A lot of the time I’m able to cruise at this altitude, no problems and uneventful flight. Every now and then though I hit a problem where all of a sudden, after hours cruising at FL450, I can’t maintain the altitude and the air speed drops until I am stalling. Today I had to drop to FL250.
Struggling to find a pattern. Thought it was related to wind speed but doesn’t seem to be. Maybe external temperature (happened today when the sun came out). Just wondering if anyone could clue me into what is happening? It’s not the bug where external temperatures reach 200 C.
Wind has no effect on the aircraft operational ceiling. Outside temperature could be the issue. Or maybe you are accidentally extending something? Gear, flaps, spoilers, reducing thrust?
Sounds suspiciously like the live weather temperature bug. If it happens again, check the OAT. If its +250c then that would be why you’re losing power.
The maximum altitude of the CJ4 is 45,000 ft. At maximum altitude, there are the minimum amount of air particles to provide lift. This means that any change in pitch or power to increase altitude will stall the wings. Making any turns can also stall the aircraft. Also, flying on the edge of stalling, turbulence can pitch the aircraft a small amount and stall the aircraft.
45.000 ft is likely a limitation from structural standpoint (pressure cabin). Depending on weight, the CJ4 might be able to go even higher than 45.000 ft purely from a performance perspective (or when heavy, not reach 45.000 ft at all). There is no such thing as “minimum amount of air particles”, the aircraft ceiling is depending on weight and atmospheric conditions (temperature and pressure = density) when flying higher you simply need to have a higher True Airspeed (TAS) for the same performance. Performance of the aircraft (lift) is depending on the Calibrated Airspeed (CAS), this is what is displayed on the airspeed indicator. The aircraft itself has the same performance at sea level as it would have at 45.000 ft when flying the same CAS (assuming Mmo is not exceeded).
Having sufficient engine thrust to climb that high and maintain a cruise speed with sufficient buffet margin is an entirely different story however. Engine performance is depending on air density, lower density means less mass through the engine which means less thrust. To compensate for the loss of thrust, a higher fuel burn is needed, eventually the engine reaches maximum operating temperature and further increase in fuel burn is not possible without damaging the engine, thus from this point forward thrust decreases with increasing altitude. Simply speaking thrust = force = mass x acceleration, the lower mass flow can be compensate for by increasing acceleration of air through the engine which is done by burning more fuel to increase temperature inside the combustion chamber, until reaching temperature limit.
Anyway, this doesn’t explain why the OP can fly at 45.000 ft for hours and then all of a sudden loses speed until stall. The maximum operating altitude should be increasing as fuel is being burned off, the aircraft should be accelerating instead as time passes by.
I‘ve never flown at that altitudes in the sim but I have seen sudden changes of wind direction in the thirties, in the forties depending on the aircraft load and maybe reaching coffin corner this might turn into a stall? I haven‘t really cared about the CJ4 and don‘t know its limits but I wouldn‘t expect it to be able to climb much further. Certain Learjets go up to 51000ft, maybe Gulfstream, but I‘ve never heard of a Cessna to be able to do that.
From an engineering/technical POV, an aircraft’s maximum altitude is based on many factors including engine design and performance and aircraft design. An aircraft’s maximum altitude (CJ4 - 45,000 ft, C172 - 14,000 ft, C208 - 25,000, TBM 930 - 31,000 ft, etc.) means “there isn’t enough air up there” to go higher.
As you say, the operational ceiling is depending on may factors, not necessarily performance (which is the “there isn’t enough air up there” you are speaking of). An aircraft ceiling does not mean that there isn’t enough air (not sure what that means anyway, I assume you mean air density is too low), performance wise an aircraft operational ceiling is depending on weight (amongst other things), which means that this is not a fixed value. The upper limit is usually determined by the aircraft structure, at 45.000 ft the pressure cabin will be at maximum differential pressure to keep the cabin habitable. When the aircraft is not too heavy the aircraft ceiling purely from a performance point of view might be well above 45.000 ft, but its capped at 45.000 ft by other limitations.
Can’t create a new topic yet so I’m adding my report to this one. In MSFS 2024, flaps are increasing the stall speed where it should lower it. Currently, the more you extend the flaps, the higher is the stall speed (which should be the opposite). It’s not only the PFD speed indicator, the stick shakers and the stall follow the same principle. I think there is somehow an inversion between the flap setting and the stall speed. I saw this phenomenon on the citation longitude and I thinkg the C4J has a similar issue.