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High Density Altitude Takeoff Leaning Technique

Frankster13

Active Member
I am considering a trip in my RV-14A from the San Francisco Bay Area back to Grand Junction (elevation 4861 ft.) or Montrose CO (elevation 5,759 ft.). I am interested in leaning techniques for takeoff to maximize performance and information of the area from anyone that has flown at high altitude airports. I have the RV-14A with a 210 hp Lycoming O390. I would be flying with two persons and 30 lbs. of luggage. Any thoughts?
Would you takeoff with half tanks or full tanks?
 
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DA around my home airport can reach 10k plus in the summer heat. Technique I was taught and use currently is during run up back mixture off slowly until first noticeable drop then add two turns.
 
The point is to lean some so that the engine is not running super rich and losing power. IMHO, it doesn't have to be super-precise leaning.

One trick is to lean in the pattern in flight before landing, remember where that setting was and then enrichen just a bit.

In my old Cessna, I learned where a good mixture setting was and used that memorized setting.

And you can take off a bit rich and lean once you're in the air and clear of obstructions.
 
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In my opinion you have the perfect scenario being based at sea level. Note your takeoff EGTs on a sea level takeoff. High DA takeoff should be leaned to a similar number at full power. If you are full rich your EGTs will be very low, if it runs smooth at all.

Otherwise the non technical method I was taught is lean until rpm drop and then add about 4 “turns” on the knob. Not to be confused with full revolutions. I don’t like this method because “turns” is open to interpretation and not precise.
 
I fly out of KLMO at about 5000’ and brought my plane (RV 7A, then F1 Rocket) from KFCM (about 900 feet elevation). I have not adjusted mixture (fuel injected) from where I had it in MN. I found that it didn’t make a lot of difference leaning on takeoff but that being said I routinely lean a bit to get EGTs for takeoff to about where they were in MN, about 1” or so lean from full rich. Takeoff roll is longer and RoC is lower than MN but plenty of power. Landings are also faster. Have been to higher airports without any difficulties. Of course when I do that I fly in the mornings before winds and temps come up.

I hope this helps -

Mark
 
In my opinion you have the perfect scenario being based at sea level. Note your takeoff EGTs on a sea level takeoff. High DA takeoff should be leaned to a similar number at full power.

I second this technique, and, further, I’d do it during the takeoff roll, assuming adequate runway length.
The other option is to lean during run-up, find peak egt, then enrichen by 150 F, and trust that your injection system works properly. However, if runway length/engine power allow it, I’d suggest running richer than this. With most no-cowl flap RV’s you’ll see high CHT’s unless you run richer than best power.
 
The two airports mentioned in the original post, Grand Junction and Montrose, have 10,000' runways.

At those two airports, you are not going to have a performance problem with an O-390, 210 hp, RV14A, especially departing in the morning as recommended. All good suggestions above for leaning. But if you do lean for maximum performance, then keep a close eye on your CHT's on takeoff and climb out.
 
2 guys above suggested adding 2 turns, another one said 4 turns. Obviously a rotating knob mixture control. What's the prevailing wisdom, where you've got a throttle quadrant, and the mixture control is a sliding lever??:confused:
 
2 guys above suggested adding 2 turns, another one said 4 turns. Obviously a rotating knob mixture control. What's the prevailing wisdom, where you've got a throttle quadrant, and the mixture control is a sliding lever??:confused:

You just had to mention a quadrant! Hahaha. Just to be clear, the down and dirty method is not my preferred method and I never use it. Just a method I was taught in 152s back in the day. I always use EGT.

I was taught how to lean in a Piper with quadrant but for the life of me I can’t remember the experience. I must be starting to get old. :p
 
In my opinion you have the perfect scenario being based at sea level. Note your takeoff EGTs on a sea level takeoff. High DA takeoff should be leaned to a similar number at full power. If you are full rich your EGTs will be very low, if it runs smooth at all.
I second this technique, and, further, I’d do it during the takeoff roll, assuming adequate runway length.
I will be the third to recommend this technique. I even use it to lean for best power as I climb in altitude, and I fly in Florida.

:cool:
 
I will be the third to recommend this technique. I even use it to lean for best power as I climb in altitude, and I fly in Florida.

:cool:

When I visit Denver, I pull the knob back to a bit less than I think will work and confirm that I am still plenty rich on the runup. Then, a couple seconds into the TO roll, I look at the EGT and lean to my normal ROP EGT for full power that I have observed on most every other TO that I do. I often have my son watch the EGT number and read off changes to me. I took off from a 5000' strip on a 11K DA day with no issues using this method in the 10 at full gross. I also used the appropriate amount of flaps to help get off.

