Re: Hush Kits

From:         David Lednicer <>
Date:         31 Mar 95 02:41:28 
References:   1
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	The state of the art in hush kits seems to be to first mix the 
core and bypass flow internally before then mixing this flow with 
external air drawn into a shroud.  The idea is to get as much mixing 
before releasing the exhaust flow.  Also, on JT8D aircraft, there is an 
Inlet Guide Vane (IGV) respacing change made to reduce inlet tones.  

	I worked on the Sound Solutions 737 hush kit, which is RIP now.  
It was similar to Nordam's, but our shroud retracted after take-off.  
Besides the standard IGV mod, we used the P&W mod 3 mixer to mix core and 
bypass and then we had a 14(?) lobe mixer for exhaust and external 
mixing.  As I noted, our shroud was only back aft of the mixer for 
take-off and landing and the thrust reverser was integral with the 
shroud.  Nordam's shroud is fixed and they suffer a cruise fuel burn 
penalty because of this.  They use the stock 737 (DC-9) thrust reverser 
which is bolted on to the aft end of their shroud.

David Lednicer             | "Applied Computational Fluid Dynamics"
Analytical Methods, Inc.   |   email:
2133 152nd Ave NE          |   tel:     (206) 643-9090
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