Mixture rich for taxi?
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what about the latest generation of Aero piston engines, the ones without a mixture control? all jabiru engines have no manual mixture control, either do most rotax engines, as for the new range of Diesel engines, i cannot comment. The Jabiru and Rotax engines have auto pressure sensing carburettors. and from what i have heard in general hangar talk, is they set themselves to full rich below up to about 1500 AMSL... simple logic, air is the most dense at sea level, hence the aerodrome, and to get the best out of the engine, the mixture would be at the rich end of the scale... of course i am no expert on engines and the auto mixture setups these days...
I think the other reason only basic leaning techniques are taught is that more often than not the student is struggling with a multitude of other things during the flight. If I tried to teach any of my PPL nav students how to lean as Chimbu has described (or even touched on some of that stuff) we would never have found the large towns we were looking for. For someone doing an AFR or refresher training I think this sort of thing would be ideal to go into. Same with the Mooney proficiency course, why not talk about some of these things along with operating "over square" during the course. Those sort of activites are the IDEAL time to cover off more complex ways of operating the aircraft.
Rather than confuse the issue, we taught to lean to peak, then 50F ROP. The first time they did this, it could take up to 10 minutes for them to get there (trepedation in unwinding that mystical red knob) but towards then end a minute or two.
The stuff that Chimbu is talking about really is advanced stuff. If I can't get the student to find a town or follow a line on a map I don't want to get bogged down in a big way on mixture control. Not debating the merits of any of the stuff above (I have certainly learnt a bucket load from it) but it just irratates me that as one of those instructors that did a rating straight away, thoroughly enjoyed the job and tried to learn as much as I could and pass it along to my students, I am still classed as a complete moron by those that have probably never even tried instructing.
Whilst I don't fly anywhere near as much as I used too (new job) I will go through and read these articles that Chimbu has suggested to learn more and pass that info along if/when I go back to instructing.
Rather than confuse the issue, we taught to lean to peak, then 50F ROP. The first time they did this, it could take up to 10 minutes for them to get there (trepedation in unwinding that mystical red knob) but towards then end a minute or two.
The stuff that Chimbu is talking about really is advanced stuff. If I can't get the student to find a town or follow a line on a map I don't want to get bogged down in a big way on mixture control. Not debating the merits of any of the stuff above (I have certainly learnt a bucket load from it) but it just irratates me that as one of those instructors that did a rating straight away, thoroughly enjoyed the job and tried to learn as much as I could and pass it along to my students, I am still classed as a complete moron by those that have probably never even tried instructing.
Whilst I don't fly anywhere near as much as I used too (new job) I will go through and read these articles that Chimbu has suggested to learn more and pass that info along if/when I go back to instructing.
Grandpa Aerotart
AWOL57 I would never suggest you are a complete moron because you are unaware of the stuff I have been talking about. If you were teaching 'full rich' all the time I would label you ignorant rather than moronic. Moronic is a different thing all together
But they should be learning it in ground school...'engine systems and instruments' it was called when I learned to fly in 81. I agree that much of it would be beyond the spare brain capacity of ab initio students to cope with in flight
50F ROP is bad for the engine down low where sufficient air is available to develope more than 65% power. If you are running at 75% power 80-100F ROP is good...what you are effectively doing is cooling the engine with excessive fuel flow.
At 65% power and below you can run at 50F ROP or even peak EGT if the engine will run smoothly there. This is because at higher power settings anywhere in the vicinity of 50F ROP will cook at least some of your cylinders and with only the pathetic typical engine instruments you will have no idea which ones. At 65% power, whether that is achieved by being high or reducing the throttle to minimise the air available for combustion, you have a situation where < air mixed with < fuel = efficient power but less power..less power = less heat. Excessive heat is the number one enemy.
