Turbocharged engine, leaning for takeoff at High DA?

[RussR]

I may have a gap somewhere in my knowledge.

Recently I flew into an airport at 8000 MSL. DA was about 10,000. This was in a Cessna 421C, a turbocharged airplane.

When I went to take off, I pushed the power up with full rich mixture and the engine bogged down, way down, almost quitting. This is the behavior I would expect from a non-turbocharged engine if I went full rich at 10,000 DA.

When I leaned it out some it returned to life and I took off with no problems.

But this engine is fully capable of making sea-level rated power at 10,000. MP is right where it normally is for takeoff at 39" with the automatic wastegate keeping it there. So should I not be able to go to full rich regardless of DA?

Is it model specific? Or might there be something that needs adjusting on this airplane? I seem to remember encountering this same issue with other airplane models as well.

I have read the POH and it doesn't say anything different about high-altitude takeoffs.

I have taken (and given) mountain flying instruction, but it has always been in NA airplanes, so if this is a gap in my knowledge please help me fill it in.

 

[Checkout_my_Six]

physics.....what happens to the mixture when the NA density increases? The mixture gets richer...cause there is less oxygen. You needed to lean. Nothing wrong with what you figured out....good thing you had plenty of runway to make that determination.

Now....you are thinking that boosted pressures should compensate for NA?....what about the OAT? Hi OATs require leaning to make power.

My routine takeoff in my turbo is to go full MP redline....then adjust mixture fuel flow to takeoff max power on the roll....and go from there. Once clear obstacles....enrichen the mixture to keep the CHTs down.

 

[wsuffa]

The Lyc manual for certain TC engines has a phrase: "lean only the minimum amount necessary for takeoff at high altitude airports (above 8000'')"

That may well not apply to every engine, and was not included in the POH (that I recall) yet was in the engine manual. I recall having to do that only once with my plane, but I don't recall where.

Many TC engines operate above SL pressure during takeoff/climb - depending on the engine and TC controller (if any) it may still be too rich without leaning. But leaning can put you into a situation where temperatures become a problem during climb. YMMV.

 

[jesse]

You were too rich to generate enough non-boosted power for the turbos to spin up and it sounds like you may have applied throttle way too quickly, making the situation worse. Bit of a chicken and egg problem. Ease the throttles up and I bet you’d have a better result.

Once you’re making your full sea level MP, you’d definitely want to be at full rich.

 

[denverpilot]

Yeah. Slower.

Even properly tuned turbodiesels smoke at this altitude if you stomp on the pedal, until the turbo spools.

Many outfit the turbo stuff (cars mostly, less availability in aircraft) with intercoolers for bad designs that heat the air significantly before they reach the turbo, also.

Ambient temp on the ground is usually higher sitting on pavement than in flight at 10K. Turbo works a lot harder to give the usual in flight result. The thing is sucking hot air and the engine is rich, unless you’re give it time and some forward speed to push cooler air in there and turbo RPM to spin up.

Also I suppose it should be said... any adjustments done wrong at sea level will show up as a much bigger problem quickly up here...

 

[hindsight2020]

Continental fuel system overdelivers by default (line return setup), and the turbo spool up is not instantaneous, so you got bogged down in the spool up regime. You needed to spool up with the mixture leaned, then richen as you got the engine stabilized in the boosted pressures. A bit of a d---k dance, as has been highlighted already, but that's them breaks in piston land.

Otherwise your understanding of your engine operating allowances is not incorrect. Once you spool up the turbo and stabilized above ambient pressures, you should be able to run without problems at full rich mixture settings, provided you're below the critical altitude and your fuel system is not miscalibrated all to hell (not impossible in a FI setup). 10k DA is certainly full power full rich territory on takeoff for most variable or auto wastegate installations.

 

[Jamie Kirk]

Flying my new to me Saratoga II TC home from Michigan to California we stopped at a high density airport in Arizona and could not get the engine to run and I thought we had a problem.

Nope, just needed to aggressively lean it.

 

[EdFred]

Flying my new to me Saratoga II TC home from Michigan to California we stopped at a high density airport in Arizona and could not get the engine to run and I thought we had a problem.

Nope, just needed to aggressively lean it.

Bartelt?

 

[Jamie Kirk]

Bartelt?

Yup.

 

[Bill Greenwood]

One procedure doesn't fit every airplane. I was flying my friends North American SNJ with 550 hp radial supercharged engine and took off full rich at our 7800 ft elevation airport. It went, but black smoke was pouring out, it was way too rich. I cant recall how I leaned it for next takeoffs, but I did and it was fine.

On the other hand in my 36 TC Bonanza with Continental TSIO 520 U B, it is critical to takeoff and climb full rich, or you risk overheating exhaust valves. You take off 36" mp and fuel flow up to 36 gal per hr, and don't lean until you reduce power below 30 inches for cruise, ie, 28" and 2300 rpm lean to bout 17, 18 gph.

