The author with his chief supporter and critic (his wife!) plus his Nimrod 5 design
with which he has notched up so many firsts.
Many articles have been written teaching the novice the elements of aerobatics, but this exposition is intended to carry on where most leave off and thus assumes that the reader is already a reasonably competent flier. What further steps are then necessary to enable him (or her) to enter the competition field?
Beginners often ask 'How do you learn to fly the F.A.l. stunt schedule?' There is no simple answer except to say 'Study the manoeuvre diagrams in the rule book, then go out and practise.' But this presupposes that the flier has a suitable model and can fly it with safety. Before being concerned with the schedule, and before building a competition model, it is important to be able to fly inverted with confidence. Understandably, if in trouble the usual 'panic reaction' is to attempt recovery into normal flight but in many cases this is impossible and an inverted recovery, or even landing, is necessary and always preferable to an unsuccessful attempt to get the model upright again!
If my own early thoughts were anything to go by, it is a commonly held belief that a competition stunt model is difficult to fly compared with, say, a combat model. Not so! Obviously, there are great differences, but in level flight both are equally easy to fly., To describe a stunter as sensitive to the controls is misleading; the word responsive is a better description. Manoeuvrability available is tremendous, but it is not achieved by sacrificing stability, as is the case with many smaller models. Newcomers to stunt can run into trouble through lack of appreciation of the models' limitations, particularly in square manoeuvres, where they snap on full elevator with the result that the model virtually stops dunng the turn and cannot climb vertically with enough speed to provide adequate line tension. This situation worsens with each corner resulting in a battle to retain control, the intended manoeuvre being forgotten! The first thing to remember then, is not to try for very tight, square, corners at first. Keep all your manoeuvres fairly large, and above all smooth - no jerky wrist movements.
Choice of model depends largely on the builder's previous esperience, but for a first stunter choose the simpler designs; a complicated structure tends to be heavier, Avoid wingmounted undercarriages as they do not stand up well to the inevitable hard landings and keep the finish light. That super paint job may look good but it can be very heavy - save it for the second model when you have a better idea how much weight can be 'spared'.
Once you have the model flying and feel reasonably confident take a careful look at the trim. There are two points which require attention for optimum performance end ability to hold line tension. First does the model tend to roll in towards you in upright or inverted flight? This shows up best during high flying when line tension is low Corrections should be made by twisting the flaps in the opposite direction until any rolling tendency is removed. The other probable fault is that the model may tend to climb or dive in level flight, often accompanied by a tendency to fly tighter inside than outside loops or vice versa. If the model climbs, bend the flaps down relative to the elevators until a 'straight' trim is achieved. Finally, try a wingover as slow as possible. With little or no line tension when overhead, any tendency to roll or veer off is revealed.
Learning the stunt schedule is now largely a question of practise, plus of course determination, concentration, attention to detail and a willingness to learn from others. Above all, do not be disheartened if you do not do very well at first. It is no exaggeration to say that your first competition does more for your standard of flying than weeks of practice,
Careful preparation is essential to give the model the consistency and mechanical reliability necessary if one is to be free to concentrate on flying. The day before a competition give the model a thorough inspection, checking such items as engine mounting bolts, cylinder head bolts, silencer fixing, tank fixing and glowplug condition, Make sure that the fuel system is free from leaks and blockages. A fuel line filter prevents the jet from becoming blocked, but remember that in time it too will become congested.
