Mar, 15 2006 @ 03:28 AM
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Originally posted by Zaphod58
The reason that the intake of an engine compresses the air is to force it to slow down.



the reason you slow the air to subsonic speeds is so that the fuel (kerosene) has time to burn. that's why scram jets use either hydrogen or methane.
turbines can only produce x amount of thrust. you go to a ramjet for an increase in speed and a scram jet so you don't have to carry the oxidizer with you and can use the oxygen in the atmosphere

[edit on 15-3-2006 by bigx01]



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