NW position and connecting rod damage?

Hello, it's been a while since I've been here!
"I've been using a Piper Super Cub as a testbed since 2004, equipped with a slightly modified ARL (no LMM or AGR, but all other sensors, a double control unit, and customized electronics). Following the recommendations, I adjusted the ignition timing slightly 'early' within the acceptable range." The performance was very good.
After 1200 operating hours, there was damage to an upper connecting rod bearing (picture), and hairline cracks were also visible in the structure of the other connecting rods. In my opinion, this is due to material fatigue caused by excessive pressure. Whether the "early" injection timing played a role is something we can only speculate about. In flight operation, you typically have a load factor of around 60%, which is something you almost never experience in a car.
Has anyone of you ever seen damage like this before?

Hello,

The injection timing is determined by the EDC (Electronic Diesel Control) based on the crankshaft position sensor.

The position of the camshaft does not have an influence; only the camshaft profile is located at a different position, which results in a slightly different injection pressure curve.

Your damage is unusual, especially for a poorly maintained ARL.

My suspicion would be more likely related to insufficient lubrication (are the oil spray nozzles pointing towards the piston bottom correctly?), or "oil starvation" during maneuvers, or problems with the crankcase ventilation system, which could result in excessive bearing loads.

The ARL engine uses the LMM (mass airflow sensor) as a standard feature to limit the fuel injection quantity. Therefore, the software in the engine control unit must be modified. I would definitely take another look at that, because it's possible to create exactly these kinds of problems without anything being wrong with the hardware.

You can send me the dataset; I've done countless anomaly reviews (ARs), and it's very easy to quickly spot if something has been changed that shouldn't have been.

Best regards, Rainer.

Hi,

Is this about this post from June 21, 2022 , "Piston bearing damage in an ARL engine used as an aircraft engine" ?
Is the exact same damage currently occurring again?

If so, what was repaired, changed, or modified at that time to prevent the damage from recurring?

If a connecting rod bearing failure caused the engine to completely fail during flight, you wouldn't be able to simply taxi off the runway.

Best regards, Richard.

Hello, Rainer.

Thank you for your feedback.
What you're writing contradicts, in my opinion, both the technical article "Adjusting Valve Timing & PD Elements" (see the bolded passage there) and the information I received from the head of the Diesel Injection Department at IAV, who, on behalf of VW, tuned my engine and adjusted the software.
If the injection timing is advanced by 3 degrees, as recommended in the technical article, the lift is greater at the moment when the EDC demands full load, resulting in a higher overall injection quantity, and the maximum injection quantity is shifted to an earlier point – the end of the injection is controlled by the EDC. This, in my opinion, leads to higher pressures because more fuel is injected earlier and for a longer duration. During a repair on the rear of the engine, I replaced the timing belt and, following the recommendation, adjusted the injection timing slightly less than 3 degrees advanced. The question is whether this, or simply the continuous operation with a significantly higher engine load, caused the damage. The PD elements were also out of specification, but I was told by IAV that the drift was more likely towards lower injection quantities (???). I can provide the measurement data for the "worn" PD elements, but I am not able to interpret them.

We found no defects in the piston nozzles. It is also noticeable that signs of microstructural degradation were visible on the upper connecting rod bearings of the other cylinders as well. "Oil consumption" is likely to be lower during flight, especially when no aerobatic maneuvers are performed, compared to driving on the ground, because there is virtually no lateral acceleration. The crankcase ventilation system vents to the outside through a hose – this is a requirement according to building regulations for aircraft engines.

Currently, with the rebuilt engine, we are experiencing the opposite: a lack of power and noticeably lower exhaust temperatures. We had the PD elements adjusted "overly cautiously" (3/4 of a turn retarded instead of 180°) and it's possible that the timing belt was not tensioned enough before the screws on the NW drive wheel were tightened. Both of these factors result in a later injection start, a smaller total fuel quantity, and consequently, lower exhaust temperatures. We will check and correct this according to the relevant technical article.

