Rough engine on run-up
Thread Starter
Joined: Apr 2010
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From: Düsseldorf, Germany
Hey guys!
Aerozepplin, thanks for those hints! Guess I'll spend the night reading then.
A&C: You're right, lecture of the flight manual is not optional. However, being only taught the basics about leaning, I want to be on the safe side, as many other greenhorns, and prefer to fly a bit too rich before I know more about the subject. But, until now, my fuel numbers always worked out
And to continue with those 3000ft: That's about 500ft above the pattern altitude of our surrounding fields and I will most probably have gone through my inbound-checklist already a couple of minutes ago when I started my descend.
If I go x-c I want to climb as high as possible. If there's somewhat minimum VMC, I just won't fly. 3000ft for me means patternwork and practicing maneuvers, so no leaning as I'll hit the throttle quite often.
So yes, you're right, there is no reason why not to lean at any altitude, but I guess it always depends on local factors, as so many other things
BackPacker: The guts it is then
Going for a beer ...
Alex
Aerozepplin, thanks for those hints! Guess I'll spend the night reading then.
A&C: You're right, lecture of the flight manual is not optional. However, being only taught the basics about leaning, I want to be on the safe side, as many other greenhorns, and prefer to fly a bit too rich before I know more about the subject. But, until now, my fuel numbers always worked out
And to continue with those 3000ft: That's about 500ft above the pattern altitude of our surrounding fields and I will most probably have gone through my inbound-checklist already a couple of minutes ago when I started my descend.
If I go x-c I want to climb as high as possible. If there's somewhat minimum VMC, I just won't fly. 3000ft for me means patternwork and practicing maneuvers, so no leaning as I'll hit the throttle quite often.
So yes, you're right, there is no reason why not to lean at any altitude, but I guess it always depends on local factors, as so many other things
BackPacker: The guts it is then
Going for a beer
...Alex
Joined: Jan 2004
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From: Canada
Yes you should always apply a gut check to every takeoff so if it doesn't seem right it is better to do alow speed abort than continuing with a sick airplane. However gut checks work best when they start with a comparision to hard data points and low hours PPL, in particular, do not have the reservior of experience to rely solely on "gut checks"
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From: U.K.
Big Pistons Forever
I entirely agree with your comments about the need to check static RPM at the start of each take off . But my experience in the UK is that very few PPL pilots actually perform this check,or if they do, then Check Power means no more than note the RPM is vaguely in the right area without any real understanding of what the correct figure should be and what tolerance is acceptable. As you said in your previous post.
In the UK at least it appears not be taught. Yet after all the mantra of pre take off checks of mags and carb heat function, the static RPM is the one instrument check that confirms whether or not the engine is delivering the correct power. Getting airborne with a malfunctioning engine when the evidence has been there right in front of you is inexcusable in my book. I wouldnt mind betting it has been responsible for some of the take off accidents we have experienced in the UK.
Professional pilots understand the need to perform this check every take off and only continue if the correct power is achieved, so why not PPL holders too ?
There is a complication. Some aircraft types may be fitted with any of a range of propellors of different pitch, and this may affect the static RPM.. For example the Robin DR400 may be fitted with a fine pitch prop for glider towing giving a static RPM of 2500, yet the same aircraft with a cruise prop will produce only 2300, and others with a compromise prop will give 2400. So if I am going to fly a new aircraft, including one of a type with which I am familiar, I always ask about the static RPM. And how often do I get a sensible answer ?
I entirely agree with your comments about the need to check static RPM at the start of each take off . But my experience in the UK is that very few PPL pilots actually perform this check,or if they do, then Check Power means no more than note the RPM is vaguely in the right area without any real understanding of what the correct figure should be and what tolerance is acceptable. As you said in your previous post.
In the UK at least it appears not be taught. Yet after all the mantra of pre take off checks of mags and carb heat function, the static RPM is the one instrument check that confirms whether or not the engine is delivering the correct power. Getting airborne with a malfunctioning engine when the evidence has been there right in front of you is inexcusable in my book. I wouldnt mind betting it has been responsible for some of the take off accidents we have experienced in the UK.
Professional pilots understand the need to perform this check every take off and only continue if the correct power is achieved, so why not PPL holders too ?
