A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

How do helicopters keep from spinning around uncontrollably? How come we haven't heard much about the Dead Sea scrolls?

December 30, 1994

Dear Cecil:

I've never been able to figure out helicopters. The big propeller obviously makes them go up and down, but how do they go backward, forward, and sideways? I happen to know the little propeller in the back is needed to keep the helicopter from spinning like a top due to engine torque, so that can't be it. Any ideas?

Cecil replies:

If I can explain this, by God I can explain anything.  Helicopters go forward and backward by altering the pitch of the main rotor blades, i.e., the angle at which the blades meet the wind. Up to a point, the steeper the pitch, the more lift. (If you've ever stuck your hand out the window of a moving car and waved in the airstream, you know what I mean.)  The trick is to alter pitch unevenly, so you get more lift in, say, the back of the helicopter than in the front. This is accomplished with the system of rods and levers you see near the rotor hub. To go forward, the rods increase pitch (and thus lift) when the rotor blades are (sorta) in back of the helicopter and decrease it when they swing round to (sorta) the front. This causes the helicopter to tilt forward and the rotor pulls it ahead.

Now, about that "sorta."  See, although you want to increase lift in the back of the helicopter, that's not exactly where you increase the pitch. Due to a phenomenon called gyroscopic precession, you need to apply the lifting force 90 degrees in advance of where you want the lifting to actually occur. Mystified? Here's an illustration that will make things slightly clearer.

Another problem: When the helicopter is moving forward, the rotating blade generates more lift when advancing (and thus biting into the wind) and less lift when retreating.   Various ingenious mechanisms compensate for these things, but the pilot needs to be aware of them when maneuvering.

Anyway, to turn a helicopter, you push the cyclic control, which in most helicopters looks like a joystick, in the direction you want to go.  The cyclic control alters the pitch of the rotor blades at the appropriate points during their rotation, causing you to veer off in the desired direction. There's also a collective control, which alters the pitch of the blades uniformly. This is used to change the helicopter's altitude or speed, depending on the situation.

Dear Cecil:

Years ago the media had a big hype about the discovery of the Dead Sea scrolls. Since then, nothing. Were the scrolls translated? What, if anything, was discovered? Or is this another dry hole like the shroud of Turin?

Cecil replies:

Of course not, you loser. The key difference is that the shroud of Turin was a fraud, while the Dead Sea scrolls were legit.  The more complete scrolls were translated within a short time after discovery and shed a good deal of light on the origins of Christianity and pre-Christian Jewish life.  There were also many fragments, work on which proceeded at a pace some scholars found exasperatingly slow.  But more on that in a mo.

The first scrolls were discovered in a cave near the Dead Sea in 1947 and many more were found later. Most experts believe the initial find, at Qumran, was the library of a monastery opf Essenes, an ascetic Jewish sect, that was hidden shortly before the Romans swept through and destroyed everything in 68 A.D. The scrolls contain copies of major chunks of the Old Testament (although nothing of the New) that predate previous manuscripts by a thousand years. There are also quasi-biblical texts and religious works, an Essene rule book, and so on.

Considered individually, most of the scrolls are of limited interest to nonspecialists except perhaps for a copper scroll listing the locations of Jewish treasures presumably hidden from the Romans. (The directions are so cryptic and the sites have been so altered, however, that so far as I know no treasure has been recovered, if in fact it even exists.) Collectively, however, the scrolls suggest Jesus' ideas weren't entirely original but rather were partly rooted in the beliefs of the Essenes — a shocking notion at one time but less so now.

The big news in recent times has been unhappiness over the slow pace of scroll research.  Access to the scrolls for many years was limited to a small committee of scholars.  As the years rolled on and little research was published, other scholars began complaining and demanded that the rest of the world be allowed to have a crack.   The editorial committee resisted, but in 1991 an ingenious crew of outsiders announced they had used a computer to piece together one document from a previously published concordance.  A short time later a California library announced it would allow unrestricted access to its complete set of photographs of the scrolls, and researchwise it's been pretty much open season since.

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