Today we'll be covering how fuel leaks work in helicopters.
If you've ever been shot up in a helo, you've probably run into a situation where you seemed to have a fuel leak that eventually stopped before the full tank emptied. Helos aren't configured to have any indication of their fuel tank integrity, unlike planes, so it isn't immediately obvious as to what's going on when this happens.
The way it works is as follows. There's a fuel tank damage selection in each helo, and when that takes damage, it influences your fuel capacity. The way it does this is that as it gets damaged, it creates a corresponding fuel leak. If it's low damage, it's a small leak. If it's greater damage, it becomes a larger leak. If it's completely destroyed, it will leak until empty, but at any other damage state it will leak only until it has hit the corresponding percentage of fuel remaining. So if you take 80% damage to the fuel tank, 80% of your fuel will drain, leaving you with 20% remaining. Take 90% damage, you'll be left with 10% fuel.
The greater the damage, the larger the leak, and the faster it will drain. At full damage you can expect to have roughly one minute worth of flight time left, assuming you took that damage on a full tank. At lower damage you probably won't even notice that you lost fuel due to how slow and subtle it is - for instance, on an MH-6, it would take several minutes for a 20% leak to take your fuel from 100% to 80% - faster than normal, but not by a dramatically visible degree.
The fuel bar is color-coded so that when you hit 50% fuel, it turns amber. When you hit 30%, it will turn red. Once you're below 15%, it will begin flashing between red and amber.
From what I've seen, Arma helicopters tend to have between an hour and a half to three hours worth of fuel, depending on how they've been configured. Thus even if you lose 95% of a full tank, you'll still likely have several minutes of flight time remaining to get into a friendlier airspace.
If a helo has more than one fuel tank, the damage to each tank will influence that proportion of fuel. The only one I've tested so far with multiple fuel tanks is a Super Stallion, so this isn't much of a concern for helo pilots, but it does play more of a factor if you're flying a jet.
If you notice you have a fuel leak, there's no real way to know how bad it is definitively. What you can do is make a reasonable guess. If it looks like it's draining fast, it's a bad one, obviously. If you seem to have taken a lot of damage to other components of the aircraft, you can probably assume a comparable amount of damage to the fuel. Light damage, you may be ok. Moderate damage, you'll want to monitor and see if it stops at some point. Heavy damage, you might as well assume that the tank has been fully ruptured. The complication is that it's often difficult for the fuel hitpoint to actually become damaged, so you may have heavy overall damage with nothing wrong with your fuel, or you could have taken a single good hit to the fuel tank that destroyed it without hurting the rest of the helo. You can never be entirely sure.
Whatever the case may be, noticing a fuel leak means that you need to be prepared for an emergency landing or an autorotation. Your goal should be to land as soon as possible, which is to say that you need to consider the tactical situation, terrain, distance to friendlies or your home airfield, and so forth, and fly to the best place possible before either landing under power or conducting an autorotation. Make sure you announce your situation over the radio as well as your intentions. This will help others find you if things don't work out.
If you plan to stretch out as far as you can before doing an autorotation, a good technique is to head in the direction you want to travel while continually climbing. Altitude is options when it comes to autorotating, and you want as much altitude as possible while you still have the opportunity.
If you land and find that the tank didn't fully empty, you can take off again to try to get closer to or even all the way back to base on the fuel remaining, just bear in mind that any further damage will result in a short window in which to conduct a landing or autorotation. The best precaution to take at this point is to fly as high as you reasonably can and make sure you're flying over terrain you can land in on short notice.
That's it! That's how fuel leaks behave in Arma.