Fuel Mixture

[Iridus]

Do you fly R22s or other piston engine helicopters with the fuel mixture fully rich or does it have to be leaned during runup like a plane?

[Flying Pig]

Leave it full rich

[Jaybee]

We always leaned the Bell 47.

 

It would be heresy to suggest doing so in the Robinson's but I would lean in between tour rides because also being the resident A&P I didn't want to clean the plugs every 50 hours.....

[avbug]

Do you fly R22s or other piston engine helicopters with the fuel mixture fully rich or does it have to be leaned during runup like a plane?

 

 

Be careful leaning. In piston aircraft engines, two of the most misunderstood topics seem to be carburetor heat/icing, and the use of the mixture control. It's rare that I meet an instructor who has any understanding of either one, let alone a student.

 

If you're leaning the engine on your fixed wing airplane during runup, what does that do to the mixture at takeoff power settings?

[Guest pokey]

 

 

 

 

If you're leaning the engine on your fixed wing airplane during runup, what does that do to the mixture at takeoff power settings?

 

 

i give up. whats it do? does what you do on runup have anything to do with the engine on takeoff power setting?

[Eric Hunt]

In your propellor-piston engine, there is a great big flywheel (the prop) that keeps the engine turning even if you have mistakenly leaned it too far and it cuts out momentarily. In a helicopter, the freewheel unit allows the engine to stop while the rotor keeps on spinning.

 

So, it can be dangerous to lean the engine in your helicopter in case you take it too far, and you are then in autorotation while trying to restart the engine. Wouldn't be any fun.

[Guest pokey]

In your propellor-piston engine, there is a great big flywheel (the prop) that keeps the engine turning even if you have mistakenly leaned it too far and it cuts out momentarily. In a helicopter, the freewheel unit allows the engine to stop while the rotor keeps on spinning.

 

So, it can be dangerous to lean the engine in your helicopter in case you take it too far, and you are then in autorotation while trying to restart the engine. Wouldn't be any fun.

 

 

oh, i see, please explain how the prop keeps the engine spinning on the ground

[Flying Pig]

It doesnt keep the prop running on the ground. But when you are flying an airplane and you lean it to much and it sputters, you can just push it back in and the prop spinning in the wind will re-start the engine because its directly connected. In a helicopter, the engine will stop because MR doesnt keep the engine going like in an airplane engine. Like he said, in a helicopter the freewheeling unit comes in to play and the engine dies.

[Eric Hunt]

Listen to the Flying Pig, he has got it in one.

 

Pokey, you don't try to lean the mixture on the ground. At sea level you want it full rich. Even at Colorado, you would most likely leave it full rich for takeoff and landing. Why do you think there is a guard over the mixture control??? To stop people fiddling with it, and to prevent it being pulled when Bloggs goes for the cyclic trim.

 

At altitude, where the air is thinner, the mixture could be leaned out to get the stoichiometric level correct, around 15:1, but this is only for economy, which is not all that much of a change in a helicopter. And for cooling, having the excess fuel in the mixture helps keep the temperatures down.

Edited January 16, 2016 by Eric Hunt

[avbug]

"Excess fuel in the mixture" does not keep the temperature down.

 

Which keeps the engine cooler; 50 degrees rich of peak, or 50 degrees lean of peak?

 

When leaning at partial power (eg, during a "run-up"), how does that impact full throttle operation?

[Eric Hunt]

50 degrees lean of peak temp (stoichiometric mix) gives less power and less temp, but uses less fuel - the proportionate reduction of power is more than made up for by the reduced fuel burn.

 

50 degrees rich gives the same power as peak, but a lower temp due to the wasted fuel evaporating and cooling the mix.

 

But this is something you do in a plank, not a Robinson product.

 

"Leaning at partial power e.g.during a runup" - where does it talk about this in the Robinson flight manual? At no stage does the mixture control get touched between pushing it down to start and pulling it up to stop. Anything else is a non-recommended procedure, and your insurance company would love to wash its hands if you did this and it caused an incident.

[MLH]

 

 

oh, i see, please explain how the prop keeps the engine spinning on the ground

 

Inertia - the prop acts as a flywheel.

[Eric Hunt]

 

 

Which keeps the engine cooler; 50 degrees rich of peak, or 50 degrees lean of peak?

What gauge are you going to use in a Robinson to do this? Cylinder head temp doesn't do it, due to the thermal lag in that big lump of iron, and there isn't an exhaust gas temp gauge fitted.

[avbug]

What gauge are you going to use in a Robinson to do this? Cylinder head temp doesn't do it, due to the thermal lag in that big lump of iron, and there isn't an exhaust gas temp gauge fitted.

 

 

I'm not, and it's irrelevant. The question wasn't asked to determine how to lean an R22. It was asked relevant to the subject of leaning an engine.

 

Leaning a piston aircraft engine without multipoint EGT sampling is a crapshoot and can be a dangerous proposition until the engine is operated at less than 75% power, given the variances in mixture from one cylinder to another.

 

Insofar as leaning to rich of peak (up to, and including full rich operations), fuel doesn't "cool" the mixture. A rich mixture means incomplete combustion, and in some cases, combustion beyond the cylinder.

 

In large radials it was common for us to adjust mixture by the color of the exhaust at the stacks and collector.

[Canadian47]

We always leaned the Bell 47.

Jaybee,

 

I assume this is in cruise but could you expand on this a little? My instructors told me to never touch the mixture and in fact the mixture control was removed from the '47s at the flight school. My '47 has an altitude compensating carburetor. I don't know if all the 47's do but I still think it makes sense to lean a little in cruise.

 

Glenn

[lvflyer]

I was surprised to find out when I bought my Enstrom that it was designed to be properly aggressively leaned since all my learning was in R22s. The Enstrom will not run at full potential without leaning. The old Enstroms relied on EGT gauges whereas new ones and retrofitted ones, like mine, rely on Turbine inlet Temperatures on an engine analyzer. Believe me it makes a huge difference in performance and economy. Never lean an R22 it is de-rated.

Edited January 19, 2016 by lvflyer

[Gilberto_Farthing]

Sounds resourceful!!!

Thanks for sharing.....

[Jaybee]

Jaybee,

 

I assume this is in cruise but could you expand on this a little? My instructors told me to never touch the mixture and in fact the mixture control was removed from the '47s at the flight school. My '47 has an altitude compensating carburetor. I don't know if all the 47's do but I still think it makes sense to lean a little in cruise.

 

Glenn

My Instructor had owned the same D1 for thirty years. We leaned on the ground. Coming straight out of earning my Private airplane rating I never gave it a second thought until I flew a Robinson for the first time.

 

edit -

first reply was on phone,,,

 

no I would not lean in cruise - though from an airplane perspective it would make sense. As stated previously in the thread if you over lean the mixture in an airplane you just push the knob back in no big deal. if you over lean in a helicopter then you enter an autorotation because of the sprag clutch.

 

Jeff