Density Altitude T/O Proceedures

[Pictreed]

I'd like to hear different methods for setting mixture for high density altitude takeoff. 

Tim

[Jeff_S]

During run-up at near full RPM, lean until you see your regular EGT ranges for a takeoff at sea-level altitude. That's probably around 1200° but go by what your engine usually shows. That's your fuel setting for takeoff.

But I wouldn't worry about this unless you're really in the mountains. If you're in the flatlands and its just a really hot day, I would use normal takeoff procedures.

[Vance Harral]

My method for an airport at 5000' MSL where DA approaches 8000' in the summer: advance throttle to 2000 RPM during the runup as normal, lean for peak RPM, then nudge the mixture forward a half inch or so from there.  On the takeoff roll I might make a quick adjustment based on EGTs, but I don't devote a lot of time or attention to it.

If that sounds imprecise, it is.  It should be.  If the difference between clearing the trees or not is a few tenths of a GPH in your mixture setting, you made a serious judgement error attempting to take off in the first place.

Edited August 30, 2016 by Vance Harral

[carusoam]

1) The O1 has a calibrated blue box for EGT.

2) 2-300°F ROP.  

3) G1000 panels use a white box.

4) Be confident in the procedure and how well it is working in your plane, before loading up your aviation college friends (Patrick's last flight).  People that were proven smart enough to know better...

5) Best done solo until you are comfortable.

6) Patrick's plane went into the trees at the end of the runway in Eastern PA.  No mountains required.  Hot and heavy, high DA....

7) Remember to use the full length of the runway.  The extra 200' of back taxi may make a difference...

8) warm temperatures rob power and thrust and lift... A trifecta of bad stuff.

9) Patrick's plane was a 200hp M20J.

Best regards,

-a-

[Pictreed]

I was taught Jeff's method.  It will be for a possible trip to Fort Collins in a couple weeks.  

I will definitely leave early in the morning on the way back. 

I might get some instruction while I'm there. 

[ArtVandelay]

I would not adjust for peak EGTs, you want to be about 100+ degrees ROP. I used standard runup procedures, full RPM seems excessive to me.

[N201MKTurbo]

27 minutes ago, Pictreed said:

I was taught Jeff's method.  It will be for a possible trip to Fort Collins in a couple weeks.  

I will definitely leave early in the morning on the way back. 

I might get some instruction while I'm there. 

When I bought my first Mooney I lived in the Denver area. I considered Ft Collins to be a low altitude airport.

[Pictreed]

I think I'm jonesing over it too much.  I've departed Midland with over 5000' density alt in a 172RG that was in horrible shape engine wise with a worried pax because we weren't climbing but it wasn't that bad. I need to make sure I go over the performance charts.

I'll get with some local CFI/Mooney Spacers to do some patterns to see their technique when I get there. 

[kmyfm20s]

With runways as long as KFNL I usually just leave the mixture 1/4" out and adjust it in or out on the ground roll. If its a shorter, high DA runway I will do a static run up and stay closer 25-50 ROP, since detonation is unlikely and I want all the power I can get. After I get off the ground and clear the obstacles I will richen it up to cool the cylinders if necessary. Static full power run ups at an airport like KTEX always makes me laugh. The plane rumbles around less at 2700 rpm than at sea level 1700 rpm. 

[Bob - S50]

When I flew through RKS and LMT this summer, I just took a guess.  I pulled the mixture out a couple inches to what seemed reasonable based on where it is in the climb at those altitudes when I'm using a target EGT.  Once I was at full power just after brake release I took a look at the EGT and made a quick adjustment.  If the EGT was too high I pushed it forward a bit.  If the EGT was only a little low I didn't mess with it.  If the EGT was way too low, I pulled the mixture out a bit.  Once I got airborne and cleaned up I then leaned to target EGT.

John Deakin uses the sawing method.  He just pulls and pushes the mixture in and out feeling for the difference in power.  Pull too far or push too far and the power drops.  He finds the sweet spot for max power based on seat of the pants.  I didn't have the nerve to try it though.

[Trailboss]

I would concur with Vance above.  Run-up to 2000 RPM, lean to peak, then 1 turn rich on the knob.

Forget summer, I took off from Evanston, WY last Saturday at 0730, OAT was 10C, DA 7900'

[N9201A]

Too many of us do this for the first time in a long time when it is for real.