It is important for folks to understand the leaning a carb is different than leaning an FI servo. A carb must be leaned to a specific power setting and any changes to that need further adjustment of the red knob On a servo, the leaning mechanism is somewhat variable and power changes, within limits, will have a similar amount off leanness. With a carb, you cannot lean to a setting at runup (1800 RPM) and expect that setting to work at 2700 RPM without being dangerously lean.

While I have never done it, I would be a bit worried that leaning to an EGT taget at 1800 RPM with an FI may leave me too lean for 2700. I have not experimented with the variable range in the FI leaning to be sure this wide of a range is supported, so I don't use that runup leaning method.

Larry
 
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Practice at altitude?

It seems exploring and practicing high DA TO and leaning can be explored and practiced at altitude. I realize it’s not purely static, but slow it down to Vs1 plus a few (or even more than a few knots, Vx maybe?) trim for takeoff, set it up and go a few times. Slow flight practice bonus! Seems like an easy way to simulate a mixture starting point without the stress of an actual takeoff in the mix. I did this during my phase 1, and came up with a guide of turns vs DA that seems to be a good starting point.
 
My Cessna Manual

It is important for folks to understand the leaning a carb is different than leaning an FI servo. A carb must be leaned to a specific power setting and any changes to that need further adjustment of the red knob On a servo, the leaning mechanism is somewhat variable and power changes, within limits, will have a similar amount off leanness. With a carb, you cannot lean to a setting at runup (1800 RPM) and expect that setting to work at 2700 RPM without being dangerously lean.

While I have never done it, I would be a bit worried that leaning to an EGT taget at 1800 RPM with an FI may leave me too lean for 2700. I have not experimented with the variable range in the FI leaning to be sure this wide of a range is supported, so I don't use that runup leaning method.

Larry

MY Cessna manual says to lean at full throttle run up, not at 1800 RPM, when preparing for high density takeoff. Although with the tired Cessnas I fly, I dont think they get much above 1800 anyway at full throttle static.
 
It is important for folks to understand the leaning a carb is different than leaning an FI servo. A carb must be leaned to a specific power setting and any changes to that need further adjustment of the red knob On a servo, the leaning mechanism is somewhat variable and power changes, within limits, will have a similar amount off leanness. With a carb, you cannot lean to a setting at runup (1800 RPM) and expect that setting to work at 2700 RPM without being dangerously lean.

While I have never done it, I would be a bit worried that leaning to an EGT taget at 1800 RPM with an FI may leave me too lean for 2700. I have not experimented with the variable range in the FI leaning to be sure this wide of a range is supported, so I don't use that runup leaning method.

Larry

Since I wrote the post referred to, I’ll comment:
1. I did say that, wrt setting up best power during a normal runup, ‘you need to trust your FI system’ to maintain that mixture at full power.
2. I very much disagree with the quoted post. The entire purpose of a carb or FI system is to provide a constant fuel/air mixture over the range of throttle settings, and if it is not doing so it is not working properly. (Before someone else brings it up, yes, some systems are designed to add extra enrichment at full throttle. This is to add detonation resistance at full throttle sea level, but at any rate means at high density altitudes you’ll be a little extra rich, which is much better than being too lean.)
3. Yes, Cessna recommends a full throttle run up. But in the real world, that needs to be balanced against (1) possible prop damage from any loose rocks/gravel that are pulled up into the stationary prop arc at 2700 rpm; (2) the near certainty of very high CHT’s on our tightly cowled engines with virtually no airflow.
 
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I will put my asbestos suit on before I post this.

About 20 years ago, I overnighted at Rawlins (KRWL). Field elevation 6,817 and runway length 7,000. I thought I had the mixture adjusted correctly for the takeoff roll in the morning. I pulled onto the runway, added full throttle (I have a constant speed prop so RPM control [blue knob] was full forward) and did not get full (2,700) RPM. (IIRC, I only had 2,300 or 2,400.) I moved my hand to the mixture, rotated it out until I got full RPM and was airborne in a second or two longer than what a normal low altitude takeoff would have been.

This is not the best technique but it was how I learned to adjust mixture for higher elevation takeoffs. Yes I have been to Leadville and Taos also.

Full power runup with my 160 HP and constant speed prop is not possible as the airplane is not heavy enough to keep from skidding even at higher altitude airports. I guess at mixture setting and will make mixture adjustments as necessary on the takeoff roll.
 
Ground roll

Full power runup with my 160 HP and constant speed prop is not possible as the airplane is not heavy enough to keep from skidding even at higher altitude airports. I guess at mixture setting and will make mixture adjustments as necessary on the takeoff roll.

If your plane is not haevy enough for a full power run up, I am guessing the ground roll is pretty short. Just saying.
 
If your plane is not haevy enough for a full power run up, I am guessing the ground roll is pretty short. Just saying.

From your signature, you haven’t finished your RV yet....you’re in for a treat!

Most single and two-seat RVs with a constant speed prop will slip the brakes or skid at full power on the ground.