Arrive with plenty of time for a practice test flight to establish the motor setting, then relax, Always be ready to fly when called - remember that the previous flier may call an attempt. The starting procedure should become routine with everything carried out in a well rehearsed sequence; do not leave too much to do at the flight line. Have the model fueled up before you enter the circle and check items such as prop nut tightness, wing bolt security etc. My own procedure is as follows:
Before entering tie circle (while preceding competitor is performing} reel out the lines and check all connections and the handle adjustment. Check wing bolts and cowl for tightness. Check propeller nut. Remove vent plug. fill tank and replace plug. When called upon to fly, enter the circle promptly, check wind direction and position of the judges, end place the model at the selected starting point (more on this later). Position the accumulator/toolbox behind the model in a convenient place for when model is inverted for starting. Check that the judges and timekeeper are ready. Remove the tank vent plug and top up the fuel to ensure the tank and engine feed pipe are full (the pipe tends to drain if the model is left standing). Invert the model and with your assistant holding it, prime the motor. Flick the propeller several times until the motor is freed up and feels 'right', then connect the accumulator and check the circuit. I use a testing circuit which includes a 2.5 volt torch bulb, but an ammeter may be used instead. A bulb limits the current through the circuit and a switch is used to short circuit the bulb for starting. Switch on and turn the engine over holding the propeller, feeling for a 'kick' as the piston passes the top of its stroke. Now signal to the judge/timekeeper that you are going to start and make sure that the signal is received flick the propeller, and with luck the engine will start first time.
Bob Gieske, a top American pilot, with his famous modified 'Nobler', The 'Nobler', a really classic model, is one of the few true contest designs available commercially as a kit, and could hardly be bettered as a first 'serious' stunter.
With the model ready for take-off, check the connections at the leadouts before walking to the centre. Check the handle connections and try the control movement before signalling for takeoff; your assistant should not release the model until your hand falls after the signal.
Hand signals should be given clearly and with confidence. Raise the hand above the head for one lap before each manoeuvre. This may seem excessive but bear in mind thet beIween manoeuvres the judges must record the scores. Remembar two laps are required between manoeuvres so the model must pass where they are performed (downwind) once before starting the next item. Start the signal three-quarters of a lap after the previous manoeuvre, and finish it after a further lap. leaving a quarter of a lap before the start of the next item. Note that the hand is raised when the model passes the downwind point for the first time, ensuring thst the required two lap interval is maintained.
Choose the starting position with care, especially in windy weather. The accepted position is with the model facing downwind, but this can produce problems with wing mounted two-wheel undercarriages, as the wheels are often further back, causing the model to tip forward in a strong tail-wind. I prefer to place the model upwind of the circle as from this position the model does not encounter a strong tail-wind until its groundspeed is sufficient for the controls to be effective.. In addition, weathercock effect on the fin helps to keep the nose pointed outwards on take-off.
Let us now go through the schedule with a detailed look at each manoeuvre. It will be assumed that the model flies anti-clockwise and references to the left and right-hand sides of a manoeuvre correspond to the view seen by the pilot.
First the take-off. With most models a sufficiently long takeoff run is obtained by letting the model fly itself off with the controls at neutral, If a tricycle or two wheel wing mounted undercarriage is used, the modal may be held on the ground for a longer run, but remember that a smooth lift-off becomes more difficult as the speed increases. Adopting a crouching position with the handle near the ground prevents the inboard wheel lifting too soon. A common fault is too steep a climb; the model should not reach the normal flight level (five feet) until it is over the starting position. The first two laps of level flight also form part of the take-off manoeuvre. Signal during two further laps before starting the reverse wingover.
This manoeuvre should be positioned in line with the wind, starting at the upwind side of the circle. The judges should be directly upwind, so use them as a reference to ensure both halves of the manoeuvre are on the same line. Which way should the flier turn as the model passes overhead? Being left handed, I use the following technique; Stop turning just before the start of the reverse wingover and than as the model passes overhead turn back (clockwise), continuing to turn with the model during the inverted half lap. Stop just before the entry to the second half of the manoeuvre and as the model passes overhead for the second time Start turning (anti-clockwise) again, continuing as it recovers into level flight. If you are right handed continue turning forward during the first half of the manoeuvre stopping as the model recovers into inverted flight. Turn back (clockwise) during the inverted half lap, stopping just before the entry to the second half of the wingover. Then as. the model passes overhead for the second time turn forwards (anti-clockwise) again continuing as it recovers into level flight.
