LOP the horse is not dead
- Thread starter drgwentzel
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Doggtyred
En-Route
Oh, help. Somebody just tell me what settings to use, and reassure me I won't wreck the engine...?
How about learn the principles and understand why... then make your own decisions where to run...
Amelia
Pre-takeoff checklist
Yes, I do, Ted, and understand the basics of what it's telling me... beyond that, it's a little iffy.
And yes, Dave, learning the principles would be great-- but I'm an old lady with no mechanical expertise whatever. I worry that if the knowledgeable folk on both sides of the issue who DO understand the principles can't agree, there's not a lot of hope for the likes of me.
And yes, Dave, learning the principles would be great-- but I'm an old lady with no mechanical expertise whatever. I worry that if the knowledgeable folk on both sides of the issue who DO understand the principles can't agree, there's not a lot of hope for the likes of me.
John Collins
En-Route
The concert pianist doesn't consult the piano tuner on how to play the concerto.
Ted
The pilot formerly known as Twin Engine Ted
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iFlyNothing
I find that most of the people who understand the principles do agree, but a lot of people who claim to understand the principles don't.
I offer an advanced engine operations course that goes under the fundamentals, and we'll fly in your plane and establish some good power settings and mixture settings that will give your engine longer life. PM me if you're interested.
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Snorting his way across the USA
Local A&Ps seem to think LOP is a bad idea for my TSIO-360LB. I should run 50 to 100 ROP. And others say LOP offers a big savings, runs cooler, and I should always run LOP. I've tried it both ways, and I really can't tell the difference in how the engine sounds- seems happy either way. A Mooney engineer suggested ignoring the Mooney 231's POH, that 31" and 2500 RPM was ideal cruise setting for all altitudes. I love simplicity. Does that work with LOP? Oh, help. Somebody just tell me what settings to use, and reassure me I won't wreck the engine...
I'm sure that engine is similar to that of the TSIO 360 F I'm used to. I ran 2300 rpm and 28 inches below 10,000 feet, and 2400 rpm and 26 - 27 inches above 10,000 feet, which worked fine for LOP. Mine had an intercooler, which caused MP's to be 2-3 inches below a non-intercooled engine. That corresponded to 65% power from my power charts. 31" and 2500 sounds like more than that but there may be some differences in your motor. As long as you keep it under 65%, you will be fine running LOP, you can't blow up anything. You can safely run LOP above that but you have to have a good engine monitor.
If I need the speed and need to push it to 75%, the penalty I pay is I have to run ROP. But the speed difference isn't all that much, and if you save one fuel stop over a long trip, that's a huge reduction in block time.
Jaybird180
Final Approach
My reading and research on the Mooney says that max efficiency for that airframe (due to induction design) is at Full Throttle cruise (see numerous MAPA Flight Test articles on this subject). This is for normally aspirated (NA) models. Amelia's 231 is turbocharged, so I'm not sure that advice would apply.
Additionally, reading Deakin, he mentions that turbo motors are operated differrently in LOP mode than NA motors.
So I wouldn't be in a rush to accept NA advice and apply it to a 231 without understanding what the instrumentation is telling you.
Additionally, reading Deakin, he mentions that turbo motors are operated differrently in LOP mode than NA motors.
So I wouldn't be in a rush to accept NA advice and apply it to a 231 without understanding what the instrumentation is telling you.
Ted
The pilot formerly known as Twin Engine Ted
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iFlyNothing
All naturally aspirated engines will be most efficient at full throttle because there is no power being devoted to producing manifold vacuum.
With turbochargers, there are a lot more dynamics involved. More importantly, you have to worry about cylinder pressures, detonation, and pre-ignition. You also have to look at how the turbocharger is controlled. But the answer is not a simple "full throttle all the time."
Well, that depends on whose school of thought you use with your LOP ops, and what exact power settings you run, plus your installation. There are too many variables. Deakin tends to take a very simplistic view, and I don't think that necessarily applies itself well throughout the fleet.
I'm not sure anyone was telling Amelia to operate her TSIO-360 like one would operate a naturally aspirated engine.
At low power settings, the difference in fuel consumption between running it according to manufacturers recommendations for 'best economy' and runnig it based on APS recommendations is 2.7%.
The advantages of APS "recommendations" (actually developed decades before APS existed) go way beyond just fuel consumption. To attempt to limit the discussion to fuel consumption is missing a lot.
Have any of the wonderful benefits of running an engine LOP empirically been shown to exist relative to running the engine at peak ?
Skylane81E
Final Approach
IIRC Advanced Pilot Seminars
A company that is affiliated with GAMI, the manufacturer of balanced fuel injectors. The third company in the mix is Tornado Alley Turbo (TAT). All three are based in 'three letter town' (Ada, OK).
The three companies work in concert. One sells the theory through seminars, well placed editorial content and pretty nifty management of new media outlets. The other two sell the hardware.
skidoo
Line Up and Wait
OK, So what is the APS recommendations, as compared to running at peak TIT?
And, that is 2.7% of what?
They'll tell you if you pay 1 million dollars :wink2: .
