high generator load after power up
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From: Den Haag
Yes, but when starting the first engine it's generator isn't immediately online - the first high load is taken by the battery. As soon as the first engine's generator comes on line it will try to replenish the battery. If the second engine is then set to crank, the first generator may get overloaded because it's replenishing the battery and supplying a load to crank the engine.
The earlier Squirrels reputedly had a delicate quill drive to their starter/gennies. The generator switch wasn't selected on until after engine start was complete because in starter mode the quill drive is driving the engine. In generator mode the quill drive has a reverse load, i.e. the engine is driving the generator. The critical part was the sudden reverse load/torsion, caused by driving to being driven.
The earlier Squirrels reputedly had a delicate quill drive to their starter/gennies. The generator switch wasn't selected on until after engine start was complete because in starter mode the quill drive is driving the engine. In generator mode the quill drive has a reverse load, i.e. the engine is driving the generator. The critical part was the sudden reverse load/torsion, caused by driving to being driven.
The second scenario is also accurate and is one reason why the GEN Switches are checked as being OFF in the prestart checks. Obviously all of the above only relevant for those types with a combined starter/genny - big aircraft typically use MGB driven AC Gennies and may also use pneumatic starters.
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From: Wandering the FIR and cyberspace often at highly unsociable times
212, As always, it's important not to over-generalise and to refer to the appropriate RFM. The RFM for the A109 requires the generator switches to be selected ON prior to engine start.
As for the other types, yes, I'm aware having flown an aircraft with only AC gennys for over ten years and another with an APU/air starters for four years.
As for the other types, yes, I'm aware having flown an aircraft with only AC gennys for over ten years and another with an APU/air starters for four years.
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From: Den Haag
212, As always, it's important not to over-generalise and to refer to the appropriate RFM. The RFM for the A109 requires the generator switches to be selected ON prior to engine start.
As for the other types, yes, I'm aware having flown an aircraft with only AC gennys for over ten years and another with an APU/air starters for four years.
As for the other types, yes, I'm aware having flown an aircraft with only AC gennys for over ten years and another with an APU/air starters for four years.
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From: Wandering the FIR and cyberspace often at highly unsociable times
212, Yes, and if I've got the right bloke, I'm likewise aware of your past experience; however I was unsure when it seemed that you were telling me about other system types 
.
Having thought more about this, Ascend might actually be referring to the earlier 109's, i.e. A to C models, which are quite different animals with Allison engines as per the earlier Squirrel models (and those models fit into a different aircraft group these days; so I'm not qualified to talk about them). I'm inclined to think this because the max generator load on the later models (P&W engines), before cranking the second engine, is actually 160 Amps, rather than the stated 150 and that limit only appears in the "Quick Engine Start" checklist, which wouldn't normally be used on the first start of the day when everything is cold. Also, I've got an A109S RFM in front of me right now and I can't find any warning about turning the generators on after engine start.
.Having thought more about this, Ascend might actually be referring to the earlier 109's, i.e. A to C models, which are quite different animals with Allison engines as per the earlier Squirrel models (and those models fit into a different aircraft group these days; so I'm not qualified to talk about them). I'm inclined to think this because the max generator load on the later models (P&W engines), before cranking the second engine, is actually 160 Amps, rather than the stated 150 and that limit only appears in the "Quick Engine Start" checklist, which wouldn't normally be used on the first start of the day when everything is cold. Also, I've got an A109S RFM in front of me right now and I can't find any warning about turning the generators on after engine start.
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From: Gold Coast, Australia
Ascend Charlie is quite right: the earlier (Allison powered) A109s had a 1 minute period between starting the engine and turning on the Generator, for the reasons discussed 
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From: Den Haag
Ascend Charlie is quite right: the earlier (Allison powered) A109s had a 1 minute period between starting the engine and turning on the Generator, for the reasons discussed
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From: After all, what’s more important than proving to someone on the internet that they’re wrong? - Manson
Older "classic" A250 powered aircraft had no current limiters apart from full "welly" from the Starter / Gen.
The battery would recover after a minute a so and the demand would be acceptable. VR only knows about V after all and they were for the most part analog.
I think from memory 355 F1's onward had current limiters for cross-gen start and earlier ones you could juice up the battery a bit but turn OFF the GEN for start of the second one.
Had one customer with an F who shall remain nameless that would forget on average about every 3 months - ping!
Modern ships have current transformers all over the place and electronic control.
The battery would recover after a minute a so and the demand would be acceptable. VR only knows about V after all and they were for the most part analog.
I think from memory 355 F1's onward had current limiters for cross-gen start and earlier ones you could juice up the battery a bit but turn OFF the GEN for start of the second one.
Had one customer with an F who shall remain nameless that would forget on average about every 3 months - ping!
Modern ships have current transformers all over the place and electronic control.
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From: Great South East, tired and retired
Ours was an A109A Mk II Plus Widebody, heavy as all 5h1t, lots of cast-iron instruments and such, and the C20R engines. And yes, we did have to wait before bunging on the generators. Both engines had to be started off the battery, couldn't bring one gen on line after the first to start the second.
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From: Wandering the FIR and cyberspace often at highly unsociable times
Ascend, thankfully technology has moved on. There aren’t many Allison powered 109s in common use in U.K. now but the “E” models and later are very abundant.
