Not a clearly quantifiable effect...first, even though you can add a "LEAK" and an "EMPTY" effect to a tank's damage system, dp's don't appear to talk directly to the fuel gauges in a manner to properly simulate this, so even though the tank's damage system has a leak and empty tag, the gauges don't reflect this. On many missions i've taken multiple hits including fuel tanks and returned home without being able to determine whether the tanks were draining due to the damage or just normal fuel consumption to base.
Secondly, in CFS2 combat its very difficult to get a single, clean hit in a fuel tank only so that you can isolate and measure this effect properly. In taking a volley of gunfire, the serious damage is spread out between multiple parts besides the tanks in such a way that the many parts fail together and the plane goes into a death plunge, leaving no opportunity to measure leakage. So even if you set up a one-on-one engagement with an enemy AI, how can you control the damage you take in the engagement and limit it to a single hit on a tank for a controlled experiment? Thirdly, i would caution against obsessing too much on this -- this is a player-centered sim that puts you in the lead of a combat flight in most operations. Do you really have the time to manage a group of wingmen in pitched battles while farting around with a leaky tank experiment? :mixedsmi: Those boyz need constant attention and TLC and the CO will grade on how many make it through the campaign, not how well your leaky tank idea worked.