The lean of peak concept is that in order to avoid excessive cylinder pressures and CHTs, you either have to put in too much fuel or too much air. If you run your engine at the 100-150 rich of peak that is the common operating paradigm, you achieve safe engine conditions by dumping fuel down the exhaust stacks. If you move from peak to 20-90deg LOP, you achieve the safe pressures and temps by using excess air. This is dependent on how much power you are squeezing out of your engine. At low power settings (65%), you can pretty go all the way up to peak and still remain safe. At higher power settings, e.g. 75-90%, you'll have to move further to the lean side of peak (e.g. 90deg LOP) to remain safe.
In order to do this safely, you need to know where each cylinder is relative to 'forbidden zone of death' while at the same time keeping an eye on where your TIT is going. Hence the recommendation to have a well calibrated multi-probe engine analyzer, a calibrated TIT gauge and a fuel flow instrument.
BSFC min (minimal brake specific fuel consumption) of most engines is somewhere around 10-30 lean of peak. At low power settings, the difference in BFSC between running your engine exactly at 'peak' and running the 5,10,20deg lean of it that the proponents put forward is somewhere around 3%.
So if you have a Lycoming engine that runs smooth and happy at peak EGT AND you cruise at or below 65% of rated hp, the maximum you can gain in fuel efficiency by going 5/10/20deg lean of peak from there (where BFSCmin lives) is 3% while maintaining the same power output (TAS/CAS whatever you want to measure this with).
Now, whenever I mention the modest improvements in fuel consumption that LOP will provide compared with Lycomings recommendation for 'best economy', the chorus in the background starts to intonate: 'Bbbutt the other benefits, the benefits, the beneeefits, dont forget the ben-e-fits'.
Now, you ask what those benefits are. The claim is that:
- there is less fuel contamination in the engine oil
- longer lasting exhaust parts
- longer lasting spark plugs
- longer lasting everything
- it makes your breath smell better
- you get chicks.
Now, in a turbo engine and if you want to pull higher power settings, hte equation is a bit different. The company recommendation is not to go below 'full rich' for anything above 75%. If you do that, you are going to burn lots of dinosaurs. The claim is that if you operate your engine deep on the LOP side, you can maintain safe parameters for CHT (as a proxy for cylinder pressure/stress) while getting the same amount of power available on the rich side of the curve. That is probably correct, if you can operate there (the balance of your fuel injectors is right, your magnetos are correctly timed, the slack in your accessory drive is not excessive, the cylinders are well matched in power output) with your turbocharged lycoming, you may indeed be able to get the speeds available with high power settings without cooking your turbocharger, valve or cylinder heads in the process. There are a number of people who do fly their TC Lycomings (TB21, post-restart Cessna 182/206) in that manner and report no ill effects. One thing to keep in mind though is that those engines contain some sinfully expensive parts in their exhaust systems, the penalty for getting things wrong is steep.
(your mileage may vary, this is neither medical, accounting nor legal advice, objects in mirror may be closer than they appear)
PS: In about 20 minutes, you will find a reply from someone who will quibble with some minor technical details stated above. This will be followed by the insinuation that getting a number wrong means that I have no idea what I am talking about. I can live with that.
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Jaybird180
Final Approach
Are you implying a conspiracy exists to defraud the GA community into following a 'bogus' philosophy?
No. What I am implying is that the interrelationship between the three entities may not be clear to everyone who reads about them on social media sites such as this. The recommendations come from the same people that make a living selling the hardware. Nothing wrong with that as long as every purchaser of the product knows that relationship.
It's like 'JD Power' is owned by GM or 'Consumer Reports' by Tupperware.
airguy
Cleared for Takeoff
It's a 172R model with IO360 and Gamijectors, and it has just about every speed mod possible (fairings, flap gap seals, wingtips, you name it) so my numbers are higher than a factory bird. I true out 119-120KTAS in cruise running LOP, in the 6000-8000 foot range. I've never tried for max power speed at cruise because I'll be running 2600-2650 RPM and I'm just not comfortable with that - so I run wide open throttle and pull the mixture back to control power, targetting 2500 rpm. That works out to roughly 75-100 degrees LOP.
Yes, I know I could repitch the prop and maintain 2500 at best power and pick up a few knots - but I like the climb performance just where it is and I'm happy with the cruise speeds I see with the associated fuel-burn. I don't need the prop repitched badly enough to go get it, I'm happy with what I have. I'm building a Vans RV9A for my go-fast bird, this 172 is just something to fly until the Vans is flying.
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Skylane81E
Final Approach
OT but what tips did you find for a camber wing cessna?
airguy
Cleared for Takeoff
I didn't - they were put on by the previous owner. We bought it with all mods already in place. It was owned by a retired doctor that used it for nothing but personal transport from his home in Florida to his family in Maryland, and he bought/installed every toy you could find for it. His eyesight and hearing were going fast and his son convinced him to give up flying. Every speed mod I've ever seen, plus a couple I was unaware of; full IFR 2-axis coupled AP, TIS and Nexrad, moving map display, engine conversion, it's a work of beauty, not many like it.
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Skylane81E
Final Approach
Cool, I'd like to know some more about them if possible.
airguy
Cleared for Takeoff
I'll have to dig in the logbooks and get the info on them.
Skylane81E
Final Approach
If you don't mind I would love to know, but if not no biggie either
/threadjack
/threadjack