2000 rpm, 25" MP, 155 MPH 7.5 GPH, Anything wrong with this picture?

[garytex]

I was stuck under a 3000 ft layer yesterday, and bored, and set up like this. Peak EGT was about 100 df lower than at a higher RPM, noise was waaaay down, CHT's all just below 300, no particular engine vibration, I lost about 8 MPH and 1GPH from 2500 rpm, seemed like a nice way to ease along. I didn't keep it that way too long, I just couldn't stand the fear that I might be doing something insidiously damaging to the engine. Probably not, but I thought I would poll the membership, and see if anyone else has any experience with this. Book shows 19" MP with 2000 RPM

Thanks, Gary

[SkyPilot]

I used to run the Beaver at 29" and 1900 rpm all year long. No problem, mind you it was super-charged...

[danb35]

Nothing at all wrong with that. Go for it! Just make sure it complies with whatever the red arc is in your plane/prop (on mine, it's 1950-2350 and < 15" MP, so it would be just fine).

[carusoam]

RUNNING over "square", ie 25"/2500rpm, with good CHTs....

You are at least beating up an OWT.

What you could expect by doing this...

Running 25" MP....

- relatively higher than usual internal cylinder pressures ICPs, compared to running 19" MP book value. Near 25% more fuel/air.

- held for a longer period of time. 2,000 vs 2,500 rpm... 20% increase in time from firing to down stroke completion. 20% more Time elapse from firing to TDC.

- challenges regarding timing... Timing initiates plug firing in degrees before TDC, without regards to how fast the cilinder is moving.

Slowing the rpm down...

- increases time elapse between firing and actual cylinder arrival a TDC. (this is probably the danger zone)

Things to consider such as engine detonation, or ICPs building up before the cylinder reaches TDC.

- ignition timing. Increasing timing from 20 deg to 25 deg btdc increases the ignition start further away from TDC...giving more time to build pressure btdc.

- slowing the rpm increases the time available of building pressure btdc.

- high fuel flow/MP increases the ICP.

Without a detonation sensor, can you sense something going wrong and fix it before it's too late?

The reason that OWTs exist is the lack of data available for our engines in a wide array of potentially useful regimes.

There are risks you take when operating outside the regime that the engine manufacturer recommends, real or not.

Engine builders try to give us a wide birth to operate in. Pushing the limits is a way to find where they are.

This is an opinion to help support the destruction of OWTs. It may not be factually correct. Ymmv.

Your thoughts?

Best regards,

-a-

[scottfromiowa]

Can it be done without your plane falling out of the sky?...Yes. Is it O.K. for engine length between TBO? I don't know? My thoughts were the the same as Dan's regarding prop limitations. Great speed at a great fuel flow with less noise. Sounds like a winning formula. I have NEVER had that kind of speed with that low a fuel flow...EVER in my M20E. Was there a wind component helping this flight?

[jetdriven]

I probably wouldnt run a full 25" while ROP at 2000 RPM, but LOP enough would be alright. IIRC the Lycoming Operators Manual allows 2100 RPM at 25" ROP.

[rbridges]

I've started running a little oversquare, but I usually don't drop below 2250 rpm. Unless I'm imagining it, it seems the engine runs noticeably cooler. I read an article that says this happens due to less friction from the prop spinning.

[HRM]

I thought that as long as you were not running in the red (tach) and CHT's were in the 300's you were golden.

[Mikey30V]

Running at low RPM/high MAP and lean is essentially what Charles A. Lindbergh taught the P-38 drivers in the Southwest Pacific to do in order to extend the Lightnings' combat radius.

[MagicCarpet]

I feel that you folks might be overcomplicating it. I've had my bird for almost 11 years and she is still running strong. I got my license in 1980 in a Cardinal with a 180 HP engine, and the engine technology has not changed much. My old CFI at that time (Clarence Hart) taught me how to treat these engines.

With my I0-360 A1A

Taxi... lean such that the engine idles well but any more leaning will cause rough operation. This will vary on airport elevation.

Takeoff... firewall forward on all knobs, however, if taking of from high altitude airports, lean properly before brake release.

Rotate... at positive rate of climb (~50-100ft AGL), 26 squared keeping needles out of the Red lines.

Climb to desired altitude at 26 squared, monitoring and adjusting RPM as necessary to stay out of RPM Redline. As you climb, MP will drop staying below RPM.

At level off... below 3000 ft. leave mixture full in. Above 3000 ft. lean to 100 Deg. ROP. Lean only above 3000 ft MSL.

You may find that this is the manufacturers recommended procedure as well. If you want to play with any other parameters to save 1 or 2 GPH, go ahead. It's not worth the risk of damaging your engine. There is no secret here, the technology of our engines has been around for decades, there is no new secret. Treat them the way they were designed and you will make it to TBO without any problems. You LOP guys can play with this all you want, for the sake of experiment. But you must have GAMI injectors, adding a possible a degree in Mechanical Engineering in engine technology and maybe even have worked for Lycoming for a while to learn their engines.

