Mixture & Rudder Trim

[KCDW]

My instructor, who I have an immense respect for, basically told me to ignore the above during my flight training.

All well and good, but now I've grown up and have started wearing long trousers, I've started wondering...

Recently, I have tentatively started reducing the mixture above 3000'. But to be honest, I do feel "so what", as I rent my planes and so don't directly benefit from reduced fuel costs. Anyone out there to put me right on this?

As for the rudder trim, I have never so much as touched it. Don't feel a need for it in the Warrior. Only time I have heavy rudder usage is in a sustained climb, but they don't last very long. Again, do people use it?

[flyboy6876]

KCDW

I use rudder trim quite extensively, especially on nav flights. I've found that it saves a lot of wear and tear on my legs and does'nt fatigue me as much as sitting pressing on the rudder pedals constantly.

Mixture is not just a case of fuel conservation but also affects the aircraft engine. I do adjust the mixture at the top of the climb and on descent (or any other time I change power settings). You may want to read up about this a bit more in your text books.

[BEagle]

1. Rudder Trim. Your feet are less sensitive than your arms, so carrying an out of trim rudder force is less noticeable - unless you're talking about an aeroplane on asymmetric power. However, use it to keep the ball centred with no residual foot loads and your flying will be more comfortable. Plus your heading will be less likely to wander on a navigation exercise.

2. Mixture. In the UK, there is normally no need to adjust the mixture below 3000 ft UNLESS you have an operating CHT gauge. Most Warriors don't have one, those that do (or have EGT gauges) often have U/S installations. The old trick of pulling back the mixture until the onset of rough-running, then pushing it forward a bit can do a lot of harm to an engine at high power settings UNLESS THE CHT CAN BE MONITORED!! I've had to replace a 'cooked' cylinder pot on an otherwise sound engine which had only done 600 hours because some idiot leaned the mixture excessively. Fuel is cheaper than engines - leave it at fully rich below 3000 ft unless you can monitor the CHT!

[knobbygb]

Rudder trim. Unfortunatley the Warrior is so easy to fly without virtually any rudder input that it really instills bad habits in students. I recently converted to another type and was surprised at just how important it can be to keep the ball in the centre. I can understand you not using the rudder trim much (many types don't have it), but I'm not sure it was a good idea to activley tell you to ignore it! Please, at least check it's centered pre-flight, if nothing else. If someone's been flying crosswind before you, you could get a nasty surprise on takeoff.

Mixture. I too was surprised not to be taught this during training. I know we don't get chance to fly higher thasn 3000ft much in the UK, but a PPL is a license to fly just about anywhere in the world and this should be an integral part of the course, surely? I recently flew in the USA and had to ask the checkout instructor to demonstarte mixture leaning as we were regularly getting up to 6000 or 7000 ft. Without fail, I forgot to reset the mixture during descent - because I'd never done it before and my UK checklist doesn't have a 'descent checks' section.

[KCDW]

Thanks guys,

Knobbygb - hadn't thought about centering the rudder trim on pre flight before - scary!

Beagle - time for my monthly stupid question, what other way of leaning the mixture is there? How do you know if you've leaned it enough if it you don't hear it go rough first?

[Davidt]

Rudder - set it and forget it on a stable tourer like a Warrior, but have a go in someting uncoordinated like a Citabra if you dont use your feet your all over the place.Get back in your spam can and feel how much more coordinated your turns are!

Mixture - lean any where never mind the 3000 ft old wives tale , Piper and Lycoming both recommend leaning on the ground ( remember full rich for take off). Read the poh for the technique recommended for your engine. Fuel might not matter to you now but some time you will want to go somewhere and best economy will be important. I fly an aircraft with a fuel flow guage and it make a hell of a difference 22gph full rich as opposed to 11.5 gph properly leaned. having said that as a student you should do as instructed and minimise work load til things happen automatically. Once you've wrapped your head round the basics read john Deakins articles on engine management on www.avweb.com

[MLS-12D]

I agree with Davidt. You may as well pick up good habits now, even if you are renting (not owning) a foregiving plane like the Warrior.

Mixture leaning is especially important when operating aircraft with engines designed for 80/87 fuel (if you know where to get this, please let me know!). See generally http://www.lycoming.textron.com/support/publications/maintenancePublications/serviceLetters/SL185B.pdf

No, you don't have to have a CHT/EGT indicator to lean a non-turbocharged engine safely; although it is certainly more efficient if you do happen to have one. If your usual airplane is fitted with an EGT gauge, see http://avstop.com/AC/2-18.html

When mishandled (which is not limited to aggressive leaning; it also includes "set at full rich always"), the mixture knob can lead to fouled plugs, increased fuel burn and expense, burned valves, and possibly a fuel exhaustion accident. Well worth getting some proper instruction. If your current instructor says that it's really not worth borthering about (below 3000' or otherwise), get a more experienced instructor.

