Odd startup question--generators

[ClipperLuna]

Quick question about the generators. The last item on the starting engines checklist says to switch the generators on after all engines have started. I was wondering the reason for this. I mean, I would have thought it would be preferable to bring them on-line as each engine is started so you can use their power to help with starting the other engines. Or would this overload them as the starters are engaged?

[alan CXA651]

Hi.
If you have the engineer doing the prepare for eng starts , and you then start the engines , you will see him turn the gens on for the engine that you have just started .
my start up is 3,4 GPU off , 2,1.
regards alan.

[ClipperLuna]

Yes, and that makes sense, bringing them on-line so you can take advantage of their power. I was more just curious why the manual said to wait until all the engines are running to switch them on. This instruction must have carried over from the C-69 manual; it's the same way there.

[CAPFlyer]

The only thing I can think of is that the generators aren't rated to deal with the load during start or there was concern about the relays for the same reason, but considering the L-049 uses inertia instead of direct drive, that wouldn't be an issue in our case.

Personally though, I tend to follow the checklists because usually they're written a certain way for a reason - and often it's because someone broke something or set something on fire because they didn't follow the checklist.

[AviationAtWar]

It's a pretty large amp load, especially if only one or two engines are running, with little cooling airflow. I've even seen automotive alternators fail under high heat, high load conditions with low vehicle speed and lack of cooling airflow.

[CAPFlyer]

Not really a problem. The stuff that takes a high load shouldn't be online when on the ground or you can shed any high load items (like the heater) during start if you're not using the GPU. The plane is designed to operate normally on 2 generators, so once you get the second engine going, any concern of heat should be abated.

[Lufthansa 380]

I usually start 3 & 4 with the GPU, then turn gen 3 and 4 on, remove the GPU and start 2 & 1. Don't know whether there is a concern when starting the first two engines without the GPU.

[CAPFlyer]

Not really. Heck, just an hour before this post, I was removing the GPU plug from the right wing of a Beech King Air 350 after it had started engines. The plug is only about 6 feet behind the right prop, so there's definitely danger, but by following proper procedure, there's not really much risk. At least it's not a Swearingen Merlin with the plug about 3 feet in front of the right prop. We're not allowed to disconnect the GPU from a Merlin if the #2 engine is running because we're not allowed within 5 feet of a moving prop at any time

Disconnecting the GPU on a DC-3 is even worse, located on the centerline of the fuselage, behind the prop arc - which means you walk between the running engines to get to it (something we don't do at work, but I've done in a volunteer capacity, there's about 4 1/2 feet of clearance to the prop tips). At least with the chocks you can approach from the wingtip and stay behind the prop arc.