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As you can see in this picture the APU of the A400M is on the side under the right wing, including the RAM-Air-Turbine.

  • Why is the A400M APU on the side of the fuselage instead of the back?

  • Why is the RAM-Air-Turbine not on the bottom of the fuselage?

enter image description here

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1 Answer 1

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The A400M is designed to operate from unpaved surfaces.

For the APU (number 70 in the following cutaway), it's space and proximity. You've got the wing box above the fuselage, plenty of space to add things there. Also easier maintenance access. Proximity as in less wiring and tubing to run inside the airframe, saves on weight and complexity. And FOD. The inlet would be away from the debris and dust the wheels kick up.

The RAT is indeed on the bottom of the fuselage, in the LH sponson just forward of the LH main gear, number 41 in the cutaway (source)

A400m cutaway

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  • $\begingroup$ The RAT is in the LH sponson just forward of the LH main gear not on the upper surface. $\endgroup$
    – user68075
    Mar 5, 2023 at 17:39
  • $\begingroup$ Correct, number 41 in this cutaway. $\endgroup$
    – sophit
    Mar 5, 2023 at 17:55
  • $\begingroup$ Why would FOD matter for a RAT? The RAT is rarely used, and it's never used on the ground. $\endgroup$ Mar 6, 2023 at 2:00
  • $\begingroup$ @AnonymousPhysicist It might be necessary to land with the RAT deployed, perhaps at an unimproved strip if that is the only airfield close by. In that case, reducing the risk of FOD damaging the RAT would be a consideration. $\endgroup$
    – Ralph J
    Mar 6, 2023 at 3:41
  • $\begingroup$ @RalphJ Why would anyone care about damage to the RAT after landing? If it was deployed, then the aircraft already has extreme damage, like the failure of several engines or a missile ruptured multiple hydraulic systems. $\endgroup$ Mar 10, 2023 at 0:08

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