Flight Technique: Are You Set Up for Success?
Why too much travel and expo can hinder your progress
Why too much travel and expo can hinder your progress
This month, I will take a break from addressing good and bad flying habits to focus on common control setup mistakes that often lead to a variety of bad habits and other problems. As usual, the following information centers around improving low (normal) rate “precision” flight control, as opposed to the entirely different setup required to perform extreme 3D stunts. The most important step when setting up an airplane is to first determine what kind of flying you will be doing and then to keep that in mind at each step of the setup process. You also need to recognize that the low-rate control throws and exponential (expo) percentages suggested by a plane’s manufacturer are merely starting points. Pilots who want to perform at their best must subsequently adjust the control throws and expo to suit their immediate skill level (that is, an advanced pilot is not going to prefer the same settings as the average sport flier, and vice versa). A willingness to change control settings is especially important in view of the significant influence of 3D flying on the sport. As you know, 3D flying requires setting up an airplane with very large control-surface deflections along with large amounts of expo to make the plane otherwise manageable. 3D setup standards have tipped the scales so far that, no matter what type of plane you put together today, the manufacturer’s recommended low rates almost always prove to be too much for most pilots. Pilots who want precision handling will often need to reduce the manufacturer’s low-rate percentages to be able to comfortably take off, maneuver, and land—at least that is what traditionally would be done by those who base their setup on first-hand experience rather than hype or hypotheticals.
THE “WET NOODLE” EFFECT VERSUS ONE-TO-ONE CORRELATION
In the current era, pilots quite often forgo reducing lowrate control-surface travels when the plane proves to be too sensitive in favor of introducing more expo. Indeed, many pilots have convinced themselves that using large amounts of expo enables them to achieve the best of both worlds—i.e., keep larger low-rate control-surface travels in case they’re needed and offset them with larger amounts of expo. On the surface, that seems to make sense, and frankly, it would be great if it were that simple. The reality, however, is that large amounts of expo remove the oneto-one correlation between the pilot’s control inputs and the response of the plane that is so crucial to flying with precision.
Put simply, flying with excessive amounts of expo on low rates is akin to driving an older car or riding lawnmower in which the steering is no longer tight and linear but rather has become sloppy and irregular. If you’ve never driven a vehicle that lags or doesn’t directly correspond to the steering inputs, you won’t fully appreciate the analogy.
But if you have, you no doubt recall how difficult—if not impossible—it was just to try to maintain a straight line.
You will also recall that, as a result of the slop/lag, you were always playing catch-up and had to make constant corrections. Contrast that to the predictability and rest periods that you get between inputs when driving a newer vehicle with a tight, linear steering response. Hence, whether flying or driving, the key to precise maneuvering is “positive” control that enables you to anticipate results and correct any unwanted movements the instant they occur, along with reducing the number and size of adjustments needed (Figure 1).
The specific challenge of flying with excessive expo and a nonlinear soft center—aka the “wet noodle”— control response is that the lack of positive control allows deviations to grow larger before the pilot’s corrections begin to have a noticeable effect. Of course, the larger the deviation becomes, the larger the correction also ends up becoming, which then also has to be corrected. This is particularly problematic near the ground because pilots tend to not be quite as patient (Figure 2). When pilots, for example, fail to get the response they need after the initial attempt to correct a deviation, they will naturally increase the size of the input. When they do, the exponential increase kicks in and they get more reaction than was expected or needed, thus prompting the need for additional corrections. (See YouTube for endless rollercoaster landing examples.)
Obviously, there are pilots who can fly well despite using excessive expo, but it is harder to fly precisely, particularly in turbulence, and they have to make far more control inputs than those who aren’t flying with excessive expo. It is, therefore, common for those who fly with excessive expo to plateau within a few years due to their constant corrections, not leaving any openings for learning new maneuvers or dealing with wind.
To be clear, expo is awesome and enables us to achieve the most honest and precise-handling airplane possible. It’s too much expo that creates problems! A certain amount of expo is always needed to offset the changing geometry of the rotating servo arm, which causes the control surface to initially deflect at a higher (faster) rate than it does approaching the travel limit. As a rule, approximately 10 to 15% expo on low rates is a good starting point to
EXPO IS AWESOME AND ENABLES US TO ACHIEVE THE MOST HONEST AND PRECISEHANDLING AIRPLANE POSSIBLE.
compensate for the changing servo-arm geometry and achieve a linear deflection rate throughout. If your plane has oversize 3D control surfaces, start with approximately
20 to 25% expo to help compensate for the inherent greater sensitivity. (You can be fairly certain that an airplane has oversize control surfaces whenever “3D” is mentioned in its ad description.)
When precision is the aim, expo should never be used to make a plane docile or to compensate for a poor setup or overcontrolling tendencies. If the plane is too responsive, the correct response is to reduce the low-rate percentage before you start adding more expo. When low rates have been optimized for takeoff, landing, and precision flying, the aim is to use just enough expo to achieve a linear control response and thus retain a “connected” control feel between you and the plane, like the feel of a brand-new car.
If you later run into a scenario or your flying progresses to a point of needing to add more travel, you will then need to add more expo to maintain the same general handling. If you start sensing, however, a lag or “wet noodle” control feel between your inputs and the airplane, you’ve gone too far with the expo and can expect it to become difficult to make the plane do precisely what you want if you don’t reduce it.
