Half Master off while starting

[PA31Ho]

Hey all... I was in the airplane the other day with somebody new, and I noticed that he started up the airplane with the alternator side off. He said that's what he normally does. What would be the pros/cons of doing this? I tried searching for it here so if it's in another thread that I didn't find, just paste the link.

Thanks!
Nick

 

[rumpletumbler]

He just started the plane without the alternator online. Folks can feel more like a JET MAN when they do that.

 

[PA31Ho]

well, he does fly a king air... hehe

 

[SuperFLUF]

It saves a little juice by not sending batt power to the alternator during the start. The con is that if you forget to turn the Alt. side on after start you will run into some problems down the road when the batt goes dead and is too weak to power up the alternator.

I do it but I have added it to the after start checklist in case I forget.

 

[midlifeflyer]

There are some aircraft where that's listed as the starting method in the POH.

One of the places I fly out of uses the method. I think their reasoning is the same as SuperFLUF's.

I actually like it as a solid alternator check on start. Seems to me that bringing the alternator online after the engine starts and watching the needle rise and go to normal is a much better operational check than, say, wiggling the flap lever during the run-up. I've ended up using it as my SOP.

 

[SiuDude]

The aircraft I fly now has 3 switches: Master (Battery only), Alternator Field, Alternator. The switches are located at different places on the panel. The master goes on prior to start. Both of the alternator switches go on after start. Nothing wrong with doing it as you described.

 

[rumpletumbler]

So do mine! We feel like JET MEN!

 

[Goose Egg]

What does the operating handbook say? Do it like that.

-Goose

 

[Kingairrick]

In the King Airs you have to do it like that. The starters and generators are the same piece of hardware (starter/generators.) Maybe he just likes doing things the same way all the time.

 

[Vik]

I'm one of those that believe that the Alternator doesn't need to be on until the engine is on. I don't turn it on until the engine is running. There is no point turning it on.

Now in airplanes w/ generators, I don't turn them off. Which can be an issue if someone that flies the plane before you turns them off, and you happen to glance over that item on the checklist.

 

[Moonfly201]

I was told that the reason some POH's recommend the alternator by left off-line during start-up had to do with preventing voltage spikes.

Once the engine is running the alternator and voltage regulator have stabilized and are providing proper voltage, the alternator switch can be turned on.

 

[gfvalvo]

I was told that the reason some POH's recommend the alternator by left off-line during start-up had to do with preventing voltage spikes.

Once the engine is running the alternator and voltage regulator have stabilized and are providing proper voltage, the alternator switch can be turned on.

I've heard just the opposite. Turning on the alternator AFTER engine start can cause excessive voltage spikes. Also, the alternator switch provides current for the alternator's field coil. Without that it's not making any voltage. Therefore, even though the engine is running neither the alternator nor the voltage regulator is doing anything. I guess you could call that "stabilized", but I don't think it's what you meant.



Greg

 

[Vector4fun]

IIRC, there's a tech note on the Cessna Pilot's Association web site that reccomends turning the alternator on separately after starting, for just the reasons SuperFLUF and midlifeflyer mentioned. Having said that, I recall there's nothing harmful with turning both on at the same time.

 

[avbug]

In aircraft that use a "split switch," you're talking about two different switches. That the switches are the same color and close to each other is the only functional commonality. Some are mechanically interlinked such that one may be turned off without the other, but the other is turned off, they both go off.

Use the proceedures recommended or directed in the approved data you've received. In most cases that's your aircraft flight manual or pilot operating handbook. These proceedures may vary from manufacturer to manufacturer, and will certainly be aircraft specific.

Generally speaking, you should leave the electrical generator (alternator or generator) off during engine start. This is true weather it's an integral starter generator, or separate starters and generators.

Turning on the alternator or generator during the start means that a certain operating resistance is had by the gen/alt. This means youre engine is carrying a bigger load, or meeting more resistance during the start. Your aircraft battery, if used as the electrical source for the engine start, is working harder; more current and a bigger voltage drop occurs.

Leave off the gen/alt to make life easier on your battery and starter motor.