When you are running '50F ROP' in a typical aircraft only one of the cylinders is 50F ROP. Some others will be 80 odd ROP (safe) and some will be near peak (not safe). As an example the CHT in my old triplex gauge (mandated to be installed by CASA
) is reading one of my coolest cylinders..1 or 3 I am unsure which. There is a 50+ degree F difference between that cylinder and my warmest, 4 and 6. So if I ran 50F ROP at 75% power and was happily looking at 400F on the CHT (60F under redline) my cylinders 4 and 6 would be sitting around peak EGT and cooking at the redline. They would be two fecked units within 500 hrs...this is what leads to premature top overhauls caused by low compressions and cracked cylinders.
Combine the last paragraphs with 'don't enrichen the mixture on descent and this is why..." and I think you have given the average PPL the right information.
I agree it all sounds very complicated when you first try and get your head around it...but it really is quite simple.
The breakthrough comes when you stop thinking about what they taught you the throttle, pitch and mixture controls did and understand what they really do...or do as well as what you were taught they did.
EDIT for Ultralights
I don't know about the rotaxs etc but I would suggest their operating parameters are so narrow that a basic pressure sensitive carburetor suffices..Bonanza engines have them too but they don't work very well...I would be very carefull about operating those engines hot and high...you could get in real trouble at heavy weights.
Thielert engines have FADEC. They lean the mixture to the most efficient settings automatically taking into account all parameters like prop rpm, air density, throttle position etc....interestingly Cirrus recomends LOP in the cruise.
Edited for incorrect memory on Cirruses engine setup.
.
But they should be learning it in ground school...'engine systems and instruments' it was called when I learned to fly in 81. I agree that much of it would be beyond the spare brain capacity of ab initio students to cope with in flight
50F ROP is bad for the engine down low where sufficient air is available to develope more than 65% power. If you are running at 75% power 80-100F ROP is good...what you are effectively doing is cooling the engine with excessive fuel flow.
At 65% power and below you can run at 50F ROP or even peak EGT if the engine will run smoothly there. This is because at higher power settings anywhere in the vicinity of 50F ROP will cook at least some of your cylinders and with only the pathetic typical engine instruments you will have no idea which ones. At 65% power, whether that is achieved by being high or reducing the throttle to minimise the air available for combustion, you have a situation where < air mixed with < fuel = efficient power but less power..less power = less heat. Excessive heat is the number one enemy.
When you are running '50F ROP' in a typical aircraft only one of the cylinders is 50F ROP. Some others will be 80 odd ROP (safe) and some will be near peak (not safe). As an example the CHT in my old triplex gauge (mandated to be installed by CASA
) is reading one of my coolest cylinders..1 or 3 I am unsure which. There is a 50+ degree F difference between that cylinder and my warmest, 4 and 6. So if I ran 50F ROP at 75% power and was happily looking at 400F on the CHT (60F under redline) my cylinders 4 and 6 would be sitting around peak EGT and cooking at the redline. They would be two fecked units within 500 hrs...this is what leads to premature top overhauls caused by low compressions and cracked cylinders.Combine the last paragraphs with 'don't enrichen the mixture on descent and this is why..." and I think you have given the average PPL the right information.
I agree it all sounds very complicated when you first try and get your head around it...but it really is quite simple.
The breakthrough comes when you stop thinking about what they taught you the throttle, pitch and mixture controls did and understand what they really do...or do as well as what you were taught they did.
EDIT for Ultralights
I don't know about the rotaxs etc but I would suggest their operating parameters are so narrow that a basic pressure sensitive carburetor suffices..Bonanza engines have them too but they don't work very well...I would be very carefull about operating those engines hot and high...you could get in real trouble at heavy weights.
Thielert engines have FADEC. They lean the mixture to the most efficient settings automatically taking into account all parameters like prop rpm, air density, throttle position etc....interestingly Cirrus recomends LOP in the cruise.
Edited for incorrect memory on Cirruses engine setup.
.
Last edited by Chimbu chuckles; 1st Nov 2006 at 15:43.
Cheers Chimbu though I wasn't aiming it at you in particular about the moron thing 
It just annoys me that all instructors are labelled as such. The majority of instructors I have worked with are looking out for their students and learning where they can (we often did a day in the hangar when we could) to learn what we could.