A Merlin, at least the Rolls version, supercharged V-12, has automatic mixture setting as part of the carburetor , you don't lean, you cant lean as there is no mixture control. As you open throttle from idle to 44 in mp, the carb is leaned auto, above 44 or + 7 lbs boost it goes to rich mixture. A great way to have it and one less thing for the pilot to do. When Packard built the engine, the Americans thought they had to show they were smarter than Rolls, ( they weren't) and put a manual mixture control next the the throttle and now I hear pilots argue about which setting it should be in.

 

[RussR]

Thanks for the great replies all.

I thought I have been advancing the power smoothly and gradually, but perhaps not gradual enough. My habit in this airplane is to advance the power to 25" or so, pause for a few seconds, then advance it the rest of the way to max. Why? Because that's what they guy who did my insurance-required training recommended. Maybe I need to slow it down even more.

But other comments made me think about the mixture some more as well. So, what I am gathering (which makes sense), is that since until the turbo really gets going, it isn't really affecting the MP much (which should be obvious, of course), which means that until it really gets spooled up you need to treat it as a normally-aspirated engine when it comes to having it leaned for altitude. Then as the turbo kicks in, advance the mixture to full rich for cooling on takeoff.

That does match with what ultimately happened on that flight. When I leaned it out, it ran up to full power just fine, but I didn't want to leave it like that for long, so on takeoff roll I increased the mixture gradually to full rich. I may have stopped just shy of that, actually. I will admit I was a bit hesitant to do this since that's what (I thought) had caused it to stumble before. But since all my climbouts, even at 10,000 MSL are at full rich, I figured it SHOULD work. And sure enough, it did. The engine ran fine all the way back home.

So, thanks all. I will incorporate this discussion into other training I do on other turbocharged aircraft as well.

 

[Let'sgoflying!]

This interests me as I have a TC engine (TSIO-550) and will be flying at higher DA airports. So far from 7000'DA I have not noticed anything.

Is this issue explained by this hypothesis: Any TC engine is truly a NA engine at low power until the turbos spool up?
I had thought that completing (in Continental's case) section 6 of M-0 would allow for this, ie it would set up the low power fuel metering for the measured MP.
I have not had to lean my TC engine so far, for any take off. (well, I lean it slightly as I have set the full power fuel flow a tad over Continental's max in case I ever need it).
I do take, I am guessing, 5-maybe 8 seconds from power off to full power ie pretty slow.

 

[Rgbeard]

Lycoming TIO-540 here.

At high DAs I will lean a little during Taxi.
But back to full-rich for takeoff, as per the manual.
I've gone out from elevations as high as 7,000ft, so not super-high
I've gone out from that same elevation with DA just above 10,000. That's getting there.

It caught me, by surprise, just how much further forward the throttle goes to get to my takeoff setting. The first time I almost thought the turbo wasn't there. Haha.

 

[Bill Greenwood]

Russ this is important, it should be something that's in the pilot manual for that plane, you do have that manual don't you? If not, try asking the type club for their recommendations. If you run the engine full mixture rich, no real harm should result, just lower power for takeoff and possible carbon fouling of plugs. But on the other hand if you lean it and the engine requires full rich, then you risk overheating the engine , maybe even detonation damage or a hole in the piston. In my TSIO 520, I open the throttle slowly, perhaps 4 or 5 sec to ful,but there is no lag in the response no apparent lag in turb spool up as there might be if I pushed the throttle right up. It s vital to be FULL RICH with this engine.
I do lean right after start for taxi but full rich before takeoff.

 

[Checkout_my_Six]

well....you can be too rich. And you will quickly hear the engine quit if it's too rich.....then if you're on to it you'll lean and it will come back to life. Been there done it at 50 above the runway. ...not fun.

Lean for best power (do this on the roll after I see redline MP)....your engine will not over heat for a minute or two till clear of obstacles. After clear, gear up flaps up, add back the mixture to cool down the cylinders and climb on. I do this regularly....and I never see CHTs above 380 in my TSIO520.

 

[Jamie Kirk]

well....you can be too rich. And you will quickly hear the engine quit if it's too rich.....then if you're on to it you'll lean and it will come back to life. Been there done it at 50 above the runway. ...not fun.

Lean for best power (do this on the roll after I see redline MP)....your engine will not over heat for a minute or two till clear of obstacles. After clear, gear up flaps up, add back the mixture to cool down the cylinders and climb on. I do this regularly....and I never see CHTs above 380 in my TSIO520.

This is my experience also. Saturday I flew to big bear and DA was 9k’, I almost had fuel to cut off for taxi, anymore and it would almost stall the motor.

Rolling from the hold short line I added some throttle and started adding mixture, engine almost died. Quickly pulled mixture back and progressed the throttle. I then progressed the mixture but I wasn’t full rich till well into the climb.

