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FenderManDan
 Post subject: EGT and mixture check
PostPosted: Mon Jan 30, 2012 3:16 pm 
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On run-up do you actually perform a peak EGT or best power check or do you just lean the mixture enough to check the needle movement on the EGT gouge?

Engine in question is C-172R fuel injected.

Cheers,

Dan


Last edited by FenderManDan on Mon Jan 30, 2012 3:46 pm, edited 1 time in total.

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robertsailor1
PostPosted: Mon Jan 30, 2012 3:34 pm 
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Can't tell you what is recommended for your aircraft but all I ever do is lean the mixture and look for the rise in the EGT to confirm its working.


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Rowdy Burns
PostPosted: Tue Jan 31, 2012 8:16 am 
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FenderManDan wrote:
On run-up do you actually perform a peak EGT or best power check or do you just lean the mixture enough to check the needle movement on the EGT gouge?

Engine in question is C-172R fuel injected.

Cheers,

Dan
What does the POH say? I have never flown a fuel-injected C172 but I would bet it would state something like "lean for maximum RPM > 3,000 otherwise full-rich" in the amplied normal procedures (latter half of Section 4).

Not that it matters, just curious - steam or glass?


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ahramin
PostPosted: Tue Jan 31, 2012 7:27 pm 
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He's asking about the runup rowdy. The point of the mixture check during the runup is to make sure your mixture control is working properly. What constitutes proper operation?

As you pull the mixture out the fuel mixture becomes leaner. You can see this by a rising EGT. The mixture control should also be able to cut off the fuel supply completely, so if you keep pulling and the engine quits, you know that part is working properly.

I don't think you would gain any information about whether or not your mixture control is working by doing a peak EGT or engine power procedure. Remember, you are on the ground taking up space, running your engine at higher than taxi power, burning fuel. Runups should be done in the minimum amount of time necessary to ensure that everything is functioning properly.


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RenegadeAV8R
PostPosted: Tue Jan 31, 2012 9:41 pm 
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FenderManDan wrote:
On run-up do you actually perform a peak EGT or best power check or do you just lean the mixture enough to check the needle movement on the EGT gouge?
Engine in question is C-172R fuel injected.


During the Run-up, you lean the mixture in order to burn off the carbon deposite on the spark plugs. The engine is running at a low power setting and you can lean aggressively; the RPM will rise then the RPM will slightly drop if you keep leaning.

Leaning to verifing if the leaning mechanism is functioning can be done at idle power. In fact, before taxiing it is a good practice to lean the mixture to prevent spark plugs fooling; and you will see the EGT rise.

:)


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Big Pistons Forever
PostPosted: Wed Feb 01, 2012 1:50 am 
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For fuel injected engines like the one on a new build C 172 R or S model, lean enough to get a rise on the EGT and reduction on the fuel flow gauge. This will prove the FCU is working.

For carburated engines, lean slowly and you should first observe a slight RPM rise and then a drop as you continue leaning. Under No circumstances on Any aircraft should you lean so much that the engine dies other than at low RPM when you want to shut down the engine at the end of the flight.

As for leaning on the taxi, I think this is airplane dependent. I have to aggressively lean the O 235 in my Grumman AA1B on the ground or it will almost instantly foul the plugs. But for a C 172 with the O 320, leaning or not seems to make absolutely no difference so I just leave the mixture at full rich (caveat this is at a near sea level airport)


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Colonel Sanders
PostPosted: Wed Feb 01, 2012 3:17 am 
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BPF: do you get any RPM rise do you get when you lean that 172
on the ground? How far do you have to pull the mixture to get
max RPM on the ground? I'm guessing not very far.

It sounds like that particular carburetor might be set up pretty lean, if it's
running on 100LL and doesn't lead foul the bottom plugs. That's ok if it
never flies in the cold, but if it ever does, don't be surprised if the prop
stops on final.

My experience is that any Lycoming should have it's mixtures leaned
for max RPM on the ground to minimize lead fouling of the bottom
plugs. Also, if you have to sit and wait, idle at 1100 to 1200 RPM
to keep the temps up.


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Big Pistons Forever
PostPosted: Fri Feb 03, 2012 1:18 am 
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Colonel Sanders wrote:
BPF: do you get any RPM rise do you get when you lean that 172
on the ground? How far do you have to pull the mixture to get
max RPM on the ground? I'm guessing not very far.

It sounds like that particular carburetor might be set up pretty lean, if it's
running on 100LL and doesn't lead foul the bottom plugs. That's ok if it
never flies in the cold, but if it ever does, don't be surprised if the prop
stops on final.

My experience is that any Lycoming should have it's mixtures leaned
for max RPM on the ground to minimize lead fouling of the bottom
plugs. Also, if you have to sit and wait, idle at 1100 to 1200 RPM
to keep the temps up.


I use full rich on the ground on every C 172 I fly (O 320 E2D, O 320 H2AD, O 320 D2J). I have never had a problem with fouled plugs and the plugs look normal on the 100 hr inspections. I also teach and practice that on every runup the mixture is slowly leaned with the carb heat on to first look for a RPM rise and then a drop. Like I said this engine/airframe just doesn't seem to foul the plugs even with lengthly taxi or takeoff waits with the mixture at full rich. I do however insist that the engine be set at 1000 RPM if the airplane is stopped.


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habs.fan
PostPosted: Fri Feb 03, 2012 11:32 pm 
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Big Pistons Forever wrote:
For carburated engines, lean slowly and you should first observe a slight RPM rise and then a drop as you continue leaning. Under No circumstances on Any aircraft should you lean so much that the engine dies other than at low RPM when you want to shut down the engine at the end of the flight.


Why not?


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Colonel Sanders
PostPosted: Sat Feb 04, 2012 4:43 am 
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Because the engine stops?


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Big Pistons Forever
PostPosted: Sat Feb 04, 2012 6:15 am 
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habs.fan wrote:
Big Pistons Forever wrote:
For carburated engines, lean slowly and you should first observe a slight RPM rise and then a drop as you continue leaning. Under No circumstances on Any aircraft should you lean so much that the engine dies other than at low RPM when you want to shut down the engine at the end of the flight.


Why not?


Leaning the engine to such an extent that it dies during the runup will often cause a backfire. This blows out the baffles in the muffler and causes exhaust system cracks. There is no reason to lean to engine stoppage to check the mixture. You need only until you see a small ( approx 100 RPM) drop to prove the mixture control and the carb are functioning correctly.


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Rowdy Burns
PostPosted: Sun Feb 12, 2012 7:19 pm 
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ahramin wrote:
He's asking about the runup rowdy. The point of the mixture check during the runup is to make sure your mixture control is working properly.
Hmmm gotcha! I'm just surprised the POH would say something like "Mixture.....check for EGT needle movement" or if this is just another 'generally accepted good practice' seperate from the more common "Mixture....lean for maximum RPM above 3,000"


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ahramin
PostPosted: Mon Feb 13, 2012 3:37 am 
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POH says Mixture ................. Check


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