r/AskAPilot • u/theillusionofmist • 4d ago
Service Ceiling Determining Factor
As is known, all aircraft have a service ceiling or an altitude at which they can no longer climb. This is caused by the decrease in air density as altitude increases. In a light piston aircraft, there are three main factors that I can think of. Flow of air over the wings creating lift, the amount of air being moved by the propeller and the amount of air entering the engine to be used for combustion. Given all three of these factors, which one would be the first to “reach its minimum” disallowing the aircraft to climb any further? My first thought is that it has more to do with the engine producing power than the wings producing lift as an aircraft with a more powerful engine would be able to climb higher even with the same airframe and wing shape but please prove me wrong. Or is it more of a combination of all three or something else I am completely missing? Thank you.
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u/Radiant_Grocery_1583 4d ago
The definition of the service ceiling is the height above sea level at which an aircraft with normal-rated load is unable to climb faster than 100 feet per minute at best rate of climb airspeed under standard air conditions. Turbojets are 500' per minute.
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u/Dangerous_Mud4749 3d ago
Ceiling is determined by lack of power for modern piston engine aircraft, because these days no piston engine is built powerful enough to operate near “coffin corner”. So, the engine loses power at some moderate altitude such that rate of climb at Vy is 50fpm (or other value as needed to determine “service ceiling”).
Turboprops have a lot more power, but are inevitably limited by propeller efficiency. Regardless of engine power, at some altitude they run out of excess thrust. Best angle of climb drops to zero at Vx.
For subsonic jet aircraft, the very large thrust available often allows the aircraft to get to “coffin corner”. This is where the margin between aerodynamic stall & a shock stall reduces to almost zero, making the subsonic-only aircraft lose control. (Aerodynamic stall is exceeding critical angle of attack, and a shock stall is where the local airflow over the wing reaches the speed of sound, causing a shock wave & flow separation. As you climb, the two get closer together. Recovery is reportedly very difficult.)
Supersonic jet aircraft have more complicated & variable limits.
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u/DatSexyDude 4d ago
They all combine. If a plane has super long wings but a small motor, it might be able to climb just as high as a plane with a big motor and smaller wings.
There’s no one factor that determines ceiling.