PPRuNe Forums - View Single Post - Engine "Core Lock"
View Single Post
Old 5th Jun 2005, 00:48
  #3 (permalink)  
Milt
 
Join Date: Oct 2003
Location: Canberra Australia
Posts: 1,300
Likes: 0
Received 0 Likes on 0 Posts
Good Grief!!

Let's hope that any engine that "Siezes"because of inadequate clearance between rotating and stationary parts gets an instant reject especially if some attempt has been made to crank. A bit like trying to crank your car engine immediately after a seizure.

There was a similar problem over clearances with Avon engines in the RAAF's F86 Sabres. Many would vibrate excessively in the climb through medium altitudes and enough for pilots to reject. No amount of coaxing could reproduce the vibrations on the ground and many engines were completely overhauled at great expense for no result

Elaborate flight test instrumentation and numerous flight tests eventually pinpointed the problem.

The Avon engine, and I guess most others, have what is called a balance piston as part of the rotating spool. Using compressor bleed air pressure on one side and atmospheric pressure on the other side the resulting imbalance is supposed to take out most of the end thrust on the spool bearings.

Trouble was the balance was too accurate under some conditions and the spool floated rapidly back and forth against the bearings.

The fix was to increase the clearances around the labyrinth seal on the periphery of the balance piston thus ensuring that there was always some residual end thrust on the bearings.

Have there been similar problems with other engines?
Milt is offline