We are all learning all the time and I look forward to getting into some of those articles. Getting my head around it sounds like relativity lessons at uni! All the same though I will be having a read.
Thanks
It just annoys me that all instructors are labelled as such. The majority of instructors I have worked with are looking out for their students and learning where they can (we often did a day in the hangar when we could) to learn what we could.We are all learning all the time and I look forward to getting into some of those articles. Getting my head around it sounds like relativity lessons at uni! All the same though I will be having a read.
Thanks
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[quote=Atlas Shrugged;2935992]Is this a serious question?
te]
Yes, it was a serious question and through the posts of positive contributors such as Chimbu Chuckles and links to pelican perch given by other contributors I am now more knowledgeable.
Perhaps instead of ridicule you could add something constructive next time?
te]Yes, it was a serious question and through the posts of positive contributors such as Chimbu Chuckles and links to pelican perch given by other contributors I am now more knowledgeable.
Perhaps instead of ridicule you could add something constructive next time?
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AWO 157.
Before a student starts on navigation training he will have undergone many hours of general handling both in the circuit and in the training area. It takes just a few minutes to teach a student how to lean the mixture correctly. There is then ample opportunity to double check on his knowledge of mixture use during subsequent flights well before "complicated" flying like straight and level on a navex...
Isn't that where all this you beaut competency based training comes in? Box No.7 "Knowledge and correct application of mixture control". You don't tick the box until the student is competent at mixture leaning. That completed -then on to the next box of competency based training. By the time the first navex arrives your student should be able to handle a mixture control - after all you ticked the box didn't you?
I think the other reason only basic leaning techniques are taught is that more often than not the student is struggling with a multitude of other things during the flight
Isn't that where all this you beaut competency based training comes in? Box No.7 "Knowledge and correct application of mixture control". You don't tick the box until the student is competent at mixture leaning. That completed -then on to the next box of competency based training. By the time the first navex arrives your student should be able to handle a mixture control - after all you ticked the box didn't you?
OK Guys and correct me if I'm wrong or have got something 'out of context'...
But was not the PA.31 in to the water near Whyalla the result of metal fatigue in the donks (BOTH) caused by overleaning.....to 'save fuel' ...over an extended period of time I would guess ...and really 'LOP' it would seem.
Am standing to learn some more......
OVAH
But was not the PA.31 in to the water near Whyalla the result of metal fatigue in the donks (BOTH) caused by overleaning.....to 'save fuel' ...over an extended period of time I would guess ...and really 'LOP' it would seem.
Am standing to learn some more......
OVAH
When you live....
OK Guys and correct me if I'm wrong or have got something 'out of context'...
But was not the PA.31 in to the water near Whyalla the result of metal fatigue in the donks (BOTH) caused by overleaning.....to 'save fuel' ...over an extended period of time I would guess ...and really 'LOP' it would seem.
Am standing to learn some more......
OVAH
But was not the PA.31 in to the water near Whyalla the result of metal fatigue in the donks (BOTH) caused by overleaning.....to 'save fuel' ...over an extended period of time I would guess ...and really 'LOP' it would seem.
Am standing to learn some more......
OVAH
Grandpa Aerotart
Griffo no that was not the case...and based on Deakin's writings on the subject ATSB got into a big huff and wrote nasty letters to George Brailey at GAMI..he invited them over to look at the Chieftain engine in his test cell and see for themselves.
They went...they looked...they were stunned...they came back and the person who wrote the original report found himself in deep pooh.
The above was told to me by someone VERY senior in CASA Airworthiness branch
http://www.avweb.com/news/pelican/list.html
Above is a link to all of Deakin's articles...not just the engine ones. #57 and 58 are the Whyalla ones that stirred up ATSB.
There are a multitude of VERY interesting articles there as well..read the one called No Pisco Sours for me...it'll make your skin crawl. He is a fascinating fella.
They went...they looked...they were stunned...they came back and the person who wrote the original report found himself in deep pooh.
