April 28, 2008
You heard it in the Sun-N-Fun 2008 LSA Mall. Whether you were talking to pilots of Cubs, Luscombes, Bellancas, Cessnas or Beechcraft, it echoed strong in the Type Club tent. It was the talk of manufacturer's displays and the exhibition hangars. It was even touted by purveyors of very light jets. It seems like the biggest thing on pilots' minds is the cost of airplane fuel, whether mogas, 100LL or even jet varieties. There's not a lot individuals can do to affect the cost of a gallon of our gas-of-choice. But there are some things we can do to reduce our fuel consumption, and have at least some say in fuel costs.
First, let me emphasize there are some fuel tactics that might save a little gas money, but that have a negative effect on safety. Regardless of your fuel strategy do not use fuel pricing as an excuse to press on when you have too little fuel on board, to exceed best-practices engine temperatures or to violate fuel-related aircraft limitations. It does nobody any good to save a few dollars up to the point of impact.
It's probably sacrilege in the world of flying to say this, but if you can't afford to put fuel through your airplane of choice with an adequate safety margin you can't afford to fly that airplane and you need to find a cheaper way to get around. For some of us it means it's time to step down to a slower or smaller airplane to continue making the trip or the hamburger run. For others of us, very unfortunately, it may mean it's time to get out of flying until we can afford to fly safely again. If you're like most pilots, however, you can realize significant fuel savings by changing your operating technique in the plane you fly. Commit to flying safely, while investigating these techniques for controlling your fuel costs.
|Manifold Pressure/Fuel-Flow Gauge
One way to reduce fuel burn it to choose a lower power setting. You'll be surprised how little time you lose (extra flying time you get to put in your logbook!) while saving a good bit of fuel along the way.
Get out your Pilot Operating Handbook (POH) and make a few power-setting comparisons. For example, the 180-horsepower Diamond DA40 Flight Information Manual (FIM) tells us a flight at 5000 feet and the traditional, go-fast power setting of 75-percent power (about 24" mp and 2400 rpm) nets 136 KTAS while burning 11 gallons per hour (gph) at a best-power mixture setting. Drop back to 65-percent power (23" mp/2200 rpm) and you can expect 128 KTAS and 8.2 gph. Come way back to what many of us consider a very low propeller setting, 2000 rpm, and you can still get 65-percent power at 5000 feet (by running at 25.4" mp) for that same 128 KTAS at only 7.9 gph fuel burn. That's only eight knots loss of true airspeed compared to high-speed cruise, but a savings of three gph.
Now fly 200 nautical miles. At 75-percent and best power, it'll take 1.5 hours and require 16.5 gallons. The 2000 rpm, 65-percent power, economy cruise will take about six minutes more, but you'll burn only 12.6 gallons ... nearly four gallons less on the same trip with a negligible time difference. (These comparisons assume no wind.) At an average $4.94 per gallon (the AirNav nationwide average for 100LL on the day of this writing), that's a savings of $19.76 on this one flight, with no real time difference en route.
So dig into your airplane's POH and look at the real-world effects of using something other than a go-fast power setting. It'll have a big impact on what it costs you to fly.
The Economic Advantage of Tailwinds
When the winds blow strong, especially on longer trips, you might be able to get even better economy. Adjust your power setting for a planned ground speed, not true airspeed. If you're lucky enough to have a tailwind component, throttle back for the "normal" groundspeed and rake in the savings as you attain that speed at a lower fuel burn. Yes, you'll still have to fight your way into headwinds sometimes, and if they're very strong you may even be "forced" to fly at higher power settings to make any real progress. Using tailwind to reach the "normal" groundspeed with lower fuel burn when able, though, will offset the higher fuel costs of fighting a headwind when needed.
