AOPA's 2001 Bonanza Sweepstakes - Turbonormalizing vs. Turbocharging

November 11, 2009

Turbonormalizing vs. Turbocharging

AOPA's 2000 Bonanza Sweepstakes project airplane will incorporate a turbonormalizing system. There are many advantages to turbonormalizing, which is different from turbocharging.

Turbonormalizing and turbocharging are accomplished by mechanically compressing the ambient air before it's routed to an engine and used in the normal intake, compression, combustion, and exhaust cycle of operation. Turbocharging systems utilize the same external components as turbonormalizing systems.

The difference between the two is that the compressed air delivered by the turbonormalizing system is limited to the amount of pressure that would be obtained at sea level, or only slightly above (an additional one or two inches), while the turbocharging system increases the manifold pressure to a boosted value above normal sea level pressures (typically an additional six or seven inches, though 10 inches are possible in general aviation airplanes).

For instance, on the turbonormalized Cessna turbo retractable 182 (TR182), the manifold pressure is limited to 31 inches. Because of this limitation, engine manufacturers and the FAA are comfortable with turbonormalizing installations.

Turbocharging forces additional air volume and pressure, over and above what's normal in nature, to be pushed into the engine. This creates more power, but also creates more heat and opens some doors for rapid engine wear because of either uninformed or negligent engine operation by the pilot.

For instance, the takeoff manifold pressure on a mid-1970s Cessna turbocharged 210 (T210) is 37.5 inches. This boosting increases the power output of the engine. In the T210, the takeoff power is 310 horsepower, where without the turbocharging, the same displacement Continental engine in a normally aspirated Cessna 210 only makes 285 hp. Since the manufacturer has boosted the output of the same-size engine, some changes have to be made to the mechanical structure of the engine, such as the installation of lower compression pistons, and stronger cylinders. These changes don't have to be made with turbonormalized engines.

Why turbonormalize?

As all pilots are taught, the atmosphere is piled up on the earth's surface. The weight of the atmosphere is determined by a barometer, or in airplanes, by the altimeter and the engine manifold pressure gauge. As an airplane ascends during a climb there is less atmosphere above it so the weight is less. This is important because it's the weight of the atmosphere that determines how much ambient air is pushed into the engine during the intake stroke.

This means that a normally aspirated airplane loses power as it climbs - for instance, a Cessna 182 engine (a Continental O-470) can no longer deliver 65-percent power above approximately 7,000 feet msl.

Since the Tornado Alley Turbo Inc. turbonormalizing equipment that will be added to an Superior Air Parts Millennium IO-550B engine on the AOPA Sweepstakes Bonanza has the ability to compress the ambient air that is delivered to the engine during the intake stroke, there won't be any engine power drop-off until the airplane is at 20,000 feet msl. The turbonormalizing equipment tricks the engine into thinking it's at sea level, where it can deliver the most power.


There are a number of advantages. The ability to climb strongly at any altitude between sea level and 20,000 feet gives the pilot amazing latitude for operation. First, he can safely operate out West, where there are some tall mountains. For instance, .the MEA (minimum en route altitude) between Portland, Oregon, and Yakima, Washington, is 14,500 feet. A normally aspirated airplane would not have much, if any, climb ability at that altitude - the turbonormalized (and the turbocharged) airplane could easily climb up there, and could climb smartly over most weather. The pilot also can comfortably operate at altitudes that are too high for normally aspirated airplanes and too low for economical operation of turbine airplanes - generally this is the 10,000- to 14,000-msl band. This means less conflicting traffic.

The ability to fly at these altitudes also means the pilot can almost always find a smooth ride. This makes the airplane more comfortable for squeamish passengers who interpret every turbulent bump as a nudge from the devil.

The ability to climb strongly means that, should in-flight icing be encountered, the pilot can usually climb up out of the icing band of weather. Studies show that the icing band of clouds is generally approximately 3,000 feet thick. Normally aspirated airplanes that encounter a quick buildup of ice are often faced with having to descend to avoid the icing layer, which limits safety options.

Finally, the ability to deliver sea-level power up where the atmosphere is thin means that the engine can deliver a lot of thrust in a flight regime where the drag on the airplane is less. Thinner atmosphere = less drag. Less drag with the same power translates into higher true airspeeds. Tornado Alley Turbo advertises TAS of more than 200 knots at 18,000 feet. That's fast.

System components

The Tornado Alley Turbo Inc. Whirlwind II turbonormalizing system replaces the normal exhaust system and part of the induction system. The parts are:

  • Exhaust system - this component has a couple of tasks. First it safely contains the high temperature and pressure exhaust gases from the six-cylinder engine and second, it delivers the amount of exhaust pressure to the turbocharger that is necessary to maintain the manifold pressure the pilot has selected.
    • Wastegate and wastegate controller. At low altitudes the atmosphere is dense compared to the atmosphere at 20,000 feet msl. Since the system is designed to have enough air compressing and pumping capacity to deliver 30 inches (approximate sea level atmospheric pressure) at 20,000 feet, it will have way too much compressing and pumping capability at lower altitudes. To compensate for this, the system is designed to control the amount of exhaust volume and pressure that is routed to the turbocharger. The excess volume and pressure is routed overboard. The mechanism that does this is the wastegate. At 20,000 feet, the wastegate is usually closed all the way and all the exhaust pressure and volume is routed through the turbocharger. At lower altitudes, when all the exhaust pressure and volume are not needed to maintain the desired manifold pressure, the wastegate is partially open. This opens up an alternate path for the exhaust gases to bypass the turbocharger.
      • The wastegate controller is a device that controls the position of the wastegate by controlling oil pressure in a piston at the wastegate. The controller modulates the wastegate position as necessary to maintain the manifold pressure that the pilot has selected.
  • Turbocharger - the turbocharger is compact device that has two sides � the hot side and the cold side. The hot side is the side that the exhaust gases contact. When the gases impinge on the turbine wheel, it spins. The cold side, or compressor side, is connected to the hot side, or turbine side, by a common shaft. As the hot side is driven by the exhaust gases, the cold side rotates and compresses air that is then delivered to the intake of the engine.
  • Pop-off valve - this valve is installed between the turbocharger compressor and the engine intake. It opens if the pressure from the turbocharger goes above a preset value. This protects the engine from overboosting, which can damage it. The most common cause of overboosting is a stuck wastegate or a malfunctioning wastegate controller.
  • Intercooler - the intercooler is an air-to-air radiator. Ambient (ram) air is routed through this radiator to cool the compressed air from the compressor side of the turbocharger. During compression the air temperature is elevated, sometimes by as much as 260 degrees Fahrenheit. Keeping the air as dense as possible (in other words, cooler) increases the efficiency of the engine, and lowers engine operating and cylinder head temperatures.

The Tornado Alley Turbo turbonormalizng system was originally developed by FliteCraft but is now owned by the same company that owns the GAMIjectors ( Tornado Alley ( has made a number of improvements to the system, especially to the intercooler. To read a report from AOPA Pilot about the FliteCraft system, click here.