The above was told to me by someone VERY senior in CASA Airworthiness branch
http://www.avweb.com/news/pelican/list.html
Above is a link to all of Deakin's articles...not just the engine ones. #57 and 58 are the Whyalla ones that stirred up ATSB.
There are a multitude of VERY interesting articles there as well..read the one called No Pisco Sours for me...it'll make your skin crawl. He is a fascinating fella.
Have to say the nastiest engine for ground fouling I've come across is the Lycoming O-540. You can hear the engine go from 
to as you pull the mixture out.
When I did some conversion training on a new aircraft type with the big Lycoming, the instructor was dead against ground leaning and would not let me anywhere near the red knob! After that flight I made sure leaned it back to just above cutting out and left it like that for the entire taxi. This was long before I read Deakin's articles, I did it simply because the engine did not sound happy running at fully rich! The smaller engines I've used didn't sound like they cared much where they were operated mixture wise but after an engineer showed me a set of "new" plugs from an O-235 that never gets leaned I've since decided I'm doing the company whom I hire my aeroplane from on weekends a favour by leaning on the ground.
to as you pull the mixture out.When I did some conversion training on a new aircraft type with the big Lycoming, the instructor was dead against ground leaning and would not let me anywhere near the red knob! After that flight I made sure leaned it back to just above cutting out and left it like that for the entire taxi. This was long before I read Deakin's articles, I did it simply because the engine did not sound happy running at fully rich! The smaller engines I've used didn't sound like they cared much where they were operated mixture wise but after an engineer showed me a set of "new" plugs from an O-235 that never gets leaned I've since decided I'm doing the company whom I hire my aeroplane from on weekends a favour by leaning on the ground.
No FADEC on Cirrus
Just a correction and an illumination:
Cirrus SR22's at least, and most likely SR20's as well do not have FADECs They have a nasty red lever to fiddle with like every other ancient GA engine in the world.
Mixture is meaningless on a Diesel engine. They run unthrottled (in aviation applications) so you add fuel to add power, but the air stays the same - notwithstanding that the extra exhaust energy will generate more boost pressure and pump more air - this is a secondary effect. There is a limiting air-fuel ratio which is where the engine begins to smoke. It can run richer than this, but most people don't like to leave trails of black crap out the back of their aeroplanes.
A
Cirrus SR22's at least, and most likely SR20's as well do not have FADECs They have a nasty red lever to fiddle with like every other ancient GA engine in the world.
Mixture is meaningless on a Diesel engine. They run unthrottled (in aviation applications) so you add fuel to add power, but the air stays the same - notwithstanding that the extra exhaust energy will generate more boost pressure and pump more air - this is a secondary effect. There is a limiting air-fuel ratio which is where the engine begins to smoke. It can run richer than this, but most people don't like to leave trails of black crap out the back of their aeroplanes.
A
Grandpa Aerotart
Ahh..is it a prop control the Cirruses don't have? I am sure I read somewhere they had some clever system in place...or perhaps am mixing up the, so far less than successful, drive for FADEC by TCM and LYC.
Just out of curiosity I am gonna hire a Cirrus next time I am in Brissy and see what they are like...then again perhaps I shouldn't lest it dent my affection for my Bo...pilots are just aeroplane sluts after all is said and done.
Just out of curiosity I am gonna hire a Cirrus next time I am in Brissy and see what they are like...then again perhaps I shouldn't lest it dent my affection for my Bo...pilots are just aeroplane sluts after all is said and done.
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so far less than successful, drive for FADEC by TCM and LYC.
RE: LOP and 'over-square'... some years ago I read an article on AvWeb by (then) editor Mike Busch, entitled 'Operating Tips for Big-bore Continentals'. I've, searched for it recently but cannot find it. It seems very similar to what I'm seeing reported of Mr Deakin's articles, which I haven't had time to peruse yet. That article completely exploded many of the operating myths of big-bore engines and totally transformed the way I handle my engines. Aggressive leaning and 'over-square' operation have been the norm for me for some time, with no sign of distress from my engines -quite the opposite in fact. Put two identical machines side-by-side, operate one by 'conventional' wisdom and the other in the LOP/over-square regime and expect the LOP/over-square machine to out-perform the other aircraft in every measurable parameter, except maintenance down-time and expense! I'm seeing it daily.
