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whamil77

Carenado PA31T Cheyenne II Mod v3.1

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37 minutes ago, FDEdev said:

You only turn the generator ON after you have advanced the power lever(s) to 68%Ng.

Agreed, that's what I do.  After engine start, the starter is switched off, then advance power to 68%, and turn on the generator.

 

37 minutes ago, FDEdev said:

Only during a cross engine start you turn the generator OFF with the operating engine at 68% Ng

I'm not sure what you mean by a "cross engine start".  In the meantime, I'm following the checklist that accompanied Bill's mod v3.1.  It has worked every time, with no power loss in the engine that was started first.

Edited by StewartH

Stew

"Different dog, different fleas"

 

 

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47 minutes ago, StewartH said:

I'm not sure what you mean by a "cross engine start". 

Normally you are using the battery for engine start. During a engine cross start (mixed up the wording in the above post) you are using the generator of the operating engine to start the other engine, but that's not the normal procedure.

Edited by FDEdev

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9 hours ago, FDEdev said:

but that's not the normal procedure

Yes, I see that to be the case from the checklist.  I had been leaving the first engine's generator on even after achieving the ammeter reading of <100 amps.  Guess I'll revise my startup procedure slightly.  No harm, no foul.  Is there a specific reason why it's recommended to turn off the 1st engine generator before starting the 2nd?  Is it the same with normal aspirating twin engine aircraft?


Stew

"Different dog, different fleas"

 

 

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11 hours ago, StewartH said:

 Is it the same with normal aspirating twin engine aircraft?

This seems to be only valid for the Cheyenne I+II. Switching the generator to off doesn't appear in the SOPs for e.g. the Cheyenne III (not even in case of an engine cross start), King Air 350, 1900D etc.

Edited by FDEdev

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Any idea why the 1st engine's generator should be switched off before starting the second engine?  Of course, after the 2nd engine is up to speed, both generators are supposed to be switched on, according to the checklist.


Stew

"Different dog, different fleas"

 

 

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I don't know, but the manual states that this is necessary for starting the engine with generator power instead of battery power.

Interestingly this generator vs battery thing isn't mentioned in the Cheyenne III manual for the engine cross start, and the generator stays on as well. 

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9 hours ago, FDEdev said:

the manual states that this is necessary for starting the engine with generator power instead of battery power

Thanks, but I'm confused now.  "...starting the engine with generator power instead of battery power" ??  Which is it, start the second engine with battery power or with generator power?  I guess it would help to see the manual. 


Stew

"Different dog, different fleas"

 

 

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Only in the Cheyenne II manual it says for the engine cross start:

To start the second engine through the use of power from the generator of the operating engine....

Don't not the wiring of the Cheyenne II and apparently it's different from the III, but reading the manual, switching off the generator from the operating engine seems to switch the power for the starter from the battery to the generator (if it's off).  

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3 hours ago, FDEdev said:

to switch the power for the starter from the battery to the generator (if it's off).

If the generator is off, how can it supply power to the starter?  Unless you mean that switching off the generator of the 1st engine will enable the second engine to be started by its battery.  Are there two batteries, one for each engine?  I agree that the starting procedures for the Cheyenne II and III may be different because of the different electrical systems.  But this whole thing with battery start-up and generator off/on is a big can of worms, and very confusing.  Think I'll stick with the (apparently accurate) checklist and go from there. Thanks for trying to help.


Stew

"Different dog, different fleas"

 

 

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No, there's only one battery.  Just found a link for a II XL manual and it also has the engine cross start procedure, but it's called (more precisely)  'generator assist start'.

https://www.pilotundflugzeug.de/download/afm/AIRPLANE FLIGHT MANUAL PA-31T2 D-INFO.pdf

I'm way too lazy to dig into any Cheyenne manual 😉

Hope this helps clarifying things for you 🙂

 

Edited by FDEdev

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Thanks, I'll take a look.  Actually, the engine cross start procedure makes perfect sense to me.  It's when one turns off engine #1 generator in order to start engine #2 that is the hang-up.  But in fact, that is the procedure outlined in the checklist for Bill's Cheyenne II v3.1, although I will freely admit, I've been using an engine cross start procedure, and it has worked without fail and with no engine fires, btw.

Edited by StewartH

Stew

"Different dog, different fleas"

 

 

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Well I'm glad I'm not crazy and I remember correctly what I saw even though it's getting on for 20 years since it happened.  I seem to remember him explaining why he did it as well but that's long since been displaced in my head by other useless aviation and music trivia if he indeed had.  The other thing I remember was the use of differential power to assist steering whilst taxiing. He would drop the engine of the direction he was turning into beta/reverse i.e. right engine for right turn. It seemed to assist the tighter 90° turns quite nicely.  That experience really made me fall in love with the Cheyenne. Really a great airplane and I'm glad it's back in P3Dv4 thanks to Carenado and Bill's mod; I had really missed the DA Cheyenne.

Anyway, I suspect that it might have something to do with excess loading on the starter generator on that particular range (Cheyenne I-II). The fact that you have to push the engines to 68% before you can switch on the generator might be telling.

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I raised the question at work (I work in an aircraft maintenance department doing data analysis) and the consensus we came to was that it's probably because the generators have a hard time with the starting load (plus what ever re-charge it's still supplying the battery).  No one had specific knowledge of it but everyone thought it sounded like it was a loading issue.  Based on my previous assumptions and the conversations we had at work, my thoughts are that the while the generator can handle the starting load of the opposite engine, it's probably near it's capacity and thus very hard on it to do so and is therefor not the preferred starting method.

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19 hours ago, Eyaen said:

I raised the question at work (I work in an aircraft maintenance department doing data analysis) and the consensus we came to was that it's probably because the generators have a hard time with the starting load (plus what ever re-charge it's still supplying the battery).  No one had specific knowledge of it but everyone thought it sounded like it was a loading issue.  Based on my previous assumptions and the conversations we had at work, my thoughts are that the while the generator can handle the starting load of the opposite engine, it's probably near it's capacity and thus very hard on it to do so and is therefor not the preferred starting method.

Thanks for the background.  In my reply to your original post, I stated the checklist doesn't mention turning off generator #1 before initiating engine #2 start procedure.  That is not correct.  Generator #1 should indeed be turned off.  But then we experience the power reduction of engine #1 when engine #2 is started.  I don't have a problem with that as long engine #1 eventually comes up to full power, along with engine #2 and both generators finally switched *on*.  I will say that the generator assisted start, which is also included in the checklist as an alternate startup procedure for the second engine, works nicely as well.  So the pilot can choose either method, it seems.


Stew

"Different dog, different fleas"

 

 

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1 hour ago, StewartH said:

Thanks for the background.  In my reply to your original post, I stated the checklist doesn't mention turning off generator #1 before initiating engine #2 start procedure.  That is not correct.  Generator #1 should indeed be turned off.  But then we experience the power reduction of engine #1 when engine #2 is started.  I don't have a problem with that as long engine #1 eventually comes up to full power, along with engine #2 and both generators finally switched *on*.  I will say that the generator assisted start, which is also included in the checklist as an alternate startup procedure for the second engine, works nicely as well.  So the pilot can choose either method, it seems.

Certainly and for our purposes in the sim it doesn't really matter which way you do it; it's totally a matter of preference 🙂

It's an interesting subject though and to the original matter at hand: why does the power loss occur in the sim doing the standard start vs the cross gen start? Even with a work around I'm still curious about this as it's unusual behavior even based on the sim logic.

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