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An aircraft
gets its forward and reverse motion through the thrust generated by it’s
engines. It’s interesting to see how this thrust is changed into motion in
aircrafts and spacecrafts. Like any other vehicle, the aircraft too needs a
mechanism to convert the power produced by the engine into motion. An aircraft
need motion or generated speed, to produce lift. So here are some of the
different mechanisms by which an aircraft and spacecraft get it’s forward
motion.
1. By the thrust of a rotating airscrew or propeller
Both the
piston engine and gas turbine engine can have propellers mounted in front of
the engine. A gas turbine engine with propellers in the front are known as
turboprop engine. A turboprop engine require shorter runway for takeoff and
landing as compared to other gas turbine engine due to thrust developed by both
the exhaust as well as the propellers. These propellers are like small airfoils
that generate thrust. When the propellers are configured to generate forward
thrust, air pressure is more in the aft of the propeller as compared to the
forward of the propeller thus moving the aircraft forward. And vice versa when
the propellers are configured to generate reverse thrust. So the question is
how the pressure difference is created in the propeller. As said earlier the
propellers are small airfoils, so when the air passes through it, the curved part
of the airfoil experience less static pressure and the flat part of the airfoil
experience more static pressure. We know as per Bernoulli’s theorem the sum of
total pressure of air remains the same before entering and after exiting the
airfoil, so a pressure difference is created. The propellers’ angle can be
changed thus changing the pitch and the thrust.
2. By the thrust of the jet engine
Jet engine
exhaust produce thrust. It is how we divert the thrust that produce the
respective motion in reverse direction to the thrust. The motion is produced
due to Newton’s Third Law of motion i.e. ’Every action has an equal and opposite
reaction’.
3. By the thrust of the main rotors
The main
rotors in the helicopter is responsible for change in thrust and motion. The main
rotors are also airfoils and the same Bernoulli’s theorem is thus applied,
generating thrust.
4. By the thrust of the rocket
Rocket also
generate thrust by the expulsion of exhaust and thus Newton’s Third Law help in
the forward motion of the rocket. One big difference of rocket from other
engines is, it also carries an oxidiser along with the fuel.
5. By the
hot air in balloons
Hot air balloon is a
lighter than air aircraft. The hot air generated by the burning of the gas in
hot air balloons make it lighter than surrounding air thus producing the corresponding motion. By increasing or decreasing the
burning rate we can control the motion.
6. Gliders
Gliders and similar
aircrafts generate lift due to the free fall and in this way develop forward
motion.
So we can see that thrust of aircraft can be generated by varied means and this generate the accompanying motion.
WATCH
THE FOLLOWING VIDEO TO KNOW ABOUT THRUST OF AIRCRAFT :