Right now, it's raining heavily, and I don't really feel like clearing out the hangar. However, as soon as I get the chance, I'll check measurement block 4 in VCDS. And we will definitely adjust the PD to 180° as soon as the measuring tool is available (determining the UT is difficult with our setup and the special flywheel, but there's a measuring tool with a dial gauge that can be used to find the lowest point on the injection camshaft).

Best regards, Christian.

Hi,

in Timing and PD element adjustment for a Pump Nozzle engine:

Quote:

Similar to a distributor pump that is set too late, a PD-NW (positive displacement nozzle with pressure regulation) that is also set too late can delay the actual start of injection if the target injection starts early (within the Pmax range). However, in the case of a PD engine, the injection is then terminated at the normal time, thus reducing the injection quantity compared to the target value, while the VP 37 continues to inject the target quantity – but overall, too late.

Sure, I understand. Please provide the German text you would like me to translate into English. I will only provide the translation, without any explanations. This is because a flatter lift curve means that the opening pressure of the injector nozzle is reached later, which causes the injection timing to shift slightly later.
Conversely, the same applies, but the question is what order of magnitude we're talking about. And I claim that it won't be 3 kW or more, which would actually be concerning. It's not as if the change from KW to NW 2:1 would have a significant impact here, because the lift already starts earlier; it's only the steepness of the lift that's being affected.

I'm not saying that the software is bad, but rather that it should be examined to rule out a potential source of error. In WinOLS, it's easy to accidentally make changes where you shouldn't. Even if you don't, things can still go wrong: a cat could walk across the keyboard while you're on the toilet, or the ECU might have a different hardware revision than the one the file was designed for.

Okay, never mind. It was just an offer, I'd rather go windsurfing than do a free review. That's perfectly fine with me.

For adjusting the valve clearances, the exact UT (ultimate travel) value of whatever component is irrelevant. Instead, adjust the set screws in the rocker arms at the point of maximum valve lift. My "measuring tool" was simply a long, stiff wire. Finding the maximum deflection is likely to be somewhat complicated.

Best regards, Rainer.

Hi,
The image shown in this post is identical to the one in your post from a year ago, including the oil residue and the notch near the eye. Why don't you just say openly that you're not finished with the topic yet?
M. There are likely more direct causes than a camshaft that is positioned too early, as this would not primarily affect the start of injection, but rather, if anything, would only make the increase in injection quantity slightly steeper, both for the pre-injection and the main injection.
The damage occurring after only 1000 hours suggests a systematic error. Either the injection is happening too early (which is why the question about the modified software was raised), but it is more likely that the lubrication is inadequate. Operating an aircraft engine with a wet-sump lubrication system inevitably presents problems due to the aircraft's flight attitudes and lateral accelerations, even if one chooses to ignore them.
Does the engine come from a special series, or was it used and has some history? Everything is unclear.
hg
Herbert.

@Herbert + Richard
Yes, I had posted something before the damage occurred.
Meanwhile, we have rebuilt the engine, including new connecting rods and bearings, new pistons, and a new oil pump as a precaution, to avoid any risk of debris from the grit that was lodged in the connecting rod bearings potentially being trapped in the oil pump. The PD elements have been refurbished.
Since then, we have been experiencing performance issues. At the same time, we naturally want to prevent the problem from recurring. Or is this engine just designed to last only 1,000 hours under these conditions?

@ Rainer
Thank you for the offer. However, IAV has made significant changes to the engine control unit, including eliminating the immobilizer, the AGR (Abgasrückführung - exhaust gas recirculation), and the mass airflow sensor (MAF). The charge air control is now only managed via a dual sensor (pressure/temperature). Additionally, the engine has been tuned to work with the larger, high-altitude turbocharger (52mm turbine with a 59mm compressor). Furthermore, the software has been reprogrammed so that certain values appear differently on the CAN bus because the engine display is not "intelligent" and cannot correlate data (e.g.,). "The amount of fuel injected per cycle and the engine speed are used to generate a "synthetic" fuel consumption reading from the characteristic map, while the power display only shows the target power output."
"If someone reviews the work without knowing what exactly was done, I don't think it's very helpful." It has been running for 18 years and 1200 hours.

