1 hour ago, martinboehme said:

But we're certainly not doing anything close to fully retarding the throttle

We're NOT indeed!

Here are those screen shots before and after issue - note last shot i dropped mixture a little ready for relight as found moving the lever back and forth sometimes restarts engines 

also note engine death occurs EXACTLY at FL250 STD!

Duke engine dies at FL250

 

Edited May 15, 20242 yr by sloppysmusic

9 minutes ago, sloppysmusic said:

We're NOT indeed!

Here are those screen shots before and after issue 

Thanks for sharing!

First thing I note is that in that first screenshot, your manifold pressure is already coming down, even though you're only at FL 213, indicating that you've already gone through critical altitude. I assume that your OAT is above ISA and hence you're seeing a density altitude above FL 213. This would also explain why you saw the issue at a lower altitude than I did.

I did another test in the meantime, but bringing the mixture back as soon as my manifold pressure started falling. I was able to make it all the way up to FL 290 without any issues. Fuel flow at this point was about 200 pph on both engines. Referring now to the manual, I see that I should probably have brought it back quite a bit lower. Looking at the chart for 75% cruise power, I see that at a manifold pressure of 34.1 inHg (which is about what I was getting), fuel flow should only be 133 pph.

So my takeaway from this is that this aircraft needs to be operated with careful reference to the performance charts. Whether it's actually realistic for the engines to quit entirely on an over-rich mixture is another question that I'd like to know the answer to -- but I think we at least know now how to prevent the engines from quitting at high altitude.

Edit: I also note that there are useful "percent power" markings on the fuel flow gauge.

Edited May 15, 20242 yr by martinboehme

34 minutes ago, martinboehme said:

Whether it's actually realistic for the engines to quit entirely on an over-rich mixture is another question that I'd like to know the answer to

It is; at some point there is so much fuel in the combustion chamber that ignition cannot occur, instead the spark flame front is quenched by the energy converting unburned liquid fuel into a vapor state.

Edit: Just looked through the engine.cfg files and I don't see any of the new SU14 turbo and mixture parameters, so they must be doing this the workaround way in custom code somehow. So, it's hard to say how the mixture stuff is being accomplished.

Edited May 15, 20242 yr by MattNischan

18 hours ago, sloppysmusic said:

I'll try the GD tonight if you get a chance can you quickly try the B60 factory? I've only used that one so far.

For the Turbine version - looking for the COWL Flap Open & Close click spots. (Ideally, a pic)

Have been through the Manual & can't find anything.

Presume its not the Oil Cooler Doors?

T45

After testing, mixture and engine behavior looks good to me. Critical altitude is defined as the altitude at which the turbocharger will maintain its design manifold pressure at ISA conditions. The exactness of the 25000ft is a red-herring here; with conditions set to ISA (Clear Skies preset), the engine doesn't die full rich until about 28,700ft. Manifold pressure started dropping at exactly the rated critical altitude of 25000, and EGT also began to fall. Once getting to 28,000ft, the EGT began to drop much more quickly, indicating an overrich condition. By 28,700ft the EGT was down quite a bit, and at that point the manifold pressure had dropped nearly to 36inHg when the engine quit. That all tracks with what I would expect.

However, there is one significant issue that I think is caused by not using the new engine parameters: the fuel flow starts to go down more significantly than I would expect above the critical altitude even though the mixture lever is remaining in the same position. This is because prior to the new parameters, fuel flow/consumption was entirely a product of engine output HP * SFC. You also see the fuel flow drop to 0 when the engine dies, which is not correct. If the mixture lever is open, fuel is being drawn into the cylinders at the same mixture ratio as long as the engine is spinning. It just happens to not be burned and instead exits out the exhaust.

Nonetheless, the plane is awesome, my absolute all-time favorite in prior renditions and this one outclasses those by a considerable distance.

1 minute ago, Treetops45 said:

For the Turbine version - looking for the COWL Flap Open & Close click spots. (Ideally, a pic)

Have been through the Manual & can't find anything.

Presume its not the Oil Cooler Doors?

T45

Turbine version doesn't have cowl flaps.

25 minutes ago, MattNischan said:

Once getting to 28,000ft, the EGT began to drop much more quickly, indicating an overrich condition.

Interesting! I wasn't paying attention to that in my test, but this sounds like it would be a last warning (if you noticed it) that you hadn't been leaning as required.

Thanks for your input, I've learned a lot out of this whole investigation. I've never really flown turbocharged engines in the sim before.

One thing I'm wondering about: I don't recall ever being cautioned in my real-world training (on a lowly 172) that the engine might quit if I don't lean. Obviously, there are many other good reasons to lean (not wasting fuel, not fouling the spark plugs), but I'm now wondering - if I tried to run a 172 full rich at a high enough altitude, would the engine quit on me too? Or is this something that's specific to turbocharged engines?

Just now, martinboehme said:

if I tried to run a 172 full rich at a high enough altitude, would the engine quit on me too?

It would, yes. Now, the question is if you could even get a 172 to that height. I'm not exactly sure, to be honest, nor exactly sure what height that would be. But any piston engine, aviation or otherwise, does have a point at which the fuel/air ratio is too rich for combustion.

10 minutes ago, MattNischan said:

But any piston engine, aviation or otherwise, does have a point at which the fuel/air ratio is too rich for combustion

Indeed but unless you're completely preoccupied with something else you'd notice engine power drop off gradually as you climb and the climb rate or your speed would drop considerably. Planes would be actually falling out the sky if engines just died with no warning IRL with poor mixture control.

I've never had a plane in 25 years of simming die so suddenly on me during climb especially when I'm going by the book. As 25k was just above critical altitude I assumed it fair to level off there and lean using the fuel computer. Then climb again slowly after. I never got a chance to even try that. This series will certainly be GREAT addons after tweaks.

I fear many more casual simmers will buy it, slam those levers forward and ALWAYS be startled by what happens next.

1 hour ago, mmcmah said:

Turbine version doesn't have cowl flaps.

Materials shortage during production?😀

Ok, understand.

I would have thought though with a Turbine screaming away under the cowling it would get pretty warm in there.

T45

Yeah but long before the engine quits shouldn't power output fall significantky enough that maintaining a climb is no longer possible?  In which case the aircraft would reach a point of anemic equilibrium? I'm not an aircraft powerplant expert but years of being a shadetree mechanic makes this scenario with the engines essentially choking themselves to death sound quite counterintuitive.  

2 hours ago, mmcmah said:

Turbine version doesn't have cowl flaps.

It does have oil doors though !

2 minutes ago, sd_flyer said:

It does have oil doors though !

Indeed it does, and I open and close them every flight!

2 hours ago, Stoopy said:

Yeah but long before the engine quits shouldn't power output fall significantky enough that maintaining a climb is no longer possible?  In which case the aircraft would reach a point of anemic equilibrium?

It depends on the powerplant, but I would expect rough running prior to combustion failure. The power falloff on the rich end is pretty gradual so may not be noticeable from that alone, until the flamefront is quenched and ignition failure begins.

Edited May 15, 20242 yr by MattNischan

12 hours ago, PebbleBeach said:

Still waiting on your response that you initiated on the FS9 Savannah Hilton-Head International thread. Was that all BS? 😉

Mitch 

No it was not. This has simply been a very busy week. I do need to get you the terminal pictures. One thing that you can do in the mean time...Image No. 20, you can take the large Gulfstream Hangar, make a mirror of it, and place it to the right side of the office block that you currently have on the right side, as we have just completed doubling that hangar.