Water ballast barrels in the Section 41 nose section for center of gravity testing. We counted 33 in all for the whole aircraft, each of which holding around 1,000-lbs."

"Between the ballast barrels around 16 racks of test equipment and engineer’s test stations occupy the bulk of the main deck."

The reel mechanism for deploying and stowing the trailing static cone sits on the main deck just forward of the aft pressure bulkhead."

Here's a video of the 747-8 setup:

Here's a close up of the barrels one the 747-8 taken during a tour. Note there's a placard on the right explaining the water ballast system.

"Upper deck view showing ballast tanks on the A380 [F-WWOW]*. 15th November 2005"

*(Note: original source incorrectly stated G-WWOW)

Craig Boyden works on water ballast tanks for the 777-300ER that will used for flight testing.

There are several photos that crop up on a daily basis on Facebook chemtrail groups with descriptions like "Chemtrail Plane Interior". These are almost all photos of pre-production test aircraft which are fitted with ballast barrels, although there are a few that are interiors of firefighting planes. I'll try to make this post be a comprehensive explanation of all the photos. Let me know if I miss any. And if you see some chemtrail promoters using this photos in error, then please let them know.Ballast barrels are just big barrels of water that are used to simulate passengers when testing various configurations of weight and balance on the aircraft during test flights. The barrels are sometimes isolated, and sometimes connected with tubes, so water can be pumped around in flight to simulate passenger movements.Note several of the following images are copyright, and are used here under "fair use", as non-profit, educational, and critical usage.Many of the photos are very large, so set your browser to the full screen width to see them best.Here's a description of one such system, showing the Boeing 777 tests in 1994:And another in (the caption for the photo next to it says it was a 747 in 1969)Here's a photo of what looks like the same system taken in 2005. A doctored version of this commonly shows up in Chemtrail groups:Here's the same plane, showing all the test equipment and computers:And some more from 2003:And another of the 777. This one is also heavily used by the chemtrail web sites.This photo from airliner.net has been used to promote the chemtrails conspircy theory by claiming Facebook are closing accounts of people who post it:Quite possibly the copyright holder has complained to Facebook, however there are numerous other photos they could post, including this Creative Commons licensed one from Wikipedia:Note the overhead "mood" lighting is a different color, and the photo is at a slightly different angle allowing you to see where some wiring for test instruments is ported out the windows.From the outside you can see the window, looks like some kind of pitot tube:And if you pull back a bit more, you can see the plane is actually being exhibited to the public, at the Paris air show:The following are from a 747-8F, from Aviation Week [video=youtube;IxMSoxzYhG8]Another of the 747-8, taken from a different airshow:Here's the 747-8 showing all the test equipment:Another 787 image, from Wired:This A380 upper deck photo (from 2005) is commonly used by chemtrail promoters as "proof" of chemtrails:Here's a video of this A380 test setup at a public air show in China:[video=youtube;J_Wd3SSK8gQ]The large white cylinder in the foreground is a tow bar. The loop on the left end hooks to a tow truck, and the hooks at the right (the towhead) attach to the front landing gear. There are four handles on it for manual operation.This one is the A380 ballast barrels from an article in the Seattle PI.A nice HD image of the A380 upper deck:More from the A380:Another A380-861This is a nice one as it shows the ballast tanks behind the seats:This one is a bit unusual, it's a test BAe-146-300 from 1989. The ballast here is lead blocks! But there's also a single blue barrel at the back of the plane:Here's one from a 777-300ER, also gets some play in "chemtrail" groups. Photo from 2002, Seattle PICaption: