Bus Driver, I agree, and whilst spoilers aren't speed brakes, they can perform that function on jet transports.

When deployed, they spoil lift, and if you want to maintain altitude, or even lose it more slowly, you have to pull the nose up, therefore more drag because of the higher angle of attack of the wing. It's sort of like putting your hand out the window of the car. With it lying flat, not much drag, but raise the front a little, and the airflow tries to pull it off your arm.

What you're doing by raising the front of your hand is creating more lift across your hand, but also creating more drag.

Bill S, spoilers deploying on touchdown are actually tranferring the weight onto the wheels from the wing so that brakes are effective. If an aircraft bounces, the spoilers don't automatically deploy until it's back on the ground, and looks like staying there. That's controlled by a 'squat switch' on the right hand landing leg (with Boeings), and unless it's compressed to a predetermined point, the spoilers don't come up.

On all transports that I know of, roll and flight spoilers are one and the same, and only the degree and method of deployment are different. Flight spoilers are used to increase descent rate or reduce speed, are manually deployed, and can operate to the maximum degree of extension. When used as roll spoilers, they are moved by the aileron control, and move through very little degree of extension.

Ground spoilers are only deployed on the ground, along with the flight spoilers, so if you look out onto the wing soon after landing, you'll see all flight and ground spoilers extended up into the airlfow. They're automatically extended when the squat switch tells the aircraft it's on the ground.

Adding a little to what Caffeen Man said, I think the B52 had only spoiler control for turning, rather than ailerons, and as a consequence, restrictions on bank angle, because if the aircraft went beyond a certain angle, the drag just pulled it into a turn from which it wasn't recoverable at lower altitudes. A B52 was lost at Fairchild AFB about 10 years ago as a result of too much bank angle down low.