34 minutes ago, martinboehme said:

the engine won't quit at exactly the critical altitude (if you don't lean)

Just to reiterate. It did exactly that 3 times in a row for me. So predictable I took screenshots before and after as displayed above. BTW the engine manual posted is a great read. Lists CA as 19k in there and says even at 25k the following should be achievable. 

No mention of sudden engine failure in there at all. 

Critical altitude ~19,000 ft

• Aircraft will still be able to maintain 31” MAP and 85%

power at 25,000 ft 

10 minutes ago, sloppysmusic said:

Just to reiterate. It did exactly that 3 times in a row for me. So predictable I took screenshots before and after as displayed above.

You're referring to the screenshots in this post, correct?

The first screenshot there shows manifold pressure already decreasing at 21,300 ft, so critical altitude is somewhere below 21,300 ft. The engines kept running until 25,000 ft (second screenshot), so quite a bit above critical altitude.

In my test, critical altitude was around 25,000 ft (i.e. this is where the manifold pressure started decreasing), and the engines stopped running at 28,700 ft.

So the engine model does appear to give different critical altitudes based on deviation from ISA.

14 minutes ago, sloppysmusic said:

BTW the engine manual posted is a great read. Lists CA as 19k in there and says even at 25k the following should be achievable. 

You mean the PDF that @MattNischan posted? Agree that it's a great read! I assume you know this, but just to clarify for others: That PDF is for an SR22T, which has a different engine than the Duke.

15 minutes ago, martinboehme said:

the engines stopped running at 28,700 ft.

Thanks for reply as always! Sorry yes I wasn't trying to use that manual as a 'bible' for Duke more as a general ref in that it explains good power is still available up to 6k ABOVE CA and nowhere does it mention the whole issue I have at present as quoted above.

IF the duke CA is around 24k then I'm assuming up to around 29k good power should be available with mild leaning. The ceiling IS 35k right?

"the engines stopped running".

I welcome in depth simulation, gradual deterioration, necessary power/mix/prop/trim adjustments. They are the meat of the sim for me which is why I even prefer to fly the PMDG 737 series and F28 Fokker fully manual with no AP. (Yes I know the engines are different lol!).

There is a major difference between an engine that is slowly losing power during climb with obvious gradual loss of climb/speed if you do nothing to fix it and one that just DIES suddenly without even a change of engine noise first. It's acting as if the pilot just set mixture to cut off. In fact if you do that the engine DOES splutter and cough before quitting.

20 minutes ago, sloppysmusic said:

Thanks for reply as always! Sorry yes I wasn't trying to use that manual as a 'bible' for Duke more as a general ref in that it explains good power is still available up to 6k ABOVE CA and nowhere does it mention the whole issue I have at present as quoted above.

It does say that the engine still maintains 30.5 inHg manifold pressure at 25,000 ft, but I don't think it says anywhere that this is with a full rich mixture?

The procedure for a rich-of-peak climb (slide 76) says "Mixture – Maintain Fuel Flow w/in Green Arc". I'm not that familiar with the SR22T -- I've only taken it for a spin in the sim once -- but I believe this green arc moves depending on conditions. So I think it's possible that above critical altitude, the green arc will come down, thereby instructing you to lean the mixture? (Can someone more familiar with the SR22T comment? This discussion has made me interested in checking it out in the sim again!)

The presentation does also say this: "Too Rich or Too lean can lead to engine roughness or possible combustion failure" (slide 22) and "Excessively rich will flood engine (large power degrade, roughness or flameout)" (slide 23).

26 minutes ago, sloppysmusic said:

IF the duke CA is around 24k then I'm assuming up to around 29k good power should be available with mild leaning. The ceiling IS 35k right?

Ceiling is 30,000 ft (stated in the manual, and Wikipedia says the same thing). (Incidentally, this is 2,000 ft higher than the turbine Duke!)

28 minutes ago, sloppysmusic said:

There is a major difference between an engine that is slowly losing power during climb with obvious gradual loss of climb/speed if you do nothing to fix it and one that just DIES suddenly without even a change of engine noise first. It's acting as if the pilot just set mixture to cut off. In fact if you do that the engine DOES splutter and cough before quitting.

Agreed -- the engine does seem to quit very suddenly.

2 hours ago, Cpt_Piett said:

Also, I was not aware that it’s possible to climb the piston with prop full and throttle wide open. Guess I’m a bit confused re: differences in engine operations piston vs turbine. And perhaps also turbocharged piston vs “regular” pistons.