I'll keep flying my bird the way she was engineered and built by some really smart guys in the late 60's (67 M20F). She has taken my family and myself in and out of goo weather and places for almost 11 years and I never worry about the airframe or the engine because I don't alter her fundamental dynamics as orginally designed. At each annual I get complimented on the cleanliness of the engine (internal and external), the cleanliness of the spark plugs, and the compression ratios are still strong. The engine has no leaks, is very strong, and gives me a very comforting feeling when I'm flying in the crap because I know she will deliver.

Fly safe and stay within your and your aircraft's parameters...

Carter

6460Q - '67 M20F

ATP, CFII, MEI, CFI-H

CW4 USARNG (Ret.)

[jetdriven]

26 squared, 100 ROP.

The Lycoming Operators manual shows full throttle and 2700 RPM with no limit, and operations up to 6 or 7" "oversquare." Also, at or below 75% power, operation at Peak EGT is recommended. They built the engine.

[Hank]

Sorry, Carter. I fly my O-360 ROP, but there's no need to climb your Mooney with reduced power. All it does is take longer to reach altitude. Read your Owners Manual and the Lycoming book. . . .

P.S.--I can't climb above ~3000 msl at 26". So I climb to cruise at 9000/10,000 msl, full throttle, 2700, but lean it a little bit as I go up.

[201er]

At level off... below 3000 ft. leave mixture full in. Above 3000 ft. lean to 100 Deg. ROP. Lean only above 3000 ft MSL.

But you must have GAMI injectors, adding a possible a degree in Mechanical Engineering in engine technology and maybe even have worked for Lycoming for a while to learn their engines.

I'm sorry but these two statements seem really ignorant to me. I don't have GAMI injectors on my IO360-A3B6 engine and I get a better gami spread on lean tests than what the GAMI injectors are advertised to provide. They promise to get it below 0.5. Mine is 0.0, or 0.1 at most.

Now as for the first comment, that seems really out of place on our machines. I will grant that is what my instructor taught me for a run-down 152 with no equipment, however, our planes are far beyond just guess work. Leaving the mixture full rich (someone correct me if I'm wrong) effectively puts you at about 250-350ROP. Not only are you wasting a ton of gas for absolutely no good reason, it's also putting a lot of carbon into the engine AND reducing your effective power. Even near sea level at 75% power or below (and not even going LOP) my mixture knob comes back a good ways.

This generic approach leads you to neglect case by case information. For example, 100ROP is not necessarily a good place to be. Under certain conditions your CHTs may exceed 400F at 100ROP which isn't great.

I think we should seek to greater educated ourselves, learn to understand our engines and airplanes, use all available information, and put this to use rather than to rely on generic rules of thumb that are supposed to keep any beginner or dummy out of trouble. Just my four half pennies.

[MagicCarpet]

I expected you folks to jump in...

Rules of thumb that can be used in flight are usually based upon fact.

Here's the quote's from my operators manual:

Take-off and climb:

1. Apply brakes to stop wheel rotation

2. Retract the gear

3. Reduce the propeller rpm to 2550-2600

4. Retract the flaps

5. Establish climb-out altitude.

. . . .

The next paragraph states the following:

.... Recommended power setting for normal climb is 2600RPM and 26 inches manifold pressure.

For cruise, my aircraft manual states the following:

"To obtain best power setting (maximum airspeed) setting, lean to peak temperature and then enrich the mixture until the indicator shows a 100 F drop."

Here is what my Lycoming Engine Operator's manual states:

"On engines with manual mixture control, maintain mixture control in 'Full Rich' position for rated take-off, climb and maximum cruise powers."

"Maximum Power Cruise. The engine must always operated on the rich side of Peak EGT...."

Section 3, 7.c.1 "LEANING TO EXHAUST GAS TEMPERATURE GAUGE"

a. Normally aspirated engines with fuel injectors or uncompensated carburators

(1) Maximum Power Cruise (approximately 75% of power) - Never lean beyond 150 F on rich side of peak EGT unless aircraft operators manual shows otherwise. Monitor cylinder head temperatures.

I use 3000 MSL as an altitude to start worrying about leaning. Above that altitude I'm going to cruise for a while and not change altitudes therefore no frequent changes in engine conditions (temps).

As I mentioned, my plugs are always a good color with no fouling, my compressions are good, bore scoping shows the cylinders have no abnormal wear, and the oil analysis results from the lab returned "Normal".

Maybe you should read your manuals again.

[201er]

Climb (best rate)

1. Power - Full throttle & 2700RPM

2. Mixture - Lean for smooth operation

Cruise

When cruising at 75 percent power or less, lean the mixture after cruise power is established in accordance with one of the following methods:

To avoid retypying this long section I'll just paraphrase that it's Economy at 25ROP or Best Power at 100ROP.