One final thought: I've been more of a lurker than an active participant in these forae for a long time... mainly because the threads usually degenerated into vituperative flaming or flogging the '89 dead-horse. It's very encouraging to see such an interesting, instructive and educational thread persist... congrats to all participants! Keep it up
Last edited by kiwiblue; 1st Nov 2006 at 16:22.
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CC........most of the peolple I know who own/operate Mooneys/Bonanza,s/Barons are either DR,s or proctologist,s.....something Ive noted over the years.....
But on a more serious note,your posts on this subject have actually taught me a few things for sure,and I have downloaded your posts(to reference) to try on my own stratocruiser,and if you have info pertaining to the C-185 and its ops,Skywagon,IO 520D Continental .....would be interested to hear......great posts and well worth the read...PB
But on a more serious note,your posts on this subject have actually taught me a few things for sure,and I have downloaded your posts(to reference) to try on my own stratocruiser,and if you have info pertaining to the C-185 and its ops,Skywagon,IO 520D Continental .....would be interested to hear......great posts and well worth the read...PB
Last edited by pakeha-boy; 1st Nov 2006 at 18:16.
Grandpa Aerotart
Ahh the mighty Skywagon. I owned a 1963 model in the early 90s. I have MANY hrs instructing in them in PNG too, including doing peoples initial tailwheel endos in them and route/airstrip endorsing in PNG.
The IO520 is VERY nearly the same engine as the IO550B in my Bo...if you don't have Gamijectors and an all cylinder monitor, I have an EDM700 with fuel computer but the 800 has a few extra features I would like, get them installed asap.
The money they will save you in fuel and maintenance, including extended engine life, will pay for them many times over in short order.
The ultimate C185 would be one with a Gamispec TNIO550B...PHAAOOR
If anyone is interested this is a Gami lean test I did in my Bo not long after the Gamijectors were installed. It was done at 21/2500, 8500' with the cowl flaps open. Look at how far before peak EGT peak CHT occurrs and at the high numbers attained by the three hottest cylinders. As an interesting aside these cylinders usually run hotter in Bonanzas and is a baffling issue. Cylinders 2,4 and 6 sit behind the alternator which inhibits airflow into that side of the cowl...new baffles, specifically optimised for Bonanzas will lower those numbers by about 40-50F and will be installed soon. When they are it should give me some more TAS (more fuel=more power=go faster=most excellent) while still keeping well below 380F on which ever cylinder runs warmest post new baffles.
http://www.fototime.com/{16048238-E9...9}/picture.JPG
You will note that all CHTs and EGTs peak within <.5 gallon/hr. This is most excellent and the reason why the engine runs smoothly LOP. But the CHTs peak 70+F before the EGTs peak. The figures at the very bottom, 74LOP etc, are how far LOP I got before discontinuing the test...it was where very slight rough running became apparent. See how quickly the CHTs fall away past peak EGT...cooler and cleaner because little excess fuel is left over after combustion is finished...CO2 is not present either, which can be a problem operating ROP.
This is why I always harp on about 380F and temperatures being the big enemy. Note that tensile strength is the verticle axis and temperature the horizontal axis. At the published redline 2/3rds of the tensile strength is gone...at 380F 2/3rds of the tensile strength remains...roughly. Repeated exposure to high temps even 30-50F below published redline permanently weakens the cylinder metal and leads to cracking and ovaling of the cylinder barrels which leads to loss of compression. If you think it isn't a common or widespread issue take a look through the aeroplane adds and see what % have been top overhaulled around mid TBO...it is frightening.
The IO520 is VERY nearly the same engine as the IO550B in my Bo...if you don't have Gamijectors and an all cylinder monitor, I have an EDM700 with fuel computer but the 800 has a few extra features I would like, get them installed asap.
