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Fan Blade Tip Clearance  
User currently offlineThyengine From Turkey, joined Dec 2005, 4 posts, RR: 0
Posted (8 years 8 months 3 weeks 9 hours ago) and read 6409 times:

You know, in ESM's (Engine Shop Manual) are Fan blade tip clearance limits(min,max). This tip clearance gives different performance resullts (EGT,EPR..etc.) between test cell and on-wing.
Could anybody make a comment what the result would be both in test cell and on-wing If we either adjust the clearance to min or max?

6 replies: All unread, jump to last
 
User currently offlineFr8Mech From United States of America, joined Sep 2005, 5400 posts, RR: 14
Reply 1, posted (8 years 8 months 2 weeks 6 days 22 hours ago) and read 6284 times:

Greater tip clearance results in reduced engine efficiency due to the air escaping between the tip and shroud.

A clearance closer to the minimum will increase efficiency but depending on how close the tolerance is, may run the chance of fan lade rub. This may be a simple rub on the abraidable lining or cause an unacceptable vibration condition.



When seconds count...the police are minutes away.
User currently offlineLiedetectors From United States of America, joined Jul 2005, 360 posts, RR: 0
Reply 2, posted (8 years 8 months 2 weeks 6 days 19 hours ago) and read 6238 times:

Quoting Fr8Mech (Reply 1):
, may run the chance of fan lade rub.

This correct. One way they get around this is for the tips to actually slice into a foam like material to better seal around the tips. I was skeptical at first but when i saw this in person i was made a believer. Another techique is to determine how much the blade will expand due to thermal expansion and design the casing to expand as well to avoid the casing deterioration.

I do believe the engine makers use a combination of both, thus when the blade expand they slice into the foam to make a good interference to prevent air leakage.



If it was said by us, then it must be true.
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 3, posted (8 years 8 months 2 weeks 6 days 19 hours ago) and read 6237 times:
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Quoting Thyengine (Thread starter):
This tip clearance gives different performance resullts (EGT,EPR..etc.) between test cell and on-wing.



What variables account for the difference between performance results on-wing and off-wing?




2H4





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User currently offlineThyengine From Turkey, joined Dec 2005, 4 posts, RR: 0
Reply 4, posted (8 years 8 months 2 weeks 6 days 10 hours ago) and read 6173 times:

Quoting 2H4 (Reply 3):
What variables account for the difference between performance results on-wing and off-wing?

What variables? We can just take on EGTM for the whole performance variables...


User currently offlineManzoori From UK - England, joined Sep 2002, 1516 posts, RR: 34
Reply 5, posted (8 years 8 months 2 weeks 4 days 8 hours ago) and read 6039 times:

Quoting 2H4 (Reply 3):
What variables account for the difference between performance results on-wing and off-wing?

Carcass bending due to G loading primarily.

On a testbed the engine is very static whereas on wing at the end of the take-off run when the pilot pulls back on the stick, the rotation of the aircraft an hence the pylon introduces all sorts of G and gyroscopic loads into the engine carcass which will result in some degree of deformation. This can lead to increased tip rubs.

hth

Rez
 Big grin



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User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 6, posted (8 years 8 months 2 weeks 4 days 6 hours ago) and read 6014 times:
AIRLINERS.NET CREW
DATABASE EDITOR




Quoting Manzoori (Reply 5):
Carcass bending due to G loading primarily.



Ahhhhh....thanks, Manzoori! It seems so obvious now...




2H4





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