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I was intrigued to find this picture below. There was so much space around the engine. So what is inside of that extra space? Or is it just a hollow casing?

enter image description here

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Details about the picture as provided in the image source:

[Last Year] A Southwest Airlines Co. flight landed safely Saturday morning following a major malfunction of one of its two engines during a flight across the Southeastern U.S.

The Boeing Co. 737-700 was flying from New Orleans to Orlando early Saturday operating as flight 3472 when it suffered the failure, causing the jet to quickly divert to Pensacola International Airport in northern Florida at 9:40 a.m. CDT, according to a statement from the airline.

A Southwest spokesman said its initial reports indicated no injuries were reported among the 99 passengers and five crew aboard.

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    $\begingroup$ "major malfunction" seems like it is downplaying that a little. I'd go with a minor unplanned dissasembly myself. $\endgroup$
    – Baldrickk
    Jul 4, 2017 at 17:16

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Yes a bit of the engine called the nacelle is missing. This is an aerodynamic structure that slows the air down before it enters the compressor, the pointy bit in your photo. In the drawing underneath it states Inlet Cowl. It has some thickness, because it requires a certain nose shape for its function. Mainly a hollow casing indeed, but with a high tech shape.

enter image description here

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    $\begingroup$ Not "Just a hollow case". This is also where the anti-ice for the engine intake is. Without that, you're essentially limited to flight in clear skies -- which drastically curtails commercial flight. $\endgroup$
    – Brock Adams
    Jul 5, 2017 at 8:52
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    $\begingroup$ I've slightly changed the phrasing. This video seems to indicate that the anti-icing is mainly a hot air conductor from the compressor to the inlet: a pipe, which is also a hollow casing :) $\endgroup$
    – Koyovis
    Jul 5, 2017 at 9:12
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In the image the front part of the engine nacelle (the inlet region) is missing. This region is usually hollow, with the equipment (like control unit) and tubing coming after the separator wall visible in the photo. The main purpose of the missing region is aerodynamic.

In the image below, you can see the equipment and various other items covered by the cowlings (which are open). The separator wall can be seen in the far end of the engine, near the fan blades. Though this is not the 737-700's engine, the design is similar.

Engine nacelle

Engine with cowlings open; image from kativ.eu

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    $\begingroup$ I imagine there will be some ducting and accomodation for the anti-icing system? $\endgroup$
    – ROIMaison
    Jul 4, 2017 at 16:39
  • $\begingroup$ @ROIMaison You're right... That region hosts the ducting for anti icing system... $\endgroup$
    – aeroalias
    Jul 4, 2017 at 16:47
  • $\begingroup$ In fact, look at the stuff behind the separator wall. See how much of it is below the fan? That stuff is moved to the side on the 737 engines to improve ground clearance. That is why they are oddly shaped. $\endgroup$
    – Harper - Reinstate Monica
    Jul 4, 2017 at 19:02
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What is missing from your photo is the engine inlet. As someone stated, the inlet does contain some anti icing components, likely a swirl nozzle for a commercial application.

The engine inlet structure is composed of an inner composite barrel, and outer composite barrel, a forward bulkhead, an aft bulkhead, and the inlet lipskin.

The inlet attaches to the forward mounting flange on the fan case (the forward most flange).

Anti-ice ducting from the core interfaces with the inlet, which has another tube (most commonly with some sort of flexible component for thermal expansion) that spans the distance between the forward and aft bulkhead (which appears to be hanging back from about the 11 o'clock position on the engine from what is left of the aft inlet bulkhead).

This then interfaces on the forward side with the anti-ice distribution system in the area inside the lipskin, known as the "D-Duct". The area between the bulkhead of the inlet is indeed empty.

The inlet is specially designed for acoustic attenuation.

The components you are expecting to see are contained in two places: the engine core and the engine fan compartment. Depending on the engine, these two locations house the electrical, fuel, hydraulic, pneumatic, and oil components of the engine. These systems are commonly referred to as the "EBU" or engine build unit or engine build up.

Source: I am an EBU Systems Design Engineer

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The area immediately at the end of the fan blades is filled with a fairing compound. It is smoothed to within a few thousandths of an inch (slightly) bigger than the diameter of the fan. This compound sits in a depressed are built into the support ring for the cowl. It keeps the air flowing smoothly through the fan blades. Between the support ring and the cowl there are some control actuators and support structure. Also the bleed air ducts for engine anti ice may be routed there. It will all depend on the model and manufacturer design considerations. Modern cowls are actually designed to provide forward lift and airflow acceleration. First used on WW2 radial engine aircraft.

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    $\begingroup$ Welcome to Av.se! $\endgroup$
    – Ralph J
    Jul 5, 2017 at 3:31
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Above all, the clearance in the engine pod is to facilitate routine maintenance and quick visual assessment during turnaround cycle of operations. Further, this greatly helps in efficient engine replacement cutting down on 'Downtime' ! This is one of the factors, I feel.

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  • $\begingroup$ Above all, the clearance around the engine behind the fan section is to provide a channel for smooth by-pass air flow. In the last picture you can see that this particular design has a separate inner cowling around the non-fan portion of the engine, as opposed to building the by-pass channel into the rear section of the nacelle that in the IPB example also houses the thrust reversers. The easily raised cowlings provides very fast access for maintenance purposes; but, turn inspections for modern engines is little more than a walk-around looking for leaks or external damage. $\endgroup$
    – Ron Gordon
    Jul 6, 2017 at 4:22

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