This might be the least talked about spec on your plane but varies widely from one aircraft to another and within the same models according to hp, weights and prop choices. What a range difference from an 80 hp CH 701 with two people at 12000 to 19000 on a Super Cub.

Ever look at this as a combined measure of capabilities of your backcountry plane or do you just value each performance spec individually that contributes to the sum total that we call the service ceiling?

I have a low powered airplane with a relatively low service ceiling. The airplane is also very sensitive to changes in gross weight and density altitude. So I do consider the service seiling as a go/no go factor if there is terrain above 6000 feet in my route. I can easily clear 8000 foot terrain solo but at maximum gross weight (full fuel and 250 total pounds of passenger and cargo) I don't plan to fly over any terrain above 6000 feet.

I thought that this was an interesting thing to explore, so I simply got in my plane and headed for the sky. Bottom line: 1/4 fuel, no passenger, the crap that's normally in the baggage area, a welding oxygen tank, and I found that 18,000 is about the end of the climb.

It was fun to glide for 20 minutes with power off to get back to the airport.

I fly a Savannah with a 912ULS.

tom

Dirtstrip, you're right, you don't hear much about service ceiling but I think it's an good number to consider when you think about takeoff performance at higher density altitudes.

The legendary backcountry planes have high service ceilings such as the Cub, Beaver, C180. Consider the normally aspirated 230hp C180.  At it's ceiling of 21,500 feet, at gross, it's keeping 2550 pounds aloft on 85hp (minus 3% hp per 1000'), thats not too shabby.

With summertime temperatures where I fly, I regularly take off with the density alt. exceeding 10,000 sometimes 11,000'.  The TU206 I fly has a ceiling of 27,000'.  I really don't plan on going up there, not in a 206 anyway, but it makes for decent takeoff and climb, even at 11,000' DA.

Savannah-Tom wrote:I thought that this was an interesting thing to explore, so I simply got in my plane and headed for the sky. Bottom line: 1/4 fuel, no passenger, the crap that's normally in the baggage area, a welding oxygen tank, and I found that 18,000 is about the end of the climb.

It was fun to glide for 20 minutes with power off to get back to the airport.

I fly a Savannah with a 912ULS.

tom

Tom, Wow, you went right out and tried it.

The 20 extra ponies with only about a three pound weight gain over the 912 makes a big difference in ceiling.
Did you use the oxygen on you or the engine

Thanks for going above and beyond for a demo.

Glad I didn't ask about crash survivability.

Hmmm, so at 27,000' in my glider over Minden, Nv I was still climbing @ 100' fpm I guess that's the SC

Glidergeek wrote:Hmmm, so at 27,000' in my glider over Minden, Nv I was still climbing @ 100' fpm I guess that's the SC

Using mountains/wave/convection is cheating.

(at least while trying to establish performance limitations...)

I learned about density altitude on my trip to palm springs this last week. I've never been above 9500 before but I had my new 182 up to 12500. She was loaded to 3000 lbs and the last 2000' was a little slower (0-520 in it). If I was climbing to 17000' cant imagine how long that would have taken

Garth

4Whitey wrote:Dirtstrip, you're right, you don't hear much about service ceiling but I think it's an good number to consider when you think about takeoff performance at higher density altitudes....At it's ceiling of 21,500 feet, at gross, it's keeping 2550 pounds aloft on 85hp (minus 3% hp per 1000'), thats not too shabby.

Ceiling is definitely related to excess horsepower (climb horsepower), and how the plane may react to different load/DA conditions.

Another calculation you can make is to use glide angle, Vy, and weight. For my 182, I get about 7.8:1 glide ratio at 86 mph at gross. That means the plane is going down at 4.9 m/s, and at 2800 lbs, that means I'm burning off gravity energy during descent at the rate of about 82 hp (sounds suspiciously close to the 85 hp mentioned above, doesn't it? They are measuring very close to the same thing!).

