Gyros By James Goss       Since I have been playing around with hovering an airplane for about the last year or so I have been wondering if using a gyro on the rudder would aid us when trying to hover a plane. I have had several pilots tell me that they have tried a gyro but it didn't seem to help them hover. Others have said they really work great on the rudder, elevator, or ailerons.       About two years ago I installed a Pilot Assist (PA-2) to control the elevator for a Sig something Extra. The PA-2 is a photo-activated device that was designed to be installed in the fuselage and help maintain level flight of the craft by comparing the light above and below the craft.  The system really works nice when used in this mode, but I wanted to use it for hovering. I mounted the PA-2 in a window in the left wing panel and covered it with clear film. The system was switched on and off from my radio using channel five. The plane could be in level flight and would kick up into a hover when switch five was activated. It worked best on a cloudy day or when the sun was overhead, but it was controlling the elevator and not the rudder. I never figured out how I could use it on the rudder. It is the rudder that is hard to master while in a hover; it is relatively easy to keep up with the elevator. Where the rudder becomes complicated is during a torque roll when the plane reverses itself and you are viewing it from the rear of the plane instead of its front. The hover itself is fairly simple if you use the ailerons to counter the torque roll while keeping the plane in a fixed position.      A lot of pilots have gotten good at hovering and torque rolls but it requires a lot of practice. I have found that it also requires the right plane with an engine that has enough power to pull the plane out of a hover and go straight up with authority. What I really like to see is a plane touching the grass with its tail while doing a torque roll. Being inches off the ground leaves absolutely no room for error in your control. If you bump the rudder or elevator in the wrong direction, just for a split second, you are in for a crash. So to be safe at ground level I think a gyro would give us more time to respond. I am experimenting with a head and hold gyro on the rudder at this time and I will let you know how it worked out next month. At first attempt they do not appear to aid in hovering as much as I had thought they wood, or maybe I do not have them adjusted to the correct settings.      Gyros come in three types, the mechanical one like Jerry described above, piezoelectric type (crystals), and the newest ones AVCS (Angular Velocity Control Systems). The AVCS uses a chip that has a mechanical sensor integrated on the chip with the other electronic components and is said to be much more accurate that the Piezo type. They cost between $60 and $400 and only weigh a few ounces.     More next month on gyros.

Gyros : Part Two By James Goss     Gyros have been around for many years and you probably remember your science or physics teacher in school holding up a rotating bicycle wheel demonstrating gyroscopic action. The new generations of gyros have really changed since the day of the totally mechanical gyro. Today we have the Piezo Gyro and the AVCS Gyro, I will tell you about these a little later. I have recently become interested in gyros because I would like to use them to improve the hovering of my airplanes. The trend today is to hover your plane while descending toward the ground and finally touching the rudder in the grass and then go vertical. Hovering is probably one of the most impressive 3-D maneuvers a pilot can perform. The term 3-D describes any maneuver you do with your plane while it is stalled.      Up until a few years ago a stall was something you didn't want your plane to encounter because a stalled airplane will not fly. Now here we are trying to stall them on purpose. Some of the best maneuvers can be had when the plane is stalled, throw the sticks to the corners and watch it spin and tumble. Now I will admit that you are taking a chance with your plane each time you deviate from the normal flying patterns and enter the 3-D realm, but I will be the first to tell you that it's a lot of fun and puts the fun in fun-fly. I don't guess I have any planes that I would not try to tumble or spin at one time or another. Even my giant scale planes get their chance to spin and tumble every now and then.      The question comes up that if you are using a gyro to hover, or in any maneuver, are you really flying the plane. Full-scale planes use gyros and you think of the pilots as flying them so why not the same logic with R/C planes. My answer to this question is yes; you still must input your controls. Did you know that you are using a feedback system each time you fly your plane. Your servos have internal feedback systems that tell the dc motors to stop when they reach their destination. The gyros are very similar in that they generate and error correction voltage when the plane's heading change. So just think of a gyro the same as you do the servos, a tool that improves your airplanes flying capability.   