There is a complication. Some aircraft types may be fitted with any of a range of propellors of different pitch, and this may affect the static RPM.. For example the Robin DR400 may be fitted with a fine pitch prop for glider towing giving a static RPM of 2500, yet the same aircraft with a cruise prop will produce only 2300, and others with a compromise prop will give 2400. So if I am going to fly a new aircraft, including one of a type with which I am familiar, I always ask about the static RPM. And how often do I get a sensible answer ?
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From: Amsterdam
I just checked the POH for the DR400-120 and in the take-off checklist it does specify a minimum of 2200 RPM.
According to the POH you can get this aircraft with three different types of props, and the minimum static RPMs are respectively 2200, 2250 and 2220.
According to the POH you can get this aircraft with three different types of props, and the minimum static RPMs are respectively 2200, 2250 and 2220.
Joined: Jan 2009
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From: Oxford, UK
Alex, just to extend slightly the discussion about leaning.....
flying from an airfield that is more than 5,000' above sea level adds another consideration! Density altitude.
The Wright Brothers found this out when the Flyer that had flown nicely from the Kitty Hawk Beach in North Carolina, was less than enthusiastic when they tried to take off on a hot summer day in Ohio! (Back to the drawing board!)
flying from an airfield that is more than 5,000' above sea level adds another consideration! Density altitude.
The Wright Brothers found this out when the Flyer that had flown nicely from the Kitty Hawk Beach in North Carolina, was less than enthusiastic when they tried to take off on a hot summer day in Ohio! (Back to the drawing board!)
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From: london
....... although but a distant related thread - there was that other instance when an a/c newly returned from its annual C of A check experienced a form of 'rough running' - causing much white knuckle attempts to clear the boundary - When it was later discovered the
propeller had been fitted 'back to front !
propeller had been fitted 'back to front !
Joined: Apr 2009
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From: `
While not the reason for running rough in this case, it could also be caused by running on ONE Magneto instead of BOTH. The a/c shakes like !!!! when full power is applied after a simulated forced landing and is only running on one mag. I only ever simulated FMMGT checks after that. It was a silly new PPL mistake. 
Posted in the hope that others may learn from my mistake.
Posted in the hope that others may learn from my mistake.
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From: Londonish
Personally I have to confess I'd expect that with 2 cylinders 'out' it'd run like a lame donkey! Would be suprised to achieve run up RPM - I'd expect it to be painfully obvious something was wrong on takeoff. Notwithstanding the diagnosis, it sounds more like a fouled plug.
There's no reason that the thing should shake with one mag off either, on the occasion of an engine developing a somewhat unpleasant vibration after meeting a rain shower, I finished up completing the flight on just the right mag because it was misfiring and shaking when the left was on - there's two for a reason.
Consider also that I'm pretty sure your static RPM will be affected by density altitude (but so will the power output of the engine, so I'm not too sure of the exact relationship..)
There's no reason that the thing should shake with one mag off either, on the occasion of an engine developing a somewhat unpleasant vibration after meeting a rain shower, I finished up completing the flight on just the right mag because it was misfiring and shaking when the left was on - there's two for a reason.
Consider also that I'm pretty sure your static RPM will be affected by density altitude (but so will the power output of the engine, so I'm not too sure of the exact relationship..)
Thread Starter
Joined: Apr 2010
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From: Düsseldorf, Germany
Hey Mark,
I can only say what I witnessed Mag check was ok (RPM drop on each of the mags). And yes, it was quite shaky, but it definitley went up to 1700RPM. It turned out that one cylinder had almost no compression and another was quite low on it.
However, I'm still on the status I got from a first quick check from our mechanic and haven't had any updates.
I'll keep you guys posted on the final diagnostic.
Cheers,
Alex
I can only say what I witnessed
Mag check was ok (RPM drop on each of the mags). And yes, it was quite shaky, but it definitley went up to 1700RPM. It turned out that one cylinder had almost no compression and another was quite low on it.However, I'm still on the status I got from a first quick check from our mechanic and haven't had any updates.
I'll keep you guys posted on the final diagnostic.
Cheers,
Alex
Joined: Feb 2009
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From: England
When running on only half the cylinders but with full throttle, I would not be surprised to see the engine actually reach that RPM so you would not necessarily find anything wrong then.
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From: Scotland
Originally Posted by Mark1234
There's no reason that the thing should shake with one mag off either, on the occasion of an engine developing a somewhat unpleasant vibration after meeting a rain shower, I finished up completing the flight on just the right mag because it was misfiring and shaking when the left was on - there's two for a reason.
