Maximizing Aircraft Efficiency

Are you getting the most performance from your airplane? The fact is a considerable amount of unused performance gets overlooked by the average owner/operator. Both performance and range can be improved through common operational techniques, performing regular maintenance procedures and careful planning. Most of this “hidden performance” can be gained back from wasted fuel and increases in the airplanes useful range. In turn, you can reduce the annual operating costs. And with average aviation fuel prices nudging $6 a gallon in the

U.S., who wouldnt want to enhance their airplanes efficiency?

Thankfully, its not as complicated as it may seem. You just need to make the machinery work the way it was designed to work. One method is to ensure the airplane is as mechanically sound as it can be. Then, well look at improving its basic aerodynamics, followed by some smarter flight planning. Finally, well look at ways to save fuel while airborne.

Well start with maintenance. Not just repairs, but maintenance considered from an operational point of view. One way to think of it is as preventive maintenance. Still, theres more to it than just preventing something from going bad: You want to enhance the airplanes efficiency by ensuring all components are operating as they should. The goal is to get all of the systems and parts of the airplane working together.

Commercial airlines have found in their records that a new airplane loses performance at a predictable rate. This performance loss results from mis-rigging, airframe dents, pressurization leaks and hard-to-find gradual increases in total weight. They all contribute to drag and reduced efficiency.

Airlines, of course, pay close attention to these details since the results are reflected in their net earnings. The general aviation pilot and aircraft owner can follow the same concept.

A maintenance program, trying to get the best fuel efficiency, will first need to look at the airplane rigging. Proper rigging will cut fuel waste, and increase fuel efficiency. This is especially true since GA aircraft in recent years have picked up considerable flight time. Almost any airplane with at least 1000 hours on it can lose a few knots in airspeed due to out-of-specs rigging.

Checking an airplanes rigging includes looking at anything that sticks out into the airstream: cowl flaps, wing flaps, landing gear doors, emergency exits, baggage doors and cabin entrance doors. They all have specifications for alignment, and should be checked at regular intervals and adjusted as required. Any item not aligned will cause additional drag. If any of the exterior surfaces are mis-rigged, they may require compensating flight control changes, which will further increase drag.

Another important rigging item is in providing accurate trim adjustments, by checking the trim tabs against the cockpit trim position indicators.

The accuracy of cockpit instruments also needs to be carefully checked. When trying to maximize efficiency, its very important that the information presented on the cockpit instruments is accurate. Trying to achieve a careful cruise control can come apart if the speed instruments arent accurate. While instruments are being checked, the groundspeed readouts from DME, GPS or Loran should be included, since in-flight decisions are often made on the basis of their information. Also, flight planning and power setting errors can develop if the outside air temperature indicators are in error.

The airplane can be constantly out of trim if the slip indicators are in error-the rigging instructions in many maintenance manuals start by ensuring the turn-and-slip indicator is plumb with the airframe.

Another area important to reducing drag is the airplanes exterior surface, whether metal, fabric or composite: To minimize drag, the airframe should conform to the original design contours. It doesnt take much-a couple of hard landings, perhaps, depending on the airplane-for things like the wing-to-fuselage mating to get out of alignment. Small nicks and dents on the leading edges of the wings, the nose and cockpit area, and the engine cowlings will disturb the airflow, adding drag.

Most airplanes have too many antennas. There are the original antennas and the add-ons, and then improved avionics are added. There are also different varieties of these antennas. Some are low-drag, and others produce a greater amount. Replacing or removing excess or inefficient antennas can decrease drag significantly. Then the remaining antennas need to be checked for proper alignment and sealing to the fuselage or tail surface. They should be located in areas of low pressure on the fuselage. Each airframe type has good and bad (i.e., low-pressure and high-pressure) areas where antennas can be mounted. Consult with your type club on where optimal antenna-mounting locations are and make sure your avionics shop knows what to do.

Other drag producers are door stops, fasteners on access panels, assist handles and temperature probes in high-pressure locations. All of these produce drag. If they are eliminated, adjusted or relocated, youll see the airplanes performance increase.

