Full throttle not always best when LOP?

[scottfromiowa]

Do you have fuel flow instrumentation? That is all you really need in addition to the OEM stuff to very efficiently (and simply!) cruise LOP at 65% power and below. Upon leveling off, close cowl flaps, set the cruise rpm of your choosing, lean to the LOP fuel flow of your choosing, and you are done. Anything under 8.7 GPH will keep you under 65% as long as all four cylinders are LOP, which they will be at WOT below 8500 feet.

My preferred LOP fuel flow is 8.5 GPH, which will give you 140 to 145 KTAS depending on altitude. You can go a long way in a 201 at that power setting, and your engine will love you for it.

A JPI FS-450 costs about a grand laid in. Well worth it even if only to greatly simplify engine management.

Jim

I get your speed Jim, but it takes me another gallon an hour (9.5) to do it in my M20E.

[aaronk25]

Second that 8.2gph 2400rpm 145k-148kts it's always the extra 10-12kts that cost money or is supposably burning my engine down.

[Shadrach]

I fly most of the time at around 9.2GPH.....but last night facing 40Kt headwinds I wanted everything I could get without running rich.  I still think the limiting factor of % of HP on these engines is keeping them cool.  I mean a marine engine at 360C.I. is rated at 350HP and easily can cruise at 300HP continuously.  So why, given that the oil and chts will stay cool is damaging to the engine?

 

On the experimental side, the Cool Jugs (liquid cooled cylinders for o-360) claim you can cruise at 100% because they stay cool.  Well 20F air is almost as good as liquid cooled.

 

I've read the Mike Busch stuff and he is more concerned about staying away from 50ROP and High CHTs than he is about internal Cylinder pressures. 

20F air is not as good as liquid when it comes to exchanging heat, nor can it be as uniformly distributed as liquid. Does the marine engine you mention turn at 2500RPM?  Piston speed matters...even more so in a fixed timing engine.  I'm not saying that you're goin to kill your engine in any way. I'm just saying that you're running an agressive power setting and your jutification for doing what your doing has a few holes in it... Your ICPs may still be in range with what is acceptable, but I don't know that they are... 

[aaronk25]

I fly most of the time at around 9.2GPH.....but last night facing 40Kt headwinds I wanted everything I could get without running rich. I still think the limiting factor of % of HP on these engines is keeping them cool. I mean a marine engine at 360C.I. is rated at 350HP and easily can cruise at 300HP continuously. So why, given that the oil and chts will stay cool is damaging to the engine? On the experimental side, the Cool Jugs (liquid cooled cylinders for o-360) claim you can cruise at 100% because they stay cool. Well 20F air is almost as good as liquid cooled. I've read the Mike Busch stuff and he is more concerned about staying away from 50ROP and High CHTs than he is about internal Cylinder pressures. 20F air is not as good as liquid when it comes to exchanging heat, nor can it be as uniformly distributed as liquid. Does the marine engine you mention turn at 2500RPM? Piston speed matters...even more so in a fixed timing engine. I'm not saying that you're goin to kill your engine in any way. I'm just saying that you're running an agressive power setting and your jutification for doing what your doing has a few holes in it... Your ICPs may still be in range with what is acceptable, but I don't know that they are...

Agree air isn't as good as liquid, so I'm sure there are spots that don't get as much cooling, but given heat will radiate though the metal, much like it does by transferring heat from inside to outside of the combustion chamber, I would venture to guess hear transfer takes place outside the cylinder too.?.? I feel a lot more comfortable running flat out when temps are below 0C than climbing out of Dallas when it's 108 out with full mixture and cowl flaps working hard to keep temps under 400. I understand the ICP issue and if I end up putting a set of jugs on it so be it, but I'm at 1500 hours on the engine and oil analysis other indicators tell me it's running fine. The marine engines take a 7.4 mercruiser makes 380hp and is rated at continues power at 100% but I ran to if these engines 1500 hours at 80% power settings with no issues. They make .83 hp per cubic inch compared to the io360 at .55 per cu inch. Just my opinion and I don't have any solid proof, but given a aircrafts low power output compared to other engines, it's hard for me to believe we can put the cylinder assembly in a condition that could over stress it, with the exception of overheating it, which I believe is a real concern. I mean 8.7 to one compression, which is high for a stock aircraft engine is very little compared to other engines. I think the big denominator is heat, not pressure and sure the more pressure exerted on something the shorter the life span but I'm guessing the difference is a inconsequential and failure delta is well beyond the normal service life. I normally cruise 65% LOP but if I get 40kts on the nose Ill squeeze every bit out Incan get and mine doesn't go any faster ROP.

[Shadrach]

Aaron, it's not all about HP per CI. that's a rat hole. You're talking about a liquid cooled engine with variable ignition timing. If you balanced and blue printed an IO360, installed an electronic ignition system and ran it to 4500 RPM you could probably get 1.5hp per CI, but that really doesn't tell you anything about what kind of stress the engine is under when lugging along at 2500 RPM with the spark firing at 25btdc. As I said, I'm not saying that your hurting a thing, but if it were me, I'd look for a more solid reasoning then just comparing it to an engine of a different design with different operating parameters and more sophisticated controls.

[jetdriven]

A big part is RPM. a .83 HP /CU IN engine at 4500 RPM probably enjoys less cylinder pressure than a .55 HP/CU IN engine at 2700 RPM.   Rotax engines last 1000 hours but they run at 5300 RPM and produce 100 HP from 80 CU IN.  But they have a gear drive and a small prop to drive.

[aaronk25]

A big part is RPM. a .83 HP /CU IN engine at 4500 RPM probably enjoys less cylinder pressure than a .55 HP/CU IN engine at 2700 RPM. Rotax engines last 1000 hours but they run at 5300 RPM and produce 100 HP from 80 CU IN. But they have a gear drive and a small prop to drive.

That is true work load higher in each revolution. A diesel such in my VW must have a lot more cylinder pressure, but I recognize our aircraft engines don't have the structure some of these other engines have to deal with the stress. Ok I'll cut the fuel back some and slow up a few knots.