Leon, are the G-Reg Grobs doing circuits and bumps and are they using 100LL, 91/96UL or mogas? Maybe the way in which the Air Cadet aircraft are operated (the 12 minute circuits VX275 mentions) and 100LL makes them more susceptible to plug fouling?
Mechta
Same fuel from the same pump (100LL), same airfield but different airframes (ie. Vigi vs G109B). Thus I can't understand why the Vigi seems to have more incidences of a rough running engine than the civvy G109B? It is a small sample size, as I said before, of 3x G109Bs and 4x Vigis, but I can't remember any time over 3 years that the civvy 109Bs had a rough running engine at all - they've had a nose-over and a hard landing, but that's a different matter! The civvy 109B sorties are slightly different in that they tend to fly for 30 mins in the local area before coming back for a few glider circuits (normally teaching students how to deal with overshooting or undershooting glide approaches before going around for a further approach under climb out power). So I guess it could be the fact that VGS mainly fly circuits only, but I would have thought the problem would manifest itself on the civvy 109Bs at the same airfield over a 3 year period at some point? They do fly at least 12 hours a week and sometimes as much as 20 hours a week - in a year I would estimate around 4-500 hours across this civvy fleet. The only explanation I can think of is that the modification to the fuel system has something to do with it or that the FRCs/SOPs for the Vigi are different to the POH procedures for the 109B?
Of course, it could be that this particular VGS has had a run of bad luck with their engines or have the 'dogs' of the Vigi fleet?!! Or that the civvy 109B operator has been increadibly lucky?!!
As I said, I just dunno! It's just an observation and my own only plausible explanation as to why, that's all...
LJ
