Jim Mannall (above with his famous Nimrod design) has been amongst the top few aerobatic fliers in this country for more years than he probably cares to remember, and his treatise on how to fly the aerobatic schedule has been much sought after reading by budding pilots.
The menoeuvres so far completed comprise the basic shapes used in aerobatics.
The manoeuvres that make up the rest of the stunt schedule continue to make use of the basic round, square and triangular shapes but they become more complicated. making it increasingly difficult to maintain your concentration. Perticularly beware of the temptation to rush through the final menoeuvres in the fear that the motor may cut early - remember this as the schedule continues with the horizontal eights.
These should be positioned with the intersection between inside and outside loops directly downwind, thus the first inside loop must be started with the model still travelling downwind. There is a temptation to start this first loop too late so that the intersection is not downwind and in turn the outside loops are displaced round the circle away from the downwind point . At best the result is a badly distorted shape due to the wind blowing across the figure, or at worst line tension may be lost completely at the top of the outside loops. Even with the intersection correctly placed the wind has the effect of pushing in each side of the manoeuvre so that the inside and outside loops overlap in the centre This is very easily seen by the judges and every effort should therefore be made to avoid it!
As the model climbs away from the point of intersection, the loops (both inside and outside) should be opened out slightly to gain sufficient distance round the circle during the top half of the loop to enable the bottom half to be completed without being blown past the starting point. Remember that the model slows as it travels upwind during the top half of each loop, so be prepared for rapid acceleration during the bottom. downwind half. In windy weather this latter half of each loop must be very tight to avoid overshooting the centre of the eights.
It is equally important in the square horizontat eights that the centre vertical climb should always be in the same place, as any deviation is easily spotted. Let us first consider the shapes of the inside and outside square loops which make up the eights. The base angles of a normal square loop (previously discussed) were 100 degrees and the top angles 75 degrees. For the square eight the angles at the top and bottom of the centre vertical climb must be changed to 90 degrees (as stated in the rule book) to allow the inside and outside loops to coincide along the line. The other angles are unchanged and the top horizontal side of each loop is therefore slightly shorter than the other three sides.
The 'eights' start at the first corner of the inside loop. Make particular note of the position of the vertical climb using some fixed object (a distant tree, building etc.) as a reference. The model travels this same vertical line four more times during the two eights, hence the importance of marking its position. Ease off at the second corner keeping the included angle more than the rule book's 90 degrees. The model is travelling upwind during the whole of the inverted top leg and must reach the third corner with sufficient line tension to produce a very tight turn. The line tension available at this point depends largely on the flying speed, so again remember to keep that second corner 'loose'. The third corner needs to be tight but not so acute as in the square loops since the model is further round the circle from the downwind position and will be blown towards the centre of the eight during the vertical dive.
The fourth corner comes up very quickly as the model accelerates in the dive. Practice and good reactions on the flier's part are essential to produce a straight vertical dive followed by a tight fourth corner recovering smoothly at a height of five feet. It is common to see the third and fourth corners merged into one - the second corner can be the cause of this: If it is too sharp the model loses height along the top of the square and there is no space between the third and fourth corners. The next corner puts the model into a vertical climb again (did you use your marker?) ready to start the outside loop.
Now it is really important to maintain the model's speed. The first outside corner should be little more than a gentle nudge. Give yourself room, make the top of the loop too long rather than too short or it will be impossible to avoid overshooting the centre when the model returns inverted along the bottom of the loop. Now you are starting the second eight, notice how much slower the model is going now. For practice try doing four or more consecutive square eights and you will realise how important it is to maintain the flying speed. There is a natural tendency to make the second eight smaller as the model slows down. If this is a problem try making both eights larger. The maneouvre finishes as the model completes the vertical centre climb for the fifth time - it is usual to do a further outside corner so that the model follows the top of the outside square loops before deecending to normal level flight.
The vertical eights start as the model passes through the point of intersection of the inside and outside loops flying inverted at 45 degrees elevation, but how you arrive at this position is left open. However it is quite sufficient (and easiest) to do a half loop, and to continue round the same loop to start the 'eight'. Try to start the half loop slightly before the downwind point as the model will then be travelling upwind at the mid-point of the 'eight' and this helps during the start of the top outside loop. The size of the loops must be judged accurately so that the top of the figure passes through the point directly over the flier's head. In windy conditions a definite effort must be made to tighten up the deecending half of the outside loop to prevent the model being blown down befow the 45 degrees elevation.