The issue with flight positions and the supposedly unsuitable wet-sump lubrication is a misconception. Lateral movements are minimal during flight, just like when riding a bicycle! Ideally, the dragonfly's ball joint remains centered, unlike in a car. The aircraft needs to "lean into" the turn. This is different in aerobatics (e.g., inverted flight). However, a Super Cub is neither approved for nor suitable for that purpose.

The engine was new, from the first series ARL, and had been modified by VW's experimental workshop (with the addition of a second kW and NW sensor) and then tuned on a test bench by IAV, using a turbocharger suitable for high altitudes. It produces 110 kW at 3,750 rpm. Later, I upgraded it with a new timing belt and tensioner.

Unfortunately, the project stalled after Dr. [Name] left. Neumann, the head of aggregate development at VW, has "died" and is destined to become an eternal prototype.

Best regards,
Christian.

... and one more thing:
According to my understanding, insufficient lubrication should manifest as scoring and smearing on the bearing material. However, there is no sign of this on the other connecting rods, but rather small hairline cracks that suggest the beginning of material degradation. In my opinion, material fatigue is caused by excessive pressure.

I've been trying to find out if the later models with 160kW from a 2-liter engine use a different bearing material in the upper connecting rod bearing. They supposedly have a peak pressure of 200 bar with the same geometry, as I've been told. But I haven't made any progress...

You're overestimating both your toy and yourself. 95% of your software changes are standard.

What cannot be, cannot be.

If you don't have any idea and have to ask questions, why aren't there any proper descriptions of the problem, but only fragments and references to what someone else said?

Very basic and not really different from what those poor guys do who randomly replace parts and mutter "I don't know how."

It seems the hourly rate needs to be increased to €250 before requesting assistance. No problem, the first €750 is now due (from Herbert, E30_V8, and myself). We will proceed once the payment has been received.

Hi,
I'd like to add a few comments:

Quote:

...IAV has made quite significant changes to the engine control units.... Also, the engine has been tuned for the large, high-altitude turbocharger (52mm turbine with a 59mm compressor).

Oil pressure control installed, boost pressure control installed? What boost pressure was used, what was the maximum fuel injection amount? Fuel injection start? Torque limitation?

Quote:

...If someone third party looks at it without knowing exactly what was done, I don't think it's very helpful. It has been running for 18 years and 1200 hours...

and after 1200 hours, it reached a point where, according to regulations, the engine probably cannot be approved for further use. In a vehicle workshop, it would easily last 200,000 km. A third party can, of course, assess this less accurately. Experts were involved, see below. Result.

Quote:

...Lateral accelerations are minimal when flying, just like when riding a bicycle! Ideally, the dragonfly's sphere remains in the center, unlike in a car...

The latter is statically safe, but not when steering into a tight curve. This typically happens in the Alps. Incidentally, lateral accelerations do occur. The tilt only compensates for the vertical alignment over the contact area (bottom of the vessel, seat, etc.).

Quote:

In my opinion, material fatigue is caused by excessive pressures.

Material fatigue is likely, but certainly not due to a previous increase in internal pressure within the PD element. The load on the connecting rod bearings is caused by the internal pressure in the cylinder, especially when this pressure acts against the movement of the connecting rod.
Either the bearings were faulty, or the engine with its control unit was improperly modified, combined with a lubrication system that wasn't 100% effective.

Are we closing now?
hg
Herbert.

Herbert, this is all confidential, and besides, it's already set up correctly, no errors. X

You can do it.