Why Is The Engine Inlet At An Angle?

dhawald3 · Tue Jul 19, 2011 2:50 pm

I was wondering after seeing engines on many aircraft that when viewed from side the inlet is at an angle from the verticle

I was trying to find the answer but could not find any written explanation anywhere.

What I have deduced myself is that it could be for noise reduction or for the engine to intake more air when in low speeds when the aircraft flares for landing.

If anyone can shed more light on this.

SlamClick · Tue Jul 19, 2011 3:06 pm

Most likely answer: They are optimized for cruise flight and these planes fly at something like two degrees nose-up deck angle. Also, if you look for wind tunnel pictures you will see the airflow starting to rise a few feet out forward of the wing. So from an airflow perspective they are just about square-on.

CCA · Tue Jul 19, 2011 3:06 pm

The wing while creating lift changes the relative airflow of the air before it gets to the wing, it's called upwash and its angled slightly up and the inlet is optimized for this direction of airflow. Engines are also toed in due to the bow wave effect of the fuselage. There are several subtle aerodynamic changes usually all optimized for when the A/C is in cruise.

tdscanuck · Tue Jul 19, 2011 11:53 pm

In addition to the above, it also helps with engine performance at high angles of attack. With large deflection angles, the airflow into the inlet gets disturbed. For what are hopefully obvious reasons, you don't get negative angles of attack very often so you primary look at improving high positive angle performance.

Tom.

SchorschNG · Wed Jul 20, 2011 5:34 am

Quoting CCA (Reply 2):
The wing while creating lift changes the relative airflow of the air before it gets to the wing, it's called upwash and its angled slightly up and the inlet is optimized for this direction of airflow. Engines are also toed in due to the bow wave effect of the fuselage. There are several subtle aerodynamic changes usually all optimized for when the A/C is in cruise.

You can see how this effects engine installation when you look at the MD80, where the engine is angled upwards as it is affected by downwash.

CCA · Wed Jul 20, 2011 7:53 am

Spot on, another good indicator is the rain gutters above the doors which also pops up frequently on airliners.

HAWK21M · Wed Jul 20, 2011 11:12 am

It serves to get max Airflow into the engine due to its orientation.
Also notice the plan view of a powerplant the tilt is noticeable too OR the Inlet cowl is tapering towards one side[toed in].

Why Is The Engine Inlet At An Angle?

Why Is The Engine Inlet At An Angle?

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