UPDATE 7/13/2013: After flying with the heading hold gyro mode, called "3D Control Mode," for a while I am going to downgrade the F-TEK to a B overall. I don’t like the frequent heading resets, others might like it fine.This gyro is best suited to people who will click it on for some maneuvers and off for (most) others.
Another issue is the mushy plastic of the gain control potentiometers, which degrade too quickly.
I’ll soon be adding the F-TEK 30A to the list of Z8RC-tested Gyro systems. This one is a little cooler, and more expensive at $93, as it combines 3-axis inertial accelerometer with a 3-axis gyro. Three flight modes are programmable to any 3-position radio switch, knob or slider. A 2-position switch can be used to select between Mode 1 or 3, or with mixing, two 2-position switches can be used to access all three modes. The modes are:
- Mode 1 turns the unit off
- Mode 2 is called “3D Control Mode,” it acts like a 3-Axis gyro in tending to resist uncommanded aircraft movement, but adds inertial information that tends to hold the computer-assisted inputs until the plane returns to it’s last commanded attitude
- Mode 3 is called “Emergency Recovery” and it attempts to level the wings while returning pitch attitude to a saved, stored position whenever the controls are neutralized. The F-TEK memorizes a designated attitude, which is perfectly level by default, but user-assignable within a certain tolerance range
Essentially, the unit enables an “attitude hold” Auto-Pilot function, where the attitude is pre-selected. There is also a GPS and barometric pressure enabled version (F-TEK 31AP) that allows automatic altitude control, programmable point-to-point autopilot navigation, and a return to starting point function for about $220. Return to and orbit the starting point is automatic upon a lost signal
• Easy installation
• 3-axis accelerometer and 3-axis gyro stabilization
• Self-leveling flight stabilization
• 3 flight modes selectable by transmitter
• Easy access gain adjustments for flight tuning
• F-TEK 30A Flight Controller
• USB connection cable
• Required wire leads and mounting accessories
F-TEK 31AP includes GPS point to point navigation, barometric altitude hold, and return to starting point functions
The F-TEK 30A package is more complete than most aircraft gyros.
The F-TEK 30A provides at least twice the stabilization of other 3-axis gyros—which isn’t always good.
Like all aircraft flight controls, the F-TEK takes some getting used to. But where other gyros blend into the background most of the time, this gyro system is more prominent in 3D mode, and has an overwhelming presence in Emergency recovery mode, by design. I’ll take it mode by mode, then provide a few video examples:
Mode 1: OFF
There shouldn’t be much to say about turning the unit off, but there is, because unlike many gyros with an on/off function, this one actually works. For starters the F-TEK provides a transmitter on/off switch, which many gyros do not. This is invaluable because gyro stabilization has drawbacks as well as benefits, so the ability to quickly click the unit off can eliminate most of the drawbacks. Second, in off mode, the gyro is completely out of the control loop, not just gained down very low and/or causing servos to react slightly differently. Off = gone. Nice.
Mode 2: 3D Control Mode
As stated above, in this mode the F-TEK provides at least twice the stabilization as any of the other gyros I’ve tested. This is great for maneuvers that tend to stabilize on a line, like inverted flight and Knife Edge. It is not good for maneuvers that change direction, like simple turns or tumbles. This is basically true of all gyros, so this balance of benefits and drawbacks is not unique to the F-TEK, only more pronounced because it is better at holding the aircraft steady.
For the times you want stabilization, the 30A is pretty amazing. For example, the Sbach 342 serving as my test platform requires a dose of forward elevator pressure to maintain inverted flight. With Mode 2 engaged, the plane requires very little push to stay arrow straight. Most gyros have some impact on inverted flight or Knife Edge flight, but continuously succumb to gravity over time since they do not remember or strive to hold an initial attitude, they only resist uncommanded changes from the current condition.
That probably sounds pretty cool, and it is, but there is an unintended consequence to this approach. I am still getting used to the gyro, but it is easy to accidentally reset the last commanded attitude, which is a problem. To illustrate what can happen, let’s say you are doing a Knife Edge 360 degree circle at 100 feet altitude. Normally, you’d roll the wings to 90 degrees and blend the appropriate amount of rudder and throttle to maintain Knife Edge flight, then use elevator to create the circular flight path. With the F-TEK engaged, as you roll some rudder is blended automatically to keep the nose up, so you don’t need as much rudder stick deflection to establish a platform. Eventually, some combination of stick deflection and gyro-commanded rudder create the total steady state rudder input as the plane carves around the circle. Now let’s say the plane starts to climb a little, so you relax your rudder input. If you relax your portion of the rudder input to the point of hitting the neutral stick position, the gyro resets it’s goal of holding the last commanded position, so it releases it’s portion of the rudder input too, causing the nose to fall unexpectedly the instant the stick centers.
