Hey everyone,

Quick question. I've not got a lot of experience flying at sea level in GA aircraft and want to know your thoughts on this. When taking off at lower altitude and your MP is above the green arc, it seems like I had read that you should reduce MP as soon as practical to the top of the green arc and then add throttle as you climb to keep it there until you reach WOT. After my trip to Death Valley it got me to thinking about this and how the act of reducing MP could deactivate the power enrichment valve that is helping to cool the engine.

So, how should this be done in a normally aspirated engine? Leave it alone and let it come down on its own as you climb or reduce power to the top of the green arc and add throttle as you climb to keep it at the top of the green arc until you reach wide open throttle. (I've read some stuff from Mike Busch that advocates adjusting power and another from John Deakin saying leave it alone). So I thought I'd get your thoughts.

Thanks!

http://www.avweb.com/news/pelican/182045-1.html?redirected=1

http://www.avweb.com/news/airman/184350-1.html?redirected=1

First, how accurate is that MP gauge? Most of them are sorta ball parkish....

My vote is just leave it alone. With that little bit of "overboost" you're not going to hurt anything.

I've worked these airplanes at 400 msl and an OAT of -40 a good bit, and those engines always went to TBO.....those are pretty significant overboosts. And on a couple occasions, I performed takeoffs at "somewhat" colder temps.....

MTV

I agree with MTV. O-540 Lycomings on Pawnees and CallAirs get near TBO and we are wide open unless going downhill or coming back empty. What is a manifold pressure guage?

mtv wrote:First, how accurate is that MP gauge? Most of them are sorta ball parkish....

My vote is just leave it alone. With that little bit of "overboost" you're not going to hurt anything.

I've worked these airplanes at 400 msl and an OAT of -40 a good bit, and those engines always went to TBO.....those are pretty significant overboosts. And on a couple occasions, I performed takeoffs at "somewhat" colder temps.....

MTV

400 msl and -40F is nearly -7000 ft DA.

Would an engine with the mixture at full rich in these conditions be running super lean?

Leave alone, However if you ever fly a turbo pay attention

Scolopax wrote:

mtv wrote:First, how accurate is that MP gauge? Most of them are sorta ball parkish....

My vote is just leave it alone. With that little bit of "overboost" you're not going to hurt anything.

I've worked these airplanes at 400 msl and an OAT of -40 a good bit, and those engines always went to TBO.....those are pretty significant overboosts. And on a couple occasions, I performed takeoffs at "somewhat" colder temps.....

MTV

400 msl and -40F is nearly -7000 ft DA. This should produce about 50 inches of M.P. in a naturally aspirated engine. These should be good conditions for breaking in an engine.

Would an engine with the mixture at full rich in these conditions be running super lean?

Never asked and never an issue. Sometimes in those conditions....after I started thinking about it....I'd roll the prop back to 2700 for takeoff.

BUT, this is specifically why it's so important to use the induction block off plate on these aircraft at all times in cold temps. This ensures that the engine induction is breathing cold air mixed with air taken from inside the cowling, so somewhat warmed.

MTV

Scolopax wrote:
400 msl and -40F is nearly -7000 ft DA. This should produce about 50 inches of M.P. in a naturally aspirated engine. These should be good conditions for breaking in an engine.

Could you elaborate on this?? Didn't know a naturally aspirated engine could get more than ambient barometric pressure, which would be in the 29-31" neighborhood.

After takeoff I back MP out to the top of the green and back out the prop even though there is no 5 minute limitation on max power on the 205 like the 206-7-10s. figure if I really need it I will use it but mostly just burns more gas. FWIW

Rolling back the rpm also makes for happier neighbors. We have one guy here that comes in to the pattern to land at 2800 rpm. He us hard of hearing and we suspect he leaves at at full rpm all the time.

kestrel wrote:Rolling back the rpm also makes for happier neighbors. We have one guy here that comes in to the pattern to land at 2800 rpm. He us hard of hearing and we suspect he leaves at at full rpm all the time.

Not such a big deal on the 205.
Red line is 2625.

Thanks guys. I wanted some real world, experienced pilot input at low altitudes since most of my GA time has been above 4K feet. Just want to be sure I'm not inadvertently doing something wring on the few occasions I wander to lower altitudes.

This is part of a Mike Busch Article that was confusing me:

Once the gear is up and the airplane is climbing through pattern altitude (1,000' AGL), it's time to reduce to cruise-climb power. (In a normally aspirated airplane, it's acceptable to remain at full-throttle and to let Mother Nature do the job; in a turbo, the pilot has to make the power reduction.)

