Leaning mixture = increase in RPM
Avoid imitations
Joined: Nov 2000
Aviation Qualifications: ATPL
Posts: 15,110
Likes: 1,083
From: Wandering the FIR and cyberspace often at highly unsociable times
Yes, and yes.
Fully rich gives some extra fuel, ensuring the engine doesn't suffer detonation.
Best power comes slightly leaner, albeit with a risk of detonation at low rpm and high MAP.
Fully rich gives some extra fuel, ensuring the engine doesn't suffer detonation.
Best power comes slightly leaner, albeit with a risk of detonation at low rpm and high MAP.
Joined: Aug 2004
Posts: 2,105
Likes: 50
From: Aberdeen
Even excluding the risk of detonation, the extra rich mixture is essential to prevent overheating inside the combustion chamber at high power. Lycoming states that for its engines generally, the mixture must be fully rich for power levels above 75%. Leaning the mixture at high power will give a bit more power/rpm but causes rapid engine damage such as burning of valves and possibly burning of holes in the piston crown.
HC
HC
Joined: Apr 2003
Posts: 3,012
Likes: 1
From: USA
Mighty,
Auto-lean carbs were part of many WWII piston engines, and in the Bells that I flew back when men were men, but they were expensive and complex. Now cars use metered injection, with computers and sensors that were unheard of back then. These should be available in aircraft as soon as one engine manufacturer gets off his duff and does it - the savings in fuel alone will ake it an immediate winner in the marketplace.
I must say that the best leaning technique is to have a good digital EGT gage for each cylinder, and then you can lean whenever you wish.
Recall that very rich mixture is a way to assure slightly worse power but assured exhaust valve temperature, leaning to perhaps 50 degrees cooler than peak EGT assures peak power, and leaning to peak EGT yields best fuel consumption (although those who pay for the overhals often make it peak +25 degrees!)
Auto-lean carbs were part of many WWII piston engines, and in the Bells that I flew back when men were men, but they were expensive and complex. Now cars use metered injection, with computers and sensors that were unheard of back then. These should be available in aircraft as soon as one engine manufacturer gets off his duff and does it - the savings in fuel alone will ake it an immediate winner in the marketplace.
I must say that the best leaning technique is to have a good digital EGT gage for each cylinder, and then you can lean whenever you wish.
Recall that very rich mixture is a way to assure slightly worse power but assured exhaust valve temperature, leaning to perhaps 50 degrees cooler than peak EGT assures peak power, and leaning to peak EGT yields best fuel consumption (although those who pay for the overhals often make it peak +25 degrees!)
Joined: Dec 2003
Posts: 643
Likes: 30
From: Global Vagabond
Mighty, the technology is there for cars, but to adapt & get APPROVAL for the same for aero engines is massively expensive. It will happen eventually but in the meantime we're stuck with the stone age.
Put simply, Its all down to production volumes
Put simply, Its all down to production volumes
Joined: Oct 2002
Posts: 135
Likes: 0
From: USA
Problem is...
One of the key components of the automotive injection system is not compatible with avgas. The oxygen sensor is a key sensor for determining proper mixture. Unfortuately all O2 sensors to date are quickly killed by the lead in avgas.
There are some homebuilt aircraft here in the states that are using the trusted & mechanically proven bullet-proof lycoming engine but with modern ignition and injection fitted. Great combination. But, for them to run in "closed loop" mode with O2 sensor, they're limited to mogas.
HOSS-1
There are some homebuilt aircraft here in the states that are using the trusted & mechanically proven bullet-proof lycoming engine but with modern ignition and injection fitted. Great combination. But, for them to run in "closed loop" mode with O2 sensor, they're limited to mogas.
HOSS-1
Joined: Nov 2001
Posts: 571
Likes: 0
From: Alderney or Lancashire UK
If you lean, the rpm increases as flame front propagation speeds up (mixture burns faster), until the mixture leans to stoichiometry - the ideal mixture. If you keep going past that and lean more, the rpm drops again as flame propagation slows again - to the point where it is required to open the throttle to maintain RPM.
As Nick said it is quite possible to run a piston lean. A few years ago I decided to utilise the techniques favoured by John Deakin and run lean of peak EGT. This yields a fuel saving of around 30 to 35% from full rich. My Lycoming runs smooth to about 70 deg on the lean side but it took a huge amount of work to get it to run right. I usually run 50 degrees lean of peak. The data from the engine monitor is stored and periodically checked against reference flights to make sure all stays in tune. It aint exactly a technique for low hour or Robbie pilots.
I did my LPC last week and it even makes the examiner squirm uncomfortably when I pull the mixture out 2 inches and open the throttle wide at 1000 feet.
Ive been doing it for 4 years and it's saved me a fortune. It was worth the effort. The engine runs cool, clean and produces no carbon monoxide. cabin levels drop from 30-50 ppm when rich to zero when lean. It would save a hell of a lot of avgas if it could be done automatically on all pistons. We are indeed still in the dark ages.
To read John Deakins brilliant work (if you have a few hours spare) goto
http://www.avweb.com/news/pelican/list.html
the early articles go through the basics. Number 18 is a good place to start. You have to register to read the articles.
As Nick said it is quite possible to run a piston lean. A few years ago I decided to utilise the techniques favoured by John Deakin and run lean of peak EGT. This yields a fuel saving of around 30 to 35% from full rich. My Lycoming runs smooth to about 70 deg on the lean side but it took a huge amount of work to get it to run right. I usually run 50 degrees lean of peak. The data from the engine monitor is stored and periodically checked against reference flights to make sure all stays in tune. It aint exactly a technique for low hour or Robbie pilots.
