Simviation Forums

Okay I have always had 'auto-mixture' on, but I would like to be cool and have it OFF, so I need to know when to apply different amounts of mixture (Lean, full, ect) So any advise would be great

When you get to altitude, 3,000 MSL or higher, start twisting out the mixture until the RPM's start to fall off and push it back in until it stablizes.

Alternatively, you can use the CHT guage, but I've never had one in any airplane I've flown except the Mooney. I'd still rather do it with the RMP and my ear.

Okay I have always had 'auto-mixture' on, but I would like to be cool and have it OFF, so I need to know when to apply different amounts of mixture (Lean, full, ect) So any advise would be great

For normally aspirated (Carburettor) Piston Engines the Mixture should be set Full Rich for take off, cruise, and landing.
(This also helps to cool the Cylinders).

For altitudes above 5,000 Feet ASL the Mixture can gradually be weakened to maintain the correct Petrol/Air mixture for to generate full power Power.
Slowly reduce the Mixture until the Engine starts to falter and run rough, then slightly increase until the Engine runs smooth again.
Observe the Engine RPM, and Suction Gauges...and note any change in airspeed.

Remember to apply Full Rich for landing...to keep the Cylinders cool to prevent engine overheating!

(A Weak Mixture generates heat!)

If taking off from an altitude higher than 5,000 Feet ASL remember to weaken the Mixture slightly for full power!

Paul...G-BPLF...FS 2004...and a packet of Dolly Mixture Sweets... ...!

MSFS has a unique bug, that actually helps in setting mixture.

In order for MSF to

...and don't forget to pull the Mixture Knob to Full Weak to stop the Engine(s)....!

(This will empty the Carburettor Fuel Bowl to reduce the possibility of an accidental Ignition Start).

...THEN switch off the ignition!

NOT just switch off the Ignition to stop the Engine(s) (Grounding the Magnetos).

....and don't forget to apply Full Rich to Start the Engine(s).... ...!

Paul...G-BPLF...FS 2004...ate all the Dolly Mixtures... ...!

..its fun, (and educational!), playing with the Throttle, Mixture, and Carb Heater controls...and observing the Gauges and sound of the Engine(s) to the response... [smiley=thumbsup.gif]...!

Is there a method to the madness of finding the correct mixture setting for high elevation take offs?

ex: When taking off at La Paz, Bolivia, it's a hit and miss game trying to find the mixture/power optimization to get enough speed to take off.  I'm guessing that's why there is such a long runway there, and maybe my choice of aircraft isn't suited to those conditions.

[quote]Is there a method to the madness of finding the correct mixture setting for high elevation take offs?

ex: When taking off at La Paz, Bolivia, it's a hit and miss game trying to find the mixture/power optimization to get enough speed to take off.

So I was doing it correctly without even knowing I was. 

Those kind of take offs make for an exciting challenge at times.  8-)

[quote]Is there a method to the madness of finding the correct mixture setting for high elevation take offs?

ex: When taking off at La Paz, Bolivia, it's a hit and miss game trying to find the mixture/power optimization to get enough speed to take off.

Thanks for the advice guys 

With a fixed pitch prop, the answers about leaning the mixture at takeoff power until the rpm drops a bit, then enriching slightly to get the peak rpm, are right.

A constant-speed prop, however, will try to maintain the preset rpm. Lean until it starts sounding a bit rough, then enrich the mixture to smooth it.

References to altitude should really refer to "density altitude," not height above sea level. The aircraft's operating manual should have information about proper leaning.

I've flown from Tucson, Arizona and Edwards AFB in the Mojave Desert. At those 2,300' msl fields, the density altitude easily hit 6,000' on a hot August afternoon.

Art

...taking off at La Paz, Bolivia

I attempted that with the 172.

La Paz is over 13,000ft ASL, the C172 has a service ceiling of something like 14,000 ft. That's a recipe for disaster.

cheers,
Joe

With a fixed pitch prop, the answers about leaning the mixture at takeoff power until the rpm drops a bit, then enriching slightly to get the peak rpm, are right.

A constant-speed prop, however, will try to maintain the preset rpm. Lean until it starts sounding a bit rough, then enrich the mixture to smooth it.

References to altitude should really refer to "density altitude," not height above sea level. The aircraft's operating manual should have information about proper leaning.

I've flown from Tucson, Arizona and Edwards AFB in the Mojave Desert. At those 2,300' msl fields, the density altitude easily hit 6,000' on a hot August afternoon.

Art

I'll quote myself

...taking off at La Paz, Bolivia

I attempted that with the 172.

La Paz is over 13,000ft ASL, the C172 has a service ceiling of something like 14,000 ft. That's a recipe for disaster.

cheers,
Joe

It gets worse...

I did it in a C150 and real world weather.

http://205.252.250.26/cgi-bin/yabb2/YaB ... 1262614320

NEVER did it get over 60kts IAS, and the rpm struggled the whole time... But... I did it. I guess this is where RTFM takes on a real urgency. 

...taking off at La Paz, Bolivia

I attempted that with the 172.

La Paz is over 13,000ft ASL, the C172 has a service ceiling of something like 14,000 ft. That's a recipe for disaster.

cheers,
Joe

It gets worse...

I did it in a C150 and real world weather.

http://205.252.250.26/cgi-bin/yabb2/YaB ... 1262614320

NEVER did it get over 60kts IAS, and the rpm struggled the whole time... But... I did it. I guess this is where RTFM takes on a real urgency.