LifeofReiley
Well Known Member
What's the use talking here... this Egg guy will be out of business very soon. I feel sorry for anyone who has invested in this.
In general though most 912 makes it to 1500 TBO, and they routinely go 2 and 3 times past that when used as trainers.
I can't read Norwegian and Google translator can either. Can you translate?
Look there are gear boxes that have not failed and there are gear boxes that will fail, sooner or later. This idea of a mechanical device never, ever failing is a dream, yet to be discovered. That's the prime argument against the gear box PSRU's, if its there, it can fail. The corollary: Direct drive engines don't have a gear box to fail, so failure is eliminated. That is with out debate.
Now you can argue Lyc cranks fail. True, but see above, all mechanical things made by man are subject to failure. The crank however is "solid state". It's a moving part but has no internal moving parts itself (unless it has damper weights). Prop is bolted to the crank, done. The simpler you make it the better for reliability. Lyc and Continental figured out if they make the displacement large enough they don't need higher engine RPM, while still being powerful and efficient. Of course nothing is 100% efficient and compromises are always made.
This does not take away from the fact gear boxes can be made to be safe and reliable. The above is just philosophical; if its not there to fail, it can't fail. Many a Continental, Lyc, Pratt, Wright where produced with integral gear boxes. They worked fine, but you had to be careful back driving the prop. Most radials have a gear reduction. They all work fine. On the other hand they where integral, pressure lubricated and had tight tolerances, which adds cost and weight. They used magnesium where they could**. During overhaul its another thing to do and expense. Even finding someone to work on geared engines can be a challenge.
**BMW makes a in-line 6 cyl magnesium/aluminum composite engine; the core is aluminum (with steel sleeves) and the outer engine case is of magnesium, fused together. It saves 24% weight. Magnesium has pros and cons but they put the materials to best effect. The way the make and fuse/bond/marry the alum and mag parts is interesting. Some Cessna twins have magnesium rims. If they ever catch fire, you RUN. Magnesium burns like the sun (and almost impossible to extinguish).
The gearbox was sent to Rotax for examination, but no news as of yet. The report doesn't say anything about maintainance and history of the engine, not at this time.My Norwegian is a tad rusty.![]()
It would be interesting to know more about the history of that engine, and how it was maintained. Was there any follow up investigation? On the other hand, one gear box failure certainly is not a trend with as many Rotax 912 / 912S's that are flying. What this tells me is gear boxes can be made reliable for aircraft applications. The reason I even bring Rotax up is to use it as an example so the VAF engineers can look at it and learn.
Cars have detonation sensors, which are little microphones. May be a "resonance sensor" on the gear box could warn of gear box rattling? May be the noise is so high it would be impossible to differentiate the noise. May be a vibration sensor. Jet engines have a vibration sensors that displays in the cockpit and recorded by the aircraft. Its used for maintenance.This would beat the snot out of the bearings.
The arrangement of the helical gear angles means torque reversal at a resonant RPM would indeed drive the shafts fore and aft axially (the arrows) at a rate in the hertz range. This would beat the snot out of the bearings. The beating would be much reduced if axial freeplay is carefully shimmed or otherwise kept to a minimum, but offhand I don't think there is any way to eliminate all of it. I can't tell what Jan does to minimize freeplay from just a photo. In this design it needs to be minimized. You can tell the operators absolutely, positively do not run in a resonant range (apparently below 1400 in this case), but that only reduces the total number of hits in a given period of operation. You still must pass through that range at startup, so minimizing axial freeplay to keep the hits small would increase bearing life.
Dan or Ross,
Do you have any experience or knowledge of using a Hyvo chain in the PSRU? That's what is inside mine.
Hard to beat tapered rollers bearings to handle all loads. Look at a lathe or an older car front wb setup. With proper lube, these last a lifetime with high thrust and radial loadings.
Operating data: David admits to running his system at an RPM that generates noise from the box. What we don't know is how often, and if it is likely to be common among other operators.
How about it? Can we set aside the flag waving and discuss reality?
Now consider the layshaft. Assume the bearings are not preloaded. If you're at 800 RPM and hearing gearbox clatter, the layshaft is banging fore and aft about 27 times per second.
I'm guessing those might be mirror-paired angular contact bearings behind the prop flange, hopefully with preload. If so, there is no bearing impact at all.
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<<The frequency is not that high.>>
Hmmm, that's interesting. Actually 27 hz is based on a wrong input; I was thinking you had a 4-cyl but you have a 6. (800 RPM x 6)/120 is the 3rd order exciting frequency (firing events), or 40 hz. The 6th order (piston inertias) is even higher. Right offhand I can't recall if the 1-1/2 is a major order with a flat 6. Even if it were, it would be 20 hz and still too high by your estimation. One of these has to be matched by some natural frequency to resonate. Lemme think about it.
Can you take a guess? Trivia tip; the average fellow can't verbally count faster than about 4 hz.
Can you take a guess? Trivia tip; the average fellow can't verbally count faster than about 4 hz.
I think (hope) the factory has resolved the gearbox issue. Time will tell. Allan
And frankly, they are not estimates. Given a specific RPM, number of cylinders, and engine type (4 stroke w/ even crankthrow spacing), the frequency is quite precise.
Can you think of a driver (an exciting frequency) for your cycle, whatever hz it may be? For sure the prop doesn't just randomly "get ahead of" the engine.
Please don't think I'm picking on you; not my intent at all. I'm really very pleased to see you thinking about system mechanics.
Hi Bill,
Thanks for joining in.
<<pertubate the A/F to the point that it also cycles on engine rpm...This can the in the 3-10hz range.>>
Ah ha, an unusual driver! Ross, you're our FI guy, know anything about it?
<<Analytically, the freq analysis was a sorting tool, but we had to do dynamic analysis to get actual stresses on both to solve the problem.>>
Bless you. I keep preaching about the need for live measurement among PSRU suppliers, but sometimes feel like a mad voice in the wilderness. Can you tell us a little about the methods and tools used for the dynamic analysis?
Dan, It may not be all the normal engine driving variations. The Sube has fuel injection and A/F control. If it still has the O2 sensor and operates on the original maps, it can pertubate the A/F to the point that it also cycles on engine rpm. (Note: this perturbation done to facilitate NOx removal with the catalytic converter.) This can the in the 3-10hz range. Someone else who is more familiar with automotive may can give more exact numbers. Just another potential variable to consider. If the OBDII is operational it could be tracked.
Bill
We seem to be getting into the "peer-review process" as emphasized on another forum re climate change data. Some peer-review of the EGG PSRU is a very good idea. This technical discussion is way over my head but clearly we need it.
No thanks necessary!
Amazing transformation happening here from "Shoot the Messenger" to "Peer Review Process". No thanks necessary!