ECO-nomical Autopilot

And now for an autopilot thats completely different.

1

The aileron control tab is simple and easy to install. The servo mounts to a close-out plate installed like an inspection cover in the aileron.

Forty years ago, when I had the money to rent an airplane fancy enough to sport actual upholstery, it was not uncommon for those Cessna 172s or Piper Arrows to have autopilots installed in the panel. The only problem was, we never dared use them. The primitive technology used in those days did not work well (or at all) in a rental fleet. If you engaged them, they were as likely to roll you inverted or take you someplace you didn’t want to go as they were to actually help out on a long cross-country.

The digital revolution has changed all that, and nowhere as much as in Experimental aviation. Modern autopilots can fly just about every aspect of a cross-country flight—including the approach and holds if necessary—better and more efficiently than their flesh-and-blood operators.

One of the leading dedicated autopilot manufacturers in the Experimental world is TruTrak Flight Systems, based in Springdale, Arkansas. Company founder Jim Younkin started out in the aviation business as the father of the Century series of autopilots, but later developed the earliest digital units under his own company. The DFC, Altrak, Digiflight, Digiflight II, and Sorcerer are found in countless Experimentals, and have been joined recently by the newer Vizion units—all of which are amazing when it comes to flying an airplane in smooth, bumpy, or IFR conditions. But as capability has increased, so has complexity, and the current owner, Andrew Barker, had an urge to build a simple, inexpensive, two-axis autopilot for those who only need it to do a few things: hold a heading, hold altitude, and hey—while, you’re at it, can it follow the magenta line on my GPS’s moving map?

The entire autopilot controller fits in the control head and takes almost no space in the panel. Combined with the tiny servos, it adds less than a pound to the average aircraft, depending on the amount of wire needed.

Airshow coverage sponsor:

The results of this desire are now available in the ECO autopilot from TruTrak. Targeted to cost right at $1,000, the ECO does just a few things—and does them very well. As an autopilot, it carries out those three basic functions—heading hold, nav track, and altitude hold—and most of the time, who actually needs more on a VFR cross-country? (If you just have to have the airplane do a teardrop entry to a hold while descending and capturing a new altitude, TruTrak will still be glad to sell you one of their more capable units.)

But this box does more than just provide an autopilot. Barker is a firm believer in doing something to decrease the number of accidents caused by loss of control—pilots simply getting outside of their comfort zone or envelope. The ECO is designed to provide full-time automatic envelope protection (AEP). Basically, it helps warn the pilot of overbanking or getting into a high- or low-pitch situation.

Remember when you first flew with an instructor, and they might have given you a little help by keeping two fingers on the stick, adding just a touch of pressure to nudge you back in the right direction? This is exactly what the ECO does; it provides a little restoring effort to the controls when it senses the pilot is flying outside of a defined attitude box.

ECO servos are easily mounted to a close-out plate with aluminum angle. When the plate is installed, the servo will be inside the aileron or elevator.

Architecture and Installation

The ECO is very different from most current autopilots because it uses small high-quality R/C servos and piano-hinge trim tabs to “fly” the control surfaces, rather than moving control cables and pushrods directly. The control head fits a 2-inch hole and is about an inch thick. It needs power and ground, plus a serial GPS input. Three wires go to each servo, and the servos can be embedded in the control surface or mounted externally. This is a simple add-on to an existing plane.

The tabs are actually nothing more than a wide piece of piano hinge, sized lengthwise to match the authority needed for the size of airplane on which they will be installed. On the RV-10 we flew for this test, the tabs were about nine inches long. Riveted to the tab is a control horn, and this is connected to the servo via a simple pushrod. The servo itself is mounted to a plate in the control surface—one aileron and the elevator each need a servo for two-axis control. The tabs are pop-riveted to the trailing edge, much in the fashion of a fixed tab that you bend to correct for an out-of-trim airplane.

The ECO control head fits in a 2-inch hole (here it is installed in an adapter plate) and has a highly readable color display and just two buttons.

Installing the servos in the control surface is simple: TruTrak supplies a template for you to use for cutting a rectangular hole the proper size, then you install nut plates around the perimeter, much as you would for an inspection hole. The servo itself is mounted to a cover plate, and the plate screwed on to the hole. The pushrod exits through a slot cut in the skin, extending out the back of the mounting hole. Probably the longest part of the installation will be running wires through the wing and to the tail (this is when you will be wishing that you ran a string through a conduit when assembling the wings because you could use it to pull those wires now.).

Adding the control head to the panel is just as simple: Cut or find a 2-inch hole, add power and ground, and run a serial data line from your GPS. The ECO will listen to steering commands from any GPS that is tracking to a waypoint—simple as that.

More Than an Autopilot

While Barker’s dream to provide a simple autopilot for a low price might seem grand enough for anyone with a simple VFR airplane, there is far more to the ECO concept than just flying the airplane while the pilot enjoys the view and manages the flight. Heeding the current call by the FAA to do something about the continued high rate of Loss of Control (LOC) accidents, Barker realized that this simple autopilot had all the hardware necessary to give the casual pilot a little help now and then—all it would take was a little software, since the mechanics were already in place.

