Old 19th Apr 2018, 07:02
  #232 (permalink)  
Join Date: Jul 2013
Location: Everett, WA
Age: 64
Posts: 2,457
Originally Posted by freshgasflow View Post
An earlier post mentioned that while engines are designed to contain blade separation, engines are not designed to contain disc failure. As a SLF i would be grateful if someone will explain what are discs in an engine. A link to a diagram would be great. I googled it and could not find a diagram showing engine discs. I know this must be a very basic question for those in the know, but it would help us , SLF , to follow things. Thank you.
At a very basic level, the 'discs' are what hold the fan, compressor, and turbine blades - the 'hub' of the wheel if you will. The fan disc is massive - several feet in diameter on most turbofan engines - and needs to be heavy duty enough to not only restrain the centrifugal force of the (relatively) large and heavy fan blades spinning at several thousand RPM, but also the thrust loads since the fan produces the majority of the thrust on modern engines. A fan disc failing is seriously bad news - a piece several feet across with massive rotational energy. We have a saying 'where does 1/3rd of a fan disc go? Anywhere it wants to" Google 'Sioux City DC-10' to see what can happen when a fan disc lets go.
The compressor and turbine discs are similar but smaller (some newer engines use a compressor 'spool' - a cylindrical piece that holds the compressor blades for multiple compressor stages, replacing several individual compressor discs). Since they are smaller, compressor/turbine discs have less mass than a fan disc, however the high pressure section of the engine spins far faster than the fan (upwards of 10,000 rpm - sometimes higher than 20,000 rpm depending on the engine) so they also have massive rotational energy.

A burst disc - with all it's energy - will go almost perfectly tangential to the axis of rotation (cert requirements give a +/- 10 degree cone for burst disc debris, vs. +/- 30 degrees for 'lower' energy debris such as blades.

Does that help? Teaching isn't my forte
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