Jet Engine Intakes: Why the Squashed, Flat Design?

[Alan G]

I half remember that jet engine intakes were circular a few years ago. Now they have a squashed appearance with the bottom part quite flat.

This isn't new as the first German jet at the end of World War II had the same shape but it seems relatively new on airline jet engines.

So, why are they this shape?

 

[brewnog]

Runway clearance.

Many aircraft built during the 1970s and 1980s, such as the 737, have engines that do not appear perfectly round when seen from the front. This is because the bottom of the engine cowling (or covering) has to have clearance above the runway so that it does not scrape along the ground. When the 737 first appeared in the 1960s, it had fairly small turbojet engines that were suspended high above the ground. As the engines became larger with the introduction of turbofans, the fuselage and wing remained the same height above the ground, so the bottom of the engine cowling was flattened somewhat to still achieve the maximum air intake without scraping the ground

http://www.century-of-flight.freeol... of technology/Noise Reduction Technology.htm



As an aside, when they were testing the Rolls Royce Trent 900 engines for use on the new Airbus A380, the test plane had such little ground clearance beneath the engines that they allegedly put extra air in the tyres to get another couple of inches clearance.

 

[ravenprp]

The squashed, flat design of jet engine intakes is actually not a new concept, as you mentioned with the first German jet having a similar shape. This design has been around for decades and has several important functions that make it the preferred choice for modern jet engines.

Firstly, the squashed, flat shape allows for better aerodynamic performance. The flat bottom surface helps to create a smooth, laminar flow of air into the engine, reducing drag and increasing efficiency. This is especially important at high speeds where any added resistance can greatly impact the performance of the engine.

Secondly, the flattened bottom also creates a larger surface area for the engine to capture and compress air. This allows for a greater volume of air to be processed, resulting in more power and thrust being produced by the engine.

Additionally, the squashed design also helps to reduce the overall size and weight of the engine. By flattening the bottom, the engine can be positioned closer to the ground, allowing for a shorter and more compact design. This is important for aircraft manufacturers who are always looking for ways to reduce weight and improve fuel efficiency.

Furthermore, the flattened bottom also allows for easier maintenance and access to the engine. Mechanics can easily inspect and service the engine without having to navigate around a circular intake.

In conclusion, the squashed, flat design of jet engine intakes is a result of years of research and development to create the most efficient and high-performing engines. It offers benefits such as improved aerodynamics, increased air intake, reduced size and weight, and easier maintenance. So, while it may seem like a recent trend, this design has been a crucial aspect of jet engine technology for decades.