You should check-out the Cirrus SR22TN because it’s a “Smart Turbocharged Design.” In 2006, two industry leaders Cirrus Aircraft and Tornado Alley Turbo, Inc. teamed up to create the smartest turbo design in general aviation history. In fact, “Smart Turbo” became the brand moniker for the Cirrus SR22TN Tornado Alley Turbo-Normalized factory installed STC.
The Cirrus SR22TN Tornado Alley Turbo-Normalized installation includes dual-intercoolers, dual-turbochargers, dual-wastegates with absolute pressure control and a GAMI fuel injector system on the Teledyne Continental Motor IO-550-N to deliver 310 horsepower performance all the way up to 25,000 feet MSL.
Reason 1 – Smart Turbo Design
- Absolute Pressure Control
- GAMI Fuel Injector System
- Integrated propeller and throttle linkage
Intercoolers are not always found on previous generation turbochargers with other manufacturers. Tornado Alley includes computer optimized dual-intercoolers on either side of the upper-deck. The intercoolers lower air temperature and reduce induction air pressure from the turbochargers.
Overboost protection is designed into the system in the form of an overboost poppet valve which will open if manifold pressure exceeds 34 psi. Before that level of operating pressure occurs, Cirrus Perspective Crew Alert System (CAS) provides audible and visual alerts. Visual caution and warning alerts appear on both the PFD and MFD.
A large air intake is located in the front right cowl and is covered by an air filter. Induction air enters the cowling and passes through the air filter to the lower-deck where the airflow is then divided into the right and left turbocharger compressors.
Dual-turbochargers are located underneath either side of the engine in the lower deck. The turbocharger uses accelerated exhaust gases to spin a compressor to raise the pressure of induction air sent to the intercoolers.
Each Tornado Alley turbocharger has stainless steel hot section heat shields which protect the engine and other surrounding components. Not always found in competing systems, these strategically located heat shields, and several more, help the Tornado Alley Turbo system run cooler.
The turbochargers are lubricated via the engine oil system, and are capable of +100,000 RPM. The Tornado Alley design allows for lower Turbo Inlet Temperatures (TIT), which are typically between 1580 – 1630 F. Maximum TIT is 1750 degrees F.
Normal cylinder head temperatures in climb and cruise are below 380 degrees F.
Dual wastegates are not always found on competing products. Some manufacturers use one wastegate which requires a high temperature cross-over exhaust tube around the lower deck behind the engine, i.e. Continental all factory turbocharged engine used on the Cirrus SR22T and Corvalis TTx . This configuration adds heats to the engine and the fuel pump raising vapor lock problems.
Each Tornado Alley turbocharger has a dedicated interconnected wastegate, which avoids the use of a high temperature exhaust cross-over tube. The wastegate controls the amount of exhaust allowed to flow through the turbocharger. Pressure produced by the turbocharger is a function of wastegate exhaust flow.
A spring holds the wastegate open, which is the default position. An opened wastegate allows exhaust to bypass the turbo. A closed wastegate sends more exhaust through the turbocharger. The Absolute Pressure Control system closes the wastegate to send more exhaust air through the turbo to compress induction air going to the intercoolers.
Absolute Pressure Control
Pressure from the upper-deck is plumbed into the Absolute Pressure Control unit (APC). An aneroid inside the APC will expand and contract based on pressure in the upper-deck. Movement of the aneroid controls oil pressure to the wastegate.
When the upper-deck pressure drops the aneroid expands allowing oil pressure to close the wastegate which sends more exhaust through the turbo.
Tornado Alley Turbo uses “lifetime” blue high-temperature fire-proof silicon fuel and oil lines in the engine compartment, which cost more initially but last over the ownership life of the engine and airframe. The smaller cleaner form factor improve surrounding air flow and allow easier access to components during maintenance.
GAMI fuel injector system
The turbo system would be incomplete without the GAMI fuel injector system. There is a fundamental inherent imbalance with the standard factory engine design and fuel system which impedes efficient lean of peak operation. For example, the fuel distribution manifold (fuel spider) location naturally requires some lines to be longer than others to reach all cylinders.
The GAMI system corrects the imbalance by providing each cylinder position a tuned GAMI fuel injector nozzle to deliver closely matched fuel/air ratios to all cylinders. Pressure from the upper deck is plumbed to each injector to prevent any back flow of fuel through the injector at high altitude.
The complete Tornado Alley Turbo-Normalized installation with GAMI injectors allows the TCM IO-550-N motor to efficiently run lean of peak at all altitudes.
The GAMIjector System is not on normally aspirated SR22 series from the factory, but some owners may have aftermarket installations.
Integrated propeller and throttle linkage
The original integrated propeller and throttle linkage in the Cirrus SR22 is an elegant design that combines exceptional functionality and simple ease of use. The Cirrus SR22TN Tornado Alley Turbo retains this feature which includes variable RPM control.
It’s my understanding that the variable RPM control feature was eliminated beginning with the 2010 Cirrus SR22T Continental all factory turbo installation. A negative of that change is during descents from flight levels, with the propeller fixed at 2500 RPM, the prop drives the motor. Having the prop drive the engine during descents and approaches is harder on the engine.
Next week, “how the Smart Turbo Design optimizes the TCM IO-550-N motor for performance efficiency.”
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