Perfecting an aerobatic sequence

You've planned the ideal aerobatic display sequence, and now it's time to practise it – again and again...

By Bob GrimsteadOnce you've designed an aerobatic display to be proud of – a personalexpression of flying artistry, a pleasure to watch and rewarding tofly – you'll need to put all this theory into practice. I start by climbing my aeroplane to a great height (3,000 feet or more)and fly part of my new routine – say, the first half, or the firstcouple of passes – to see how it goes, and to find any awkward parts.Next, I do the same with the remainder of the sequence, bit by bit,until I am happy it is all practicable. Then I try stringing the wholething together. After flying the sequence a dozen or more times above3,000 feet to establish which will be the tricky figures andcombinations, I re-write it until it becomes easier and stays more orless in place over the ground. Do not expect your own first ideas to be perfect. I often have tomodify, or even rewrite a planned sequence several times before itbecomes feasible, let alone entertaining or visually interesting.Later, after I have a workable routine, I will undoubtedly makerepeated changes and minor adjustments to make it more practical, saferor simpler – or suited to different venues with longer or shortercrowds or angled display lines. Over my five years of low-level aerobatic display flying, this has beena continuous process of evolution. Next, when I am satisfied the wholething is workable, I can string it all together and practice it fiftytimes, experimenting with maximum and minimum airspeeds for the variousfigures and combinations. This is important. Flying high-energy,high-speed aerobatics is super-safe, but squanders your height.Conversely, flying all the figures at their minimum speeds minimisesheight loss - but courts disaster. You do need to be aware of the safespeed band for every manoeuvre.Because I fly two otherwise identical aeroplanes with ASIs in knots andmph, andbecause, in the hurly-burly of a display it can be difficult to recallnumbers instantly, I’ve marked a safe speed bracket for all normalmanoeuvres on both instruments.Flying my finalised sequence forty or fifty times also helps to fix itin my mind. If it does not happen naturally during rehearsal, then Ideliberately botch or miss out a figure here and there, to establish asafe alternative sequence afterwards. I also intentionally snap thethrottle shut at various awkward points through the routine to practisemy preplanned recovery from engine failure. It’s tempting to skip thisstep, and it takes guts, but you should already be well-endowed withcourage if you’re going to be a low-level display pilot. In 2009, two Samson Pitts pilots crashed while relying on their enginesto pull them out of the low-level ‘cobra’ manoeuvre. In one instancethe big radial merely coughed, in the other it shed its propeller. Onepilot was badly injured, but the other - Australia’s foremost contestand display pilot - died. Practising for power failure is important.Luckily, in a long-winged, low-drag Fournier like mine, providing I amflying over a runway, I can be fairly sure of gliding in to a safelanding, although completing some manoeuvres without power can beexciting as the airspeed falls. Closing a Fournier’s throttle whilepassing through the vertical pulling up into a loop or stall turn canbe most instructive! It is not easy to confirm one’s positioning up at3,000 feet, so I gradually come lower to see how things go. At first Ibring it down 500 feet at a time then, approaching my legal minimum, Ireduce the height by 100 feet at a time, carefully noting safe gatesfor each figure. By now I should be able to fly this sequence in mysleep, in any possible combination of wind directions, with preplannedrecoveries for any cock-ups or unexpected problems, and the ‘safetyenergy’ (height and speed) gates absolutely fixed in the forefront ofmy mind. This should give me spare mental capacity to deal with theunexpected ‘on the day’. And don’t kid yourself; the unexpected andunplanned always happen.Inviting a critic

