Engine problem?

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AKar
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Re: Engine problem?

Post by AKar »

Which brings an interesting side note: simplified, there are limitations, and then there are another kind of limitations. The first ones are those from POH and mandatory placards. These are what interests the pilot, and are mandatory (for various reasons) for safe operation of the aircraft. Essentially, go/no-go, or do-not-exceed stuff. The latter ones are those that give you some pass/fail criteria for maintenance runs for instance. These are typically measurements in more controlled circumstances that are of interest in finding if the aircraft is safe for being signed off for a longer period of time than a single flight. The effort is to detect any significant, potentially still developing issues or deterioration by relatively controlled sets of test criteria.

In some sense, I think it is beneficial for a casual weekend pilot to be aware of certain criteria that are given outside his scope of work. On the other hand, it is outside his scope of work, and a properly managed and maintained airplane should not force the pilot to judge any vague clues.

Now, what comes to simulation, an all-green airplane should lie somewhere in between of 2350...2400 RPM as per AMM, in zero wind. But this brings in another little dirty secret of aviation. Like cars, many airplanes would fail several tests and criteria imposed by AMM maintenance procedures for example, if checked carefully against them. Sometimes even knowingly and on purpose. As an innocent, classic example, some GA types have landing gear struts that perform unacceptably, if serviced to the book values. Other findings would perhaps be less innocent, but are they important? Mainly not. It is like your annual vehicle inspection: you don't feel too shocked if there was a fail. More like, okay, I'll fix that.

But, the thing with the sim is that we can simulate various things, including an after-maintenance run-up if we wish. For utmost realism, the behavior in those circumstances should be reachable, or clearly spoken out as a real-life issue. But then again, any development group should remain considerate towards their sources of data. Few are entirely comfortable on exposing all their operations and dirty reality. Talking about some can of worms here, in some sense.

Anyways, a bit off-topic, more of 'philosophical' approach on recreating real-life imperfectness realistically.

-Esa

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Nick - A2A
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Re: Engine problem?

Post by Nick - A2A »

Interesting discussions, but just to help clarify Ilya's original observation, the maximum static RPM in the 182 does seem to hover around the 2300 mark (to be more scientific, I'd say 2300±6) with T, P and M full forward and at standard atmospheric pressure at sea level. This is as tested on my (P3Dv4) system anyway, with a newly reset *log.dat file.

Image

This is a bit different to the numbers you mentioned Scott...
Scott - A2A wrote: In the case of our airplane, a perfectly tuned Accu-Sim 182 will generate about 2380-90 RPM static.
As described above, the simulated propeller governor does seem to be disproportionately affected by very low airspeed through the prop (a headwind of 15 kts will increase RPM by ~70).

Nick

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AKar
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Re: Engine problem?

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Nick M wrote:As described above, the simulated propeller governor does seem to be disproportionately affected by very low airspeed through the prop (a headwind of 15 kts will increase RPM by ~70).
Yep, that would ground the airplane for professional mechs working against earlier data, most certainly.

Now, that would not be a governor issue at first to me. That is because it appears to govern properly to the 2400 at some airspeed, so it governs properly to the set higher limit.

If I had such in real life, and was certain that the engine was inspected fine, my next step would be a wild card to inspect the propeller blades for correct p/n, and then the fine pitch settings.

Edit: of course a bit irrelevant for the simulation, but of interest for the general physical background anyway! :)

-Esa

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ilya1502
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Re: Engine problem?

Post by ilya1502 »

Scott - A2A wrote:don't think computer but think analog, real, imperfect as this is the world we live in and how we built Accu-Sim.
Scott, thank you for the input. This is exactly what I did. And like I said, if I noticed a similar thing in the real world, I would immediately ground that aircraft. An engine running at 2300 rpm rated at 2400 rpm after a complete overhaul in ISA conditions almost at sea level is absolutely non-normal, grossly non-normal, and it was 2300, not 2380 or even 2350. Actually, Nick has provided very good objective data (and this means this is not a problem of my local setup) and Esa seems to agree with me on grounding an aircraft showing this. Please, don't take it as an offence. This just my view as a pilot. Accu-sim is an absolute masterpiece, but I'd say that this particular aspect of C182 should be re-tuned.

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AKar
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Re: Engine problem?

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ilya1502 wrote:And like I said, if I noticed a similar thing in the real world, I would immediately ground that aircraft. An engine running at 2300 rpm rated at 2400 rpm after a complete overhaul in ISA conditions almost at sea level is absolutely non-normal, grossly non-normal, and it was 2300, not 2380 or even 2350.
And just to underline a bit, this is approximately correct for the 182T, but not in general. Some airplanes even with constant speed props are allowed to not reach the full rated RPM at standstill. They only reach it at some forward speed during the takeoff run. Even in 182T, it is allowed to be just short of maximum.

One needs to know the published limits, case by case.

-Esa

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