Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
"Engines In Sync" - What Does This Mean?  
User currently offlineCedarjet From United Kingdom, joined May 1999, 8058 posts, RR: 54
Posted (12 years 9 months 3 weeks 15 hours ago) and read 4908 times:

Hey now. Heard many references to engines being 'out of sync' and indeed I'm very familiar with the sensation from sitting at the back of many MD80s and hearing that weird throbbing sound.

What does 'sync' mean, how is it achieved, any info or observations please. Including an answer to the question, "Can engines not being in sync cause damage to the airframe, at least in as much as pop a few weakened rivets?" Is it important to the operation of the aircraft, or is it just a crowd pleaser for the back rows?


fly Saha Air 707s daily from Tehran's downtown Mehrabad to Mashhad, Kish Island and Ahwaz
5 replies: All unread, jump to last
 
User currently offlineFlight152 From United States of America, joined Nov 2000, 3388 posts, RR: 6
Reply 1, posted (12 years 9 months 3 weeks 15 hours ago) and read 4874 times:

Does it have to deal with a boy band? Big grin Big grin Big grin

User currently offlinePurdue Arrow From United States of America, joined May 1999, 1574 posts, RR: 8
Reply 2, posted (12 years 9 months 3 weeks 9 hours ago) and read 4847 times:

"Sync" is short for "syncronized". The engines are in sync when they are turning at the same rate. The pulsing sound you hear when the engines are not in sync comes from the different frequencies of the sound waves. I don't think it's damaging to the airframe (though I could be wrong), but it is not comfortable for the occupants and doesn't provide even thrust on both sides. It can be very fatiguing to flight crews to have that pulse in the background.

User currently offlineFBU 4EVER! From Norway, joined Jan 2001, 998 posts, RR: 7
Reply 3, posted (12 years 9 months 3 weeks 7 hours ago) and read 4829 times:

You mentioned the MD-80,but the DC-9 is worse regarding this matter.
On the DC-9,the pilots themselves have to manually synchronize the engines.Usually,it is the N1 (low pressure) fans that are synchronized,but,engines being the individuals they are,N2 (high pressure) fan synchronization might occasionally be better.I know some airlines have auto synch. on their -9's,but here in SAS we don't.
On the MD-80 and 90,there is a switch on the overhead panel which allows the pilots to select either EPR (default position),N1 or N2 synchronization.The autothrottle system has to be engaged to allow auto synch. which operates by adjusting the engine fuel controls automatically.



"Luck and superstition wins all the time"!
User currently offlineCedarjet From United Kingdom, joined May 1999, 8058 posts, RR: 54
Reply 4, posted (12 years 9 months 3 weeks 6 hours ago) and read 4828 times:

How close do the RPMs have to be to cancel each other out?

And is it, how can I put this, possible to achieve with different RPMS, ie they are in sync if the RPMs are the same, or if one is 2%/4%/8%/16% apart? Just curious cos it seems to be a kind of harmonic effect.

Thanks for the info so far, especially from Flight 152 (I was on a plane with N'Sync once, they threw peanuts).



fly Saha Air 707s daily from Tehran's downtown Mehrabad to Mashhad, Kish Island and Ahwaz
User currently offlineFBU 4EVER! From Norway, joined Jan 2001, 998 posts, RR: 7
Reply 5, posted (12 years 9 months 3 weeks 6 hours ago) and read 4817 times:

Achieving 100% perfect synchro is almost impossible as there will almost invariably be a slight difference between the N1 and N2 spools.You can synchro N1 but there will be a difference between N2,if you synchro N2,there will be a difference between the N1 spools,so you try to use the mode that gives the least noise.The auto synch uses one engine as "master" and "slaves" the other to this.Not sure about tolerances,but the number 1,5% seems familiar from somewhere.My AOM doe not mention any values or limits.


"Luck and superstition wins all the time"!
Top Of Page
Forum Index

Reply To This Topic "Engines In Sync" - What Does This Mean?
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
What Does This Mean In A Flight Plan? posted Sun Sep 14 2003 01:32:23 by Wardialer
What Does This Mean? posted Thu Feb 2 2006 23:04:52 by JetADude
What Does This Mean? posted Tue Apr 24 2001 06:47:22 by Bruce
WHat Does This Mean? posted Mon Apr 9 2001 07:59:38 by Chopper
"Metering......." What Does It Mean? posted Thu Jul 26 2001 22:14:38 by Trickijedi
What Does This ATC Communication Mean posted Wed Feb 22 2006 21:49:19 by LouA340
Part Of This Flight Plan? What Does It Mean? posted Fri Jul 30 2004 02:52:09 by Wardialer
What Does This DC-3 Sign Mean? posted Thu Aug 1 2002 20:53:48 by Mr Spaceman
What Does This Button Do On An A330? posted Wed May 17 2006 20:08:00 by MM
What Does ETOPS Mean? posted Tue Aug 30 2005 00:54:34 by Longhornmaniac

Sponsor Message:
Printer friendly format