I did my LPC last week and it even makes the examiner squirm uncomfortably when I pull the mixture out 2 inches and open the throttle wide at 1000 feet.
Ive been doing it for 4 years and it's saved me a fortune. It was worth the effort. The engine runs cool, clean and produces no carbon monoxide. cabin levels drop from 30-50 ppm when rich to zero when lean. It would save a hell of a lot of avgas if it could be done automatically on all pistons. We are indeed still in the dark ages.
To read John Deakins brilliant work (if you have a few hours spare) goto
http://www.avweb.com/news/pelican/list.html
the early articles go through the basics. Number 18 is a good place to start. You have to register to read the articles.
Last edited by Gaseous; 9th March 2007 at 07:31. Reason: to add link
Joined: Aug 2004
Posts: 2,105
Likes: 50
From: Aberdeen
There are various short articles about mixture and leaning Lycoming engines at
http://www.lycoming.com/main.jsp?bod...operation.html
which make good reading.
HC
http://www.lycoming.com/main.jsp?bod...operation.html
which make good reading.
HC
Joined: Nov 2001
Posts: 571
Likes: 0
From: Alderney or Lancashire UK
HC
Lycoming articles are great and well worth a read but were written about 30 years ago when gas was cheap and carbon footprint and global warming not thought of. Lycoming do not recomend running properly lean as the engines they produce will not run that way without reworking the fuel injection system.
Cheers G
Lycoming articles are great and well worth a read but were written about 30 years ago when gas was cheap and carbon footprint and global warming not thought of. Lycoming do not recomend running properly lean as the engines they produce will not run that way without reworking the fuel injection system.
Cheers G
Joined: Mar 2002
Posts: 458
Likes: 0
From: Kings Caple, Ross-on-Wye.orPiccots End. Hertfordshire
Mixture leaning
As an ex Enstrom sales whizz kid (before Robinson took over) I always took great pains with my new owners to explain the correct leaning procedure for the Enstrom Turbo charged models, but as Nick Lappos says, it is essential to have at least an Alcor EGT, or preferably the more sophisticated indicator for each cylinder.
The FM advises that at MAP up to 29 hg, (some say 28 hg) a figure of 1550 degrees will provide the highest BHP (205) and for absolute ecomomy 1650 can be used. If 29 hg is set straight & level the ASI on the 280C model will usually indicate 100 mph and around 120 lbs per hour fuel flow. ERPM should be set at 2825.
If the mixture is leaned to 1550 degrees, the rpm will move up around 50 to 75rpm, the ASI will show an increase (usually 5 mph) and the fuel flow will drop to 95 lbs per hour. Further leaning to 1650 will reduce fuel flow to 83 lbs per hour. So more performance and greater range on a lower fuel burn and at £5 a gallon, there's a good fuel cost saving to be made.
PS ... Don't forget to return to rich mixture for landing!
Hope this helps some Enstrom owners, but note the above does not apply to the turbo 'A' models.
Dennis Kenyon.
.
The FM advises that at MAP up to 29 hg, (some say 28 hg) a figure of 1550 degrees will provide the highest BHP (205) and for absolute ecomomy 1650 can be used. If 29 hg is set straight & level the ASI on the 280C model will usually indicate 100 mph and around 120 lbs per hour fuel flow. ERPM should be set at 2825.
If the mixture is leaned to 1550 degrees, the rpm will move up around 50 to 75rpm, the ASI will show an increase (usually 5 mph) and the fuel flow will drop to 95 lbs per hour. Further leaning to 1650 will reduce fuel flow to 83 lbs per hour. So more performance and greater range on a lower fuel burn and at £5 a gallon, there's a good fuel cost saving to be made.
PS ... Don't forget to return to rich mixture for landing!
Hope this helps some Enstrom owners, but note the above does not apply to the turbo 'A' models.
Dennis Kenyon.
.
Joined: Feb 2007
Posts: 7
Likes: 0
From: all over
When you are in a R 22 you push the mixture all the way in when you want to fly it and all the way out when you have finished flying it, play with it in the air and it is only a matter of time before you finish flying whilst still in the air.
LEAVE IT ALONE!
Choppergod has spoken.
LEAVE IT ALONE!
Choppergod has spoken.
Joined: Mar 2002
Posts: 458
Likes: 0
From: Kings Caple, Ross-on-Wye.orPiccots End. Hertfordshire
Mixture control useage
Just to confirm my previous notes relate specifically to the Enstrom marque and the 'more aware' pilot.
Robinson 'carburettor' models should be operated as Choppergod advises.
For the most efficient use of the Enstrom HIO 360 C series engine, Lycoming recommend the procedure I specified.
Mixture leaning is not a 'no-go' area. In many areas it is mandatory. Try taking off at Nairobi Airport with a 'full-rich mixture' Piper Aztec to discover why.
Dennis Kenyon
Robinson 'carburettor' models should be operated as Choppergod advises.
For the most efficient use of the Enstrom HIO 360 C series engine, Lycoming recommend the procedure I specified.
Mixture leaning is not a 'no-go' area. In many areas it is mandatory. Try taking off at Nairobi Airport with a 'full-rich mixture' Piper Aztec to discover why.
Dennis Kenyon
