Justin, a commercial pilot from Texas, asks: What determines an airplane’s “service ceiling?” Is the airfoil or the engine the limiting factor?
Technically, it’s both — along with wing loading, drag, air density, aerodynamic efficiency, weight, air temperature, the coefficient of lift, and a bunch of other stuff that only aeronautical engineers understand.
But in all practicality, for us general aviation pilots, it’s the engine that limits how high we can go.
Here’s the deal: As long as your engine has enough thrust to move your plane through the air fast enough for the wings to generate lift, the airplane will climb.
Of course, two things happen as we go up, up, up, up. First the air gets thinner. That means your wings will have a harder time generating lift.
At the same time, a typical aircraft powerplant, thanks to the same thin air, won’t be able to generate the same power that it can closer to the ground. At some magic point, between the lowering lift and the lowering power for speed, your climb becomes anemic.
When the anemia reaches 100′ per minute of climb, you’re at your service ceiling.
For what it’s worth, there’s also something called the absolute ceiling, which is the maximum altitude that an aircraft can sustain level flight, also sometimes referred to as the maximum usable altitude or the maximum operating altitude.
So how do I know that the engine has a greater part to play than the wing in all flavors of ceilings? Well, if you put a more powerful engine on a plane — or an engine capable of generating more power — you can raise its service ceiling.
The best illustration of this is to take a look at the Cirrus SR22 and SR22T. They’re basically the same airplane except for the fact the “T” model costs a hundred grand more, and has a slightly lower useful load. Oh, right, and the “T” has a maximum operating altitude that’s a whopping 7,500′ higher than the non-T model, on the same wing.
How is that possible? Because the “T” stands for turbo, and the turbocharged version of the same basic Continental IO-550 that graces both models lets the SR22T’s powerplant maintain higher levels of power higher into the atmosphere than the normally aspirated version.
Like all turbos, it does this by compressing the engine’s intake air to “normalize” it to sea level pressure as the plane climbs through the thinning atmosphere. That means more thrust on top of the clouds, and the ability to fight off that anemia for thousands of feet more.
Bottom line: If you like high flight, don’t pass up any chance to get a turbocharged engine.
William E. Dubois is a commercial pilot, ground instructor, and once flew a twin in Colorado that had a single engine service ceiling that was below the surface of the ground he was flying over.