Magneto/ Propeller pitch.

[novicef]

Just wondering why when a propeller is cycled from fine to coarse pitch it manages to clear a rough running magneto?

[the wizard of auz]

No, it will never help an engine running rough due to magneto problems, although when doing runnups, it can help clear oiled/fouled plugs, by increasing the workload on the engine and making it burn a little hotter.

[tinpis]

It helps clear any gunk out of the sphincter valves in the primary thronomister section.

[tlf]

I had an expert instructor, he must have been coz he had lots of gold on his shoulders, well he told me to always use one magneto only at a time, that way if it failed you'd always have a good spare. If you run them both at the same time they are both likely to break at the same time.:}

[scrambler]

I believe that the change in pressure in the cylinder may help to dislodge carbon deposits on the plugs.

[Andy_RR]

I think the pressure in the cylinder is changing quite rapidly every revolution - even at a constant speed and load.

[Lefthanded_Rock_Thrower]

A load of Bollocks, a rough running mag ( as opposed to a U/S mag, lead or plug ) is generally one of two things :

1) a little moisture in the Mag causing arching, or,
2) Carbon / Oil deposit on the plug, this is best removed by increasing the burn temperature in the cyclinder, for example run up to full power and gently lean this mixture for about 30 seconds.

So in other words, having run the engine up to do the prop check has infact increased the cylinder temperature and probably burn't off the crap on the plug.

[Takan Inchovit]

Just wondering why when a propeller is cycled from fine to coarse pitch it manages to clear a rough running magneto?

It had to be a rough running prop then. :hmm:

[Harry Cooper]

Actually its not a load of bollocks.

I used to use that technique all the time to clear the plugs on C210's to save running up engines over loose gravel. If the prop was cycled a few times after locating a fouled plug, at around 1700 rpm, then nine times out of ten it would fix the situation without having to resort to high power runs. Obviously that is only good when it is a fouled plug not a magneto problem. I heard about the technique at a forum with Richard Collins (from Flying magazine) at Oshkosh a few years ago. He said it increases the pressure inside the cylinder effectively blowing the plug clean. I think that was a very simplified explanation but I could care less - it works.

[ABX]

Gudday Harry,

I am not a LAME or any sort of mechanic, but I've been around a few engines ...

Not disputing that the technique you described works, however, I suspect that the engine cylinder pressure does not change by raising or lowering the rpms, after all if an engine has a (for example) 12 to 1 compression ratio, it will produce it (12/1) at 500 rpm or 2500 rpm.

I tend to favour the higher engine temps burning off combustible contaminants and also increased engine vibes shaking loose any solid stickies that may come loose, such as carbon (before it burns off) or oxidisation etc.

Obviously 1700 rpm is enough in your example and I guess if it can be done at that rpm all the better.

Just my two cents, now standing by for correction.

Cheers,

ABX

[Harry Cooper]

Fair call.

Until I had seen that forum I had never heard of that technique to clear a plug - beats destroying a good propellor for nothing.

As for how it works I am unsure. By cycling the prop at those mid-range RPM's you still gain a fair wad of extra Manifold Pressure, effectively I would think, increasing the volumetric flow through that or those cylinders - if more air or in this case charge is entering the cylinder then I gather that the operating pressure would be higher at the power stroke. Maybe this technique "mimics" higher operating pressures and temperatures by cycling the prop at lower RPM's. I'd like to find out more though if anyone has any ideas?

[Chimbu chuckles]

These engines are 'fixed timing'....this means that if you slow the RPM down significantly the peak power pulse happes closer to top dead center.

In simple terms x amount of fuel and y amount of air are introduced through the inlet manifold and a spark occurrs at a fixed time..at normal RPMs that spark lights off the mixture with the piston at the ideal point, so the peak power pulse happens about 16 degrees of rotation past TDC from memory, to get maximum leverage applied to the piston to spin the crankshaft which spins the prop and the knee bone is attached to the leg bone.

That mixture is igniting into a combustion chamber that is relatively large and getting larger relatively quickly as the piston accelerates downward.

If you slow the RPM the combustion chamber is relatively small, as the piston is closer to TDC, and it is not accelerating away, initially, as quickly so the Peak Power Pulse, the maximum pressure in the cylinder, is much greater and that creates more heat as well...clearing crap off your plugs and blowing it out the exhaust valve (you hope). I think it is fairly easy to understand how cycling the prop briskly (not brutally or violently) from fine to coarse pitch at a middle of the road power setting would tend to loosen crap off the plugs.

