And in those days men shall seek death, and shall in no wise find it; and they shall desire to die, and death fleeth from them.
And the shapes of the locusts were like unto horses prepared for war; and upon their heads as it were crowns like unto gold, and their faces were as men's faces. And they had hair as the hair of women, and their teeth were as teeth of lions.
And they had breastplates, as it were breastplates of iron; and the sound of their wings was as the sound of chariots, of many horses rushing to war.
And they have tails like unto scorpions, and stings; and in their tails is their power to hurt men five months. - Revelation 9:5-10.
Indeed the helicopter is a possibility. It would appear to a first century man as some kind of armor plated locust with mens faces; their wings (rotors) do sound similar to the description of an army of horse-drawn chariots rushing into battle, as we are all familiar with today, but what could be the 'hair as the hair of women and their teeth were as teeth of lions"?
These 'locusts' have "less than lethal" capabilities that have yet to be incorportated into such a weapons system. They will have the ability to 'sting' people with such a painful torment that lasts five months and causes them to seek death rather than the suffering they will be exposed to. Of course, if taken literally, it could be some sort of creature as yet unknown to modern man. In either case, one must remember that John had no words in his vocabulary to define it in today's language: His account must be understood as an eye-witness description of technologies or events unknown in his day.
As literalists contend, could it be some sort of insect such as the giant asian hornet. The stinger on the hornet is 1/4 inch long and extremely painful. You can see it in a National Geographic video clip at http://news.nationalgeographic.com/news/2005/10/1012_051012_hornet_video.html It's wingspan is about three inches. Whatever John saw, natural or man made, it's going to be a dread plague on men.