Control Optimization

Transcription

1 Control Optimization Control Hookups Dual Rates Flight Modes/Conditions M AX R ES O LU T I O N EFLRS75 = PRECISION [D/R & EXPO] AILERON Pos-0 Low D/R 70% L 70% R Pos-1 High 100% L 100% R EXP +15% +15% +25% +25% Exponential Differential Mixing SURFACE DEFLECTION D LINEAR PRECISION 25% 50% 75% 100% STICK DEFLECTION NOTICE: Learning to program modern radios is unquestionably the greatest hurdle for most pilots. However, the simple solution is to create another model memory in the radio for each airplane that won t be used for flying so that you are free to learn and even experiment with the settings without any concern about messing things up. Also note that trying to learn how to program a radio sitting on a couch reading the manual does little good. For things to make sense, you must have the airplane in front of you with the switches on in order to see cause-and-effect. When concerns about making a mistake are removed because you re going to end up erasing the practice model memory at some point, you may actually find learning to program the radio stimulating and fun! 11

2 Control Setup Introduction There are a number of control setup fundamentals to consider before a pilot can begin taking advantage of the radio capabilities aimed at fine tuning a precision flying setup. Firstly, how a model handles (and thus the skills required to fly it) is mainly determined by how fast and how far the control surfaces deflect, regardless of whether the airplane is small, large, high or low performance. I.e., it s possible to make a high performance aerobatic airplane relatively docile by reducing the control surface travels, or make a primary trainer reasonably responsive by increasing travels. In short, YOU primarily determine how an airplane will handle. Thus, while the manufacturer s recommended low rate and expo percentages are usually ok starting points, don t make the mistake of thinking that they are what the manufacturer intends you to stay with or get used to. Sticking with the logic that the best airplane setup is the one that compliments the type of flying the person does most often, each pilot must fine tune the controls to suit his or her current skill level in order to fly their best. Furthermore, whenever you here someone claim that one aerobatic airplane flies better than another, if you exclude psychological influences, the differences are usually setup related and often both can be made to fly equally well simply by changing a travel or exponential setting for example. Indeed, once you ve graduated to a tapered wing plane like an Extra, Edge, MX, Cap, Sukhoi, Yak, etc., they are all equally capable and any differences that are not setup related are usually so minor that only an expert flyer could detect them. What matters is will yours be set up to promote rapid advancement and how far will you take it? It s important to note that airplanes set up to achieve the extreme control surface deflections needed to fly 3D also require large amounts of programmable exponential to reduce control sensitivity around neutral. However, using large amounts of expo means sacrificing the 1-to-1 correlation between the control inputs and airplane response that s so important during precision flying. Thus, when not flying 3D, you should avoid using large amounts of expo in order to maintain a more predictable linear control setup favorable to precision aerobatics, takeoff and landing, etc.. In fact, for a lot of reasons, most pilots would be wise to delay the distraction of trying to set up their planes for 3D until their skills and confidence have evolved to where 3D flying is even an option. The point is that it doesn t matter what the airplane is capable of it fails to survive long enough to start trying new things. Consider that every year thousands of perfectly good aerobatic airplanes are damaged or sold simply because they are set up for what pilots hope to do with them in the future, but in the mean time they end up looking for another airplane when the one they were flying proves too difficult to fly (and land). On the other hand, those who set up their airplanes to suit their immediate comfort level not only experience a boost in confidence that enables them to concentrate on flying well, their success just made any future goals more likely to be achieved. 12 KPTR: Sometimes the best solutions are so simple that they re easily overlooked...to immediately start flying better, adjust the travels to your liking, rather than you trying to adjust to the plane!

