[xoxoxoBruce]

I read the C-17 takes 20 hours of maintenance per hour of flight time. I've also seen numbers for the cost per hour of air time, in fuel and routine maintenance, for different aircraft. The numbers at mind boggling, and don't even include major overhauls after so many hours of flight time.

OK, here's some from the Air Force at TIME...

Here’s a sample of what it costs to keep these Air Force aircraft airborne for one hour last year (the so-called “ownership” cost-per-flight-hour, which includes modifications):

A-10C Warthog Attack Plane — $17,716
AC-130U Spooky Gunship — $45,986
B-1B Lancer Bomber — $57,807
B-2A Spirit Stealth Bomber — $169,313
B-52H Stratofortress Bomber — $69,708
C-130J Hercules Cargo Plane — $14,014
C-17 Globemaster Cargo Plane — $23,811
C-20B VIP Plane (Senior Pentagon Officials) — $32,212
C-32A VIP Plane (Vice President, Cabinet Officers) — $42,936
C-5B Galaxy Cargo Plane — $78,817
CV-22B Osprey Tilt-Rotor — $83,256
E-3B Sentry AWACS Radar Plane — $39,587
E-4B Flying Headquarters — $163,485
F-15C Eagle Fighter — $41,921
F-16C Viper Fighter — $22,514
F-22A Raptor Fighter — $68,362
HH-60G Pave Hawk Helicopter — $24,475
KC-10A Extender Tanker — $21,170
MC-130H Combat Talon II Special Operations Plane — $32,752
MQ-1B Predator Drone — $3,679
MQ-9A Reaper Drone — $4,762
RQ-4B Global Hawk Drone — $49,089
T-38C Talon Jet Trainer — $9,355
T-6A Texan II Turboprop Trainer — $2,235
U-2 Dragon Lady Spy Plane — $30,813
UH-1N Huey Helicopter — $13,634
VC-25A Air Force One — $161,591

I'd guess that's fuel, parts , and the people who do the work, plus maybe their bosses.