Could this vibration have been caused by the rain shower / carb ice? switching off one mag so reducing the amount of "bang" & thereby reducing power & vibration?
Last edited by Crash one; 14th May 2010 at 17:45.
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From: Canada
A few additional comments
1) There is no way an engine with two dead cylinders would make minimum static RPM although it would certainly make runup RPM. There may not necessarily be a lot of vibration depending on which combination of cylinders are dead, thus the importance of a power check a the start of the takeoff roll
2) While a quick check of the engine instruments to ensure they are in sensible possitions, is a very good idea at the start of the takeoff run the mantra "in the green" is often mindlessly applied to all flight regimes. This is a particular pet peeve of mind. When established in the cruise the engine guages should be checked regularly but not to assure that they are "in the green", rather to note the exact position of the needle on each guage and then ask the question " has there been any substantial change". If the answer is yes, then some thinking should be given as to why. Engines almost never just up and stop, they will almost always give some warning. For example impending catastrophic internal failures are almost always preceded by rising oil temperatures and declining oil pressures. By the time both have exceeded their red lines you had best have a field ready for the forced approach. If you have being paying attention you would have seen the situation devloping and started a diversion right away with the likely result of a uneventfull landing at the nearest airport.
2) Re the question of descent and leaning. This is what I do (for your typical trainer/light tourer with a fixed pitch prop and no multi probe EGT guage)
a) Slightly enrichen the mixture
b) Establish a nose down attitude which will give a 500 FPM descent rate
c) As the aircraft accelerates the RPM will start to rise so,
d) Reduce the throttle to maintain the cruise RPM I had before the descent
e) Trim
f) When I reach the desired attitude fine tune the RPM and relean
Prior to starting a descent, one of the worst things you can do is go to full rich, particularly on cold days and for long descents as this dumps a load of excess fuel into the cylinders which will cause the cylinder head temperature to dramarically drop, a great way to cause cylinder head cracking.
1) There is no way an engine with two dead cylinders would make minimum static RPM although it would certainly make runup RPM. There may not necessarily be a lot of vibration depending on which combination of cylinders are dead, thus the importance of a power check a the start of the takeoff roll
2) While a quick check of the engine instruments to ensure they are in sensible possitions, is a very good idea at the start of the takeoff run the mantra "in the green" is often mindlessly applied to all flight regimes. This is a particular pet peeve of mind. When established in the cruise the engine guages should be checked regularly but not to assure that they are "in the green", rather to note the exact position of the needle on each guage and then ask the question " has there been any substantial change". If the answer is yes, then some thinking should be given as to why. Engines almost never just up and stop, they will almost always give some warning. For example impending catastrophic internal failures are almost always preceded by rising oil temperatures and declining oil pressures. By the time both have exceeded their red lines you had best have a field ready for the forced approach. If you have being paying attention you would have seen the situation devloping and started a diversion right away with the likely result of a uneventfull landing at the nearest airport.
2) Re the question of descent and leaning. This is what I do (for your typical trainer/light tourer with a fixed pitch prop and no multi probe EGT guage)
a) Slightly enrichen the mixture
b) Establish a nose down attitude which will give a 500 FPM descent rate
c) As the aircraft accelerates the RPM will start to rise so,
d) Reduce the throttle to maintain the cruise RPM I had before the descent
e) Trim
f) When I reach the desired attitude fine tune the RPM and relean
Prior to starting a descent, one of the worst things you can do is go to full rich, particularly on cold days and for long descents as this dumps a load of excess fuel into the cylinders which will cause the cylinder head temperature to dramarically drop, a great way to cause cylinder head cracking.
Joined: Jan 2004
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From: Canada
.
There's no reason that the thing should shake with one mag off either, on the occasion of an engine developing a somewhat unpleasant vibration after meeting a rain shower, I finished up completing the flight on just the right mag because it was misfiring and shaking when the left was on - there's two for a reason.
Consider also that I'm pretty sure your static RPM will be affected by density altitude (but so will the power output of the engine, so I'm not too sure of the exact relationship..)
There's no reason that the thing should shake with one mag off either, on the occasion of an engine developing a somewhat unpleasant vibration after meeting a rain shower, I finished up completing the flight on just the right mag because it was misfiring and shaking when the left was on - there's two for a reason.
Consider also that I'm pretty sure your static RPM will be affected by density altitude (but so will the power output of the engine, so I'm not too sure of the exact relationship..)
