What is wrong with the Merlin engine?
Cunning Artificer
Join Date: Jun 2001
Location: The spiritual home of DeHavilland
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Why, of all the hundreds of parts in an aero engine, this one item should be singled out, is beyond me. Perhaps it was the easiest of all to take out and get lost.
They had to be cleaned, gaps set and then individually tested for leakage and operation on a special test rig. The ignition system was critical in getting the required power output and smooth running. Did you ever notice piston engined aeroplanes turning into wind and running engines at full power before entering the runway? The pilot would set high power and then switch off each magneto in turn to see if there was an RPM drop ("Mag Drop"). If there was, the aircraft doesn't fly - it goes back to the flight line to have an ignition system change.
The pilot would set high power and then switch off each magneto in turn to see if there was an RPM drop ("Mag Drop"). If there was, the aircraft doesn't fly
Gnome de PPRuNe
Join Date: Jan 2002
Location: Too close to Croydon for comfort
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The Lancaster is airborne, presumably on an air test... 
If the aircraft doesn't have a mag drop it means something is wrong,
Join Date: Dec 2007
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Long time ago but I seem to remember the the mag. check was carried out at zero boost, before the rpm were up in the propellor constant speed range. An rpm drop was essential but not to exceed 50. If there was no drop you knew that you had a live mag. and you knew which one. (Banter) see your 2500 hours on Shacks Oxenos and raise you 800 on Lancs as well!