Paul
 
2. I very much disagree with the quoted post. The entire purpose of a carb or FI system is to provide a constant fuel/air mixture over the range of throttle settings, and if it is not doing so it is not working properly.

In the case of a carb, this is only true at red knob settings greater than what the carb needs to achieve that goal. Carbs do not have an adequate method of dealing with air density, the way that an FI servo does. Therefore, they add a gross fuel flow valve upstream of the jets to allow the pilot to override the fuel metering function on the rich side, by reducing fuel available to the jets. This valve can reduce total flow to the jets, allowing the pilot to force the leaner mixture necessary due to reduced air density.

You can prove this on your own. Go to 10K and lean for 150 ROP at full throttle. Then decend to 3K and go WOT to see what happens. You can also leak for 150 ROP at 3K and climb to 10K without touching the red knob and see what happens.

On a carb, the red knob sets max fuel flow through the carb. THerefore, the carb cannot self-adjust the mixture above this gross flow setting. A servo uses a very different leaning mechanism and allows greater variability.

Larry
 
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Larry, we seem to have drifted off topic. I think everyone agrees, neither a carb nor a FI system properly keeps fuel/air mixture ratio constant when the air density is changing. But the OP was about high density altitude take offs, where setting the mixture and then taking off are both done at the same density altitude. If you change the throttle setting but not the altitude, the carb should maintain the same fuel/air ratio. That’s exactly its function, what it was designed to do.
 
If below 75% power full power run up and max RPM or First Cyl to peak EGT (and enrich slightly for smooth operations. No EGT lean to roughness than enrich for smooth operation.
For fixed pitch prop MAX RPM and enrich slightly.

Watch this video from Rod Machado. Link is queued to where he gets into technique. Recommend your go to start of video
https://www.youtube.com/watch?v=eBUfWI4C6sE&t=258s

This is what Lycoming says to with your normally asperated dinosaur juice to thrust conversion machine.
https://www.lycoming.com/sites/default/files/Fuel Mixture Leaning Procedures.pdf

KGJT ?
Carbureted ?
Fixed or Constant Speed Prop ?
EGT gauge or gauges ?
Fuel Flow gauge with table calibrated in % power ?

I'll assume YES, YES, CS, EGT all jugs, NO calibrated FF to DA % Pwr Chart

So full power, first to peak is the lean setting for about max power. Personally I enrich 100-150F from peak.

I typically don't do full power runups on the ramp/runup area which can pick up rocks and ding the prop. Also it is mostly likely hot and static full power runups will get your engine cooking under the cowl. Not really great. especially for Carb'ed planes (vapor lock). I will lean approximately for DA and then make adjustments on roll. My Approx lean starting point is during runup (2000 RPM typically but may bump it up to 2100 to 2200 RPM), ignition L&R check, prop cycle, carb heat/alt air check, lean to where I see EGT starts to rise. Tank selected as desired boot pump on. I adjust the mixture on the roll. You can also use engine sound and feel.

Most certified GA airplane AFM/POH have recommended technique to lean for high altitude departure. If you don't have high DA leaning for takeoff in your POH, consider adding it. Do you have takeoff distance and climb rates at different weights and DA's in your POH? Fuel Flow (FF) can be used to determine power vs DA vs Pwr. It requires you make a chart or table.

KGJT is just under 5000 ft elevation seen a 85 degree day this year already. DA = + 8000 ft very possible summer time. So that is about 75% power. Therefore leaning for maximum power is needed. Aggressively leaning above 75% power could cause detonation and engine damage or failure.
.
KGHT has a 10,000 ft Rwy and a 5,000 ft Rwy. Take off is not an issue. However what about departure climb, enroute climb out and enroute planning? High winds in mountains areas is a different story than the flat lands. If they are high at surface or at altitude it can create severe turbulence and down drafts. You might want to review FAA and other publications on mountain flying flight planning and operations.

Another great video... no fear of the RED KNOB
https://www.youtube.com/watch?v=_VfiPuheeGw

Have a fun safe flight. :)
 
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Larry, we seem to have drifted off topic. I think everyone agrees, neither a carb nor a FI system properly keeps fuel/air mixture ratio constant when the air density is changing. But the OP was about high density altitude take offs, where setting the mixture and then taking off are both done at the same density altitude. If you change the throttle setting but not the altitude, the carb should maintain the same fuel/air ratio. That’s exactly its function, what it was designed to do.

