Piston engine ops

[Crizz]

Is it wise to go back and lean the mixture on the good engine after you secure the dead engine?

Maybe... but if you are at a high altitude you are most likely going to drift down anyways. I would opt to stay on the rich side especially when in a full power emergency situation.. no need to grenade your good engine simply to make an additional 10 HP.

I guess my commentary only applies to N/A light twins... I have no experience in anything else.

 

[WrightAvia]

If you have the presence of mind to not feather the good engine, you should have the presence of mind to set the operating engine at it's optimum. That means not shoveling too much fuel down it's throat. That means, closing the operating engine's cowl flap, if it is cool enough. That means closing the dead engines cowl flap, period.

If you have this engine failure at cruise and you are drifting down into ICING conditions because you choose to p!ss 10 horsepower out the exhast pipes as unburnt fuel and p!ss away a bunch of thrust, because you didn't close the cowl flaps...that is your problem.

 

[Crizz]

Whoa settle down man... there are 1000 different situations in which different courses of action may be applicable. Sorry Ronin, apparently I am not worthy of any commentary whatsoever.

 

[WrightAvia]

dude I wasn't being high minded...it's just that the teletype loses something in the translation

That extra 10 horse power, may be all it takes to keep your altitude. Or at least carry you to the fixed distance marker...instead of the scene of the accident.

 

[metrodriver]

Greyhound, on a normally aspirated engine: no. If you are at an altitude where pushing the tthrottle forward actually results in more power, push your mixture up just a little (quarter of an inch or so). If you push it all the way forward you might make the mixture so rich that you lose power or maybe even lose the engine. If you're so high that you don't gain extra power, than leave the mixture where it was (the good engine doesn't know its stablemate just died)

A story from an aircaft owner I flew with for a few hundred hours years ago in a Geronimo Apache: he was in Colorado Springs on a hot day and had a low country CFI in the left seat with him. Before take-off they went through the whole procedure of leaning the mixtures, and take-off clearance comes. CFI taxies onto the runway and without thinking does the low country thing: push everything forward. So the plane rolls down the runway, slowly (slower than normal) gaining speed. Then a call from the tower: ' is everthing allright? There is a lot of smoke coming from your engines'. Owner looks at the mixtures, pulls them back to where they were set during run-up and says: 'how now'? Tower: 'yeah it's gone'. Suddenly the aircraft started to accellerate a lot faster.

OK, question for the new CFI's: you're flying around (or taxiing, doesn't matter) and you notice your rpm dropping and the engine starts to run rough. Wow, you think, I might have carb ice. What is the FIRST thing you do? Hint: it applies to this thread.

 

[340drvr]

The last few posts above have it correct. At high density altitude with a normally aspirated engine, anyplace a checklist says "Mixture-Rich" implies the red knob goes forward to wherever you had it set when you did your runup and leaned for best power. NOT necessarily all the way to the firewall.
You might not get it exactly to the sweet spot, but after awhile, you get a feel for where it's set after runup (6 clicks back, 1" out, 3 fingers aft, whatever). That point can be thought of as "full rich" for your ground altitude. This "set point" is then used if the procedure calls for mixture-rich for engine out, before landing, etc.
Now, some thought must be applied if departing, say, Leadville, CO and arriving in Galveston, TX, but the idea is still the same.

 

[MarineGrunt]

If you have the presence of mind to not feather the good engine, you should have the presence of mind to set the operating engine at it's optimum. That means not shoveling too much fuel down it's throat. That means, closing the operating engine's cowl flap, if it is cool enough. That means closing the dead engines cowl flap, period.

If you have this engine failure at cruise and you are drifting down into ICING conditions because you choose to p!ss 10 horsepower out the exhast pipes as unburnt fuel and p!ss away a bunch of thrust, because you didn't close the cowl flaps...that is your problem.

So say for example we're in cruise, and the mixture is set where we want it, then there's an engine failure. Are the mixtures better off not being pushed to full rich? I understand leaning the operating engine for best power, but I've never been tought anything other than pushing them all the way up.

