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Operating normally aspirated engines at high density altitudes - Setting a Target EGT?

Reply from Advanced Pilot Seminars (who published the PowerPoint presentation quoted in the OP):

“If you ever get a chance to take off from near sea-level, store that target number in your memory. As a rule of thumb, most 8.5:1 compression ratio engines will have a target EGT around 1300°F”

My 0-470L Cont. is 7.0:1, so maybe nearer 1400°F?

I’ve found Martin Pauly’s YT video really useful:

Question: How does he fly, apparently solo, at 140kts, 9,000’, at least 2 cameras and sound, with a rather static landscape outside? Just curious.

Last Edited by 2greens1red at 28 May 10:09
Swanborough Farm (UK), Shoreham EGKA, Soysambu (Kenya), Kenya

Mike Bush has something to say about leaning. See here local copy

I don’t know your aircraft so have no clue on the instruments you have available. In general, EGT is not the most essential thing to monitor. Worst advise is to slowly lean your engine to peak EGT to then richen to e.g. 50 degrees ROP or e.g. 20 degrees LOP. Hot EGTs are not the issue. Hot CHTs are the issue.

Mike Bush wrote a book about engines with two chapters on leaning which is available on Amazon. It is not complicated, also not in Africa, but it pays off to read these chapters in his book.

Last Edited by AeroPlus at 28 May 12:13
EHRD, Netherlands

Thanks for the Busch links – they look useful; I’ll absorb both.

Current instruments in my 182P are basic:

RPM / MP (10-50) / EGT (just 25F/div marks) / CHT (200 – 500 uncalib) / Oil temp (just 225 mark) / Oil press (0-50-100) / Carb Temp C (-50 thru yellow -10 – +10 then up to 50)/ Suction 2-8

Oil pressure gauge is unreliable (exhibited on ferry, and confirmed on test bench). Our engineer is keen on an engine monitor, and fuel flow would be useful. So EDM 830 is currently being investigated (aircraft imports (and accessories) are tax-free to Kenya, though there’s a 1.5% Railway development tax).

Swanborough Farm (UK), Shoreham EGKA, Soysambu (Kenya), Kenya

In my POH, it is said:
- below 5000ft DA, let it full rich
- above, lean to get max RPM

This for a C182T with EGT/CHT/FF equipment, they suggest to keep it simple.

PS: they say that by doing so, you would get max FF for altitude, as placarded in the cockpit (see above), as a second order of confirmation.

Last Edited by PetitCessnaVoyageur at 28 May 13:28

That sounds right to me, but it means that as DA rises through 5001ft you suddenly need a lot more runway

I don’t think that is real-world physics.

But I can’t think of a better solution, given that Lyco don’t authorise peak EGT above 75% of max rated power.

The proper answer is probably engine dependent.

Shoreham EGKA, United Kingdom

Short answer: monitor CHT to stay below specific temperature for your engine. If you fly ROP and want to cool the cylinders further richen the mixture. If you are flying LOP, close the mixture further. Best way to go from full rich to LOP in the cruise is to do it quickly. The engine will tell you when it stutters and is not running smooth, so you can smoothen it out. EGT as well as CHT probes are probably on one cylinder, so no exact science. Leaning as is often written in older POHs to go find peak, then to enrichen a bit or fly a bit leaner or software on screens where you are slowly doing a lean session and finding peak first to them lean is not a good solution and not good for your engine as you don’t want your engine to operate more than say 3 seconds in that hot CHT range. Read Busch’s book or the 2 chapters only and you should be all set! Enjoy the flying in Eastern Africa!

Last Edited by AeroPlus at 28 May 13:32
EHRD, Netherlands

Here’s an example of a 182’s performance at 8,000’ DA:

Swanborough Farm (UK), Shoreham EGKA, Soysambu (Kenya), Kenya

Good video about performance at high DA. What I personally do on departure from Courchevel or in Africa in a normally aspirated engine aircraft is lean a bit on departure to get the extra performance. I just listen to the engine and don’t use exact EGT values. It is just a bit. I do the same when in the climb. I always climb ROP, mostly full rich or max allowed FF for best cooling. Then at some altitude I notice the drop in performance and lean a bit. Maybe I should do this different but so far this worked out ok for me. I am not sure if exact EGT values would help in this respect. Maybe somebody else would know.

Last Edited by AeroPlus at 28 May 14:00
EHRD, Netherlands

I can confirm from countless attempts to stall the plane at FL200 that the power output is not critically dependent on the EGT.

I tend to find about 1330F is best, but it is really a struggle to see the difference between say 1310 and 1350… maybe 1-2kt at most on the IAS.

1330F is also the departure EGT at sea level.

Obviously it scales with the OAT, like everything else the engine does. But OAT has a much more direct effect on CHT than EGT, obviously because EGT is so much a bigger number. 20F extra (say Greece) on CHT is noticed but 20F extra on EGT isn’t.

I wonder what size runway 2greens has? If it is 400m, you want a PT6 Hmmm, wait, half of Africa already runs on those

Shoreham EGKA, United Kingdom

AeroPlus wrote:

I am not sure if exact EGT values would help in this respect.

They just look cool when we talk very precise about them, like talking about power settings, approach speeds and climb speeds
For “engine life” CHT/OAT is your best friend, “performance cost” EGT/FF is what you look after vs “performance benefit” is the delivered TAS/ROC

My guess if you can feel by look/sound what is max TAS/ROC to FF while watching-out for your engine CHT/OAT constraints then you should not really care about EGT peak, ROP, LOP values but I find picking few data points of these from POH or others pilots testing give me a good start if I am new to a given aircraft, later I can tweak left and right once I am used to aircraft performance

Sort of do you climb at Vx, Vy or at cruise speed? sometimes none of them….

ESSEX, United Kingdom
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