With both roll and pitch channels available for control, it was simple to envision that you could let the system sense current bank and pitch attitude regardless of whether or not the autopilot was engaged, and if pre-set limits for either axis were exceeded, give the system the authority to move the airplane back toward center. The system is, by default, armed to help the pilot anytime it is powered. It can be disabled at any time with the simultaneous push of two buttons if the pilot would rather not have the help, and the actual limits at which it starts to help the pilot are adjustable.

TruTrak president Andrew Barker preflights the aileron servo and tab before a demo flight.

Now the argument over airplanes that protect the pilot from himself is an old one, debated anywhere two or three pilots get together over adult beverages. The phrase, “If it ain’t Boeing, I ain’t going,” is a well-worn dig at the Airbus line of aircraft that have built-in envelope protection as part of their fly-by-wire software design. The truth is that almost all fly-by-wire systems have some sort of protection—the only question is how hard it is for a pilot to override it if they determine that it is being applied inappropriately. For those on the side of understanding the benefits of a protection system, but who want to be the final authority on what the airplane does, the ECO system is good news—for it is much easier to override than a typical engaged autopilot.

The way the system works, flying by trimtab, when the AEP kicks in to correct what it perceives to be an overbank condition, the pilot does not feel a significant push on the stick, as they might with a typical autopilot servo connected directly to the control system, Rather, the force felt is simply one of an out-of-trim condition—easy to override in just about any light single you are likely to find. As stated earlier, it is more of a tiny push back, as one might get from a good instructor trying to nudge an inattentive pilot back to the straight and narrow. Even as a fan of pilots having complete control, I found the AEP to be gentle and a nice feature. I’d probably set the limits fairly wide on a typical aerobatic-capable machine like many RVs, but on airplanes designed for smaller bank and pitch angles, I’d probably accept the nudge closer to the standard rate turn.

The wiring to the servos is simple—three conductors in a shield. It is very slender and easy to secure to a hinge point.

As currently designed the AEP reacts to excessive pitch angles, but Barker is still thinking this through. Pitch excursions can be determined by speed, pitch angle, or angle of attack (AoA), and while pitch is the current parameter, he admits that to prevent the standard stall/spin scenario, AoA would be superior to the other two. Currently, the ECO does not sense any air pressures, and adding either an airspeed or AoA sensor would require additional hardware—but it is something that he is considering to make it more useful in all potential LOC scenarios. We think that having AoA protection, at least as an optional component, would greatly enhance the capability of the AEP to keep a distracted pilot out of trouble.

Flying the ECO Autopilot

So how does it fly? Remarkably well. In fact, it was hard to tell the difference between it and the much more sophisticated Sorcerer that was also installed in the airplane. We took off from our airpark runway with the envelope protection armed, but the autopilot disengaged. There is no drag from autopilot servos in the control system because there aren’t any connected to the control system. Barker engaged the Sorcerer as we climbed to altitude, mostly to let it automatically trim the airplane out—a neat feature of the top-of-the-line full authority unit. Both the Sorcerer and the ECO were listening to the serial output guidance of the Garmin 430W, so we could test them easily against each other. Once leveled at about 3,000 feet AGL, we engaged the ECO and let it hold pitch and heading. I was immediately impressed at the precision with which it did both. Even as we passed through mountain/wind-induced bumps, the ECO had plenty of authority to hold both pitch and roll to tight standards. Applying minor pressure on the stick to disturb the unit was easy, and the ECO just as easily drove straight back to the target values.

Setting a “Direct TO” course on the Garmin 430W to a waypoint about 15 miles behind us, we pushed and held the lateral control button to switch the ECO into nav mode. As soon as it engaged, it began a very nice standard rate turn to the right to intercept the course. Because it was actually getting left/right steering commands to the preset course line, it turned past the (now) direct heading to set up an intercept to the course, then tear-dropped onto the magenta line, again with crisp precision. During all this turning, altitude didn’t vary by more than 10 feet—and this was with bumps. Any question of the authority available with 9-inch trimtabs was dispelled with this demonstration.

Once established on course, we disengaged the ECO, reversed course, and did the same thing with the much more sophisticated Sorcerer. Aside from the bigger autopilot deciding to turn the other direction, you couldn’t really tell one from the other, except that maybe the ECO was just a little quicker rolling into the turn and crisper on the roll-out as well. Of course, it was easy to determine which autopilot was flying by pushing on the stick to try and drive them off course. The Sorcerer pushed back directly on the control stick through the control pushrods, while the ECO simply made the airplane feel out of trim. The ECO was definitely the more friendly of the two, while the Sorcerer was a bit more insistent.

The elevator tab installs just like the one on the aileron. External servos are being considered for tube-and-fabric airplanes to simplify construction.

Protect Me!

Next up—trying the automatic envelope protection. We disconnected the autopilot and began hand flying the RV-10, a wonderfully solid, yet responsive, airplane with plenty of speed. Entering a standard rate turn, I established a bank of about 30 degrees, then steepened it up to let the AEP show its stuff.

