Flight Technique/Setup for Precision Control
Don’t be misled by the numbers or hype!
Don’t be misled by the numbers or hype!
This month, I will be taking a break from addressing good and bad flying habits to point out some common control-setup mistakes that diminish “precision” flight control. Logic dictates that the “best” airplane setup is the one that best complements the type of flying a person does most often. Most fliers in the sport aspire mainly to execute nice takeoffs and landings, racetrack patterns, loops and rolls, and similar maneuvers. The problem is that all too often people forgo the setup standards that would complement the majority of flying they do and, instead, set up their planes for extreme scenarios or 3D stunts they rarely, if ever, attempt or encounter.
A prime example of this is hooking up the control pushrods or cables to the outside holes of long servo arms. This is normally done to achieve the large control-surface deflections needed to fly 3D or to appease a primitive “more is better” mindset. Since everything in aviation is a tradeoff, however, the consequence for mechanically setting up an airplane with large control-surface deflections is that precision handling is sacrificed.
Before I explain why, it is important to mention that becoming a 3D pilot requires massive amounts of practice and lightning-fast reflexes. Hence, the reality is that most people in this sport won’t ever be able to fly 3D but will remain sport and/or scale fliers. So the question is, why do so many sport pilots set up their planes with essentially a 3D control setup?
The answer is that there is the widespread belief that large amounts of exponential (expo) can be used to achieve the best of both worlds—that is, a person can set up large control-surface travels in case they’re needed but use large amounts of exponential to make the plane also easier to handle. On the surface, that seems to make sense, and frankly, it would be great if it were that simple. Anytime large amounts of expo are used, however, pilots lose the oneto-one correlation between their control inputs and the response of the plane that is so critical to flying with precision. (Imagine how difficult your car would be to drive if the linear steering response was replaced with irregular steering that was noticeably sluggish or unresponsive around neutral but then exponentially increased the farther you moved the wheel.)
Furthermore, hooking up the controls to the ends of long servo arms significantly degrades control “resolution.” Here’s what we mean by “resolution”: A servo’s movement corresponds to the percentage or “steps” programmed into the radio. Increasing and decreasing the travel percentage in the radio increases or decreases travel by adding or removing steps (you can see this by holding the control stick at maximum and watching the control surface notch up a step as you increase the travel percentage). Connecting the pushrod closer to the center of the servo arm results in a very small (fine) amount of control movement with each step (Figure 1). Consequently, a higher travel percentage has to be programmed into the radio to achieve a given travel, thereby increasing the “resolution” of a given control-surface movement. As a result, handling and control becomes noticeably smoother and more precise.
Conversely, connecting the pushrod near the end of the servo arm sacrifices resolution and results in a coarser (abrupt) controlsurface movement. Of course, 3D pilots must sacrifice resolution to achieve the large travels necessary to perform extreme 3D stunts. By doing so, however, those planes are harder to fly precisely and feel less “connected” due to the large amounts of expo they require. That is why pro pilots who fly both precision and 3D often dedicate different airplanes for each flying style, with the control hookup locations being one of the primary differences. Certainly, a select few can do both at a high level with the same airplane; however, the precision side requires exponentially more concentration and effort on their part to avoid seeing the plane twitch every time the controls are moved.
That said, prior to attaching the pushrods, you will need to decide whether the plane will be used primarily for precision flying or 3D, and if you’re smart, you’ll optimize the setup for what you do most often. When your aim is to fly with utmost precision handling and control, you’ll want to connect the pushrods or cables to the holes closest to the center of the servos, and the furthest-out holes on the control horns to achieve maximum resolution (Figure 2). You’ll then increase or decrease the radio percentages to initially achieve the recommended travel and later the desired handling. If you max out the percentage in the radio and still need more travel, you will then have to sacrifice some resolution by moving the pushrod out on the servo arm and/or closer to the control surface.
DON’T BE FOOLED BY THE NUMBERS
If you page through any modelaviation magazine or site today, it’s obvious that the sport is heavily oriented toward 3D flying. The influence of 3D has so severely tipped the scales that, whether you’re flying an aerobatic airplane or a warbird, the manufacturer’s recommended low- (normal-) rate travels often prove to be too much for most pilots. Pilots aiming for precision handling will, therefore, often find it necessary to reduce the manufacturer’s low-rate percentages to be able to take off, maneuver, and land comfortably.
Accomplished pilots wouldn’t hesitate to change the rates to whatever feels best. Yet the average pilot often lacks the confidence to deviate from what the manual says, despite sensing firsthand the need for a change. If you’re ever going to realize your full potential as a pilot, you need to understand that the low-rate control throws and exponential
percentages suggested by a plane’s manufacturer are merely starting points. Pilots who want to perform at their best must subsequently adjust the rates to suit their immediate skill level.
