Radio Control Model World - Jul '94

by Stan Yeo

INTRODUCTION

An analysis of 'arrivals at my local slope over the last few weeks revealed that 90% of the crashes resulting in damage occurred after the decision to land had been made. Occasionally there was a mishap on launching but there were surprisingly few crashes as a result of flying error during the 'lie back and enjoy it' section of the flight. An analysis of the landing accidents suggested that they were the direct result of basic flying skills falling apart under pressure.

The purpose of this article therefore is to help the not so confident flyer develop the skills required to carry out a successful landing. My definition of a successful landing is one where the model 'arrives' in a comparatively elegant (controlled) manner, undamaged and within a reasonable distance of the pilot (20 - 30 metres). These skills will develop naturally over a period of time but progress will be much quicker if the pilot understands what they are and adopts a systematic approach to learning them.

The skills required of the pilot are he/she must be able to:

1. Fly the model in a straight line away from the slope in a controlled shallow dive.

2. Fly the model cross wind, parallel to the slope face, constantly making adjustments for fluctuations in wind strength.

3. Fly the model toward themselves, instinctively reversing the Rudder/Aileron controls.

4. Control the attitude of the model in a tight turn under pressure.

5. Recognise the flying speed of a model irrespective of ground speed.

Obtaining these skills needs a conscious effort as the percentage of a normal flight that contributes towards developing them is quite small. So how do we develop them? Many years ago I once asked a top model flyer how he became so good. The curt reply was "practice". He then proceeded to tell me how he would pick one manoeuvre and practice it continually until it was perfect. Whilst it is not necessary to aim for the same level of perfection we should be aiming for a high level of competence if, for no other reason than to stop needlessly bending models.

PRACTISING THE MANOEUVRES

The most important thing to remember when practising manoeuvres is to keep the model high and a reasonable distance from the slope. There are two main reasons for doing this:

1. It is easier to judge the attitude of the model with the horizon as a reference.

2. If the manoeuvre does go wrong there is less risk of damage because there is more space in which to recover the model back to normal flight.

Consequently all manoeuvres recommended in this article should be carried out at a reasonable height and distance from the slope. Obviously as you become more competent then the closer the manoeuvres can be carried out to the slope.

The Dive

Being able to fly the model in a controlled shallow dive is fundamental to the landing approach. Not only is it is imperative, that whilst landing, the nose of the model is not allowed to point upwards, but it is often necessary to 'drive' the model forward on the final approach in a shallow dive to penetrate into wind. To do this the pilot must be able to hold in a small amount of down elevator, against the control stick springs, and steer the model at the same time. This is not easy particularly if the model is coming towards you. The way to practice this manoeuvre is to position the model just in front of the slope, at a height of approximately 50 ft, and dive the model away from the hill at an angle no greater than 20 degrees whilst at the same time keeping the wings level and the model flying away from the hill. The dive angle will depend on the model, the 'draggier' the model the greater the angle. Initial attempts usually result in the model diving off to one side with very little ground being gained away from the slope.

After successfully completing the dive the excess speed gained must be dissipated without the model entering a 'zoom' climb and presenting the underside of the aeroplane to the wind. If the model is allowed to enter a nose up climb it will not only get blown back by the wind but it could also enter a vicious stall. Having sacrificed height for a more forward position the model will now be low in the sky and an uncontrolled stall, close to the hill, could prove embarrassing. The way to prevent this happening is to very gently ease off on the down elevator until the excess speed has been 'bled' away. If the model does start to 'zoom' re-apply the down elevator and try again, more gently. If the model does stall it is unlikely to do so without dropping a wing in which case use this to your advantage and complete the 360 degree turn. Trying to recover the model against the turn could take longer and prove more hazardous. The 'zoom' climb is usually more of a problem with rudder elevator trainers than three function intermediate models.

Flying Crosswind

Being able to fly crosswind is again very important to being able to land a model successfully. Most landings techniques involve flying crosswind at some point. In light wind conditions the best lift is found close to the slope face and if the model is to be kept airborne the pilot must be competent at crosswind flying.

There are two fundamental skills to be mastered in crosswind flying. One is flying the model on a predetermined track relative to the ground. The other is flying the model towards yourself and instinctively reversing the control inputs. Instinctively reversing the control inputs is the more fundamental skill and probably the most difficult to master.

