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David-aviator

Well Known Member
At 9500 MSL (11,450 DA) a few numbers were recorded with regard to LOP.

It took a while to get everything stabilized. RPM was set to 2500 with a resulting MP of 19.0. Fuel flow was set to 7.9 gph.

None of the EGT's peaked until reaching 6.8 gph on fuel flow. At that point #1 #2 and #3 showed the first decrease in temperature. #4 was still climbing but just by 2 degrees. RPM never increased but did begin to drop off at 7.6 gph.

The next step was 6.7 gph. Much to my surprise, #1 EGT increased to 1470 from 1455 after showing a 1456 to 1455 decline at 6.8 gph. RPM had dropped off to 2440. At that point I terminated the effort as the trend made no sense. Could a decreasing RPM affect EGT?

I am inclined to concluded LOP will not work without a constant speed prop.

Is anyone doing LOP with a fixed pitch prop?
 
INjector balance?

Any reason to suspect injector balance a the cause of the odd cyl out?

You seem to have three pretty tight and one bucking the trend . . .

Just guessing. Rick 90432
 
I'm inclined to think there is something else happening! I have run LOP several times with FP & carb. There's no reason why LOP won't work with a fixed pitch prop.

Pete
 
I run LOP with my carb'd O-320/Catto three-blade. My experience is that it works, but not at all throttle settings. I don't mean all MAP settings, but throttle positions. There are several "Sweet spots" where it works great, others, not so well. I find more latitude if I have the carb heat pulled. At a couple positions I can go very lean (losing significant rpm) without roughness. Kinda dumb, however. My EGTs will be within 10-20 degrees across the board when everything is right and all cylinders LOP. As one setting is around 150 mph at 4-5000', I use it a lot for short flights. WOT will not work LOP on my engine, but with a slight pull it will.

Bob Kelly
 
videobobk said:
I run LOP with my carb'd O-320/Catto three-blade. My experience is that it works, but not at all throttle settings. I don't mean all MAP settings, but throttle positions. There are several "Sweet spots" where it works great, others, not so well. I find more latitude if I have the carb heat pulled. At a couple positions I can go very lean (losing significant rpm) without roughness. Kinda dumb, however. My EGTs will be within 10-20 degrees across the board when everything is right and all cylinders LOP. As one setting is around 150 mph at 4-5000', I use it a lot for short flights. WOT will not work LOP on my engine, but with a slight pull it will.

Bob Kelly
Click to expand...

Thanks for sharing you experience.

I need to do this again. #1 #2 #3 appeared to peak at the same fuel flow, #4 was still increasing but very slowly. What blew the experiment out of the water was #1 started down the lean side and suddenly increased 15 degrees above what appeared to have been peak. Could be that drop from 1456 to 1455 I thought was peak was not peak, but just an instrument glitch.

It was interesting to see fuel flow drop off from 7.8 to 6.7 (minus 15%) and TAS from 153 to 149 (minus 3%) up to that point.

The light is beginning to come on. :)

For now, I will confine this effort to above 9000'. I don't think I can harm the engine up there.
 
I'm doin' it!

Hi David,

I?m flying LOP with a fixed pitch prop.

I?m no pro, but I?ve logged about 500 LOP. 100 hours of that was in the Mooney Ovation. The remaining 400 hours has been in the RV-6 with a Sensenich 72FM85 on a parallel valve 360 using a Bendix RSA-5 injection servo and GAMI?s. In a nutshell, here?s the procedure I use.

I take off and climb at full rich up to about 9500 MSL and then climb at best RPM to my cruising altitude?usually 11,500 MSL or 12,500 MSL. I cruise LOP only. I descend LOP only maintaining whatever MAP was set during cruise flight. Once I enter the landing pattern, I go back to full rich.

My RV-6 will spin 2800+ RPM in level flight if mixture and MAP are not properly managed. Using the mixture control alone, the RPM?s can be brought down to about 2350 or 2400 RPM before the engine gets rough. I?ve completed long cross country legs running LOP while at altitudes varying from 3,500 MSL to 17,500 MSL at MAP ranging from 12? to 24? and at RPM?s ranging from 1700 to 2700. At the higher MAP, make absolutely certain the engine is lean enough. Using the mixture control, I keep the RPM?s below about 2600 whenever I?ve set 24? MAP and I watch carefully to make certain that all CHT?s stay below about 350 degrees.

As an aside and clarification, with my RV-6, LOP operations are possible at any throttle position allowing at least 1700 RPM or so.

Hope this helps. Good luck!
 
David-aviator said:
None of the EGT's peaked until reaching 6.8 gph on fuel flow. At that point #1 #2 and #3 showed the first decrease in temperature. #4 was still climbing but just by 2 degrees. RPM never increased but did begin to drop off at 7.6 gph.