The money they will save you in fuel and maintenance, including extended engine life, will pay for them many times over in short order.
The ultimate C185 would be one with a Gamispec TNIO550B...PHAAOOR
If anyone is interested this is a Gami lean test I did in my Bo not long after the Gamijectors were installed. It was done at 21/2500, 8500' with the cowl flaps open. Look at how far before peak EGT peak CHT occurrs and at the high numbers attained by the three hottest cylinders. As an interesting aside these cylinders usually run hotter in Bonanzas and is a baffling issue. Cylinders 2,4 and 6 sit behind the alternator which inhibits airflow into that side of the cowl...new baffles, specifically optimised for Bonanzas will lower those numbers by about 40-50F and will be installed soon. When they are it should give me some more TAS (more fuel=more power=go faster=most excellent) while still keeping well below 380F on which ever cylinder runs warmest post new baffles.
http://www.fototime.com/{16048238-E9...9}/picture.JPG
You will note that all CHTs and EGTs peak within <.5 gallon/hr. This is most excellent and the reason why the engine runs smoothly LOP. But the CHTs peak 70+F before the EGTs peak. The figures at the very bottom, 74LOP etc, are how far LOP I got before discontinuing the test...it was where very slight rough running became apparent. See how quickly the CHTs fall away past peak EGT...cooler and cleaner because little excess fuel is left over after combustion is finished...CO2 is not present either, which can be a problem operating ROP.
This is why I always harp on about 380F and temperatures being the big enemy. Note that tensile strength is the verticle axis and temperature the horizontal axis. At the published redline 2/3rds of the tensile strength is gone...at 380F 2/3rds of the tensile strength remains...roughly. Repeated exposure to high temps even 30-50F below published redline permanently weakens the cylinder metal and leads to cracking and ovaling of the cylinder barrels which leads to loss of compression. If you think it isn't a common or widespread issue take a look through the aeroplane adds and see what % have been top overhaulled around mid TBO...it is frightening.
Last edited by Chimbu chuckles; 1st Nov 2006 at 17:53.
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Interesting thread..
I have just started towing banners and in doing so my CHT has been stabilising just under 400F and I wasn't sure if this was going to cause any long term damage. So I did a little research and in my travels found this article from Lycoming about leaning techniques.
Thought it might be interesting as a myth buster.
http://www.lycoming.textron.com/supp...ps/SSP700A.pdf
I have just started towing banners and in doing so my CHT has been stabilising just under 400F and I wasn't sure if this was going to cause any long term damage. So I did a little research and in my travels found this article from Lycoming about leaning techniques.
Thought it might be interesting as a myth buster.
http://www.lycoming.textron.com/supp...ps/SSP700A.pdf
And for those of you who run 50 ROP, note that CC’s lean test table at the link shows that at 50 ROP you are at peak CHT plus or minus a couple of negligible degrees.
If your aircraft only has a single EGT gauge, you could be ‘lucky’ and have a big fuel flow differential between cylinders and only be cooking one at 50 ROP indicated.
Wombat: I think Deakin has pretty well demolished that document, which, interestingly enough, says:
Bolding in original.
The problem is the lack of aircraft instrumentation, lack of balanced fuel flows in stock engines, lack of pilot knowledge, and lack of competent engine management.
If your aircraft only has a single EGT gauge, you could be ‘lucky’ and have a big fuel flow differential between cylinders and only be cooking one at 50 ROP indicated.
Wombat: I think Deakin has pretty well demolished that document, which, interestingly enough, says:
Lycoming is in complete agreement that it is possible to operate an engine on the lean side of peak TIT. It is done on
engines in our well-instrumented Experimental Test laboratory every day. There is nothing detrimental in operating an engine in
this manner.
engines in our well-instrumented Experimental Test laboratory every day. There is nothing detrimental in operating an engine in
this manner.
The problem is the lack of aircraft instrumentation, lack of balanced fuel flows in stock engines, lack of pilot knowledge, and lack of competent engine management.