The jet era of aviation is a time now that has certainly revolutionized the way we travel. However, despite what others may say about propeller driven aircraft being outdated and not as efficient, there is still a very large demand for both jets and propeller driven aircraft. Power-driven airplanes have been thrusted by propellers since the first aircraft took to the air in 1903. Since then, science has done a complete make over on propeller-driven aircraft to make them extremely cost efficient, and even fast! There are five main types of engines that are used today that employ the use of jet engines and propeller engines; Each of which have modern designs in aircraft that are made to be extremely efficient. These types of engines include: internal combustion propeller engines, turboprop engines, turbo shaft engines, turbojet engines, and turbofan engines.
The first of these engines is the internal combustion engine. This was the very first type of engine to be used in an aircraft, and is still employed on many aircraft today. It is mostly used in private aviation, flight training, and small charter operations. These airplanes are usually not pressurized because they fly at a fairly low altitude, and therefore there is less technology that has to be invested in making a strong pressure vessel. These airplanes do not cost a lot of money to operate, and they are perfect for people who just want to go out on a nice Sunday afternoon for a scenic flight. Before jet engines were invented, internal combustion propeller engines were used in large airliners, but the problem nowadays in using these aircraft for large commercial operations is that they are not nearly as fast, the engines are not as reliable, they do not produce as much power, and therefore can not carry large amounts of payload long distances. However, in the flight training industry, they are perfect for training new pilots. They are good for teaching people how to fly because things happen slower in the airplane, and the engine is a lot easier to manage.
Secondly, there are turboprop engines. Turboprop engines are essentially a jet engine connected to a propeller through a reduction gearbox. Turboprop airplanes are very useful for companies that need more power, longer range, and efficiency in transporting moderate amounts of payload over long distances without having quite the same amount of fuel consumption as a jet engine.
Thirdly, there is a turbo shaft engine, which is used on helicopters. It works identically the same as a turboprop engine, except obviously that the reduction gearing has to shift the power vertically to spin the helicopter's rotor. The major advantages to having a turbo shaft engine in a helicopter instead of a conventional internal combustion engine is simply because the helicopter will be able to lift a lot more, travel a greater distance with a heavy load, and be able to operate at higher altitudes.
The last of the jet engine family are the turbofan and the turbojet engines. The difference between the turbofan and the turbojet is that a turbofan has a very large fan blade at the front of the engine that not only supplies air for the combustion in the jet engine, but also acts a propeller to assist with the efficiency of the engine, and to keep fuel costs lower. The turbojet engine is a higher performance engine, because there is less mass in the moving parts, but they are much louder, they burn a lot more fuel, but they produce a lot more thrust. Turbofans are used in the major airline industry simply because of their efficiency, and the fact that they operate very quietly compared to a turbojet. You may see turbojets used on older airliners, such as the Boeing 707 and the older 737s, but mostly in the modern aviation industry, turbojets are used in fighter aircraft that require such performance.
Having said all of this, it really depends what the objective is in using the aircraft. Not all aircraft require the power of a jet engine to do the job. Jet engines are very expensive to operate and maintain. Many companies choose to go with alternatives to a turbofan or turbojet such a turboprop that so they can get much higher efficiency for transportation than an internal combustion engine without the cost of operation associated with a turbojet or turbofan. Likewise, why would a flight school operate anything more powerful than a single engine internal combustion propeller-driven airplane when there are only two people in it? Propeller airplanes are certainly going to be around for much loner as they are cheap to run, and excellent for flight training. Something also that wasn't mentioned lot before in this article is the technology involved with creating an aircraft cabin that can withstand the pressures of flying at the altitudes that jet aircraft fly at. It gets to be a very expensive operation if you do not have the operational need for it!