Cheap Performance: Tune It, Rig It, Fly It Right

Speed and efficiency. We always want more of it, and there are plenty of aftermarket speed mods that promise to tack on a few more knots here and there, while saving fuel. But many owners overlook the easy things that can boost performance and when it comes down to it, proper maintenance—overall—could be one of the best speed and efficiency mods you can make to an airplane that just doesn’t seem to be making book speeds or at least performing the way it did when it was new. Start with how you operate the engine using the lever with a red handle.

The Mixture—Work It

Obviously, how you use the mixture control dramatically influences fuel burn and how the engine starts and runs while you are still on the ground. A good habit, especially with some high-output Continental and Lycoming engines, is to lean the engine aggressively to the edge of roughness while at idle power but of course always do the run-up at full rich, but then bring it back to maximum lean settings. You generally won’t hurt the engine, and you will have the extra benefit of reducing spark plug fouling—something that also wastes gas and time. It’s easy to foul the plugs with extended ground running, and some engines are more prone than others. I always wondered why some pilots would sit for long periods in the run-up area (after long periods sitting in the tiedown) waiting for takeoff clearance with the mixture at full rich and the power back at idle, only to abort the run because there was a fouled plug. In some cases on stubborn engines, it could mean a visit to the shop to pull the plug(s) for cleaning. And even if the plugs don’t foul (and you miss the mixture on the before-takeoff checklist), don’t worry about forgetting to move the mixture to rich for takeoff—the engine will let you know about it when you put the power in.

Additionally, lean at any cruise altitude at 75% power or less simply because it saves fuel. Many pilots are taught early on to lean at 5,000 feet, or 3,000 feet, or, oddly, to not lean at all. Sure, not leaning lends to simplicity, but it certainly won’t work with all engines. It’s a win-win because of performance gains, and it saves fuel at virtually any cruise altitude and certainly at anything above a few thousand feet. Consider operating at 5% reduced power from usual book power settings because in general, the speed penalty is negligible, but the fuel savings are dramatic by comparison. Take it one step further and experiment with different power settings (always follow the POH and flight manual supplements) to find the best settings that result in improved fuel use and speed efficiency. Typically, the higher manifold pressure/lower corresponding rpm settings are considered to be a little more efficient than high rpm and low manifold pressures.

Power Settings, Altitudes

A longtime Beech Bonanza owner makes a good point that flying at higher power settings makes more heat, and climbing at shallower rates gives you more speed over the ground and cooler cylinders and it usually offers a more shallow deck angle for better outside visibility. Also, flying at higher altitudes generally means cooler temps outside and makes the aircraft more efficient. “When I fly at 11,500 feet, the OAT is right around freezing (no visible moisture) and I fly at full throttle with good leaning techniques and still get 59 to 60 percent power. Now the engine is loafing along and the cylinder heads run between 300 and 350 degrees F,” said Larry Weitzman of the Continental engine in his Bonanza. 

And of course there’s lean-of-peak operations, and with a graphic engine monitor and GAMIjectors it makes for a smoother-running engine, which could help engine longevity. “You can fly lean of peak, especially at 65 percent power or less at altitude, and that makes for less fuel flow and less heat. You fly a little slower by half a dozen knots or so, but overall MPG goes up a bit,” Weitzman said.

Think about vibration, too. As one example that comes to mind, some engines seem much more happy at 2400 rpm than 2100 rpm and a high manifold pressure to achieve the same power setting. Stick with the most vibration-free setting if the difference is noticeable enough to be felt.

Of course, maintain the engine the right way, and this includes making sure the ignition and air induction systems are in top shape while also making sure the fuel delivery system is properly tuned. You’ll be surprised at how many engines are simply out of tune.

Make It Fly True

As we’ve covered in previous reports, a sure way to lose speed is to fly with control surfaces (and landing gear doors and cowl flaps) that are out of rig. “I picked up almost 15 mph cruise speed just getting all the flight controls and landing gear doors properly rigged. Correcting the engine cooling baffles and seals netted another 5 mph cruise speed and dropped cylinder head temperatures 50 degrees F,” Steve Zeller told us.

It’s something that should be checked during regular inspections, but make sure the wings, tail, and controls meet the maintenance manual’s specs for incidence, symmetry, control balance, and cable tension. It doesn’t take much to put a plane out of rig, and if there is a small tab that is bent significantly on a control surface for control harmony, it can cost speed and extra fuel burn. It’s a domino effect because improperly rigged control surfaces can alter the plane’s handling and can also prematurely wear hardworking components like autopilot servo motors.

Even parts you might not consider can cause a speed penalty because of induced drag. This includes cracked wingtips or tail caps or other fiberglass external components. Antennas cause drag, too, so when replacing comm antennas, as one example, try to stick with ones that are designed (and installed in the same configuration) as the ones that were the model’s OEM standard. There’s a reason why antennas have speed ratings. Ones that are rated for speeds under the airframe’s actual speed can damage the aircraft’s skin—or even come off the aircraft. I recall a Piper Arrow that kept shedding thin ELT whip antennas because they were installed in a location prone to disruptive harmonics. And whatever you do, make sure the shop doesn’t take the easy way out and leave unused antennas on the airframe. Remove any antenna that doesn’t have a purpose. There are still plenty of ADF sense antennas (that’s the long wire that runs along the top of some aircraft) left in place that should have been removed a long time ago.

Instrument Error

This is a real tail chase. It’s not so much a problem with newer solid state EFIS, but mechanical airspeed indicators can develop error over time and unless a shop with the right test equipment picks up on it, you might never know the difference. Some airspeed indicators can also be a source of pitot error because of case leakage. One way to tell if an airspeed indicator has error might be during landing or even on takeoff. Pay close attention—do the airspeed readings match the power settings?

Even worse is incorrect tachometer readings, which can lead to excess rpm settings or inadvertent operation in restricted rpm bands. Both items can cause premature engine wear. While it’s a problem easily solved by digital engine monitor upgrades, it’s worth sending mechanical tachometers to a qualified instrument shop to test for accuracy.

Moreover, the standard per AC 43.13-1B, Chapter 8 for tachometer accuracy is plus or minus 2%. Those that are out of spec require replacement, and my experience is that tachometers in older airplanes are often out of spec. At a minimum they should be checked at each annual by a portable digital tach checker. A staple in my toolbox is the TrueTach II optical tachometer, which is accurate to within 1 RPM, runs on a 9-volt battery, works from inside the cabin (point it at the spinning prop) for up to five propeller blades, and has an operating range from 240 up to 7,000 RPM. Sporty’s sells it for $249.

Slicken’ It Up

I’ll go out on a limb and suggest that keeping the paint finish freshly polished/waxed might add a knot or two. I’ve heard from several owners who invested big in ceramic paint coatings on new paint finishes who swear the aircraft picked up a slight increase in cruise speed. We’ll look at ceramic coatings—and top budget speed mods—in an upcoming report in The Smart Aviator. In the meantime, keep the engine well tuned, the airframe well rigged, and experiment with mixture and power settings to find the sweet spot for best speed and efficiency. If anything has worked well for you, we wanna hear about it.