Looking at 912 failure modes......

[Guest Maj Millard]

Most of the fancy Euro cars use Pierburg pumps such as Porsche, Mercedes, BMW etc etc............their's is an interesting website by the way.................................................Maj...

 

 

[Old Koreelah]

I often wondered why fuel injection and electronic ignition were so long arriving in aircraft engines. Pilot workload should be greatly reduced by modern engine management systems. Now that Rotax has brought us the engine of the future, the reality sets in...They depend on a totally reliable supply of electricity. A back- up battery system would seem to be in order.

 

 

[turboplanner]

You're on to it OK.

 

I ran electronic ignition in the race car, and the system I changed from engine to engine emitted a high pitch sound as soon as you flicked the switch on. You knew while sitting in the car whether there would be an issue or not. Some of the others were nightmares.

 

 

[Willborne]

Following on to the post reporting the Tecnam/912 failure recently I'd like some input on any 912 failures you've experienced or heard of.Personally I've probabily flown with ten or more different 912s in the past 15 years, and done around 500+ hours on my own 912s in the Lightwing.

Additionally as an unlimited L2, I see a lot of other peoples' problems when they have engine dramas.

 

Bearing in mind that around 60% of all engine failures are fuel related !!....including running out of it.

 

In my experience I would suggest the following list are the most potential failures you may expect with a 912. Listed as most potential first, to least potential.

 

1. Engine stoppage due to carb-mount rubber failure or leakage.

 

2. Engine stoppage, or rough running due to pilot leaving fuel boost pump on ( exceeding max carb operating pressure, causing flooding or over-rich mixture).

 

3. Engine stoppage due to incorrect carb settings or adjustments.

 

4. Ignition failure (normally detected on ground during mag checks)

 

5. Carb icing due to nil carb heating or improper usage by pilot.

 

6. Internal mechanical failure due to incorrect oil usage.

 

7. Mechanical fuel-pump failure.

 

Explanations: 1...The early carb-mount rubbers were a harder compound-they lasted longer. The newer one's are softer, and seem to want to crack and fail around 250 Hrs. I am on my third set at 700 hrs TT -all failures detected during ground inspections.

 

2...Rotax have recommended minimum and maximum fuel operating pressures for the Bing carbs. Leaving elect boost-pumps on in some installations can overpower the carb bowl floats, and cause over rich mixture to the engine. Fitting and monitoring a fuel-pressure guage is recommended. 3...The Bing carb is as basic as they get, however people still tinker with them unnecessarily, and operate them with incorrect adjustments or settings- refer to Rotax maintenance manual for correct settings and adjustments. 4...The Rotax 912 ign boxes produce around 40,000 Volts. Cranking engine over with spark plugs out, and ign switches on, does not allow this high voltage to ground via the spark plugs, and will ruin the solid state ign box. Normally one circut completely dead during mag checks. Inflight ign failures are rare. If cranking engine for oil pressure during initial start or after oil change, ground ign leads/plugs and ensure ign switches are OFF!...5....Carb heat systems should be fitted, and used when required. All carbs are subject to icing in the right conditions. 6...The Rotax engine and gearbox require a synthetic fortified, approved oil for reliable operation. Use of incorrect or non-approved oils will cause damage which can lead to failure. 7...Mechanical fuel-pump failure is rare, but when it occurs can cause engine stoppage. A friend recently had one fail at 250 hrs. Check pumps regularly for leakage from seep hole, and replace if found........................................................................................Maj....

Maj,

The Operating handbook for my Tecnam Golf was amended to leave the boost pump on at all times. However I have a fuel pressure gauge. I must admit to leaving it off (by mistake) once when on cruise for an hour and it operated no worries. Would you know why I would have to leave the boost pump on all the time?

 

Willborne

 

 

[Guest Maj Millard]

I have no idea Willborne, who put that requirement in the pilot operating handbook ??.............Normal usage is ON for take-off, landing, and over suspect country, thus saving the boost pump for more important stuff like when your mechanical pump fails, or you need boost pressure during an unplanned in-flight restart...................Maj...