In the meantime, here are some on-line articles worth reading:

http://www.foxflying.com/EngineLean.htm
http://www.cyberair.com/tower/faa/app/p8740-13/0978-13.html
http://www.lycoming.textron.com/support/publications/maintenancePublications/serviceInstructions/SI1094D.pdf
http://www.flightsafety.org.au/articles/l0053.php
http://www.eci2fly.com/Tech_Ref/Service_Instructions/93-6-7.pdf
http://www.avweb.com/news/columns/182084-1.html

[KCDW]

MLS-12D

Thanks for the links - this is why PPRuNe is so good!

To be fair to my instructor, this was only for when I was on the PPL, and he didn't want to confuse things at that time.

[bookworm]

If your current instructor says that [leaning is] really not worth borthering about (below 3000' or otherwise), get a more experienced instructor.

or one who can do arithmetic!

For a 200 hp Lycoming IO-360 run at 65% power, the difference between the best-power and best-economy settings is about 1.5 USG/hr or 6 litres/hr. Over the useful life of an engine, that's going to add up to something like 10,000 litres of AvGas. Depending on your outlook on life, multiply by either pounds per litre or trees per litre to understand the impact. Note that full rich mixture is not 'best power'. It involves burning even more fuel for less speed.

But please let's not ignore BEagle's point. Running continuously high CHTs is not recommended. Leaning does not necessarily increase the CHT, but it can do at approximately best power. The kindest way of running for the engine is properly leaned but at a medium power setting -- say 65% rather than the maximum permitted 75%. That will do more for the CHTs than cooling with buckets of excess fuel.

[MLS-12D]

KCDW - Yes, I certainly agree that leaning is not something that has to be bothered with during primary instruction, when the student is already overwhelmed with other, more important matters. Now that you are more advanced, hopefully your instructor will be open to teaching you leaning procedures . If not, well, you know what to do. ;)

Bookworm: good points. Personally I almost always cruise at 65% (I'm not going to get anywhere fast in the aircraft I fly, so why not?!).:D

[ratsarrse]

At the weekend, I was practising circuits with my instructor. I noticed that at some point after take-off, he'd leaned the mixture without me even noticing. I asked why, but the response was 'I'll tell you later when you're not quite so busy.' Fair enough, but naturally by the time we were back on the ground, I'd forgotten all about it. This thread has reminded me about it, but no doubt by the time I go flying again I'll have forgotten. So, what do people think? Speculation and reasons why you'd lean the mixture in the circuit...

[Flyin'Dutch']

Apart from the obvious and already mentioned benefits of leaning you better give this subject some thought if you want to reach anywhere near the range/duration as quoted per book.

Of course is leaning easier with an EGT but in a fixed pitch machine you can just:

1. set the revs as per the power you desire
2. slowly lean the engine until the development of rough running
3. enrich slightly.

As long as your power is set at less than 75% there is no chance of doing any damage. (See the Textron site for this)

I think the reason why most instructors don't tell pupils on how to lean is...........................................because they don't know how to it properly themselves.

FD

Advantages of leaning are: Less fuel consumption; less lead deposits in the plugs; less valve stem problems; less engine wear; longer range; saving money etc

[Sultan Ismail]

Just like to add my 2 cents worth, in particular response to the first post.

Pre take off checks are either done from a mnemonic or a checklist, my own experience since day 1 on the PPL, was using the mnemonic, TMPFHIC.

T - Trim, Throttle Friction

M - Mags Master Mixture

The Mixture also pitched up later in the FREDA and HASEL checks.

I now use a checklist produced by AFE and this also includes the Trim and Mixture in the checks where my nmemonics had them.

So. Are you being correctly taught? Where are the nmemonics and checklist?


Another 2 cents worth, my PPL training was from an airfield at 3000' msl, mixture leaning was standard procedure after the mag drop test, this demonstrated the additional power available after leaning and cleaned the plugs after the mag drop.


In later years, when flying from 5500' msl it was normal to do the power check at max rpm and then lean, similar to methods described in the other posts, and use this setting for takeoff. Now before anybody screams, at 5500' you are not developing 100% power, so the comments from Flyin'Dutch' still stand.

However on a turbocharged or turbo normalised machine it was always mixture rich at take off.


Old habits die hard, I would suggest that KCDW gets into the right habits ASAP.


Sultan Ismail

[flyboy6876]

KCDW

Have a look here. Some good info.


www.pprune.org/forums/showthread.php?s=&threadid=85797 (http://)

[KCDW]

flyboy6876 - your thread didn't work.

All, thanks for the input. Have to say that I am amazed at how many of you were seemingly taught mixture adjustment at PPL. I was definitely given the impression it was outside the syllabus.

Sultan, I have to say that you will naturally think that knowledge of using the mixture is a necessity if you learn to fly in places like Jo'burg :) . I would venture it is not one when your PPL aerodrome is at 72' and there's Class A from 3000' or so.

