Introduction: Model Flying: Perfecting the Roll
Originally an article from RCM&E Magazine Peter Rondel talks us through how to perform a spectacular roll with a model aeroplane.
The roll is a very pretty manoeuvre that has many variations, and to perform perfectly is quite a challenge on both pilot and model.
A roll, of sorts, can be performed by banging in full aileron and hoping for the best... the model will surely start to roll, but will head for terra ferma as it does so! Anyway, in this episode we’ll look at how to execute a roll using all controls to avoid altitude reduction, and how to perform consecutive rolls from one end of the field to the other. In a future series we’ll look at taking this forward to the hesitation roll and one of my favourites, the slow roll.
Using the clock analogy (this time with the fin as point reference), the model is level and upright when the fin points at 12.00, height being gained using up elevator. Conversely with the fin pointing at 6.00, height is gained using down elevator. When the fin points to 3.00 or 9.00 it’s effectively in knife-edge and ‘top rudder’ has to be used to gain height, using the rudder like an elevator to lift the nose. In simple terms, at 12.00 or 6.00 you don’t need rudder and at 3.00 or 9.00 you don’t need elevator, but you do need transition from one input to the other through the quarters... sound too complicated?
Well, for starters you needn’t worry about it too much, but it does become more important later on. The simplest way to get used to doing nice rolls is to take it in easy stages.
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Step 1: Take It Easy
Be happy with the roll characteristics and roll rate of your model. Take it to height and hit full aileron. How fast is it rolling? Can you keep up with it and stop it exactly where you want to? Do you think you would have time to put in some elevator during the manoeuvre? To make life easier for yourself at the beginning you may need to switch in (or reduce) rates - at full stick you want about 1 roll per 1 - 2 seconds.
Ultimately the aim of the game is to be able to perform consecutive rolls in a straight line without dropping any height. Often people cheat the real deal by pulling a bit of up first then performing the roll without correction, so they finish up at a similar altitude to where they started.
Fine, but that’s not really flying the manoeuvre. You’ll know when you’re doing it properly because height will neither be gained nor lost. I like to get people to perform this manoeuvre in the ascent to begin with. That is, pulling in up elevator at the beginning to create a positive angle of attack - let’s say a flight path of 30° relative to the horizon. This gives an element of security for the pilot and safety margin for error - when a tail control input is incorrect or put in at the wrong time, a roll can become hairy very quickly. The aim is to achieve the roll, with tail adjustments, in a consistent climb. We’ve cracked it when the model finishes the manoeuvre and is still angled at 30°. Thereafter we drop that angle until the entry angle is at zero.
To start you should think only about elevator as the correction control. Every time the wings are level (upright or inverted) you need a blip of elevator - just a tiny blip - ‘up’ for upright, ‘down’ for inverted. Practice this whilst aiming to achieve a sequence of three rolls.
This might look a bit untidy and you may see the model jerking on each blip. No matter. Go round again and again and get the amount of the blip right so it’s not wildly off - i.e. that you’re blipping enough only to get back to the required flight path and not past it.
Step 2: Blend the Blip!
The rudder’s not being used at the moment so the manoeuvre will never be perfect, but it can be pretty good. When you’ve sussed the blipping technique try to blend the blip, i.e. bring it in gently a little earlier than level wings, and let it off a little after but making a steady transition - a curved input as opposed to a blip.
This technique should lead to reasonably smooth rolls climbing consistently at the 30° angle of attack. As confidence grows, lower the angle of the flight path until you’re close to level flight. Don’t go all the way to zero without introducing half a dose of elevator at the beginning.
To start a roll properly from straight and level you must first master the use of rudder; however you should be really comfortable with elevator only correction before moving on to rudder practice. The truth is that elevator only is the full extent of tail correction that many club fliers use, so be proud of yourself to get this far. Can you do it in both directions? No? Well go back and do the same again but the other way around!
Step 3: Rudder? Bring It On!
Rudder is one of the most influential yet under-used controls on a model. Master it and all sorts of manoeuvres become safer and easier to achieve. The slight downside is that in many designs rudder response is not remotely pure - i.e. instead of a pure yaw response you get roll or pitch reaction as a side effect. If you have a computer radio and someone on hand to help, there may be some merit in programming out some of these side effects.
My preferred way to teach use of rudder in the roll is to split the roll in half. A common error is to bring the rudder in too late and leave it on too long. In actual fact you should be looking to gently bring in the rudder almost as soon as the roll is started, along with a small dose of elevator.
Another common and more scary error is the application of wrong rudder direction. The way I remember it is that, when entering a rolling manoeuvre from upright, the rudder application should be in the opposite stick direction to the aileron. If the aileron stick is pushed out of the box then do the same with the rudder; if pushed into the centre, then the rudder stick goes centre too. Get used to that, it’ll help later in the series.
As before, start and end in the same heading. Remember that you don’t need much input; you’re doing 4 zones of correction and these zones will all transition from one to the next. With an accurate pattern plane the four zones are all very similar, just requiring different directions of control input. The clock analogy and the text below should explain roughly what you’re looking to achieve input wise.
Zone 1. Wings level with the fin at 12 o’clock. Start the roll and immediately begin to introduce a tiny amount of rudder. Fin at 12.30, introduce up elevator, then at 1.00 more rudder, maybe a little more elevator. 2.00 - more rudder, come off the elevator. 3.00 - rudder only. If by this time it’s gone bendy, turn around and start again until you can keep the first quarter straight-ish. Zone 2. Begin to reduce rudder, and at about 4.30 start to introduce a little down elevator. At 5.30, the rudder is back to the same small dose you had at 12.30; here you’re well into the elevator blend practiced earlier but remember you don’t need as much as before because half the height correction has already been achieved with rudder. At 6.00 only the elevator’s on. Are you heading in the same direction as when you started? Probably not at the first few attempts but keep practicing until it happens.
Zone 3. 6.30 - reduce elevator like before and begin to introduce opposite rudder. Zone 3 matches Zone 1 but in reverse - as you go through, reduce elevator and increase rudder until 9.00 when rudder only is being held in.
Zone 4. Reducing the rudder again and introducing a half dose of elevator toward 11.00 should put the model back on track.
This all sounds like a lot to take in and different models will behave in different ways so treat this as a guide. It’s good practice to think through the list and practice the motion of the sticks from the comfort of your armchair; rehearse the combinations of controls so that when it comes to being in the air you can concentrate with the amount and timing of input as opposed to which way to push the sticks. When you’re happy with this manoeuvre do two in a row and so on, and as you get more confident lower the starting angle of attack.