The gyros only slow down the fall out from a maneuver, you still have to make constant decisions as to what input is needed. It can best be described as flying your plane under water. The movements will be slower, but they still occur, you just have a little more time to think. By practicing hovering with the aid of a gyro you will soon be able to hover without them, but never as well because the gyro can respond much faster than the eye to hand response of any human. No human can move that rudder and elevator as fast as a gyro feedback system. Believe me when I say that seeing a 37-40% planes hover two feet off the ground while doing torque rolls all the way down the field is impressive in anybody's book.      Gyros are not just for hovering; they help stabilize your plane during all maneuvers such as tracking through a large loop, a slow roll, knife-edge flight, and any others you can think of. The better gyros can be switched on and off from your radio transmitter. As an example you are going to install a gyro on your rudder to aid in hovering your plane. If you are using a gyro that is not switched, and they can be got for about $60, you will plug the gyro into the rudder channel on your receiver and plug the rudder servo into the gyro. You can now adjust the gain and centering controls with a small screwdriver. That's all there is to it. If you are going to use a better gyro, one that is switched on and off by your radio, there is another connection to make. You still plug the gyro into the rudder channel on the receiver and plug the servo into the gyro just as before, but now you also plug the gyro into channel five, or any channel that is controlled by a switch on your transmitter. In flight when you want to turn the gyro on and off, simply activate switch five on your transmitter. You may want to switch the gyro on and off in flight because some maneuvers that you like to do may be altered. Remember that the gyro tries to keep your plane on the same heading at all times and some 3-D maneuvers requires a constant heading change.      The Piezo gyro works on the Piezoelectric principle. When a mechanical pressure actuates a quartz or ceramic crystal, the crystal will generate a voltage in proportion to the force applied. The voltage will only be generated while the force is being applied. When the force is removed the voltage dampens back to zero. The force that acts on the crystal being used in our planes is the centrifugal force exerted on a body in motion. When the plane turns off it's heading the inertia of the crystal produces a force that excites the crystal and an alternating voltage is produced, then amplified, then compared to a reference voltage, and finally an error voltage is created that tells the dc motor in the servo which direction to move. All this happens in a very short amount of time. A human might make one or two corrections per second as compared to hundreds of corrections generated by the gyro.      The newest gyros are called AVCS gyros. This stands for Angular Velocity Control Systems.  On the same chip they have integrated electronics and micro mechanical machines that work together and makes an extremely accurate device. This is what the manufacture says about them:      AVCS systems far surpasses piezo-crystal heading hold systems for stability and drift cancellation. Forward, climb, descent, knife-edge and other flying attitudes are maintained even when the wind shifts. Very low drift SMM (Silicon Micro Machine) gyro sensor practically eliminates trim changes during flight. Conductive resin case improves EMC resistance (electrostatic and electromagnetic wave interference).   Setting up the gyro can be a little tricky if it is your first try. You will need a computer radio so you can adjust the ATV on channel five and mixing of other channels may be required. The gyro operates in two modes, normal and AVCS. You can arrange it to be in normal mode when the channel five switch is to the rear and in the AVCS mode when it is to the front or vise versa if you like. If you set the ATV to less than 40%, that channel will be turned off. To set the gain you must set the ATV from 60 to 120%. You must be careful in the AVCS mode because in that mode your rudder will not automatically return to its neutral position, it will hold its position until the plane responds to its new heading. The normal mode is best for most of our aerobatics because the rudder will return to neutral after each deviation in heading. You should never take off in the AVCS mode.   It has taken me a little while to become somewhat familiar with gyros, but I have had a lot of fun doing it. I finally got it working right last weekend and it was very windy that day. Even in the high wind I had some very nice hovering. The wind would blow the plane backwards for a great distance while in a true hovering position, very unusual to see. I believe gyros are well worth the effort and I know they are a lot of fun when used on one axis such as the rudder. So if you want to try something new, install a gyro on your rudder, elevator, or ailerons.