Now it’s time to persuade an aerobatic expert to watch you. You mightthink you know what your sequence looks like, or how safe it is, butonly a knowledgeable aerobatic performer, critically regarding yourflying from the crowd’s point of view, can truly determine what yoursequence looks like, how accurately you are flying the figures, and howsafe you are. This is another vital step which takes courage, and alsoone you might prefer to skip, but all professional display pilots andaerobatic competitors invite such critiquing. Believe me, it not onlyimproves your flying and the look of your presentation, but it mightwell keep you alive. Several such sessions with different critics will help even more. It istempting to practise early in the morning or late in the afternoon,when the wind drops to a zephyr and the temperature is low, giving bothyour engine and your wings their best performance, and this iscertainly the easiest way to start. However, I believe it is much moreimportant to practise in the worst possible circumstances, so that youare used to them, and do not find yourself suddenly confronted withdifficult conditions for the first time during a display, when yourmind is already preoccupied.High temperatures rob your engine of power and your wings of lift.Strong and gusty winds need lots of small, sharp and draggy controlinputs, while a steady on, or off-crowd wind requires you to make manycorrections with occasional sideslips in some manoeuvres. All this robsyou of energy. Worse from the point of view of sapping your aeroplane’s get-up-and-go,is a strong along-crowd wind, which will probably force you to fly athigher than optimum speed into wind, to prevent being blown away. Theproblem is that, whenever you are flying at more than your aeroplane’ssteady maximum speed, you must be descending and eating into your totalenergy margins, so you need to start higher on a breezy day.A thirty-knot wind at 1,500 feet forces me to fly an extra two milesduring a four-minute display. Not only might it make me overrun my timeslot if I don’t remove at least one pass from my sequence, but it mightbring me lower than expected. A gusting wind or thermal turbulence reduces stall margins, so I haveto fly either faster or more carefully. All this robs the routine ofenergy, so I need to start higher than normal and perhaps fly moreprecisely than usual on a windy day. Most difficult of all is the fierce on-crowd wind. For obvious reasons,a gap is drawn between the crowd line and the display line. It isimportant not to cross the display line, but the crowd line isabsolutely inviolate. Not only is it vital to practise with an on-crowdwind, but I find myself most closely studying my routine, the site andother performers in those conditions. Low-speed aeroplanes get a smallmargin of just 100 metres between display and crowd lines, but theseare the types that are most affected by the wind, so it is prudent togive yourself an extra fifty metres or so of margin in breezyconditions.In the final analysis, if you do get blown across the display line, itis far better to roll wings level, open the throttle wide, climbdiagonally over the crowd and apologise later, than to pull hard tryingto avoid them – although resisting this impulse in the heat of themoment can be very difficult. Once again, practice is the answer.Best use of the worst of conditions

For all the foregoing reasons, whenever possible I try to fly mylow-level practices just after lunch, in the worst hot, bumpy, gusty,breezy conditions. That way I am confident to fly in thesecircumstances when I encounter them. Doing this also gives me a goodidea of how much height to add at the beginning of my routine if Ihappen to find the air rough at a particular display. On the big day,if I do get blown downwind, just once, in the middle of my routine, Ican keep the throttle wide, gently pitch up thirty or forty degrees andthen pitch down again when the airspeed gets low. This gives a kind ofhumped figure that looks to the uninitiated as though it might be somesort of aerobatic manoeuvre. It takes ten or fifteen seconds and is allflown at below 100 mph, so it actually gains a useful hundred feet ofheight as well as getting me a quarter of a mile back to windward. If I become really low, I stop aerobatting and fly a balanced360-degree turn. This takes fifteen to twenty seconds, gains me nearly200 feet and only the experts know it’s not a proper manoeuvre. Believeme, I’ve done it and been congratulated by the organisers on my‘thrilling display’.From time to time, on show day the visibility will be limited, robbingyou of a clear horizon reference, or there will be a low cloudbase,limiting your start height. Again, it is a vital to have encounteredand practised in these conditions beforehand, and I always carry a‘flat’ sequence card in my overalls. This features merely a successionof loops and barrel rolls, and one full cloverleaf, with gentlewingovers and steep turns as the turnaround manoeuvres at each end ofthe display line. I can fly all these without losing any height, evenin the most difficult conditions. Yes, it is more boring to watch thanmy usual routine, but it is better for the poor, sodden crowd than justlooking at my rainsoaked aeroplane parked on the flight line.And we Fournier fliers have two advantages over the bigger, heaviertypes. With a small looping and turning radius, our low speed enablesus to stay within the crowd’s visual range on a murky day, so we canperhaps fly when the unlimited competition machines, warbirds and jetscannot. It is essential to practise these ‘flat’ routines, initially infairly good weather, and then in poorer weather, so you can become usedto the myriad unexpected difficulties (like water droplets streamingback over your canopy or spraying on you through the gaps, orcondensation from your exertions forming inside it) and the visualillusions of reduced visibility and cloudbase. Then you must stick toyour personal limits, rather than guessing whether or not you can flyon a particular occasion. And, believe me, there is a very strongtemptation to go ahead and fly your display when you’ve practised formonths but the weather is poor and everybody else seems to be gettingon with the show.Setting your personal limits

