Power Settings

[ddnebert]

Start by saying that I have a non-conventional engine/prop combination.
Being new to the constant speed prop I am a little at a loss as to what the ideal operating numbers are for econ and 'regular' cruise.

Background - Note: these are a bit different from the stock Vans:

• O-540-B4A5 235HP carb. engine, 2575 max rpm
• Low compression Superior cylinders
• Hartzell HC-C2YR Prop with F8468R3 blades (81") and Hartzell gov.

A few questions regarding thoughts on settings:

1. For climb I have been applying full throttle and RPM settings, leaning as I climb. I get to 8500 fast enough and have no temperature issues. Sound good so far?

2. For cruise at height I reduce RPM to 2375-2400 and restrict throttle a little. I don't know just how much since I don't get any feedback on power percents. My flight averaged fuel burn is pretty reliably 12gph based on a mixture of 1-4 hour flights. I don't have a fuel flow meter installed (yet). Does this sound like a good cruise setting? Again, no temperature issues.

3. For descent I reduce the throttle and RPM to roughly 2300/23" though I often see higher EGTs then on some cylinders. CHTs are always even and close 160-180F. Is this expected?

4. Leaning - I used to fly a Warrior and leaning was easy even with one set of sensors, you'd lean until it got rough and then back off a little to an ideal setting. Given I am carbureted but have a CS prop, what is the procedure, and is it even possible to get LOP behavior for greater fuel efficiency?

Curious if there are any other operators out there with similar settings and thoughts to share.

 

[BobTurner]

My suggestions:

1. Search the internet for a power chart for your engine.
2."restrict throttle a little at altitude". Can you be more specific, e.g., use the Manifold Pressure (MP) gauge along with a power chart. Above about 8000' even full throttle will not generate powers above 75%, so many pilots just run wide open throttle above that altitude.
3. Descent powers seem a bit high to me. At 23"/2300 I'd get going pretty fast unless the descent rate was low. CHT's are quite low, which is generally a good thing but makes me wonder if the instruments are reading correctly.
4. Leaning. Set the power to 55% or so - maybe 20" MP, 2200 RPM - and go ahead and lean, and watch your 6 cylinder EGT gauge. Note where each EGT peaks as you slowly lean. If you can get all 6 cylinders on the lean side of peak EGT before the engine runs rough, then yes you can operate lean of peak. Ideally you'd get 25 or even 50 lean of peak on all cylinders, but with the carb it is unlikely the engine will not miss at such settings. As Im sure you know, don't do this at high power settings.

 

[RV10inOz]

Doug, would you run your engine with a dirty clogged up air filter? No I did not think so, so why pull the throttle back at all. The engine is most efficient with WOT.

Your climb procedure sounds valid, WOT, Max RPM, and lean to achieve an EGT on any one cylinder similar to what you get at sea level takeoff and passing about 500 feet (to allow a stable reading). Then every 2000' lean back to the TARGET EGT.

The 235HP engine at take off should consume close to 23 GPH at sea level. At altitude I would expect you could get back to 11GPH or maybe a fraction less, depending on the alignment of the planets in your carby engine. Using a overall flight average is not really an accurate measurement but it looks about right.

As for lean till it runs rough, then screw it in a bit......erase that from your memory. Too many other things influence the "rough" and it is not a good measure of anything.

You have an expensive aeroplane and it must have 6 EGT/CHT and fuel flow. The fuel flow must be checked to be accurate.

If you would like some in depth education PM me. happy to help.

BTW.....I often get carby 180 & 160HP's to run LOP....but only just, so this has to be done at settings that equal 75% or less as a rough rule of thumb.

Best Regards

David