3 EFL R S75 Maximum Control Surface Resolution for Precision Flying When possible, the ideal control hookup for smooth precision flying is to attach the pushrod to the hole closest to the center of the servo and the furthest out hole on the control horn to achieve maximum resolution and mechanical advantage (torque). Then, increase/decrease the radio percentages to achieve the recommended travel and ultimately the desired handling. If more travel is needed even after maxing the percentage in the radio, you ll have to sacrifice some resolution and mechanical advantage by moving out on the servo arm and/or closer to the control surface. Explained: Servos are designed to move a certain number of incremental steps at 100% travel. Increasing and decreasing the travel percentage in the radio increases or decreases travel by adding or removing steps, yet the size of the steps remain the same. Connecting the pushrod closer to the center of the servo means that a higher travel percentage will have to be programmed into the radio due to the very small (fine) amount that each step is actually moving the pushrod, thus increasing the resolution of a given control surface travel. On the other hand, achieving the same travel with the pushrod connected near the end of the servo arm will require a lower travel percentage in the radio, thus reducing resolution and causing a more coarse (abrupt) control surface movement for each incremental step that the servo arm moves. Of course, 3D pilots must sacrifice resolution in order to achieve the large travels necessary to perform extreme 3D stunts. Therefore, before attaching the pushrods, you ll have to decide whether the plane will be used primarily for 3D stunt flying or precision aerobatics. Once again, there s no in-the-middle and those who try to set up an airplane for both will end up with a plane that does neither as well as it could. While it s true that some exceptionally skilled pilots are able to fly precision with a 3D setup, it takes immense amounts of concentration and practice, with the slightest lapse in concentration immediately resulting in jerky flying. EFLRS75 Inside hole 1/2 travel = many fine steps. 60 (150% travel) 30 (75% travel) 25 1/2 Neutral Pushrod travel Outside hole 1/2 travel = less than half the steps and resolution relative to the inside hole. The servo arm resolution is extremely fine close to the center of the servo, and more coarse (chunky) near the end of the servo arm. Thus, connecting the pushrod at the end of the servo arm results in a more sensitive/touchy control response, whereas connecting the pushrod closer to the center of the servo produces a smoother more precise control response and feel. Maximum resolution and mechanical advantage is achieved with the pushrod attached to the hole closest to the servo and furthest out on the control horn. Just make sure that there isn t any binding near the travel limits with this arrangement. KPTR: When set up for maximum resolution, the control response is much smoother and more closely matches the precise inputs and intentions of the pilot! 13

4 Setting True Control Surface Neutrals Some of the obstacles that pilots encounter stem from a fixation on lining up only part of the control surface at neutral and failing to step back and look at the position of the surface overall. Note that most lightweight wood ailerons, rudders and elevators are inherently twisted for part or all of their length, and thus you should never exclusively use the inboard root or tip of the control surface to set neutral. Instead, you must look at the entire length of the control surface and identify any twists or bows, and then average the twist to set the true neutral position. E.g., a little down at the tip, up at the root, and neutral at the half-span, is true neutral! Furthermore, to reduce the potential for programming errors, and to simplify the fine tuning process at the flying field, as a rule, always try to mechanically set the control surface neutrals, and only use the radio to fine tune things when it becomes absolutely necessary. (Full length twisted aileron example) Half span = Do not exclusively use the inboard root or tip of the control surface to set neutral. Instead, identify and average any twists to set the true neutral control surface position.! Also, do not make the mistake of lining up the forward leading edges of the rudder and elevator balance tabs with the leading edges of the horizontal and vertical stabilizers. Doing so with a twisted control surface won t be truly neutral! When the twist is averaged, the balance tab will appear askew, but the surface overall will be neutral and therefore more favorable to early flying success. true aileron neutral Aerodynamic balance tab! Vertical stabilizer This is a good place to mention that when setting up dual servos on a single aileron, only connect one servo to the control surface. Then line up the other ball link with the hole that will be used on the other servo arm and watch that the ball link remains lined up with the servo arm throughout the full range of travel. If the 2nd servo ball link lags behind or outruns the servo arm, make the necessary adjustments to avoid damaging the servo or the control surface. (Twisted elevator halves example) Despite one elevator looking like it is up, and the other down, they are actually both neutral when the twists are averaged. EFLRS75 Before attaching the 2nd servo ball link, watch that it remains aligned with the hole in the servo arm throughout the full travel. 14 KPTR: Amidst all the programming distractions, don t forget to step back to see whether the setup looks correct overall.

