K

Kansas7

Member
Hope to gain some information from the collected experience here on VAF.
I have been flying my -7 for about 1 1/2 years now and love the airplane. I use it to commute between jobs and most of the time am willing to trade a few minutes of flight time for the fuel savings of running LOP. My engine will run fine down to more than 100 degrees LOP. and I do so most of the time.
I have been talking to my brother who flies an Aztec and wants to give the LOP operations a try. He has been flying it but does not get the same response to LOP that I get. I know that the engine on the -10 is the same as the one in his Aztec so our question is to the -10 operators " does your IO540 give you the same response as the 4 cly Lycomings when running LOP?" :confused:

Thanks for the Help

Here is what he is seeing on the Aztec.


Here's the deal. I'm trying to run 50 degrees LOP at 65% power.
Yesterday was the third time I've tried it with the same results every time. At
6500 feet MSL power set for 22" and 2200 RPM I'll lean to 12 GPH as directed
by the owners manual. Give the engine time to settle maybe 5 minutes, then
start to lean slowly. The EGT rises steadily until you feel the engine
start to lose power. Power loss is confirmed by a rise in MP and a decrease
in RPM. The EGT will peak when the tach shows about 200 RPM decrease. If
I richen the mixture until I'm back to 12 GPH everything comes back to 22"
and 2200 RPM. I find it physically impossible to fly LOP... that is I don't
think I could maintain altitude IF I were to leave the mixture 50 degrees
LOP. EGT rise is 50 to 75 degrees between 12 GPH and where I can feel the
power starting to diminish.My EGT system is an old analog gauge that
displays only one cylinder at a time but can be selected to each of the six
cylinders. Total variation across the six cylinders is less that 25 degrees. Now
here's another oddity, I'm flying an Aztec and this happens on BOTH
engines. Left engine FI system has less than 10 SMOH and the right is high time.
Can somebody explain what's happening? Is it possibly the fact that I'm
already down low enough in the power band that LOP isn't going to happen?
I'm totally lost and I'll listen to all opinions.
Thanks in advance for helping a non-RV'er

Thanks for reading this far
Dave
 
LOP is going to result in power loss - see engine charts. The benefit is the reduction in fuel flow as a % of full rich is greater than the associated power loss resulting in higher miles per gallon.

To maintain altitude, reduce airspeed.
 
Thanks for the quick replys
The IO360 Runs just fine LOP But the IO540 just wont run that way
We have searched and read every thing that we can find on the subject for several weeks now but just cant get the IO540 to run LOP.
Have any of the -10 guys seen this on their engines?
Yes we know that the power will drop off but it drops so much before it gets 50 degrees LOP that the prop governor cant hold the rpm. The airspeed decays to the point that level flight is no longer possible. The power should drop to the 59% or so range at what we are trying for.
Dave
 
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Dave, I run LOP fairly often in my -10 with an Aerosport IO-540 F.I.

I think that part of his problem is instrumentation. I have digital D-100 engine info and each cylinder's EGT is shown degree by degree and it has a LEAN mode. Whichever cylinder peaks first, has it's EGT reading replaced by a little square box with -10 or similar in it, indicating 10 degrees lean of peak. If I continue to lean, the numbers in the box increase and I stop at 50 LOP. By then the other cylinders will also have peaked and run anywhere from -30 LOP to 50 LOP.

My CHTs drop by 30 degrees or so and I give up about 10MPH in cruise TAS but fuel flow is down to around 12 GPH, instead of 15.5

Tell him to lean very slowly and keep an eagle eye on the EGT gauge and notice the peak, if he can with that old analog gauge.:) If it's a 2 1/4" gauge, it's gonna be hard to see. He may well be running LOP without knowing it!

Best,
 
Do a search on GAMI test. You can even do a rough one with the single readout, just cycle through the cylinders. If you don't have fuel flow gauge, just keep track of mixture knob (clock it). This will allow him to figure out if he has good enough mixture balance for LOP.
 