 

[Crizz]

Id have to agree that you would want to lean for best power. I was making the point that you probably do not want to "lean the piss" out of the good engine you have just to make the absolute most power, especially if you are in VMC (not the bad kind ) over flat land.

I was in no way saying to push the mixtures full foward, but rather to stay on the rich side of peak.

I will have to say, Multi Private all the way through MEI it was procedure during the "Mixtures, Props, Throttles...." to shove them all the way forward.

Thanks for the commentary guys.

 

[metrodriver]

marine and grizz, read my last post on page 1 of this thread, the answer is right there.

 

[WrightAvia]

If you enrichen the mixtures on piston twins on short final, you may find yourself with an engine stalled on the roll out, maybe even both.

I never pushed the mixtures to full rich on short final or base. Nor the prop levers. The advancing of the prop levers was unerving to the passengers and you were almost guaranteed to have an engine stumble off and quit on roll out, with the mixtures full rich. You could almost hear the engines go soggy, in the descent into the pattern if you pushed em up. So I left em alone.

A go around requires that you push up the mixtures, push up the props and push up the throttles anyway. As does the engine failure memory items.

 

[Skaz]

Final appr checks: Reds, Blues, Greens or PUFF: Power, Pitch, Undercarriage, Flaps, Fuel & Fuel Pumps.....

Before commencing the descent I adjust the mixtures too, in the cruise the FF on the 402 is around 90 - 95 lbs/hour, for the descent I set it 100.
I richen then mixture on finals, maybe not full rich, but richer than operation at flightlevel anyway. Climb setting after take-off is 120, so thats a good refrence for me to aim at.

As for the props....this is a bit sticky as it would be heavily biased per personal preference. Top of Green at least, the last little bit that makes the most noise...um, I prefer to push the props full fine, just in case a go-around is needed. You might not alway have time to push all the levers forward, if your hands are on the throttles levers.

With a patient in back (we do medevacs), and stable approach with good conditions, I sometimes leave the props TOG, but usually they go full fine.

right, tell you guys what...I have always done the take-off in the C402 with the mixtures full rich....next one I do ( did 4 today, should have remembered!) I'll lean it out a bit and check the difference.....

 

[lookup]

Prop settings...

On my little ole' O-360 I find that by the time I am down to about 15" MP, the prop has already set itself to fine and moving the prop control full fine makes no difference... other than to be ready for a go-around. During some instruction in a geared engine bird, I was told to NEVER NEVER NEVER let the props drive the engine... ever ever... never never... The SOP in the Commander 520 was to wait until short final (<15" MP, or not at all) for the props to come up..


I do all my mixture settings in small increments going up or down, based on EGT gauge readings. (no FF gauge) MP settings also in slow increments on descent..

It sucks when you're the only one to blame if something breaks AND you're stuck with the entire bill...

LU

 

[340drvr]

Just to clarify:
There's a critical difference in leaning procedures between turbocharged and normally aspirated. Those turbo 520's in the 402 want "full rich" for takeoff at most any elevation (maybe not Tibet or La Paz, but that's another story). I would start with the red knobs full forward, monitoring FF as I approach full power. As long as FF stays in the green, full rich it is. Sometimes things are out of adjustment, and FF goes way over the top, in which case you'd lean back to top of green fuel flow. (Works for the 340, anyway, same TSIO-520)

 

[greyhound]

That's what I thought.....

In a lot of schools, they want you to firewall everything if you lose an engine on a piston twin. Even at cruise.
That did not sound right to me.
If you're going to be on one engine for a while, I'd take good care of it so it can take you to your landing spot.(hopefully not a crash site)
By taking care of it I mean leaning it, and using cowl flaps to help keep it at normal operating temps.

So are we still going to teach everyone to just push the mixtures all the way forward in the event of engine failure on the seminole?

If we are, let's also remind the student to lean for best power after the dead engine is secured.

