I take a lot of long trips in my Cessna T310R, and more than half of them involve cruising up in the high teens and low Flight Levels, simply because those are the altitudes at which my airplane is happiest, fastest, and most efficient. But from what I’ve been able to tell, the great majority of piston pilots shy away from using the high-altitude capabilities of their airplanes. Most pilots of normally aspirated airplanes seem to confine most of their flying to altitudes of 10,000’ and below, and even many pilots of unpressurized turbocharged airplanes like mine have never flown in the Flight Levels. It’s even surprising how many pilots of pressurized birds seem averse to flying much above the low teens.
That’s a shame, because it’s at the high end of the altitude spectrum that most of our airplanes achieve their best efficiency—and in many cases, their best speed as well. I’m not just talking about turbocharged airplanes. Most normally-aspirated birds are perfectly capable of cruise altitudes well into the teens.
Look at a plain-vanilla, fixed-gear, normally-aspirated Cessna Skylane:
Cessna 182Q Skylane range profile page from POH.
At a low altitude like 4,000’, maximum cruise speed is 139 KTAS at 75% power. Continue climbing until the airplane “runs out of throttle” at 8,000’ and max cruise climbs to 144 KTAS. That extra 5 knots will save you 9 minutes on an 800 NM trip when you take the extra climb into account. (5:38 instead of 5:47, no big deal).
Continue climbing to 12,000’ and max cruise drops back to 139 KTAS (same as at 4,000’), but at a much more fuel-efficient 64% power (which is all you can get at that altitude with wide-open throttle). The same 800 NM trip will take 6 more minutes at 12,000’ than at 4,000’ (5:53 to be exact) because of the longer climb, but burn a whopping 12 gallons less fuel in the process—if avgas costs $5/gallon, that’s $60—and increase IFR range by a full hour and 130 NM!
How far can we take this? Don a cannula and climb to 16,000’—high enough to fly right over the Front Range of the Rocky Mountains IFR—and max cruise drops to a still-respectable 130 KTAS at a miserly 53% power. Because it takes a Skylane nearly 40 minutes to climb from sea level to 16,000’ at max gross, the 800 NM trip will take a half-hour longer than at 12,000’ (6:23), but will save 20 gallons ($100?) and increase IFR range by a full two hours compared to our 4,000’ benchmark.
To fly an
800 NM Trip
Normally-aspirated, fixed-gear 182Q
(maximum gross weight, standard day, no wind,
88 gallons, 45 min reserve)
Unless you just happen to like low-and-slow, there’s no logical reason to cruise a Skylane lower than 8,000’ because doing so makes all the numbers worse: cruise speed, trip time, and range. On the other hand, climbing to 10,000’ or 12,000’ will cost you a negligible amount of time, and reward you with substantially lower fuel burn and increased range.
These calculations are all based on zero-wind, but in real life the winds aloft are often a decisive factor in determining the best altitude to choose. If you’re headed eastbound, odds are you’ll have a tailwind—and the higher you fly, the better it’ll be.
In wintertime, climbing up high to catch favorable winds can pay off spectacularly. In the low-to-mid teens, 50 knot tailwinds are commonplace and a 70 or 80 knot tailwind is possible. Even in summer, when winds tend to be relatively light, going high can pay off. Here are some typical summer winds I pulled off of DUATS:
6000 9000 12000 18000
STL 2410+18 2809+12 3110+07 2917-04
SPI 2510+18 3010+12 3211+07 2919-05
JOT 2511+17 3012+12 3116+06 2926-07
EVV 2509+17 3012+11 3216+07 3018-05
IND 2411+16 3011+11 3114+07 2922-06
FWA 2312+15 2812+10 2916+06 2926-07
CVG 2210+15 2809+11 3012+07 3021-05
CMH 2210+14 2710+10 2914+06 3026-07
CRW 2108+15 2509+10 2908+06 3225-05
AGC 2010+12 2510+09 2813+05 2930-09
EKN 1907+13 2608+09 2810+06 3028-07
PSB 1911+11 2509+08 2813+04 2930-11
EMI 9900+11 2905+09 2811+05 2927-10
Even in these docile summertime conditions, we can expect 10 to 15 knots more tailwind component at 16,000’ than at 8,000’, which almost exactly offsets the TAS advantage of the lower altitude (144K vs. 130K). By climbing up high on an eastbound trip, we’ll go just as fast, burn considerably less fuel, and increase our IFR range nearly 400 NM! Not to mention that it’s almost always smoother and cooler up high. What’s not to like?
During the winter, when the winds tend to be stronger, going high on eastbound trips tends to be an even better deal, saving both time and fuel.
For turbos, it’s even better
If you’ve got a turbocharger, the argument for flying high becomes compelling, because the higher you fly in a turbo, the higher your speed, range and efficiency—at least up to the low Flight Levels in most turbocharged airplanes. These birds really shine up in the high teens and low twenties, and pilots who don’t take advantage of this capability don’t know what they’re missing.
For example, take a look at the “Range Profile” page for my Cessna T310R:
Cessna T310R range profile page from POH.
Starting at 180 KTAS at sea level, max cruise speed at 73.6% power steadily increases with altitude to a relatively blistering 221 KTAS at FL200. (Above that altitude, available power starts dropping off fairly rapidly.)
|To fly an
800 NM Trip
Turbocharged, twin-engine Cessna T310R
(73.6% cruise, maximum gross weight standard day, no wind,
163 gallons, 45 min reserve)
At the same time, range with IFR reserves climbs from 820 NM to 970 NM. Naturally, trip time and fuel burn for the proverbial 800 NM trip both drop accordingly—from 4:14 and 143 gallons at 5,000 to 3:45 and 125 gallons at FL200.
Personally, I don’t push my engines this hard. I almost always throttle back to between 60% and 65% power and settle for around 205 KTAS at FL200 at a miserly fuel burn of 26 gallons/hour, giving me a range of well over 1,000 NM with IFR reserves (or 1,200 NM if I fill my 20-gallon wing locker tank).
Once again, these figures assume no-wind conditions. Add in the wind on an eastbound trip and the results can get downright exciting. In the winter, I’ve seen my groundspeed edge above 300 knots from time to time. That’s fun! During the summer, on the other hand, I’m happy with 230 or 240 on the GPS readout.
Needless to say, you pay the piper going westbound. But if the winds aren’t too strong, it may still pay to go high rather than low. In my airplane, I gain 22 knots of true airspeed by climbing from 10,000’ to FL200. So if the headwind at FL200 is only 10 or 15 knots stronger than at 10,000’ (which is usually the case in summertime), higher is still better.
In wintertime, of course, westbound aircraft are all in the same boat, turbo or non-turbo. We bounce along at the MEA, try not to look at the groundspeed readout, hope the fillings in our teeth don’t fall out, and think about how much fun the eastbound part of the trip was (or will be).
Enjoy the high life!
If you’re one of those pilots who comes from the “I won’t climb higher than I’m willing to fall” school, you’ve got nothing to be embarrassed about. Believe me you’ve got plenty of company. But you’re also missing something really good.
Do yourself a favor: give high a try. It’s cooler and smoother up there. Your airplane flies faster and more efficiently up high. ATC will usually give you direct to just about anywhere. You’re above terrain, obstructions, and often the weather and the ice. The visibility is usually terrific. So are the tailwinds, if you’re lucky enough to be going in the right direction. Try it…you just might like it!