It's very difficult to fly LOP without a quick reacting EGT system. Even GAMI doesn't recommend LOP operations if you do not have proper instrumentation. Since you say thet the RPM is dropping I wold suspect that you are running way too far LOP. The CS prop should make allowances for the drop in power when running LOP. Another cause of the rough running could be that the injectors are not well matched. This will cause the leanest cylinder to start missing before the richest is even LOP. Also, I only run LOP with wide open throttle.
 
LOP ops

I spent some time in my flyoff doing LOP ops. The way you need to do this is how GAMI suggests http://www.gami.com/gamijectors/leantest.php
If you are getting more than .5gph from first to last consistently you need to get airflow nozzles and either go larger .0285 or smaller .0275 or less for the cylinders to get them closer to the range.
I have mine to about .4 (subject to change with the weather, etc) and can get down into the 10.5-11gph range depending on altitude for 65%. Running smoothly.
As mentioned previously, the EMS is critical to doing this, you want it to be 50 LOP and see the EGT temps go down and stabilize. If you have data logging capability for the engine that really helps, you fly it through a series of tests than evaluate on the ground.
Stick with this, it is worth the effort.
Pascal
 
LOP Ops

FYI: When operating LOP, the horsepower is directly proportional to the fuel flow given that all of the fuel is consumed. The formula is: (14.95x FF)/Rated Max HP. e.g. (14.95x7.9gph)/180= 65.6% PWR. Some people use 14.9 and others round off to 15.0. The procedure is to note EGT at approx 500'-1000' AGL after T/O and climb WOT leaning to maintain the noted EGT as you climb. After reaching desired altitude plus a min or two, preform what is called "The Big Mixture Pull" which is as you said leaning fairly quickly until you notice a reduction in power (you are now LOP). At this point you enrichen until you reach peak and then lean again to desired FF. After doing this several time, you will no longer need to search for peak. You can just select the desired LOP power or desired FF. As mentioned by others, you need to do the GAMI Spread test prior to attempting to run LOP. The desired GAMI Spread is < .5 gph with < than .4 or less being the better target. One neat thing is to calculate (or use wiz bang MFD) the fuel remaining at your destination. IF you are not comfortable with the reserve, lean until the fuel remaining is more to your liking......

Gerry
 
I routinely run my RV10 LOP with an IO-540-C4B5, that came out of an Aztec, with no problems. I matched my nozzles with Don at Airflow Performance.
As others have noted, mismatched nozzles could be the problem here. Another thought is some issues with airflow in the Aztec cowling. I know that RV10 operators with the Sam James cowl had some of these issues.
Again, as others have noted, accurate engine monitoring equipment will really help.
 
Gerry Hatch above has nailed it. :)

The IO 540 in fact all Lycomings are funny beasts compared to the TCM's. The TCM IO550 is beautiflly balanced it seems in airflow and responds well to tuned injectors. Some of the 470's not so well.

For the Lycoming, the induction system is not as nice to play LOP, and it has random results as a result. It just means that it is a lot harder to tune the injectors. I have flown an IO540 straight from Lycoming and it went LOP no trouble at all. On the other hand our IO540 in the RV10 would barely get the first few over peak and it would run as rough as a hairy goat! It took several attempts at getting something half right before we could actually get serious about it. Luck of the draw. Remember the injectors from Lycoming all meet a +/- tolerance for fuel flow, and depending on which end of that spectrum and which cylinders flow what air volume.....well the chances are not good you will get a good one out of the box.

Next point is being a certified aircraft and all that, he can't just grab a fist full of injector restrictors from Don and just play around. Maybe he can fly over to Don's or GAMI and get it sorted.

He MUST HAVE a proper all cylinder monitor. In the certified world a EDM 850 these days is nice :) or any suitable unit from the EDM range which includes fuel flow.

He could and should do an APS course.
 
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Thanks
Hopefully we will get back in the air this weekend to try again. We do have a fuel computer so we have good feedback on the actual fuel flows for the engine. It really doesn't run rough it just never starts back down on the egt's before the power falls off big time. Maybe the gauge is slow enough that we can't catch it before it falls off. He and I have been running IO540's for thousands of hours and these 2 engines just don't behave like they should. They run great, make good power and have had proper maintenance.
Thanks for all of the help if we find something out will post it back here.
Dave
 
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