That is the minimum power required to stay in the air for the Skylane. So at 6000 feet, where the book says the engine produces 77% power, or 177 hp, I have roughly 90 hp left to climb with. That means I can theoretically make 2800 lbs go upwards at 1060 feet per minute. In reality, I get around 720 feet per minute, and that means my propeller is only about 69% efficient in converting shaft horsepower into thrust after beating the air into submission, which happens to be about exactly right from the Mcauley data for my 2-bladed prop (71% book value). In any case, you can use this info to fill in the blanks of a POH.

The SC on my 182B is 19K pluss change. As the 182's got heavier, in order to keep the same usefull load they lowered the SC.

The marketing department decided that the customer wanted a certain usefull load so they loaded that much in the plane and went up tell it couldn't. If marketing figured we wanted a lower usefull load, the plane would have a higher SC. So does that mean that if I want to lower my SC, I can raise the usefull load .

Tim

180HP normally aspirated... 19000. Been to 18800 before with 2 people 3/4fuel and plenty bags!

Since we are comparing normally aspirated aircraft with similar stall speeds, service ceiling is a rough indicator of shortfield performance. Fixed versus constant speed props aren't a consideration, since the CS ones are probably at fine pitch both at takeoff and ceiling. As lesuther implies, rate of climb and ceiling are related, since they both depend on excess HP. However, an aircraft with a higher ceiling and a higher stall speed may require a longer takeoff roll and climb at a shallower angle than one with a lower stall speed and less excess power (think of a jet). As qmdv points out, reducing load below gross will help shortfield performance, and the ceiling will increase above book value.

If we start comparing ceilings then, besides mentioning weight, we need to express them in terms of density altitude. Ceiling is at constant DA, but the measured altitude varies with temperature and density.

I've climbed my M7-235C to 17,500. A few years ago I did a Vy climb at gross, recorded the time every thousand feet, plotted it (it was quite linear), and extrapolated service ceiling to be a density altitude of 19,500 versus the published value of 20,000. That was before rebuilding the engine.

'59 PA24 - 250 Comanche at FL190 still climbing at 400 fpm. 2 average size guys and 60 gal fuel. What a traveling machine.

Never had a NA Cessna above 14K.

Around here 3K is nosebleed altitude.

gbflyer wrote:Around here 3K is nosebleed altitude.

That would be nice. Don't even get off the ground till almost 5k around here.

I value each performance spec individually. The reasons I do this is because even at 10K DA I can get off the ground and climb reasonably well. Once I approach service ceiling climb rate drops off quick. Not sure why the Luscombe behaves like this, perhaps it is because of the long wing.

10K + hours in a C207, and 9,995+ of those hours below 3,000 MSL, and most of that at/below 1,000 MSL.

Now down here in the wilds of Nevada with my overpowered O-300-B C172TD, some hot summer days I just sit and look at the sky... 'Cause I know that thing ain't gonna get off the ground.


Gump

Equating service ceiling with high altitude performance typically fails to take into account 2 things: density altitude and how long it takes to get to that maximum 100 fpm climb. That's part of why there's excess tin in the high country around here. People look at the 14,200' SC of a 172 and think that they can clear a 12,000' peak with ease, failing to take into account that the density altitude may very well be 15,000' or 16,000' over that peak at the time. Or they figure their 15,300' SC of a 152 means that they can fly into the mountains, failing to take into account that at about 9,000' DA, the 152 is only climbing at about 100 fpm but will continue to climb at that same anemic rate up to its 15,300' SC.

My 180 hp P172D tops out at about 15,000' DA, and the last couple hundred feet are at 100 fpm, so I consider its SC to be about 14,800'. But I've flown it at 16,500' MSL, and on that day, it got there pretty easily--cold, clear, etc.--and kept it there even cranking back the prop to 2400 rpm, so it probably could have gone higher. And I've certainly had days when it topped out at 12,000'.

