The slowest flying aircraft? Uncovering the art of F1D's extreme slow flying

F1 pursues speed, but do you know what F1D pursues? It pursues the other extreme of speed, slowness! And it is slowness in the sky. However, if the plane has no speed, how can it fly? Today, we will use this slowest plane in the world to introduce why this is the case.

Before we get into the theory, let's take a moment to get to know our protagonist today - the F1D aircraft. The F1D aircraft is an extremely lightweight, extremely slow indoor free gliding model aircraft. They are designed for long-term flights in indoor environments and are usually used in free gliding model aircraft competitions. What is a free gliding model aircraft competition? It is a special flying competition that allows model aircraft to fly in the direction of the wind and soar in rising thermal air currents. The model aircraft is completely free to fly along its own route without any ground control. If you have ever thrown a folded paper airplane or a balsa wood glider purchased from a small store, then you have experienced the most basic form of free gliding models.

There are two main types of free-flying models: indoor flying and outdoor flying. Indoor models are very light, fly very slowly, and are usually powered by twisting rubber bands to drive large propellers. Hand-thrown gliders and gliders that are catapulted into the air with rubber band loops can also be flown indoors. They are often flown in school gymnasiums, auditoriums, and similar large open spaces. Indoor models are one of the cheapest and easiest ways to get started with model building, and suitable flying fields can be found in most places. Outdoor models are usually larger and heavier than indoor models. Advanced types have very high performance. Under ideal conditions, some models can stay in the air for nearly an hour at a time. Others can be carried tens of kilometers by thermals before returning to the ground. The most advanced types can glide for more than ten minutes after only five seconds of powered flight. To prevent the model from being lost, most outdoor free-flying models are equipped with a timer device to limit the amount of time the engine can run. Other timer-operated devices bring the model safely back to the ground before it is carried away by thermals. But whether indoor or outdoor, they are all slow.

This seems to contradict the reason why lift is generated, because according to common sense, the wing of the aircraft must be able to move through the air at a sufficient speed to generate lift to lift it. Let's review first: the basic principle of lift generation can be explained by Bernoulli's principle and Newton's third law of motion. Bernoulli's principle states that when the speed of a fluid, such as air, increases, its pressure decreases. The wing of an aircraft is designed with a curved upper surface and a relatively straight lower surface. This design is called an airfoil. When air flows over the wing, the air speed on the upper surface is faster and the air speed on the lower surface is slower. According to Bernoulli's principle, this speed difference causes the pressure on the upper surface to be lower and the pressure on the lower surface to be higher, thus generating an upward lift. In addition to Bernoulli's principle, we can also use Newton's third law to explain lift. Newton's third law of motion tells us that for every action, there is an equal and opposite reaction. When air flows over a wing with a certain inclination, the wing pushes the air down and the air pushes the wing up. This reaction force also contributes to a part of the lift. If you only look at the above explanation, you will think that speed is a winning weapon, but please don't ignore another crucial factor in lift generation - wing design. In fact, a large wingspan and a suitable airfoil design can also generate enough lift at low speeds to enable the aircraft to hover and fly slowly. Specifically, they work like this: The wingspan refers to the distance from one end of the wing to the other. A large wingspan means a larger wing area, which helps to disperse the weight of the aircraft and provide more lift. Because lift is proportional to wing area, aircraft with large wingspans can generate sufficient lift even at low speeds. The airfoil, that is, the cross-sectional shape of the wing, directly affects the air flow speed and pressure difference. The special curved design allows the air on the upper surface to flow faster, thereby reducing the pressure, while the relatively straight design of the lower surface makes the air flow slower, thereby increasing the pressure. This greater pressure difference allows greater lift to be generated even at slow speeds.

So don't be fooled by the fact that the F1D looks simple or even crude. In fact, its design is extremely sophisticated. In addition to the large wingspan and high-lift wing shape, it has several other key factors that allow it to take off easily and stay in the air for a long time - first, extremely light weight. The weight of an F1D aircraft is usually around 1.4 grams. In order to achieve such a light weight, it must use ultra-light materials such as carbon fiber skeletons, extremely thin plastic films and extremely light rubber bands during the manufacturing process. This allows the aircraft to lift itself smoothly even if it only generates a small lift; second, high-performance rubber bands. The F1D aircraft uses the torsional force of rubber bands as a power source. Rubber bands store energy through torsion, and when released, they drive the propeller to rotate, providing forward thrust for the aircraft. Although the thrust is small, it is enough to propel the lightweight F1D aircraft to fly. Third, excellent aerodynamic design. The wings and tail of the F1D aircraft are exquisitely designed, optimizing the balance between lift and drag, and effectively reducing the flight speed. As a result, the energy consumption of the aircraft is also reduced to a very low level, allowing the rubber band power to be maintained for a longer time. Fourth, in order to ensure stable flight, each part of the F1D aircraft must be precisely adjusted. The angle of the wing, the thrust axis of the propeller, and the center of gravity position all need to be precisely adjusted to ensure the stability and balance of the aircraft during flight.

How about it? After understanding the above knowledge, you will understand why it can be the slowest flying aircraft in the world. Well, what else can this aircraft do besides participating in the free gliding model aircraft competition that you may not even have heard of, and relieving stress? In fact, their design and technology also have certain practical application value, which can be summarized as follows: education and training, innovation and research, and entertainment and hobbies. The design and manufacturing process of F1D aircraft involves multidisciplinary knowledge, such as aerodynamics, material science and mechanical engineering. They are excellent tools for learning and teaching aerodynamics and engineering principles, and can help students and enthusiasts understand the principles of flight and manufacturing processes. At the same time, the lightweight and efficient design of F1D aircraft is inspiring for the research and development of micro-UAVs and other small aircraft. Researching and improving the technology of F1D aircraft can provide reference for the design of lighter and more efficient unmanned aerial vehicles. For model aircraft enthusiasts, making and flying F1D aircraft is a very challenging and fun activity. By continuously optimizing the design and adjustment, enthusiasts can experience a great sense of accomplishment. This makes it another battle between man and nature, and like other outdoor sports such as fishing, sailing or hunting, it requires a certain amount of observation, patience and judgment, which are also the elements for success in other fields.

This article is a work supported by the Science Popularization China Creation Cultivation Program. Author: Uncle Rocket

Reviewer: Dai Yuting, Professor of Aircraft Department, Beijing University of Aeronautics and Astronautics

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.