Leaning for Best Power?
 

The other day I flew in and around the Vic / NSW mountain range. Quite a bit different from the majority of flying I've done as a PPL since obtaining my licence only a few years ago.

As part of this trip I did a stop and go at Mt Hotham (elevation circa 4,300'). Even though this question has occurred to me before, it wasn't until I did the takeoff at Mt Hotham that I truly wondered that perhaps I have missed something in my training.

As I took off to the north west the terrain gently climbs. I was pretty light with half fuel and only 2 pax in a 180hp cessna 172. I realise I was at 4,300' to begin with and density altitude was closer to 6 - 6.5k feet, although was surprised about the climb performance.

So I have two questions I'm hoping some of you very experienced guys / girls out there can help me with:

1) I assume that I should have tested for max power before taking off - by applying full power and leaning until best power is indicated?

2) Assuming the answer to 1 is yes, then when climbing I was always taught to full rich, full power and climb to desired level then power back (if appropriate based on height) then lean. If it makes sense to lean at say a takeoff at a density altitude 6,000', should I be leaning as I climb above 5,000 ft (up to max 10,000' VFR limit)?

Thanks for your help.

If you have an engine monitor, the procedure is:

(1) Take off at sea level on a ‘standard’ day.

(2) Note the EGT of a cylinder (I usually monitor the EGT and CHT of my hottest cylinder) just after take off.

(3) During the climb, lean every couple of minutes to get to the same EGT on that cylinder (no need for absolute precision - close is good enough).

When taking off at higher density altitudes:

(1) Lean to until you reach the same EGT as you noted at #2 above.

(2) Do #3.

This assumes that your engine’s fuel flow has been set up properly.

If you maintain full rich for the entire climb, you are steadily losing power compared with the mixture that is an optimal compromise between power and being kind to your engine.

As the APS people say: It’s now how hard you run your engine, but how you run your engine hard.

Thanks Lead Balloon - I have no individual cylinder monitor, just the general CHT and EGT monitor for the engine as a whole.

In that case, use the single-point EGT reading. Provided you are always using the same reference instrument/temperature - as you are bound to do if you have only have one - it’s better than nothing.

Thanks, I'll give that a go.

I've got nothing, just Tacho and my ears and eyes.

Suggestions LB, please?

Kaz

Where is our old friend Jabawocky..? He's normally all over this stuff like a rash..!

Kaz - full throttle, stand on the brakes, lean until it sounds like it's working better and off you go. Continue climbing - simple.

You *could* climb at full power and full mixture till your desired altitude, however you'll definitely be losing some power wasting fuel by running too rich, so the advice above is good. The approach you've given is certainly a simple method that it sounds like the school has been teaching it's PPL's.

The approach of testing full static power is an interesting one and I'm assuming not many of us would have done that before, or had to do it before, however it does seem quite valid. My only concerns though are that if you're pushing the envelope that far that you need to do this, then you may have been outside the safe and legal envelope for the aircraft performance. Or... you're panicking a little as performance had degraded not that badly, it just possibly scared you as you're not used to that level of performance. Where would you have drawn the line if you didn't get full rpm that you'd get at sea level during your static run-up?


If it's any consolation, I was listening to a couple of 172's with 3-4 pax and camping gear taking off out of the recent Mt. Beauty fly-in, heading east towards the high ground. They were both climbing and one pilot said to the other, "is your stall warning going off yet" and the other replied, "almost constantly" !!! The latter made the decision to turn around, gain some height and then clear the higher ground more safely.

It's always worth checking the POH. From a C172 POH:

Prior to takeoff from fields above 3000 feet elevation, the mixture
should be leaned to give maximum RPM in a full throttle, static
runup.

Also know the best rate and angle of climb, from the same POH 74-72 KIAS best rate and 62-67 KIAS best angle depending on altitude.

(Figures may be dependent on model, check your own POH.)

