Start up procedure

[Vespa]

Hi, I'm trying to start a cold and dark C172 Cessna...no luck so far...even reading the manual no way to start the Aircraft (and I don't want to use the automatic start).
The basic step I perform are:
- Battery on
- Generator on
- Mixture full forward
- fuel pump for a couple of seconds
- fuel on
- magnetos both....and start.

Any hints? Thanks

[Sazoga]

I think you're doing it wrong.. First, what means generator? Only use the alternator (who charges the battery), when the engine is running!

-Battery on
-Fuel shut-off valve in
-Fuel selector both
-Mixture cut-off
-Throttle 1/4 inch in (about ~20%)
-Magnetos both
-Fuel pump on
-Mixture full rich (about 2-3 seconds, because of overpriming)
-Mixture cut-off
-Fuel pump off
-Mixture >50%
-Magnetos to start
-Adjusting mixture for ground priming (about 60% is good)
-Throttle in idle not under 1000rpm
-Magnetos check
..

That's the way I do it, the pilots I know are doing it and how I saw it in videos. And btw it works fine

[Vespa]

Thanks a lot for feedback and hints...I'm going to try it.

[AKar]

-Mixture full rich (about 2-3 seconds, because of overpriming)
-Mixture cut-off
-Fuel pump off
-Mixture >50%
-Magnetos to start

Wrong again The mixture must be all the way off until the engine catches after starter engagement. Then smoothly push it in to full rich. It's a 'feature' of the Bendix RSA fuel injector that it floods the engine if there is no good airflow in the intake system and the mixture is not cut off.

-Esa

[Sazoga]

And as I said: With cut-off or without mixture full rich, my C172 isn't going to start. And in EVERY C172 (reallife) start-up video, the mixture is full rich for engine start. It's a way better as mixture cut-off and then smoothly push to full rich during engine start. But okay, if it's wrong, I don't know why it works (a lot better).

[AKar]

And as I said: With cut-off or without mixture full rich, my C172 isn't going to start. And in EVERY C172 (reallife) start-up video, the mixture is full rich for engine start. It's a way better as mixture cut-off and then smoothly push to full rich during engine start. But okay, if it's wrong, I don't know why it works (a lot better).

Then there is something wrong with your installation (assuming that your technique is right). Mine starts very well using correct procedure.

Regarding the real life videos, please note that the pre-R model 172s are carburetted - this means that they use the same start-up procedure the Cherokee uses. That is, mixture at full rich at start. Only the latest R and S models from the 172 lineup use Lycoming IO series (fuel injected). And by quick googling, Youtube videos show the correct mixture-out procedure for those models.

I may add, that several updates back I tested if the A2A Cessna would start using incorrect procedure of having the mixture pushed to around mid-range - and it did. Of course, I've not tried, nor suggested that anyone would try that for me, in real life, but logically per fuel injector design that should be highly unlikely except if pure luck occurs with an un-primed cold engine, and quite common first step troubleshoot is to assure that the mixture was really full in. I might for fun do a few tests with my current setup tomorrow or day after.

-Esa

[Vespa]

So, to make it clear, the procedure should be:
-Battery on
-Fuel shut-off valve in
-Fuel selector both
-Mixture cut-off
-Throttle 1/4 inch in (about ~20%)
-Magnetos both
-Fuel pump on
-Mixture full rich (about 2-3 seconds, because of overpriming)
-Mixture cut-off
-Fuel pump off
-Magnetos to start
-Adjusting mixture for ground priming (about 60% is good)
-Throttle in idle not under 1000rpm
-Magnetos check

Correct?

[Oracle427]

Negative. Follow the checklist using the shift-8 and shift-2 menus or the manual, or a real one available online.

-Complete your preflight checklists...
-Battery on
-Fuel shut-off valve in
-Fuel selector both
-Mixture idle cut-off
-Throttle 1/4 inch in (about ~20%)
-Fuel pump on
-Mixture full rich (about 5 seconds)
-Mixture idle cut-off
-Fuel pump off
-Magnetos to start for about 4 turns
-Mixture smoothly to full rich when the engine fires
-Watch oil pressure and immediately shut down engine if it doesn't rise to green arc within 30 seconds.
-Set throttle to idle at 1000rpm
-Alt switch on
-Lean mixture for ground ops
-Nav light On
-Avionics On
-Flaps up
-Follow the rest of the engine start and then off to a pre-taxi and run-up checklist...

[afcraig2010]

Why can't the alternator be turned on with the battery? We've got two R models in our club and it's what I trained on. The checklist (real world) says master on, so both on. I have heard that it can ease the load of the alt/gen if you wait until after you start (in a discussion about the warbirds). Is it really that much of a difference?

And to add to the real world start procedures, I cut this video to start right as he's going to prime and start. The other's are correct about previous 172's; they all have carburetors (like the Cherokee). http://youtu.be/Yh5-fIc4SQU?t=1m44s I can't attest to the accuracy of the rest of the video, just wanted to show everyone the prime and start procedure.

[AKar]

Why can't the alternator be turned on with the battery? We've got two R models in our club and it's what I trained on. The checklist (real world) says master on, so both on. I have heard that it can ease the load of the alt/gen if you wait until after you start (in a discussion about the warbirds). Is it really that much of a difference?

On the other hand, one could think of the opposite: when you switch it on from the switch after the start, there will be an almost instant surge of power. So, some say it is easier for the alternator to have it switched on for the start. But, then again, I recall that the ACU was directly powered by the battery bus which is subject to large transients during engine start, another question would be how it handles those. So, go figure..

-Esa

[Great Ozzie]

Why can't the alternator be turned on with the battery? We've got two R models in our club and it's what I trained on. The checklist (real world) says master on, so both on. I have heard that it can ease the load of the alt/gen if you wait until after you start (in a discussion about the warbirds). Is it really that much of a difference?

