ChatterBank1 min ago
Helicopter take-off
40 Answers
When a helicopter is running and on the ground what happens to it physically to make it take off? Presumably the rotor speed is increased but is that all, do the blades alter angle (like flaps)? Just wondering.
Answers
So... Ok... where to start? First, the rotors on a helicopter are nothing more than moving wings. If you could see them up close they have the same upper contour as an aircraft wing has and produces lift in the same way. (Thank you Mr. Bernoulli). As the rotor rotates counter clockwise as seen from the cockpit (on American helicopters)
22:45 Fri 07th Oct 2011
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So... Ok... where to start? First, the rotors on a helicopter are nothing more than moving wings. If you could see them up close they have the same upper contour as an aircraft wing has and produces lift in the same way. (Thank you Mr. Bernoulli). As the rotor rotates counter clockwise as seen from the cockpit (on American helicopters), the rotor produces lift on the right side of the circle, but as the rotor moves into the left side of the circle it must produce more lift than the right side, since it's moving away from the oncoming air (when the craft is flying forward). In fact there's a limitation on every helicopter on how fast in can fly (normal airplanes can fly too slow and stall). If it flys to fast the left side of the rotor arc cannot produce enough lift and that side will stall, creating a very dangerous condition called "retreating blade stall".
So (stay with me here) all of this is controlled by the pilot, but not directly. As AlBags introduced, the pilot is controlling the rotor head through the stick like control that moves up and down. This in turn controls the rotor head (the device at the base of the rotor system on the shaft from the engine). This device is ingenious in that it automatically alternates the angle of each blade as it rotates. As the blade on the right side of the arc moves forward, the cyclic decreases the blades angle, and as it moves into the left side or retreating side it automatically increases the angle (called the angle of attack and shortened by AlBags as AOL) thereby equalizing each blade with the other.
The other stick like control in the pilot's left hand can be moved freely in all directions. This one is called the collective and simply tilts the entire rotor head in the direction the pilot wants to move. (The previously described cyclic control also provides the pilot engine power control through a motorcycle like throttle).
On standard helicopters, there are also pedals on the floor that similarly control the tail rotor whose sole purpose is to provide ant-torque power to keep the body of the helicopter from spinning under the rotor on top (thank you Mr. Newton). In the case of the Chinook (and other similar designs), each entire overhead rotor system spins in opposite direction to the other, thereby cancelling the results of Mr. Newton's Third Law.
All very complicated, which is why "Rotorheads" (semi-affectionate name for helicopter pilots) all seem to very nervous... they'e just waiting for something to go wrong. It's often said that helicopters don't actually fly... they just beat the air into submission...
I'm sure my attempted word picture is clear as mud, but it's the best I could do without my proverbial greenboard and chalk...
So (stay with me here) all of this is controlled by the pilot, but not directly. As AlBags introduced, the pilot is controlling the rotor head through the stick like control that moves up and down. This in turn controls the rotor head (the device at the base of the rotor system on the shaft from the engine). This device is ingenious in that it automatically alternates the angle of each blade as it rotates. As the blade on the right side of the arc moves forward, the cyclic decreases the blades angle, and as it moves into the left side or retreating side it automatically increases the angle (called the angle of attack and shortened by AlBags as AOL) thereby equalizing each blade with the other.
The other stick like control in the pilot's left hand can be moved freely in all directions. This one is called the collective and simply tilts the entire rotor head in the direction the pilot wants to move. (The previously described cyclic control also provides the pilot engine power control through a motorcycle like throttle).
On standard helicopters, there are also pedals on the floor that similarly control the tail rotor whose sole purpose is to provide ant-torque power to keep the body of the helicopter from spinning under the rotor on top (thank you Mr. Newton). In the case of the Chinook (and other similar designs), each entire overhead rotor system spins in opposite direction to the other, thereby cancelling the results of Mr. Newton's Third Law.
All very complicated, which is why "Rotorheads" (semi-affectionate name for helicopter pilots) all seem to very nervous... they'e just waiting for something to go wrong. It's often said that helicopters don't actually fly... they just beat the air into submission...
I'm sure my attempted word picture is clear as mud, but it's the best I could do without my proverbial greenboard and chalk...
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My father says it was the same with B-36s Eddie. He remembers them being here in the 50s and you could hear the reverberation a couple of minutes before you saw them. Even when they were high they were so big he says he could still see them when all other planes were just a contrail.
How I would have loved to have seen those! Zeppelins too!
How I would have loved to have seen those! Zeppelins too!
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