The B-17G in Aces High II
The B-17 in Aces High II is a late G model with improved defensive firepower. Before the formation bombing option, a single B-17 alone was a frightening target to attack, bristling heavy machine guns in mostly twin turrets. Carrying a decent bomb load this defensive firepower gave the B-17 the ability to attack heavily defended targets and still inflict serious damage. Overall the B-17 is probably the most survivable bomber while packing what is the fourth largest bombload.
 Aces High II Performance Charts
 Flying the B-17G
The B-17G really changed with the addition of the formation bombing option in the 1.10 release of Aces High. Before that it was typically seem as a medium-heavy bomber with excellent defenses (or at least the best for a bomber in the game). Attacking B-17s was about a 50:50 proposition with well planned/executed attacks probably 80:20 in favor of the fighter while poorly executed attacks were more likely to be 90:10 in favor of the bomber defenses. The 1.10 release of AH changed that quite a bit though in a couple of major ways:
First, the bombing model was changed in general to make bombing runs a more difficult and deliberate thing. Long, essentially straight, bomb runs at constant speed and without any violent maneuvers are required in order to hit targets. This made the bombers far more vulnerable since they couldn't maneuver to avoid fighters. Prior to this bombing model change it was not atypical for bombers to maneuver almost like fighters, denying decent attack angles and making the balance of encounters lean towards the defense. Setting up a decent position and attack run against bombers in the new model is now possible and is highly effective.
The second change was the introduction of formations, which allowed 3 aircraft to be flown and controlled by a single lead pilot. This addressed two issues with the B-17, and most other bombers. The first was an increase in total bomb load which increased to 3 times the normal load. This made the B-17, which carried only 6K of bombs, now capable of packing 18K which was highly significant. The three bomber formation also tripled the defensive firepower of a bomber formation, making attacking one more difficult, especially if you intend to survive.
Best use of the B-17 is a medium level attack in order to achieve maximum accuracy. Higher altitudes offer more security from defenders but can also make your attacks less effective (i.e., you'll miss more, not that you can't get hits at 25, 30 or even 40k, just that you'll be less likely to get hits, and hit what you were aiming at). An altitude between 15K and 20K seems to be working best as you have decent speed and reasonable accuracy if you calibrate properly. Take 1K bombs to hit heavy targets or 250lb bombs to hit light structures. Remember that every drop you make will release the same number of bombs from each aircraft in your group so don't drop more than you need to in order to ensure targets destruction.
Defensively the firepower of a B-17G formation is awesome. In most engagements the arcs of 2 or more gunner positions should overlap and double your fire of other comparable bombers. With 3 bombers in a formation the firepower climbs even higher and poor attacks will be highly suicidal if you can hit the enemy target. Defensive fire-range is typically in the order of D1.4 for rear shots, less for high angle deflection shots. Fire only the position you are at (your secondary fire button) until you think you are on target and then open fire with the primary trigger to unleash the full firepower of defensive guns.
To escape, a shallow dive towards a home field or friendly forces (if either are closer than about 2 sectors) can usually make intercept by enemy fighters difficult. Shallow dives push up intercept speeds and make it less likely for an attacking plane to position properly for attack. It also buys you time for friendly support (if any) and drags the enemy lower. Alternately, if help is a long ways off, or if you intend to hit more targets, you may want to concider climbing as soon as you drop, or as soon as you see that fighters are upping, as this makes you an unappealing target for less patient, or newer players.
The B-17 is a solid plane, and can absorb a lot of damage and keep flying. I've been in a B-17 attacked by a group of 163's and we didn't loose a single plane, although we lost 1 engine, and the left gun. Provided you don't make any huge mistakes such as letting a 262 slip within D200 without seeing him, then you will likely make it home again.
 Fighting against the B-17G
It's smart to get a feeling for the defensive abilities of a bomber group before attacking. Some bomber pilots have experience levels that will make every second spent within D900 of a bomber a punishing experience, although as long as you don't fly in a perfectly strait line, you will likely make it within firing range. Thus, the attacker needs to consider the time spent at close range, the potential for inflicting serious damage in one pass, possible assistance from other friendly contacts, and methods of escape. Attacking from high angles with steep dives and high speed seems to be the most effective for survival although it is also a difficult skill to master. A competent bomber gunner is going to make even a pass like this an unhealthy experience though a less experienced gunner many not even land a single hit on you from such a high deflection shot. Climbing above the bomber, making a dive, and using the speed from that dive to come up on him at 400+ mph also seems to work, although it isn't quite as effective as a steep angle of attack.
If you can, try and attack to disrupt the bombers before the attack, or at a point where they are more vulnerable like a turn or during climbing. At these times the pilot of the bomber is usually less likely to be manning or watching the guns for attacking fighters. But be carefull if you know he has a gunner, or suspect he has a gunner, as this will increase the situational awareness, and allow the bombers to shoot back, without missing their target.
The B-17 is one of if not THE toughest plane in the game. I've seen them limp home on 2 engines, with no rudders, and smoking. I've seen them attacked by 163's and loose only 1 bomber after 3 passes as well. You need to take into appreciation how much damage a B-17 can take, and how much damage you can cause.
 External Links
Soda's Aircraft Evaluations