Normal cruise-climb in a Continental-powered airplane is normally 75% power. In many aircraft (including most Cessna singles and twins), this occurs at top-of-the-green manifold pressure and top-of-the-green RPM. Don't fixate on the engine gauges while making this power reduction, especially in IMC. Learn to do it mostly by feel and sound, with just occasional quick glances at the power instruments.

Once the power reduction has been made, its time to lean the engine for climb. Some airplanes have a recommended cruise-climb fuel flow marked on the face of the fuel flow gauge (e.g., with a blue triangle). If yours doesn't, look up the correct fuel flow in the POH and mark it on the gauge or put it on a placard next to the gauge.

If your primary CFI taught you not to lean below 5,000 feet, please purge that idea from your cortex right now. You should always lean the engine whenever it's operating at 75% power or less, regardless of altitude. You should be leaned for climb, cruise, descent, landing, and taxi. The only time you should be full-rich is for start, takeoff, and go-around.

In a normally-aspirated airplane, you'll have to add throttle every 1,000 feet or so to maintain cruise-climb power. With a turbo, the automatic wastegate system should hold your manifold pressure more-or-less constant as the aircraft climbs. Some fall-off is normal, however, especially if you use single-weight oil. So check the MP occasionally and re-tweak the throttles as necessary.

Scolopax wrote:400 msl and -40F is nearly -7000 ft DA. This should produce about 50 inches of M.P. in a naturally aspirated engine

Nope.

bart wrote:

Scolopax wrote:
400 msl and -40F is nearly -7000 ft DA. This should produce about 50 inches of M.P. in a naturally aspirated engine. These should be good conditions for breaking in an engine.

Could you elaborate on this?? Didn't know a naturally aspirated engine could get more than ambient barometric pressure, which would be in the 29-31" neighborhood.

I was thinking incorrectly out loud Bart. Sorry. The pressure would not be elevated, but the density of the air would be increased to that of air at -7000 feet at standard temperature. Lots of oxygen in that air, but the pressure would not be significantly higher, because that would require much more atmospheric mass above.

Grassstrippilot wrote:Thanks guys. I wanted some real world, experienced pilot input at low altitudes since most of my GA time has been above 4K feet. Just want to be sure I'm not inadvertently doing something wring on the few occasions I wander to lower altitudes.

This is part of a Mike Busch Article that was confusing me:

Once the gear is up and the airplane is climbing through pattern altitude (1,000' AGL), it's time to reduce to cruise-climb power. (In a normally aspirated airplane, it's acceptable to remain at full-throttle and to let Mother Nature do the job; in a turbo, the pilot has to make the power reduction.)

Normal cruise-climb in a Continental-powered airplane is normally 75% power. In many aircraft (including most Cessna singles and twins), this occurs at top-of-the-green manifold pressure and top-of-the-green RPM. Don't fixate on the engine gauges while making this power reduction, especially in IMC. Learn to do it mostly by feel and sound, with just occasional quick glances at the power instruments.

Once the power reduction has been made, its time to lean the engine for climb. Some airplanes have a recommended cruise-climb fuel flow marked on the face of the fuel flow gauge (e.g., with a blue triangle). If yours doesn't, look up the correct fuel flow in the POH and mark it on the gauge or put it on a placard next to the gauge.

If your primary CFI taught you not to lean below 5,000 feet, please purge that idea from your cortex right now. You should always lean the engine whenever it's operating at 75% power or less, regardless of altitude. You should be leaned for climb, cruise, descent, landing, and taxi. The only time you should be full-rich is for start, takeoff, and go-around.

In a normally-aspirated airplane, you'll have to add throttle every 1,000 feet or so to maintain cruise-climb power. With a turbo, the automatic wastegate system should hold your manifold pressure more-or-less constant as the aircraft climbs. Some fall-off is normal, however, especially if you use single-weight oil. So check the MP occasionally and re-tweak the throttles as necessary.

As I read this, he's saying it's acceptable to maintain WOT through the climb in an NA airplane, since as you climb your MP is naturally reduced by the lowered atmospheric pressure. However, if you choose to reduce power with throttle after take-off, you'll have to add throttle to maintain your cruise-climb MP every 1,000 feet or so until you're back at WOT.

Flying my old C206, three blade, IO-520, I usually took off full power, at about 200AGL, pull RPM, MP and mixture to the top of the green. Then keep pushing in throttle and mixture to stay at the top of the green.

When it was just me in the plane and doing my 0615 departure (field elevation 6750'), my good neighbor procedure was take the runway with prop pulled back ~3/4", full throttle, bring RPM up to 2400 and adjust mixture to top of the green. But if the plane was heavy, I'd do the full power TO.

