Three line control systems
These pages will grow to contain details from a variety of publications which span a considerable period of years. It is a fact of aeromodelling history that many of the speed control systems were invented and refined over 25 years ago and no better mechanical versions have yet been produced. They are therefore the main systems currently in use today. It is a happy fact that all handles will function with all bellcranks. Some refinements may be absent if the systems are not adequately matched, but these are usually a small price to pay. Such deficiencies are usually limited to a throttle that cannot be left 'unattended': a constant throttle setting must be maintained by the pilot by keeping a constant finger position, and this will be due to unbalanced residual forces within the system. The flexibility of matching any bellcrank with any handle has the great advantage that both items can be upgraded within the life of any model as it develops, but without any adverse intermediate effects.
The J.Roberts Flight Control System
This was the original progenitor of all the mechanical 3-line systems, first produced commercially in the 50s by the American company formed by J.Robert Smurthwaite. It consisted of a matched handle and bellcrank which provided a fully compensated and balanced throttle control system. Elevator control was independent of throttle control, throttle settings were able to be left at any position and all 3 control lines were kept under equal tension. The original units were not designed for the relatively high stresses of Carrier and early bellcranks were probably marginal in respect of strength. The system was subsequently produced in a stronger form by the company of Sturdi-built and the modern versions, now manufactured by companies such as L&R and Brodak, have again been strengthened so that they are now quite suitable for Class 1, as well as BCD. The 3-line handle is produced in 3 different colours and there are 6 different variations on the bellcrank theme. Brodak products are distributed in the UK by Irvine Engines Ltd and the handles and bellcranks should be straightforward to order through any model shop, although they are not cheap. Expect to pay about £13.50 for each bellcrank and about £40 for the handle (1998 prices).
Brodak instruction sheet 240dpi A4 page 123k
Electronic Throttle control
An alternative to the vagaries of 3-line control is to use electronics, with electrical signals passed down the wires and a servo at the model end operating the throttle.
Fred Cronenwett is one of the acknowledged whizzes at this black art, and has a page specifically devoted to electronic throttles. (The rest of the site is worth visiting too).
Of course, like so many things in life, there is a trade off. The upside is that you have only two lines, with consequent less drag during the high speed run, and less line weight pulling the model in during the low speed run. You also have full throttle control with slack lines.
The downside is that you need a power source and Tx at the handle, insulated lines, and battery and servo on the model. Time will tell...
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