It should also be realised that doing this at very high power settings could put you into detonation...the reason why the spark is timed to occurr when it does is because at full power on takeoff if the peak power pulse occurred with the piston much closer to TDC the detonation margins would be reduced to near nothing...just in case someone reading this is tempted to think that if doing this at modest power settings works then doing it at high power settings works better:ugh:

Hope that helps explain it novicef.

Edited to add some highlighting and restructure one sentence just a tad for jamair the pedant:ok:

[A37575]

clear the plugs on C210's to save running up engines over loose gravel. If the prop was cycled a few times after locating a fouled plug, at around 1700 rpm

I would have thought 1700rpm is certain to pick up loose stones as the vortices under the prop tips can be seen quite clearly on a wet surface during a normal run up at that rpm.

[Jamair]

Chuck - 16 degrees PAST TDC??!!:mad: If the Pelican were dead, that one would make him spin in his grave - if he hears it it might just knock him off his Perch anyway!!:eek: I'll put it down to temporary alcohol induced madness.....? See Deakins PP #18 - Mixture Madness.

Ignition happens BEFORE TDC.:= PPP (peak pressure point) occurs about 16 degrees AFTER TDC, as it takes a consistant time for the flame proagation to fully develop.

As for the rest of the topic - FIIK. Running up to 1500-1700 or whatever on a leaner mixture sure does clean oily plugs; never tried the prop cycling thing for that purpose though. Damn sure it does sod-all to the maggies.:rolleyes:

[Lefthanded_Rock_Thrower]

Sorry Chuck, would have to disagree with you on that one.

Spark goes in at usually 20 or 22 before TDC ( retard points on the LH mag are usually about 10 degrees less ).

The increase of RPM to 1700 increases the burn temperature, even when fully rich, therefore will generally burn off carbon/oil.

The 540 or 520 does not have vacumm advance system or similar ( that i am aware of ).

The volumetric efficiency does not vary all that much ( excluding ring and valve leak ) with RPM.

[Chimbu chuckles]

Quite frankly I find that leaning brutally on the ground as soon as the engine is running smoothly stops me getting fouled plugs...I simply never get them in the Bo.

None the less my previous post, as amended to completely satisfy my old mate jamair:E , is the theory behind why cycling the prop might, if the fouling wasn't too bad, clear it.

[Jamair]

Jeez Chuck you must be bored - I've just got home from a late shift & I'm winding down from dealing with some 'difficult' clients - WTF are you still doing up? You should be getting some shut-eye in prep for your Captains Course tomorrow....:ok:

[Chimbu chuckles]

weekend off, except I will be studying for Flight Time Limitations exam on Monday, and it's 2 hrs earlier here than there.:ok:

[Sunfish]

What will not change if the prop is cycled at constant manifold pressure is brake mean effective pressure (BMEP), this is equivalent to torque.

I would have thought that the way to increase combustion temperatures would be to increase manifold pressure at constant RPM. This would increase BMEP and temperature within the cylinder.

In other words, assuming the governor is governing (>2000 rpm?) playing with rpm aint going to do anything because the engine isn't going to "see" any change.

Messing with the power level via the manifold pressure (ie throttle) should change things.

Personally, leaning does it for me.

OK all you experts, tear me to shreds.

[the wizard of auz]

The governor is being over ridden by using the prop lever to change pitch. thats why the engine slows down when the prop is cycled. the engine will try to maintain the speed it was running at due to the manifold pressure being set and therefore the engine is required to do more work, resulting in a higher burn temprature as the piston is harder to push downwards and the combustion process is held in the cylinder longer before being released.

[The Messiah]

Get a life you sad people. I'm serious.........get a life. This can't be all you have can it????? Talking about combustion pressures and temps in an A-36 is really bad and sad.

[Chimbu chuckles]

Gee Messiah....no it's not all we discuss around here...but how an engine works is interesting too...no-one twisted your arm or held a gun to your head so you could, if the mood took, just nick off...I am sure we'd all appreciate it:ok:

[The Messiah]

2781 posts...............get a life.
Last time I checked the magnetos control when the spark occurs and nothing else. No pulse no spark. It's pretty simple stuff. Detonation and pre-ignition aside.
The overcomplication of the most simple principles that you lot crap on with here amazes me. Horiz opposed aeroplane engines were designed 50 odd years ago to be as simple as possible so that try as they might, even pilots couldn't stuff them.
The KISS principle is the foundation which aviation was built around yet you tossers (Chimbu et al) refuse to follow it. You need to get hobbies.
The most harmful thing to any aircraft is a bored pilot.