It is easy to demonstrate this problem. Start a simple turn from level flight by banking the wings and blending a touch of elevator, leave the rudder neutral. The plane wants to turn due to the bank and elevator, but the rudder gyro wants to maintain the initial course, so it starts to fight the turn causing the airplane to slip heavily around the turning flight path. So far in this scenario, the rudder stick has not moved from center. Now, let’s say you make a throttle input that unintentionally creates a tiny rudder stick signal, no matter how small, then the tail instantly snaps out of the induced slip and gets inline with the current heading. This feels wrong in the air, because you did nothing that should affect a yaw change.
It’s hard to say if this is “a problem” inherent to F-TEK’s approach, or a drawback balanced by getting some pretty nifty new tools. If you adopt the latter point of view, it follows that as you become more proficient with the gyro, you might click it on to exploit its advantages then click it off to avoid the pitfalls.
A related “issue” is the need to constantly “fly the tail around” during turns, helicopter style. Like a heli, the airplane’s tail becomes very resistant to weathervaning, giving the appearance of strong adverse yaw. This flight characteristic forces consistent use of the rudder, which isn’t all bad.
Hovering ease is improved, even a little more than a traditional gyro.
Overall, the level of stabilization offered by the F-TEK in Mode 2 is unmatched by other gyros I’ve tested. That definitely comes at the expense of some extreme maneuverability (when turned on), but F-TEK Mode 2 did not limit maneuverability as much as traditional gyros I’ve tested.
Mode 3: Emergency Recovery Mode
This mode is even more interesting than Mode 2.
If you only use Mode 3 to recover the plane from orientation woes, then it is undoubtedly a thing of goodness. To use it, engage the transmitter switch and set the throttle to a cruise setting. The plane instantly rolls upright and establishes the memorized level attitude. It works great.
It is tempting to use Mode 3 as a basic training mode, since all you have to do is “let go” and the plane re-levels itself. It’s a little like the good ‘ol F-16 autopilot trick, where some guys would set the autopilot to “altitude hold” before a dogfight, then hold the spring-loaded pinky paddle switch to temporarily disengage it while fighting. If the Gs put you to sleep, your hand would fall off the stick and the spring loaded paddle switch would open, the autopilot would engage and attempt hold your current altitude.
Unfortunately, Mode 3 only allows 30 degrees of commanded bank while it is engaged, so maneuvering the plane is onerous and turn radii become very large. The Instruction Manual warns:
f) Warning: The Auto Stabilization Mode will provide a smoother leveled landing for your aircraft. However, note that the turning radius is larger when in this mode. Please ensure your landing area has adequate clearance for this larger radius.
When I read that, I thought it was because the gyro inputs might counter a bit of your control inputs, and thus could be overcome by the pilot if desired. But in fact, a ground test confirms that the F-TEK phases out any pilot commands after the plane hits 30 degrees of bank. If the plane exceeds 30 degrees for some reason, the gyro issues proportional reverse aileron to command the plane back to a maximum of 30 degrees of bank. If the aileron stick is released, the plane automatically returns to, and holds, level flight. So it is impossible to turn tightly in Mode 3, no matter what you do with the sticks.
Mode 3’s behavior feels unnatural and is overbearing for basic flight training, but there is no doubt that it would be harder to crash if one fully understood the mode’s maneuverability limitations. For those with no choice or a strong desire to self-teach, Mode 3 is an option to be considered.
I have not attempted to land in Mode 3 as of this writing.
Here are a few video comparisons with the test airplane in Mode 2. These were the first few flights with the both the plane and the gyro, so I sucked a lot more than necessary. In fact, the first landing is from the Maiden:
The Sbach’s tail wheel has an adjustable spring tension. I left it way too loosey goosey for manual takeoff tracking, but the F-TEK tackled it with ease:
Note the desire to knife edge as the rudder resistance to yaw builds:
Extreme maneuverability is reduced, as expected, but the F-TEK’s impact is lighter and smoother than traditional gyros:
My flare combined with the F-TEK’s desire to hold attitude resulted in a big balloon, but the stability of the gyro still aided a reasonably smooth touchdown. Consistent control during landing would be easily mastered with practice. The landing roll is phenomenally straight considering my Sbachs very squirrelly tail wheel under (too) low spring tension:
This is a hard grade, because the F-TEK 30A takes basic flight stabilization to another level, but it’s accelerometer-based approach brings a few logical quirks. Technically/mechanically, the unit performed flawlessly. If you take the time to learn explore the quirks in benign situations and understand the unit’s limitations, I think the the improved stabilization capabilities and Emergency Recovery Mode definitely outweigh the limitations and justify the price: A+