Washing and waxing the airplane can reduce drag. Dirt on wings creates almost the same effect as frost. It reduces the kinetic energy of the boundary layer, increases drag, and in some cases, increases the airplanes stall speed.

Reducing weight means understanding that every added pound of weight requires an additional pound of lift. Induced drag is generated right along with lift. There are immediate and direct benefits associated with weight reduction.

A good way to start reducing weight is to identify all of the items that are tucked away in the cabin and are no longer necessary. Are there things like this on board? Some examples might include polishing wax, tools, a spare case of oil, tie-down gear and survival equipment. Do you need this stuff for every flight you make? Surely there is some ground-based storage space where these items can be stored until theyre really needed.

When considering airframe upgrades, also think about what weight might be saved, or removed. The task of removing an old antenna, for example, isnt done unless the associated cabling, avionics and mounting racks are eliminated, also.

How can we improve engine operation? One of the major ways is to consider how an engine is operated and the preventive maintenance applied: How can we best operate the engine to achieve improved reliability and efficiency? Many of the answers are close by in the Pilots Operating Handbook.

Most owner/pilots understanding of how aircraft engines are designed is pretty thin. But thats not good enough. If a pilot intends to get maximum performance, reliability and longevity from a high-performance aircraft engine, he will need to know more than the bare minimum about how the engine is put together.

To help the pilot understand there is the engine manufacturers handbook, and the instructions from the airframe and engine manufacturer. Sit down and read the overhaul shop manual also. Its well-written, and easy to understand. If there are things that you dont understand, check with your A&P.

Go over the sections about the crankcase, crankshaft, dampers, connecting rods, pistons, piston rings, camshaft, tappets, valves, valve guides and turbochargers. These are areas where trouble develops, and you should, (as owner/pilot), know what their functions are.

Piston engine airplane operators need to have a qualified A&P mechanic check spark plugs, magnetos and fuel injection on a regular basis. Some of this a private pilot can do as preventive maintenance, but you still need some training on how to do it and what to look for. Getting that training by asking your A&P for some of his time is money well-spent.

Especially if you are flying a fuel-injected engine capable of operating lean-of-peak EGT, investing in some additional training to fully understand the leaning process also is money well-spent. Programs like the Advanced Pilot Seminar (www.advancedpilot.com) are excellent resources.

To get the best airplane performance, use climb and cruise profiles. Because they represent most of the fuel consumed, the climb and cruise segments of a flight have the largest potential for operating fuel conservation.

Before selecting a climb profile, the cruise altitude needs to be selected. The best calm-air climb for piston-engined airplanes-considering engine cooling, forward visibility and passenger comfort-uses the maximum rate-of-climb for the available power. The sooner cruise altitude is reached, the sooner power can be reduced, draggy cowl flaps closed and mixture leaned to best economy.

For descent, the common practice (aside from ATC instructions) is to begin the letdown at some distance out, converting altitude into increased groundspeed at a reduced power setting.

A more fuel-efficient procedure is to maintain cruise altitude until closer to the destination, then start a descent. The airspeed (and trim!) in the descent is the same as during the cruise segment. Maintain that airspeed and the desired descent rate by reducing power as required. Maintaining cruise speed in the descent is the most efficient, since an increase in speed will cause a heavy drag penalty.

Finally, how will you know whether any of your efforts bear fruit? How will you know what works well on your airplane, whether its cost-effective and how to measure its effects? Accurate record-keeping, thats how.

Once comprehensive records are kept on an airplanes performance there is a body of information to use in planning. Its then possible to know how much fuel is being wasted or saved by engine operation changes, or by new procedures.

Accurate record-keeping should include:

Flight time, power settings and refueling records, kept and analyzed for each flight.

Conservative fuel consumption records-figure time from start-up to shut-down.

Tracking maintenance costs, especially those related to improving efficiency.

Of course, were required to maintain complete logbooks on the airplane, but nothing prevents us from exceeding those requirements. Setting up a spreadsheet is the way to go. Even an adding machine has its value.

As aircraft operation gets more and more expensive, spend some time and effort to minimize the cost instead of spending more and more money. Done correctly, you can fly more often.