How do Airplanes move forward?
Hey friends, Happy Wednesday!
Let’s look at how airplanes move forward after being airborne, this week. I aim to write my newsletter issues in a way one can follow them while traveling on a bus, having a coffee, waiting for your food, etc. Let's jump in!
How do airplanes move forward?
9 months ago, I had written a newsletter on how aircrafts generate lift. It is not needed to understand this week's issue. But you can explore the topic additionally if you're interested.
Zooming out, Newton’s third law of “Every action has an equal and opposite reaction” is the essence of anything that moves us through the world. Such is the case with airplanes as well.
Passenger planes typically use jet engines, specifically turbofan engines. These engines work by drawing in air from the surroundings through a propeller fan at the front of the engine and pushing them in. After mixing with fuel and igniting, the hot gases then exit the engine.
Figure 1: Propeller blades in an engine - Passenger airplane
According to Newton’s third law, as the exhaust gases are expelled backward with a significant force, an equal and opposite force is applied to the aircraft, pushing it forward. This is the primary source of thrust for the airplane to move forward and travel distances while being airborne.
The propeller fans that draw air from the surroundings usually have twisted blades poking out at angles from a central hub spun around by an engine or a motor. But why are the blades twisted?
Additional Info: Why do Propeller fans have twisted blades?
This is my favorite part of this week’s issue.
Different parts of a propeller move at different speeds as seen in Figure 2 (Right): the ends of the blades move faster than the portion near the hub (because the distance moved by the tip of the blades is more in a given time than the portion of the blade closer to the hub/center as it is a circular motion).
Figure 2: Twisted design of the blades in a propeller (Left). Two points traveling different distances in a circular motion (Right). Source: Global Spec and Khan Academy
Without the twist, the propeller would produce uneven thrust on the hub and ends (more thrust at the ends of the blade due to higher speed), leading to excessive stress. This twisted blade design prevents structural strain. (Thrust is the reaction push force)
As the portion of the blade is moving slowly near the hub, it is more twisted and designed to cut air at a larger angle of attack as shown in Figure 2 (Left). The ends of the blade move faster so they are less twisted and cut air at a lower angle of attack. This ensures that the propeller generates a uniform force and a consistent thrust along its length. It also prevents noise and helps in aerodynamic efficiency.
Thank you for reading!
Have a nice rest of the week, and take care!
Until next Wednesday,
Chendur
