A different kind of "rocket" can also take plastic bags to the sky

Review expert: Qian Hang, aerospace science expert of the First Academy of China Aerospace Science and Technology Corporation

Plastic bags and rockets seem to be two things that cannot be connected at all. Where did the combination of plastic bag and rocket come from? Can it really take off into the sky? Let's take a look below!

Plastic bag rockets require plastic bags! We need to prepare a large plastic bag and blow it up, as shown below:

At this point, you may be in a dilemma. How long will it take to blow up such a big plastic bag? Then, let's try blowing air inwards from a certain distance from the bag opening. Look, the plastic bag will swell up immediately!

After inflating the plastic tube, tie the bag mouth and stick a few small tail fins on the end of the plastic bag. In this way, a plastic bag rocket is ready.

The amazing Bernoulli principle

Why can such a large plastic bag be blown up in one breath at a certain distance from the bag mouth? I wonder if you still remember the electric fan cooling secrets that I shared with you before? It mentioned the "Bernoulli principle", which means that the pressure is low where the flow rate is high.

If you blow air at a position slightly away from the bag opening, the gas flow rate in the middle of the bag opening will be greater than that around it, forming a low-pressure area in the middle, and the air with higher pressure around it will automatically flow into the bag.

Tail wing

The purpose of adding tail fins to a rocket is mainly to improve aerodynamic stability during straight flight.

When flying in a straight line at high speed in the atmosphere, the rocket will encounter various disturbances. When the rocket engine does not have enough power to recover, the rocket will lose stability. If not corrected in time, under the combined effect of inertia and air resistance, the tiny disturbance will be rapidly amplified. The tail will provide force in the opposite direction, which can greatly improve the stability of the rocket. In this way, the plastic bag rocket with a tail can fly more stably!

However, the more tail fins, the better. Generally, three or four tail fins are placed symmetrically. When the rocket deviates slightly from its path, the tail fins will use the air resistance generated in the opposite direction to bring it back to the original track. If there are only two, the disturbance in the plane parallel to the tail fins will not be corrected, and the rocket will deviate from the course. If there are more than four tail fins, the effect will not be improved, but too much air resistance will be generated, affecting the flight.

Application in daily life

When you are sitting on a plane, have you ever wondered why this huge aircraft can take off? I believe some people have guessed it, and that’s right! The Bernoulli principle is used in the takeoff of the plane!

The airfoils of aircraft wings are specially designed. When the air flows over the upper and lower surfaces of the wing, the distance on the upper surface is longer than that on the lower surface, and the airflow velocity on the upper surface is faster than that on the lower surface.

According to Bernoulli's principle, the pressure is low where the flow rate is high, and the pressure is high where the flow rate is low. Therefore, the pressure on the lower surface is greater than the pressure on the upper surface, resulting in a pressure difference. This pressure difference is the lift that makes the aircraft fly .

In addition, when waiting for the high-speed train on the platform, the staff will constantly announce reminders to "stand within the safety line while waiting for the train", which is also due to Bernoulli's principle.

A moving train will cause the air nearby to flow rapidly. At this time, the air flow rate between people and the train is much greater than the air flow rate behind people. Therefore, the strong pressure from behind the back will push people forward.

Next, let's talk about the tail of the aircraft. The tail is an important part of the flight control system. The tail is mainly used to control the pitch and yaw of the aircraft, and to ensure that the aircraft can fly smoothly. The tail is a device installed at the tail of the aircraft to enhance the stability of the flight. Most tails include a horizontal tail and a vertical tail , and a few use a V-shaped tail. The tail can be used to control the pitch, yaw and tilt of the aircraft to change its flight attitude.

The tail is generally divided into a vertical tail and a horizontal tail. The horizontal tail consists of a fixed horizontal stabilizer and a movable elevator, while the vertical tail consists of a fixed vertical stabilizer and a movable rudder.