L-188 From United States of America, joined Jul 1999, 30129 posts, RR: 58
Reply 1, posted (16 years 2 weeks 6 days ago) and read 1643 times:
There are several hush kits for the 727.
Allthough technically not a hush kit one of the most popular options for owners is to replace the two outboard motors with the same engines that power the MD-80. As part of this conversion the center engine thrust reverser is removed and replaced with a mixing baffle. The more powerfull JT8-200 engines make up for the lost of center engine thrust caused by the mixing baffle. They also allow for a lower engine thrust setting so the motors are less noisy.
The Northern Aircargo 727 on the top is not hush kitted.
The Corperate 727 on the bottom has the MD-80 engine conversion. Also it is sporting the Valsan winglet modifacation too. Sorry for the far away shot.
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Markus From United States of America, joined May 1999, 275 posts, RR: 0
Reply 3, posted (16 years 2 weeks 5 days 12 hours ago) and read 1643 times:
The center engine is not removed. Only the thrust reverser is removed and replaced with a mixing baffle. The center engine is still an intrigal part of the plane. The new engines just provide more thrust than did the old ones.
JETPILOT From United States of America, joined May 1999, 3130 posts, RR: 28
Reply 4, posted (16 years 2 weeks 5 days 4 hours ago) and read 1643 times:
There are two parts of a jet engine that can be hushed. These are the intake and exhaust.
The intakes are lined with special sound absorbant material to quiet the sound of the air entering the inlet.
The second area that can be silenced is the exhaust. The best method for doing this is to use exhaust gas mixing.
The reason turbofans are so quiet is because they use cold slow moving fan exhaust to surround the hot fast moving core exhaust. The lower the bypass ratio the more noisier it is.
727 Engines being a low bypass type are very noisy. The trick of a hush kit is to mix the slow moving fan exhaust with the fast moving core exhaust to quiet it down. That is the reason for the lobe type exhaust nozzles found on earlier 707's and DC8 Turbojets. Those are caled gas mixers. GIII's have them also.