Post by liam*Post by \\¯`·.žbizž.·Ž¯/Breen Gin (RFC 52 Titles) <Champions-of-Scotland>
Post by Breen Gin (RFC 52 Titles)Post by Jonathan BryceI doubt it. The gig was almost certainly planned before Celtic
knew they were going to finish second in last year's league,
nevermind be drawn with Arsenal in their second qualifying round.
Whooooooooooooooooooooooooooooooooooooooosh
A bigger whoosh than the sound of a helicopter making a sudden U-Turn!
Do helicopters do whoosh sounds?
In laymens terms, yes.
In aeronautical engineering terms a helicopter /does/ many different types
of sounds:
*Thickness noise*
Thickness noise is dependent only on the shape and motion of the blade, and
can be thought of as being caused by the displacement of the air by the
rotor blades. It is primarily directed in the plane of the rotor.
*Loading noise*
Loading noise is an aerodynamic adverse effect due to the acceleration of
the force distribution on the air around the rotor blade due to the blade
passing through it, and is directed primarily below the rotor. In general,
loading noise can include numerous types of blade loading: some special
sources of loading noise are identified separately.
*Blade-vortex* *interaction* *(BVI) noise*
BVI occurs when a rotor blade passes within a close proximity of the shed
tip vortices from a previous blade. This causes a rapid, impulsive change in
the loading on the blade resulting in the generation of highly directional
impulsive loading noise. BVI noise can occur on either the advancing or
retreating side of the rotor disk and its directivity is characterized by
the precise orientation of the interaction. In general, advancing side BVI
noise is directed down and forward while retreating-side BVIs cause noise
that is directed down and rearward. It has been shown that the main
parameters governing the strength of a BVI are the distance between the
blade and the vortex, the vortex strength at the time of the interaction,
and how parallel or oblique the interaction is.
*Broadband noise*
Another form of loading noise, broadband noise consists of various
stochastic noise sources. Turbulence ingestion through the rotor, the rotor
wake itself, and blade self-noise are each sources of broadband noise.
*High-speed impulsive (HSI) noise*
HSI noise is caused by transonic flow shock formation on the advancing rotor
blade, and is distinct from loading noise. The source of HSI noise is the
flow volume around the advancing blade tip, hence it cannot be captured by
examining only the acoustic sources on the surface of the blade, HSI noise
is typically directed in the rotor plane forward of the helicopter, like
thickness noise.
*Tail rotor noise*
While most noise from a helicopter is generated by the main rotor, the tail
rotor is a significant source of noise for observers relatively close to the
helicopter, where the higher-frequency noise of the tail rotor has not yet
been attenuated by the atmosphere. Tail rotor noise is particularly annoying
to the human listener due to its higher frequency (as compared to the main
rotor) which places it directly in the band in which the human ear is most
sensitive.
Another audible phenomenon caused by helicopters is Greetin Faced Timmy
(GFT) noise. This is caused when the MacDonald effect causes 60'000 cheers
to turn into cries of "come back" followed by a loud roar of jubilation in
the other side of town.
;o)
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