I agree with a servo, but not a carb. If I take my carb'ed engine to 10K DA it will be very rich at high power settings without using the red knob to lean. Lets say my engine wants 13 GPH at SL and 2700 RPM, yet wants only 11 GPH at 10K DA and the same RPM. The carb cannot adjust for that on it's own, as it meters mostly off of air velocity through a fixed oriffice (the venturi) and that doesn't change much due to density (it changes some, but not a lot). If you recall, back in the 70's the car manufacturers used to offer high altitude packages and these were just different jets in the carb to flow a leaner mixture. Hence the need to restrict fuel flow via the red knob. The red knob can only set a max fuel flow rate. It doesn't create a somewhate sliding reduction like the FI servo does (it has a more sophisticated mechanism).

Now let's say that at 10K DA, my engine wants 11 GPH at 2700, yet it only wants 8 GPH at 1800 RPM for the same air fuel ratio. If I lean during run up to 8 GPH to make the engine happy at 1800, I will be very lean at 2700, where the engine wants 11 GPH. This is why the POH's for O series engine all say to runup to full throttle then lean for high DA and I agree with that. Only making the point that it doesn't work if the mixture is adjusted at 1800 RPM and then take off at 2700 RPM. And this is due to the carb's gross fuel flow valve that is tied to the red knob.

At full rich, the carb does exactly as you describe. But once you start reducing fuel flow via the red knob, it no longer does, as you have restricted total fuel flow and limited the top end of the fuel flow.

Larry
 
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I had been leaning aircraft for best power forever flying in Colorado. Now that I have a g3x with tons of info on chts and egts I have changed my technique to running almost full rich on the take off run. I usually am just a few turns lean resulting in 14-16gph or so and 1200 on EGTs. If I use the roughness plus a few turns in, EGTS spike on the ground roll (not really an issue in itself) but will eventually result in things getting a bit warm. It makes sense when you are running a flight school plane and ultimately just want best power for the best performance but I like to think I run my engine for longevity. I never get any roughness and prefer to keep things cool at the expense of a bit of extra fuel. Performance in the -14 is generally not an issue even at full gross. Once a few hundred feet is reached I pull back RPM to ~2500 RPM and begin leaning to 150 ROP (~1250ish) for climbout. Once at cruise I will switch and run 50-75 LOP (~1350). This procedure will allow me to climb straight out of boulder to 13,000 ft plus over the divide while keeping CHT's well under 400 (usually mid 300s on climbout and low 300s in cruise. ) I also sometimes run LOP in a 125 KIAS climb which with the G3X is easy to be precise about and keep things equal or even cooler.
 
I had been leaning aircraft for best power forever flying in Colorado. Now that I have a g3x with tons of info on chts and egts I have changed my technique to running almost full rich on the take off run. I usually am just a few turns lean resulting in 14-16gph or so and 1200 on EGTs. If I use the roughness plus a few turns in, EGTS spike on the ground roll (not really an issue in itself) but will eventually result in things getting a bit warm. It makes sense when you are running a flight school plane and ultimately just want best power for the best performance but I like to think I run my engine for longevity. I never get any roughness and prefer to keep things cool at the expense of a bit of extra fuel. Performance in the -14 is generally not an issue even at full gross. Once a few hundred feet is reached I pull back RPM to ~2500 RPM and begin leaning to 150 ROP (~1250ish) for climbout. Once at cruise I will switch and run 50-75 LOP (~1350). This procedure will allow me to climb straight out of boulder to 13,000 ft plus over the divide while keeping CHT's well under 400 (usually mid 300s on climbout and low 300s in cruise. ) I also sometimes run LOP in a 125 KIAS climb which with the G3X is easy to be precise about and keep things equal or even cooler.

I'm based over in Durango (KDRO) at 6,689 ft above MSL. I've got an O-360-A1A. During run-up I adj mixture to full-rich, throttle up to 1700 rpm, and then lean for about a 30-40 rpm rise from full-rich. I typically take off from KDRO at about 1,270 F EGT and 12.8 gpm. Once airborne I'll raise the flaps and immediately pull the prop back to 2500 rpm. I'll climb out to about 1000' AGL at 2500 rpm then pull the prop back to 2400 rpm for the remainder of my climb. Typical climb airspeed is 125 mph IAS. I will lean during climb to maintain ~1275 F EGT. Once at cruise altitude, I'll level off, pull the prop back to 2300 rpm and lean to about 7.3 gpm. Like you, my CHT's during climb are around 330-340 F and low 300's during cruise. Peak EGT on Cyl#1 during cruise is about 1394 F. I typically fly about 5-6 F LOP which is about as good as I can squeeze out of my carbed engine (with one PMag). At these altitudes, I typically fly WOT at all times except during descent and landing. I'm not suggesting this is optimal, but it seems to work well for me. I'm always looking for suggestions how to improve on this.

In 2017, when I redid my tailwheel endorsement in a Citabria (FP prop) over in Ft. Collins (KFNL) at 5,016' above MSL, the CFI/owner would advise running up full rich to 1800 rpm, then lean for max rpm, and then adjust the mixture knob to a position ~halfway between there and full rich for takeoff.
 
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