Still it's now on the agenda, I've been reading up:

* Don't do it at 100%, wait till you've settled into 65-75% RPM
* Lean till either the tacho peaks out, or the engine roughens, then enrich till the engine's smooth.
* Relean every altitude change
* Enrich on downwind checks (so that's what the M stands for in BUMFFICHH ;) )

Thanks all!

[FlyingForFun]

KCDW,

Just to clarify one of your points: "Relean every altitude change." Maybe amend this to:

"Enrich before every altitude change, re-lean on reaching the altitude."

When climbing, the extra fuel is nice because it keeps the engine cool. When descending, if you don't enrichen the mixture at least a little bit first, then you'll be running too lean as the descent continues, which is very bad for the engine, and you might not notice because you'll be at low power settings.

As with all aspects of flying, far better to do it with an instructor than learn from these forums. I'd suggest finding a willing instructor and doing a half hour of dual.

FFF
-------------

[A and C]

And just how often have you heard that !.

Well I,v had it said to me thousands of times over the last twenty years , but I have yet to see it writen in a Lycoming or Continental manual.

The fact is that it is a bit of aviation folk lore left over from the dark past of british aviation when if it was a light aircraft the thing that powerd it was a Gypsy Major.

Yes guys its a Gypsy Major limitation ! ............for all other types read the flight manual and save your selfs 20% on the fuel bill.

[dmjw01]

"Don't do it at 100%, wait till you've settled into 65-75% RPM"


Forgive me for being pedantic, but that's not quite correct. You should cruise at or below 65-75% POWER - this is not the same as 65-75% RPM, and it's not the same as 65-75% THROTTLE. If you cruise at 65% RPM, I'd be surprised if you maintain straight and level!! ;)

Example for my own aircraft (a 1959 C172)...

I generally cruise at a gentle 2300 RPM. This is 85% of the rated RPM (2700). At 2500 feet, this is only about 57% power. At 5000 feet, it's now only 54% power. At 7500 feet, it's 51% power. But note that all these figures are for the same RPM.

I'm always below 65% power in the cruise, so therefore I always lean at all altitudes - even when pottering along under the Gatwick CTA at 1500 feet. This gives me a fuel-burn of about 25 l/hr or thereabouts. I don't bother leaning in the circuit though - there simply isn't enough time.

You need to take a look at the POH for your aircraft, which should contain a table telling you percentage power at various combinations of RPM and altitude. Remember also that "percentage power" is a percentage of the maximum rated power of the engine - i.e. the power achievable at sea level. Even at 2500 feet you'll probably not get more than 85-90% power even at full throttle.

Obviously all of this applies to non-turbocharged, fixed-pitch aircraft.

[BEagle]

I've no problem with leaning off the mixture at any altitude after take-off if you've got a fuel flowmeter and CHT gauge!

The military used to fly the Bulldog at 2600, best power mixture, MAP as req'd for most of the time - mainly for performance and 'single lever' methodology for the students. But it drank fuel.... I once flew one from Abingdon to St Mawgan with the prop back as far as I dared and MAP up just below the point of over-boosting with the mixture leaned as far as possible. The aircraft flew just as well at the same speed as my gas-guzzling chums in the formation - but I landed with 3 gallons more than they did! BUT it was necessary to keep a very close eye on the CHT and to select a richer mixture periodically.

Pity we'd stopped teaching the students how to set the engine up for long range economic cruising - but they were all training to be future jet pilots!

[A and C]

I,v never had a problem with CHT in a light aircraft even when down in the med at temps of +43c or more and I think that the only non-turbo people who do are the glider tugs as they use high power settings at low airspeeds.

The limitation that seems to give me the most problems is oil temp after even a short taxy in a southern european summers day the temp is such that a "step climb" is required to keep the temp out of the red arc.
This seems to be a taxi problem as I came close to shutting the engine down at the hold of 09R at Heathrow on a cool day due to high oil temp after the longest taxi I have ever had.

For me the key to getting the leaning right is the EGT indicator as this gives almost instant indication of the mixture.

As to running at low power setings Lycoming recomend 60% for maximum engine life and I have found that this will give me the best range and would recomend it for the long range cruse but use of this setting all the time has a tendancy to cause the piston rings to stick and oil consumption to increase ,I have found that after about 9 hours of 60% I fly one hour at 75% and this seems to avoid the ring sticking problems.

[englishal]

The idea of leaning the mixture is to allow the engine to produce maximum power. In the UK its not a big deal, but if you ever fly from any high DA airports then it can be vital to lean prior to take-off. [as in the Mixture - Best Power pre take-off checklist item].

Rgds
EA:D

[Tinstaafl]

Leaning the mixture is not necessarily, or even just, about producing best power, although it can be eg leaning for take-off at high density altitudes.

Best range or endurance is at least as important.

Financially, best economy by reducing fuel consumption is also a consideration.


Lean at all altitudes as long as the manufacturer's leaning parameters have been met.