During engine start, with the gen/alt on, your battery acts to "absorb" transient voltages, but it can't protect equipment on line. Voltage will rise and fall, and transient voltages may exceed the ability of the protection equipment (eg, regulator) to control during the start process. Accordingly, a potential exists to damage equipment on line.

Leave off the gen/alt to protect equipment on any affected bus. Avionics, radar, etc, are the most susceptible to voltage spikes.

Further, as mentioned before, initiating field current after start enables a positive check at operating speed for the gen/alt for voltage and current flow.

Leave off the gen/alt until a stable start has been achieved for a better positive check of the gen/alt and electrical systems.

Above all, follow the proceedures provided by the manufacturer for your aircraft, always.

 

[midlifeflyer]

IIRC, there's a tech note on the Cessna Pilot's Association web site that reccomends turning the alternator on separately after starting, for just the reasons SuperFLUF and midlifeflyer mentioned.

Would it be possible to get a copy of the note? My information is second-hand and it would be interesting to read.

Goose Egg, a general FYI. Unfortunately, there are good operating practices that don't necessarily appear in the POH. In the non-turbocharged piston world, for example, most call for the mixture to be full rich for landing. But do it at a high density altitude airport and you've compromised safety. The flip side is that you have to be careful - certain airplanes need to go to full rich for landing even under those circumstances.

 

[avbug]

Dont' change what is in the approved aircraft flight manual. If the manual specifically calls for a power setting or equipment setting for takeoff or landing, then use it.

Are you going to get yourself into trouble if you properly lean for landing? No. But the manufacturer doesn't know you, doesn't know your capabilities, and hasn't had the opportunity to train you. Accordingly, proceedures are developed for everybody, taking into account the fact that these proceedures will work and will be successful. Will the manufacturers proceedures sink you? No.

Is it possible to wring more performance out of an aircraft? Yes. But the manufacturer isn't there to show you how, or provide proceedures for running to the ragged edge of performance (and this includes leaning practices); only how to stay well inside the operating envelope in every respect, and stay safe.

 

[TurboS7]

Good post. You should charge for that Avbug. My wife loves you because when you answer something I don't have to spend any of my time doing the same.

 

[midlifeflyer]

Dont' change what is in the approved aircraft flight manual. If the manual specifically calls for a power setting or equipment setting for takeoff or landing, then use it.

Are you going to get yourself into trouble if you properly lean for landing? No. But the manufacturer doesn't know you, doesn't know your capabilities, and hasn't had the opportunity to train you. Accordingly, proceedures are developed for everybody, taking into account the fact that these proceedures will work and will be successful. Will the manufacturers proceedures sink you? No.

You're more than welcome to attempt a go-around Leadville (9927 msl) in a full rich CE-172. I'm not planning to.

 

[avbug]

Mark,

You may note, as you quoted me, that I very specifically stated "Are you going to get yourself into trouble if you properly lean for landing? No." You have a problem with which part of that statement?

 

[midlifeflyer]

avbug,

The part that said

"If the manual specifically calls for a power setting or equipment setting for takeoff or landing, then use it.

[snip]

Will the manufacturers proceedures sink you? No."

 

[Rez O. Lewshun]

Since we are talking about leaning and mixture.....

I have seen techniques on starting...

Pull the primer out, let it fill with gas..and as the primer is pushed back in, engage the starter......

And manufactuer references?

The intent...? Don't prime it three times only to have the gas run/drip down into the airbox........

 

[avbug]

I stated correctly. The manufacturers proceedures should be followed. The aircraft can certainly be flown outside those guidlines for greater performance,but I have already addressed that.

Follow the manufacturers guidlines. These will not get you into trouble. You can push them, you can fly the airplane to the ragged edge of performance capability if you like. You can fly rich of peak or lean of peak without any damage if you like. You can do just about anything you like. However, I'm not going to make general recommendations to operate outside manufacturers guidelines without addressing the specific airman. Neither should you.

I don't have an aircraft flight manual for a 172 before me right now,and can't comment on what it stipulates about high altitude landings right now. Regardless, follow the recommendations.

