LOP, Cold Air and Down Low

[Bcone1381]

Are you running wide open throttle? Introducing a little turbulence into the induction system by slightly closing the throttle, or adding alternate air might help atomize that cold fuel.

[David-aviator]

Originally Posted by Bcone1381

Are you running wide open throttle? Introducing a little turbulence into the induction system by slightly closing the throttle, or adding alternate air might help atomize that cold fuel.

...with fixed pitch prop it is about 20" MP, throttle way back. Summer heat same conditions except OAT LOP works, winter cold it does not.
It's not a big deal, just another little mystery.

[noelf]

This is not just a temperature dependent operation. My Superior engine operators document says not to lean the mixture below 3,000 ft. What is not clear is if they mean msl, agl, or density altitude. Turns out it is density altitude.

I fly with a Dynon D10-A and it computes DA for me. That is what I use for leaning. In summer time, the 3,000 ft DA point is sometimes just sitting on the ground. In the winter time, it is sometimes 5,000ft msl.

[RV10inOz]

David, can I refer you back to my previous post?

I do suspect that you are trying to do the same setting regardless of the DA, and in winter with colder and denser air if you are trying to set the same fuel flow, it will not work. You are trying to get too far LOP effectively.

This is not just a temperature dependent operation. My Superior engine operators document says not to lean the mixture below 3,000 ft. What is not clear is if they mean msl, agl, or density altitude. Turns out it is density altitude.

DA is what effects the engine. And while Superior print what they print, that is so dummies do not do dumb things at high power, but I can assure you there is no scientific reason not to run LOP at 1000' but "do not lean the mixture" really means do not lean it on the rich side of the curve at high power settings.

[frazitl]

I have a superior 180hp with FI and two mags. I have best luck with 60% power or less set before going LOP. Approach it very slowly and as long as you have good fuel / air distribution you should be able to get 20 to 30 degrees LOP on all cylinders before it gets rough. Good luck...

[RV10inOz]

Originally Posted by frazitl

I have a superior 180hp with FI and two mags. I have best luck with 60% power or less set before going LOP. Approach it very slowly and as long as you have good fuel / air distribution you should be able to get 20 to 30 degrees LOP on all cylinders before it gets rough. Good luck...

At that low power setting that is what I call a well set up engine. At 60% power you want to be 10dF LOP with some maybe out to 20-30 but the last to peak need only be 10.

Going to 20-30 is going to cost you speed. But that will increase your range through less parasitic drag

[David-aviator]

Originally Posted by frazitl

I have a superior 180hp with FI and two mags. I have best luck with 60% power or less set before going LOP. Approach it very slowly and as long as you have good fuel / air distribution you should be able to get 20 to 30 degrees LOP on all cylinders before it gets rough. Good luck...

Could be I am not patient doing this...have you done it at 30F? The engine seems to get rough before EGT peaks.

[rleffler]

Originally Posted by David-aviator

Could be I am not patient doing this...have you done it at 30F? The engine seems to get rough before EGT peaks.

Rough before peak, sounds like your injector restrictors aren't balanced. It would appear that your cylinders are peaking at different flow rates. The roughness is caused by one or more cylinders that are leaner than the others.

Have you done any of the testing defined by AirFlow Performance or GAMI?

It will make a world of difference.

[David-aviator]

Originally Posted by rleffler

Rough before peak, sounds like your injector restrictors aren't balanced. It would appear that your cylinders are peaking at different flow rates. The roughness is caused by one or more cylinders that are leaner than the others.

Have you done any of the testing defined by AirFlow Performance or GAMI?

It will make a world of difference.

Good point, I have not balanced the injectors.
Most of first 100 hours was learning to land the darn thing, getting around to details of late.

[DanH]

Originally Posted by David-aviator

Yesterday it was same, 34F, MP 20" and fuel flow 6 gph. Eased the mixture forward to peak, or just a little rich of peak, and the engine liked it a lot, got very smooth. But going on lean side of peak it does not.

I'd bet with Bob here. You have Airflow Performance fuel injection; Bendix/Performance would be the same:

At high fuel flows, the fuel divider's diaphragm and piston are fully raised, and equal division of the fuel supply to the individual cylinders is a function of the restrictor size installed in each nozzle.

Given standard 0.028" restrictors, fuel division becomes a fuel divider function as fuel flow drops into the 6 to 7 GPH range (the exact value depends on the nozzle sizes). Dividers generally do a good job, but sometimes not as good as division by nozzle; the fuel delivered to individual cylinders can unbalance slightly.

You can check by recording a GAMI spread at 24/24 and some specific LOP setting, say 20F LOP. Now repeat at low MP and low fuel flow, and see if your GAMI spread widens. A poor GAMI spread at 24/24 says you need to balance flow by swapping restrictors for slightly larger or smaller sizes. If you have a tight spread at high fuel flow, but it widens at low flow, it's a divider spool function.