Cary

Cary wrote:Equating service ceiling with high altitude performance typically fails to take into account 2 things: density altitude and how long it takes to get to that maximum 100 fpm climb. That's part of why there's excess tin in the high country around here. People look at the 14,200' SC of a 172 and think that they can clear a 12,000' peak with ease, failing to take into account that the density altitude may very well be 15,000' or 16,000' over that peak at the time. Or they figure their 15,300' SC of a 152 means that they can fly into the mountains, failing to take into account that at about 9,000' DA, the 152 is only climbing at about 100 fpm but will continue to climb at that same anemic rate up to its 15,300' SC.

My 180 hp P172D tops out at about 15,000' DA, and the last couple hundred feet are at 100 fpm, so I consider its SC to be about 14,800'. But I've flown it at 16,500' MSL, and on that day, it got there pretty easily--cold, clear, etc.--and kept it there even cranking back the prop to 2400 rpm, so it probably could have gone higher. And I've certainly had days when it topped out at 12,000'.

Cary

Cary,

Good you brought it up, because a lot of pilots learn about DA the hard way. But, I don't think anyone was "equating" service ceiling with "good" performance at the service ceiling or anywhere near that altitude. It seems that we were just saying the ceiling one of the important performance numbers when you consider how a plane will perform at altitude.

I started my flight training in the summer Flagstaff, AZ (7,014'DA) in a 150hp 172 (service ceiling 13,100' DA)....

With DA's around 10,000', I moved up to a 200hp 172 pretty quickly.

Cary wrote:Equating service ceiling with high altitude performance typically fails to take into account 2 things: density altitude and how long it takes to get to that maximum 100 fpm climb.

Service ceiling is an indicator of excess HP. Absolute ceiling is a direct indicator. CS props yield a reasonably flat efficiency curve at Vy from sea level through service ceiling (my 2 blade McCauley varies from ~30% at initial roll, to ~55% at rotation to ~70% at Vy to ~72% at cruise). Service ceiling is an excellent benchmark to use when imagining how much performance you are likely to have at high DA. With a CS prop, if you know the absolute ceiling for a particular load condition, and a climb rate for the load condition at a particular altitude, then you can calculate the rate of climb for any altitude below the ceiling with surprising accuracy, and also for another load condition. It's just Newton's second law (F=ma) from high school. The numbers from the POH are demonstrated numbers, but you will come up with VERY similar numbers if some other items, like ceiling or glide ratio, are understood.

For a fixed pitch propeller, the observation that climb performance deteriorates much more rapidly with DA is a very real. The reason has nothing to do with the wing (or at least very little directly), but the fact that decreasing HP available at higher DA is compounded by decreasing propeller efficiency...a double whammy. And efficiencies for fixed pitch props drop precipitously. So less HP is generated, and less of what is left is converted to useful thrust (the rest is used to heat up the air/make noise).
http://www.epi-eng.com/propeller_technology/selecting_a_propeller.htm
Fixed pitch propellers are a compromise, and many quickly fall below 60% efficiency very fast. I flew a 175 with a CS prop that was fine at 14k' DA for instrument training. It was positively painful to try the same thing in a 175 with the same engine and a fixed pitch prop.

My old 56 182 is rated to 20,000 + at gross . I've been to 23,000+ in winter with 2 aboard (oxygen mask on )and about 1/2 fuel .Standard 0-470-L engine. Now that I'm going to a more powerful motor expect to do a lot of high altitude cruising.

I've never been to an altitude where oxygen was required. But I do value having some decent climb rate at 10-12k for the times when I'm in that range headed over the mountains. No need to go higher in the NW, but I haven't flown in Colorado either.

First real experience with this was heading over the Cascades as a pretty newly minted pilot in a rented 172 in the summer when there was some wind so I wanted to be a bit higher to stay out of low level turbulence. Took a while for my thick skull to realize that the airspeed was really low not because there was an engine problem but because my density altitude was pretty close to the service ceiling...