It’s possible, but absolutely not recommended. With a turbocharged engine, you will typically use full boost and maximum prop RPM on takeoff, but will reduce manifold pressure and prop RPM once established in a climb. On the Duke, I have typically been using 35 inches MP and 2400-2500 RPM. 

If you ran the engines at max MP and RPM continuously (in the real aircraft), at least at lower altitudes, you’d be lucky to get 100 hours before an overhaul was required.

 

8 minutes ago, JRBarrett said:

f you ran the engines at max MP and RPM continuously (in the real aircraft), at least at lower altitudes, you’d be lucky to get 100 hours before an overhaul was required

Yes you don't need to thrash the engine during climb but if you did that would be a degradation issue which is modelled separately in this Duke. The issue is a turbocharged engine EXPECTS to be run full mixture until the variable (and therefore unexpected) arrival of critical altitude. You can assume when MP starts to drop that you have passed CA I guess. But dropping from 34 to say 32 should not exactly be a warning of pending and imminent disaster.

11 minutes ago, martinboehme said:

Agreed -- the engine does seem to quit very suddenly.

This really IS the whole focus of the issue. Absolutely no warning like someone switched the mags off.

29 minutes ago, martinboehme said:

The procedure for a rich-of-peak climb (slide 76) says "Mixture – Maintain Fuel Flow w/in Green Arc". I'm not that familiar with the SR22T -- I've only taken it for a spin in the sim once -- but I believe this green arc moves depending on conditions. So I think it's possible that above critical altitude, the green arc will come down, thereby instructing you to lean the mixture? (Can someone more familiar with the SR22T comment? This discussion has made me interested in checking it out in the sim again!)

Just did a test with the SR22T in the sim, and the green arc on the fuel flow gauge did indeed start coming down at around 19,000 ft, as did manifold pressure. Below 19,000 ft, the top of the green arc on the fuel flow was around 40 GPH (which corresponds to full rich); at 25,000 ft, it was only 25 GPH. So it's necessary to lean quite markedly above critical altitude (a reduction in fuel flow of almost 40% over only 6,000 ft).

As a test, I pushed mixture to full rich at 25,000 ft, and the engine kept running. Not sure if this is realistic or not. It didn't change the EGTs, which certainly seems wrong -- the additional fuel should cool the exhaust gas by evaporation.

Edited May 16, 20242 yr by martinboehme

40 minutes ago, martinboehme said:

Just did a test with the SR22T in the sim, and the green arc on the fuel flow gauge did indeed start coming down at around 19,000 ft, as did manifold pressure. Below 19,000 ft, the top of the green arc on the fuel flow was around 40 GPH (which corresponds to full rich); at 25,000 ft, it was only 25 GPH. So it's necessary to lean quite markedly above critical altitude (a reduction in fuel flow of almost 40% over only 6,000 ft).

As a test, I pushed mixture to full rich at 25,000 ft, and the engine kept running. Not sure if this is realistic or not. It didn't change the EGTs, which certainly seems wrong -- the additional fuel should cool the exhaust gas by evaporation.

The 22T is turbo normalized vs the turbocharger in the Dukes.  I'm not sure how that affects things though.

5 minutes ago, ryanbatc said:

The 22T is turbo normalized vs the turbocharger in the Dukes.  I'm not sure how that affects things though.

The SR22T has a maximum manifold pressure of 36.5 inHg, 6.5 inches greater than sea level pressure. That's turbocharged, not turbo-normalized, right?

3 minutes ago, martinboehme said:

The SR22T has a maximum manifold pressure of 36.5 inHg, 6.5 inches greater than sea level pressure. That's turbocharged, not turbo-normalized, right?

Oh I think you're right.  The older Cirruses were TN.  I used to work for them in that timeframe but I've basically not kept up with their changes.

Just now, ryanbatc said:

Oh I think you're right.  The older Cirruses were TN.

Got it -- I wasn't aware that they'd changed this!

1 hour ago, martinboehme said:

So it's necessary to lean quite markedly above critical altitude (a reduction in fuel flow of almost 40% over only 6,000 ft).

Sort of, but not exactly. Mixture maximum at 25K is about 29.5gph, and the top of the green arc is around 25gph. So, you're only leaning by 4.5gph at that altitude, or by 15%.

1 hour ago, martinboehme said:

I pushed mixture to full rich at 25,000 ft, and the engine kept running. Not sure if this is realistic or not. It didn't change the EGTs, which certainly seems wrong -- the additional fuel should cool the exhaust gas by evaporation.