What I found most interesting was the way envelope protection felt. Because the autopilot is flying a trimtab, when it suggests that maybe you’re getting too steep in a turn, it pushes back on the stick simply by driving the airplane “out of trim.” This is a much more comfortable feeling than having a standard autopilot servo pushing directly on the controls. I flew a fairly steep military 8 (much to the chagrin of the envelope protection), and it just felt like I needed to re-trim the airplane—it was easy to do what I wanted regardless of the autopilot’s insistence that we return to normal flight. But it was also apparent that I was outside the envelope.

There are many aerobatic pilots who prefer to fly with the pitch trimmed for some force. This keeps tension on the controls and removes any “dead band” that you would feel if the airplane was trimmed neutral. This means that the pilot is always flying out of trim to some extent, and this is about how it felt to fly beyond the AEP’s designated envelope. It’s not much different than some older light planes that actually have no adjustable trim capability from the cockpit—you get used to holding a little stick all the time.

So, does that mean that it is easy to miss the ECO’s attempt to drive you back into the envelope? Not really. It is definitely noticeable—but not objectionable. The great thing about it is that if you intend to fly some aerobatics, you can press and hold both roll and pitch buttons simultaneously, and the AEP function will be disabled. Now you can fly without interference from the autopilot. I could easily see myself disabling the AEP for local fun flying, yet engaging it when I was IFR or flying in a high/hot/heavy situation where I could get close to the edges of the envelope.

I am sure that many of those pilots who object to the concept of envelope protection (the airplane protecting the pilot from himself) would find this demonstration to be eye-opening and, in the end, decide that the system is really not a bad thing to have. They might never have an inattentive moment, in which case, they’ll never need to know it’s there—but if it does activate, it will at least serve as an attention-getter and could just save them from a distraction that could lead to a serious mishap.

Great Potential

The ECO is a revolutionary product when it comes to providing capability for a reasonable price. For most of what pilots do with an autopilot, the ECO is more than enough to fill the bill—and that bill, at $1,000, is incredibly low. Envelope protection is a new feature to most pilots, and while we expect some to poo-poo it openly or behind closed doors, it really doesn’t hurt to have it. The feature can be easily disabled if you really want, the envelope can be set to whatever aggressive style you like—and it just might save a few lives. What’s not to like?

TruTrak’s ECO is not the first Experimental system to provide it—Garmin’s G3X includes envelope protection as well, but with a different implementation.

TruTrak plans to pursue certification of the ECO to help address the fact that it is not just Experimental pilots who have loss-of-control mishaps—or who might like to have an autopilot that doesn’t require a second mortgage to install. The fact that LOC accidents are high on the FAA’s current hit list makes the timing of the ECO release fortuitous, and bodes well for a potentially easy path to certification. Imagine all those Cessnas and Pipers with rudimentary autopilots out there—and the fact that they can get some LOC protection as well, for no additional charge. While Barker predicts that certification will increase the price by some amount, there is still no doubt that it will be far less than the cost of fixing—much less replacing—an old technology unit in any certified machine.

TruTrak has always been an Experimental avionics company, so it is exciting to see them turning their attention to the certified market as well. Experimental aviation should inform and provide new technology to the certified world; that is originally what Experimental airplanes did. Doing so in this case, with the ECO, could increase both safety and utility for thousands of aging airplanes that need new pilots—a win for the entire aviation community.

A Matter of Practical ECO-nomics

In a time when most avionics are getting more and more capable simply because we get excited by new features, the ECO is a step in the direction of economical flight with fewer features—for a much lower cost. We found the ECO was able to fly an airplane the size of an RV-10 effortlessly, and do so with the three features most pilots use the most. In addition, it can look over your shoulder and keep you within a pitch and roll envelope that you can define—not bad insurance if you get busy. We’d like to see an AoA module added to really improve the odds of avoiding that stall-spin accident, and it sounds like Andrew Barker at TruTrak believes that too. Yet even while that is under development, the ECO is an affordable alternative to a full-fledged autopilot—and yes, it flies just fine.

Previous articleEAA reacts: FAA reauthorization bill passes Senate committee
Next article"I Certify…."
Paul Dye
Paul Dye, KITPLANES® Editor at Large, retired as a Lead Flight Director for NASA’s Human Space Flight program, with 40 years of aerospace experience on everything from Cubs to the Space Shuttle. An avid homebuilder, he began flying and working on airplanes as a teen, and has experience with a wide range of construction techniques and materials. He flies an RV-8 that he built, an RV-3 that he built with his pilot wife, as well as a Dream Tundra they completed. Currently, they are building a Xenos motorglider. A commercially licensed pilot, he has logged over 5000 hours in many different types of aircraft and is an A&P, EAA Tech Counselor and Flight Advisor, as well as a member of the Homebuilder’s Council. He consults and collaborates in aerospace operations and flight-testing projects across the country.

1 COMMENT

  1. I have a Wittman Tailwind W8. Auto pilot? Not me…. until now. I am definitely interested and plan to give them a call.

LEAVE A REPLY

Please enter your comment!
Please enter your name here

This site uses Akismet to reduce spam. Learn how your comment data is processed.