5 Dual Rates/Flight Modes/Conditions and Travel Considerations While a computer radio with dual rates/flight modes and exponential is not mandatory for flying precision aerobatics, it s a great asset when fine tuning the airplane s handling to make it easier to fly, and a must to fly 3D. Typically, high rates are set up to achieve maximum travels for extreme 3D flight and taxiing in strong winds, whereas low (normal) rates provide optimum travels for precision aerobatics, takeoff and landing. While it might sound like dual rates would enable precision aerobatic pilots to ideally set up different control responses for different maneuvers, those who do so often end up taking longer to achieve proficiency because they are, in effect, having to learn to fly TWO different handling airplanes! Just like driving a car, it proves to be much easier to master one consistent setup and learn to change the size of your control inputs depending on the situation than to try to juggle different rates. Therefore, it s recommended that dual rates principally be used to switch between precision flying and extreme stunt or taxi mode. Tip: When using dual rates, it s recommended that all the dual rate (and expo) settings be put on one switch to make it simpler to switch back and forth. Page through any R/C magazine today and it s obvious that 3D flying is a major influence on the sport. Because 3D tends to bias manufacturers to recommend larger control surface deflections for both high AND low rates, most pilots will find it immediately necessary to reduce the manufacture s low rate percentages to be able to takeoff, maneuver, and land comfortably. Notice: When setting up the control surface travels or making adjustments, it is critically important that you physically measure the control surface deflections in ALL directions! For a variety of reasons, it is very likely that you will have to program different percentages to achieve the same control surface travel in both directions. Pilots often neglect to physically measure all the control surface deflections in both directions because they assume that things are equal based merely on the numbers they read off of the transmitter. Consequently, some pilots end up unhappy with the way their planes handle, or assume that having to make numerous and/or large adjustments at the flying field is an indication of a faulty design. In some cases there may simply be more left aileron travel than right, or one elevator half deflects more than the other, and except for that their airplanes are fine. Note: Remember to continually re-check the positions of the curser, D/R, and flight mode/condition switches when programming the high rate, low rate, and exponential settings for each control. (Sooner or later everyone, including the pros, overlooks this and has to go back and reprogram -- assuming they catch it.) [D/R & EXPO] AILERON D/R Pos-0 Low 74% L 70% R Pos-1 High 150% L 143% R EXP +15% +15% +40% +40% Different percentages are often required to achieve equal deflections on the actual control surfaces in both directions. = = = = KPTR: Transmitter settings should be based on actual deflections and your current skill/comfort level, not # s on a screen! 15

