Mixture control
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What about mixture control technique during climbs?
Let's say we are climbing from 3,000ft to 8,000ft, initially with mixture full rich. As you climb, what do you do with the mixture?
Gradually lean? How? Following RPM? Sound?
Let's say we are climbing from 3,000ft to 8,000ft, initially with mixture full rich. As you climb, what do you do with the mixture?
Gradually lean? How? Following RPM? Sound?
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That's something I've always wondered about. SOP at my club is for full throttle you go full rich. Does that apply to any altitude, say climbing from FL55 to 75?
Ah you got there before me BP.
Ah you got there before me BP.
That Club SOP sounds like its not saying the same thing as the flight manual.
In the light piston singles I fly, I have fuel flow gauges, so I lean in the climb to the figures the flight manual says to lean to.
Otherwise, lean gently in the climb, taking note of the sound of the engine. Err on the side of slightly rich - but leaving the thing at full rich is poor technique. Even below 5000 feet, engines still work better at a correct fuel-air mixture.
In the light piston singles I fly, I have fuel flow gauges, so I lean in the climb to the figures the flight manual says to lean to.
Otherwise, lean gently in the climb, taking note of the sound of the engine. Err on the side of slightly rich - but leaving the thing at full rich is poor technique. Even below 5000 feet, engines still work better at a correct fuel-air mixture.
EGT will always be more accurate then the fuel flow gauge especially the non electronic gauges which simply measure fuel pressure which is used to approximate fuel flow. These gauges will never be accurate enough to use as the sole source of information to lean.
A properly calibrated electronic fuel flow gauge like the JPI one is much more accurate but I am willing to bet that there is not one single aircraft in the entire UK available for general training/hire that has one.
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EGT will always be more accurate then the fuel flow gauge
If you're using a relative EGT (the old pointer type, with no numbers), finding the peak is pretty easy. These are pretty safe, as once you find peak lean, you richen it up as required, and you certainly will not be more lean than you intend for that cylinder, though you might be more rich.
If, however, the EGT is the type with tells you a temperature as a number, that value can have errors as a result of the position of the probe in the exhaust stack. EGT probe manufacturers often describe very specific positions for the probe tip, both relative to the diameter of the pipe (usually in the middle), and distance from the exhaust flange (4" - 6" seems familiar). Sometimes the exhaust system geometry prevents installing the probe in the right position, and sometimes it's just installer carelessness.
In any case, get to know how to interpret the information your EGT gives you, and remember that unlike many other instruments in the plane, it is very unlikely that the EGT has been calibrated, and confirmed to be reading correctly as installed.
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I think the bottom line is that anybody flying a carburreted engine, with their fairly standard mismatch of fuel distribution, and without a multicylinder EGT/CHT instrument, is flying with hands tied behind their back as far as getting optimal economy, and they have to play it very safe, and they need to fly full rich a lot of the time when somebody else with the proper kit can operate optimally.
An accurate fuel flowmeter is a huge asset but not for engine management as such; it enables you to fly long trips with confidence, and if necessary make intelligent diversion decisions well ahead of time.
An accurate fuel flowmeter is a huge asset but not for engine management as such; it enables you to fly long trips with confidence, and if necessary make intelligent diversion decisions well ahead of time.
I think the bottom line is that anybody flying a carburreted engine, with their fairly standard mismatch of fuel distribution, and without a multicylinder EGT/CHT instrument, is flying with hands tied behind their back as far as getting optimal economy, and they have to play it very safe, and they need to fly full rich a lot of the time when somebody else with the proper kit can operate optimally.
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In a climb at full power, there is already a "fuel enrichment" due to full throttle being applied, so I guess leaning to max RPM (or thereabouts, as it's not going to be as accurate as leaning during a cruise since you are climbing & ambient conditions etc etc are constantly changing) but I think the chances of being on the lean & therefore overheating side is less because of the full throttle enrichment? - True / False / Somewhere there...
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This comment relates to a typical spam can rental aircraft with no significant engine instrumentation and a carbureted engine.
False.
in a carbureted engine you are unlikely to be able to operate lean, just less rich.
at climb power and speed near sea level you need to be quite rich to keep temperatures and pressures at a safe level. if you lean 'a bit' it is relatively easy to wind up at exactly the wrong point and pulling 120% of max power out of the engine (unless it fails).
at higher altitude (as you approach the altitude you can only obtain 75% max power), you need to keep leaning to best power in order to get book climb and at these lower power levels can set any mixture without damaging the engine (subject to having enough cooling airflow to keep CHTs under control )
Last edited by mm_flynn; 1st Jan 2012 at 10:13.
