Descent mixture?

[UKJim]

Hi,

I am not a pilot so I am a bit noob to this but I get I need lean mixture on the ground while taxiing etc - then full mixture for takeoff - then lean it to max RPM in the cruise but what should I be doing on decent?

Obviously I lower the throttle and even when the mixture is fully rich the EGT dial remains at the bottom. Should I be leaning the mixture to just above a stall?

Thanks,

[spacejunkee]

Here you go, this is from page 55 in the pilots manual:

DESCENT
1. Power — AS DESIRED
2. Mixture — ADJUST for smooth operation
3. Altimeter — SET
4. NAV/GPS Switch — SET
5. Fuel Selector Valve — BOTH
6. Wing Flaps — AS DESIRED (0° - 10°
below 110 kias, 10° - 30° below 85 kias)

In my limited experience, if you're below 3000 feet you can be full rich. If landing at higher elevations, know that you will need to lean the mixture to achieve maximum available power. When I was landing at 6000' I had mixture set to around 70-80% I believe.

[Tigerclaw]

I think you should bare in mind that a full rich mixture at idle can, and most probably will, foul the plugs on the way down. And when you might need power, there won't BE any As the check list says, regardless of altitude, LISTEN to your engine, and lean for smooth operation.

[whiic]

I'm not a real pilot but...

I would use a lean / very lean mixture during descent and not enrich the mixture until I'm on final, in attempt to keep the plugs cleaner. Leaning the mixture typically causes EGT to rise (until it falls down again when lean of peak) but during descents you are usually throttling the engine to such an extent that regardless of how rich or lean you run it, the needle will be at the low end of the gauge (i.e you don't get any reading out of it). Therefore ignore the EGT gauge when you're not using full or almost full throttle.

During descent, I would use the leanest mixture that sounds smooth. It's not too critical because you're no longer aiming for A) lowest engine temperature per performance (take off and initial climb), B) maximum performance (i.e maximum rpm during climb at 3000+ feet) nor C) best economy (cruising at either peak or slightly lean of peak EGT). You just want to keep the plugs clean, completely disregarding temperature (since it's not an issue in this phase of flight), performance (since you're converting altitude to airspeed) and economy per horsepower (since your target horsepower is very close to zero). The biggest worries during a steep descent would be to keep the plugs clean without overspeeding the airframe.

To keep the plugs clean, you need some throttle. If you can't give much throttle (to keep airspeed in control), a very lean mixture might be useful. It should however not be too lean (i.e not "just above a stall"). That's why you tune by ear to the point of rough running, then enrich until it runs well and a bit extra for safety margin... and keep listening for changes in running as you descend since it'll need enriching when you get to thicker air.

On a less steep descent (i.e cruise descent) done with full or near-full throttle, I would use the EGT gauge to tune in some nice lean of peak mixture. This requires that the EGT stays within the gauged temperature range.

[Scott - A2A]

I only use full mixture on takeoff and climb under 3,000ft. Otherwise, I'm leaning.

Scott.

[UKJim]

Thanks for the info guys! I'll keep it all in mind next time I fly!

During descent I've been having throttle around 10-15k rpm. Then I've been leaning the mixture but it sounded very grindy. Putting full rich sounded better but I am worried about the plugs.
I'll have a practice and see what works best

[Tigerclaw]

Isn't it a lot of FUN LOL.

[spacejunkee]

I think you should bare in mind that a full rich mixture at idle can, and most probably will, foul the plugs on the way down. And when you might need power, there won't BE any As the check list says, regardless of altitude, LISTEN to your engine, and lean for smooth operation.

Definitely makes sense. We need to always be aware and control the things we can control, effectively. That's what makes this trainer so fun in my opinion, having real consequences for not following proper procedures that could have disastrous results.

Thanks Tigerclaw and everyone else for stressing the importance of mixture.