 

 

[Guest Maj Millard]

'Facthunter, Re: your post #13. Some earlier 912s had problems with valve trains not pumping up after oil changes or from first start-up, if the oil system wasn't 'purged' correctly per Rotax instructions. If a lifter failed to 'pump-up' it would generally lead to valve train damage shortly after. Rotax issued several Service Bulletins in response to this, plus came out with two upgraded and thicker/stronger valve spring retainers.(the item that would eventually crack and fail)

 

Of main importance is the need to pressurize and 'purge' the oil system after any oil change, or before first start-up. This is partly due to the 'dry-sump' configeration of the 912, and the fact that many different aircraft configerations have oil-system lines routed differently.

 

Most owners/operators understand this requirement now, and additionally the need to 'turn over' the engine with plugs out, on the starter, until an indication of oil pressure is observed.

 

the service Bulletins pertaining to all this are quite clear and have been refined after several amendments. I haven't heard of any valve train damage leading to failure now for several years.....................................Maj...

 

 

[Guest nunans]

So i was reading above where turning the engine with the plugs out can damage the ignition so how do yo do the purge

 

 

[flyhi]

So i was reading above where turning the engine with the plugs out can damage the ignition so how do yo do the purge

Have the ignition switches "OFF"

 

 

[Guest Maj Millard]

Correct...and just to be doubly sure I put the plugs back into the plug caps, and ground out the plugs back to the case with a bit of lockwire, or alternatly with aligator clip leads...one for each plug (4). You only need to pull one plug per cylinder..not all eight to 'motor the engine. But as in the prev post, the main thing is to double check your switches are in the OFF position..............................................................................Maj...

 

 

[Guest nunans]

I see. So it's easiest if you have separate ign switches instead of a key operated ga style mag/start switch.

 

 

[Head in the clouds]

I see. So it's easiest if you have separate ign switches instead of a key operated ga style mag/start switch.

That's a good point, if you have the Off, Mag 1, Mag 2, Crank type of keyed switch you have a bit of a problem, because to crank the engine you have already turned the mags On. You can still ground the plugs as MM says but then be aware that the plugs will be sparking and there will be fuel being ejected from the plug holes. I did exactly that once with an outboard and set fire to the engine because I had the carby bowls removed trying to find a flooding problem. The fire melted the plastic floats and then I had even more of a problem...

 

So in the circumstance you describe it might be best to ground the HT leads with some old plugs and MM's lockwire method but close the plug gaps right up so that there is no sparking, just a direct short to ground.

 

Alternatively you could maybe just ground the plugs and leave the key (mags) switched off and apply power via a +ve wire to the starter solenoid to make it crank that way.

 

 

[Kyle Communications]

If the mag switches are off the ecu's will not fire so there should be no spark regardless of the ignition switch as the mags are turned off

 

 

[Head in the clouds]

If the mag switches are off the ecu's will not fire so there should be no spark regardless of the ignition switch as the mags are turned off

The setup being discussed does not have separate mag switches. My C172, for example, had a key which, when turned one click it turned on the left magneto only, second click turned on the right magneto only, third click turned on both magnetos, after that was a spring resistance to 'crank', when the engine fired you released the key and the spring returned it to the 'both' position (much like a car key going through the 'aux' position to 'ignition on' then crank following that). For run-up checks you turn the key back to 'right', then 'both' again, then two clicks back to 'left' then back to 'both' again. It was impossible to crank the engine without having the mags on.

 

 

[Kyle Communications]

Ok I see the confusion sorry about that. I think the separate switches like in mine are the safest way to go

 

 

[Head in the clouds]

Ok I see the confusion sorry about that. I think the separate switches like in mine are the safest way to go

Well.... not the safest way to go at all as I see it. With a key controlling the Master, Mags and the Cranking, and provided you always did your 'dead cut' checks after each flight, then you could be reasonably confident that you could handle the prop safely during pre-flights as long as the keys were in your pocket. With separate key and switches for master and mags it's not quite so safe at all.

 

In helicopters we were taught to leave the rotating beacon switch on and always take a look back at the machine as you walked away, that way if you accidentally left the Master on then you would see the beacon illuminated. Many folks adopt that practice for their fixed-wing so that if the beacon is on then they know the prop is not 'safe'.