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We have an EDM830 fitted and rarely to the CHT's, EGT and TIT get so hot that you can't lean in a climb. I lean using TIT and use that as my benchmark, and as long as TIT remains comfortable then CHT and EGT remain green and I'll lean in all phases of flight.
Actually with high altitude capable aeroplanes like ours which has a ceiling of 20,000, if you went full rich at high altitude during certain flight phases you'd likely have a rich cut and the engine would stop.....or you just wouldn't make your ceiling.
Actually with high altitude capable aeroplanes like ours which has a ceiling of 20,000, if you went full rich at high altitude during certain flight phases you'd likely have a rich cut and the engine would stop.....or you just wouldn't make your ceiling.
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Reading thread with interest , plus Peterh337 article on engine management, plus Deakin's Perch.
Could the knowledgeble give their opinion on engine management in the aerobatic scenerario. Which I suppose is not disimilar to the Parachute Pilot's scenerario.
Object:-- rapidly ascend to (for training) 3-5,000' short distance from airfield. Manoeuvering at max power, occasional power red for very short periods, occasional inverted, rapid ascent descent in altitude band. then back on ground asap. Preferably without the engine failing on me or those to follow.
Kit:--Lycoming AEIO-360 160bhp , cs prop, no cowl flaps, instruments(oil T's & P's, fuel flow, CHT in degrees centigrade, MAP, tachometer)
Strongly suspect instrumentation would not meet more exacting standards (no gami, JP, multiple cht probes)
MY main concern is not fuel consumption but trying to reduce engine stress and failure rates.
Any tips (other than give up aero's) gratefully received)
TIM
Could the knowledgeble give their opinion on engine management in the aerobatic scenerario. Which I suppose is not disimilar to the Parachute Pilot's scenerario.
Object:-- rapidly ascend to (for training) 3-5,000' short distance from airfield. Manoeuvering at max power, occasional power red for very short periods, occasional inverted, rapid ascent descent in altitude band. then back on ground asap. Preferably without the engine failing on me or those to follow.
Kit:--Lycoming AEIO-360 160bhp , cs prop, no cowl flaps, instruments(oil T's & P's, fuel flow, CHT in degrees centigrade, MAP, tachometer)
Strongly suspect instrumentation would not meet more exacting standards (no gami, JP, multiple cht probes)
MY main concern is not fuel consumption but trying to reduce engine stress and failure rates.
Any tips (other than give up aero's) gratefully received)
TIM
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This opens up the whole ancient "shock cooling" debate which will run and run but I think the main bit on which there may be a consensus is that you should avoid rapid drops in CHT when the CHT is high to start with.
The evidence for the above comes from glider towing ops - example.
What "high" means is open to debate but probably it means pushing 400F. Above that, the aluminium used in the cylinder heads starts to lose strength fairly rapidly.
Rapid increases in power don't seem to be a problem, provided the engine (oil etc) is warm enough to start with.
The evidence for the above comes from glider towing ops - example.
What "high" means is open to debate but probably it means pushing 400F. Above that, the aluminium used in the cylinder heads starts to lose strength fairly rapidly.
Rapid increases in power don't seem to be a problem, provided the engine (oil etc) is warm enough to start with.
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So I should basically forget about the mixture given the flight profile and leave it full rich (it's a UK airport so airfield elev is I presume irrelevant), and it's slow with the power reductions and speed increase.
Attached article was interesting. With a CS prop what MP reduction would be equivalent to the 150 / 100 rpm throttle reduction the author was recommending. Or is this the wrong way to look at the problem.
TIM
Attached article was interesting. With a CS prop what MP reduction would be equivalent to the 150 / 100 rpm throttle reduction the author was recommending. Or is this the wrong way to look at the problem.
TIM
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I know zilch about aerobatics but I thought that most of it is done at mostly constant-ish power settings...
If there are large power changes involved then I don't know how you can protect the engine.
The rule I use for flight tests (my own; I am not an instructor) where e.g. a PFL or unusual attitude recovery will be done is to fly at 18" or below (120kt in my case) for a couple of minutes. That gets the CHT down to about 350F.
16" may be even better; that roughly corresponds to what you fly a reasonably steep final approach at, and obviously you always close the throttle after that
If there are large power changes involved then I don't know how you can protect the engine.