In strong winds it is far easier to start a wingover just before the upwind point is reached, but then the second half is very difficult, if not impossible, to complete. Try to start the first half just past the upwind point, then the second half which is entered from inverted flight with the model qenerelly flying slower, will be much easier. The rule book does not define the exit corner radii and it is therefore not necessary to make them very tight. Make them reasonably small, but keep the model's speed up and exit on a smooth recovery at the correct height, especially on the inverted half lap. A common fault is to pull-out too sharp, allowing the model to 'overshoot' the corner and zoom up, A sharp pull-out kills speed which cannot be regained in half a lap, making the serond half of the wingover rather dlfficult! The wingover demands more confidence in the motor then any other manoeuvre. since should it stop or falter during the first few feet of the vertical climb, line tension is lost and recovery is very difficult...
The three inside loops which follow are one of the simplest manoeuvres in the schedule, although it is very difficult to score high points for them. An inside loop is generally the first manoeuvre that a beginner learns, and in consequence any errors are established early. To achieve consistently round loops of the correct size requires serious practice with a helper giving a second opinion on accuracy They should be round with a line angle of 45 degrees at the top, while the second and third loops should be placed exactly over the first, Some models tend to 'walk round the circle' during consecutive loops, or the size of the loops may change as speeds build up, particularly in wind, After the last loop make an additional half-loop into inverted flight.
Remember to give a hand signal during the first two inverted laps, The two judged laps should be smooth and level - beware the tendency for the model to drop when travelling downwind. Keep the height at five feet. Count the inverted laps carefully, make sure vou have completed two laps after the hand signal before signalling again (two more laps) for the outside loops.
These should be identical in size to the inside loops. again followed by en extra half loop to recover into normal level flight, Some models speed up so much when performing loops in windy weather that the third loop is a trial of strength! This can be eased by looping with the modal travelling into the wind at the bottom i.e. go past the downwind point before starting them, but this does make it difficult to maintain a smooth shape. and there is a tendency to put a 'flat' on the bottom of each loop.
Neil Billington was perhaps one of the most improved pilots of 1972 - culminating a most successful year by topping the team trials last September. Success due mainly to constant practice, and determination to succeed.
So much has been said about the difficulties of square manoeuvres that the newcomer may be forgiven for thinking that tight corners are all important. Not so: the most common error is to make the corners too tight, forgetting that the model must fly smoothly in 'straight' lines between the corner and to do this flying speed must be maintained. Concentrate on the shape of the figure; get the four sides in the right places and keep it large. With practice, the corners will tighten but they must be smooth, Most important.the model should leave the corner without wobbling or jerking, and should be heading in the right direction with sufficient speed to reach the next corner under control. The actual shape of a square loop is difficult to define, Since the model flies on the surface of a hemisphere, lines which appear straight to the flier are not truly straight and will not appear straight to the judges, A compromise must be made. The two obvious alternatives are;
a) A figure in which the four angles are all right angles. This gives a short top leg only 70 per cent of the base length and is not a good solution,
b) A figure with all sides and all angles equal.,
I believe the latter to be the best solution, being very close to a true square. Indeed it is found by taking a true square of the appropriate size and placing its four corners on the surface of the hemisphere on which the model flies. It is then possible for the model to fly along four 'straight' lines (as seen by the flier) between the four corners. Unfortunately although this gives four equal sides (actually equal areas of four great circles) and also equal angles they are not right sngfes, but slightly obtuse. The actual angle area depends on your viewpoint, only the flier sees four equal angles end they are almost 100 degrees. (99 deg. 54 min. for the purists!)
The rulebook definition is very close to the figure just described, the difference being that the top leg is defined as inverted level flights at a constant elevation of 45 deg. The flight path between the top corners is thus not a great circle, and should appear curved to the flier. The two top angles are 75 deg. 26 min. (I know that seems far too acute, but that is how the geometry works out) and the base angles are 99 deg. 54 min. Note that in the ideal figure the elevation is only 45 deg. at the top corners, it increases along the top leg to reach a maximum of 49 deg. 54 min; at the centre of the figure.
