September 1, 2006
By Peter A. Bedell
Now that aviation fuel costs more than $4 a gallon in many parts of the country, it has become a more significant expense in the overall operation of an airplane. Unfortunately, many of the habits we formed in operating airplanes when fuel was one-quarter or even one-half of what it costs today are not optimal given the current fuel prices.
By no means is the following a comprehensive list of every way to save fuel. It is simply a listing of some techniques and products that will save fuel or reduce fuel costs over the long term. If you have additional fuel-saving tips and techniques, please share them with us on AOPA Online.
Wind awareness. Winds always have a significant impact on the efficiency of airplanes. Ride a nice tailwind in an efficient airplane and you can relax knowing that you're getting better gas mileage than in your Buick. In contrast, powering into a strong headwind means spending lots of time burning lots of fuel to go a short distance. A technique to minimize or maximize the effects of wind is to climb shallowly into a headwind and steeply into a tailwind. When climbing into a tailwind (assuming the tailwind gets stronger as you climb), you can spend more time in the stronger push aloft by climbing at or near your airplane's best-rate-of-climb speed. In addition, the quicker you get to altitude, the quicker your climb fuel burn will reduce to the cruise range. For a headwind, the opposite technique works well in most cases. A flatter, higher-speed climb will allow you to put more miles behind the airplane while in the lighter winds at lower altitude. Typically, leveling off at the lowest smooth altitude will be the best trade-off for comfort and efficiency. Myriad Internet weather sites provide excellent forecasts of winds at various altitudes. The use of air data computers for this purpose is discussed later in this article.
Lean-of-peak operations. Airplanes with multiprobe engine monitors and balanced fuel-air ratios in every cylinder are great candidates for lean-of-peak (LOP) operations. In a nutshell, an engine running LOP is more of an air pump than a fuel pump. On the lean side, your engine will not make as much power, but fuel flow drops off precipitously. Some engines may run smoothly LOP without any modification. For those that won't, check out GAMIjectors by General Aviation Modifications Inc. These tuned fuel injectors achieve the balanced fuel-air ratios needed for an engine to run smoothly LOP.
A set of these nozzles starts at $800 per engine, but the potential fuel savings can pay for the nozzles in a few hundred hours depending on type of engine. Be sure you're well versed in LOP operations before getting too adventurous with the red knob. Jockeying of the mixture can lead to serious engine damage if running at high power. GAMI's Web site is a good start for those interested.
Lean aggressively on the ground. Although piston-aircraft engines burn comparatively little fuel on the ground, the practice of leaning on the ground has always been good for engine condition. In many cases, the engine simply runs smoother and cleaner since you won't be washing down the cylinders with excess fuel that contaminates your oil besides being wasteful. It also curtails spark-plug fouling. Afraid you'll forget and take off with the mixture leaned? If so, lean so aggressively that the engine will starve of fuel at anything higher than your run-up rpm. You won't forget it then. At the low power settings used during ground operations, you can lean as much as you can without fear of damaging the engine.
Fly high. Most nonturbocharged light aircraft are most efficient at altitudes around 6,000 to 11,000 feet depending on aircraft type and whether the propeller is fixed or variable pitch. At the higher altitudes there is a trade-off between available engine power and the lower drag of the thinner air. I remember a particular Piper Arrow I flew often that could maintain its superlative 140-knot true airspeed from 7,000 feet all the way up to 11,000 feet. At the higher altitude, the fuel flow was a modest 8 gallons per hour compared to 11 gph at 7,000. One caveat is the length of the trip to be flown; if it's a short trip, the fuel used to get to altitude will negate the extra true airspeed gained by flying higher. In addition, altitude can really take a toll on the human body because of the lack of oxygen. Bring an oxygen bottle, if necessary.
Seek out the smooth air. Flying in turbulence can slow your cruise speed down by 5 knots or more. Besides being a more comfortable ride, the lack of turbulence can save fuel.
Go slowly if you're going the wrong direction. Sometimes the runway in use at your departure or destination airport is not the one most advantageous for your route of flight. If the runway points south and you want to go north, it makes sense to climb at your airplane's best-angle or best-rate-of-climb speed to minimize the miles flown in the wrong direction. In other words, if you have to go the wrong direction, at least you can trade that time for altitude. Otherwise, on arrival, once you're past the airport, slow to the minimum practical airspeed since you're going the wrong way. Besides saving fuel and time, these techniques reduce your airplane's noise footprint over areas surrounding the airport.
Preheat. Most pilots are well aware of the importance of preheating aircraft engines in cold weather to minimize engine damage, but preheating also can be used in more balmy temps to minimize engine warmup time, which consumes fuel. It can take 10 minutes or more to warm a 500-pound engine up to operating temperature from a start temperature of 55 degrees Fahrenheit. Plugging in your engine several hours prior can get the engine to its operating temperature by the time you are ready to depart. Then you can taxi right to the runway and take off as soon as you're done with your preflight checks. As mentioned, piston-aircraft engines burn very little fuel on the ground at idle, especially if properly leaned, but the cumulative effect of eliminating warmups will save fuel over time.