The rule I use for flight tests (my own; I am not an instructor) where e.g. a PFL or unusual attitude recovery will be done is to fly at 18" or below (120kt in my case) for a couple of minutes. That gets the CHT down to about 350F.
16" may be even better; that roughly corresponds to what you fly a reasonably steep final approach at, and obviously you always close the throttle after that
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(I know zilch about aerobatics)
I am not that far ahead of you. I've been advised to keep 25/2,500. It's kept pretty much there continuously (to maintain energy levels) but occasionaly reduced ie. spin entry or to reduce torque/prop drag effects.
Without proper instrumentation it all seems abit hit and miss. When the article talks about maintaining speed and then only gradually increasing this is fine if been holding a constant Vy/ cruise climb. But if your speed varied in the last 2 minutes between (in the case of the plane I am presently flying) 50kts and 175kts which speed should I be using as a base line?
Any way many thanks for your help and Happy New Year.
TIM
I am not that far ahead of you. I've been advised to keep 25/2,500. It's kept pretty much there continuously (to maintain energy levels) but occasionaly reduced ie. spin entry or to reduce torque/prop drag effects.
Without proper instrumentation it all seems abit hit and miss. When the article talks about maintaining speed and then only gradually increasing this is fine if been holding a constant Vy/ cruise climb. But if your speed varied in the last 2 minutes between (in the case of the plane I am presently flying) 50kts and 175kts which speed should I be using as a base line?
Any way many thanks for your help and Happy New Year.
TIM
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Regarding shock cooling....We run a turbocharged engine and have never even come near the shock cooling environment. In the cruise one can slam the throttle closed and point the nose down and temps cool off pretty slowly...certainly slow enough to avoid shock cooling. The EDM monitors shock cooling and we've never come close...
I can't remember off the top of my head but in the cruise with cowl flaps closed we run at the low 300's for CHT. Even in a long climb at 90 kts CHTs don't exceed 400F - more like 380F (limit is 475F), and cooler on a 100 Kt climb (at 36"MP, 2575 RPM)......in UK weather of course......
So I believe it when Pelican's Perch says, that it is a myth
I can't remember off the top of my head but in the cruise with cowl flaps closed we run at the low 300's for CHT. Even in a long climb at 90 kts CHTs don't exceed 400F - more like 380F (limit is 475F), and cooler on a 100 Kt climb (at 36"MP, 2575 RPM)......in UK weather of course......
So I believe it when Pelican's Perch says, that it is a myth
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I can't install a CHT probe in the present aircraft because it's "club "aircraft. If it was my own aircraft; I was primarily cruising single engine; and after reading the above I'd have the works (gami, individual cyclinder monitoring JP fuel flow0 and make savings elsewhere. As much for safety as for fuel economy.
I think I remember Deakin saying the rate of temp drop when you switch the engine off is greater than that quoted to trigger shock cooling; although probably starting at a lower base than descending immediatly after a steep climb. The glider/ pilot engineers article is quite persuasive / worrying. Life would be alot easier if shock cooling was a myth.
I do love thread creep.
TIM
I think I remember Deakin saying the rate of temp drop when you switch the engine off is greater than that quoted to trigger shock cooling; although probably starting at a lower base than descending immediatly after a steep climb. The glider/ pilot engineers article is quite persuasive / worrying. Life would be alot easier if shock cooling was a myth.
I do love thread creep.
TIM
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I don't think shock cooling induced damage is a myth but clearly there are so many variations in operating conditions.
For example my cruise CHTs are around 370F, and I can get the EDM700 rapid cooling alarm very easily, simply by enriching the mixture a bit too quickly. I also have to work hard to keep CHTs below 400F; have to trim to 120kt ASAP after takeoff and even then it is close. On a hot day they touch 420F.
Clearly my TB20 engine is very differently cowled to Englishal's Commander 112 engine.
If you cannot persuade them to install a simple and cheap gauge which might make their engine last longer, then you don't need to worry if it doesn't
For example my cruise CHTs are around 370F, and I can get the EDM700 rapid cooling alarm very easily, simply by enriching the mixture a bit too quickly. I also have to work hard to keep CHTs below 400F; have to trim to 120kt ASAP after takeoff and even then it is close. On a hot day they touch 420F.
Clearly my TB20 engine is very differently cowled to Englishal's Commander 112 engine.
I can't install a CHT probe in the present aircraft because it's "club "aircraft.