Lots of useful information in the POH. Its use is very poorly taught.

Mixture use by John Deakin author of The Pelicans Perch.
 

Suggest you read the complete set of engine handling articles by John Deakin author of the Pelican's Perch series. Excellent article there on mixture use.
https://www.avweb.com/news/pelican/182084-1.html

What On eyre said!:ok:

SOP when operating out of mountain strips in PNG.

I'm too new to post a URL! Google "lycoming service instruction 1094 pdf". I found it very useful.

John deakin stuff really helped me when I was flying cessnas around. Good read for anyone in GA

Ironically, although this procedure may well result in the engine delivering around the maximum power it can in the circumstances, that outcome may not be optimal.

When you go ‘balls to the wall’ on a properly set up, normally aspirated piston aero engine at sea level in standard conditions, the engine is not delivering the maximum power that could be delivered by the engine. It’s actually (or should be, if the engine’s set up properly) richer than the mixture that would deliver maximum power.

You could suck more power out of the engine, by leaning. But that would be bad.

The optimal ‘high power’ sea level settings for normally aspirated piston aero engines are richer than the mixture that would deliver maximum power. That’s for the good of the engine.

At aerodromes at really high density altitudes there’s probably no mixture setting that could result in damage to a properly set up, normally aspirated piston aero engine. But at 3,000 to around 6,500’, badness can happen if operating for extended periods at the mixture that produces the maximum power output for the engine.

It's an AUSTER! Mechanical brakes NBG over about 2000 rpm :ok::O

Thanks for that and I seem to be doing it right. Not up in the mountains much but often high on a hot day and have to progressively lean as I climb.

Kaz

[QUOTE=StickWithTheTruth;10019990]

The approach of testing full static power is an interesting one and I'm assuming not many of us would have done that before, or had to do it before, however it does seem quite valid. My only concerns though are that if you're pushing the envelope that far that you need to do this, then you may have been outside the safe and legal envelope for the aircraft performance. Or... you're panicking a little as performance had degraded not that badly, it just possibly scared you as you're not used to that level of performance. Where would you have drawn the line if you didn't get full rpm that you'd get at sea level during your static run-up?
/QUOTE]

I was well within the envelope and I would describe my state of mind as panicking. Climbing out of YHOT with terrain slightly rising at a density altitude of about 7,000', hence climb performance was vastly different from sea level ops, brought to the front of mind my question about leaning as you climb because I never have done it. If it does produce more power without damaging the engine, then a greater climb rate would have given me more peace of mind.

With only a few hundred hours under my belt I still constantly think about the what ifs of an engine failure in my flight planning, before flight on takeoff, just after takeoff and the whole flight! As I said, given the terrain was rising and my climb performance was sub (sea level) standard, my margin of safety (for a glide to an appropriate level) was not increasing as quickly as I am use to.

P.S. You have to be joking (or he was) about the 172 pilot with the stall warning consistently going off?!?!?! I flew into Mt Beauty the other day and back to Porepunkah. There's no way I'd do a straight out departure in any direction except straight out the Kiewa Valley. Circle around the airfield to gain height and enjoy the incredible scenary - most spectacular place I've flown into!

If you’re really interested in getting optimal performance from your engine, only fly aircraft with an all-cylinder monitor (after you’ve read and absorbed the content of all of John Deakin’s articles that Centaurus has conveniently linked for us). I lean during the climb to maintain the ‘balls to the wall’ sea level EGT on my hottest cylinder. With the fuel system and timing set up properly, all CHTs remain (and can be seen on the monitor to remain) below my ‘caution’ temperature of 200c.

Interestingly, the ‘steam driven’ original single point CHT gauge rarely reaches the bottom of the green arc, much less get anywhere redline. I reckon I’d have to get the cylinders to melting point before that gauge would redline.

So LB don't you think your original single point gauge just might be faulty !!

They weren't joking about the stall warning. It was mildly concerning to hear it.