There is no restriction that you have to climb at 26 squared. There have been many articles and discussions that suggest that climbing full power keeps the engine cooler and the climb duration shorter. There is nothing that says you shouldn't lean below 3000ft. In fact the manual is quite explicit in saying that if you're below 75% power you should be leaning and it's not based on altitude.

[scottfromiowa]

"Maybe you should read your manuals again"...CARTER QUOTE

I have Carter. I have also upgraded my engine instrumentation and educated myself on LOP operation.. Although I bought a plane made in the 60's there have been a lot of engine management improvements made possible by better engine instrumentation. Happy to hear how YOU fly. P.S. My Cayman S sounds the best at Redline, but getting there is half the fun.

[carusoam]

Dp

[scottfromiowa]

"Maybe you should read your manuals again. "

Quote of the day top honors...

That builds camaraderie.

We're you having a bad day, or is it your cowling is better than mine day?

Just didn't expect that...

Best regards

-a-

It's a CW4 thing...you wouldn't understand

[jetdriven]

I expected you folks to jump in...

Rules of thumb that can be used in flight are usually based upon fact.

Here's the quote's from my operators manual:

Take-off and climb:

1. Apply brakes to stop wheel rotation

2. Retract the gear

3. Reduce the propeller rpm to 2550-2600

4. Retract the flaps

5. Establish climb-out altitude.

. . . .

The next paragraph states the following:

.... Recommended power setting for normal climb is 2600RPM and 26 inches manifold pressure.

For cruise, my aircraft manual states the following:

"To obtain best power setting (maximum airspeed) setting, lean to peak temperature and then enrich the mixture until the indicator shows a 100 F drop."

Here is what my Lycoming Engine Operator's manual states:

"On engines with manual mixture control, maintain mixture control in 'Full Rich' position for rated take-off, climb and maximum cruise powers."

"Maximum Power Cruise. The engine must always operated on the rich side of Peak EGT...."

Section 3, 7.c.1 "LEANING TO EXHAUST GAS TEMPERATURE GAUGE"

a. Normally aspirated engines with fuel injectors or uncompensated carburators

(1) Maximum Power Cruise (approximately 75% of power) - Never lean beyond 150 F on rich side of peak EGT unless aircraft operators manual shows otherwise. Monitor cylinder head temperatures.

I use 3000 MSL as an altitude to start worrying about leaning. Above that altitude I'm going to cruise for a while and not change altitudes therefore no frequent changes in engine conditions (temps).

As I mentioned, my plugs are always a good color with no fouling, my compressions are good, bore scoping shows the cylinders have no abnormal wear, and the oil analysis results from the lab returned "Normal".

Maybe you should read your manuals again.

What does that POH and Lycoming Operators manual say about leaning at 75% power and below? I am a firm believer that you must run the engine well rich above 75% power. I dont know anyone who reccomends otherwise. Also, 3,000 MSL is a good rule of thumb for leaning, but it should be 3,000 density altitude. On a summer day in Houston, that is at ground level.

Our engine at a 7000' DA, 2500 RPM, full throttle, at 80 ROP runs a 381 CHT and a 11.7 GPH FF. Pulling it back to 25 LOP costs you 6 knots, but the CHT is now 343 and the FF is 9.8 GPH. Do that math. 9$ an hour saved, over 2000 hours? Thats $18,000. Enouhg to pay for a majority of that new engine.

[scottfromiowa]

Off to appointment...I'll try to keep 'er under redline. Everybody have a great T-giving. Traditions are good: Daughter put up tree and decorated new house...Let the X-mas fun and insanity begin!

[carusoam]

Scott,

I saw your post after I dropped mine. Clearly, I didn't get it...

Does the Cayman have an air cooled engine or air cooled is only for airplanes now?

Best regards,

-a-

[jetdriven]

del

[jetdriven]

Maybe if you climb at 22 squared, I bet it would last forever then. Of course it would only climb 200 FPM, but in 90 miles you could finally reach 8000 feet.

[fantom]

Our engine at a 7000' DA, 2500 RPM, full throttle, at 80 ROP runs a 381 CHT and a 11.7 GPH FF. Pulling it back to 25 LOP costs you 6 knots, but the CHT is now 343 and the FF is 9.8 GPH. Do that math. 9$ an hour saved, over 2000 hours? Thats $18,000. Enouhg to pay for a majority of that new engine.

Those figures are spot on.

And doing the math, you will have flown another 75 hours, or so. Not a bad thing :-)

[rbridges]

so, let me see if I get this.

I usually push full forward for max RPM and Max MP on takeoff/climb. I usually start with full mixture and start pulling it back as I climb. I have an engine monitor and I keep temps below 380 (cylinder) and 1400 (exhaust).

Is it OK to start with less than full rich on takeoff? It burns a boatload of fuel; usually 16gph at first until I start leaning back. How do you know how rich you need it? Engine roughness and EGT?