 

[metrodriver]

Skaz, look out! I think your engines on the 402 areturbo charged.
For these you don't lean on take-off. The sole purpose of the turbocharger is to maintain an airflow into the engine that stays constant all the way from sea level up to its service ceiling (I believe that's what it's called where the maximum altitude is at which the turbo can deliver its rated pressure, there might be another term for it, I forgot). So your engine doesn't know at what altitude it is. This is different for normally aspirated engines.
On a normally aspirated engine the throttle controls the throttle plate in the carburator, which allows the amount of air sucked into the engine. There is also a link to a fuel opening that regulates the amount of fuel being sucked into the airstream in the venturi of the carburator. Now when the plane goes up to altitude the throttle stays in the same position (and so the fuel allowed to go in the airstream), but the airstream itself is getting less because the air is less dense up there. The result is now that you get too much fuel for not enough air (rich fuel mixture). So they designed the mixture control, which controls another 'valve' that controls the amount of fuel going to the fuelcontrol that is attached to the throttle linkage.

Nobody bit into the question I posted on the bottom of page 1 of this thread. If your engine is running rough because of carb ice, FIRST pull back your mixture control till your engine runs smooth, THEN pull your carb heat. Why? All that ice in the carburator was limiting the airflow into the engine, but the amount of fuel was the same as before, so you have a very rich mixture, so rich the engine started to choke on it. If you had pulled the carbheat first you would have allowed warm air (which is less dense then the cold air) and water (engines up to this day don't burn it very well) to make your fuel mixture even richer. Now you probably become a statistic (there are quite a few each year because of this reason): your engine quits because of all the fuel, no air and water, and trying a restart is unsuccesfull because there is no heat source anymore to melt the ice. So after you damage your plane landing in some farm field the FAA decides to test run your engine and it runs perfectly fine and your accident gets as probable cause: failure of the PIC to properly monitor engine conditions.
When the carbheat is melting the ice and you see the rpm go up, slowly push the mixture to where you had it before.

 

[Timebuilder]

That's a great piece of info on the carb ice, metro. It's always a pleasure to learn something new. Thanks!!

 

[avbug]

Why? All that ice in the carburator was limiting the airflow into the engine, but the amount of fuel was the same as before, so you have a very rich mixture, so rich the engine started to choke on it.

Not so, grasshopper.

Fuel flow in a carbureted engine is proportional to the pressure drop at the venturi; that's what draws the fuel into the carburetor throat. The pressure drop is regulated by airflow; restrict the amount of air, (or the velocity through the venturi, and you'll see less pressure, and less fuel.

Plug up a venturi with ice, and you'll see lower fuel flows, and generally eratic fuel flows, too.

If one is to lean prior to applying carburetor heat, the primary reason is that the mixture will be enriched with the application of carburetor heat (due to decreasing air density), not because greater fuel is flowing due to ice.

The engine is nothing more than a big suction machine. It sucks in air, it sucks in fuel. Less air flowing into the engine means less fuel. Don't try to compensate for that with mixture.

That discussion aside, prioritize. If your engine is going to choke on ice, then get rid of the ice. That's the priority. Fine tuning can come later. Take the steps you need to take (carburetor ice...apply as required), and then clean up. You have time.

 

[TurboS7]

With over 9000 hours in props I never thought I would see the day that I would see a thread like this. I love 'em when it is warm and hate 'em when it is cold.

 

[TurboS7]

I guess I will throw in my 2 cents. The procedures for shock cooling are correct but conservative, they will result in long engine life. With a Cont. especially the C402C you can taxi with the mixtures rich. If you take off with them leaned back you will cook your engines. You can check the idle-mixture setting my bringing the mixture back to idle cutoff, if the RPM rises 50RPM the drops off it is set correctly. The big problems we had operating in cold weather with the Cont were engine case cracks and cylinder cracks. Overall I had better luck with Lyc in the cold weather and better luck with the Cont in hot weather. Piston engines are way harder to run than any turbine, it is ironic that the higher the dollar value airplane the easier it gets to operate.

 

[TurboS7]

One more for sub-zero carburetor ops. Don't use carb heat as it will heat up the carb throat and cause carb ice, just the opposite of what it is suppose to be.