I teach leaning for ever takeoff, and proper leaning for every landing. I also have the opportunity to teach to the specific airman, and ensure that the airman uses proper techniques. Cessna doesn't have this opportunity sitting in a little room writing the manual. The manual is written for everyone, and generically following the proceedures will not get you in trouble. You may be able to do better.

That is not, however, the issue.

 

[gfvalvo]

Best Mixture Setting for High Elevation Landing

I've always wondered this about ops at high-elevation airports. Let's say I'm taking off from Denver. During run-up on the ground I lean for best power using whatever technique the manufacturer recommends. Now I take off and climb to say 11000 feet. Obviously, I'll lean further for this higher altitude. Now it's time to return to Denver. What's the proper mixture setting? The only "calibrated" settings are full rich and cut-off, neither appropriate for landing. Do I leave it alone, try to find ABOUT where I had the knob for take off, or something in between? I would think the best setting for take off would be the best setting for a go-around, but how do I find it?

 

[avbug]

If you descend, you must lean. Any time you make a change in airspeed, power, or density altitude, you must change your mixture setting.

If you lean for descent, you'll need a richer setting for the go-around.

One cannot generically dictate leaning for a go-around; the needs change with the aircraft and engine (and compression ratio), as well as ambient conditions.

As a general concept, if you leaned for takeoff (leaning during the runup is inadequate), and are returning to the same location, you can use the same mixture setting used for departure if there hasn't occured a major atmospheric change.

The cutoff and full rich positions on your mixture control are not calibrated. These are adjusted for control travel; the control travel should not bottom out without a slight cushion; cutoff is whatever the cutoff point on the carburetor reaches, plus a cushion in the control travel. Full rich, however, opens the mixture, which then becomes dependent upon airflow in the carburetor to set fuel flow.

Calibration takes place in carburetor design (and fuel system design in the case of injected systems), and in the jetting of the carburetor, and selection of fuel nozzles.

 

[midlifeflyer]

As a general concept, if you leaned for takeoff (leaning during the runup is inadequate), and are returning to the same location, you can use the same mixture setting used for departure if there hasn't occured a major atmospheric change.

Why wouldn't you go to full rich, like the POH says and avoid the go-around issue altogether?

 

[midlifeflyer]

Do I leave it alone, try to find ABOUT where I had the knob for take off, or something in between? I would think the best setting for take off would be the best setting for a go-around, but how do I find it?

That's where avbug and I =do= agree. Unless things have changed drastically, go back to the approximate setting you had on takeoff, or estimate the setting that you will need.

As you correctly note, the issue isn't the landing, it's the go-around. Chances are that if your estimate is a bit off, a small adjustment will fix it. - much the way, in an aircraft with altitude-based fuel flow targets, we might approximate the setting based on the run-up and tweak on the roll.

Of course, that procedure all depends on the airplane. There are some in which you would simply go full rich for landing. For example, the Cirrus has an altitude-compensating fuel pump.

 

[gfvalvo]

If you descend, you must lean. Any time you make a change in airspeed, power, or density altitude, you must change your mixture setting.

Lean for descent? I'd think you'd go richer.

As a general concept, if you leaned for takeoff (leaning during the runup is inadequate),

I meant lean for best takeoff power using method recommended by manufacturer. Be that on runup or WHATEVER.

...,and are returning to the same location, you can use the same mixture setting used for departure if there hasn't occured a major atmospheric change.

That's my question. How do I find that same knob setting again (assuming that I leaned further during flight)? There is no position indicator scale on the mixture control.

The cutoff and full rich positions on your mixture control are not calibrated

You're interpreting my use of the term "calibrated" too literally. I meant there are only two knob settings that you can repeatedly hit exactly the same every time: full forward and full backwards.

 

[gfvalvo]

Why wouldn't you go to full rich, like the POH says and avoid the go-around issue altogether?

If full rich wasn't the right setting for take off, won't it be wrong for a go-around also (same airport)?

 

[midlifeflyer]

If full rich wasn't the right setting for take off, won't it be wrong for a go-around also (same airport)?

Yes it would. I was commenting on avbug and my disagreement about following the POH literally when it says "Mixture -- RICH" for descent and landing.

I answered your procedural question in a separate post.

Sorry. The confusion is my fault.