Reversing the Controls

One way to approach this problem is, first work out a personal rule which suits you that will automatically reverse the control inputs when the model is flying towards you i.e. always move the control stick towards the down-going wing or left = right, right = left. Then keep repeating it to yourself when the model when the model is in this position. One day, after the process has become instinctive, you will suddenly realise that you are no longer using this 'prop'. It may help to practice 'reversing' the control inputs with the model on the carpet at home before trying it out on the slope. At the very least I would certainly give it some thought, away from the flying site, if only to implant your own personal solution into your sub-conscious.

The second step in developing this skill is to start doing large 360 degree turns and neutralising the rudder or levelling the wings if an aileron model, when the model is coming towards you at 45 degrees. After one or two seconds re-apply the rudder/aileron control and complete the turn. The most important thing to remember is the original direction of the turn!! This is very important as flyers often forget what manoeuvre they were doing prior to getting disorientated. Novices, trying to land, frequently forget the model was turning left or right when it is coming towards them nose on. Silly I know, but these things happen under pressure.

From this humble beginning, gradually extend the time the model is flying towards you, reverse the direction of the turn and reduce the angle the model makes to the slope until it is parallel. At the same time, try putting in the opposite control for a short period before completing the turn. The next step is to extend the length of the 'crosswind' leg and fly the model closer to the hill. You will have by now noticed that the model is being blown sideways towards the hill. To counteract this the nose of the model must be turned into the wind slightly, the amount depending on the strength of the wind. Due to the continuous fluctuations in wind strength this angle will need continual adjustment if the model is to be kept on track. As your crosswind flying skills develop so will your ability to automatically reverse the control inputs when the model is flying towards you.

Turning Exercises

When a model aeroplane is banked beyond 10 - 15 degrees, particularly a rudder elevator model, there is a tendency for the nose drop and the model to enter a spiral dive. If the spiral dive is not controlled then the model will lose height and build up speed. When the wings are levelled this excess speed will result in the 'zoom' climb mentioned previously. Being able to control the angle of bank and the attitude of the model in a turn is again fundamental to good flying. Sometimes tight turns are necessary but the tighter the turn the more difficult it is to carry out, hence the need for practice.

The secret to good turns is to use the right amount of up elevator to keep the nose up (without stalling the model) and at the same time remove some, or all, of the banking control input (rudder/aileron) as the turn becomes established. This is most important on rudder elevator models, because an element of the applied rudder is also down elevator. Practice doing turns and see how tight you can get them without stalling the model or building up excessive speed. Once you have mastered single 360 degree turns try multiple 360 degree turns and complete turns in one direction immediately followed by one in the opposite direction (figure 8's).

Most landing techniques require the pilot to fly downwind, turn crosswind and then turn into wind for the approach and landing. Both the crosswind turn and the turn into wind are hazardous but for different reasons. The crosswind turn because there is a tendency to over-bank and the in to wind turn because the model often enters a steep climb on completion of the turn.

The main reason for over-banking on the crosswind turn is the pilot has overestimated the airspeed of the model because of the its high ground speed. So when the decision to turn crosswind is made, usually too late, the model is slow to respond. The pilot, on realising the model has gone too far downwind, starts to panic and inputs more control. The resulting turn is much too tight with insufficient elevator to stop the nose 'digging in'. If the pilot is able to prevent a crash at this point the model often ends up flying downwind with a crash waiting to happen. The secret is to:

1. Maintain the model's flying speed on the downwind leg.

2. Initiate the crosswind turn in plenty of time remembering that the model will continue to travel downwind until the crosswind track is established.

The turn into wind presents a different problem. Here the model has a tendency for the nose to rise as it leaves the turn allowing the wind to get underneath it and blow it backwards in a deeply stalled condition. From this there is little hope of regaining control and making a safe landing. The two main reasons for the nose of the model rising as it leaves the turn are:

1. The airspeed is too high for the attitude of the model.

2. The up elevator applied in the turn is not removed quickly enough.

To counteract this tendency the pilot must be ready to apply a small amount of down elevator. It is at this point that all those hours spent 'contour flying' the hill and practising flying towards yourself pay dividends as this is a crunch situation that requires a cool nerve and a steady hand. It is worth remembering that the wind is at its strongest at the top of the slope due to the venturi effect of the hill (see diagram)

SUMMARY

The aim of this article is to help you develop the basic flying skills needed to make safe landings the norm rather than the exception. Having read the article I hope it has helped you to analyse the skills required and given you a clearer picture as to how to develop them.