Leaning for high density altitude take off

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JOhnH

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I have read a couple of threads about this but haven't found exactly what I was looking for. Living in Florida we don't practice high altitude take offs much. We are also sort of new to complex aircraft.

We are now flying around the West. Yesterday we left KELP (el ~4,000 / DA~6,000). We first attempted to lean to max RPM during run up. Duh. Constant speed means just that. So then we ran the engine up to 1700 and leaned to peak egt. But even then we only saw relatively low values and only slight increase.

The POA merely says to lean according to current conditions but doesn't give procedures.

Later this week we plan to go to Santa Fe. Elevation ~ 6,400 and DA > 9,000. I figured I could use some good advice on proper leaning for this takeoff. The plane is a '67 Bonanza V tail with an IO520 with Gami injectors. Just two of us and luggage.
 
I don't know if the flow gauge in your Bo has it, but I used to fly a Debonaire that had a leaning scale by density altitude. You went full throttle, and leaned to the DA on the scale. It worked. Short of that, you would have to do a full power runup and lean about 50 degrees rich of peak.
 
Sac Arrow said:
I don't know if the flow gauge in your Bo has it, but I used to fly a Debonaire that had a leaning scale by density altitude. You went full throttle, and leaned to the DA on the scale. It worked. Short of that, you would have to do a full power runup and lean about 50 degrees rich of peak.
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I guess part of my question was whether it is ok to do a full power run up on the ground. If so I expect it would need to be kept as short as possible.
 
My method. No guarantees. BTW, I have a CS/controllable prop so I can change RPM or not, as I choose.

At elevations above 4000' MSL I lean to peak EGT on the hottest cyl at 2000RPM then I go about 150F richer from there. this is roughly 10% richer than peak EGT which is going to be close to perfect stoich. Plan to watch your CHT on climbout and adjust mixture as needed once the gear is up and stowed.

BTW, I am not a fan of KSAF.
 
JOhnH said:
I guess part of my question was whether it is ok to do a full power run up on the ground. If so I expect it would need to be kept as short as possible.
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Yup, the naturally-aspirated folks do them all the time around here. After you do the first one they are quick/easy to do. I don't know your engine but I'd suggest somewhere around 100 to 125 degrees rich of peak. Perhaps the POH suggests a temperature for best power. I would not use peak EGT or anywhere near peak for take-off power.

Spending some time/$ for high DA operations and mountain flying training is a good idea if you're planning to spend much time around our hills.
 
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On my aircraft, I do lean to peak RPM with a constant speed prop. Not sure why this wouldn't work on a Bo also. With the prop control set to max RPM there shouldn't be anything stopping the RPM increase.

On a normal summer day in Denver, if I start full rich at 1700, by the time I'm done leaning I'll often have reached 2000 RPM. If I start a bit lean of full rich and 1700 RPM, then lean to max RPM I'll end up at 1900.

With a TR182, aggressive leaning is a rule. Full rich is virtually always too rich in that airplane and it's notorious for, and I have personally encountered, fouled plugs.

I always lean to peak RPM during runup even at sea level. I lean for taxi right after startup also. If the engine is warm I sometimes even lean a bit for startup and then dial it back even more before taxi. Sometimes it's so lean that I have to enrich it a bit when I power up to taxi or it will try to die while taxiing. I then go not-quite-full-rich during runup, power up to 1700, and lean to peak RPM from there.
 
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Yes, you can lean to max RPM in a CS prop if the throttle is low enough that you're on the stops. There may be a correction factor depending on model, to project part throttle to full throttle. When in doubt, do a full throttle run up.

The full rich on takeoff thing depends on density altitude. On a stupid-hot day, you may need to lean for takeoff even at low-elevation airports. Like Fresno in August (BTDT, and you could really feel the power loss when going full rich).
 
Clark1961 said:
Yup, the naturally-aspirated folks do them all the time around here. After you do the first one they are quick/easy to do. I don't know your engine but I'd suggest somewhere around 100 to 125 rich of peak. Perhaps the POH suggests a temperature for best power. I would not use peak or anywhere near peak for take-off power.

Spending some time/$ for high DA operations and mountain flying training is a good idea if you're planning to spend much time around our hills.
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Yep. Colorado Pilots Assoc. recommends a full-power runup at mountain airports.
 
Sac Arrow said:
I don't know if the flow gauge in your Bo has it, but I used to fly a Debonaire that had a leaning scale by density altitude. You went full throttle, and leaned to the DA on the scale. It worked. Short of that, you would have to do a full power runup and lean about 50 degrees rich of peak.
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Yes. All the Bos and Barons I've flown had the DA on the fuel flow gauge.

Absent that, full power runup while adjusting the mixture works. You can do it on the runway at the beginning of the takeoff roll. Go full throttle and adjust mixture to get best power. You'll be able to tell by the sound and feel alone.
 
Fearless Tower said:
What don't you like about SAF?
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Too many runways to choose from? too many coyotes on the many runways? the standard 20 to 30 kts of wind? the tower folks who can't see you on the downwind to one of the many runways?

:D

SAF can be entertaining in many ways...
 
Clark1961 said:
Too many runways to choose from? too many coyotes on the many runways? the standard 20 to 30 kts of wind? the tower folks who can't see you on the downwind to one of the many runways?

:D

SAF can be entertaining in many ways...
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Why can't tower see you on the downwind?

I was just there a few weeks ago. Even did a night IFR departure. Didn't see any issue with any of the above.
 
My Lycoming 360 Hartzel constant speed prop carbureted runups at 2000rpm. Lean until rpm drop, richen a little. Just like a fixed pitch prop.

The prop govenor is made so it allows an rpm drop, THEN starts going constant speed . Built this way on purpose so you can lean it. Its not actually at the stops, but it acts like it. Its sort of like "hunting" with cruise control or any control system. They enlarge that zone a bit, so you can use fixed pitch prop leaning techniques.
 
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The general procedure taught by most CFIs in Colorado is to do the leaning to max RPM at run-up power (where the prop acts like it is is fixed) and make a minor adjustment for full power needs and cooling. That minor adjustment is typically three twists of a vernier mixture control or 1/4-1/2 inch of a lever control.

Simple and a good ball park, although, especially until one has some experience with it, one should be prepared for the need for a tweak. A very brief movement to full power on the ground will tell you.
 
In my Dakota (CS prop), I lean to max rpm starting at a rough guess for the mixture and 2000 rpm. Once I find peak, I go a tad more rich.
 
Target EGT method. Easy Peasy, especially if you are coming from Florida.

My full power takeoff EGT at sea level is 1290 degrees.

I dial that temp in early in the takeoff roll at every airport and maintain that EGT through climb.

Done.

http://www.advancedpilot.com/tech.html
 
Sac Arrow said:
I don't know if the flow gauge in your Bo has it, but I used to fly a Debonaire that had a leaning scale by density altitude. You went full throttle, and leaned to the DA on the scale. It worked. Short of that, you would have to do a full power runup and lean about 50 degrees rich of peak.
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The T-41B has the same thing.
 
ElPaso Pilot said:
Target EGT method. Easy Peasy, especially if you are coming from Florida.

My full power takeoff EGT at sea level is 1290 degrees.

I dial that temp in early in the takeoff roll at every airport and maintain that EGT through climb.

Done.

http://www.advancedpilot.com/tech.html
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I'm sure you know that you are not producing full power when you are full rich at sea level. Your engine produces rated power, but not full power. The same will be true for altitude adjusted power setting by this method. You will produce rated power for the altitude reduction, but no more. So, while this is safe, if one relies in the book values for take off and weight, one could get more power out of the engine from the derated DA value by tuning to a better EGT value, while not worrying about detonation margin.

Frex; If your engine is rated at 250HP at sea level with the mixture full rich at 2700RPM, you will make that power on a STP day, but there is more power available by getting closer to stoich. At altitude, the derated power may be only 200HP when following the target EGT method, but more HP is available by raising the EGT from rich of peak, to closer to peak. This can be done safely without worrying about detonation or pre-ignition because you are still well below the HP rating at STP.
 
I'm just here for the word "stoich". :)

Seriously though, don't overthink this whole thing. Unless you need every bit of BHP your engine can muster (and you already know because you did the takeoff calculations and you already know you're going to need three times as much runway as at home, today, while it's hot out...) leaning to max RPM on run-up and a couple of richer half turns of the vernier mixture is going to be fine. Then adjust like you're cruise climbing at home up to 8000+' since at any DA where you'll need to worry about it much, that's probably what you took off at around here. Airport at 5883, and it's warm out...

If you need every bit of the engine power then you'll want a full power run-up. If your book says you'll be making 65% BHP today or less on the ground, leave it there. If you'll be making a little more, give it a half twist in and be prepared to adjust on climb out.

If you have an EGT gauge or a nice engine monitor, feel free to get precise, but thousands of airplanes have successfully conquered the "lean for takeoff" out here without them for decades. No sweat.

The bigger problem here is ground leaning. In fact, we don't even start our O-470 full rich anymore after our mechanic showed us how silly that was, years ago. Set that mixture to where it'll idle richer than you'd set it for taxi and it'll fire in a single blade. And then lean the crap out of it for taxi to the point where if you add throttle it'll cough, and you have to twist that vernier on the mixture a half a turn to make taxi power. I lean very aggressively on the ground. I have to twist the mixture in two full turns before the run up can even happen.

Had a friend who came here from elsewhere have an incident where they had fuel pouring out of the bottom of a 182 cowl because they were used to doing everything full rich. Very lucky on a hot summer day that they didn't have an ignition source under that engine.

But don't get too wrapped around the axle about it. Lean some for start, lean aggressively for taxi, richen it up a bit and lean to peak RPM at run-up well below the prop governing speed, and tweak that a tiny bit richer -- and in all but the "I need every last ounce of power to make this takeoff" scenario, you'll be fine. If you do, full power run up and try to park it somewhere clean of debris. If no where is clean of debris, get it close and do it during the takeoff roll, but be ready to abort it if the runway is that small to begin with.

After enough time in the same airplane, you'll be able to set it by just knowing where it should be, and you'll know if something is weird because it won't be where it should be during taxi. (I get an almost 200 RPM rise when I lean aggressively for taxi, at idle. In fact if it's level, just leaning appropriately will give me enough power to just barely start rolling forward with the brakes off and is plenty for taxiing out, once the inertia is overcome.)
 
Did Deakin or some other pundit not say big bores should be run at 250ROP on t-o & climb?
 
Let'sgoflying! said:
Did Deakin or some other pundit not say big bores should be run at 250ROP on t-o & climb?
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I don't think it was 250, but you're probably thinking of the "red box". I try to keep ours at least 75 ROP, not 50 as the book says. 50 is squarely in that high pressure range that isn't kind to the engine, if you are a "believer" of this stuff. I believe the box is not as much of a problem at low BHP, but that'd be a question for the "experts".

By the time I reach cruise altitude out here except in the dead of winter, I'm down into that 65% BHP range where nothing I can do can really harm the engine, other than not keeping it cool enough.

Ours just is one of those that hates even attempting LOP operation so we usually keep it ever slightly richer than peak at WOT and cruise altitude -- where it would be fine to run it at peak, technically, but done because peak will keep the CHT quite high on ours.

We'll see it on the single CHT gauge and also as an increase in oil temp over a long flight at cruise. Slightly rich, I like where the needles end up a better for my tastes, but it's very airframe and engine specific when tweaking for cruise at high altitude/high DA.
 
docmirror said:
I'm sure you know that you are not producing full power when you are full rich at sea level. Your engine produces rated power, but not full power. The same will be true for altitude adjusted power setting by this method. You will produce rated power for the altitude reduction, but no more. So, while this is safe, if one relies in the book values for take off and weight, one could get more power out of the engine from the derated DA value by tuning to a better EGT value, while not worrying about detonation margin.

Frex; If your engine is rated at 250HP at sea level with the mixture full rich at 2700RPM, you will make that power on a STP day, but there is more power available by getting closer to stoich. At altitude, the derated power may be only 200HP when following the target EGT method, but more HP is available by raising the EGT from rich of peak, to closer to peak. This can be done safely without worrying about detonation or pre-ignition because you are still well below the HP rating at STP.
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I sure do. I also saw the OP was asking about flying out of El Paso (runways up to 12,000' at 3900' altitude) and Santa Fe (8300' long), not Leadville or Johnson's Creek.

Rated power will give book number performance every day of the week, without surprises. Which will work just fine for the OP's question, with 2 pax in an IO 520 Bo.

For a guy from South Florida flying into major airports, this will work just fine -- and he won't be belching black smoke and limping off the runway.

If we want to complicate his request with the typical POA stream of conflicting and/or complicated posts, we can do that too... but I don't think that's what he's looking for. :confused:



JOhnH said:
I have read a couple of threads about this but haven't found exactly what I was looking for. Living in Florida we don't practice high altitude take offs much. We are also sort of new to complex aircraft.

We are now flying around the West. Yesterday we left KELP (el ~4,000 / DA~6,000). We first attempted to lean to max RPM during run up. Duh. Constant speed means just that. So then we ran the engine up to 1700 and leaned to peak egt. But even then we only saw relatively low values and only slight increase.

The POA merely says to lean according to current conditions but doesn't give procedures.

