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Turn on ALT before engine start? (Logic and experience)

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gmcjetpilot(at)yahoo.com
Guest

Posted: Fri Sep 01, 2006 10:39 am Post subject: Turn on ALT before engine start? (Logic and experience)

Bob:

   

  I probably don't have scientific evidence of why I have 

the opinions I do or why it differs from yours. I do have 

logic and personal experience to share. 

   

  We do agree that checklist are good, and from an 

electrical standpoint most alternators (not all) don't care 

if you turn them ON before or after start. OK? 

   

  HOWEVER given the choice I say turn the ALT ON with 

the BAT before start and than back OFF together with the  

BAT after engine shut down. I'll explain. 

   

   

  **Let me tell you all a little story first**

  One of my students many years ago was going on one of 

her solo cross country flights. Well she made one 

mistake and turned the battery on and accidentally left 

the ALT off (Cessna split switch). She took off enroute 

and did not note the discharge,  mistake two. Never the 

less I can see it happening to anyone. She realized her 

error and proceed to turn the ALT on. Because the 

battery was now discharged it demanded a large current, 

it popped the CB with the combined load of lights, radios 

and battery charging. She did not think to "load shed" 

first, before resetting the CB. 

   

  Well from then on she was perfect. She noted the CB 

pop, let cool, reset once and left it out when it popped  

the 2nd time. She did a 180 and than did an electrical 

load shed to save the remaining battery. Nearing the 

airport she powered the Comm up and landed without 

further incidence. Yes she should have turned the ALT 

on first; Yes she should have checked for charge right 

after start; Yes she probably would have been successful 

resetting the CB if she would have turned the strobes and 

avionics off first, before turning the ALT on; however I 

never  taught her this. To be sure from than on I went 

over this in detail with all students using Machado's 

water flow analogy. (End of STORY)

   

  

Here is how I arrived at my opinions:

  

ONE - ANYTHING that can assure you don't make a 

mistake, like in the above story, is good. KEEP IT 

SIMPLE. Turning the ALT on first before start with the 

BAT is one of those KISS methods and step reducing 

things. IT MAKES SENSE to me and is LOGICAL to 

me, less steps are better. It's obvious if the BAT is not 

on, Right? Nothing happens. Turning the BAT/ALT on 

together is goodness in my opinion, you're less likely to 

forget the ALT. Tie the ALT and BAT together 

procedurally. We can agree to disagree. My argument or 

logical reason is LESS STEPS are BETTER from a 

human factor stand point (not electrical). 

  

The caveat is if the AFM calls for something different, 

like an old twin with  generators or the B737 I use to fly, 

than do that. (The B757/767 brings the Gens online 

automatically; yea!)

  

TWO - Most factory planes call for ALT/BAT turned on 

together; why not follow a standard which will aid 

transition and proficiency of other pilots across different 

planes, aka, why be different?  My over all 

recommendations to anyone designing their panel or 

procedures, keep it simple and follow the traditional 

layouts and procedures as much as possible. Cessna puts 

the master, BAT and ALT switch together in a split 

toggle design for a reason, they are normally actuate 

together. I think Cessna got it right. Again it's my 

OPINION and apparently Cessna's opinion. Granted in 

my above story even the split switch is not fail-safe, but 

  it helps.

  

Bob, you can INSERT your argument in HERE that 

there should be a low volt idiot light. I agree, but that is 

POOR  Airmanship to rely on idiot lights to configure the 

plane's electrical system properly. 

   

  

If you want me to prove my opinion or explain my logic 

better than I already have, I can't. I have no top secret 

oscilloscope plots to prove my opinion. It really is not 

  an electrical thing, it's more human factors.

   

  My opinion is based on 12,000 hrs flt time & counting, 

CFI, ATP, airline and engineer for Boeing, which 

involved evaluating check list and teaching flight crews. 

As a former CFI-CFII-MEI, in over 20 different 

make/models of GA planes, almost all did not REQUIRE 

a separate ALT throwing step. You say so what? I say 

follow the standard. However if the AFM/Checklist say 

do it, than you are bound by FAR's to follow it. Can you 

imagine forgetting the ALT because of a modified 

procedures which got you into a pickle like my student 

but  violating airspace because you where NO RADIO. 

Than the FAA asks, why? you say: 

   

  **Oh I throw the ALT switch after start, even though the 

checklist says otherwise, because I think it's better, 

but I forgot this time.**   

   

  hummmm

   

  Can you say violation and licence revoked? I love pilots 

who are too cool to BLINDLY follow checklist. Follow the 

darn checklist. It's not trivial or just to evaluate pilots by, 

it's the safety net of aviation, use it. Some day pilots flying 

a C-150 may be in a G-V or B747 and good checklist 

discipline is critical. Its just good Airmanship and I don't 

need any data to prove standardization is goodness.

   

  Experimental, do what ever you want, but suggest you try 

to consider the traditional or standard procedures as a 

starting point.



