Lean of peak operation question

[DanH]

Originally Posted by Mark33

So is there a rule of thumb for that "percent power setting"?

65%, and it's not a hard limit, merely a recommendation.

I would love to run LOP but my engine starts to spit and sputter if I try to go any leaner than peak.

Then don't.

Personally I think roughness is about the only bad thing you can cause with a mixture knob at 9500 feet.

[rv6ejguy]

Originally Posted by rdrcrmatt

I've always wanted to try it in the climb, but the window to hit seems pretty narrow and always moving. Leaving it WOT and using fuel to control power means flying it like a diesel! If only we could actually get a good compression ignition engine.

Most of these folks are flying Rockets or light angle valve RVs with really good power to weight ratios. They actually use the prop pitch more to regulate power than mixture and the EFI controls the AFR while you climb and descend automatically.

[N49ex]

It never ceases to amaze me how crazy LOP discussions get. My take away from reading this thread is "everyone, please, pay attention to what Dan H. is saying here. His input is what makes clear sense without all the mythology".

One thing that I think is exceedingly useful in getting past the mythology is to have direct access to A/F ratio. I have an article coming out in Kitplanes in a couple of months on my experience adding A/F ratio direct data (a display in my panel that I tune to my desired ratios for particular operating regimes), and it is a wonderful way to really know where you are operating, rather than the crazy dance of finding peak EGT, then leaning or enriching either side of stoichiometric mixture. And to pre-empt an uprising about how leaded gas trashes oxygen sensors, there are some sensors available that are tolerant to LL levels, particularly if running LOP.

Reinhard Metz

[tim2542]

I don’t believe % power indications from an engine monitor will be accurate when LOP, at least the GRT’s use a Lycoming % power table that goes out the window when LOP.
15.7 x fuel flow / rated HP works when LOP.
Edit: that works with 8.5:1 compression ratio, I don’t know the number for others C/R’s
Tim Andres

[rv6ejguy]

Originally Posted by RV8JD

Dynon's EMS units attempt to calculate % Power correctly when LOP:

http://preflight.dynonavionics.com/2...dynon-way.html

Thanks for the link. I always wondered what they were taking into account for the % power calcs.

[woxofswa]

I think that it is very important to understand these concepts and know what our machines can do. However, glancing through the latest (excellent) KitPlanes buyers guide has reinforced the idea that while every airplane design is somewhat of a compromise, there are still a wide variety of worthy missions and aircraft designed to fulfill them. An RV10 in particular is a marvelous machine, but I wouldn?t classify it as an economy ride.

If one has chosen a fast design, paid for a fast design, built a fast design, then by golly, it seems to me they ought to enjoy opening her up and letting the big dog eat.

Nobody buys a Corvette to drive like a Prius.

[togaflyer]

Reading all the post and doing some more read up on the red box theory, it has been very informative and helpful. I realize my mistakes and misunderstandings. Looking forward to my next flight and LOP. Thanks to everyone!

[lr172]

Originally Posted by rdrcrmatt

I've always wanted to try it in the climb, but the window to hit seems pretty narrow and always moving. Leaving it WOT and using fuel to control power means flying it like a diesel! If only we could actually get a good compression ignition engine.

I do LOP climbs when not in a hurry or when it's cool, producing more power. Don't be afraid, just pull the mixture to known LOP EGTs. The window doesn't move fast and it's not as dangerous as some would have you believe to be outside the window for short periods. Just keep leaning as you climb to maintain your target EGT. I tend to move to LOP climb after 3000' to avoid some risks.

Larry

[scsmith]

Originally Posted by rv6ejguy

I'd be interested in the reasons the VE changes with CHT as well.

This question seems to have gotten forgotten as the thread moved along. I think what happens is that there is some conduction heating of the intake tubes from the cylinders that heats the intake charge as it flows through the intake tubes toward the cylinder.

I have certainly noticed that if I go LOP at top of climb and lean to a target fuel flow and expected EGT and CHT, then check back a little while later, there has been further drop in EGT and CHT both -- because it is now farther LOP. I usually just leave it, because exactly as Dan says, if it is running smoothly, it is fine.

While I am climbing at 100F or so ROP so the EGT's are lower, the CHT's are higher than the stabilized cruise LOP CHT's. So at top of climb, the cylinders are hotter than they will be once stabilized. After a few minutes at cruise, the cylinders are cooler, and so presumably the intake tubes are cooler too, so there is denser charge which makes it leaner for the same mixture lever position.

Make sense?

[rv6ejguy]

Originally Posted by scsmith

This question seems to have gotten forgotten as the thread moved along. I think what happens is that there is some conduction heating of the intake tubes from the cylinders that heats the intake charge as it flows through the intake tubes toward the cylinder.

Make sense?

VE is the actual mass flow pumped vs. the theoretical mass flow pumped based on the rpm and displacement. The heating of the charge air in the intake tubes either through conduction at the flange or from impingement of the cooling air from the fins above on the steel tube below would be virtually immeasurable given the short time duration the charge air is in the tube between intake strokes, the small surface to volume ratio and low thermal conductivity of the steel.

I don't see that CHT would have any significant effect on how much mass flow is processed through the engine which is determined by flow restriction within the head, valves, intake and exhaust systems plus the delta P inlet to outlet (sometimes we'll have favorable or unfavorable acoustic effects helping or hindering VE at certain rpms).