The next step was 6.7 gph. Much to my surprise, #1 EGT increased to 1470 from 1455 after showing a 1456 to 1455 decline at 6.8 gph. RPM had dropped off to 2440. At that point I terminated the effort as the trend made no sense. Could a decreasing RPM affect EGT?
Click to expand...
I've seen this strange second peak in EGT on a cylinder a couple of times on my IO-360-A series engine, if I get too lean. My theory is that if a cylinder gets too lean, maybe there is incomplete combustion in the cylinder, and a bit of fuel burns in the exhaust after the exhaust valve opens, causing an EGT increase. I've only seen this when leaning too far. As soon as I richen the mixture slightly that EGT value comes back into line where it should be.
 
penguin said:
I'm inclined to think there is something else happening! I have run LOP several times with FP & carb. There's no reason why LOP won't work with a fixed pitch prop.

Pete
Click to expand...

Thanks to all for the information. If LOP is possible with a carb it sure ought to be with fuel injection, no matter the prop. I just need to work with it some more.

Kevin, what you describe with a second peak is what appeared to have happened. Also, with magnetos, the flame pattern is late and could be extending into the exhaust port. That would not happen with electronic ignition at 30+ degrees BTDC.
 
rv620mr said:
Hi David,

I?m flying LOP with a fixed pitch prop.

I?m no pro, but I?ve logged about 500 LOP. 100 hours of that was in the Mooney Ovation. The remaining 400 hours has been in the RV-6 with a Sensenich 72FM85 on a parallel valve 360 using a Bendix RSA-5 injection servo and GAMI?s. In a nutshell, here?s the procedure I use.

I take off and climb at full rich up to about 9500 MSL and then climb at best RPM to my cruising altitude?usually 11,500 MSL or 12,500 MSL. I cruise LOP only. I descend LOP only maintaining whatever MAP was set during cruise flight. Once I enter the landing pattern, I go back to full rich.

My RV-6 will spin 2800+ RPM in level flight if mixture and MAP are not properly managed. Using the mixture control alone, the RPM?s can be brought down to about 2350 or 2400 RPM before the engine gets rough. I?ve completed long cross country legs running LOP while at altitudes varying from 3,500 MSL to 17,500 MSL at MAP ranging from 12? to 24? and at RPM?s ranging from 1700 to 2700. At the higher MAP, make absolutely certain the engine is lean enough. Using the mixture control, I keep the RPM?s below about 2600 whenever I?ve set 24? MAP and I watch carefully to make certain that all CHT?s stay below about 350 degrees.

As an aside and clarification, with my RV-6, LOP operations are possible at any throttle position allowing at least 1700 RPM or so.

Hope this helps. Good luck!
Click to expand...

It does help. Thanks.
 
Understand the physics

I?m sure this has been discussed before. It?s not un-common to see a double peak in EGT when leaning LOP under some instances. This is because a lean mixture takes longer to burn, plus takes more spark energy to light it off. So what you?re seeing is the mixture still burning after the exhaust valve starts to open. I suppose that if that at that setting you changed the ignition timing you could prove the point by advancing the ignition timing. Personally I have never done this, as I have never been a plane that you could vary the ignition timing from the cockpit and measure it.

Another factor your getting into is the influence of the flow divider starting to divide the fuel to each cylinder at low fuel flows. With a 360 Lycoming and standard .028 injector nozzles the nozzle backpressure at 7 GPH is 1.4 PSI. This is in the operating range of the flow divider. In order to get the flow divider out of the way at these low flows you have to increase the nozzle back pressure by installing smaller nozzle restrictors. For instance installing .024 restrictors raises the nozzle backpressure from 1.4 PSI to 2.6 PSI at 7 GPH. 2.6 PSI will drive the flow divider open and not influence the flow division. Of course you have to be sure there is enough available fuel pressure in the system to satisfy all the pressure drops in the system at max power. So we are limited to how small a nozzle restrictor we used based on the available fuel pressure and the max fuel flow the engine will use.

All this cool information is discussed and explained in our Fuel Injection 101 Class. Last class this year November 6-8, 2009. There's still some empty seats.

Don
 
Good point Don

I wondered if the ignition timing was at issue here.

I have never seen the double peak and I always assumed it was because my electronic ignitions was advancing the spark at low MP (up to 42 degrees on the Pmag). I limited the advance to 38 degrees in deference to the fact that I use mogas which burns a little faster than 100LL.

Of course its much more efficient to advance the spark at LOP and low MP precisely because fuel burning while the exh valve is open is inefficient.

I love the AFP FI system incidently..Its been flawless, engine is a smooth as glass all three fuels (E10, mogas and 100LL) and balanced down to .2 GPH right out of the box.

Frank
 
LOP with a carburated engine?

My elderly RV-6A is equipped with a carburated Lycoming O-320. In the past I've done my mixture leaning by listening for the rough engine sound and settling for that. This seemed to reduce fuel flow and I was happy. Since then I've installed a Dynon D-180 and it supplies lots of information I never knew I needed. The Dynon has a lean mixture feature which shows which cylinder is lean and by how many degrees. Now I see that not all cylinders are in the LOP mode at cruise. Sometimes I can get all cylinders LOP, sometimes not. I've been told that I risk engine damage by running some cylinders LOP and others (probably) just rich of peak. Since the engine is carburated and I can't afford fuel injection, am I going to cause some serious problems by continuing to fiddle in this way?

Frank Russell
RV-6A, 1322 hrs on the Hobbs
 
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