The photographer of this photo asks ........
"There is a huge tube in there, anybody know what it's for?"
I'd like to know the answer too.
Actually, there are 2 metal tubes that can be seen inside this KLM 747-206's belly. One's close to the wing root and the other huge one is deep inside under the middle of the cargo hold floor.
What are these tubes used for?
For the fun of it, I'll take a guess. They're both used for the 747's Environmental Control System. The smaller tube supplies hot bleed air from engines #3 and #4 to the Air Conditioning Pack's Heat Exchangers and Air Cycle Machines (these 3 A/C packs are located near the main landing gear bays). The air then flows from the A/C packs (at cabin air temperature) via the huge tube in the belly and is then transported via ducts to all the overhead air vents in the passenger cabin, cockpit, & cargo hold, where it's used to pressurize the aircraft and control air temperature.
That's just a guess ....am I close?
Photo © Tim de Groot - AirTeamImages