Later this week we plan to go to Santa Fe. Elevation ~ 6,400 and DA > 9,000. I figured I could use some good advice on proper leaning for this takeoff. The plane is a '67 Bonanza V tail with an IO520 with Gami injectors. Just two of us and luggage.
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Fearless Tower said:
You can do it on the runway at the beginning of the takeoff roll. Go full throttle and adjust mixture to get best power. You'll be able to tell by the sound and feel alone.
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This, do it on the take off roll. You will be able to feel the best power then add a little throttle for a rich TO mixture. :yes:
 
ElPaso Pilot said:
I sure do. I also saw the OP was asking about .

If we want to complicate his request with the typical POA stream of conflicting and/or complicated posts, we can do that too... but I don't think that's what he's looking for. :confused:
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The thing I like best about high density altitude threads is the difference in recommendations made by people who regularly fly in those conditions and those who don't.
 
denverpilot said:
I believe the box is not as much of a problem at low BHP, but that'd be a question for the "experts".
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Not an expert, but that is what Deakin says - there is no red box at higher altitudes/low BHP. In most NA pistons, you can put the mixture anywhere above 7--8k and you won't be in the red zone.
 
I fly an IO550 Bonanza from a 6,000 feet msl airport and I would just forget the full power run up business. Just lean it back a few gph, and on the roll lean a little more over a few second period. Believe me, you'll know it when you start losing power so put in enough to feel the power come back and you are in the ball park. Contrary to what a lot of people think, I believe more planes have crashed at high density altitude from over leaning than running rich.
 
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midlifeflyer said:
The thing I like best about high density altitude threads is the difference in recommendations made by people who regularly fly in those conditions and those who don't.
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Doesn't mean we know jack about his Bo or IO-520.
 
Just lean for max RPM during runup. Simple pimple.

I just don't understand why people don't lean for max RPM at all elevations. I guess if you've tried it and determined that your engine gets best RPM full rich at sea level, so be it. But my engine always benefits from some degree of leaning - even at sea level. Maybe it's because mine has a turbo, dunno, but I recall doing this on my C172 years ago also.
 
petrolero said:
Just lean for max RPM during runup. Simple pimple.

I just don't understand why people don't lean for max RPM at all elevations. I guess if you've tried it and determined that your engine gets best RPM full rich at sea level, so be it. But my engine always benefits from some degree of leaning - even at sea level. Maybe it's because mine has a turbo, dunno, but I recall doing this on my C172 years ago also.
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errr.... constant speed props ....
 
petrolero said:
Just lean for max RPM during runup. Simple pimple.

I just don't understand why people don't lean for max RPM at all elevations. I guess if you've tried it and determined that your engine gets best RPM full rich at sea level, so be it. But my engine always benefits from some degree of leaning - even at sea level. Maybe it's because mine has a turbo, dunno, but I recall doing this on my C172 years ago also.
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If you are leaning before take off near sea level, in a plane with a turbo that might not translate well for others on this forum. Know the limitations before you try this at home. The mixture control has a full rich setting for a particular reason.
 
docmirror said:
If you are leaning before take off near sea level, in a plane with a turbo that might not translate well for others on this forum. Know the limitations before you try this at home. The mixture control has a full rich setting for a particular reason.
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That's why you do the runup at 1700 RPM. The turbo changes nothing at that RPM.

But it may have something to do with why my mixture control is so rich when at full - dunno.

In any case, why are you suggesting that leaning for max RPM during runup might not translate well for others? We've been hashing the "lean for max RPM" thing to death in this thread. Is there some elevation or engine type (turbine notwithstanding) above which it's OK to lean to max RPM -- but not below? I'm not aware of any.
 
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As I indicated in a previous post. My Lycoming 0-360 with a Hartzell constant speed prop leans the same way as a fixed pitch prop at its runup rpm of 2000.

At altitude it seems to lean the same way at ANY rpm.

The answer is complicated, but the prop gives enough of an rpm drop to let you know when its getting too lean. The reason it works like that is SO YOU CAN LEAN IT.

I dont know if all constant speed props work that way or not. I would think they would. Why? So you can lean them.

One thing you can do. You are in Florida. You are going to visit Denver. Go up to Denvers altitude above Florida and lean for max power. Note how far out the lean knob is. That is about how far out you want it on the ground in Denver.

Hope that helps.
 
petrolero said:
That's why you do the runup at 1700 RPM. The turbo changes nothing at that RPM.

But it may have something to do with why my mixture control is so rich when at full - dunno.

