Just how high can it fly?

7 Answers

1. 
   

   
   

   Felix on Nov 30, 2010

   The POH should contain the maximum ceiling of an aircraft. Every airplane has a max ceiling, and it really depends on the engines. I don’t have the C172 poh on hand, but i believe the ceiling is somewhere around 10,000ft. You should confirm in your POH.
   The engine in your Cessna 172 needs a specific air to fuel mixture to maintain it’s power. Eventually at a high enough altitude the air is so thin that there is more fuel than air and combustion doesn’t occur efficiently. Therefore reducing the power of your engine. This then slows the airplane down, and the airplane can no longer maintain a speed above stall speed.
   Turbocharged engines are capable of higher ceilings because they compress air to provide a better fuel to air mixture. This allows them to go up to the Flight Levels and maintain lift.
    

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2. 
   

   
   

   Kent Shook on Nov 30, 2010

   A lot of it depends on engine power. A normally aspirated, piston-powered engine is going to have a tough time making it to the flight levels. Turbonormalizing or turbocharging allows the engine to make power to higher altitudes. Turbine engines also work well at higher altitudes, but even they will run out of air to breathe eventually. Super-high altitude airplanes have used rockets, and NASA has done some work on Scramjet technology which works at very high speeds and altitudes.
    
   Aerodynamically, as you climb, if you are able to develop the same amount of engine power, you’d be able to maintain roughly the same indicated airspeed. However, aerodynamic flutter, which is one of the things that can determine Vne, is sensitive to your *true* airspeed, which increases with altitude if you’re maintaining the same indicated airspeed. So, your maximum indicated speed will go down, and some airplanes meant for flying in the flight levels have a “barber pole” indicating the maximum allowable speed for their altitude rather than the red radial line we’re used to for indicating Vne. The “barber pole” actually moves as the airplane climbs, indicating the reduction in the maximum speed.
    
   On the other end of things, as you climb, the air is thinner, so to maintain the same amount of lift you’ll need either a higher airspeed or a higher angle of attack. As stated above, airspeed becomes more limited on the high end at higher altitudes, and a higher angle of attack will eventually lead to a stall. 
    
   Combine the two effects, and the allowable envelope of airspeeds decreases as you climb. In addition, if you get high enough, there are mach effects to consider. (See http://en.wikipedia.org/wiki/Coffin_corner_(aviation) ) Aircraft like the SR-71, U-2, X-15 and the like that were meant for high performance, high altitude flight had many design considerations to allow them to fly where they did.
    
   As for your C172, the service ceiling is between 13,000 and 15,000 feet depending on the model. 15,000 feet is a pretty average service ceiling for a normally aspirated, piston-powered airplane, almost all of them range between 13,000 and 18,000 feet. The service ceiling doesn’t mean that’s as high as the plane can fly, though – The service ceiling is the density altitude at which the airplane is only capable of climbing 100 feet per minute at gross weight, the absolute ceiling is where the airplane cannot climb at all any more. As you climb, Vx goes up and Vy goes down, they meet at the absolute ceiling of the aircraft.
    
   Personally, the highest I’ve flown a normally aspirated piston single was 17,500 feet MSL, at a density altitude of 18,848. This was in a C182, whose service ceiling is 18,000 feet – And I was still climbing at 200 fpm when I got there. How was I able to climb above the service ceiling, and still be getting better than 100 fpm? Well, I was about 300-400 pounds under gross weight, so I had more excess horsepower available for climb.
    
   For reference, at that altitude I was at full throttle and it only gave me 12″ of manifold pressure, which is a setting I normally use on final approach when flying the pattern VFR. My indicated airspeed was 80 mph, which is also my target airspeed on final when VFR. As I recall, that gave me a true airspeed of about 103 knots, and with the 30-knot tailwind I had, I was right back at the 133 knots that I normally cruise at down low in that airplane. But, it was an interesting exercise.

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3. 
   

   
   

   Jim Foley on Dec 01, 2010

   One factor that most people overlook when talking about this subject is aircraft pressurisation.  As the aircraft asends, the cabin needs to be pressurized, so the pilots can live (duh!).  Most civilian large aircraft won’t pressurize the cabin to more than 6 or 8,000 ft.  If the cabin pressure remains at, say 8,000 ft, as the the aircraft climbs, the pressure differential becomes greater and greater.  If the structure is not strong enough to whithstand these pressurs, it will catostrophically fail.  The 737 has a service celing of 41,000 ft.  Theoretically, the engines have plenty of power to create lift and climb higher, but due to the cabin pressure limitations, it it were to go much higher, the structure would collapse.  This is true for most larger narrow- and wide-bodied aircraft.

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4. 
   

   
   

   Kent Shook on Dec 02, 2010

   An aircraft does not need to be pressurized to climb high – But the pilot (and any others aboard, too) does need to wear oxygen. Cannulas work below 18,000 feet, above that you need a mask. If you go REALLY high (and I’m not sure how high) you’ll need a pressure suit.
    
   Also, a pressurized aircraft won’t just explode if it climbs too high. The pressurization systems can only maintain a certain pressure differential. For example, a Beech Pressurized Baron (B58P) can only maintain a cabin altitude of 8,000 feet up to around 18,000 feet. But, if you climb to 20,000 feet you’ll simply have a cabin altitude of 10,000 feet. Climb to 25,000 and the pilot will need to wear oxygen despite the plane being pressurized – So, the limitations are practical ones, not structural.
    
   Going higher simply involves a lot more science, and a lot more design considerations. Certification limits are established with the known science in mind. Most of our small airplanes simply can’t climb high enough for anything other than the basics to matter. Another more stringent set of requirements kicks in above 25,000 feet, so many airplanes that are capable of going higher are only certified to 25,000 feet. There’s another set of requirements above 41,000 feet and very few airplanes are certified above 41,000. A few airplanes are certified to 51,000, the only civilian airplane I can think of certified to go higher than that is the Concorde. 

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5. 
   

   
   

   Steve Pomroy on Jan 04, 2011

   Hi Flyer.
    
   As noted above, the principle restriction on our maximum altitude is engine performance, with a few additional practical considerations like pressurization and our need to breathe.  But you may also be interested in noting that there are other limitations that we don’t often run into simply becasue we hit the engine limitations first.  These include critical mach (resulting in the dreaded “coffin corner”) and the reduction in Vne due to reduced damping in lower-density air.
    
   I’ve written about these in a bit more detail here:
    
   http://www.flightwriter.com/2010/10/how-high-can-you-fly.html
    
   Incidentally, Kent mentioned the need for a pressure suit.  The altitude at which this occurs is around 60,000′.  The air pressure at this height is low enough that the boiling point of water matches our body temperature.  So body fluids vaporize and we run into great difficulties!
    
   Cheers,
   Steve Pomroy
   http://www.flightwriter.com

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6. 
   

   
   

   JB on Aug 13, 2012

   Like Steve said above, just throwing on bigger engines doesn’t solve the problem and grant you safe flight at a higher altitude – even if you CAN get there. I flew a type of jet that was re-engined with enough thrust to literally “out climb the wing” based on a given weight.

   For instance, I could go straight to FL410 with the available thrust, but the wing didn’t like that very much and let you know too. We could end up with a very narrow hi/lo speed buffet margin (aka coffin corner).

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7. 
   

   
   

   Sean marshall on Mar 17, 2015

   I have gone only to 1500 feet but it was a bad day for flying

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