The principles between the SR22T (TSIO-550-K) and the Duke engine (TIO-541) are similar enough for illustrating turbo engine usage, but their fuel delivery systems are from totally different eras. The TIO-541 uses a 50s mechanical diaphragm and ball fuel injection metering system, which means that it doesn't have the ability to alter metering based on engine load. In other words, if your mixture lever is set to a 10:1 air/fuel ratio, you'll get 10:1 over the entire throttle range.

However, the TSIO-550-K, while still mechanical and not ECU based injection, does have the ability to change mixture over the engine volumetric load range with some additional valving. So the mixture lever in the same position might be 10:1 at full MAP and maybe only 12.5:1 at 75% MAP. That's why in the SR22T full mixture in those conditions is only a bit above the green band and not hugely above it. Our received data indicated that the EGT bottoms out somewhat around the top of the green band, maybe only 5 or less degrees of drop outside of that, as the energy transfer becomes less efficient (the fuel surface area is not increasing because the droplets are getting bigger, and mostly the fuel is starting to come out of the exhaust as liquid).

The practical implications for this in the Duke are that full rich is set within the detonation margin for full rich at full design MAP, which is extremely rich. A turbo engine can get away with that at boosted MAP without stalling because the additional air volume (nearly double in the Duke) being compressed also contributes to a large amount of combustion chamber heating. You need all that fuel vaporizing to keep chamber wall temperatures out of auto-ignition. However, once the air volumes are being reduced (reduced MAP), chamber temperatures come down, and now all that fuel can quench the flamefront.

2 hours ago, JRBarrett said:

With a turbocharged engine, you will typically use full boost and maximum prop RPM on takeoff, but will reduce manifold pressure and prop RPM once established in a climb.

It depends on the engine. The SR22T normal climb is full throttle and mixture all the way to cruise, or a reduced cruise climb if you desire. The Duke POH has two climb power settings listed: maximum power climb and cruise climb. Maximum power climb is listed as Max Continuous Power (defined as 2900RPM at 41.5inHg). So certainly Beech, at least at the time, seemed to think you could, since MCP is a certification point, i.e. the engine must be certified to provide MCP at all times without impacting the overhaul interval.

That being said, a lot of these things tend to devolve into manufacturer and engineer vs pilot religious type arguments. I tend to favor the manufacturer recs and specs as they don't suffer from as low a sample data size ("well, when I did this with my plane it did X"), but it isn't always 100% clear cut. Hence all the heated pilot arguments about following or ignoring book leaning procedures.

4 minutes ago, MattNischan said:

It depends on the engine. The SR22T normal climb is full throttle and mixture all the way to cruise, or a reduced cruise climb if you desire. The Duke POH has two climb power settings listed: maximum power climb and cruise climb. Maximum power climb is listed as Max Continuous Power (defined as 2900RPM at 41.5inHg). So certainly Beech, at least at the time, seemed to think you could, since MCP is a certification point, i.e. the engine must be certified to provide MCP at all times without impacting the overhaul interval.

Just because you “can” doesn’t necessarily mean you “should”. I am speaking from the the viewpoint of an A&P mechanic who has maintained (and repaired) a variety of turbocharged piston engines over the years. At least in the case of the Duke, with the TIO-541 engine, I would never advise an opener/operator to make a habit of running at MCP for a protracted amount of time. There may be occasions where it is necessary do so - climbing out of a high density altitude airport at high gross weight for instance, or if there is a reason why time-to-climb to cruise altitude must be minimized for operational reasons, but the engine absolutely will not make TBO if MCP is used all the time, even if the certification says it will.

To say nothing of the increased fuel consumption 

The SR-22 may be a different matter entirely. I moved out of piston GA to corporate turbojet maintenance quite a few years ago, and have never worked on newer generation engines like the TSIO-550-K

47 minutes ago, JRBarrett said:

but the engine absolutely will not make TBO if MCP is used all the time, even if the certification says it will.

Yeah, not trying to discount anyone's experience here, by any means. Just pointing out that sometimes these things start to fall into some grayer areas, and engines/recommendations differ quite greatly. For an older design like the TIO-541, I totally buy that.

Always fun to talk about these things with folks that have had their hands on them!

Edited May 16, 20242 yr by MattNischan

1 hour ago, MattNischan said:

Sort of, but not exactly. Mixture maximum at 25K is about 29.5gph, and the top of the green arc is around 25gph. So, you're only leaning by 4.5gph at that altitude, or by 15%.

Ah, thanks - hadn't considered that fuel flow would of course reduce as manifold pressure reduces. Makes sense in hindsight.

Thanks for all of the detailed explanations - this is one of the best threads I've seen on Avsim in a while!