Remember while you're distracted by mixture/EGTs etc on takeoff how critical speed control is. The climb performance lost from diverging from Vx/y can be startling. Next time you're at altitude, slow down and practice a climb out as if from a high DA situation. See what your airplane can actually do and what a difference speed variations make.

Sloppy technique doesn't matter at SL and 1,000 fpm climb. But it will create problems at high DAs, especially with the stress of the ground not falling away as it usually does. You did plan your safe route out and around ground obstacles and/or back to the field at 100' all, right? Why crash trying to clear an obstacle when nearby terrain falls away or a heading change avoids it?

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[midlifeflyer]

1 hour ago, N9201A said:

Too many of us do this for the first time in a long time when it is for real.

Remember while you're distracted by mixture/EGTs etc on takeoff how critical speed control is. The climb performance lost from diverging from Vx/y can be startling. Next time you're at altitude, slow down and practice a climb out as if from a high DA situation. See what your airplane can actually do and what a difference speed variations make.

Sloppy technique doesn't matter at SL and 1,000 fpm climb. But it will create problems at high DAs, especially with the stress of the ground not falling away as it usually does. You did plan your safe route out and around ground obstacles and/or back to the field at 100' all, right? Why crash trying to clear an obstacle when nearby terrain falls away or a heading change avoids it?

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Not a bad idea but it is very difficult to truly approximate a high density altitude takeoff situation. You can manage to hit maybe one or two variables but not all of them. From a basic human factors standpoint, an anemic climb at 7,000 AGL looks and feels nothing like the same climb at 50 AGL when the density altitude on the ground  is 7,000' and the end of the runway is coming faster than usual. 

[midlifeflyer]

FWIW (I've posted it before; it's a cut and paste), here's the technique typically taught by CFIs in Colorado:

If you are operating for the first time in a high density altitude environment, local instruction is always your best bet because it's not just about the effect on power. That said, this is the method generally taught at flight schools in Colorado.

Target leaning for max power is done at runup this is for two reasons other than it just works for all but a very few make/models (yes, it definitely works in a 182).  One is that leaning at full power can be hard on the brakes of higher performance engines; the brakes might not even hold in some. The other is that, a constant speed prop will act like a fixed pitch one when set at runup rpm.

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. 

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 (a lot of instructors I know 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. The exact check varies. It's often simply getting expected rpm but you might have a table of fuel flow targets for takeoff to measure against. Personally I have never had to move the mixture more than a 1/2 twist or its equivalent - 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.

 

[N9201A]

You're making my point for me. The focus should be on the numbers and performance not "look and feel" and "faster than usual." As far as end of runway coming, you did plan your abort point before commencing your takeoff roll, right?

Obviously one cannot safely duplicate terrain proximity while at a safe altitude from it. But that's not what you're duplicating; it's the aircraft performance, which should be the focus...NOT the extraneous distractions that will cause/contribute to an accident that could've been avoided had the pilot stuck with the objective and ignored the subjective.

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[TTaylor]

Just for a little comfort if you are new to flying at higher density altitude, you don't have to lean for take off.  I often operate at 8,000 ft DA or higher.  Lean for taxi, but just push full rich and max rpm on take-off.  Pull the rpm's back to climb (usually 2600 rpm for me) after gear-up and climb rate is established.  After about 1000 ft agl start leaning keeping at least 100 degrees rich of peak.   Last week I climbed from 100 feet msl to 13,5000 from central California to cross over South Lake Tahoe.  I just leaned holding 100 rop for the entire climb.  

If you are concerned about leaning too much so that you are developing less than full power, just don't lean.  

[midlifeflyer]

8 hours ago, N9201A said:

You're making my point for me. The focus should be on the numbers and performance not "look and feel" and "faster than usual." As far as end of runway coming, you did plan your abort point before commencing your takeoff roll, right?

Obviously one cannot safely duplicate terrain proximity while at a safe altitude from it. But that's not what you're duplicating; it's the aircraft performance, which should be the focus...NOT the extraneous distractions that will cause/contribute to an accident that could've been avoided had the pilot stuck with the objective and ignored the subjective.

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I don't disagree on the "shoulda". My point is the fact is that we do see and feel the environment when we take off. We can prepare ourselves with knowledge of performance and adjust our expectations a bit, but the sensations and extraneous distractions of look and feel are not easy to overcome. 

