You wont be able to pick up Black Project until you complete Torenos missions at the airport, at which point The Truth will drop by and convince you to see what the heck the government has going on at Area 69. Area 69, get it?
Fourteen-year-old humor aside, this is a pretty cool mission if you like wandering into heavily secured army bases. The soldiers here, and there are plenty of them, all pack M4s, so youll want to kill off the one by the gate, then turn his weapon on his friends. The M4 can either be auto-aimed or manually aimed, so click your R1 key periodically to see if theres anyone within auto-aim range.
You have two options so far as penetrating the underground lab goes: you can either play it stealthy by avoiding the searchlights and making it to the control tower to unlock the blast doors, or you can just go hogwild and kill everyone you see, taking all of their ammo before proceeding to the grate on the far side of the base and dropping through. Theres a set of body armor near the control tower, and a health recharge at the bottom of the vent itself, so try to clear out a path between the two before recharging yourself completely and dropping down to the interior of the base.
After you reach the base, the time limit is no longer relevant; feel free to stick around past 5:30 if you wish, since the mission wont automatically end at the point. The close quarters here make it a bit more difficult to take out the guards, so try to get their attention and lure them back out to chokepoints before killing them at a distance; theyre deadly with their M1s at short range. Luckily, there are no fewer than four suits of armor scattered around in the base, so you should be set on those.
In order to reach the Black Project, youll have to reach the bottom of a missile silo, but before you head there, search around and find the control room to disable the SAM sites. The missile silos stairs are overrun with guards, making it a difficult place to penetrate; we found it helpful to crouch-and-roll down the stairs, keeping our guns pointed towards the middle of the silo, and locking on to enemies when we heard them firing at us. Before you pick up the item at the bottom of the silo, though, return to the upper levels and find a fresh set of armor.
After you grab the jetpack, bust out of the silo and head for the nearest wall of the army base. If you disengaged the SAMs in the control room, you shouldnt have any trouble making it to the rendezvous with The Truth.
Now that you have a jetpack, you can use it to pick up a minigun, if you wish. There's a minigun floating above a gray bracing on the railroad bridge on the northeastern side of San Fierro. Getting it repeatedly will involve a lot of long trips to a save point, but you should be able to get a bunch of ammo for it if you're willing to put a little time into it.
The last mission before you can acquire the airstrip as an asset sees CJ hijacking a train while using the jetpack. The train itself is uncovered, so youll be able to fire on the soldiers aboard from midair, but they, of course, will be firing back, and theres a lot of them, so bring along a suit of armor if possible. After you eliminate the soldiers, shoot the crates until you find the jar of green goo, then return it to The Truth to get your cash.