My apologies then, I guess I'm not fully understanding your position. Sorry!

Harpoon1 wrote:My apologies then, I guess I'm not fully understanding your position. Sorry!

No apologies necessary, you make a good point and I can't refute it, just offer my interpretation of the information. I updated my last post to better explain what I mean.

Good discussion!

Still not "tracking" you.

What is it that I (or Deakin's) has said that you disagree with?

I wouldn't dare disagree with what the experts say!

In summary, my first response for the OP was - if you weren't sure whether or not to lean at takeoff at DA at or above 5000ft, I say you certainly should lean. The accepted practice as I understand it, is to lean for best RPM in a fixed pitch which should coincide with "best power" / best fuel flow in a CS prop aircraft. Basically, the point where the engine works hardest and develops max hp for T/O.

Someone suggested leaning until the engine runs rough, then giving the mixture a few turns rich (leaned for economy). My response to that was, that is a bad idea:
Aside from not generating max power for T/O, it's common knowledge that high power & very lean mixture operations can put you into the danger zone for detonation and pre-ignition. See the graph in the article for example (although the MAP is too high, for turbo engine): http://www.avweb.com/newspics/pp43_detonation_scale.gif

At very high altitudes, you made the very valid point that a normally aspirated engine cannot develop enough power to enter that zone. My response is at some mid-altitudes you would still want to lean but are at risk of entering that zone if the leaning is too wrong.

Esentially my point is, unless your engine is well instrumented or you are at very high altitudes, leaning incorrectly prior to T/O puts you at risk of detonation or pre-ignition when you apply full power. Some engines configurations wont; some others can.

If I have something completely wrong I stand to be corrected.

With the exception of these first statements, I'm in complete agreement with everything you posted. I think! 8t)

In summary, my first response for the OP was - if you weren't sure whether or not to lean at takeoff at DA at or above 5000ft, I say you certainly should lean. The accepted practice as I understand it, is to lean for best RPM in a fixed pitch which should coincide with "best power" / best fuel flow in a CS prop aircraft.

And maybe we're talking past one another but, in general I think you should lean anytime your above sea level, well, a couple of thousand feet or so or more above sea level. And, I think leaning for "best power" (50-80 ROP)below 7-9 k feet is NOT the best practice and is ultimately just asking for trouble and not a prudent thing to do.

Harpoon1 wrote:With the exception of these first statements, I'm in complete agreement with everything you posted. I think! 8t)

In summary, my first response for the OP was - if you weren't sure whether or not to lean at takeoff at DA at or above 5000ft, I say you certainly should lean. The accepted practice as I understand it, is to lean for best RPM in a fixed pitch which should coincide with "best power" / best fuel flow in a CS prop aircraft.

And maybe we're talking past one another but, in general I think you should lean anytime your above sea level, well, a couple of thousand feet or so or more above sea level. And, I think leaning for "best power" (50-80 ROP)below 7-9 k feet is NOT the best practice and is ultimately just asking for trouble and not a prudent thing to do.

I agree about leaning whenever possible, why waste fuel and dirty the engine?

Maybe the quirk is about the definition of the point the engine develops "peak power" (a sales term...) maximum horsepower/RPM? I know the literature mentions 50-80 ROP for "peak power". I just assmed that is supposed to be peak horsepower.
I don't T/O at high altitude often, but when I enrichen the mixture prior to changing from cruise to climb, I always move the red knob a relatively loooong way in before the engine develops full power. Well past 50-80 ROP. So I can't explain that.
Maybe that is habit not science, I don't watch EGT when I enrichen, I watch the engine MAP / RPM if anything (they don't show much with CS prop) and stop when she "sounds about right" for a climb.

Edit: I wouldn't know where to enrichen to if I was only watching EGT prior to a power change for climb.

Edit: I wouldn't know where to enrichen to if I was only watching EGT prior to a power change for climb.

Really? After all this back and forth, all my links, all your insistence you've read them before and you still "wouldn't know where to enrichen to watching the EGT". Great!