I believe you are talking about two different pieces of equipment... alternators and generators definitely different in how they produce electricity. There may be some issue with getting a generator up to a certain speed before bringing it online (I have no idea there). Years ago, alternators began taking the place of generators - tho the term is now used interchangeably. Alternators, afaik, 'come online' at idle speeds; so that not an issue. (edit: and as Esa alluded to - better electronics with these systems today)

I was going to start off by saying, the reason for split masters is to give the pilot community one more thing to have to debate about. One does hear it from time to time.

There are a couple times when you do not need to be energizing the alternator circuit (and wasting the battery). Prior to engine start sitting on the ramp, you know (by how busy it is) that it is going to be a while to get your IFR clearance out of there. You don't want to start and sit there idling away for 10 minutes - so only the battery needed for that (to use the radio). Another situation, if there is an alternator failure inflight, and the reset does not work... no point in having the alternator circuit online when you are time limited on that battery (based on load etc.).

How much load does the alternator put on the start? I would think "not a lot" i.e. not enough to be concerned about with a good battery (from either the elec. draw or mechanical draw). Now... if I was out in the sticks somewhere and realized during the start procedure I have only one or two cranks left - and the choice is walking 20 miles to civilization or zapping the battery in the start - then I reckon take that alternator offline (why have a load when I need that last ounce of energy). At an attended airport, I do not want to be in that situation, as running the battery down to zip (from excessive cranking) is hard not only on the starter (if not allowed to cool down) but it is also hard on the life of the battery. These are not deep cycle batteries.

It may be one of those things that has the appearance of being a wise thing to do i.e. it appears "smart" but in reality, has a negligible effect. Want to save a battery? Don't use the starter. That is something that puts a *tremendous* load on the battery.

A fwiw... I do not deviate from the POH unless I have golden advice from someone much more experienced in that specific operation than the guys & gals who wrote the manual (and they can convince me why). So I see no reason not to turn ALT on for a normal start.

-Rob

[afcraig2010]

Thanks for the input from both of you. I didn't realize there was a difference of alternators and generators. To me, the electrical system can be one of the most confusing systems in a plane.

[AKar]

Yes, alternators have primary advantages of having reasonable output straight from idle rpm and in that they usually need sliding contacts only to pass the comparatively small field current to the rotor via slip rings. The alternator output is rectified in diode bridges to a half-wave sine whereas old-school generators employ commutator that is subject to wear and even to arcing. Their regulating principles are somewhat similar, that is, by changing the field current according to actual output versus desired voltage, though of course advances in semiconductors show in how the regulator/control unit is actually made. Both can be cut-off by disabling the field current (except in permanent magnet generators of course that are employed in some places, though not related to this topic!), but usually the generators have no specific ON/OFF switch. I'm no expert in shunt generators, but I think they use the residual magnetism to get the initial field current to 'start it up' when the thing starts turning, resulting in poor low rpm performance.

-Esa

[ft]

What does the manual say?

It says BAT and ALT goes on together, prior to engine start.

If you do not know better, stick with the manual.

IIRC, this is as the alternator system requires a certain power/voltage available to come online. If you have a weak battery, or start on a cold day, the start may just zap your battery to below this level and you're then unable to get the alternator going - i e by inventing a procedure you've basically gone and broken a functioning airplane and ruined the day.

Manufacturers very rarely put things in the book just for the hell of it.

With the alternator on before engine start, this will not happen.

Rgds,
/Fred

[AKar]

IIRC, this is as the alternator system requires a certain power/voltage available to come online. If you have a weak battery, or start on a cold day, the start may just zap your battery to below this level and you're then unable to get the alternator going - i e by inventing a procedure you've basically gone and broken a functioning airplane and ruined the day.

Well, generally it's not the alternator that is the critical part. Enough field current tends to be available at minimal battery voltages. What eventually happens is that the battery contactor (or some other relay) will open, or the starter contactor won't keep closed during prolonged starting attempts, as their energizing current drops below the required to keep the relay closed. Some planes actually have minimum battery voltage requirements due to the fact that some critical relays will not connect the power from other sources even if that power was otherwise made available. The 172 seems to have none. I know no one who's been adventurous enough to run the battery dry while sitting in the airplane to find out which relay trips first (though it happens occasionally on every airfield 'unsupervised' as someone leaves the master on...it happens sometimes in the airliner world too!).

The point is, if you manage to crank the engine alive, it shouldn't be critical on whether you get your alternator started or not after that.

It says BAT and ALT goes on together, prior to engine start.

This is implied, yes. "Normally, both sides of the master switch should be used simultaneously; [...]" However, using only the battery side is not specifically discouraged, though its obvious consequences after prolonged operation on battery only are of course mentioned... Some airplanes have specific advices against the operation with battery switch on and being the only power source for any extended period of time unless in an emergency, but their reasoning is unrelated to the decreasing battery voltage, as it is obvious, but found in other details of the system.

If you do not know better, stick with the manual.

This is a good advice generally.

Manufacturers very rarely put things in the book just for the hell of it.

But they sometimes incorporate pointless, inapplicable or even plainly ridiculous recommendations or practices. The aviation is no different in that from many other fields. I'm not saying that having the alternator on or off during engine start includes any of that - but it is just one of those discussions for which no overall conclusion seems to be available. Personally, I'd just slap it on together with the battery, unless specifically advised against. Or then not... Depending on the situation, I can buy the arguments from both 'camps'. But without a specific caution, I wouldn't be afraid of instantly causing any harm with this issue. More intelligent GCUs keep the thing off the system anyway until certain conditions are met.



-Esa