Originally Posted by
mrfox
Further research on the topic of spillage drag has led me to the text Gas Turbine Performance (P.Walsh/P.Fletcher)
You mean the reference book I quoted all the way up at post #6? 😒
im not sure what to say... everything is in that text to arrive at a sound conclusion and I’m sceptical of the references that arrive at the differing conclusion that the windmilling case is more efficient than the locked case.
From the referenced text, it is fairly evident that it’s not so much what happens with the fan (for turbofans), but what happens in the core
Excluding the aerodynamic implications of a windmilling core/fan vs a locked core (as applied to single or dual spool), in practical terms it would be best to lock the core of a malfunctioned powerplant to alleviate risk of <further> damage to the powerplant and/or it’s accessories.