Fan Blade Tip Clearance — Tech Ops Forum

Sponsor Message:


My Starred Topics \| Profile \| New Topic \| Forum Index \| Help \| Search

Fan Blade Tip Clearance

Thyengine From Turkey, joined Dec 2005, 4 posts, RR: 0
Posted (7 years 5 months 1 week 2 days 13 hours ago) and read 5095 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

Fr8Mech From United States of America, joined Sep 2005, 4253 posts, RR: 12
Reply 1, posted (7 years 5 months 1 week 2 days 3 hours ago) and read 4970 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!

Liedetectors From United States of America, joined Jul 2005, 357 posts, RR: 0
Reply 2, posted (7 years 5 months 1 week 2 days ago) and read 4924 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.

2H4 From United States of America, joined Oct 2004, 8950 posts, RR: 62
Reply 3, posted (7 years 5 months 1 week 2 days ago) and read 4923 times:

AIRLINERS.NET CREW
HEAD DATABASE EDITOR

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

Intentionally Left Blank

Thyengine From Turkey, joined Dec 2005, 4 posts, RR: 0
Reply 4, posted (7 years 5 months 1 week 1 day 15 hours ago) and read 4859 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...

Manzoori From UK - England, joined Sep 2002, 1516 posts, RR: 37
Reply 5, posted (7 years 5 months 6 days 12 hours ago) and read 4725 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

Flightlineimages DOT Com Photographer & Web Editor. RR Turbines Specialist

2H4 From United States of America, joined Oct 2004, 8950 posts, RR: 62
Reply 6, posted (7 years 5 months 6 days 11 hours ago) and read 4700 times:

AIRLINERS.NET CREW
HEAD DATABASE EDITOR

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

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

2H4

Intentionally Left Blank