Have you ever wondered why jet planes are designed the way they are? There is a simple yet profound rule that influences the design of every jet plane you’ve ever flown on. It’s called the area rule, and once you understand it, you’ll start seeing its impact everywhere.
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Discovering the Area Rule
The area rule reveals the ideal distribution of cross-sectional area along the length of a transonic or supersonic plane. This distribution, including the wings and engines, results in a reduction of wave drag, which is the drag caused by shockwaves forming over the plane as it nears the speed of sound.
While planes never achieve this ideal distribution in reality, designers have made significant adjustments to improve performance. One example is the Concorde, which had a distribution similar to the ideal, but could have been closer had the fuselage been tapered over the wing.
The Impact of the Area Rule
The area rule was discovered when planes started pushing the boundaries of speed. Designers noticed that adjusting the position and shape of plane features had a significant impact on performance. For example, the F-102 Delta Dagger was originally designed with a straight fuselage. However, by tapering the fuselage over the wings, designers were able to bring its maximum speed from 0.98 Mach to 1.22 Mach.
Narrowing the Fuselage or Lengthening the Hump?
In some cases, it may not be feasible or economically viable to narrow the fuselage over the wing, such as with the Concorde. In these situations, it makes more sense to make the fuselage larger before the wing, resulting in a less dramatic change in cross-section. The Boeing 747-800, for example, featured a longer hump for this reason, which allowed for increased cruise speed, passenger capacity, and fuel economy.
The Placement of Engines
The area rule also influences the placement of engines. In most large planes, the engines are mounted slightly forward of the wing, rather than directly under it. Mounting the engines directly under the wing would increase the cross-sectional area. Similarly, in narrow-body planes, the engines are often mounted above and behind the wing to minimize the wings’ contribution to the cross-sectional area.
FAQs
Q: Are there other examples of the area rule in action?
A: Yes, there are countless other examples of the area rule in the real world. Can you name any? Share your thoughts in the comment section below, and we might send you a free Techal t-shirt!
Conclusion
The area rule has revolutionized the design of jet planes, enabling engineers to optimize their performance at high speeds. By understanding the ideal distribution of cross-sectional area, designers have made significant advancements in reducing wave drag and improving overall efficiency.
Next time you step onto a jet plane, remember the area rule and appreciate the engineering behind its design. For more fascinating insights into the world of technology, visit Techal.
