If you’ve been following my articles (see links below) then by now you should be quite familiar with using the 12-hour clock face to describe the position of the model through rolling manoeuvres, where upright and level has the fin pointing to 12.00.
For the one-roll rolling circle we’ll introduce a second clock face, which will describe the circuit (circle) flown whilst executing the single roll. This way we can visibly understand the attitude of the model at any given point in the circle / roll simultaneously, from the comfort of an armchair!
The lessons learned in earlier instalments for consecutive, slow and hesitation rolls all apply. The concept of a rolling circle (however many rolls you do) is simple; it’s like executing commands for an ordinary rolling manoeuvre except in comparison the timing of the elevator and rudder inputs are generally advanced or retarded. You’re also likely to require more control of these surfaces as they’re being used to both sustain altitude and alter direction throughout the manoeuvre.
Put simply, looking at basic elevator correction in a roll, a dose of down is applied when the model is inverted (fin at 6.00) to keep the nose up. Apply that elevator a little early, say at 5.00, and you’ll push the roll off course as the nose-up correction occurs before the wings are level… this is the basic principle behind performing rolling manoeuvres that aren’t intended to be executed in a straight line.
Apply this principle to both directions of elevator and rudder inputs and you get the idea.
ONE AND ONLY
The one-roll rolling circle is a manoeuvre that’s quite difficult to perform properly, and is another figure where the right model makes all the difference to piloting success rate. It’s a good idea at this point to take the principles discussed and try multi-roll rolling circuits – it’s all good practice, but start high because it’ll inevitably go wrong to start with, and don’t worry too much about the path symmetry – just try getting around a circuit. Another tip is to keep the roll at a manageable speed; reduce aileron rates to begin with if necessary, and, just like the rolling manoeuvres we’ve discussed in the past, begin with elevator-only correction before adding rudder.
We’ve touched on ‘high alpha’-type manoeuvres recently, particularly in the recent discussion on knife-edge. In a nutshell, a model that performs high alpha knife-edge well will give you a head start. If your model’s not too confident in knife-edge then the figure will need to be performed at higher speed in a larger circle, and will most likely never be accurately or easily performed.
Accurate rudder control is a key factor in performing this manoeuvre.
CLOCKING ON
Using the pair of clock faces, the one-roll rolling circle can readily be rehearsed in the mind. Clock 1, the ‘roll clock’, describes the roll where the fin begins and ends pointing to 12.00. Clock 2 represents the planned circuit (circle). Because it’s safer and easier to perform the manoeuvre starting close in and turning out, Clock 2 (circle) sits with the top closest to you. This way, as with Clock 1 (fin), we can start and finish at 12.00 where the wings are level and the model upright. At 6.00 on each clock face you’re 50% through the manoeuvre, inverted with half the circle and half the roll complete. At 3.00 and 9.00 on the circle the model is in knife-edge position.
In ‘armchair planning’ the manoeuvre there’s great benefit to be reached by laying your hands on a small toy plane or plastic model – failing that glue two bits of balsa in a cross then stick a fin on one end to make a stick plane. The first version of the manoeuvre to practice from the comfort of your armchair is an approach from left to right, with a left-hand circuit and a right roll. Let’s do the first quarter first, which means we’re going counter-clockwise around Clock 2 – from 12.00 to 9.00, whilst the fin travels from 12.00 to 3.00 on Clock 1.
Now let’s think about this… what’s the first control required from straight and level? You might think aileron, because that’s how rolls normally start. But that induces a straight-line roll, and we’re looking to achieve a very slow roll on a circular path.
So the first input to start the circle is rudder – left rudder in this case. In practice you’ll have at least one of the tail controls applied to some extent all the way around the circle. Sitting comfortably, apply left yaw to your stick plane to demonstrate the result. Now the roll needs to be initiated – bank the stick model a bit, say 45°, to drop the right wing. If you released the rudder at this point the plane would straighten up and carry on rolling right – right? So, you can see that the rudder is doing a job all the time – when the model is more level the rudder is doing more turning whilst the elevator maintains altitude, but when the model is nearer knife-edge position the roles of the tail surfaces are exchanged.
