Flight Tech­nique: Are You Set Up for Suc­cess?

Why too much travel and expo can hin­der your progress

Model Airplane News - - CONTENTS - By David Scott

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.

EX­PO­NEN­TIAL TIPS

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.

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