[ABX]

Chimbu Chuckles, how went the exam? If it is possible to know someone on PPRuNe, I'm sure you be in the left hand seat before too long. (I'm guessing that your exams are part of captaincy progression?) Best of luck anyway.

the messiah ... perhaps you thought this was jetblast? Maybe the goat is for you.

Does anyone know what happened to the fish? I had a look at his recent posts and couldn't see any obvious reason to be made P.N.G. (perhaps the mods were looking for the mess.)

If you post something worth being banned for do they delete the post after they push the ban button?

Hope to see you back soon Sunfish.

[ABX]

BTW Chimbu Chuckles,

I flew J* into Cooly on 17/12/2006 and saw one of your 767s on the apron with a large line of black BMWs at the bottom of the steps...

Didn't happen to be there on the day did ya?

[ForkTailedDrKiller]

"Chimbu Chuckles ...... I'm sure you be in the right hand seat before too long"

ABX - Would that be a promotion or a demotion???!!!

FTDK:cool:

[Chimbu chuckles]

Nope wasn't there...so far so good:ok:

[J430]

So what happened to Sunfish.....what did he do?

Miss his ranting, its entertaining in the least!:}

J:ok:

[ABX]

Thanks Forky, I've edited my post to reflect the true direction of career advancement, I assure CC that in fact the Captain sits in the left hand seat.

Groan - had a little brain/finger interface problem earlier. (One of the two was obviously not working properly!):*

[ForkTailedDrKiller]

J430 - The SolarPisces is alive and well (see the previous page to this thread).

FTDC:cool:

[ABX]

Yeah, but unless he paid for a strange personal title he is banned ... right?


Sunfish
Banned... Persona Non Grata

[ForkTailedDrKiller]

Messiah, I share your frustration at the PPRuNer tendancy to take some of the more straightforward elements of aviation and turn them into a complex dissertation, and would sight the 5 or 6 pages of a previous thread on "how to land a C182" as an example of this, not to mention the tendancy to turn flying a C152 into a B747-like multi-crew operation.

None-the-less, as someone who has tried hard for 33+ years to stay on top of my particular aviation niche, I have to say that I have learned a few things from hanging around in here - particularly from guys like Chuckles who, because of their inherent personality type (CC have you ever had a MBTI done?), have obviously spent a lot of time studing and thinking about most aspects of their flying - backed up by a bunch of hard won experience.

For example, as a result of hanging around in here, there is no doubt that I have a much better understanding of the most effective way to operate the IO520 up front of the BE35 that I fly, eg since I began leaning it soon after starting I have not had to deal with fouled plugs vs having to clear fouled plugs maybe 1 in every 4 starts.

However, as I pointed out in an earlier thread, the negative side of this is that when I taxy, the Bo no longer has the "cool" burble that I have loved for 33 years - it just runs smooth as a baby's bum, damn it!

I figure that if I pick up one thing that maybe stops me from smacking in, then its worth putting up with a bit of crap!

FTDC:cool:

[Jamair]

.....and if you don't like it - leave.:D

[Chimbu chuckles]

Wossa MBTI?:uhoh:

[DraggingAir]

CC,

Myers-Briggs Type Indicator. It's absolutely fascinating stuff. From Wikipedia: "Myers-Briggs Type Indicator (MBTI) is a personality test designed to assist a person in identifying some significant personal preferences."

Many modern psych tests are based on the same principles adopted in the MBTI. I reckon you are a ENTJ.

You can take a quick test at http://www.humanmetrics.com/cgi-win/JTypes2.asp. A web based test is of course much less valid than a properly administered test.

DA.

[SNS3Guppy]

By cycling the prop at those mid-range RPM's you still gain a fair wad of extra Manifold Pressure, effectively I would think, increasing the volumetric flow through that or those cylinders - if more air or in this case charge is entering the cylinder then I gather that the operating pressure would be higher at the power stroke. Maybe this technique "mimics" higher operating pressures and temperatures by cycling the prop at lower RPM's. I'd like to find out more though if anyone has any ideas?


Good guess, and it sounds reasonable, but wrong.

