Reasons Why Engines on Commercial Jets are Tilted or Slanted

If you look at a commercial jet from the side, you’ll notice that the jet engines on the wings are somewhat pointed or tilted downward, and not straight relative to the ground. This isn’t as noticeable from the front, but when you look at a wing-mounted jet engine from the side, you’ll see that it’s slightly tilted downward. At first, I thought it was just a design choice, but it turns out they’re angled that way for the performance purposes of the aircraft.

Aligning Engines with Local Airflow

One of the primary reasons why jet engines are tilted downward is to align them with the local airflow during cruise conditions. When a plane is cruising, it usually maintains a slight nose-up attitude. This causes the air to flow off the wing at a downward angle, known as the downwash angle. If the engines were parallel to the ground, they would experience uneven force on the fan blades. This would compromise their efficiency and performance. Tilting the engines down by a few degrees allows them to meet the airstream at the same angle, effectively solving this problem.

Reducing the Pitching Moment

Another crucial reason for tilting the engines is to manage the pitching moment caused by the thrust generated by the engines. This thrust creates a force that has a tendency to pitch the plane’s nose either up or down. The direction of this force depends on the engines’ position relative to the plane’s center of gravity. To counteract this, the engines are tilted down, reducing the pitching moment and making the plane more stable and easier to control.

Additional Functions of Engine Tilt

• Aerodynamic Alignment: The tilt aligns the thrust vector with the center of gravity of the aircraft, enhancing stability and control during crucial flight maneuvers like takeoff and landing.
• Ground Clearance: The downward tilt provides additional ground clearance, preventing the engines from scraping the runway or taxiway.
• Engine Mounting: The tilt creates better attachment points on the wings or fuselage, distributing the engine’s weight and thrust more evenly.
• Exhaust Clearance: The tilt minimizes the risk of direct engine exhaust impingement on the wings or tail, reducing the chance of damage.
• Noise and Vibration: The tilt helps direct engine noise and vibration away from the aircraft’s structure and cabin, contributing to a quieter and more comfortable ride for passengers.

Variability in Engine Tilt

The amount of tilt can differ between various aircraft models. It depends on multiple factors, such as design, size, weight distribution, and the intended purpose of the aircraft. Engineers carefully calculate the tilt to maximize efficiency and safety during different phases of flight.

While tilting the engines offers several advantages, it’s not without its drawbacks. The most notable are increased drag and noise. Engineers have to find the optimal angle that balances these disadvantages against the benefits, and this angle can vary depending on the specific design and functionality of each plane.