Yellow Arc RPM

[jetdriven]

you can follow the POH, but that was based on current thinking in 1976. 

[Shadrach]

Which is not so current today...of course, if you get her up "on the step" it won't really matter where you run her as the reduction in induced drag will make up for any short comings in the POH recommendations!!!

[danb35]

Glad to see I'm not the only one who doesn't go full rich on approach.  Usually I don't touch the mixture from its cruise setting until shutdown.

[Jeff_S]

"Hear hear!" for those who don't touch the mixture knob on descent. I, too, just leave it alone in most circumstances. I'm already LOP in cruise so there's no danger of increasing CHT's as I go down (since descending has the same effect as leaning) and since I'm not trying to draw full power the fuel flow isn't an issue.

If I sense the engine is starving of fuel a little bit I may gently add a skosh of fuel, but never full rich. That just floods the cylinders, wastes gas and fouls the plugs.

But I will admit, I've flown with a few other folks who I could see getting a little antsy when I didn't reach for the fuel knob. I understand the power of ingrained habits.

[Jeff_S]

Wow, I've been doing practically the opposite of you. Except for descents and landing, the throttle stays full the entire flight and I control power with the prop knob and mixture.

And I will add that yes, throttle stays WOT for climbout and cruise at altitude, but in low-mid altitude cruise I tend to bring it back to reduce power a little bit to let me get to LOP settings safely. Of course, IFR ops and normal descent/landings require varied use of throttle as necessary.

[Hank]

Apparently there are three camps of Mooney flyers:  1) ROP; 2) LOP; 3) O-360s with carbureutors who don't worry about it.

Management of your fuel-injected engine is different than my carbed one. Just look at how many hot-start procedures there are, while I have "normal" start and "cold" start [applies when the air is cold, not the engine, i.e., near or below freezing]. There are more C's than anything else . . .

[John Pleisse]

Can someone enlighten me? Are there published or perscribed LOP OPS by Lycoming for the IO 360 series engines?

[danb35]

Lycoming thinks pilots are too stupid to be able to run LOP safely/efficiently.  Lots of other people disagree.  Check out John Deakin's articles at AvWeb at http://www.avweb.com/news/pelican/182146-1.html for a good start.

[Shadrach]

No N4352H, to my knowledge, Lycoming has never published a "recipe book" specific to their engines and I doubt their legal department will ever recommend that they do so.

[John Pleisse]

There are 5 threads for this and I don't want to hijack the RPM question, but if there are no procedures for it, these cyliders and valves go to tbo with out abuse and these engines sip gas. I don't get it. Why do it?

[Shadrach]

"And I will add that yes, throttle stays WOT for climbout and cruise at altitude, but in low-mid altitude cruise I tend to bring it back to reduce power a little bit to let me get to LOP settings safely. Of course, IFR ops and normal descent/landings require varied use of throttle as necessary."

So let me understand this...

You climb ROP WOT.

Your plane runs well LOP.

You like to cruise LOP.

You understand that when running LOP, air is used in surplus to slow the combusion event (resulting in cooler temps).

But when at mid to low alt, you reduce throttle (block surplus air) to the engine and create turbulance in the induction system to the engine "just to let you get to ROP safely"...?

It'll work out ok because the fuel servo reduces FF when you reduce throttle (power) , but if it runs as well as most 4 cyl lycs do LOP you should be able to run it as cool LOP at 200ft as you can at 7500ft... Why not just pull to deceleration richen to peak and lean...  My engine does beautifully at 1500ft WOTRAO 28.5" 2500rpm and 45 LOP...in the dead heat of a Mid-Atlantic summer... 

[Shadrach]

If you don't get, it then don't do it.  There is so much info out there for free, that I'm sure you've weighed the pros and cons as you see them. 

My reasons are:

1) It facilitates a combustion event in which the peak effective pressure and the mean effective pressure are much closer together than the settings "ROCOMMENDED" in the POH. A "rich of stoic" combustion event has higher peaks and lower valleys. Which is harder and hotter on an engine, although the engines have demonstrated that they will take it...for a while.

2) It's always cooler for a given power setting then 100ROP at that power setting and far coller than 50ROP.

3) My oil stays much cleaner.

5) My belly stays somewhat cleaner.

6) It eliminate CO form the exhaust gases

7) BSFC goes up considerably when compared to 100ROP and even more so at lower altiudes where the POH "RECOMMEDATIONS" forbid leaning.