   

    

  

 

  Exception to the RULE - Internally regulated Alternators

   

  Again it does not matter from an electronics stand point 

for most alternators when you turn them ON or OFF except 

for internally regulated alternators. Since there's no I-VR 

 alternators on factory planes, it only affects experimental 

aircraft that use them.

   

  I always have recommended I-VR alternators be ON 

before cranking the engine and OFF after engine shut 

down. The logical reason is, I-VR alternators are based 

on an automotive application. I again ask rhetorically,  

"How many cars need the driver to activate the alternator 

separately?" The answer is none. If using a I-VR 

alternator, it's logical to operate it the same way as it 

does in the automobile, for which it was designed.

   

  The second reason for  not cycling internally regulated 

alternators while they're spinning is they can fail. From 

my experience and those of many I have helped and 

corresponded with, who had I-VR alternator problems, 

they all had a common thread, they played switch 

monkey with the ALT (IGN) switch. Anecdotal yes, but 

it's what I got, take it or leave it. 

   

  Technically IC chips inside some I-VR's have delays and   

soft start functions most external voltage regulators  

don't have, including the B&C unit. By using an internal  

V-regulator to switch high amps ON/OFF is needless and 

counter to its design. Again, no scientific bench test or 

scope traces to show. Take it or leave it. Fact is I-VR's are 

microprocessor controlled in many cases and don't need 

or benefit from pilot switch monkey intervention (my opinion). 

   

  Again my LOGIC, my  EXPERIENCE, my OPINION and 

research into I-VR designs is the basis of my comments. 

I  have no scientific proof that will make you happy Bob, 

sorry. The best I got, take it or leave it.

   

   

  Now Bob tell me why turning the ALT on and off as a 

separate step, post-start is superior? (Forget electrons, 

think like a pilot for a minute.)

   

   

  Regards George M, CFII-MEI, ATP, B73/75/76/CE500, MSME



  [quote][b]

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N1DeltaWhiskey(at)comcast
Guest

Posted: Fri Sep 01, 2006 3:35 pm Post subject: Turn on ALT before engine start? (Logic and experience)

George,

  

 Thank you for the lucid explanation of how you  arrived at your opinions.  It does make sense and, to me anyway, the  rationale is solid.

  

 IMHO, the only thing I would have suggested you  leave out of your post was your challenge to Bob to argue a point - why?   Is there anything, really, to be gained?  If he disagreed with your points,  it is his option to pick up the keyboard and whack away - with the challenge, it  becomes less his choice, as a point of "honor."  This is much as a  slanderous comment many years ago might have resulted in a pistol duel  challenge.  Hopefully, we have advanced beyond that mode for  addressing disagreements.

  

 Keep up the good explanations for your opinions -  it can help us all to better understand.

  

 Regards, 

  

 Doug Windhorn

 [quote]   ---

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bicyclop(at)pacbell.net
Guest

Posted: Fri Sep 01, 2006 11:22 pm Post subject: Turn on ALT before engine start? (Logic and experience)

George,  

   

Yours is one of those dark and stormy night stories. I’ve got one like it where I blew the alternator breaker on our C-150 when the engine surged a few times and then quit. I didn’t realize that the breaker was blown. I was busy trying to find a place to land. I also neglected to shed lighting loads. The airport within gliding range was obscured by a cloud bank and while I was consulting the GPS for a heading and distance, it rebooted for lack of voltage. I did not need this extra pucker factor at this time. Once on the ground, I figured out what had happened to the electrics and also figured out what I could have done better.  

   

The thing is – Cessnas are designed to blow the circuit breaker. It’s obviously not sized right. It should be able to handle what the alternator can throw at it. It should not require exceptional airmanship to keep the electrical system running. It’s badly designed. Your student was suckered by more bad Cessna design. The split rocker switch is a bad idea. It begs to be mishandled. The POH calls for the alternator switch to be cycled during the run-up and the ammeter to be observed to verify that the alternator is charging. This is unnecessary. All that you need to do to check the alternator is to look at the voltmeter. If it’s low, shed some load and look again. You don’t need to turn it off and on to see if it is working.  

   

What we have the option to do in our “experimental” aircraft is to use a better design that doesn’t nuisance trip and that does inform us when the voltage is low so that we can figure out what’s going on and what to do about it before the battery is drained.   

   

The point Bob made was that, from the charging system’s viewpoint, it doesn’t matter much in what order you turn them on or if the engine is started first. A guy asked the question. Bob answered it. He never said that turning the alternator on after engine start was the superior technique. He just said that the charging system wouldn’t care.   

   

By the way, while you are arguing the fine point of when to turn on the alternator, please note that many of Bob’s Z figures call for a double pole master switch which turns on the master and alternator field simultaneously. That’s the way I wired our RV. It works fine. One can’t very well forget to turn on the alternator. Simple is good.  

   

Pax,  

   

Ed Holyoke  

   

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