Firewalled up to cruise altitude. Give the cylinders all the gas they can handle in climb. We started pinching pennies on -470's when fuel got to $5. Started buying cylinders too.

400 msl and -40F is nearly -7000 ft DA.

I don't know if it's quite -7000 feet, but it is impressive.

As one who spent the majority of his career above the Arctic Circle, those low DA days made for some magical flying and absolute Zen moments in an airplane. Thick air is a joy that every pilot should experience at least once in a lifetime. And until you experience it for yourself, you won't know what I'm talking about.

And down here in Nevada, on those frequent higher than my airplane will fly high DA days.... I sure miss it!

On the cold, low DA days, it gets back to the "colder it is, the slower you do everything" rule. Roll power on slowly, and watch MP's close as not to overboost. A lot of days I'd be nowhere near full throttle on take off. And in a carburated airplane, a lot of times you have to pull carb heat and raise intake DA to avoid over-leaning.

Gump

GumpAir wrote:

400 msl and -40F is nearly -7000 ft DA.

I don't know if it's quite -7000 feet, but it is impressive.

As one who spent the majority of his career above the Arctic Circle, those low DA days made for some magical flying and absolute Zen moments in an airplane. Thick air is a joy that every pilot should experience at least once in a lifetime. And until you experience it for yourself, you won't know what I'm talking about.

And down here in Nevada, on those frequent higher than my airplane will fly high DA days.... I sure miss it!

On the cold, low DA days, it gets back to the "colder it is, the slower you do everything" rule. Roll power on slowly, and watch MP's close as not to overboost. A lot of days I'd be nowhere near full throttle on take off. And in a carburated airplane, a lot of times you have to pull carb heat and raise intake DA to avoid over-leaning.

Gump

-7000' Based on an online DA calculator

It's been decades since I bothered to look. What's an E6B show on the wheel for those conditions? I vaguely remember -4 to 5K.

Gump

CamTom12 wrote:

Grassstrippilot wrote:Thanks guys. I wanted some real world, experienced pilot input at low altitudes since most of my GA time has been above 4K feet. Just want to be sure I'm not inadvertently doing something wring on the few occasions I wander to lower altitudes.

This is part of a Mike Busch Article that was confusing me:

Once the gear is up and the airplane is climbing through pattern altitude (1,000' AGL), it's time to reduce to cruise-climb power. (In a normally aspirated airplane, it's acceptable to remain at full-throttle and to let Mother Nature do the job; in a turbo, the pilot has to make the power reduction.)

Normal cruise-climb in a Continental-powered airplane is normally 75% power. In many aircraft (including most Cessna singles and twins), this occurs at top-of-the-green manifold pressure and top-of-the-green RPM. Don't fixate on the engine gauges while making this power reduction, especially in IMC. Learn to do it mostly by feel and sound, with just occasional quick glances at the power instruments.

Once the power reduction has been made, its time to lean the engine for climb. Some airplanes have a recommended cruise-climb fuel flow marked on the face of the fuel flow gauge (e.g., with a blue triangle). If yours doesn't, look up the correct fuel flow in the POH and mark it on the gauge or put it on a placard next to the gauge.

If your primary CFI taught you not to lean below 5,000 feet, please purge that idea from your cortex right now. You should always lean the engine whenever it's operating at 75% power or less, regardless of altitude. You should be leaned for climb, cruise, descent, landing, and taxi. The only time you should be full-rich is for start, takeoff, and go-around.

In a normally-aspirated airplane, you'll have to add throttle every 1,000 feet or so to maintain cruise-climb power. With a turbo, the automatic wastegate system should hold your manifold pressure more-or-less constant as the aircraft climbs. Some fall-off is normal, however, especially if you use single-weight oil. So check the MP occasionally and re-tweak the throttles as necessary.

As I read this, he's saying it's acceptable to maintain WOT through the climb in an NA airplane, since as you climb your MP is naturally reduced by the lowered atmospheric pressure. However, if you choose to reduce power with throttle after take-off, you'll have to add throttle to maintain your cruise-climb MP every 1,000 feet or so until you're back at WOT.

I kind of wondered if that's what he meant. It just wasn't clear to me.

Harsh/interesting operating environments like Gump experienced aside, both Deakin and Busch have written about partial power takeoffs and why they don't recommend them. Here's a couple one from Avweb in addition to the one from Deakin in the original post.

http://www.avweb.com/news/airman/184274-1.html?redirected=1

http://www.avweb.com/news/airman/184483-1.html?redirected=1

Thanks for all the discussion and insight guys. It's appreciated!