I would like to share a few observations concerning both the turbo-normalized and normally aspirated versions of the Commander. I have noticed similar behaviour in other Black Square aircraft, particularly the Bonanza and Baron.

In all of these aircraft, cylinder No. 4 appears to be consistently modelled as the cylinder with the highest EGT and, in many situations, the highest CHT. The behaviour is so predictable that there is little need to use the Lean Find function I already know that cylinder No. 4 will be the first one to reach peak EGT.

I understand that a particular cylinder may consistently run hotter in a real aircraft because of the geometry of the cooling baffles, uneven induction airflow, injector flow differences or probe placement. However, I find it unusual that the same cylinder number appears to be the hottest across several aircraft with different engine installations.

Could you clarify whether this is an intentional characteristic of each aircraft and its engine installation, or whether the products share a common cylinder temperature model that assigns the highest temperature to cylinder No. 4?

It is also worth distinguishing between EGT and CHT. The cylinder showing the highest absolute EGT does not necessarily have to show the highest CHT. EGT is strongly affected by mixture distribution and the position of each cylinder relative to peak EGT, whereas CHT is more closely related to cylinder pressure, power production, ignition timing and cooling airflow.

I have also noticed some behaviour in the turbo-normalized Commander that I would like to understand better.

As altitude increases, the indicated engine power appears to decrease even below the system’s critical altitude. My understanding is that a turbo normalizing system should maintain the required manifold pressure up to its critical altitude. Therefore, with the same manifold pressure, RPM, mixture setting and approximately the same fuel flow, I would expect the engine to retain broadly similar power.

I appreciate that constant manifold pressure and RPM do not guarantee perfectly constant brake horsepower. Compressor-discharge temperature, induction-air density, exhaust backpressure, volumetric efficiency and mixture scheduling may still produce a gradual change in actual power. Nevertheless, the reduction currently appears greater than I would expect from those effects alone.

I have also observed that EGT decreases steadily during a constant climb. I do not think this can be explained directly by the reduction in outside-air temperature, because EGT is primarily determined by the fuel air ratio, combustion conditions, power setting and ignition timing. Colder ambient air may affect the result indirectly, but it should not by itself cause a proportional reduction in EGT.

CHT is more complicated. My initial expectation was that it might gradually increase as the aircraft climbs because the cooling-air mass flow decreases and the turbocharger has to work progressively harder. However, I recognise that CHT does not necessarily have to rise continuously. It represents a balance between heat generated by the cylinders and heat removed by the cooling airflow.

If manifold pressure, RPM and fuel flow remain approximately constant below critical altitude, I would expect CHT and EGT/TIT to remain reasonably stable after the initial climb transient, although some gradual change would be realistic. The exact direction would depend on mixture, compressor-discharge temperature, cooling airflow, cowl-flap position and the characteristics of the installation.

Near the critical altitude, the wastegate should approach its fully closed position and the turbocharger should reach the limit of its ability to maintain the selected manifold pressure. Above that altitude, manifold pressure and available power should begin to decrease. Assuming the mixture is adjusted appropriately, I would then generally expect CHT to decrease as power falls. EGT or TIT may also decrease, although its exact behaviour will depend heavily on mixture control and fuel flow.

Could you therefore clarify how the following parameters are modelled in the Commander?

Individual cylinder fuel–air distribution.
Individual cylinder cooling efficiency.
The relationship between EGT and CHT for each cylinder.
Turbocharger wastegate position and critical altitude.
Compressor-discharge temperature and any intercooling effect.
Fuel-flow or mixture compensation with altitude.
The calculation of engine power when manifold pressure and RPM are held constant.

I would be particularly interested to know whether cylinder No. 4 is intentionally assigned less cooling or a different mixture distribution, and whether the observed reduction in turbo-normalized power below critical altitude is expected behaviour or a limitation of the simulation model.

Thank you.
Seb