Mother Of All Glitches By James Goss      Just what are glitches? Everyone in the R/C hobby will at one time or another hear about a pesky phenomenon that plagues us all from time to time. Anytime our planes perform a maneuver we are not expecting, we call this a glitch. In electronics a sudden rise or fall in a circuits voltage or current is referred to as a glitch. The term is carried over to our hobby and is defined as any unwanted signal that reaches the receiver for a short period of time and prevents the servos from doing their normal job. A glitch can come in many forms and may or may not even be noticed by the pilot. If a glitch is severe enough it may cause us to loose control of our planes and crash. A glitch can also be defined as the absents of a signal for a short period of time. An example would be the case of an intermittent flight pack switch. If the switch contacts are making contact most of the time but every now and then they open due to vibrations. Your receiver will shut down and you have no control of your plane for a short period of time, the contacts remake and you gain control again. So a glitch can be any unwanted signal that is picked up by the receiver or it can be the loss of the transmitted signal for a short time.      I would think that most of the glitches received by our planes are not from an outside source, but instead from the plane itself. I am sure static discharge is one of the culprits that will create a glitch while in the air and I will address that in another article. I classify glitches in two categories, static and dynamic. I call them static glitches while the plane is on the ground and dynamic glitches when the plane is in the air. If you get glitches while your plane is on the ground you will surely get glitches in the air. Don't take a chance on flying your plane if you are not glitch free on the ground. Do a range test as always and then another with the engine running and another with the engine throttled up. Don't just walk in a straight line while doing the range test. Walk in all directions and hold your antenna at many different angles while walking away and toward your plane.       Over the years I have only had a few glitches, that I would really call glitches, to hit my planes while in the air. Most recovered without any major problems to speak of but they really gave me a scare each time they occurred. I have mostly flown glow engines over the years and a few gas engines as well. What I am saying is that I haven't had any real problems with glitches until now. Let me tell you about my last project that has become known as the “Mother Of All Glitches”. For about the last year or so I have been building giant scale planes with rather large gas engines and still haven't had glitch problems. My latest project was a 1/3 scale Staudacher with a ZDZ 80 engine. My friend Cecil had started building a Staudacher last year and I really liked the looks of it so I also started the exact same kit. Our planes are built identical in every way including the engine and servos. Cecil covered his with Monokote and I covered mine with Ultracote. They weigh close to the same weight, but mine is just a little heavier. They are even balanced about the same, a little tail heavy. We are using a fiber optic radio activated kill switch from Electrodynamics and thought surely because of the ZDZ 80 having a shielded sparkplug wire we would have no RF interference. We have both had more static and dynamic glitches from these planes than we have ever had before. I have had about 15 flights now and they all have seen some of the most severe glitches known to mankind. I guess Cecil and I have been lucky to get them back on the ground in one piece after each flight. You may wonder why we would keep flying them if we were getting glitches. Each time we modified our planes and thought we had the problem fixed, we would have to fly them before the dynamic glitches would show up. Most of our work has been toward keeping the engine ignition noise out of the receiver, but we were working from the wrong end of the plane. It looks like it is going to turn out to be our tail bracing wires. Now we all know that we should not have any metal-to-metal contact that will allow the metal to move or rub each other. This will generate radio frequency (RF) interference that will in turn produce glitches. My plane had the Sullivan tail wire kit that uses non-coated cables with an all-metal clevis and connectors. I used two loops of wire to tie the vertical fin and horizontal stab to the fuselage. I have seen this and other methods used on gas engine planes before with no bad reactions. Each loop had eight metal clevis connections, a total of 16 in all. It was like having eight generators generating a voltage around a closed loop of wire on the tail. As the vibrations will cause the clevis to rub against the metal retainers a voltage is produced when there is an electron transfer between the two metals. The loop formed a short circuit that allowed a current to flow, and anytime there is a current flowing through a conductor a magnetic field will be developed at right angles to the wire. The field starts at the center of the wire and expands outward from the wire. This magnetic field will induce a voltage into any conductors that happen to be in the vicinity. Naturally the antenna passes by this area and has a signal induced into itself by the magnetic field. This unwanted signal (noise) becomes the glitch I am talking about. This noise will override the true signal and produce erratic operation of the servos because of a low signal to noise ratio. Once the noise gets on the dc bus it can glitch any of the channels and servos. We were getting a lot of throttle, rudder, and aileron glitches.      I was puzzled at first as to why this make up would only produce a random glitch and not a continues stream of glitches, and why the tail wire would not create problems on large glow engines. After I thought about it for a few days it finally hit me that the eight sources of RF would not all be in phase at the same time. It is just like having eight batteries connected in series aiding and series opposing. While aiding, the voltages will add and the over all output will be maximum. If they were opposing each other and had equal output amplitudes, four of one polarity and four of another polarity, the overall output would be equal to zero. While the voltages are at random amplitudes the output amount will be the vector sum of all sources. So with the vibrations of the tail the voltages would constantly go in and out of phase and only create maximum current through the loop every now and then. This corresponds to the time pattern for the glitches I was getting. I have now removed all the metallic tail wire and replaced it with nyrods. This type of interference is more predominate for gas engines because they vibrate at higher amplitude than does the glow engine.      So watch out for those metal to metal parts on your planes. Every case is different and I can't say you will always get RF interference when you do have metal touching metal, but why take a chance of this happening to your new plane. Like I said above, Cecil and I couldn't believe how strong the glitches were. Sometimes they would even kill the engine or accelerate it to a high rpm, we never new what to expect.