I've been flying my '79 Turbo Lance for about 1 1/2 yrs. now and overall am quite happy with the performance and utility it provides. It has the stock cowling with louvers installed and most of the speed mods. Also have the EDM-700 installed for engine management. I've played with LOP operations just a little bit. I like the idea and find that the theory makes sense to me but am not confident in running the engine that way. Quite a while back I did perform Gami's leaning test on the engine. I ended up all the way down to 14 gph @ 27in MP and 2400rpm with no engine roughness and if I remember correctly CHT's below 400F. The thing that sticks in my mind was the high EGT temps-1650F & higher. 1650F EGT is the redline so I think I was at the point where I was over leaning on my test. Since the engine was still running smoothly should I have continued leaning? If I had continued leaning would the EGT's likely have dropped? I am concerned that running near or at redline EGT will burn up my engine.
This has all led me to run the engine using the Piper power setting chart printed on the pilot side sun visor. I typically fly at 9500ft to 12500ft. and occationally higher. I live in New Mexico and do most of my flying in high country. I've been using 75% power-27in MP, 2400 RPM, 20 GPH. CHT's all below 400F and EGT's in the mid 1400's.
The last two days I took the airplane out and tried using Piper's 65% setting of 24in MP, 2400 RPM, and 16.2 GPH. Fuel prices have me seeking better economy! I found that my airspeed remained the same, EGT's came up to the upper 1500's and at least three CHT's were well over 400F. No good! When I returned to the higher power setting and fuel flow I am accustomed to temps came back down.
I'd like to get better economy and range from the airplane and would really appreciate any and all comments and advise!
Thanks!
David Roth
PA-32RT-300T
N2111A
It's available on-line or occassionally in a live seminar. I attended the seminar a couple of years ago. The course is all about engine management and exactly on-target for your questions.
I'm no turbo expert but I can tell you what they told us in class: the EGT or TIT redline for turbos is based on expansion of the turbine itself: when it gets too hot it expands and starts rubbing on the side of the housing. That's obviously Not Good, but it's not an instant disaster either. Apparently the turbos are built to take short periods above redline. In any event you don't "burn" anything.
The other secret is the "Big Mixture Pull". Pull the mixture smoothly over a couple of seconds until you can feel the aircraft start to decellerate in the seat of your pants. You will now be on the lean side of peak and should be back below redline. You can sneak up on peak or redline (whichever comes first) from the backside and see what LOP operations are like.
I also highly recommend the Advanced Pilot Seminar and I also did The Savvy Owner Seminar a few years back on maintenance issues. We owned a 1978 Piper Turbo Lance II PA32RT-300T which has no intercooler but has a special cooling modification with upper and lower engine louvers and special designed induction and air flow system.
We ran std. Lycoming injectors LOP for some time behind a JPI700 with all sensors and digital fuel flow. We decided later on to switch to the GAMI's.
If you fly LOP cylinder temperatures need to stay under 400F. We set the CHT alert at 400F but tried to keep CHTs at 380F. High temps. here (more than 400F) will wear the cylinders and components out quickly. The EGT limts are mainly the temperature limits of the exhaust metals and should not be exceeded - the limit was 1650F I think. TIT is the Turbo Inlet Temp. Metal Limits. The metal Limits are not so critical on approaching the limits but should not be exceeded.
Flying LOP I would get things stabilized and then do the "big pull" on the mixture to establish LOP then fine tune. Then I would push up the throttle to get lost power back and then some then carefully monitor all engine limits. I found that the CHTs stayed under 400F and the EGTs went to 1550 or 1600F well under redline and that is where I left them.
The LOP mixture ratio stays the same you just push up the throttle slowly and get your power back plus some. At annual we sometimes would replace some exhaust valve guides but lille else.
Many run LOP way past TBO on many engines with little difficulty.
Edited 1 time(s). Last edit at 06/17/2008 02:20AM by LLPayne.
I don't fly a turbo, hence I can't be more specific about exact power settings and speeds. When LOP, power is directly proportional to fuel flow: HP = 13.75 x FF for a turbo. 75% would be 16.4 gph. At that fuel flow you'll go just as fast as you do with the engine set up for 75% power ROP. You can set RPM and MP wherever you want that keeps everything within the redlines. Generally you want MP as close to wide-open-throttle as you're comfortable with - the induction system is more efficient that way. Of course you can have too much of a good thing. Too much MP and you could be so LOP that the engine won't run smoothly. The engine will let you know.
Note: the fuel flow to horsepower relationship does not apply ROP. When ROP use the power setting charts on your visor or in your POH.
Lyndon:
you wrote: At annual we sometimes would replace some exhaust valve guides but lille else.
do you think this was because LOP or did you have this before?
I just have a ex valve repalce and the mechanic told me it was because I cold the engine too fast, I know I did not, I have the 1978 TLance with intercooler.
Joeb:
you are calculating 16.4 for 75% I did a calculation on the malibu it uses 16 for 75% on 310 HP(poh), shouldnt it be something on the 15 or 15.5 for 300 hp
I don't think so. The formula which relates fuel flow to LOP power output is sensitive to compression ratio, but the engines in the Malibu and Turbo Lance both have 7.5:1 compression ratios and hence should share the same multiplier. According to theory the Malibu's fuel flow at 75% should be 17.0 gph. And 16 gph is equivalent to 71%. The Malibu's POH clearly does not agree with theory, but I've no idea why. The Piper/TCM engineers who developed the performance chart might be quietly de-rating the engine in cruise for some reason. Or the POH might just be wrong.
I have read than the formula on the continental engine is 14.5 not 13.75
will that make the number on the malibu?
also did you read my post to lyndon on the exhaust valves? what do you think?
"I have read than the formula on the continental engine is 14.5 not 13.75"
Like I said, it depends on the compression ratio. Normally aspirated engines with about an 8.5:1 compression ratio use a multiplier of 14.9. It doesn't matter if they're Continental, Lycoming, or something else. Turbo'd engines have lower compression ratios - 7:1, so the multiplier is 13.75. I've already checked - the Malibu's engine has a 7:1 compression ratio.
"will that make the number on the malibu?"
It doesn't matter. The POH is what it is - I'm not going to speculate on why because I have no facts on which to base an opinion.
"also did you read my post to lyndon on the exhaust valves? what do you think?"
Exhaust valve guides wear out prematurely because the cylinder head gets too hot and junk gets cooked onto the valve stem. Cooling rate has nothing to do with it. That's what I think.
Regards,
Joe
Edited 1 time(s). Last edit at 06/28/2008 08:17AM by JoeB.