Does leaning for a "Target EGT" ring a bell? From the link in my first post. And is precisely how anyone should lean for ANY high altitude takeoff, albeit with an engine monitor or at least a single point EGT/CHT.

Have a good one, I'm done.

Harpoon1 wrote:

Edit: I wouldn't know where to enrichen to if I was only watching EGT prior to a power change for climb.

Really? After all this back and forth, all my links, all your insistence you've read them before and you still "wouldn't know where to enrichen to watching the EGT". Great!

Does leaning for a "Target EGT" ring a bell? From the link in my first post. And is precisely how anyone should lean for ANY high altitude takeoff, albeit with an engine monitor or at least a single point EGT/CHT.

Have a good one, I'm done.

Hahaha - ohhh dear - you assume me reading something means I'm going to follow it blindly! NO!

No thanks, I'll consider it and use the information if I see fit.

The fun of flying is being the pilot in command. Some aspects of flight I play by the numbers for good reason, others it's just unnecessary 'computing'. If all I'm going to do is turn an EGT number into an action, why not have a computer do it??? No thanks.

In that situation I dont need an EGT to know when I've enrichened it enough, and there is no risk, so why enrichen to an EGT value? Just for the sake of flying the numbers? That sure would appeal to an IFR type guy, but I love day VFR amongst the mountains - eyes outside whenever possible. Sometimes you need to use the instruments, and know how to do it right, but I prefer not to fly 100% that way. Different strokes. You can judge that if you want to....

Thanks for the convo.

I still use full rich.

Getting back to the OP's original comment, the OP's hypothetical take off from an 8000' elevation on an 85F day puts him into the 10,500'--11,500' density altitude range, depending on altimeter setting--which is getting pretty close to the edges of many small airplanes' performance envelopes. Properly leaned, a normally aspirated engine will be producing less than 2/3 of its sea level power at that high a density altitude.

Even at his home airport at Grand Junction, that means that he's not developing nearly as much power as he could for take off, because DA there at 85F would be around 7500'--nearly a 25% reduction in engine power from sea level power. IOW, a 160hp engine is producing about only about 120hp, if it is leaned properly, and who knows how much less if it isn't leaned properly.

Some 40 years ago, this is how I was taught at Laramie (elev. 7377') to lean for take off, without any sophisticated engine instrumentation (normally aspirated engines): whether fixed pitch or CS prop, at normal run-up rpm (1700-1800 rpm), lean until there is a very slight rpm drop, then enrichen about half an inch of the mixture control's movement. That turns out to be pretty close to what others did at full throttle, which was to lean to maximum rpm, but it has the advantage of sucking up fewer FOD creators.

Now I have an Insight G1 engine analyzer on my O-360, which allows me to see that I've adjusted the mixture to about 150F ROP for the leanest cylinder, but honestly the results are very similar.

On an unimproved strip, I prefer to do my run-up as a rolling run-up while back-taxiing for take-off at a lower rpm than the book says, to avoid sucking anything into the prop. That means very little glancing at the instruments, going by sound more than anything, to avoid driving off the strip. I pretty much set the mixture by how far I know (because I know my airplane pretty well) the mixture control should be out from the panel, during the rolling run-up. That also means that I don't do what Sparky Imeson advised in his "Mountain Flying" book, adjusting the mixture on the take-off roll while looking at the engine analyzer and achieving best power mixture that way, not out of any disrespect for his methods, but simply because I'm not a good enough pilot to be able to take off from a narrow strip while looking inside the airplane. I figure I can tweak the mixture, if necessary, once I'm off and away from the obstacles.

None of these comments apply to turbo-charged engines. All that I've ever flown were not to be leaned at all until reaching cruise levels and adjusted for cruise power settings, because the turbo made up for the higher density altitudes. My experience was limited to T210s, T206s, and Mooney 231s, so there may be some which would be different from that.

Just my $.02 worth.

Cary

If there is an enrichening valve present in a carbureted engine you'll have to lean at full throttle, yes?