 

However if you have separate mag switches then the Master (and hence beacon) might be switched off but the mag switches could still be on, meaning the engine/prop is live. Consequently I would fit a compound master/mag/crank keyed switch to my current project for safety if I could source one at a price that didn't have 'aviation' written on it, so I have had to have separate mag switches too :-(

 

And note that this situation is even more dangerous in our kind of Rotax engined planes than it is in the Cessna because the Cessna engine is stopped by cutting off the fuel with the mixture control, so even when 'live' it should not start without richening the mixture again, whereas the Rotax could start simply by moving the prop. So it means there's no room for error at all in terms of checking that the mag switches are off (regardless of the keyed Master switch) before handling the prop.

 

 

[Kyle Communications]

On my installation the mag switches could be on but unless the ignition switch has been put into the on position the ecu's would not work as there is no DC to the ecu modules unless the master starting switch has been switched to the on position the next position is to actually start the engine it has the std return spring. On mine you can have the engine running but if you turn the ignition switch to off the engine will stop as the ecu's have no power so no spark. Rotax tell do not turn the engine off by the ignition switch without having the large capacitor installed otherwise you take out the regulator but this can happen at times by mistake so the option is to fit the capacitor but the nine should be only stopped by the 2 switches...they are not really mags as you know they are ECU's

 

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[Head in the clouds]

On my installation the mag switches could be on but unless the ignition switch has been put into the on position the ecu's would not work as there is no DC to the ecu modules unless the master starting switch has been switched to the on position the next position is to actually start the engine it has the std return spring. On mine you can have the engine running but if you turn the ignition switch to off the engine will stop as the ecu's have no power so no spark. Rotax tell do not turn the engine off by the ignition switch without having the large capacitor installed otherwise you take out the regulator but this can happen at times by mistake so the option is to fit the capacitor but the nine should be only stopped by the 2 switches...they are not really mags as you know they are ECU's.

Ahh - good point, thanks for pointing that out. My current project is the first in which I've used a 912 so I'm not all that familiar with them. I did buy the capacitor though as it looked like cheap insurance for the Rec/Reg but had a hell of a job sourcing one large enough, eventually got it out of Hong Kong on ebay for $1.50 with free postage, best value component on the entire project!

 

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[Kyle Communications]

I bought mine from RS components was a lot more at $20.00 but it is a high quality one and also had the steel clamp and mounting base. They tell you about it in the rotax manual but still say "its a option"....the regulators are quite expensive so best to spend the money on the insurance. I know when I first got to start the engine a few times before the plane was ready to fly I almost did turn it off with the key but now its only the mag switches...just a habit now but you do have to keep your mind on every process....especially when like me you are a newbie at this aviation engine stuff

 

 

[Guest Maj Millard]

Good stuff all.......yes most of the ignition damage I discovered over the years was on the key type mag switch starter , mainly on Storches. When you ground the plugs out in the manner I mentioned, IE; lockwire around the threaded section at the bottom of the plug, to the engine block, there is no sparking of the plug. The spark-plug itself in normal use is a simple grounding device. The boot comes down the center core, and has to jump the gap to ground out...it is in this 'jump' that the spark is created !....Obviously when cranking the engine over to achieve oil pressure, you would also have the fuel off, and the throttle closed. On a 912 the choke would not be pulled on. The 'choke' really is an enrichment valve, not a choke in the normal sense. It is this 'enrichment valve' that provides the fuel for a start until the throttle is bought into play. (2-stroke 'chokes' were the same) That's why 912s are started with the throttle on the stop, so as not to flood the engine.

 

Oh and the Rotax will not start simple by moving the prop. There is a built-in safety in the ign circut. The engine has to be rotating at about 400rpms before the ignition will be activated. IE: cranked by the starter motor........................Maj...

 

 

[Guest Maj Millard]

The capacitor you speak of is highly recommended. It is by the way the thing that gets zapped if you accidentially hook the batt leads up in reverse. (not me !..but the previous owner of my LW did!) Cheaper to buy a new capacitor than a new regulator, and possibly a lot of other things, not to mention new wiring...........................................Maj...

 

 

[Guest Crezzi]

The engine has to be rotating at about 400rpms before the ignition will be activated. IE: cranked by the starter motor........................Maj...