If this happens the first half of the next inside loop must be very tight, but the imminent presence of solid ground is usually sufficient reminder! The second 'eight' finishes with the model inverted at 45 degrees elevation and a further half inside loop completes the recovery to level flight.
The hourglass requires both good reactions on the part of the flier and a good model. The first corner should be identical to the first corner of a triangular loop, not too tight - remember the included angle should be 67 degrees. This is followed by a long inverted climb. It is important to plan the position of the four corners in advance in order to echieve a symmetrical figure. The base of the hourglass subtends an angle of 50 degrees at the centre. The top of the figure is part of a wingover running parallel to the base and this top leg should be identical in length to the base so at each top corner the lines should make an angle of 25 degrees to the vertical. The second and third corners are part of the only outside triangular loop in the echedule and also occur in a most difficult position when line tension is very low. There is no easing up here at the second corner - by all means keep the radius large but make sure that the change in direction is sufficient to bring the model through the point vertically overhead. Did you do the second corner too soon? Now wait, remember how long the top leg should be. The third corner can be as tight as possible and should bring the model round until it seems to be almost in horizontal inverted flight.
The straight inverted descent should cut the vertical climb at 45 degrees elevation. Can you remember where the climb was? The last corner requires a steady nerve and much practice before a smooth recovery at the correct height can be achieved. Concentrate particularly on the symmetry of the figure. It is difficult to make the long straight climb and descent equal (which really means making all the angles equal) and no stunt competitor in Britain can achieve this consistently. Get it right every time and you will beat us all!
As with the horizontal and vertical eights, the overhead eights start as the model first passes through the mid-point of the figure, vertically above the flier's head. The model should be pointing downwind at this point. Complete the usual two level laps after the hourglass then do a further half lap. At the upwind side of the circle turn the model into a vertical climb as in the reverse wingovar but with a larger radius turn to ensure that you have line tension when the model is overhead. As in the wingover the flier has a choice of position. Right handed persons will naturally be facing upwind as the model enters the manoeuvre and will remain standing in that position. Some left handed fliers also face upwind, However my own (left handed) method is to stop turning about a quarter of a lap before the upwind point is reached, then as the model climbs up to the centre of the eights turn back to face downwind. Note the similarity here with the first half of the reverse wingover. The 'eights' must always start with an inside loop. To keep the shape correct open out the loop as the model flies the lower half into wind, touching the 45 degrees elevation at the lowest point. Allow sufficient distance to be gained upwind to come round to the centre of the 'eight' in the same direction as the original entry before starting the outside loop. It is not too difficult to keep the intersection in the same place but it is common for the transition from inside to outside loops and vice versa to form a cross.
The horizon is out of sight for most of the manoeuvre making positioning difficult. Try to pick out distinctive points in the cloud pattern overhead to act as markers, and stand still so that you do not become disoriented. Recovery from the 'eights' forms the second half of a wingover. The turn from vertical descent to level flight is not critical but it pays to be consistent; make a smooth turn equal in radius to a normal inside loop -such details give your flying a little extra 'style' and help to create a good impression on the judges - and that is important.
The last manoeuvre in the schedule is the four leaf clover. This is entered in level flight at an elevation of 38 degrees. It is possible to make the recovery from the overhead eights at a 38 degrees elevation ready to start the clover, but to my mind this is not good practice. It is best to be consistent throughout the flight. with at least some level flight at five feet altitude between manoeuvres, even though it is not the two full laps required by the rule book. The reason for the entry at 38 degrees elevation is that the whole figure is contained within half the circle, the model never passing behind the pilot's head. The two top loops are tangential not only to each other, but also to the vertical plane through the centre of the circle perpendicular to the central plane of the manoeuvre. The four loops are therefore smaller than other loops in the schedule, and the two top loops do not pass through the point vertically above the flier as in the vertical eight. Try to position the manoeuvre so that its centre is directly downwind. The first loop is the most difficult of the four, starting as it does high up in the circle with the wind behind the model. It is essential to reach the entry point with as much flying speed as possible in order to maintain adequate line tension over the top of the loop - this is difficult in wind as the model is blown downwards as it approaches the start of the figure. I get over the problem by climbing far too high upwind, almost doing a wing-over in very windy conditions, and using the wind to blow the model into the correct position. Not a very tidy approach, but effective in 'desperate' conditions!