 

[N7IFR]

One procedure doesn't fit every airplane. I was flying my friends North American SNJ with 550 hp radial supercharged engine and took off full rich at our 7800 ft elevation airport. It went, but black smoke was pouring out, it was way too rich. I cant recall how I leaned it for next takeoffs, but I did and it was fine.

On the other hand in my 36 TC Bonanza with Continental TSIO 520 U B, it is critical to takeoff and climb full rich, or you risk overheating exhaust valves. You take off 36" mp and fuel flow up to 36 gal per hr, and don't lean until you reduce power below 30 inches for cruise, ie, 28" and 2300 rpm lean to bout 17, 18 gph.

A Merlin, at least the Rolls version, supercharged V-12, has automatic mixture setting as part of the carburetor , you don't lean, you cant lean as there is no mixture control. As you open throttle from idle to 44 in mp, the carb is leaned auto, above 44 or + 7 lbs boost it goes to rich mixture. A great way to have it and one less thing for the pilot to do. When Packard built the engine, the Americans thought they had to show they were smarter than Rolls, ( they weren't) and put a manual mixture control next the the throttle and now I hear pilots argue about which setting it should be in.

In my Bonanza B36TC (TSIO520 UB), taking off full rich before the Turbo has spooled up above ambient altitude MP, the engine experiences "Boot-Strap Surge" and fails to develop full power. Much better solution is Always Lean for Best Power after runup at 1700 RPM, and then begin takeoff roll advancing to Full MP WOT (36"), and THEN Advance Mixture Full (34.2 gph). Before Turbo-Spools in, it is a NA engine until about 25" MAP.
also, the TSIO520-UB does not have a fuel limiter and boggs down with any fuel flow above 36 gph...

 

[Pinecone]

It sounds like a number of you need to find a mechanic who understands and follows the M0 manual fuel flow setup process.

With my TSIO-360-SB, I lean for taxi at high DA, but go to full rich for takeoff. Smoothly and moderately slowly advance power and all is good.

FYI, intercoolers are NOT to fix poor design or installation. ALL superchargers increase the air temp. And high intake air temp can lead to detonation. I would now own a turbocharged airplane without an intercooler.

 

[William Pete Hodges]

Thanks for the great replies all.

I thought I have been advancing the power smoothly and gradually, but perhaps not gradual enough. My habit in this airplane is to advance the power to 25" or so, pause for a few seconds, then advance it the rest of the way to max. Why? Because that's what they guy who did my insurance-required training recommended. Maybe I need to slow it down even more.

But other comments made me think about the mixture some more as well. So, what I am gathering (which makes sense), is that since until the turbo really gets going, it isn't really affecting the MP much (which should be obvious, of course), which means that until it really gets spooled up you need to treat it as a normally-aspirated engine when it comes to having it leaned for altitude. Then as the turbo kicks in, advance the mixture to full rich for cooling on takeoff.

That does match with what ultimately happened on that flight. When I leaned it out, it ran up to full power just fine, but I didn't want to leave it like that for long, so on takeoff roll I increased the mixture gradually to full rich. I may have stopped just shy of that, actually. I will admit I was a bit hesitant to do this since that's what (I thought) had caused it to stumble before. But since all my climbouts, even at 10,000 MSL are at full rich, I figured it SHOULD work. And sure enough, it did. The engine ran fine all the way back home.

So, thanks all. I will incorporate this discussion into other training I do on other turbocharged aircraft as well.

One thing that may be overlooked in the other comments is intake air heating due to TC efficiency. The more added pressure the turbo makes, the more added heat of air compression plus the added heat of turbo efficiency. For example, let's say the air pressure would rise 50°F from air compression alone, at 65% TC efficiency the total increase would be 77°. If you have an aftercooler then this is somewhat moderated, but if turbo only then it is not. That means at the same manifold air pressure the air is not as dense as it would be at a slightly lower altitude where less boost is required. The higher the altitude the more boost is required and the more the intake air is heated and the manifold air density is decreased. Maybe no adjustment would be needed at 6000 feet, but the more extreme the altitude the more likely you are going to have to lean. It looks like it caught up with you and you responded correctly.

 

[William Pete Hodges]

For those of you wanting more information about Turbo charging In general practice, in the diesel engine world practically all of the commercial engines are turbocharged. Typical boost ranges from 60 to 66 inches of Mercury And at that pressure the temperature of the air is around 300 to 330°F leaving the Turbo charger. Jacket water After cooling brings that air temperature down to about 200 to 220°F. Air-to-air after cooling brings that temperature down to about a 130 or so. Those numbers are based on full load engine output on a hot day. Ambient air conditions that are different from that can change everything a lot but you can see where turbocharger heating is a significant factor in air density inside the intake manifold. I hope this helps with your understanding.