I wouldn't assume that you have to use the starter motor - it can be started by hand

 

 

Cheers

 

John

 

 

[fatmal]

'Of main importance is the need to pressurize and 'purge' the oil system after any oil change, or before first start-up. This is partly due to the 'dry-sump' configeration of the 912, and the fact that many different aircraft configerations have oil-system lines routed differently.Most owners/operators understand this requirement now, and additionally the need to 'turn over' the engine with plugs out, on the starter, until an indication of oil pressure is observed.

 

the service Bulletins pertaining to all this are quite clear and have been refined after several amendments. I haven't heard of any valve train damage leading to failure now for several years.....................................Maj...

I always thought that the daily pre-first-start 'gurgle' relied upon compression leaking past the rings to pressurise the crankcase, forcing any oil 'pooled' in the case to return to the catch tank - which makes the gurgle. If you remove the plugs, then no compression, and no crankcase pressure - no gurgle? Happy to be corrected - I may learn something! :-)

 

Mal

 

 

[Kyle Communications]

My understanding of it Mal. With oil in the sump expelled like you state then when you drain the oil out of the collector then pressurise the system to get all oil out totally from the lines etc. Then you fill up the oil and pull the plug out of each cyclinder to make it easy to turn over the engine with the starter to make the oil pump then pump the oil throughout the engine you make sure of this by cranking until you see oil pressue then put the plugs back in and it is ready to start as oil is now completely through the engine

 

Mark

 

 

[Guest Maj Millard]

Ok, without referring to Rotaxs' Service bulletin 'Purging of the Rotax 912 oil system', which we should all be familiar with, the 'priming or purging ' of the oil system is recommended before the first start-up of a new installation, after an oil change, or whenever the oil system has been disturbed, IE; oil lines disconnected etc.

 

So basically in all these sceneroes, the major part of the oil is going to be in the oil tank, right ?...

 

What you are doing by spinning the engine over, is priming the oil pump so it can then pressureize the engine.

 

Some installations just require a short spin over on the starter before the oil pressure starts to rise.

 

Others, and often this includes a lot of new installations, and first start-ups, may require several runs before oil-pressure becomes displayed on the guage.

 

Additionally, Rotax recommends you put positive pressure into the oil tank, via the oil tank breather line, (max 15 Psi !) to provide a 'head of pressure' for the oil pump. This does generally move things along in my experience. The differences in time it takes to get an oil-pressure rise seems to depend on several things, including the position of the oil tank, length and run of the oil lines, and position of the oil-cooler etc.

 

Often on a new engine, you can actually feel the point when the hyd lifters fill with oil, and start operating the valve-train system, there is a little more of resistance to the starter. Generally when you feel this, oil-pressure will be there shortly after rising on the guage. In cases where constant motoring doesn't produce an oil-pressure rise, you will need to pressurize the oil tank per the Service Bulletin, to get the proper results. You'll probabily need to do this once, as there was probably just too much oil line for the oil-pump to pull the oil through first time.

 

Gurgling, or burping the engine, puts the oil from the engine, into the oil-tank, for the purpose of checking oil-quantity. The 912 engine-case is not vented in any way. It is only the oil tank that is vented. It is the crankcase pressure produced by the engine that pushes the oil into the oil tank, and this is the gurgling you hear as you turn the prop slowly by hand with the oil-tank cap off.

 

Personally I have found that this is best done right after shutdown, when the oil, and engine, is warm. I burp my engine after I have shut down, and check my oil quantity during the preflight for the next flight, when everything (especially the oil dipstick !) is cold.

 

With the plugs out and motoring, engine oil-pressure is taken just after the oil pump, and all Rotax says is to watch for a 'rise in oil pressure indication'. When you've got this rise, all should be good for a start.

 

Regardless of what I have said here, the Rotax Service Bulletin is the thing to go by...follow that and you will be fine.......................................................Maj...

 

 

[Guest Maj Millard]

kyle, There is no requirement as I understand it, to pressurize the system to push out any remaining oil. In fact doing this may introduce air into areas like the hydrylic lifters, where you definitly want oil to remain, not air.

 

If you have 'burped' the engine correctly, the majority of the oil will be in the oil tank anyway, which you drain during a normal oil change. You will never get all the oil out anyway no matter how you try, and a little 'residual' left over is not that big a deal . In fact Rotax say not to unnecessarily open, or disturb the oil system if it can be avoided.................................................Maj...