7) oh and I almost forgot, it saves gas...how much depends on what your doing but it will always produce more with less than ROP...

I am sure there are others I could come up with, but we dont wanna hijack... :-)

 

 

 

 

and it save . 

[John Pleisse]

I have a zillion questions...I'll move over to the approriate venue. I appreciate you steering me Ross. I am one of those guys who hasn't read up on it, refused to listen to proponents and always points to poor service history on big bore Continental cylinders and valves (where the practice has been prescribed for years).

[Shadrach]

No sweat, PM if you have any questions and I'll point you to what I used for sources. Whie I had a grasp of combustion science from other activities I participate in, I did not go into LOP ops willy nilly; I did lot's of research... Chances are that if you have a specific question, I know where you can find the answer.

[Hank]

So, 201er, do we have you confused yet? Sorry for introducing the whole LOP/ROP thing into this . . .

Set your desired power with the throttle/manifold pressure gage. For climb and cruise, you will obviously also use the prop lever/tach.

In low-power situations the prop will indeed be against the flat-pitch stops, and it will indeed "function" like a fixed-pitch prop. You, however, will NOT "operate" it like a fixed-pitch prop! Continue to use the throttle/manifold pressure gage to set your power. If you are in a long descent and want, for some reason, to do it at greatly-reduced power, then keep out of the restricted zone on your tach. If you are out flight-seeing and want to cruise slowly over terrain while you admire the scenery, keep out of the restricted zone on your tach. This is easily done by either observing the recommended MP/RPM chart in your POH, or adjusting the throttle/MP enough to move the tach out of that zone.

When reducing power on downwind, use the throttle. I push the prop fully forward, often just before reaching the pattern, and it stays there until my next departure/climb/leveloff. Use your favorite combination of pitch and power to maintain the proper glide, and let the tach do whatever it does. Personally, I don't watch any gage around the pattern except for occasional glances at airspeed--I figure there's a reason it's in front of me and MP/RPM is on the right side of the panel.

Power-off descents have a definite place in your flight toolbox, but they are not a typical part of my flying except for the landing phase, and even then I maintain a little power until I clear the trees, gliding to the runway over the road cut. My typical descent is power-on, IFR and VFR, I just push forward to achieve ~500 fpm and trim the pressure off; not being fuel-injected, I walk the throttle backwards and the mixture forward to maintain approximate cruise readings on MP and EGT. Airspeed will rise, groundspeed will rise, fuel flow will decrease [i don't have a gage for that] and she will often start to whistle if I've been high [descending from 8-10,000 msl to patterns of less than 2000 msl]. 130 mph indicated at 10,000' = 166 TAS in cruise; it will sometimes pass 170 mph indicated coming through 7000 msl = 192 mph TAS. Not too bad for a C-model.

But again, practice with your plane, and have someone else write the numbers down for you. Having the gages right in front of your passenger will make it easy for them to do, too.

Welcome to the wonderful world of Mooneys!

[flyboy0681]

I still stand behind my statement after catching up with all of these posts. Ask a question to a dozen flyer's about power settings and get a dozen different answers. WOT, no WOT, mixture rich on landing, mixture lean on landing, power off descent, power on descent.

I guess there's just no general consensus.

[Shadrach]

It is not about consensus...not much in flying is. I would say that if a pilot is doing something other than what the POH recommends, then s/he should be able to articulate the reasoning for doing so.  I deviate from POW recommendations all the time, and if you ask me about a specific action I take, I can tell you why I do it and explain why I think it is a superior method. That's all I need, I could not care less about the consensus.

[jetdriven]

I know this, we flew 40 LOP and averaged 145 KT TAS burning 8.3 GPH (62% power) and flew 310 NM and burned 19 GAL.  THis includes the 15 GPH, 250 ROP climb at 120 KT IAS. 

LOP is old technique from the radial airliner days and only since 3-4-5$ avgas, has got a lot of interest lately.   I am a big proponent of it, as is Shadrach and others.  The cocept of WOT and LOP until downwind is strange to the uninitiated and is not printed in the POH (Although Lycoming recommends peak at 75% or below, so LOP is still cooler than that).   We save around 1.5 GPH to 2 GPH.  Less lead in the oil and on the valve guides. Avgas being what it is,  we save 8-16$ an hour.  "Free engine reserve, just run LOP"

 

[fantom]

"I guess there's just no general consensus."

