Aircraft rely on various types of engines to generate the power needed for flight. Technology has come a long way since the 1930s when only piston engines were available, and despite being available in many forms, piston engines are limited in their performance abilities. Therefore, the demand for high-performance aircraft gave birth to modern jet engines. This blog will explore the differences between two types of jet engines commonly used in aircraft today: the turbojet and the turboprop. Although both are jet engines, aircraft that rely on turbojets are considered jet aircraft while aircraft that rely on turboprops are considered propeller aircraft. Reasonably, the main distinguishing factor between the two engines is that a turboprop makes use of a propeller before the inlet leading into the engine, whereas turbojets lack this feature. Given the difference in their design, both jet engines offer their own advantages and drawbacks, those of which we will further explore below.
The turbojet was first introduced in 1930 by Sir Frank Whittle and relies on a turbine to generate power to drive the compressor. The turboprop is a more recent and modified version of the turbojet, and it relies on its turbine to drive both the compressor, as well as its propeller. Moreover, their design differences make turbojets the more efficient option for higher altitude flight, while turboprops are intended for use at lower altitudes; though, both models remain prevalent in the industry.
The function of a turbojet engine is to compress, expand, and release air at a high velocity, and its design consists of the most basic elements of any jet engine. When in operation, air enters the engine through an inlet without passing through a propeller, where it is then compressed in the cold section. Next, the compressed air enters the hot section where it is burned in the combustion chamber before passing through the turbine which expands the air passing through it. From here, it is then released through the exhaust nozzle, generating significant thrust.
However, if you take this same basic design and attach a large fan to the front, you will have a turboprop. They operate with a gearbox situated between the fan or propeller and the main engine’s inlet controls the fan’s rotary motion, meaning its speed is independent of the turbine’s speed. As a result, the movement of the propeller directly generates thrust, pushing air backwards to drive the vehicle. Meanwhile, the turbine and exhaust generates a small portion (about 10%) of the total thrust. In fact, a majority of the energy generated by the turbine is used to power the fan.
Due to these differences in design, turbojets function better than turboprops at higher altitudes. Since air at higher altitudes is cooler, it is more efficient to rely on combustion technology as cold air expands better. On the other hand, turboprop engines offer optimum fuel efficiency at altitudes below 25,000 feet, as their propellers work best when pushing denser air found at lower altitudes.
A second difference in function is each engine type’s optimal speed range. Turbojets are ideal for high-velocity flight because the faster air can enter the engine, the greater the amount of thrust can be generated. They are best suited for flights with speeds between 370 and 450 knots. Meanwhile, turboprops are ideal for speeds that are 20%-30% lower than those of turbojets, as propellers are known to lose efficiency at higher air speeds. Turboprops offer the advantage of high fuel efficiency during optimal conditions, as well as requiring less space for takeoff and landing on the runway. This is because turboprop engines can generate a great amount of thrust on the ground and the fact that these planes have lower landing speeds. A final difference to consider between the two jet engines is the conditions that each creates in the cabin. The fans on turboprops lead to loud noises and high vibrations that passengers may find disruptive.
Overall, turbojets are more costly to purchase and operate, but they offer safer flying conditions due to the turbojet’s propeller being unfit for certain weather conditions. Depending on your specific flying conditions, either option can be the better choice, so be sure to assess your needs prior to purchasing. When you are in the market for premium engine components and other aircraft parts, look no further than Purchasing Union. With an inventory of over 2 billion new, used, obsolete, and hard-to-find items in-stock and ready for purchase, we are your parts procurement partner. Fill out a Request for Quote form today to receive a personalized quotation on any part within 15 minutes. For further questions, our team of experts is available around-the-clock to answer your calls and emails, 24/7x365!
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