The Quadruplex Mk II
The Don Brown Quadruplex radio was central in the design of Cirrus. Helen Brett told me that Tom designed all his planes
around the equipment.. The size/shape of the equipment dictated the size of the model. We know that Tom designed his Cirrus specifically to fly on proportional; Cirrus was Tom's only proportional-specific plane.
Which version of the Quadruplex was in the Cirrus? Don Brown wanted his latest radio to be used by Tom in this model. Since Cirrus was designed early in January 1963, the most advanced radio available in late 1962 would be the one. The pictures below are due to the courtesy of Tom Mavracic who has quite a collection of early proportional radios including the Quadruplex line, (Tom points out that his radios are in workable condition.) It is Tom's best guess that the model available in late 1962 would be the Quadruplex Mk II pictured below. Look at the sheer size of the components and the metal servo cases. This every early radio is quite removed from the lightweight, sophisticated computerized radios we have some 55 years later. Even the least expensive available radio today is light-years technology-wise ahead of this primitive radio--yet it was state-of-the-art then..
The Quadruplex was related to, but was not a Galloping Ghost radio, (a early ancestor of proportional.) Anyone who has seen a GG system in operation remembers how strange it looked because the control surfaces gyrated back and forth to essentially their full range during operation. These movements wouldn't seriously affect flight because the "back and forth" was so quick. People have described the GG as looking like a "wounded quail flopping on the ground". The Quadruplex was
a more refined version of the very early GG method of control with much less back and forth movements, (maybe 1/8" or so each way. The following is a description of how it worked. Tom warns that this is a greatly simplified explanation and not technically exact, but I appreciate that because I can (almost) understand it. There are much more detailed and accurate explanations elsewhere:
:A GG radio sends out a single tone (one channel). The speed of the pulse (pulse rate) and time on and off (pulse width) is how the rudder and elevator functions are controlled. Motor is via a full on or full off tone transmission which the receiver unscrambles via what is known as a POD circuit (Pulse Omission Detector). The Quadruplex MKII and "21" transmit three separate pulsed tones (3 channels) for aileron, elevator, and rudder. The receiver has three special encapsulated filter circuits to segregate the tones. Motor control is similar to the GG's POD method and is tied into the rudder channel. When you push and hold the high motor button, the rudder will quickly move to the right (or left) and return to center. Low motor does the same except the quick blip rudder is in the opposite direction. A weak point of the Mark II and "21" is that the receivers still make use of a relay to separate the rudder and motor signals from the POD circuit. The CL5 Quadruplex is a "more modern" proportional radio using feedback servos.
Mu sincere thanks to Tom for all his help on the Quadruplex including a link to a great article on the Quadruplex history which is included below:
http://www.rchalloffame.org/Manufacturer/Quadruplex/history/index.html