6 R Programmable Exponential Methodologies The high rate control surface deflections required to fly 3D would otherwise cause an airplane to be too responsive and hard to control between stunts. Thus, one of the principle uses of programmable exponential is to reduce the servo travel around neutral to enable pilots to fly with the feel of normal rates when making smaller inputs, but then rapidly ramp up beyond that. When it comes to low rates, the domination of the 3D mind-set in the sport causes most manufacturers to recommended low rates that, while lower relative to 3D rates, are still too responsive for most pilots. That is why many manufacturers recommend large amounts of expo (in excess of 25%) even on low rates, but as a consequence, pilots lose the 1-to-1 correlation between their control inputs and plane response that is better suited to precision flying. When low rates are truly optimized for precision flying, the objective is to use just enough expo to achieve a linear control response. Explained: Due to the changing geometry of the rotating servo arm relative to the pushrod, the servo arm deflects the control surface at a higher (faster) rate during the first 25% of travel than it does approaching the travel limit. Adding approx % expo on low rates is a good starting point to compensate for the inherent rate discrepancy of the changing servo arm geometry to achieve a linear deflection rate throughout. Note: As a rule, add 5-10% additional expo (= 15-25%) when the airplane features over-sized 3D control surfaces to help compensate for the inherent greater sensitivity. (Once again, you can be fairly certain that an airplane has over-sized surfaces when references to 3D occur in its name or ad description.) You should similarly set up the throttle curve with an approx. 25% mid-point reduction in order to achieve a more linear throttle response. Ultimately, the low rate expo objective is to achieve a comfortable linear connected to the airplane control feel, not to make the plane docile or compensate for a poor setup or over-controlling tendencies. Hence, if the plane is too responsive, try reducing the low rate percentage before you start adding more expo. Later, when your flying progresses to a point where you need to add more travel, add some more expo as well to maintain the same general handling. Of course, if you start sensing a lag or wet noodle control feel between your inputs and the airplane, you ve gone too far with the expo D SURFACE DEFLECTION D E F L E C T I O N PRECISION SURFACE DEFLECTION D E F L E C T I O N D Max Travel High rate 50% Expo 25% 50% 75% 100% STICK DEFLECTION EFL S75 Adding approx % expo on low rates compensates for the inherent rate discrepancy of the changing servo arm geometry in order to achieve a linear deflection rate throughout and thus a more direct 1-to-1 correlation between the pilot s inputs/intentions and the plane. Precision Actual linear low rate flight response Low rate 15% Expo curve on screen 25% 50% 75% 100% 16 KPTR: Low rate expo is intended to provide a linear control feel, not to make the plane docile. STICK DEFLECTION

7 Optional Differential Aileron Travel and Aileron-Rudder Mix Adverse Yaw: An inherent yaw/skid during banks and rolls caused by the wing with the down aileron generating more drag than the wing with the up aileron. Result: Banks and rolls are less axial and the initial skid/lag causes the plane to be out-of-sync with the pilot s inputs. Solution: Differential aileron and rudder deflecting in the same direction as the ailerons prevents the nose from skidding. Adverse yaw is thus prevented, banks and rolls are smoother and more axial, and pilots feel more connected to the plane. Adverse yaw is an inherent opposite yaw/skid that often accompanies aileron deflections (caused by the down aileron wing generating more lift and therefore drag than the wing with the up aileron). As a result, the airplane will sometimes feel out-of-sinc with the aileron inputs, especially at slower speeds and applying larger inputs. This is why some pilots can fly around OK, but then struggle to control the airplane during landing! Note that adverse yaw is especially pronounced on flat-bottom wing airplanes, and tends to be much less on symmetrical wing planes. One option to reduce adverse yaw on symmetrical wing airplanes is to program a slight (5-10%) amount of differential aileron travel (more up aileron deflection than down) to increase drag on the up aileron wing so that both wings generate similar amounts of drag -- thereby improving control and helping to make banks and rolls slightly more axial. The effect of differential tends to be small and thus doesn t completely eliminate adverse yaw. Therefore, differential aileron should be viewed as a refinement that helps make a good flying airplane just a little bit better. The principle way to eliminate adverse yaw is to input rudder in the same direction as the aileron. This is relatively easy to do with a flat-bottom wing airplane because the adverse yaw is so pronounced that the ratio of aileron and rudder inputs is typically 1-to-1. It is, however, almost impossible for a person to coordinate the small amount of rudder needed to eliminate the small amount of adverse yaw that occurs on a symmetrical wing airplane. Therefore, this a case for employing a slight 1-5%Aileron-Rudder (A/R) mix on low rates. Since the A/R mix ratio is 1-to-1 aileron-ruddder deflections on a flat-bottom wing airplane, and almost nil on a symmetrical wing, the starting A/R mix on a semi-symmetrical wing airplane would be half as much rudder as aileron deflection to eliminate adverse yaw. Note: Differential aileron and A/R mixing help upright/positive aerobatic maneuvers, but would not be appropriate for airplanes that spend a lot of time performing inverted/outside maneuvers. Thus, if your aerobatic flying features more positive maneuvers than outside, it s smart to set up your airplanes with a slight aileron differential anda/r mix, but not so much that it overly impacts outside maneuvers. Sample Low Rate Differential (3 wide aileron) Deflections 15 up travel = 3/4 12 down = approx. 5/8 Sample Aileron-Rudder Mix Ratios (measured in degrees of deflection) Flat-bottom wing = 15 Aileron travel + 15 Rudder travel Semi-symmetrical wing = 15 Aileron travel + 7 Rudder travel Fully-symmetrical wing = 15 Aileron travel + 1 Rudder travel 20 KPTR: A slight amount of aileron differential and A/R mix automatically provides a slightly crisper control feel and more axial banks and rolls during positive maneuvers.