For a given power setting, the higher you fly, the greater true airspeed you'll attain. This is because the air is thinner the higher you go, so there's less air resistance and -- as long is power is maintained -- you'll go faster. (This is the secret of turbocharging.) Most naturally aspirated (non-turbo) engines can maintain 55-percent to 65-percent power to 10,000 feet or more, so all else being equal (headwinds aloft, turbulence, icing, etc.), it pays to fly as high as practical. Won't you burn more fuel climbing to altitude? If you make a long, shallow descent on the other end, you can offset the added fuel cost of an extended climb. So you can save gas by climbing as high as makes sense for your trip. Note: Altitude helps meet the overall goal of safety, also.
|Exhaust Gas Temperature (EGT) Gauge
All too often pilots are taught simple rules for mixture control, like, "Don't lean below 5000 feet," or, "Lean it 'til it sounds rough, then turn the vernier in two turns" as a cruise-mixture technique. These habits may be expedient for high-engine-stress instructional flying, but they are imprecise and in most cases waste fuel. Learn how to properly lean the fuel mixture to glean maximum efficiency from your fuel burn (consistent with good engine-temperature management). Determine if, when and how it may be appropriate to run lean-of-peak in cruise flight with the engine(s) you're flying to save even more fuel -- and money.
"Tankering" is the act of loading up on fuel where it's (relatively) cheap, to avoid having to buy fuel where it's more expensive. Do your homework: Use AirNav or similar Web sites to find locations with lower-priced fuel near your destination and any planned fuel stops along the way. Plan to arrive at these "tanker-ports" with a safe fuel-margin in case you need to divert or the pumps are closed, but with as much room as possible in your fuel tanks to load up while the fueling's good.
Sometimes you're going up just for fun, to see the sights or buzz around on a warm Saturday morning. You don't have to give this up because of high fuel costs -- just do things a little differently. Use very low power settings when you're on local sightseeing hops to keep the fuel burn low. Get more involved with local pilots' groups and start sharing the ride. (You can legally split the direct costs of the flight under FARs and the provisions of aircraft insurance, and this sort of aerial "clubbing" is becoming more popular in the go-it-alone United States.) "Air-pool" together to major events like fly-ins and AirVenture at Oshkosh -- it's fun to share flying with other pilots in the air as well as on the ground, and if you fly a similar airplane type, you might split the flight legs and each log some time going to and from the show.
What If I Rent?
You might ask, "What if I rent airplanes? Fuel prices are figured into the rental cost of the aircraft, so as they go up, the hourly rental rate goes up and there's nothing I can do about it."
Many FBO used to offer "wet" and "dry" rates for aircraft rental, where wet rates include fuel. Occasionally FBOs will put a maximum price they'll cover for fuel purchased away from base, but otherwise they'll cover the cost of fuel out of what you pay in rent. Fuel burn is usually charged assuming 75-percent, best-power, mixture setting. This historically works to the FBO's advantage when the airplane is fueled locally, because often they can negotiate bulk fuel rates and make a little more than the posted fuel price suggests. Given the reduction in hours flown over the last couple of decades, however, a typical FBO's bulk purchases of 100LL are declining and the FBO may not get much of a discount any more.
Renting "dry" means the renter pays a lower rate for the airplane, then pays for his/her own fuel in addition to the fee. Dry rentals went out of favor some time back when fuel prices were low, replaced with the all-fees-up-front simplicity of wet rentals. But now that just a little change in operating procedure can make a big difference in the total cost of fuel, you may be able to negotiate a dry rental rate that covers all the FBO's costs (and profit) except fuel, and pay for the fuel yourself. If your operating technique burns less gas than the FBO's fuel burn assumption, you'll fly for less than the "wet" rental rate. It certainly can't hurt to ask.
Don't Skimp On Training
Make a vow to train as much as always despite the cost of fuel. Combine your flying missions if needed to log a safe amount of dual -- ask your CFI along and combine a flight review with the weekend pancake run, or hire a CFII to accompany you on a business trip and get some hood time on a flight you'd otherwise make alone. Pay the instructor for his/her time, of course, but you're ahead the cost of scheduling additional flights for the purpose of training only. You'll find most instructors like to get away from the home 'drome anyway, so chances are you'll find a qualified teacher of flight who will instruct "on the fly," as it were.
You'll most likely come up with a list of other ways you can continue to fly safely while spending less on fuel. I encourage you to use the Comments feature of this article to let others know what works for you. Together we need to change a culture where pilots are judged by the speed at which they fly into one where their worth is determined by the efficiency and economy with which they use an airplane. As the cost of flying fuel skyrockets, you need to be creative to fly safely using less gas.
Fly safe, and have fun!
Thomas P. Turner's Leading Edge columns are collected here.