By Angel MedFlight Contributor
Angel MedFlight’s Learjet 60’s are powered by two Pratt & Whitney turbofan engines. Two turbofan engines made by Garrett power our Learjet 35’s. And our newly acquired Cessna Citation X cruises near the speed of sound with the help of two Rolls-Royce turbofan engines. The common denominator here is turbofan. You’ve seen the word in print before, but if you’re not working in aviation you may not know exactly how a turbofan engine works and why so many aircraft today are powered by them.
To understand the principle of a turbofan engine, one must first comprehend how a traditional jet engine works. First, air is sucked into a chamber at the front of the engine. It is then compressed by an impeller with many blades. The compressed air then gets sprayed with fuel and the mixture is ignited. Those burning gases expand in a combustion chamber and then blast through the nozzle at the back of the engine. This is where Sir Isaac Newton’s third law of physics comes into play: for every action there is an equal and opposite reaction. When the jets of gas are shot backward, the aircraft is thrust forward.
The turbofan engine works along the same principles of a jet engine but incorporates a large fan in a duct, toward the front of the engine which sucks in air. Where the turbofan engine differs from the jet is most of the air flows outside of the core of the turbofan engine. Only some of the incoming air passes into the combustion chamber. Some of the thrust still comes from the exhaust jet, but the addition of the fan makes this engine much more fuel efficient and quieter.
Aviation West Charters Director of Maintenance Dwain Chase says the turbofan engine “takes air big and wide and compressed and turns it into a skinnier and focused air stream, like an iris.” There’s “cold” jet mixed with gas generator exhaust producing “hot” jet. The bypass system increases thrust and maximizes fuel efficiency. Chase says the turbofan provides more thrust than a standard jet engine because of the bypass ratio. “You’re almost getting a 3 to 1 advantage over just having the standard duct, the jet coming out the back.”
Chase says another big difference between the turbofan and the older jet engines is the turbofan’s smaller carbon footprint. “There’s more of a complete fuel burn and fewer emissions” with a turbofan jet. And, “by mixing so much fresh air and getting more power out of the same amount of jet fuel it’s almost like getting better gas mileage in your car.”
Angel MedFlight Worldwide Air Ambulance has an impressive fleet of jets that keep us on the cutting edge in the air ambulance industry, offering our patients the highest standard of safety and in-flight care.