It is inevitable in wind that the first loop will be started too late, so that the centre of the clover is no longer downwind. Note that the remaining three loops in the figure are in fact only three-quarters of a loop each. The level flight at 38 degrees elevation which follows the first Ioop is equal to the diameter of the loop - many people make it too short so that the left and right hand halves of the figure overlap. Next comes an outside loop at the bottom left of the figure touching the five foot level and finishing with the model in a vertical climb to the third leaf of the clover. If your positioning is good the model will be directly downwind but if you were late starting the first loop. the model will be slightly crosswind and care will be needed to ensure a truly vertical climb. The top left outside loop is not difficult. but be careful to keep it tight so that the model enters the inverted flight across the figure at 38 degrees elevation. Make sure the inverted flight is long enough before making the final inside loop at the bottom right. The model must then fly vertically through the centre of the four leaf clover and continue in a wingover into wind recovering into normal level flight.
The schedule takes approximately five minutes to complete. Allowing around half a minute from the starting signal to takeoff, the four leaf clover should be completed after about five and a half minutes, leaving one and a half minutes for the motor to cut and the model to land. The interval is very short - life was much easier when a total of eight minutes was allowed rather than the current Seven! Most people have to resort to some manoeuvring to stop the motor, as once the tank is almost empty most models will stop sooner if flown high. Tight loops (but not eights) above the 45 degree elevation also starve the motor of fuel. My own technique is to use a stopwatch and having completed the schedule, to fly at normal level flight which keeps the motor as rich as possible using fuel more quickly. Then, as late as possible, usually just before six and a half minutes, tight circles overhead after a rapid climb are generally effective in getting the motor to cut.
During the landing remember that the approach (that is the descent from five foot altitude) is marked as well as the actual touchdown - there should be an interval of one lap from the model passing through the five foot level to the point of touchdown. This means you must know one lap in advance where the model will land and pass over that point at a height of five feet. The landing itself depends very much upon the type of undercarriage used - with the more springy fuselage mounted system, threepoint landings are essential. Rigid wing-mounted two wheel and tricycle systems offer a choice of three point or main wheel landings as the model will not bounoe (or should not!) when flown onto the ground at high speed. Always try to land downwind. Some whipping may be needed to achieve this. but stop whipping before the model touches down. In the quarter lap immediately after the upwind point the airspeed drops very rapidly so aim to land in this quadrant, passing the upwind point of the circle at about one foot altitude with just enough speed to retain line tension, in the case of a three point landing. Or somewhat faster for a main wheel landing. Do not leave the touchdown too late since the airspeed starts to increase again before the extreme downwind point is reached and the model will float round into wind where a smooth touchdown is much more difficult. With two-wheel wing-mounted undercarriages the model tends to nose over if It stops facing downwind. It is wise to land with sufficient speed for the ground roll to take the model past the downwind point to come to a halt facing into wind. All this assumes that you are flying over concrete as In a competition, but if you prefer to practice over grass, both takeoff and landing are best made into wind
Let us now consider some general points about the flight. Remember that although marks are only given for the specified manoeuvres, your score is also affected by the overall impression that you make on the judges. I mentioned previously the need for a well organised starting procedure - the rest of your performance should be equally well organised. Be consistent with your hand signals and keep the level laps between manoeuvres at five feet. It looks untidy if the model flies too high and has to be brought down again to five feet to start the next item. Concentrate on each manoeuvre as you do it. forgetting about what has gone before. Do not let an early mistake have an effect on the rest of the schedule. It is of course important to remember what comes next, contest nerves can play tricks on your memory so if you era at all doubtful have someone in the centre with you to act as 'prompter'. At international events the Czech fliers, including a certain J. Gabris, always have one of their colleagues sitting in the centre with a list of manoeuvres. The most commonly omitted item is the triangular loops, so take care. you have been warned! In the heat of the moment it can even be difficult to remember how many consecutive manoeuvres you have done, particularly in the complicated tigures such as square eights. Make a point of counting to yourself the number of loops or corners.
After a competition flight leave the circle quickly ready for the next competitor, then clean the model straight away before too much dust and grit settles on the oily surfaces. Make sure the lines are safe from other people's feet - it is always safer to put them away until just before the next flight.
In this 'guided tour' of the stunt schedule I have tried to reveal some of the hidden detail behind the manoeuvre descriptions in the rulebook. An article of this nature can anticipate and deal with the problems likely to arise in each manoeuvre but it is still up to the individual to acquire the necessary skill. Thus my answer to the original question 'How do you learn to fly stunt' is still the same. 'Go out and pracflce' - hopefully. this article will make that task a little easier.
Jim (far right) has flown for Britain on many occasions, in fact he is a 'regular' team member. Here he is seen with John Newnham (left) and Steve Blake at Hradec Kralove, Czechoslovakia for the 1974 World Championships.