75% power and leaning

[Clipper1]

Hello,

Is there a general rule of thumb as to what density altitude gives you only 75% power or less? Is it fair to say that above that height you will not be able to get in the red box?

Also, has anyone had much luck running a O-360 LOP? If so, do you wait for the last EGT to peak then lean to 50 degrees? I?ve heard some people say that at reduced throttle you cause a more turbulent flow and that helps fuel distribution enabling a carb engine to be run LOP.

[RV6_flyer]

Originally Posted by Clipper1

Hello,

Is there a general rule of thumb as to what density altitude gives you only 75% power or less? Is it fair to say that above that height you will not be able to get in the red box?

8,000' is the typical altitude where you get 75% power and as you go higher, the percentage goes lower.

[N941WR]

I regularly run my O-360 LoP. To do it, I start at 65% power as reported by my Dynon and above 6500' DA.

I have two P-mags and auto plugs, which I believe makes this possible. (Any EI should help, not just P-mags.)

I use the Dynon lean feature to teach EGT's to peak and beyond.

[gmcjetpilot]

Originally Posted by Clipper1

Hello, Is there a general rule of thumb as to what density altitude gives you only 75% power or less? Is it fair to say that above that height you will not be able to get in the red box? Also, has anyone had much luck running a O-360 LOP? If so, do you wait for the last EGT to peak then lean to 50 degrees? I’ve heard some people say that at reduced throttle you cause a more turbulent flow and that helps fuel distribution enabling a carb engine to be run LOP.

Do you have a full meal deal engine monitor? What are your numbers (EGT, CHT, OT)

Search the inter-webs for the Lycoming manual for your engine. There is a power chart that gives you RPM and MAP. Those two things will give you percent power. The chart will also give your Fuel Flow (FF). You can come up with your own MAP rules of thumbs or chart. You can check POH for certified AC with your engine prop combination. If fixed pitch you can't control MAP (unless you fly higher or lower altitudes). So RPM and density altitude will give you ball park percent power. Again the info is available on the web. At altitudes of of 8500 feet you can't make over 75% power.


Yes many people have good luck running LOP with a CARB. It is a little more challenging or just might not be possible. The issue is EGT spread. You end up with one cylinder too lean and rough running or if smooth some cylinders are at worst EGT for CHT. Worst EGT is ROP about 20F to 40F.


If you can get all your EGT's at LOP or leaner with smooth running you are good. THE TRICK... with Carbs some have used is pull the throttle back slightly (the carb butterfly will redirect fuel distribution). Normally you want full throttle to avoid "pumping losses" so you fly WOT, +8500 feet or higher, full throttle. (75% or less power is good, although 65% or less is better fuel econ and engine life). The other trick is use a little carb heat. If you have a typical Van's air-box the flap might change airflow into the filter and may even out the fuel distribution. I have though of air-box changes to bias air/fuel mixture to different banks of cylinders. I never have done it. This is where Fuel Injection is best, tailoring fuel flow.

If you can't get LOP you can't get it. You may be able to make changes in your induction to balance it but that is "experimental". To get best economy lower your power setting (by flying higher winds permitting/favorable or pulling the throttle back to 65% to 55%.) Lean to rough and then enrich the mixture just enough for smooth operation. That is it no ENGINE MONITOR required. This is how it was done for +50 years....


HOWEVER observe OIL TEMP and CYLINDER TEMPS are in limits...... If you want to do LOP you should have a full engine monitor.... If you have CHT < 400F and OIL TEMP < 200F you are good regardless of EGT. CHT = 380F and OT = 185F is pretty ideal. You don't want too cold OT.... The CHT and OT I list are below the LIMIT but are max operational or best practice.... Again Lyc manual on Web will give you absolute limits... but the absolute yellow range or red line limits is abusive.... CHT and OT rule.... but avoid EGT ROP +20 to 60F. You are better running AT LOP or leaner. If you have CHT or OT issues increase airspeed and go full rich and figure out what the issue is.

[Clipper1]

thank you for the replies.

I do have Dynon Skyview with EGT and CHT on all cylinders. I'll look at the spread and try pulling the throttle back a little to see if this helps.

The numbers I saw online for Lycoming suggest DA above 4000-5000 ft mean you can't get more than 75% power. I DO have the power % displayed on the Dynon but I just wanted a rule of thumb incase that wasn't reporting correctly.

[GalinHdz]

FWIW: I have an O360-A4M and over 500hrs of flying with a full Dynon Skyview engine monitor. After trying everything my standard procedure is to set the power where I want, lean until the engine starts to run rough then enrichen until it smooths out. Miraculously the engine monitor shows I am ever so slightly LOP with CHT & Oil temperatures within limits every time.

I guess after 60+ years of experience Lycomming really knows what they are talking about.

[Canadian_JOY]

Originally Posted by GalinHdz

FWIW: I have an O360-A4M and over 500hrs of flying with a full Dynon Skyview engine monitor. After trying everything my standard procedure is to set the power where I want, lean until the engine starts to run rough then enrichen until it smooths out. Miraculously the engine monitor shows I am ever so slightly LOP with CHT & Oil temperatures within limits every time.

I guess after 60+ years of experience Lycoming really knows what they are talking about.

O-360-A1F6 here. Same story as Galin. With the heavy Hartzell c/s prop with F7666 blades it's sometimes hard to feel the onset of roughness. Through testing I've found I can get one cylinder to 40LOP while the worst cylinder is just getting to peak, but that requires very specific conditions that don't happen all the time.

The old lean-to-rough then two twists of the wrist to rich it up puts the engine in its best lean condition every time. It really is amazing how reliable this is.

Oh, I should mention I've got one P-Mag and one Slick. I bank on about 9GPH at high power cruise. The induction system on our aircraft is not "clean" like an RV so I can only make 75% power up to about 7400' Density Altitude.

[gasman]

"If fixed pitch you can't control MAP (unless you fly higher or lower altitudes). So RPM and density altitude will give you ball park percent power. "

You CAN control manifold pressure up to full throttle with a fixed pitch prop. The throttle controls RPM and MAP at the same time. To get 75%, just move the throttle till the rpm (rounded to the nearest 100) and the manifold pressure added together = 48. As this number drops, so does the % of power.

[Bill Boyd]

but always wondered if it held true as the RPM drops precipitously LOP. After you add in more throttle to bring the sum of MP and RPM back to 48, are you really at 75% power again?

[gmcjetpilot]

Originally Posted by gasman

"If fixed pitch you can't control MAP (unless you fly higher or lower altitudes). So RPM and density altitude will give you ball park percent power. "

You CAN control manifold pressure up to full throttle with a fixed pitch prop. The throttle controls RPM and MAP at the same time. To get 75%, just move the throttle till the rpm (rounded to the nearest 100) and the manifold pressure added together = 48. As this number drops, so does the % of power.

I guess I should have said with fixed prop you don't have direct control of RPM for a given MAP as you would with constant speed prop. This is why fixed pitched prop certified planes don't have MAP gauge. RPM is what you set for power. MAP is at a fixed ratio to RPM... for a given altitude.