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Many years ago, I was part of a LRRP drop taking photos from inside a KC-130 aircraft. The rear doors are (relatively speaking) huge. The top half pivots up and into the craft, while the bottom half descends down and (I assume) into the airstream.

When the main doors are opened like that, how does that affect the stability and controllability of the airplane? Would the pilot have to trim down or up, or do nothing?

While my personal experience is that plane, I wonder of any plane that opens large portals into the airstream.

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    $\begingroup$ Are you specifically asking about KC-130 only or about a rear loading ramp on any airplane? $\endgroup$
    – Farhan
    Commented Jan 26, 2015 at 15:06
  • $\begingroup$ Added to question $\endgroup$
    – CGCampbell
    Commented Jan 26, 2015 at 16:52

1 Answer 1

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Answer based on information found on-line. Related documentation:

enter image description here
C-130J Hercules
Source: Flight Global

The KC-130 Hercules is the tanker variant of the C-130 Hercules. The cargo opening consists of a door, and a ramp which can be operated separately.

  • The door is opened by rotating up and inwards the top panel.
  • The ramp is opened by rotating down and outwards the lower panel

enter image description here
Source: CQ Planes Spotting

KC-130 / C-130 have a good maneuverability at low speed.

From the the C-130 flight manual:

  • Door and loading ramp are operated at a speed of 150 KIAS, with flaps down at 50%.
  • Same conditions for flying with door and/or loading ramp open.

Low speed adjustments:

  • Reducing speed from 300 kt to 150 kt requires nose up trimming.
  • The center of gravity may be adjusted by ballasting fuel in the tanks (refueling tank and aircraft tanks).

Opening the ramp will change the aerodynamic shape of the aircraft:

  • The ramp will not be moved past the horizontal position (only need for full down position is to load cargo on the ground).
  • Moves the nose down.
  • Balanced by some trim accordingly.

If loads are dropped (pallets, paratroopers) or fuel is delivered, the center of gravity will roll back, with a significant nose-down tendency, and trimming will be required.

Opening the door will be less of an issue as seen on the image below:

  • The aircraft is near level.

enter image description here Above: KC-130J Hercules (source: Military.com).
Note that the attitude is not so far from level, in spite the door is open.

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  • $\begingroup$ Isn't the door closed in that picture? $\endgroup$
    – Jamiec
    Commented Jan 28, 2015 at 10:32
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    $\begingroup$ @Jamiec: I don't think so. The door seems to be open, and the ramp closed (up) at the same time. This is the configuration seen on this video, at time mark 6:29. Must be confirmed by an someone familiar with this aircraft. $\endgroup$
    – mins
    Commented Jan 28, 2015 at 18:27
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    $\begingroup$ When opening the ramp, the attitude is still the same—near level. It just changes the trim, so the stabilizer has to be adjusted accordingly. $\endgroup$
    – Jan Hudec
    Commented May 7, 2017 at 19:42

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