I gave just enough high density altitude and mountain transition training to pilots in Colorado to have seen it in action personally as well as in the analyses of accidents.. That's why I agreed with your post about doing it at altitude but pointed out it has limitations.

[midlifeflyer]

4 hours ago, TTaylor said:

Just for a little comfort if you are new to flying at higher density altitude, you don't have to lean for take off.  I often operate at 8,000 ft DA or higher.  Lean for taxi, but just push full rich and max rpm on take-off.  Pull the rpm's back to climb (usually 2600 rpm for me) after gear-up and climb rate is established.  After about 1000 ft agl start leaning keeping at least 100 degrees rich of peak.   Last week I climbed from 100 feet msl to 13,5000 from central California to cross over South Lake Tahoe.  I just leaned holding 100 rop for the entire climb.  

If you are concerned about leaning too much so that you are developing less than full power, just don't lean.  

Maybe. I've also seen pilots who have been lucky by having their engines quit on the ground during the takeoff roll for too rich a mixture.

[N9201A]

Training, training, training...we overcome distractions by conditioning ourselves to not be distracted. Focusing on objective performance criteria will better equip pilots to handle situations varying from what the "expect." It also creates rote responses that are safe and ingrained, so one (hopefully) does the safe thing regardless of stimuli.

How many stall/spins have we read about or seen occur because of the same issue? Pilots who always do what "looks about right" or what they "normally" do won't have a problem...until it's not working. Look and feel can trick you, as anyone who's wandered VFR into IMC can attest...if they made it out.

Sure, there are limitations to any training (it's training) but that's not a reason not to do it. And if it serves its purpose, the limitations are irrelevant.

As far as training limitations, I admit I could see out of the corner of my foggles on my instrument checkride, maybe just a little. Anyone know if the limitations statute has passed?

[midlifeflyer]

We seem to be in violent agreement.

[TTaylor]

8 hours ago, midlifeflyer said:

Maybe. I've also seen pilots who have been lucky by having their engines quit on the ground during the takeoff roll for too rich a mixture.

I have seen many more of the opposite, Too lean as they try to develop power and the engine is starved.  They end up with either a lack of power or an engine that is missing badly.  I agree it is a good idea to lean, but from what we see here in the inter-mountain west most of the problems come from being too lean rather than too rich.  I have never seen a fuel injected engine have a problem with density altitudes between 7,000 to 10,000 feet.

[MB65E]

On August 30, 2016 at 2:45 PM, Pictreed said:

I think I'm jonesing over it too much.  I've departed Midland with over 5000' density alt in a 172RG that was in horrible shape engine wise with a worried pax because we weren't climbing but it wasn't that bad. I need to make sure I go over the performance charts.

I'll get with some local CFI/Mooney Spacers to do some patterns to see their technique when I get there. 

The 172rg is a sorry excuse for a retractable gear airplane. I've have 4 people in it several times. Close to gross, and it really knows it's heavy. That's one of the few airplanes I think that the books overestimate its performance. There are a lot of tired 172rgs out there as well...

The Mooney sure flys a lot better!!

-Matt

[midlifeflyer]

15 hours ago, TTaylor said:

I have seen many more of the opposite, Too lean as they try to develop power and the engine is starved.  They end up with either a lack of power or an engine that is missing badly.  I agree it is a good idea to lean, but from what we see here in the inter-mountain west most of the problems come from being too lean rather than too rich.  I have never seen a fuel injected engine have a problem with density altitudes between 7,000 to 10,000 feet.

Interesting how perspectives can be different. I recall seeing far more too rich issues than too lean issues during my 20 years in Colorado.

[Brian Scranton]

All I ever do is fly at high DA. Lucky me, I guess. I don't notice much of a difference at DAs from 6000-7000. Any higher and if I am full rich, the engine will burp as I advance the throttle. So, I lean for DA on the run up--if you have a vernier knob, a lot of instructors teach an easy method of pulling it about an inch...or to your first knuckle. But I have found this to be less important on a very hot, high DA day--what seems to be most important, at least for me, is airspeed and angle of attack. 

On high DA days, Vr should be 70-75mph, not 65mph. And as soon as you are off the runway, level the nose in ground affect or just above it to get to 100mph, then begin your climb. If you immediately get to a climb attitude you'll just hang there at 100fpm which is SCARY. 

But again, it's really not a big deal unless you are trying to take off from a 2500ft runway. Most western runways a nice and long. So use that length and have fun!