High altitude take off. Leaning methods

[nels]

I've been contemplating a trip to Denver to visit my kids and son in law. I've never been exposed to high altitude landings and take offs. Are there any good rule of thumb practices for leaning at take off or missed landings with full power go around. Also, on landing, what should be considered full rich?

[jetdriven]

Lean to target EGT for takeoff.  For landing, just set it around 1/3rd from full rich. You can also get it exact by setting target EGT in climb and note the mixture position at 6000'.  Set it to that for landing 

[irishpilot]

I use my first knuckle on my index finger. That sets the initial mixture in the ballpark and works for CO elevations.

Sent from my Galaxy S5 via Tapatalk

[midlifeflyer]

The first knuckle is fine for taxi, but since the elevation means a loss of the max HP you can generate, you want to get a bit more precise than that in getting the most from your engine for takeoff.

This is from a write-up I did a while back:

You can do it during run-up, but recognize that it is an approximation. Here's the procedure I teach (this is assuming a normally aspirated piston). There are minor variations depending on the make and model:

When you are ready to do the run-up:

1. Enrichen the mixture (you should have leaned it for taxi, so you need to enrichen it for the run-up power demand). You don't really need to go back to full rich at this point, but there's no harm in doing so until you learn about where to set it)

2. Go to run-up power.

3. Lean. You will initially see a rise in RPM as you reach best power and then a drop  When you see the drop, enrichen back to peak. (Remember when you first learned how to lean when you learned how to fly in a very simple airplane? This is quite similar)

4. Enrichen more. On airplanes with a mixture vernier control, 3-4 twists will do it. Without a vernier, about 1/4-1/2 tends to take care of it. The enrichment is for 2 reasons: to approximate the additional requirements for takeoff and for engine cooling.

In most airplanes, this will be exactly what you need for takeoff (an a lot of instructors at high density attitude airports stop here) but bear in mind that this is an =approximation= that needs to be cross-checked, at least until you have learned that the run-up technique works for your airplane.

The cross-check should be done at full power. If the brakes will hold, you can do it while still at the runup area or before beginning the takeoff roll. But I usually do that final check on the takeoff roll (and what you do depends a lot on the airplane - some will have fuel-flow targets). I have never had to move the mixture more than a 1/2 twist - takes only a second.

Finally, remember that this isn't brain surgery. Look at your POH - that instruction to lean "above 3000') is a pretty good indication of how much leeway is built in.

For landing, if you have no idea since it is the first time, the knuckle isn't too bad an approximation, bu realize that you might need a tweak of the mixture in case of a real go-around and be prepared.

You might find it worthwhile to practice this a bit at altitude - go up to 6,000 or 8,000 msl and give it a try, realizing that it is only an approximation, especially since 6,000 msl in other parts of the country will often be a lower density altitude than the same msl in Denver.

Edited September 27, 2015 by midlifeflyer

[jetdriven]

That sounds like a heck of a lot more work than "lean to target EGT"

[midlifeflyer]

 

That sounds like a heck of a lot more work than "lean to target EGT"

Not sure it rakes any longer. Adds about 5-10 seconds to your run-up. Leaning to peak EGT can have its own issues, especially with higher performance engines and on warm days. And it shouldn't remove the need for a cross-check to see if you are getting expected performance.

I think there's a reason the method I described is the one taught by most Colorado flight instructors.

Edited September 27, 2015 by midlifeflyer

[irishpilot]

Midlife's guidance is basically lean to peak then enriched slightly for 50-100 ROP. He just steps through the procedure thoroughly. I have most of my GA flying in CO and the knuckle gets you close and then you can hone in using the mentioned steps. Happy flying!

Sent from my Galaxy S5 via Tapatalk

[DXB]

That sounds like a heck of a lot more work than "lean to target EGT"

Trying to learn about the lean to target EGT method - makes sense to me, just thinking through the practical details.  Do you start runup at full power each time at altitude to get the mixture set based on EGT?  

[N201MKTurbo]

I have about 3000 hours flying Mooneys in CO. I was based at 01V. I would just take off full rich at the low elevation airports like the ones around Denver. I would lean at the mountain airports that were above 7000 or if the runway was short. I would usually just lean it on the takeoff roll until the engine sounded strong. Back then all I had was an EGT gauge and it was not reliable.

[jetdriven]

Trying to learn about the lean to target EGT method - makes sense to me, just thinking through the practical details.  Do you start runup at full power each time at altitude to get the mixture set based on EGT?  

no, my target EGT is 1285 on # 3. So below a density altitude of 3000' I just takeoff full rich. Above that I will lean about 10-20% from full rich, and after applying full power, bump it one way or another to get 1285.  Within 50 degrees is fine.  Make fine adjustments above 500' after takeoff  

I actually like midlife flyer's technique for an airplane you're not familiar with   But for your own airplane I think target or even target plus 50 is simpler and more exact  

 

Edited September 27, 2015 by jetdriven

[Oscar Avalle]

Just watch out with density altitude, power and CHTs. The higher the temperature the higher DA and the more difficulty the plane has to keep the CHTs down... You have to balance out keeping the temps down (rich mix) and leaning for best power, at least on take off. In cruise the situation is more manageable. 

[M20F]

One thing to add is watch the cylinder temps on climb out.  If you got it a bit too lean they will heat up fairly rapidly, good cross check.  

[midlifeflyer]

 

One thing to add is watch the cylinder temps on climb out.  If you got it a bit too lean they will heat up fairly rapidly, good cross check.  

That's an important consideration. The reason for the small amount of enrichening past peak in the technique I described is twofold. One is to take care of the additional power requirements for takeoff since the leaning is done at run-up power, not full power. The other is to allow for additional cooling in the climb, A 90 degree day in Denver's relatively low altitude (I think yesterday) means not only hot air but a density altitude above 9000'. They get a lot of high oil temps in that environment, particularly from low land pilots who don't understand the need to modify their procedures.

[gsxrpilot]

My experience has been to lean for best power on the ground and use that for takeoff. Once a positive rate of climb is established, I'll richen up quite a bit to maintain good CHT.