In any case, why are you suggesting that leaning for max RPM during runup might not translate well for others? We've been hashing the "lean for max RPM" thing to death in this thread. Is there some elevation or engine type (turbine notwithstanding) above which it's OK to lean to max RPM -- but not below? I'm not aware of any.
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It's a big messy subject. The short answer is that the mixture control on all planes are set to provide a comfortable margin of detonation avoidance in worst case situations. So, you are at sea level, on a cool dry day where the engine is capable of producing rated thrust at full rich. Your full 200HP is available to you simply by pushing in the throttle to the stop and letting the engine achieve full RPM. By reducing the mixture from full rich, you move toward a more perfect stoichiometric ratio and you will be able to produce greater than rated power, but - at the decrease in detonation margin. This is true with or without a turbo, however the affects of the adiabatic heating on the intake charge of a turbo engine requires even greater detonation margin, so leaning a turbo may put you in a regime of the engine where you are producing well in excess of 200HP, and are in a danger zone for detonation at the most critical phase of operation.

This thread is about leaning at altitude. You have advocated leaning at sea level. I've no experience with every make, of every engine, on every plane, but I don't recall any operations manual for GA aircraft where leaning at sea level is indicated. Having said that, there may be one, but I'm not familiar with it. The warning I provided was general in nature, that others thinking they can get 'free' extra power by leaning below ~4000' DA may be in for a rude surprise when the jug of the engine comes out the side of the cowl.

<edit: I would not presume to advise YOU personally on your operation of your particular plane. That's completely between you and your aircraft. But - for others, please understand there is no free lunch, and leaning on the ground(for takeoff), with full throttle and high RPM is a recipe that can lead to serious issues.>
 
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docmirror said:
It's a big messy subject. The short answer is that the mixture control on all planes are set to provide a comfortable margin of detonation avoidance in worst case situations. So, you are at sea level, on a cool dry day where the engine is capable of producing rated thrust at full rich. Your full 200HP is available to you simply by pushing in the throttle to the stop and letting the engine achieve full RPM. By reducing the mixture from full rich, you move toward a more perfect stoichiometric ratio and you will be able to produce greater than rated power, but - at the decrease in detonation margin. This is true with or without a turbo, however the affects of the adiabatic heating on the intake charge of a turbo engine requires even greater detonation margin, so leaning a turbo may put you in a regime of the engine where you are producing well in excess of 200HP, and are in a danger zone for detonation at the most critical phase of operation.

This thread is about leaning at altitude. You have advocated leaning at sea level. I've no experience with every make, of every engine, on every plane, but I don't recall any operations manual for GA aircraft where leaning at sea level is indicated. Having said that, there may be one, but I'm not familiar with it. The warning I provided was general in nature, that others thinking they can get 'free' extra power by leaning below ~4000' DA may be in for a rude surprise when the jug of the engine comes out the side of the cowl.

<edit: I would not presume to advise YOU personally on your operation of your particular plane. That's completely between you and your aircraft. But - for others, please understand there is no free lunch, and leaning on the ground(for takeoff), with full throttle and high RPM is a recipe that can lead to serious issues.>
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If you say so. I don't think there is that little margin between normal operations and detonation with 100LL fuel such that you'll detonate at max RPM. It's never caused a problem in any airplane I've flown - which have mostly been Cessnas, admittedly. And in my current aircraft it's virtually required if you don't want the serious issue of fouled plugs. And they don't mention that in the manual either.

But certainly the old "YMMV" is appropriate in this situation.
 
JOhnH said:
I guess part of my question was whether it is ok to do a full power run up on the ground. If so I expect it would need to be kept as short as possible.
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Unless you have a turbocharger, you're not doing a "FULL POWER" anything at high density altitude.

WOT is not Full Power. Once you get at or below max recommended cruise power, you can set the mixture any place you want from ICO to full rich (subject to the performance degredation).
 
petrolero said:
If you say so. I don't think there is that little margin between normal operations and detonation with 100LL fuel such that you'll detonate at max RPM. It's never caused a problem in any airplane I've flown - which have mostly been Cessnas, admittedly. And in my current aircraft it's virtually required if you don't want the serious issue of fouled plugs. And they don't mention that in the manual either.

But certainly the old "YMMV" is appropriate in this situation.
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I think your mixture may be adjusted wrong. Again, you keep talking about 'your' situation, which is fine for you, but please note - you are on a public forum, having said this: "I just don't understand why people don't lean for max RPM at all elevations." Which produced my counterpoint. Leaning for max RPM at all elevations can, and in some cases of high C/R situations absolutely will produce detonation. further detonation can be catastrophic even in small doses.
 
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