They may have none, or 3 or 4, or even more, depending on the type of helicopter.
Some (such as jet commuter helicopters, or the Mi24 Hind) have a simple tricycle arrangement of 3: one nose wheel and one on each "leg". Larger ones may have 2 at the main struts and even at the nose gear. The AH-64 Apache reverses this arrangement with 2 main wheels and a small tail wheel.
Some helicopters do not have wheels but have skids. Some have small wheels built into the skids to make moving them easier. The AH-1 Cobra and some early police patrol helicopters had skids.
Large military helicopters such as the CH-47 Chinook have 4 or 6 (2 double front wheels) built into the undercarriage.
Different helicopters have different landing gear. some just have skids, some have 3 wheels, some have 4.
None. It does not need wheels. It always takes off vertically. There are some helicopters w/ wheels and they have about 3 wheels. No more than 5.
you put wheels on it
A ship, and a helicopter, I also want to point out to you that you spelled 'does' wrong.
how many passengers can the largest helicopter hold
A very larg helicopter may be able to take off with an added 50,000 lbs. of weight. A good sized modern train is going to be significantly larger than this. The helicopter's blades would likely give out as they are suddenly reversed if you just "slammed on the brakes" so to speak. If you had the helicopter going at the same speed as the train, and slowled the helicopter down as much as possible, the train would eventually stop if the locomotives were not powering the wheels (it would stop without the helicopter, too, and would be infinitely safer for the helicopter pilot). If the locomotive is powering the wheels, the helicopter's not going to do a whole lot.
helicopter
It depends on what type of helicopter.
I don't believe there are airbags in any helicopter
it really just depends on the helicopter
there as 61 helicopter crashes
black as many helicopters in armys have black helicopter