Back in the day, when a plane was too sensitive, the operator would simply move the control hookup to a different hole on the servo arm or control horn. The advent of programmable radios, however, has led to a phenomenon that often hinders pilots from making the correct adjustments to their control setups. That is, pilots are prone to making assumptions based on the numbers displayed on the transmitter screen rather than basing the setup on how the plane is actually flying.
This phenomenon is never more on display than in the springtime when large numbers of people are test flying their new planes. A pilot will set up his new plane, for example, according to the recommended control throws or maybe add a little extra “just in case.” During the test flight, the elevator proves to be overly responsive, but he’s able to get the plane back on the ground in one piece. He then accesses the menu and sees that the low-rate elevator is at 60%, so he reduces it to 55% and flies again. The plane still proves to be hard to control, so after landing, he reduces the elevator to 50%. After another challenging flight/landing, he reduces the elevator to 45%, or maybe 40%, but now he’s becoming skeptical because the changes don’t seem to be having much effect. He also starts to worry about going too far and whether he’ll have enough control when he needs it. Did you get that? Even though the elevator is too sensitive and he barely needs to move the stick while landing, he’s worried about not having enough control! He thinks this because the numbers displayed on the screen are a lot less than what he started with. So he gives up on further reducing the low-rate elevator travel and instead starts adding more exponential. After several more flights of continuing to add more expo, he achieves his goal in which the airplane is no longer overly sensitive. It has, however, become more difficult to make the plane do what he wants because of the grossly irregularly control response he’s programmed into it. At this point, he might even start faulting the plane, along with making excuses not to fly it because everything he has tried hasn’t worked as expected.
If you haven’t figured it out yet, the reason the early travel changes seemed to be having little effect is because the plane was set up with such large throws to start with that 5, 10, and 20% reductions simply didn’t go far enough. It’s not uncommon for those of us who fly dedicated 3D airplanes to end up with, for example, as little as 20% or 25% on the low-rate elevator we use to take off and land with. Yet even when pilots are damaging their planes on landing because the elevator is so difficult to manage, few people can bring themselves to ignore the numbers and keep reducing the low-rate elevator until it’s to their liking.
OPTIMIZING EXPO
For reasons I’ve explained in other articles, a certain amount of expo is necessary to achieve optimal handling. Assuming your aim is precision and you have adjusted the low rates to match your flying style, the objective is to use just enough expo to achieve a linear control response and thus a “connected” to-the-airplane feel similar to the feel of driving a brand-new car. As a rule, approximately 10 to 15% expo on low rates is a good starting point; however, if your plane features oversized 3D control surfaces, start with approximately 20 to 25% expo to help compensate for the inherent greater sensitivity. When you eventually run into a scenario or progress to a point of needing to add more travel, you will need to add more expo as well to maintain the same general handling. If you start sensing a lag or “wet-noodle” control feel between your inputs and the airplane, however, you’ve gone too far with the expo. In that case, you will need to reduce it or you will find it more difficult to take off, maneuver, and land with precision. (See YouTube for countless examples of rollercoaster landings!)
CRAWL-WALK-RUN
Too much travel and expo are almost entirely responsible for the
flood of low-time airplanes that are put up for sale each summer after they prove to be less than enjoyable to fly. Thus, you can end up with great-flying, nearly new airplanes for a fraction of what they would have cost new simply by correcting those issues. I must warn you, however, that if you buy one of those planes and set it up with less travel and improved resolution, and then the prior owner sees you greasing landings with it and sees how well it handles the wind and appears to be on rails,
he might become quite upset.
That aside, the biggest advantage of setting your planes to match your skill level is how much faster you will improve.
The fact is that your comfort and, therefore, confidence play a bigger role in advancing your skills than how fancy your equipment is or how much you practice. (If all it took were the latter, half of the active fliers in your club would be experts!) It is when your plane is comfortable to fly—and especially to land—that you’ll naturally
start thinking about trying new things. Indeed, if it’s comfortable to fly, you will likely soon want to increase the travels to make the airplane sportier or maybe even want to try some 3D flying.
Sadly, many pilots set up their planes for the way they want to fly them in the future or with some remote event in mind and, as a result, make them more difficult to fly in the meantime. Hence, whatever aspirations they had are subsequently pushed further into the future because of the extra time it takes to get used to their planes. That’s especially true if they end up having to make repairs or the first flights are so challenging that they subsequently tense up every time they fly. The point is this: Although modern technology has expanded the number of setup options available to pilots, the one thing that hasn’t changed is that pilots (humans) still learn best when they adhere to the timeless principle of crawl-walk-run.
Good luck!