King Air 200 Cross Generator Starts

[msw]

Here's a question for the King Air BE-20 pilots out there, pertaining to cross generator starts in the King Air 200 and B200's made prior to the mid-'90's. (Before they put the whatever circuit in there, after which - in the later models - you no longer had to worry about blowing a current limiter if you started an engine with the other side generator on.)

Here's the question: Some King Air 200 checklists (usually for the earlier 200's) show that you after you have the right engine running (both generators now off) - and you are starting the left engine, after the N1's up and stabilized, you put the right gen on FIRST ("cross generator assisted start") and THEN you bring the condition lever out of cut-off and up to lo idle. Later checklists, typically for the early model B200's (models prior to the mid-'90's or so) show the opposite: you bring the fuel on first, followed immediately by flipping the "cross gen" on (usually the right gen; if we started the right engine first, and are now in the process of starting the left engine)

Nobody I have asked can account for the WHY of this difference, or tell me if one way is better than the other. I have asked several King Air pilots and several King Air instructors at FlightSafety the question, and have never received a satisfactory answer. Usually, it's stuff like: it doesn't matter; or just do what the checklist says.

Do any of you guys have a knowledgeaable answer to this question? i.e. a technical reason why one way might be better than the other, and why the "King Air 200" checklist would show the former method and the "Early Model B200" checklist would show the latter? (When there is no difference in the electrical systems.)

 

[avbug]

You're talking about a battery start. After the first engine is on line, the condition lever for the right engine is brought up to high idle to help recharge the battery, prior to the second engine start. After the ammeter has reached 50% or less (100 amps on digital ammeters) on the right side, shut off the generator and start the left engine.

After the left engine has reached 12% (I prefer to see it spool until it stops), turn on the right generator. You can leave the condition lever on the right in high idle.

Once the left engine has reached 50% N1 (Ng), you may shut off the starter, and engage the starter. Prior to engaging the starter, however, you should check for a blown current limiter by noting the voltage on both busses to determine that you are showing 28 volts on each bus.

If you are showing battery voltage on one bus (24 VDC) and 28 volts on the other, then the side with the high voltage has a blown current limeter.

Once you've determined that you don't have a blown current limiter, engage the second generator by turning it on, moving the switch to reset for a second, and then releasing the switch. Check your ammeter for load sharing within 10%, return your right condition lever back to low idle (unless running air conditioning), and off you go.

The reason you don't want the right generator on until you've at least reached 12% on the left engine during the start, is to prevent blowing a current limeter. Some wait until lightoff on the left engine, which is even better.

 

[jergar999]

Soft start circuitry is the device that prevents the surging draw from the starting engine and power from the generating one from overheating a current limiter. Check with your mechanic. I have flown aircraft as old as 1980 that had soft start.

That's all I really had to add, Avbug covered everything perfectly.

 

[msw]

Cross Gen starts on BE-20

AvBug:

I agree with everything you said, but unless I missed it, you didn't answer my specific question:

Here's the scenario: Rt eng running, both gens off (you've already "re-charged" the battery after the rt eng start) and now you're gonna start the left engine.........

Left starter on, blades are turning, red fuel P lite out, yada yada yada, the left N1 peaks at about 18% - 20% (usually for our bird)...... NOW, do you:

(a) switch on the right gen and THEN bring the left condition lever out of cut-off to lo idle, to light the fire, or

(b) bring in the left eng fuel (i.e. light the fire) and THEN switch on the RIGHT GEN

The "straight 200" checklists I've seen say to do it the first way (a)

The "Early Model B200" checklists say to do it the second way (b)

Most everyone I talked to says it really doesn't matter. I like the first (a) method because I figure the starter should get the little extra "oooomph" (from the right gen) before the fire is lit on the left engine. (And the early part of the start sequence with the huge amps has already dropped off, so no chance of blowing the current limiter at that point.)

My question is why two different "sequences" when the electrical system is the same for these birds? (And I'm not talking about the later King Air B200's, where you don't worry about turning off the gen before doing the second engine start.)

 

[jergar999]

Kick the generator on at about 10%. This bypasses the initial surge and provides the most assistance in starting the second engine. With the battery charge and loads within limits kill the gen on the running engine. Hit the start on the other engine, as soon as you see 10% N1 turn the gen on, and only a second or two until its time to introduce fuel.

 

[avbug]

The truth is that it doesn't matter if you take the condition lever out of cutoff to low idle before turning on the generator, or visa versa. Technically, you should be 12% before either one, on the left engine Ng (N1).

Why one way written instead of the other? Chicken or egg?

As Jergar99 pointed out, if you provide the generator after 12%, and let the starter run a moment longer to it's limit (around 18-20% Ng), you can sometimes get a cooler start, and have much less chance of a hot start, especially when starting with a tailwind. That would be the only advantage to engaging the starter before moving the condition lever to low idle.

Conversely, the faster that starter is spinning, the less draw on the other generator when you engage it. It's mostly about the current limiter, but you don't really want to put any more draw on that 250 amp generator than need be.

If you watch the voltmeter when the generator gets engaged, you'll note that the initial voltage is higher than the generator rating most of the time. It drops down quickly, but you'll get a much lower draw if the left starter is spinning faster and under less load, and this happens after lightoff.

Six of one, half dozen another. Once the engine lights off, it's really not important. If it's really cold out and you have cold batteries, turning the generator on earlier does mean that you're getting charging going earlier...but you're only talking a few seconds either way. Much better to protect the generator.

 

[Be200pilot]

i agree with jergar999. we also turn the right gen on at 10% N1 (left engine). youll never blow a current limiter that way, but most of the time it spools up so fast that 10% is really like 12-18%, you just cant tell exactly when the needle moves so quickly.