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New Rotax 912Si Advanced in CTLS

March 8, 2012 – On Thursday, March 8, BRP-Powertrain introduced the evolution of the venerable Rotax 912S engine, the 912iS, in Gunskirchen, Austria, at a press event for international aircraft manufacturers and journalists. The “i” stands for electronic fuel injection, added to Rotax’s well-known 100-hp, four-cylinder workhorse, along with an automotive-style digital engine control unit (ECU).

The three-year development period included more than 10,000 hours on the test bench and 700 test hours in the air, BRP stated. The revamped engine is now in production and being delivered to OEMs with production slated to ramp up in May 2012.

BRP engineers modified just about everything on the old 912, and have incorporated technology enhancements such as a fuel injection system instead of the dual carburetors and digital ECU to the to ensure optimal fuel and air mixture at any altitude. The same aircraft now will feature much longer flight range, lower operating costs, and CO2 emission reduction. The new 912iS also has the same 2,000 hours TBO.

The biggest advantage of the new engine according to the manufacturer is lower fuel consumption – 21 percent less than the carbureted version. Pilots will also benefit from the wide use of the new engine management. Other advantages of the 912iS: no manual choke, no carburetor icing, and having to synchronize two carbs is no longer required.

Fuel injection is more precise, thanks to the ECU that constantly optimizes the air-to-fuel mixture resulting in better efficiency with lower pollution. Sensors monitor engine – airbox – vacuum, exhaust gas temperature, ambient air pressure, inlet air temperature, liquid coolant temperature, and throttle position. The engine self-adjusts for different atmospheric conditions and altitude.

Externally the 912iS has a new “green” look with green-painted cylinder head covers, and on the upper side of the cylinder heads, green plastic covers that hide the most evident difference: the metal fuel rails and double fuel injectors on each cylinder head. Even if the Rotax folks say that the “i” engine has a same size (actually they say it is a “bit” smaller), the area on top of the cylinders now looks bigger and a little bit taller than on the 912S. The upper-rear portion of the engine has a fancy, plastic, car-like airbox with a single throttle body and air filter. The engine block is now painted black, along with the rear engine end with the new generator.









A lot has changed under the hood. The engineers have modified cooling of the liquid-cooled heads that was needed for the implementation of the fuel injection system. The lower portion of the engine block features a deeper “V” form and the crankshaft has been modified, along with several other small details.

Unlike the proven Rotax 912S, the 912iS has a lot of electronics on board. There are three new boxes containing dual (electric) fuel pumps, the fuse box, and the ECU controller. Even omitting two carburetors, the engine dry weight increased almost 9 pounds (15 pounds if the twin fuel pumps and other equipment are included). That means 140 pounds total dry weight.

The electrical system underwent major changes compared to the carbureted engine. The electrical “powerplant” (generator) now delivers 430 watts of electric power and consists of two separate generator blocks that use the same single rotor. One is only dedicated to the ECU (16 amps) and the second is serving the aircraft electrical system with 30 amps/430 W. The generator is now the “wet” type, meaning it’s inside the engine immersed/cooled by the crankcase oil. The “i” engine uses the battery only for cranking the engine, which means battery loss in flight doesn’t affect the engine operation. The engine is, of course, fully redundant, having two independent and redundant ECUs that drive double injectors and double spark plugs for each cylinder.

Somewhat surprising to the international audience, performance remains unchanged. According to the data sheet, the 912iS still develops 100 hp at 5800 RPM. Unexpectedly, the maximum torque dropped from 94 foot pounds at 5100 RPM to 89 foot pounds at 5800 RPM. The overall engine dimensions remained largely the same, so manufacturers will not have problems with the installation in existing engine compartments.

BRP made no specific references to the price of the 912iS. On our pricing inquiry we got an answer that the new engine will be from 14 percent to 17 percent more expensive than the carbureted 912S. Unofficial estimates from some aircraft manufacturers said that the 912iS would add about $4,000.

Official BRP/Rotax fuel requirements for the 912iS are the same as for the normal 912S: min. MON 85 RON 95*min. AKI 91* (*leaded, unleaded, AVGAS 100LL or E10). BRP recommends using auto fuel up to 10 percent alcohol.