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Re: [OM] IMG: An Infrequent Visitor

Subject: Re: [OM] IMG: An Infrequent Visitor
From: Chris Trask <christrask@xxxxxxxxxxxxx>
Date: Wed, 9 May 2012 06:15:29 -0700 (GMT-07:00)
>
> > I suspect it helps, but the aircraft is noisy on the ground. 
> > Even the co-pilot called it loud.  It may be the interplay
> > between the five-bladed props and the twin exhausts of the
> > engine in each nacelle.
>
>
> It's probably the prop blades feathered but with the engine
> still turning over at normal speed.  The C-130 is pretty noisy,
> and unmistakeable, on the ground.
>
> But I suspect a former C130 pilot would know better  . . .
>

     Might be that the engine exhaust passing through the prop is the source of 
most of the noise.  On the C-130 most of the noise was due to the supersonic 
blasts caused by the adjacent props.  Since they spin in the same clockwise 
direction, the speed of the air between them is no small matter.  There is a 
"sync master" on the right side of the flight deck that keeps the props 45 
degrees apart so as to minimize the noise, if it works.  You could adjust the 
one control to change the phase angle and move the centre of the noise.

     The new Airbus M400 solved that by having the adjacent props turn in 
opposite directions.  Nice looking plane, especially with the topside spoilers. 
 But fuel efficiency and range are not very good.  It has twice the power of a 
C-130J, but the Snecma engines are fuel hogs.

Chris

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