When you cycle the propeller, you're slowing down the engine. fixed drive or geared, you're slowing the engine speed. When you slow the engine speed, you slow down the airflow through the engine. You're not increasing pressures or temperatures. Nothing is being mimicked.

Your engine is a wind machine. Pistons move up and down and draw air into the engine through the induction, and expel it through the exuast. For reasons of self-perpetuation (to make it go) we add fuel and set it off with a spark. The faster that engine runs, the more air it draws in. The slower it runs, the less. The engine induction can be thought of as a vacum cleaner hose. Your home vacum, if you were to put a hand over the hose, would develop a very low internal pressure; in the airplane this would be a manifold pressure drop, and it's exactly what happens when you close the throttle.

If you put your hand over the vacum cleaner hose and then slow down the motor, the pressure in the hose will rise, because the motor isn't drawing as hard. Close the throttle on your engine, and you see a low manifold pressure. The throttle is nothing more than an air valve; it lets more air in the wider you open it. If it's closed, it's the same as having your hand over the hose...when your engine is at idle, you have closed off most of the induction, and the pressure in the induction (your manifold pressure) becomes very low. If you could speed up the engine by without opening the throttle (which you can't)...you'd see the manifold pressure drop even more.

When you cycle the propeller and see the manifold pressure rise, it's doing so because the engine is slowing, and drawing less air. When it does this, the pressure in the induction, or induction manifold, increases, and you see a rise in manifold pressure. You probably think that an increase in manifold pressure is increasing the pressure the engine sees, and therefore means more power...this is wrong. What you're seeing is a measure of the suction from the engine, not the pressure feeding it, and certainly not the cylinder pressures. Manifold pressure in a normally aspirated engine is the pressure value to which the engine has reduced ambient pressure, and nothing more. Think about it this way...shut off your engine at sea level and what do you see? Nearly 30 inches of mercury (for those using that measurement)...your highest value with the engine shut off. Imagine that.

Cycling your propeller does not clear the engine. Doing so might make you feel better, but you're far more likely to draw up loose chips and damage your propeller than anything else. Cycling your propeller to clear a fouled plug is much akin to waving your arms to cure a wart on your foot. Makes no sense? Neither does cycling your propeller to clear a fouled spark plug.

Leaning is what is necessary. Your fuel has far too much lead...the consequence of a number of reasons but far too much tetraethyl lead, and this results in fouled plugs when not enough heat and combustion exists to scavenge it. If your engine is fouling on the ground, what you need is an idle mixture adjustment. Sometimes if your engine is fouled just a little, you can clear it by running it up a little...but this is a consequence of the higher power setting and operating temperatures...not cycling the prop. Any benifits that are perceived to come from moving the propeller are purely coincidental.

You can perform an idle mixture test by running the engine at runup speeds and power settings and agressively leaning to ensure that it's clear. Reduce to idle and let it sit for a moment, then from a full rich position on the mixture, very slowly reduce the mixture to the point of cutoff. Watch your RPM gauge. You should see a 10-25 rpm rise right before the engine dies, indicating that the idle mixture is adjusted correctly. If you see more than this, your engine is running rich. If you see less, your idle mixture is adjusted too lean. Readjustment for proper idle mixture should be done any time the aircraft base is changed to a different elevation or density altitude, and should be checked and adjusted seasonally as the idle mixture needs will vary with the seasonal base temperatures.

The governor is being over ridden by using the prop lever to change pitch. thats why the engine slows down when the prop is cycled. the engine will try to maintain the speed it was running at due to the manifold pressure being set and therefore the engine is required to do more work, resulting in a higher burn temprature as the piston is harder to push downwards and the combustion process is held in the cylinder longer before being released.


The governor isn't being overridden at all; you're changing the tension on the speeder spring and setting the governor...you're controlling the governor directly. The engine will not at all try to maintain the speed..the engine doesn't know anything about maintaining a speed. That's strictly a governor function...you set the governor, and the propeller controls engine speed. When you retard the propeller control toward coarse, slowing the prop down, the engine certainly isn't trying to increase the speed of the propeller. The engine is under a higher oad due to increased induced drag on the propeller blades, which prevents the propeller from spinning faster, and as the prop is attached directly to the engine, this slows the engine, too. See the previous discussion for why. The piston isn't suddenly trying to push harder...the engine has slowed, airflow through the induction has slowed and volume decrased and indeed less power is available...same effect has closing the throttle with respect to the amount of air flowing.

