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The 747's sixteen main-landing-gear wheels are distributed over four bogies: two four-wheel wing gear, mounted underneath the inboard wings, and two four-wheel body gear, mounted under the fuselage further back.

When the aircraft is airborne with the main landing gear extended, the wing gear tilt upwards, while the body gear remain level:

enter image description here

(Image by Ian Kirby at airliners.net, via Wo st 01 at Wikimedia Commons.)

This is mentioned, but not answered, by this earlier question.

Given that the purpose of tilting the bogies is to reduce the longitudinal forces on the landing gear upon initial touchdown, it seems like it would make more sense to tilt the body gear as well as (or instead of) the wing gear, as - being further back on the aircraft - they are closer to the ground at positive pitch angles, causing them to touch down first and experience more-severe longitudinal touchdown loads, making the alleviation of these longitudinal loads more critical for the body gear than for the wing gear.

Why does the 747 tilt its wing gear instead of its body gear?

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2 Answers 2

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enter image description here

Video of 747 gear retraction

The body gear bogies are tilted, just not as much as the wing bogies, as a still from this video depicts. The difference in the bogie tilt seems more a function of retraction mechanism than of the placement - the wing gears tilt sideways, the body gears tilt forward. The amount of bogie tilt in combination with the retraction direction results in minimum space requirements once retracted.

Stills from the video:

  1. Wing gear, sideways retraction enter image description here

  2. Body gear, forward retraction enter image description here

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    $\begingroup$ I wondered whether different airflow below body and wings could have that effect. $\endgroup$
    – U. Windl
    Mar 28 at 10:33
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    $\begingroup$ @U.Windl They could, but the bogies just hang that way in the video as well, at standstill. They seem to be balanced that way, suspended by springs around the 4-bar retraction linkage. $\endgroup$
    – Koyovis
    Mar 28 at 12:23
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Which came first:

  • Packaging the landing gear? But the landing gear can tilt/untilt on its way up instead of as soon as liftoff – the A330 and 777 examples.

  • A wider track for crosswind landings, i.e. wing LG touching down first? (See photo below.)

  • The wing LG struts being taller and therefore benefit more from more tilting for weight saving (which is the primary reason for tilting)?

Boeing covered the 747 packaging in a patent, and they even patented/studied the same when all four trucks are in-line:

➤ The tilt is not mentioned, because again, it can tilt on its way up, so it must be all those factors combined plus others. Saying it's one reason only is too simplistic.

enter image description here
See second bullet point; source: BEST 747 LANDING Smooth Slow motion, YouTube

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