The PC-24 has, under the fuselage, a kind of huge support to hold the wings.

Pilatus PC-24

If we compare with the Citation CJ4 or the Phenom 300, this difference is quite significant. Why??

Citation CJ4 Phenom 300

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    $\begingroup$ What makes you think that bulge is support structure to hold the wings? Generally in aircraft, the wings hold the fuselage rather than the other way round, but I don't think that's the purpose of this feature either. $\endgroup$ – pericynthion Sep 26 '19 at 5:56
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    $\begingroup$ @pericynthion I have no idea about structures, so probably is the other way around as you say $\endgroup$ – Ana Sep 26 '19 at 6:01
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    $\begingroup$ It could be a wing main spar carry-through (effectively the wing holding the other wing, albeit for bending loads), or luggage space, or a place for the main gear wheels to go (PC-24 has larger wheels than most similar sized jets), or an aerodynamic fairing to reduce interference drag... I'm not posting an answer because I don't know which of these (if any) it is. But it's not necessarily structural. $\endgroup$ – pericynthion Sep 26 '19 at 6:04
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    $\begingroup$ It's not a wing support, it's a plane support. ;) $\endgroup$ – J... Sep 26 '19 at 22:11
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    $\begingroup$ The paint scheme there really accentuates the heck out of it. It might work better to select a picture that has a paint scheme comparable to the other pictures. $\endgroup$ – Harper - Reinstate Monica Sep 27 '19 at 4:49

To add to the other answer...

The Pilatus PC-24 is billed as a business jet that can operate out of rough airfields. Comparing the pictures of the PC-24 to the Phenom 300 or CJ4, you can see that there is quite a bit of extra ground clearance. You can also see that the rear landing gear on the PC-24 are much more robust (dual wheels, longer travel length) than the other two aircraft.

If you look at this picture:

enter image description here Source: Wikipedia

You can see that the wheels also retract into that area. They probably wanted to keep the wing low to take advantage of ground-effect to improve short-field performance. So having a higher-up fuselage allowed them to put the engines up higher and avoid FOD damage, while the low wing allowed them an impressive short field take-off performance. The PC-24 can operate out of a field just 2,800 feet long. The Phenom 300 takes 3,200 feet and the CJ4 takes about 3,500.

So the "bump" is there to be able to handle additional loads, elevate the fuselage, and store the gear. I can't find any diagrams of the fuel system, but it's possible that it also houses fuel tanks or baggage.

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    $\begingroup$ It makes it seem quite bird-like from below. I like the styling, even if done for practical purposes. $\endgroup$ – Baldrickk Sep 26 '19 at 17:07
  • $\begingroup$ Also I have seen that the interior in the pc-24 is flat, while the cj4 and the phenom have a step. Coult it be related? To have more space in the interior or something like that $\endgroup$ – Ana Sep 27 '19 at 6:42

The huge support, or bulge, is a fairing, designed for reduction of wing root drag. So many people talk about wing tip vortex drag, but much more is created at the wing/fuselage interface, especially in uncoordinated flight. This improvement, first seen in 1930s vintage gliders (where else!), improves the airflow around the aircraft, resulting in significant fuel saving.

Importantly, this is a subsonic effect. Many super sonic aircraft actually reduce fuselage diameter near the wing to reduce drag, complying with "Area Rule".

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    $\begingroup$ Another reason for this fairing is to provide space for the main wheels to retract. The cabin needs to be circular to hold pressure and the wing isn't thick enough. I don't know why it should be different between these particular aircraft though... $\endgroup$ – Robin Bennett Sep 26 '19 at 11:24
  • $\begingroup$ They might have some fuel/cargo in there too. Overall, very practical design, keeping wings nice and thin. Possible hatchling of airliner. $\endgroup$ – Robert DiGiovanni Sep 26 '19 at 11:35
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    $\begingroup$ It's also very pronounced on the fastest bizjet. $\endgroup$ – ymb1 Sep 26 '19 at 15:21
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    $\begingroup$ Transsonic transport aircraft are usually area-ruled to some extent, but in their case the biggest increase in cross-section is the engines, and the wing root fairing shape tends to be shaped to match—including here, the wing root fairing ends just before the engines. $\endgroup$ – Jan Hudec Sep 27 '19 at 6:11

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