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Old 11-05-2013, 07:38 AM
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blackshire blackshire is offline
Master Modeler
Join Date: Jan 2009
Location: Fairbanks, Alaska
Posts: 5,984
Default "Bang-bang R/C" is back!

Hello All,

I wanted to post some information that model rocketeers who fly boost-gliders (B/Gs) and rocket gliders (RGs)--as well as Jetex/Rapier and EDF (Electric Ducted Fan) F/F (Free-Flight) modelers--might find useful.

Tonight (last night, at this hour) I tried out my Axion ASK-21 Ready-To-Fly micro R/C motorglider (see: ), testing its airborne battery pack charging system (which is an integral part of the hand-held transmitter), its electric motor, and its rudder-only (plus motor throttle) control system. This 500 mm (19.69") wingspan motorglider weighs just 21.5 grams, so its R/C equipment would easily fit in a B/G or an RG, or in a Free-Flight Jetex/Rapier jet model. Now:

After overcoming a problem that rendered the model "dead" (it was entirely my fault--please see below), I discovered that these Axion R/C motorgliders' rudder operation is of the old (1940s - 1960s!) "Bang-bang" type, where the rudder moves all the way over to the limit of its travel in response to *any* movement of the rudder control stick on the transmitter (it's definitely non-proportional, as the specifications say!). Transmitters in those days often used buttons instead of control sticks. However, the rudder doesn't physically oscillate between the two extreme positions, as rudders did in the old single-channel, rudder-only pulse proportional R/C systems. Also:

Using the "Dab, dab" technique that Charles "Chas" Gardiner suggested in his book The Basics Of...Model Gliders [see: ] (making small, smooth, and brief control stick motions, followed by centering the control stick) enables one to make smooth, continuous turns, maintaining airspeed using the throttle in order to prevent stalls. (The tiny motor/propeller puts out much more thrust than I had anticipated, as it nearly pulled the model out of my hand!). In addition, the following problem may not happen to you, but just in case it does, I've discovered a fix for it:

My Axion ASK-21 R/C motorglider didn't work at all when I tried it out for the first time tonight, until I "telescoped-in" the transmitter's antenna. (At very close range, just a foot or two, the transmitter's signal was "swamping" the receiver.) But it still didn't work (other than the motor running intermittently) until I cycled the transmitter on and off several times. This enabled the rudder servo--which I had unintentionally moved while handling the glider--to re-center itself. After that, all of the R/C functions worked perfectly and repeatably. If you procure an Axion R/C motorglider and it seems "dead" when you try it, re-setting the transmitter antenna's length (*just* for close-up testing--it should be fully-extended for flight) and allowing the rudder servo to re-center itself will correct these problems. As well:

Here is an article from the July 1957 issue of American Modeler magazine, titled "You Can STUNT Your Rudder [-only] Plane": , and Dave Fritzke's page features many rudder-only R/C models: . The Axion R/C motorgliders can perform at least the gentler aerobatic maneuvers shown in the article. While it would seem impossible for a rudder-only plane to perform aerobatics (especially loops, which require an elevator), this is not the case, and the "secret" of how it is done with only a rudder involves fascinating physics. (Jack E. Schroder's book How to build and fly Radio Control Gliders [see: 2BGliders ] covers rudder-only R/C gliders, too.)

I hope this information will be helpful.
Black Shire--Draft horse in human form, model rocketeer, occasional mystic, and writer, see:
All of my book proceeds go to the Northcote Heavy Horse Centre
NAR #54895 SR

Last edited by blackshire : 11-05-2013 at 07:46 AM. Reason: This ol' hoss done forgot somethin'.
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