Peak EGT

[skywatcher]

Can anyone advise me on how to establish the peak EGT for the A/C I fly? It is a PA28 235 and all the performance figures refer to lean/rich of peak EGT. I cannot find any reference to what this figure is or how to work it out without making a guess. Leaning until the engine sounds rough then pushing the mixture in a bit doesn't sound the way ahead. <img src="confused.gif" border="0">

[E. MORSE]

with an EGT indicator

[E. MORSE]

And than, normally one would consider the "50 degr. cooler/richer than this peak".
Wich is normally two stripes actually on the indicator.
(when it say's 25 degr F. per division one might think so)

cheers !

[Pilot Pete]

Together with the EGT indicator you do indeed lean it off just until you detect a slight 'roughness' and then richen it up a 'couple of clicks'(depends on your richness control). Are you going to get the aircraft operating manual out each time you want to lean the mixture, to check the figure? With all the variables it is quite likely that your engine may not indeed be running at optimum richness even using this figure. Trust the tried and tested method and seek further advice from your instructor on the type.

PP

[Checkboard]

Leaning until rough running, then richening the mixture works pretty well with small singles like the PA28.

If you have an EGT guage installed, then the guage has a moveable redline marker - after accomplishing the above general procedure, you move the redline marker until it is over the white EGT indicator, then lean a smidge more, and wait 30 seconds or so. If the egt has increased past the redline, adjust the redline and do the same again. Continue this until you find the peak for that operating condition, then set either rich or lean of that line as required.

The temperature you are chasing changes with different operating conditions, hence the moveable marker.

[john_tullamarine]

Keep in mind, for the larger engines, that a standard EGT probe may not be optimally placed and there is a risk that the gauge may, in fact, get the pilot into an undesirable situation. I suspect that the only comfortable way to get back to best burn with a large engine is if the installation is a little more complex and each cylinder in monitored individually.

At the end of the day, is it so important to save that extra dollar of avgas cost as a proportion of the total cost ? Would one be better running a little richer for comfort (so long as the fuel flow gauging is reliable) when considering the potential for engine damage ?

I note that a recent accident in Australia has raised this sort of consideration to a topical level ....

[ 05 January 2002: Message edited by: john_tullamarine ]</p>

[Pilot Pete]

Totally agree John T.

I used to fly the bigger Cessna piston twins and always leaned them back to 'perceptible' roughness;i.e. gently pulling the mixtures back to the 'estimated' position and then very gently to the first sign of the engine note changing at the same time monitoring the EGT gauge. Once I had established the point at which the roughness started I would then richen them up '2 clicks' as per the operating manual. I do recall that sometimes it was very difficult to establish exactly the point when the roughness was starting, in which case I would do it as well as I could then richen '3 clicks'.

It may well be worth noting for those new to the game that it is important to lean off the mixture and not just fly around fully rich (which I have seen a number of people do in my past) as this can lead to fouling of the plugs which isn't the best way to run your engine either! Does depend on how high you are intending to fly and temperature etc etc.

PP

[john_tullamarine]

... and, of course, forgetting to lean has caused or contributed to a number of lightie accidents over the years ...

[411A]

And, let us not forget those with large turbo-charged engines....operating anywhere near peak EGT results in accelerated exhaust manifold stress...expensive to correct, IE: big time bucks.

[blended winglet]

Good point there John T,

yup, endurance figures are based on correctly
adjusted mixture;
leave it full rich & fly high & the gas goes
far quicker than expected.

[dirkdj]

Before going deeper in the discussion of flying 'too lean' it is best for everybody to uderstand the basics.

Have a look at this:

<a href="http://www.pplir.org/renaissance.htm" target="_blank">http://www.pplir.org/renaissance.htm</a>

I fly lean of peak on an IO520 since about 4 years now, properly equipped with 6 cylinder engine analyser, GAMIjectors and proper understanding of what's going on. Can't hurt the engine by running lean of peak in cruise.

If the engine won't run smooth lean of peak, then the mixture is not properly distributed (most carburetted engines), there is an induction leak, or the injectors are mismatched to the airflow of the engine.