Model helicopters

Two birds were flying along. Suddenly one of them warned the other: "Be careful, there comes a helicop-cop-cop-cop-cop...."

Bad joke. But anyway, let's talk choppers!

This array of helicopters was photographed at a championship. These look quite similar, but have considerable technical differences. Some use glow-plug engines, while others have spark-plug gasoline engines, which are more reliable. It's not that a helicopter can't glide! It can, and very well, but some pilots can't, specially in an emergency...

These helicopters are mostly factory-made. Few modellers would try to build the sophisticated mechanics in the home shop. The cowlings are sometimes homemade, that's all. And let it be said, model helicopters are expensive. They cost easily two to three times as much as a model plane!

This picture may give you an idea of what's involved in making a chopper fly! The engine (a glow-plug version in this case) is mounted vertically. It has a blower attached, with some wind guides that direct the air stream to the cylinder. The thing with the HIROBO label is the silencer, and the hose that steals some exhaust gas to pressurize the fuel tank is visible. The engine has a centrifugal clutch, and then connects via a reduction gear to the main rotor shaft. Not visible in this picture is another gearing that drives the shaft for the tail rotor.
The chopper's front is occupied by electronics. The servo on top of the white fuel tank has two functions: It controls both the engine throttle and the main rotor blade pitch. You can see how it is connected to two linkages. The large black lever connects up to the rotor. Three other servos are mounted on top of it. The frontmost one to the camera (left one in the chopper) connects to a long control rod that steers the pitch of the tail rotor blades. The other two steer the main rotor differential left-right and front-back pitch.
In front of the servos is a stack containing the radio receiver (on top), the batteries, and a gyroscope unit that is an immense help for controlling this thing! Gyros brought chopper piloting into the reach of common mortals. In the age before gyros, only demigods could fly such a thing remotely without crashing it!

This is the linkage at the rotor head. The control actions are transmitted through rotating joints. To reduce control force requirements, auxiliary "Hiller" blades are used in most model helicopters. These amplify the control forces.

Despite the gyroscopic stabilization, it's not just kid's play to learn flying a chopper, although in fact kids usually learn it much easier than old people! First training is done with the chopper tied down, giving it very little range of motion and no chance to get in danger. Then the step in this picture follows: The chopper has "learning spikes" attached, so it is not as likely that the pilot can touch the rotor tips onto the ground, which would produce a very violent accident! Some pilots fly with these spikes whenever no one else is watching... :-)

At the championship there were no such cheats. There were a dozen choppers, and all pilots knew how to fly them. One nice thing about choppers is that they can stay close, as they don't need to move at all. Many pilots love to just keep the machine standing still in the air, turning around, going forth, back, sideways, etc.

This chopper won the championship. Its owner did incredible things with it! Not only did he do all those aerobatics that planes do, including rolls, loops, hammerheads and so, but also he did long inverted flights, right down to the "grass mowing" trick where the rotor blades are a few cm from the ground! Then he climbed to a good altitude, throttled up while reducing pitch, thus storing kinetic energy in the rotor. He then told everyone that a chopper is much safer than a plane, and switched off the engine! Everyone expected the chopper to autorotate down and land hard. Not so... It came down slowly, then kept altitude, flew around, climbed a bit, came down again, all that using the kinetic energy stored in the rotor's motion! After a long while that energy was almost used up. By that time the pilot landed his chopper, very smoothly... I was really impressed! I had never expected so much endurance just out of energy stored in a rotor!

This one was also flown by a specialist. Both of these have gasoline engines and are fully aerobatic.

Nice, huh? Note the electric wire closely in the background! The pilot joked about a checking it up and flew slowly along it. Some people like to pull at the devil's beard!

And here we have two specialists doing a formation flight. You should have seen it... And it's not easy, the turbulence from one chopper can easily crash the other one! It's very important to keep the relative altitudes and positions according to the wind direction, so the turbulence is blown away from the other chopper!

Well, this isn't a chopper, or... perhaps it is? I decided to include this plane in the chopper section, because I saw it hanging from the engine much more time then flying like a plane! That's what a chopper pilot does for fun when he has a powerful plane and no chopper!

As far as I know, this plane does not have any gyro stabilization, so it really is a feat to fly it in this way! And the pilot must be very confident not only in his skills, but also in his engine! After all, if the engine hesitates even a moment, the plane WILL crash! A plane definitely does not have an autorotation mode! By the way, if this baby crashes, it can be really dangerous! It's not that much smaller than a "true" plane!

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