Get your clearance before you start. Obtain your air traffic control clearance on a handheld radio or on the airplane's radio and load your flight plan prior to starting the engine. How many times have you started the engine and later waited for several minutes to get your clearance and load the route into your navigator?
Rigging. Many of our airplanes are reaching middle age and have had their fair share of airframe repairs or adjustments. One unfortunate result of all this work is that there likely have been some cumulative changes in the rigging of the wings and control surfaces. Ever wondered why it takes a swipe or two of rudder trim to center the ball of the turn-and-bank or turn coordinator? And after you get the yaw portion straightened out, the yoke is cocked to one side or the other? There's a good chance those trim tabs or control surfaces deflecting in the breeze are creating drag, robbing you of some knots and miles per gallon. If so, a rigging job can get you flying straight again. Rigging takes patience, time, and a mechanic who's familiar with the type. Owners groups have good sources of mechanics and shops that can rig your type of airplane.
Don't park your airplane with full fuel tanks. Even on relatively cool days, it's not recommended to park an airplane in the sun with full tanks. As the fuel heats up, it expands and has nowhere to go, except out the vent and onto the ground. Some airplanes (Cessna 210s come to mind) when topped off can spit out several gallons of fuel on a warm day. Some other Cessnas also are particularly prone to venting fuel if they are parked left-wing low. The fuel vent is on the left side and if parked left-wing low with the selector valve in Both, fuel can slowly dribble out of the vent. If you must top off prior to parking the airplane for a few days, tell the fueler to stop filling when the level is an inch or two below the cap. This should allow some room for expansion. Just remember that you aren't "topped off." Positioning the fuel selector to the left will mitigate crossfeeding between the tanks and additional overflow.
Carry only the fuel that's required for the trip. Many flight schools, flying clubs, and individual owners abide by a "top-off" rule in which an airplane is parked with the fuel tanks topped off. Although this may seem like a courteous thing to do, it's not the most efficient way to fly an airplane. Extra fuel is unnecessary weight and airplanes burn fuel to carry fuel. Airlines have always subscribed to this rule of carrying only the fuel that's required for a given trip, although for a jet, a huge percentage of the takeoff weight is fuel. In light airplanes, the difference is not very much, but carrying around an extra 200 pounds can mean the difference of another few minutes at climb fuel burn and a slight reduction in cruise speed. There also is a risk of not knowing exactly how much fuel is in the tanks when they are partially full. Calibrated dipsticks and fuel computers can help here. There also is the issue of condensation in the fuel tanks. A properly capped and vented fuel system should have little or no condensation accumulation even if the airplane is inactive for more than a week. Finally, some believe that rubber fuel bladders will suffer decreased life expectancy if only stored with partial fuel. Although this is anecdotal evidence, my partners and I got more than 20 years out of a set of bladders that were rarely stored with full fuel.
As with most things in aviation there are long-term trade-offs, such as the need to outlay cash to eventually save money. Many of the items listed here will set you back a few dollars, but as the cost of fuel rises, those dollars will be recouped more quickly. Meanwhile, many of these modifications provide bonus benefits that can pay off big time in the long run.
Autogas STCs. For some time autogas, or "mogas," has been successfully used as an alternative fuel for airplanes powered by low-compression engines via the approval of a supplemental type certificate (STC). Autogas can be obtained for a fraction of the cost of avgas, but its use is not without controversy. Since the STCs were obtained for a number of airplanes to use autogas, the formulation of the fuel has changed — a lot. Today, there are higher concentrations of alcohol (ethanol) in automotive fuels that are detrimental to rubber parts of an airplane's fuel system (such as fuel cells, gaskets, and O-rings). In addition, neither of the STCs (available through the Experimental Aircraft Association [EAA] and Petersen Aviation) approves the use of autogas spiked with alcohol, and it is becoming harder to find the untainted gas. No longer can you fill up a 5-gallon can at the local gas station and dump it into your airplane. AirNav lists 199 FBOs that carry mogas that should be untainted. There also are test kits available from EAA and Petersen that allow users to test whether the fuel is spiked. Although the potential to save a lot of money lies in the use of autogas, the downsides should be carefully researched.
Fuel price Web sites. The best way to save money on fuel is to pay less at the pump. AirNav and 100LL.com, among others, allow users to scour the Web for the lowest fuel prices in the area that they intend to fly. Often, you can find fuel on the way to, or near, your destination that is significantly less expensive than the fuel at your origin and destination. Using such Web sites, I've been able to save $100 or more on a fill-up of a light twin. Be sure to check with the FBO by phone to make sure the price found on the Internet is still good. A new shipment of fuel can make obsolete the price quoted on one of these sites.