Having determined on paper what shape a 'square" should be, how does one put theory into practice?
Remember that the shape must appear correct to the judges, so you will need a helper watching outside the circle to point out any errors. Plan the whole manoeuvre in advance so that you know where the corners should be. The tength of the base gives an included angle at the centre of 45 deg. its midpoint being directly downwind. Stand facing this point For the first corner, turn the model into a vertical climb, not too tight, and climb to an elevation of 45 deg. But wait, the top leg must equal the length of the base. Its position should be fixed in your mind and the model should be headed towards its left hand end, so the first cornet should have been greater than 90 deg., making the model climb toward a point to your left rather then vertically overhead. Start again, making the first corner 100 deg, and when the second corner is reached notice how the model is pointed not vertically but outwards relative to the centre of the square. Gravity and wind help us round the second corner, too much if anything, so keep the included angle large. much greater than the 75 degrees that is theoretically required. You can afford to let the model climb slightly over the first half of the inverted top leg, The third corner is the tight one, let the model come round until it is pointed inwards, symmetrical with the top of the vertical climb, If you do all this right, the last corner should be greater than 90 deg. symmetrical with the first one, Many people leave themselves too much to do in the last corner, the secret lies in that tight third corner, put more into that and the last corner is much easier. Now the second square loop begins. Is the model still going fast enough? Be particularly careful not to 'overdo' the second corner of this figure or the model will lose height along the top leg and the last two corners will be lost in the rush to get back to normal level flight before the ground swallows up the model!
Long a control-line aerobatic enthusiast, though he is also an active R/C competition flyer, Dave Day combined the virtues of two 'classic' models, the 'Spacehound' and 'Thunderbird' to produce a very smooth-flying machine.
The square outside loops are similar to the inside ones, but start with the model at an elevation of 45 deg. Begin the climb from level flight, three-quarters of a lap after the end of the inside square loops (as your hand signal begins) taking a further lap to reach the 45 deg. elevation, The first corner is equivalent to the third corner of an inside loop and should be tight, the model turning through more than 90 deg. The difficulty now is to remember where the ground is so as to accurately place the second corner - I find it helps to glance back at the horizon just before the first corner. No such problem exists in the second loop as the base line has already been established, Remember that the second loop finished with the model in level flight at 45 deg, elevation. As in the inside loops the corner at the top of the climb should be 'loose' letting the model climb slightly as it leaves the corner. The rule book calls for recovery within a quarter lap so at the point where the manoeuvre started do an extra 'half' corner putting the model into a 45 degree dive recovering smoothly into level flight at five feet.
The shape of the triangular loops can be found by placing the three corners of an equivalent triangle on the hemisphere on which the model flies - three sides of the figure era then formed by equal areas of three great circles. The true angle (again seen only by the flier) at each corner is 67 deg. The angle at the centre of the circle between the two bottom corners is 50 deg. 10 min. Position the manoeuvre so that the top corner is directly downwind. Do not make the first corner too acute, remember it should be 67 deg not 60 deg. It is remarkable how many people make the top corner very acute. Keep the second corner equal to the first and the last corner should then be correct. As in the square loops, if the last but one corner is right, the last corner is less difficult, although it is undoubtedly more difficult than the last corner of a square loop. I can only repeat the advice given earlier, keep the corners large at first, It is pointless doing a really sharp corner if the recovery is not smooth and at the correct height.
The manoeuvres so far completed comprise the basic shapes used in stunt flying. The second part of the article, next month, will continue through the schedule dealing with the more complicated manoeuvres which are all made up of parts or combinations of these basic shapes,
One of the best known of all stunt models, the 'Super Master' designed and flown by Joseph Gabris, certainly amongst the greatest aerobatic pilots of recent years.