Not quite, Mike, it's that in aviation, like in life, there are few absolutes.

[Jeff_S]

It'll work out ok because the fuel servo reduces FF when you reduce throttle (power) , but if it runs as well as most 4 cyl lycs do LOP you should be able to run it as cool LOP at 200ft as you can at 7500ft... Why not just pull to deceleration richen to peak and lean...  My engine does beautifully at 1500ft WOTRAO 28.5" 2500rpm and 45 LOP...in the dead heat of a Mid-Atlantic summer... 

You're probably dead-on right. I will freely admit I'm learning as I go so I'll try this out and hopefully add it to my repertoire. My initial rationale for pulling throttle at lower altitudes was to reduce power below 75% so I felt comfortable leaning...based on my study of Deakins et al and their articles. But I have since experimented with keeping throttle up even at lower altitudes and do realize I can keep the CHT's down if leaned correctly.

Thanks!

[flyboy0681]

Perhaps the word "consensus" was a bit harsh. Would "basic" standard procedure have sufficed?

 

 

[Shadrach]

Jeff,

I was just busting your chops a tad. You are being cautious as you move into an area of operations still new to you. And that is wise

What you're doing is fine, I just made the comment to illustrate the basic principle that when LOP we use air as the cooling agent (to slow combustion). If you remove any of the cooling agent, you will necessarily have to limit how much power you can produce. People tend to not look at consistently. LOP is an inherently lower power than ROP, by closing the throttle, you're making it more so...   I was demonstrating this the other day to a pilot passenger by opening and closing the RAM Air while LOP...which would the ram air at our alt was sufficient to drop the egt on the richest cyl an additional 20df and cause a corresponding CHT drop. I could run slightly more fuel (more power) with the RAM AIR open and be at the same value LOP.  Passenger had an "ah ha" moment.  It's fine to pull back throttle/power for the transition if you want to, but once safely on the lean side, WOT can be resumed. You'll have to fine tune mixture to desired degrees from peak, but you will remain LOP.

[flyboy0681]

Actually, my comment about following the POH was a tad much. Gary will attest that I use the Lean Find feature of the JPI to set the mixture as opposed to following the 1983 book which essentially says to lean until roughness, then back off.

The only procedures that I follow the book on is setting mixture to rich during my GUMP check and pushing the blue knob forward. But then again, that's more of a habit ingrained in me by instructors over the past 30 years.

[201er]

It's pretty simple to see why WOT makes sense by taking a look at the POH. 27" MP and 2200RPM produces 68% power. So pretty much from 2,000' DA and upward 27" is the most you can get and pulling the prop back to 2400 or 2200 will give you 75 or 68% power. Any higher and you'll need higher prop settings still. I can't imagine being lower than 2,000ft anywhere but the airport traffic pattern anyway so I may as well leave the throttle full on climb out and use the prop control in cruise to set power rather than throttle. By pulling the prop back you save a lot of gph compared to pulling the throttle back and maintaining a higher RPM to get the same equivalent power setting.

And since LOP you inherently lose some power anyway, it seems you could be WOT down to sea level and set your power exclusively by prop and mixture to remain below 75%. Am I missing anything?

Also how many of you use the Ram Air in a 201? I read a Mooney article that said it helps so little that the risk of running unfiltered air outweighs the 1/4" improvement in MP. Shadrach, I gotta check if it helps much with CHTs though!

[Shadrach]

Not harsh fly boy, I truly think that the "evangelists" at APS et al, as well as the cost of avgas will bring about a concensus at some point for injected engines. Procedures will be based on knowing the cause and not just the effect of actions taken with the mixture/throttle.

I grew up around airplanes and I can remember more than one pilot (one of whom was my Dad) explaining that we climb "full rich" because the "evaporation of the extra fuel" helps cool the cylinder at the slower climb speed... These were bright guys, but this was the 80's and most of them hadn't a clue about combustion science and the info was not readily available aside from pouring through an engineering manual...and that alone would have never triumphed the "tribal knowledge" being passed down. Students will always fly simple planes with simple procedures. I think that as engine management evolves, pilots of HP/complex/XC machines will also typically use "simple procedures", but they will understand the very complex events affected by those "simple procedures" at a practical level.  Thus a "one size fits all" approach will be replaced with "what's the objective?"(reduced temps?, more speed?, greater range?, maximum efficiency? etc.) approach...