PPRuNe Forums - View Single Post - Turkish airliner crashes at Schiphol
View Single Post
Old 2nd Mar 2009, 21:41
  #914 (permalink)  
lomapaseo
 
Join Date: Mar 2002
Location: Florida
Posts: 4,569
Likes: 0
Received 1 Like on 1 Post
I can not completely understand all the reader comments about the High compressors and turbines vs the fan rundown.

A few things to keep in mind. The high compressor and its turbine are well burried in the smaller diameters of the engine and as such they will not often be brought to a halt due to clashing with other engine parts after the aircraft hits the ground hard (assuming of course it doesn't break the engine into pieces). Add also that the RPM difference in the high pressure rotor between idle and high power is not very much different to be able to read mechanical damage due to ground impact.

Thus the eye normally focuses on the end stages of the engine which are the last stage of the low pressure turbine and the front stage of the low pressure compressor (often a fan stage). You really are skating on thin ice if all you look at is only the front or back, because you also have to factor in whether or not parts were crushed into the blades first at the front or back.

It's realtively straight forward to interpet engine rotation speed if the engines remain attached to the airframe and take a crushing load only from the front.

This obviously didn't happen in this accident so you have to spend some time looking all over for clues and not just one or two grainy photos.

and yes I do support the posters who suggest that it's the inertia of the engines vs so little drag that lets them roll forward of the airframe once detached. I grant you that if there was zero gas path damage that the engines might be under thrust for a few seconds (El Al Amsterdam) but just the initial ground impact is likely to cause the engines to surge and lose thrust immediately (see also Piedmont B737 with one gear up landing)
lomapaseo is offline