Slowly and steadily rotate the stick plane, replicating what you’d expect to see from given transmitter inputs. The roll continues at a constant rate with lots of rudder on because as you approach 9.00 on the circle it’s sustaining a positive attitude, more so than scribing the circle; down elevator has now come into play to keep the circular shape to the flight path. When it comes to practising at the field it’s likely that your early attempts at the first quarter will be rewarded with a bit of a nose dive or screw out – that’s okay, just keep practising the balance of control inputs.
Right, back to our armchair practice model. As it continues to roll past 9.00 on Clock 2 (circle), and 3.00 on Clock 1 (fin), what happens? Down elevator is still needed to keep the circular shape and the rudder stays in command of altitude adjustment, but by the time you get to 7.30 on the circle (halfway around the second quarter) you’ll have reduced the original rudder input steadily down to nothing, maintaining the circular path and height with elevator alone.
This is only for the purposes of transitioning from one rudder input to the other, however; the original left rudder input becomes right, steadily increasing the input toward 6.00. Approaching 6.00 on both clocks most of the tail control input is opposite rudder, which you need to hold in to continue the circle. Simulate this with your stick model, with and without changing rudder direction, and see what happens – take it slow so that you can really relate stick input to model attitude.
You’ll be glad to hear that the hard bit’s now done! All that’s left is to get around the other half circle, which is much like the first except reversed because you’re starting inverted. Right rudder is still on, scribing the far half of the circle, and as the roll continues the right wing begins to lift. Down elevator is still needed to keep the nose up, and most likely even more rudder to keep the nose pointing in. By 4.30 on the circle you’re pushing down elevator for height, which then wants to push the model out of the circle, so right rudder is forcing the nose back in… beginning to get the idea? By 3.00 on the circle you’re at 9.00 on the fin and in knife-edge on the other side.
In the last quarter there’s another rudder transition to make – again half way through the quarter (just like the previous change) as you move from knife-edge flight to level. Remember that the rudder never fully comes off until the circle is complete; it scribes the circle up to the last second.
SATISFACTION
For me this manoeuvre ranks as one of the most satisfying to complete properly. I first tried it with a friend’s 30% Sukhoi so there was plenty of tail authority, plenty of power and, best of all, it was slow. I cracked it first time, but not before spending a good few hours rehearsing it in my head. “This isn’t so hard” I thought… but on the second attempt I only got 1/3 of the way around before I had to abort!
When trying it for real, take your time and give yourself plenty of room – try to do it when no-one else is in the air. Worry less about achieving perfect roll-to-circle symmetry and more about getting around whilst doing only one roll. Until it becomes second nature, this is one manoeuvre where you should have time to think about the control inputs needed. As you improve you can refine the position of the roll relative to the point of the circle.
ABOUT TURN
Like most manoeuvres you’ll have a favourite direction when executing this one. Some say that rolling out of the circle (as covered here) is harder than rolling in because here you can do a bit of a cheated version requiring less complex rudder transition… try it again with your practice stick plane.
Going left to right again, apply left aileron to roll into the circle – you should begin with some left rudder, but as you’re rolling into the circle you can cheat a bit and just do a left banking manoeuvre. Approaching 10.30 on both the fin clock and circle, right rudder is needed to maintain altitude and to stop you from punching into the circle whilst elevator and aileron control the banking turn. By 9.00 on the circle you’re in knife-edge with up elevator to continue the circle.
Carrying on around, the rudder input direction doesn’t alter – elevator direction is switched but rudder is the same. By the time it gets to the third quarter of the circle (at about 4.30) the model’s in an inverted banking turn and the rudder has bled off as you re-introduce it in the opposite direction so that it’s working well at 3.00 on the opposite knife-edge. Progressively decrease the rudder as you concentrate on flying the model back around the circuit on aileron and elevator, finishing the circle on rudder.
So yes, when flying in this direction you can cheat a little. But don’t stop there – nail it both ways.