As I approach my one-hundredth display, my personal limits are now 2kmvisibility and an 800-foot cloudbase, with only light drizzle at themost. Any more precipitation will damage my wooden propeller at airshowrpm. Similarly, having a monowheel undercarriage, I will not take offin more than a 25-knot wind or a 15-knot crosswind. But I do regularlypractice in those conditions, so I will not be out of my depth when Iencounter such crud. If poor weather prevails at a venue and I have not practiced in thoseconditions during the past month, I will not fly. It is disappointing,but much less disappointing than frightening yourself and the crowd, orworse. When assessing the suitability of your routine for a particular site,do try to bear in mind the sun’s direction. In an ideal world, allairshows would put the crowd to the south-west of the display area, andschedule your flight for late in the afternoon, when the sun’s low raysmake your aeroplane and its smoke glow golden against an azure sky. Inharsh reality, many sites have the poor spectators squinting into-sun,so you need to consider your positioning and the sun’s azimuth toensure they can even see you against its glare.I believe you should practise not only in the worst wind, cloud andvisibility conditions you might encounter, but also late in the day.Airshows often run behind schedule, and if you’re the last act, youmight find yourself flying as much as half an hour later than planned.Low sunshine can blind you at an unexpected moment, and a bright, clearupper sky contrasts greatly with gloom down where the hard ground is. I recently witnessed a nasty moment when a very experienced and ablepilot flying a topnotch aeroplane had to display later than intended.The location was over calm water ringed by tall buildings. By the timehe was called on, the sun had set over the hills beyond, although thesky was still bright and his spiralling smoke trail stood out clearlyfor us spectators. His third figure was a series of downward rolls, andit was clear soon after he started that things were going wrong. Heading straight down as he was, he must have been confronted by adark, bottomless pit, with absolutely no surface clues from the flat,black water. Being a professional, he stopped and pulled to thehorizon, re-orientated himself and after a momentary pause that onlythe knowledgeable would have noticed, continued with a rather moresubdued display than he had probably intended. This just goes to showthat, however often you practise and whatever your experience, you canstill be caught out, but it behoves us all to prepare as thoroughly aspossible.There is good reason to fly at least some of your practices with smoke.As with all these other scenarios, it’s best to experience the possiblefailure modes for the first time without an audience. Will your cockpitfill with eye-watering noxious vapours during certain (or even all)manoeuvres? Will you repeatedly have to switch the smoke pump on andoff to prevent this? Is there a fire risk? I use orange marine distress smokes in wing-tip pods, and the firsttime I got a ‘flamer’ was towards the end of a display over the river,outside our front door. Glancing to my right, I saw a foot-long blazeroaring off my wing-tip. About to execute a stall turn (always to theright in a Fournier) I was momentarily frozen. Should I splash down inthe river before I fried? How would I turn around? Eventually my brainresponded, I executed the gentlest-ever wing-over and stayed on stationabove the water for an extra minute until my smokes were expended. Alittle prior exposure to this phenomenon would have saved anuncomfortable fright. But by far the best reason to practice with smokeis the thrill of flying back through your own trail. It’s sad I know,but I still get he biggest buzz from blasting though my own smoke. We fly aerobatics because we enjoy them and for the feeling of masteryover our machine, plus the freedom of using all three of the sky’sdimensions. So, practising our routine should be a pleasure we arehappy to repeat again and again. I have never found that practice makesperfect, but it continually helps me to improve, and I love doing it.Once you’re up to speed, you can bid for that airshow slot. Go for it,good luck, have fun, and stay safe. For details & videos of Bob’s Fournier formation duo, go to www.redhawksduo.co.uk