E-flite’s Sbach comes in a convenient box (above left) that not only has useful data but doubles as a storage box. Found on the back of the box (above center)
had been offered before, I still could not be- lieve my eyes. This was different. They were also announcing that the plane used a new AS3X technology in the receiver as well. I had no spare money at the time and so was not able to investigate further. I had a Parkzone Sukhoi 26M to fly and that would have to do for the time being in spite of the Gee Bee being of serious interest to me.
AS3X stands for Artificial Stabilization 3-
aXis and represents a way to deal with the aforementioned problem of wind, turbulence and certain other instabilities associated with the small micro aircraft being flown out of doors. This represents an active Stability Augmentation System or SAS and this means that on all three axes (Pitch/Eleva- tor, Roll/Aileron and Yaw/Rudder) there is a sensor that senses deviations on that axis and feeds that information back into the control system so a correction can be made. This sort of feedback system had been around for years in the R/C world in the realm of helicopters and first took the form of a mechanical gyro back in the late 1960s and early ’70s that was hooked into the tail rotor circuit. These early units were bulky, heavy discreet systems and consumed a lot of power from the battery pack. I know, I still have a few hanging around my shop. Then came the Piezo Gyro which was a solid state unit and required a waiting peri- od where the model had to remain perfectly
is information on the AS3X. The E-flite UMX Sbach 342 3D (above right) (EFLU4950) as it came in the box.
still while the system stabilized after being turned on.
Today, with the miracle of mass integra- tion you can now have three axis sensors on your tiny “brick” type receiver and is why you have to let the Sbach remain motionless for a few seconds while this system stabi- lizes. This is on page 8 of the instruction manual and if you have any R/C helicopter experience, with either the large or the mi- cro helicopters available, you will already be familiar with this procedure. It’s the fixed wing only flyers that this may be new to. Also, if you want to see what this model can do in the capable hands of a company spon- sored pilot go to
http://www.youtube.com/ watch?v=aG-h7YsL0Zs and pre pare to be humbled.
A quick word about feedback loops. For the typical R/C pilot the feedback loop looks like this. Aircraft wing dips due to a wind gust. Light bouncing off aircraft reaches pi- lot’s eye; eye sends message to pilots brain. If brain perceives the problem pilot analyzes which way the plane may be moving and the brain sends a message to the hand to move the thumb on the transmitter.
The transmitter reads this change in stick position and sends out a signal to the air- craft telling it to move the ailerons. The re- ceiver then interprets this change and sends a signal to the servo which moves the motors and gears within it so the ailerons will move to the new location, and the lift distribution
will be altered on the wing causing the wing to move back up if the pilot has interpreted the movement correctly.
This is a very long and loose feedback loop. Granted it happens very quickly, but the AS3X system has a much shorter and tighter feedback loop and goes like this. Aircraft wing dips. AS3X sensor on that axis senses movement. AS3X system sends command to aileron servos to move. Wing lift distribution changes and causes wing to move back up. A much shorter, quicker and tighter feedback loop. This is what makes the AS3X system make such a small model feel like the model is a much bigger and more stable model. The AS3X is making lots of these corrections all the time and doing it very fast.
This sort of system is what makes planes
like the F-16 (first front line fighter with a fly by wire active flight control system) fly like it does and allows a plane like the F-117 (dubbed by its pilots the “Wobbling Goblin”) able to even fly at all. (For more information see this material at
http://aerostudents.com/ files/automaticFlightControl/stabilityAug- mentationSystems.pdf).
Later in the 1990s NASA was looking at technologies like this and others for incorpo- ration into general aviation aircraft to in- crease their utility to the general population by making airplanes easier for the average individual to fly and navigate and allow sig- nificant reductions in pilot workload via a “Highway in the Sky”. Many of these tech-
Sbach 3D and its accessories (at left) out of the box. Don’t throw away the box as it makes a very handy hangar for your new model aircraft. The side force generators (above) come in two configurations. Ones on the left provide moderate increase in rudder authority. Ones on the right are for extreme 3D and provide additional rudder authority. Instruction booklet suggests flying the model without these units to start with and then decide if you want them. Once installed they need to be cemented firmly in place with foam friendly CA adhesive.
FLYING MODELS 51
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