A plane becomes a “jet” when it’s powered by a jet engine instead of a traditional piston engine spinning a propeller. The core difference is how thrust is created: a jet engine pulls in air, compresses it, mixes it with fuel, ignites the mixture, and blasts hot exhaust gases out the back. That rearward blast pushes the aircraft forward. A piston-powered plane, by contrast, uses an engine mechanically similar to a car’s to turn a propeller, which pulls the aircraft through the air.
How a Jet Engine Actually Works
Every jet engine, also called a gas turbine, follows the same four-step cycle: intake, compression, combustion, and exhaust. Air enters through the front of the engine. A compressor, made of many spinning blades attached to a shaft, squeezes that air to high pressure. The compressed air is then sprayed with fuel and ignited by an electric spark. The burning gases expand rapidly and shoot out through a nozzle at the rear of the engine.
As those hot gases blast backward, the engine and aircraft are thrust forward. This is a straightforward application of Newton’s third law: for every action, there’s an equal and opposite reaction. On its way out, the exhaust passes through a turbine, which is a set of blades connected to the same shaft as the compressor. The escaping gas spins the turbine, which in turn keeps the compressor spinning, creating a self-sustaining cycle once the engine is running.
The key components, as described by NASA, are the fan, compressor, combustor, turbine, mixer, and nozzle. The simplest jet engine design, the ramjet, actually has no moving parts at all. It relies entirely on the aircraft’s forward speed to ram air into the engine for compression. But most jet engines you’ll encounter on commercial or private aircraft are far more complex.
Piston Engines vs. Jet Engines
From the Wright Brothers’ first flight in 1903 through the late 1930s, every powered aircraft used a gasoline-burning piston engine connected to a propeller. These engines work like a car engine: pistons move up and down inside cylinders, burning fuel in controlled explosions that turn a crankshaft, which spins the propeller. They run on avgas (aviation gasoline), a specialized high-octane fuel that still contains small amounts of lead to prevent engine-damaging detonation in the high-compression cylinders.
Jet engines burn a completely different fuel, one similar to kerosene, with no lead additive. The combustion process is also fundamentally different. A piston engine creates thousands of individual explosions per minute inside sealed cylinders. A jet engine maintains a continuous burn in its combustion chamber, producing a steady stream of thrust rather than a series of power pulses.
This difference in design gives jets a major advantage at high speeds and altitudes. Propellers become less effective as an aircraft approaches the speed of sound because of aerodynamic limitations on the spinning blades. Jet exhaust doesn’t have this problem, which is why jets cruise between 31,000 and 42,000 feet at speeds well above 400 knots, while propeller-driven planes top out around 25,000 to 30,000 feet at much lower speeds.
Three Types of Jet Engine
Not all jet engines look or behave the same. The three main types you’ll see on aircraft today are turbojets, turbofans, and turboprops, and they differ in how they balance raw speed against fuel efficiency.
Turbojets
The turbojet is the original jet engine design. All of the thrust comes from hot exhaust gases shooting out the back. This makes turbojets excellent for high-speed flight, but they burn fuel at a ferocious rate and are extremely loud. The world’s first turbojet-powered aircraft, the Heinkel He 178, flew on August 27, 1939, built through a collaboration between Ernst Heinkel and engineer Hans von Ohain. Today, pure turbojets are mostly limited to military applications where speed matters more than fuel economy.
Turbofans
The turbofan is essentially an evolved turbojet with a much larger fan at the front. This oversized fan pushes a large volume of air around the outside of the engine core, bypassing the combustion process entirely. The ratio of this bypassed air to the air flowing through the core is called the bypass ratio. Modern large turbofans, like the General Electric GE90, have bypass ratios as high as 10:1, meaning ten parts of air go around the engine for every one part that passes through the core.
Higher bypass ratios translate to better fuel efficiency and lower noise, which is why virtually every commercial airliner today uses turbofan engines. At lower flight speeds, most of the thrust actually comes from the fan rather than the jet exhaust. A turbofan with a bypass ratio of zero would technically be a turbojet, which illustrates how the two designs sit on a spectrum. Turbofans are best suited for flight speeds between roughly 250 and 620 mph, covering everything from regional flights to long-haul international routes.
Turboprops
A turboprop uses a jet engine core to spin a traditional propeller through a gearbox. The combustion process is identical to a turbojet, but instead of relying on exhaust thrust, the turbine extracts as much energy as possible from the hot gases to drive the propeller. This requires more turbine blade stages than a turbojet and adds the weight of reduction gears to slow the turbine’s rotation to a speed the propeller can handle.
Turboprops are most efficient between 250 and 400 mph at altitudes of 18,000 to 30,000 feet, according to the FAA. They’re commonly found on regional airliners and utility aircraft. A turboprop like the Dash 8-Q400 carries up to 90 passengers at about 360 knots and a ceiling of 25,000 feet. A similarly sized jet, the Embraer E175, carries the same passenger count at 481 knots and cruises at 41,000 feet.
Why Jets Fly Higher and Faster
The speed gap between jets and propeller aircraft is significant. Even the latest turboprop designs max out around 290 to 360 knots in cruise. A small jet like the HondaJet hits 422 knots, and larger business jets like the Bombardier Global 5500 cruise at 600 knots. Every jet in the comparison outpaces every turboprop by at least 100 knots.
Altitude follows the same pattern. Turboprops generally cruise between 25,000 and 35,000 feet. Jets routinely operate between 31,000 and 41,000 feet. Flying higher means thinner air, which means less drag, which means better fuel efficiency at speed. Jet engines handle thin air well because they compress incoming air mechanically before combustion. Piston engines struggle at extreme altitudes because they depend on ambient air pressure to fill their cylinders, though turbocharging can partially compensate.
Fuel, Maintenance, and Operating Costs
Piston aircraft are cheaper to buy and operate at small scales. They require more frequent oil changes and engine tune-ups, but the parts and labor are relatively affordable. Jet engines have fewer moving parts in some respects and run more smoothly, but they demand specialized maintenance and eventual full engine replacements every few thousand flight hours. The fuel itself also differs in cost: jet fuel (kerosene-type) is generally cheaper per gallon than avgas, but jets burn far more of it per hour.
The practical tradeoff is straightforward. Piston aircraft make sense for short trips, flight training, and personal aviation. Jets make sense when you need to cover long distances quickly, fly above weather, or carry large numbers of passengers. The engine type determines not just the speed of the aircraft but its entire operating profile, from the altitude it flies to the runway length it needs to the fuel bill at the end of the day.