8 Knife Edge Mixes and General Mixing Principles As you know, modern programmable radios allow you to automatically mix a secondary control with your primary input in order to reduce or eliminate some of the unwanted deviation tendencies that occur during aerobatics. Exhibit A: Holding in left rudder during knife edge flight results in the airplane also gently rolling left. The most widely applied aerobatic mix is Rudder-Aileron to aid knife edge flight. Example: While holding in rudder to sustain a knife edge, most high performance aerobatic airplanes tend to gently roll in the direction that the rudder is applied. Therefore, flyers routinely mix a small amount of opposite aileron with the rudder to minimize the rolling tendency during knife edge. Rudder-Elevator is the other common knife edge mix: While holding in rudder to sustain a knife edge, most airplanes tend to pitch (tuck) toward the belly or canopy. Therefore, flyers routinely mix a small amount of up or down elevator with the rudder to minimize the tucking tendency during knife edge. Remembering that everything in aviation is a tradeoff, it s important to note that each mix that you put in may only be applicable to that maneuver. That mix may indeed turn out to be contrary to what s needed during another maneuver, or end up causing a deviation somewhere else that otherwise would not have existed. That is why you must be prudent with your mixes. For the average pilot, the process of programming mixes typically unfolds this way; When a new maneuver is practiced, a pilot will detect a tendency that he will try to eliminate using a mix. As more maneuvers are introduced, he ll start running into situations where the deviation that he wants to remove is actually caused by an earlier mix. What follows is many hours of experimentation to determine which mixes to keep, which need to be reduced, removed, or reversed, and when to take the initiative to start making the correction input(s) himself. You should at least activate/create both Rud-Ail and Rud-Elev mixes in your transmitter so they re ready to go when you need them, but start with zero percentages until you know what is actually needed. Knife Edge Mix scenario A: Mixing a small amount of right aileron with left rudder cancels the roll tendency during knife edge. M5 Reduce Mix A Add Mix D M4 M6 Remove Mix C Add Mix C M3 M7 Reduce Mix D Add Mix B M2 Practice Add Mix A Maneuver 1 Each mix tends to work best only for the maneuver that prompted it, so, to avoid having to do a lot of back tracking as more and more maneuvers are practiced, pilots must limit their mixes. KPTR: A mix can simplify the maneuver for which it is intended, but potentially introduce deviations elsewhere if not used carefully. 25

