A

andrewbutler

Member
Hello All,

I fly out of a very short field in the West of Ireland (about 350 yards with high obstacles at one end), and was pracitising slide slip final approaches today, as one end of the field has several high obstacles on finals. The point of the exercise is to come in as steeply as possible (heavy slide slip, little or no power) until the threshold, then level off with a burst of power to arrest the sink rate and touch down.

Powerplant is an IO360 with one P-MAG and one Slick, with a CS MT 3 blade prop out front. When on finals if I pull the power completely, my EGTs shoot up to over 1500, and I have to apply some power to get them down again.

I run LOP, and have read and understood John Deakin's articles so have learned a lot about what is going on inside the engine during different modes of operation. However, I haven't really been able to figure out what exactly is happening to cause the EGTs to shoot up like this when I pull the power on finals.

Can anyone help me? Is it normal or may I have a problem? Is it damaging?

Thanks for your help,
Andrew Butler,
RV7 EI-EEO 38hours
Galway, Ireland.
 
Idle mixture too rich and still burning as it exits the exhaust valve elevating the EGT's?? Just a guess.
Timing not quite right for the low RPM and causing the same as above?? Again just a guess.
 
my EGTs shoot up to over 1500, and I have to apply some power to get them down again.
Click to expand...

So what!!!!!!! If you have read again the various articles you will not be so worried.

Are you full rich during this operation?

There is no need to be, mind you if you richen up a bit from LOP settings in your cruise and descent this will ensure a good margin from a cough, just remember the go around is red knob first. There is no GA that requires anything faster than red knob/black knob assuming RPM is either fine or OK where it is.

Previous post has some good things to check also.
 
Check idle mixture

Andrew

You should have a 30-50 rpm rise when you sloooowly pull the mixture at idle. On the same engine mine was quite rich and had to be adjusted after the engine had run in.

Cheers

Peter
 
What are the chances that on the extended side slip, your have selected the tank where the fuel is moving away from the pickup. You could be on the edge of fuel starvation but it is picking back up just as you come out of the slip. I would think this could only happen with fuel tanks drawn down pretty good.

Just a thought.
 
heavy side slip angle?

I may be proposing a physical impossibility but is it possible that with a very heavy side slip angle and idle power it is harder for the exhaust to leave the pipes and thus increasing egt? Increasing the power and/or reducing the side slip angle would "unplug" the exhaust.

It may be too wild an idea...

Jeremy
 
With a constant speed MT prop set to fine pitch (go around setting) and engine at idle, you should be coming down like a boat anchor. At least that was the case with an electric MT prop. It was a huge speed brake.

The side slip may not be necessary.

I don't look at EGT's on final.
 
My Superior 180 Injected

engine does the same thing as I'm letting down for a relatively steep approach into KHND. My GRT EGT graph shows very erratic EGTS with some cylinders going cold, and some with high EGTs. First of all, at these low power settings I don't think I can hurt anything. Second, It looks to me like lean misfire and fuel burning in the hot exhaust pipe caused by the prop driving the engine (resulting in lots of air) at very low manifold pressure and very low fuel flows.

I'd like to understand this better, but I don't think we can hurt the engine with the throttle all the way out (just like leaning at idle).

What say the experts???
 
What engine monitoring system are you using? Almost all of the engine monitors allow you to dump the data. If you could provide the data to the group (especially with a system like the Dynon that allows you to get engine and flight data) it may give folks a clearer picture of what is happening.

Cheers.
 
Settings

Boat anchor, you are absolutely right. The MT is a great speed brake and perfect for short fields. However, if I am a little high, I still need the option of pulling the power all the way back. I don't normally monitor the EGTs either, but my EFIS gives me verbal warnings when they go over 1500 - and that kinda forces to me to look!

I always slideslip with right rudder, and have a mandatory "select right tank" check in my prelanding procedure. Prop is set to Max RPM, and mixture is set to full rich. My idle mixture setting is not quite correct yet. It may be still too rich.