You have several options when controlling the engine; open the throttle to increase manifold pressure (by increasing the opening/decreasing the amount of blockage to the engine), increase RPM without touching the throttle (drops manifold pressure because the opening in the induction hasn't changed, but the engine speed has increased and suction therefore increased in the induction), or any combinaiton thereof. Of their own accord, these actions will not clean a fouled plug.

Aggressive leaning will.

Lean the airplane when you're taxiiing on the ground and you won't have these problems. Do a run at runup RPM just before shutdown after each flight, and clear the engine thoroughly, before returning to an idle that's leaned out nearly to the poitn of cutoff for several minutes, before shutting down. Most owners and operators don't even know to do this, though it's been recommended operating practice by engine manufacturers for decades. Fly safe.

[ForkTailedDrKiller]

MBTI = Myers-Briggs (personality) Type Indicator

see http://www.myersbriggs.org/

In developing the Myers-Briggs Type Indicator , the aim of Isabel Briggs Myers, and her mother, Katharine Briggs, was to make the insights of type theory accessible to individuals and groups. They addressed the two related goals in the developments and application of the MBTI instrument:

The identification of basic preferences of each of the four dichotomies specified or implicit in Jung’s theory.

The identification and description of the 16 distinctive personality types that result from the interactions among the preferences (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/preferences.asp).”

Favorite world: Do you prefer to focus on the outer world or on your own inner world? This is called Extraversion (E) or Introversion (I) (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/extraversion-or-introversion.asp).

Information: Do you prefer to focus on the basic information you take in or do you prefer to interpret and add meaning? This is called Sensing (S) or Intuition (N) (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/sensing-or-intuition.asp).

Decisions: When making decisions, do you prefer to first look at logic and consistency or first look at the people and special circumstances? This is called Thinking (T) or Feeling (F) (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/thinking-or-feeling.asp).

Structure: In dealing with the outside world, do you prefer to get things decided or do you prefer to stay open to new information and options? This is called Judging (J) or Perceiving (P) (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/judging-or-perceiving.asp).

Your Personality Type: When you decide on your preference in each category, you have your own personality type (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/your-personality-type.asp), which can be expressed as a code with four letters.

The 16 personality types of the Myers-Briggs Type Indicator® instrument are listed here as they are often shown in what is called a “type table.”

ISTJ (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/the-16-mbti-types.asp#ISTJ) ISFJ (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/the-16-mbti-types.asp#ISFJ) INFJ (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/the-16-mbti-types.asp#INFJ) INTJ (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/the-16-mbti-types.asp#INTJ)
ISTP (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/the-16-mbti-types.asp#ISTP) ISFP (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/the-16-mbti-types.asp#ISFP) INFP (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/the-16-mbti-types.asp#INFP) INTP (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/the-16-mbti-types.asp#INTP)
ESTP (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/the-16-mbti-types.asp#ESTP) ESFP (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/the-16-mbti-types.asp#ESFP) ENFP (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/the-16-mbti-types.asp#ENFP) ENTP (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/the-16-mbti-types.asp#ENTP)
ESTJ (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/the-16-mbti-types.asp#ESTJ) ESFJ (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/the-16-mbti-types.asp#ESFJ) ENFJ (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/the-16-mbti-types.asp#ENFJ) ENTJ (http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/the-16-mbti-types.asp#ENTJ)

Chuck, for what its worth I suspect that you are an ENTJ.

[I]ENTJ
Frank, decisive, assume leadership readily. Quickly see illogical and inefficient procedures and policies, develop and implement comprehensive systems to solve organizational problems. Enjoy long-term planning and goal setting. Usually well informed, well read, enjoy expanding their knowledge and passing it on to others. Forceful in presenting their ideas.

FTDK:cool:

[Chimbu chuckles]

Ohh yeah...did one of those about 15 years ago....don't remember what I got.:E

Though ENTJ sounds pretty close to the mark:uhoh:

[the wizard of auz]

I posted a quite detailed response to Mr.Guppy...........and it never showed up. I'll have another go at it later. :ugh:

[SNS3Guppy]

Was it a good response or a bad response?

I hate it when that happens.

[the wizard of auz]

It was a very detailed response saying you were both right and wrong. And giving technical details as to why.
I will attempt to rewrite it tonight if I get time.
Bloody work getting in the way of time wasting. :}