9 Programmable Mixing Principles Cont. As a rule, unless you intend to only fly a few maneuvers, the most efficient and effective use of mixing is to limit your low rate aerobatic mixes to no more than 5-10%. (Having to program more than a 10% mix on low rates is likely indicative of something fundamentally wrong with the airplane that is probably causing problems in other areas as well, or, the airplane isn t meant to do that maneuver.) If the tendency that you want to correct is slight, try a 5% mix. If it is more noticeable, try a 10% mix. Limiting each mix to 5-10% (15% max) should help make your flying easier without having too much impact on other maneuvers or causing you to do a lot of back-tracking as your repertoire increases. Here again, mixes should be viewed as refinements used to make a good flying airplane even better, but because of all the variables, mixing will never make the airplane fly perfectly. Thus, at a certain point every good pilot shifts from chasing variables to focusing on learning to fly the airplane better. [PROG. Mix1] RUDD AILE Pos0-5 Pos EXP ON As a rule, try to limit your precision aerobatic mixes to under 10% in order to avoid creating deviations elsewhere that otherwise would not have existed. Tip: If the option exists, activate expo on each mix to smooth out the mix transitions. NOTICE: Many tendencies are held in check at higher speeds, and only show up when the plane is flying slower. Some tendencies show up at higher throttle settings, but not when the throttle is low. A lot of mixes are therefore only appropriate at certain airspeeds and throttle settings. This partly explains why those who look to mixing to take the place of developing better flying skills experience little overall improvement. Sure, a person could spend a lifetime flipping switches and trying to program complex mixing curves in an attempt to eliminate every unwanted tendency through the radio. But, at a certain point, the returns for all that effort are negligible. At some point, you will have to settle for being close on your setup and start focusing on improving your flying skills. Conversely, one can travel across the country today and observe flyers involved in an endless cycle of trying to dial into their radios the corrections that they could easily be making, only to have to keep repeating the process each time conditions change, or a new maneuver grabs their interest, or a different airplane is flown. Indeed, programming their radios has become their hobby! In many cases, it no longer even occurs to people that sometimes the simplest and most effective thing that they could do to improve their flying is learn to make the corrections. So, while mixes can prove very helpful, nothing will remotely impact your flying as much as improving your flying skills. 26 KPTR: Mixes are there to help you, but are no substitute for learning the proper skills needed to fly the maneuvers!

10 EFL R S75 Fundamental Setup Rules-of-thumb: Account for any twist in each control surface and average the twist to set the true neutral position. Full length twisted aileron: Half span = true neutral Optional down thrust to reduce P-factor (asymmetric propeller thrust) during positive maneuvers. Also to provide a counter force against climbing at higher airspeeds and assist inverted flight. -2 DN Positive wing incidence to generate the lift needed to support the plane s weight (rather than having to use elevator trim). JOB SPECIFIC +½ Lift C.G. Neutral stab for neutral pitch stability throughout all maneuvers and at all airspeeds. 0 Pushrods connected to the holes closest to the servos and furthest out on the control horns to achieve maximum resolution (precision) and mechanical advantage (strength). [TRAVEL ADJ] ELEV D97% U94% RUDD L85% R88% AILE L87% R92% Weight C.G. at wing s center-of-pressure pitch axis (thickest point) for neutral pitch stability throughout all maneuvers and at all speeds. Physically measure each control surface deflection to confirm proper travel in both directions (noting that different percentages are usually required to achieve the same travel in both directions). Cardinal setup rules-of-thumb for greater neutral stability and optimum precision aerobatic handling: 0 Stab incidence relative to datum ½ Pos. wing incidence relative to stab 2 Right thrust relative to centerline & fin 2 Down thrust relative to datum & stab wing s thickest point in-line with wing s center-of-pressure 2 R Right thrust to counter the effects of propwash at slower airspeeds with higher power settings. Also assists in reducing the effects of P-factor. 0 Neutral fin for neutral directional stability at higher airspeeds. 28 Program 10-15% expo on low rates to maintain a precise correlation between the control inputs and airplane response. Add 5-10% additional expo when the airplane features over-sized 3D control surfaces. Initially fine tune general handling by changing Dual Rate and/or travel percentages, then secondarily fine tune the expo settings. CAUTION: Avoid changing any part of the setup to try to help a certain flight condition or individual maneuver! The best airplane setup provides optimum overall handling that compliments the majority of things a pilot does, including takeoffs and landings. From that solid footing, shift attention to learning to fly the plane.