Speed and Fuel

My Warrior is one of the slower planes on the apron. It’s not as slow as some people claim, of course — under ideal conditions, I actually can get within 2-3 knots of the 127 knots true airspeed promised by the POH — but it makes long work of short trips compared to (say) the Mooneys or Barons, not to mention the new Cirrus and Lancair planes. I thought it would be interesting to find out just how big that difference is in real life, and what the cost is, so I plugged the best performance numbers I could find for a bunch of light aircraft into a spreadsheet, and figured out cruise time and fuel for a 400 nautical mile trip with no wind, a 20 knot headwind (normal for a low-altitude westbound trip), and a 20 knot tailwind (normal for a low-altitude eastbound trip). The results follow.

No Wind

As far as I can determine, these are all performance numbers for the plane’s optimal altitudes (depending on the engines). Unfortunately, I have not been able to find good numbers for the Lancair Columbia, so I’ve left it out: its performance should be similar to but slightly better than the SR-22. For a 400 nm trip, ignoring taxi, climb, and descent, here are the numbers:

Aircraft Speed (kt) 400 nm time 400 nm fuel (gal) nm/gal
Beech Bonanza 35 160 2:30 35 11.4
Beech Baron 55 (twin) 188 2:08 58 6.9
Cessna 172M 120 3:20 27 15.0
Cessna 182 140 2:52 39 10.4
Cirrus SR-22 180 2:13 36 11.0
Diamond Star 147 2:43 25 16.2
Diamond TwinStar (twin) 181 2:13 24 16.9
Mooney 201 160 2:30 26 15.2
Piper Warrior II 127 3:09 27 14.9
Piper Arrow 137 2:55 31 13.1
Piper Seneca (twin) 197 2:02 59 6.8

Some of the slower planes are surprisingly fuel efficient in this table: for example, the Cessna 172 and the Piper Warrior are almost as fuel-efficient as the Mooney 201, though they take a fair bit longer to complete the trip. The range of fuel efficiency is quite large: from 6.8 nm/gal for the Seneca, to 16.9 nm/gal for the TwinStar.

20 kt Headwind

A headwind should improve the relative fuel efficiency of the faster planes, since they spend less time in it than the slower ones. It will also greatly increase the time spread between the fastest and slowest planes:

Aircraft Speed (kt) 400 nm time 400 nm fuel (gal) nm/gal
Beech Bonanza 35 140 2:52 40 10.0
Beech Baron 55 (twin) 168 2:23 65 6.2
Cessna 172M 100 4:00 32 12.5
Cessna 182 120 3:20 45 8.9
Cirrus SR-22 160 2:30 41 9.8
Diamond Star 127 3:09 29 14.0
Diamond TwinStar (twin) 161 2:29 27 15.1
Mooney 201 140 2:52 30 13.3
Piper Warrior II 107 3:45 32 12.6
Piper Arrow 117 3:25 36 11.4
Piper Seneca (twin) 177 2:16 66 6.1

At this point, the slower planes (including the Cessna 182) really start to suffer. With 40 gallon tanks, the Cessna 172M is pretty-much at the limits of its fuel reserves for this trip; the Warrior, with its 48 gallon tanks is still safe (probably even for IFR), but both make for a very long trip. The Seneca is now almost twice as fast as the Cessna 172 and Warrior. Note, though, that the Baron still has only a half hour advantage over the Mooney, while burning more than double the fuel.

20 knot Tailwind

A tailwind should eliminate some of the advantage of the faster planes: they will burn more fuel, but won’t get you there all that sooner:

Aircraft Speed (kt) 400 nm time 400 nm fuel (gal) nm/gal
Beech Bonanza 35 180 2:13 31 12.9
Beech Baron 55 (twin) 208 1:55 53 7.6
Cessna 172M 140 2:52 23 17.5
Cessna 182 160 2:30 34 11.9
Cirrus SR-22 200 2:00 33 12.2
Diamond Star 167 2:24 22 18.4
Diamond TwinStar (twin) 201 1:59 22 18.4
Mooney 201 180 2:13 23 17.1
Piper Warrior II 147 2:43 23 17.3
Piper Arrow 157 2:33 27 15.0
Piper Seneca (twin) 217 1:50 54 7.5

Reflections

All of these numbers are a little misleading, of course. For example, the first part of any trip is spent climbing, and a plane that climbs slowly (like the 172M or the Warrior) will spend relatively longer than a plane that climbs fast (like the twins), slowing it down a bit. There’s also the matter of maneuvering around weather enroute, long vectors for approaches at the destination, and so on. All of these planes, then, will take a little longer for the trip than these numbers suggest — my Warrior, for example, more typically needs 4:00 takeoff to landing for a 400 nm westbound trip with a moderate headwind, and 3:00 for a 400 nm eastbound trip when you factor all of that in.

The twins are not much faster than the high-performance singles but burn a lot more gas. Of course, they have other benefits, such as a redundant engine and (often) deicing equipment, but those come at a very high price. The one exception is the TwinStar, which actually outperforms its single-engine sibling both on speed and fuel burn.

So, in practical terms, what would it mean to me to upgrade to a faster plane, like a Mooney 201 or even a Cirrus? On this hypothetical 400 nm round trip with a headwind outbound and a tailwind inbound, my Warrior uses 6:38 flying time and burns 55 gallons of AvGas (about USD 190.00 at current fuel prices). A Mooney 201 would use 5:03 flying time and burn 53 gallons: that’s a hour and a half faster and about USD 10.00 less fuel to boot. A Cirrus SR-22 would get me there and back in only 4:30, for a two-hour saving, but would burn 74 gallons, adding about USD 90.00 to the fuel cost. In other words, the Cirrus saves only a half hour over the Mooney at a cost of USD 100 extra in fuel. Most of the twins are too expensive to even bother calculating, except for the TwinStar, which manages the trip in the same time as the Cirrus using even less fuel than the Mooney.

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About David Megginson

Scholar, tech guy, Canuck, open-source/data/information zealot, urban pedestrian, language geek, tea drinker, pater familias, red tory, amateur musician, private pilot.
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One Response to Speed and Fuel

  1. Frank Ch. Eigler says:

    I can’t argue with the data, only with an assumption behind the conclusion. You may find that when people buy or upgrade airplanes, simple fuel efficiency figures are not deciding factors. Overall capability, reliability, load, range, comfort, maintenance costs, are far more significant.

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