With regards to the second point. The relationship between engine power and density altitude vs static RPM is not exact but close enough that for practical purposes the static RPM will not vary appreciably, unless you are at extremes of temperture and altitudes.
Thread Starter
Joined: Apr 2010
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From: Düsseldorf, Germany
But my mechanic says....
I just had to chuckle as I find myself in exact the same situation....
Pelican's Perch #46:<br>"But My Mechanic Says ..."
First thing our mechanic said was "Somebody running it too lean again!".
Cheers,
Alex
Pelican's Perch #46:<br>"But My Mechanic Says ..."
First thing our mechanic said was "Somebody running it too lean again!".
Cheers,
Alex
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From: Surrey
I'm sorry but I certainly don't understand that. There are two mags in order to provide a full burn, not as a redundancy / choice exercise. Both mags should fire at the same time (possibly one may be slightly advanced?) Misfiring when both are on, not misfiring when only one is on does not compute very well?
Could this vibration have been caused by the rain shower / carb ice? switching off one mag so reducing the amount of "bang" & thereby reducing power & vibration?
Could this vibration have been caused by the rain shower / carb ice? switching off one mag so reducing the amount of "bang" & thereby reducing power & vibration?
In a fully instrumented engine you can see this weakness in EGT spread well before you can feel it and then have the issue sorted on the ground (as you can relative easily isolate the plug/plugs in question).
Joined: Apr 2008
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From: France
You would however clearly feel the vibration
Increased oil consumption. Not dramatically so, about 60 percent up on the previous 50 hours, and a slightly greasy fuselage behind the engine.
Slight white marking on the cracked cylinder from gas escape.
The cracked cylinder was well down on compression, the other down enough to make it worth changing at the same time. (both on the same side)
No vibration, static rpm 2350 (expected rpm for that engine/prop combination)
Lycomings (and Continentals) are pretty agricultural engines.
There are two mags in order to provide a full burn, not as a redundancy / choice exercise
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From: Scotland
Piper Classique,
I'll try to elaborate a bit. Two mags are there to (1) provide a full burn, (2) to produce some power if one fails "redundancy", (3) they work indepently of any power supply/generator/battery, (4)they "should" both work together & I was under the impression that they were, I may have been wrong there. If there was a serious mag malfunction then yes that would upset the thing, however the rain shower, in my limited experience of flying but long experience of driving/riding circa 1957, I consider more likely to produce carb ice than a flooded ignition system. My only experience of a swamped ignition was in a MK 8 Jaguar that blew the radiator & soaked everything. Within a few minutes things had evaporated/dried enough to restart. Coil/distributor system of course.
I may be wrong again but I believe that the magneto does not produce such a good spark as the coil system? Stuffing a wet rag into the plughole on a motorcycle magneto & kicking it over gave me a belt!! but not as serious as the latest, prob non survivable, electronic stuff. Which is why it was discontinued in cars.
I'll try to elaborate a bit. Two mags are there to (1) provide a full burn, (2) to produce some power if one fails "redundancy", (3) they work indepently of any power supply/generator/battery, (4)they "should" both work together & I was under the impression that they were, I may have been wrong there. If there was a serious mag malfunction then yes that would upset the thing, however the rain shower, in my limited experience of flying but long experience of driving/riding circa 1957, I consider more likely to produce carb ice than a flooded ignition system. My only experience of a swamped ignition was in a MK 8 Jaguar that blew the radiator & soaked everything. Within a few minutes things had evaporated/dried enough to restart. Coil/distributor system of course.
I may be wrong again but I believe that the magneto does not produce such a good spark as the coil system? Stuffing a wet rag into the plughole on a motorcycle magneto & kicking it over gave me a belt!! but not as serious as the latest, prob non survivable, electronic stuff. Which is why it was discontinued in cars.
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From: France
I'll try to elaborate a bit. Two mags are there to (1) provide a full burn, (2) to produce some power if one fails "redundancy", (3) they work indepently of any power supply/generator/battery, (4)they "should" both work together
They are timed together but sometimes the timing can drift. I have timed a few mags..... "Some power" is a bit unkind. At least cruise power off only one out of two is an entirely reasonable expectation. Yes, I think we all know that a magneto does not need a battery. I have swung a lot of props in my time. As for coil ignition, we are talking about a typical Lyc/Continental here, rustic agricultural dark ages, so it's magnetos.