Auxiliary fuel tanks. With auxiliary fuel tanks, pilots have the option to tanker inexpensive fuel if the extra weight isn't an issue. Unlike in jets, the performance penalty of carrying several hundred pounds of extra fuel in a light airplane does not amount to a significant loss of efficiency, especially if the price is low. (However, with today's fuel prices, even airlines are tankering fuel if the price is right.) Besides the ability to tanker cheap fuel in your wings, auxiliary fuel tanks give you lots of operational options, allowing you to overfly weather systems and negate the need for fuel-slurping climbs back to altitude following intermediate fuel stops. Some also provide for a maximum-gross-weight increase and the resulting increase in payload. The initial investment likely will be several thousand dollars, but aux tanks ultimately will pay for themselves in convenience, fuel savings, and resale value. Check the type club for your model of airplane for available aux fuel tank vendors.
Air data computers. Airplanes with a horizontal situation indicator should have all of the necessary inputs required to install an air data computer. An ADC can provide the pilot with a real-time readout of wind conditions and true airspeed, eliminating much of the calculation and guesswork involved in seeking out the best altitude for winds. ADCs aren't cheap, but they can pay for themselves over time in fuel savings and airplane resale value. Besides, they increase a pilot's overall awareness of weather conditions in flight. ADCs for personal aircraft are made by Insight Avionics, Sandia Aerospace, and Shadin Avionics.
Volume discounts. For airplanes with voluminous fuel tanks, you may be able to secure volume discounts if you make a purchase of 50 or 100 gallons or more. Asking FBOs for a volume discount could make a significant difference in cost, especially at airports with multiple FBOs and, therefore, intense competition.
Don't throw out that fuel sample. After sampling fuel from your aircraft's fuel tanks — if you're sure the sample is pure, clean fuel — toss it back in. This is a pretty controversial procedure and rightly so. Who's to know if that sample is perfectly clean? If in doubt, toss the samples into a tug, nearby lawn mower, or container provided by the airport. It'll go further in an engine than it will if discarded. Just don't pour it into your car or anything else that has a catalytic converter in the exhaust system. Despite being referred to as "low lead," avgas has quite a bit of lead in it. A handy gadget is the GATS Jar available from pilot supply shops for approximately $20. This fuel strainer allows you to inspect your fuel sample and pour it back into the tanks. What distinguishes the GATS Jar from other strainers is its ability to separate contaminants from raw fuel to allow you to pour the contents of the jar back into the tank without having to worry about recontaminating your fuel supply.
Baffle maintenance. When cylinders run hot, the easiest way to cool them off is by pushing the mixture knob forward to cool it with fuel. That works, but it is not a very efficient way to run an engine that burns $4-per-gallon fuel. The first step should be checking the cooling-baffle condition and sealing up any leaks that may exist. If that doesn't work, consider an overhaul of cooling baffles. Factory cooling baffles were adequate when your airplane was certified decades ago. But several years of use, searing heat, and vibration have likely caused the baffling to become shoddy. Several companies make cooling kits that can drastically lower cylinder head and oil temperatures, allowing your engine to run cooler without the use of extra fuel or speed-robbing open cowl flaps.
Your own tank. If you live on your own airport or another that allows it, consider buying your own fuel tank and filling it with your fuel of choice, enjoying the convenience and low price of buying fuel in bulk. Keep in mind the shelf life of your airplane's fuel. 100LL maintains its properties much longer than autogas or Jet A. Typically, the costs of the fuel tank and pump will be recovered in just a few fill-ups of the system.
FADEC. Currently, Teledyne Continental Motors (TCM) has the only certified full authority digital engine control (FADEC) system on the piston market, and after a few growing pains it is showing promise in delivering modest fuel savings along with greatly simplified engine operation for the user.
TCM's FADEC employs sequential-port fuel injection, which squirts only the required amount of fuel into each cylinder, rather than the usual continuous-flow injection system that most TCM engines use. FADEC also optimizes the mixture for every phase of flight from ground operations to economical lean-of-peak cruise flight (see " Fly the Electrons," September 2005 Pilot).
The system costs about $10,000 per engine to install, but costs will be recovered over time in fuel savings, ease of operation, and the eventual ability to run the engine on alternative fuels such as autogas.
Airframe mods. Many popular airframes have products available via STC to increase speed. Knots 2U, LoPresti Speed Merchants, Beryl D'Shannon Aviation are all purveyors of aerodynamic cleanup products that will enable your airplane to go faster on the same amount of fuel. Although most of these products are quite pricey, many of them are a better mousetrap compared with the original equipment in terms of type of material used, quality of construction, as well as functionality and appearance.
Peter A. Bedell is a first officer for a major airline and co-owner of a Cessna 172 and Beechcraft Baron.
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