DON’T SET UP FOR FAILURE
Another reason people continue to fly with too much travel/expo is the “Tim ‘The Tool Man’ Taylor” way of thinking—that is, if some is good, more must be better! Sometimes the justification for this mindset is wanting plenty of control to recover if the pilot gets into serious trouble or in case something goes drastically wrong with the airplane, such as a wing failure or a servo breaking loose. I make sure my planes are airworthy before flying and set them up the way I like to fly them, not for some unlikely or remote event. That said, if a pilot is getting into serious trouble with a setup he’s comfortable with, he frankly has much bigger problems than how the plane is set up. Honestly, can you ever recall a situation where more control made things better and not worse? More control almost always aggravates mistakes, but more to the point, flying with more travel than you’re comfortable with increases the odds of overcontrolling and, therefore, getting into serious trouble!
The point is that, if you were going to make a mistake initially setting up a plane, it’s always better to err on the tame side, knowing that you can always add more.
That way, when your heart is pounding and hands are shaking for the first flight or two, at least the plane will fly smoothly. You might even end up pleasantly surprised by how easy it is to fly and, more important, to land. As a result, all the nervous thoughts about whether the flight will turn out well are soon replaced with thoughts about making it even better when you get it back on the ground.
What if a pilot cut way back on the manufacturer’s recommended low rates and subsequently found the controls to be too mild? There are a couple scenarios where that could become a problem: (1) You may not be able to recover if you get into serious trouble (once again, if you’re getting into serious trouble with a mild-handling airplane, there are bigger problems than how the plane is set up), and (2) you may not be able to correct in time if turbulence severely upsets the plane during landing. In reality, that would never happen because no one test-flies a new airplane in severe turbulence. In the meantime, if the controls were deemed to be too mild, you would have increased them prior to flying in turbulence. In fact, the reason you’d be flying in severe turbulence in the first place is because your confidence in your ability to fly the plane is sky-high.
Contrast that with those who employ the “Tim ‘The
Tool Man’ Taylor” approach when setting up a new plane: In addition to increasing the potential for overcontrolling and damaging the plane, these pilots usually experience so much stress and anxiety during the early flights that it takes half the summer before they can fly the aircraft without tensing up!
THE PROOF IS IN THE RESULTS
I will conclude with a relevant story. If you get the point, you will appreciate one of the main reasons why so many pilots fail to make steady progress, and as a result, you’ll know what to do to start on the path to improved flying
IF YOU ARE ONE OF THE MANY PILOTS WHO ARE FLYING WITH TOO MUCH EXPO AND TRAVEL, IT WOULD HELP EXPLAIN WHY YOUR FLYING HAS BECOME STAGNANT.
and better landings. A decade ago, a retired engineer from Canada came to my flight school for solo training.
I’ll call him Ron. Ron was exceptionally thoughtful and well prepared, so much so that he contacted me prior to attending for advice on the plane, engine, and radio combination that would most closely match what he would be flying at the school. After completing the course, Ron returned home to his private flying site to consolidate what he had learned. A few months later, he contacted me to tell me he had mastered his landings and low-level flying and wanted to sign up for basic aerobatic training. He once again asked me to recommend an airplane, engine, and radio that would most closely match what he would be flying at the school. Ron brought his new plane to the flight school (a .60-size Super Stick), and once he was able to sequence together a variety of basic aerobatic maneuvers with one of the school planes, we test-flew his plane. We made some adjustments to suit his skill level, then he flew his plane the rest of the course. A few months later, he called to tell me that he was getting really comfortable with his “airshow” routine and wanted to enroll in the precision aerobatics course. The next year, Ron showed up for class an hour early to tell me that he had recently crashed his plane. He proceeded to tell me that he became bored flying by himself, so he joined the local club, and because he could perform a variety of maneuvers one after another, he quickly became a star at his club field. At one point, he got the bug to practice inverted flight, up high at first and then gradually lower. During a low (20-foot) inverted pass over the runway, the plane unexpectedly dipped and Ron reflexively “pulled” up. Of course, the instant he pulled, he realized his mistake and started “pushing,” but there wasn’t enough altitude to recover and the plane disintegrated down the runway with several people watching. Because the wreckage was strewn down the runway, it took a group effort to pick up all the pieces. When a few of the members asked Ron what had happened, he admitted to going the wrong way with the elevator. That is when the group (including Ron) came to a consensus that if he had more elevator travel, he would have been able to save the plane. Hence, Ron suggested that when I “dial in” the planes that students bring to the flight school, I need to remember that back home they will continue to push their envelope. He suggested that I should set them up with a little extra travel to help them recover more quickly in case they make mistakes.
Here’s where we test your powers of perception: First of all, by setting up Ron’s airplanes to match his immediate skill level, he flew for two years without a single mishap and became the star flier at his club. Indeed, his success and confidence is what prompted him to try new things. You could say that Ron’s crash wasn’t the fault of the setup but actually a good sign, for he would not have been flying inverted low to the ground if his progress wasn’t so rapid and confidence so high. Indeed, if the airplane wasn’t so comfortable to fly, he might still be working on landings and individual stunts instead of all the maneuvers he was trying.
So when Ron looked to me for confirmation, I politely responded, “Ron, if you think about it, you’ll realize that it is just the opposite.” He paused for two seconds and then his eyes suddenly became wide when it hit him that if his plane had more travel, he would have put it into the ground even faster! With the way the plane had been set up, at least he was able to realize his mistake and had time to switch the elevator input and almost save the plane.
I know that what has been presented here goes against the “more is better” trend of late. If you, however, are one of the many pilots who are flying with too much expo and travel, it would help explain why your flying has become stagnant. Thus, what harm is there in setting aside your normal routine for one day to set up a mode with lower rates and 25% or less expo that you can switch to for a few minutes each flight? Note that it will take more than one flight to break the habit of nonstop corrections that will no longer be needed before you will be able to properly fine-tune and assess the difference compared to your normal setup. If you then come to the realization that flying with positive control feels superior in the same way it does with every other vehicle you operate, welcome to the club and happy flying.