My EFIS is an AFS3500 with Enginer Monitor. I will download yesterday's data, graph it and post it.

Thanks for all the replies.

Andrew.
 
andrewbutler said:
Boat anchor, you are absolutely right. The MT is a great speed brake and perfect for short fields. However, if I am a little high, I still need the option of pulling the power all the way back. I don't normally monitor the EGTs either, but my EFIS gives me verbal warnings when they go over 1500 - and that kinda forces to me to look!

I always slideslip with right rudder, and have a mandatory "select right tank" check in my prelanding procedure. Prop is set to Max RPM, and mixture is set to full rich. My idle mixture setting is not quite correct yet. It may be still too rich.

My EFIS is an AFS3500 with Enginer Monitor. I will download yesterday's data, graph it and post it.

Thanks for all the replies.

Andrew.
Click to expand...

I hear what you say about nuisance warnings.

I get one on final with EIS 4000 on cooling rate, some of the cylinders cool deeper when at idle, pushing the throttle up gets rid of it. The parameter is set too tight. It just takes getting into the system and resetting some limits to get rid of it.

With egt upper and lower limits, I think I set it at zero to defeat any warning at all. I figure is something goes wrong, egt will be the last warning I get any how.
 
G'day Oz

The John Deakin articles talk loads about good and bad CHTs at different modes of operation, but not as much about the good, the bad and the why of EGTs.

What ranges of EGTs are acceptable in an IO360? Why would it be okay to set the alarm at 1600?

Cheers, Andrew.
 
The actual EGT value is not really of any meaning. It is the measure of the temperature at that particular distance from the cylinder head. Exceptions being a Turbo engine where the TIT is important for other reasons.

Want lower EGT's.....move the probe an inch down the pipe! :p

The purpose of EGT is to look at relative numbers, not absolute values.

The changes you may see in an EGT and a CHT help you diagnose problems. For example if your alarm was at 1600, and you were flying along happily LOP and one EGT started moving about then it just climbed through the 1600F mark, the alarm alerts you....should you panic? No. Its telling you something but not likely you are about to crash. is 1650 going to hurt anything wwhile you are LOP.....NO. Chances are you have a plug not firing, so a 10-15 second mag check while touching nothing else will probably reveal which plug on which mag.

I can tell once my plug gaps get past about 22-24 thou just from my EGT's on my engine monitor. ;)

I could send you a bunch of info to read, but you would have to promise to read it every night for weeks....at least 4 lots about 7 times each so that takes you 28 days.

Attending an APS course from Ireland is only marginally easier than from down here, but there is the online course.

Cheers! :)
 
Figured it out, I think!

Earlier in the thread someone suggested I may be running too lean at idle. Yes, recently I had been trying to adjust the idle lean setting to get the correct RPM rise when pullling the mixture at idle. Assuming it was too rich (when pulling the mixture I got no rise so I assumed I was on the rich side), I leaned it. In my last runnup, when I killed my one P-MAG, all my EGTs shot up when running on the Magneto. I have since re-read some of JD articles, and sure enough, this behaviour shows up in his description of how to do do a "real" check of the sparks using a lean mixture setting. At least I can confirm that all my MAG sparks are good. When I switch to the P-MAG, the EGTs don't shoot up, they stay the same. This is a real world demonstration that the P-MAG sparks are much better at burning the mixture, even a heavily leaned one, than the MAGs. The MAG RPM drop at this lean setting was also much higher than the PMAG drop. So, I enrichened the idle mixture setting. Now have to manually lean to get the same effect. Incidentally, my PMAG RPM drop (of about 70 or 80 RPM) is always 20-30 RPM less than the MAG drop. The differential rises when the mixture is leaned.

With an enrichened idle mixture setting, the EGTs no longer shoot up when I pull the throttle in flight. Behaviour explained.

Thanks for all the replies to this one. This is a great resource!

Andrew.
RV7 EI-EEO
Galway, Ireland.
 
"Assuming it was too rich (when pulling the mixture I got no rise so I assumed I was on the rich side), I leaned it"

You obviously "assumed" wrong, so just for everone else reading this that doesn't know the process;

If you don't get a rise when pulling the mixture you are too LEAN and need to enrich the mixture by screwing the idle mix adj screw out (or adj the mixture arm if you have FI). If you get more than 100 RPM drop then you are too RICH and need to screw the mix screw in.

And if you're not sure what you're doing please find someone to help you, mistakes can be both expensive and deadly in this business!
 
If truth be known, I haven't known what I've been doing for most of the last eight years! On this occasion, the high EGTs I was experiencing were not expected, and that is why I came here, asking for help.

When looking at the issue (of correct idle mixture setting), I was using the below fuel/air mixture power curve from JD article "Mixture Magic" to try and figure out what exactly goes on when you pull the mixture when idling. Now, having given it more thought, I realise that my starting position was probably at or very near the top of the curve. Leaning the setting a bit more moved it a little left to the point where is was definitely to the left of the peak. This is when I noticed the high EGTs on my power checks.
pp18b.jpg


Now, with just a little more experience, it is now obvious from this curve why you should see a steady RPM increase as you lean out, and why the correct starting position is just to the right so you get a small RPM increase as you lean out. The thing is, when you are starting out, reading the JD articles over and over and over, and you are presented with all these different graphs, it really does take a while to assimilate all the new information into a coherent whole.

So now a couple of questions:
If idle mixture is incorrectly set way lean (to the left of the peak) what harm can it do?
What affect does the idle mixture setting have as you increase RPM?
What affect does idle mixture setting have at high RPM?

Thanks,

Andrew.
 
andrewbutler said:
So now a couple of questions:
If idle mixture is incorrectly set way lean (to the left of the peak) what harm can it do?
What affect does the idle mixture setting have as you increase RPM?
What affect does idle mixture setting have at high RPM?

Thanks,

Andrew.
Click to expand...

To answer your questions:
1) Too lean an idle mixture can cause stumbling and poor acceleration when advancing the throttle but not necessarily harmful.
2) Idle mixture has less and less effect the higher the power setting.
3) At full power the main jet is controlling max fuel flow and the idle mixture will have little or no effect.
 
Walt said:
To answer your questions:
1) Too lean an idle mixture can cause stumbling and poor acceleration when advancing the throttle but not necessarily harmful.
2) Idle mixture has less and less effect the higher the power setting.
3) At full power the main jet is controlling max fuel flow and the idle mixture will have little or no effect.
Click to expand...

So, Andrew, in flight, when you close the throttle to land, you are commanding the engine to go to "idle". When you do that, you are now using the idle circuit for fuel flow. If your idle mixture was set too lean, then it would make sense that your EGT would rise as you close the throttle.

Guessing that if you richen up the idle mixture, the problem will go away.
 
Sideslip...

Whilst many of the comments above may be useful and/or correct, they might also easily be proposing to make a mess of your engine settings.

I have spent many hours gliding and tug piloting.
Sideslipping tugs for a quick turnaround is usual OP.
Engines on glider tugs are well known for requiring caution wrt cooling, esp shock cooling.

Side slipping will ALWAYS aggravate (worsten) cooling, as the airflow across the nose is no longer straight, effectively blanking the cooling inlets, and the flow through the cowl becomes severely effected.

This is almost certainly the primary cause of your cooling situation.
Is it a real problem?
Perhaps not, but your certainly should reduce or minimise the slips.
 
Airscrew

What has sideslipping got to do with EGT? :confused:

It may have an impact on CHT due to abnormal airfow through the engine but little impact on EGT. Think about this for a minute.

As for shock cooling, this is something of great debate and many OWT's. But not relevent to this topic.
 
What are your peak EGT's in cruise when transitioning to LOP? Also, on a high agl. descend are you compensating any with the mixture?
Thomas S.
 
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