Radio Control Model World - Nov '95

by Stan Yeo

INTRODUCTION

I have been flying radio controlled slope soarers for over 30 years. My flying career pre-dates the venerable Veron Impala and Dave Hughes Soarcerer. During this time I have introduced a considerable number of people to the hobby. There is nothing more satisfying than watching one of your 'pupils' complete the metamorphous from raw beginner to accomplished slope pilot. As with all things before this transition can take place there are a number of lessons / skills to be learnt. The purpose of this article is to discuss briefly what I consider are the properties of an ideal slope trainer and the three most basic skills a budding slope pilot must acquire before attempting solo landings if their current and future models are to survive relatively intact on the slope beyond their maiden flights.

THE MODEL

I always recommend a rugged boxy rudder elevator model of 55 to 70 inches span (1.5 to 1.75 metres) such as Chris Foss's Middle Phase, The SAS Ace or the Phoenix Model Products Ab Initio or Stage 2. I appreciate this may not be some peoples recommended route to success but there are a number of reason for going along this road, some of which are listed below:

1. The models are generally very agile and manoeuvrable.

2. If designed and built correct will take a lot of punishment and are easily repaired.

3. They allow the novice pilot to fly under supervision in a wide range of conditions.

4. They encourage the trainee to think through in advance what they are going to do next (rudder control is not an instant control unlike Ailerons and needs a certain amount of forward planning).

5. They build confidence.

I know some experienced flyers will disagree with this approach and would advocate starting on an aileron model whilst others would recommend a 2 metre 'floater'. I disagree with the 'aileron' approach for a number of reasons the main ones being progress in the beginning is much slower and requires much closer supervision but perhaps more importantly, because the controls respond that much quicker, it does not encourage such a disciplined approach to flying i.e. thinking and planning ahead.

The 'floater' approach whilst not dismissed is not recommended as a first model because of the limited range of conditions the model can fly in and the limited teaching potential of the model. They are however recommended as a compliment to the main trainer because when the wind drops the 'floater' comes into its own. It is also a more suitable model on which to develop thermalling skills and conquer control reversal when flying towards yourself.

Model flying is all about confidence and judgement. If the confidence goes so does the judgement. Trying to start halfway up the ladder or progress too quickly is a good way to undermine confidence and extend the learning curve. All too often flyers discard their rudder elevator trainers too soon with disastrous results. The R/E trainer should not be abandoned until it can be flown in almost any conditions with gay abandon, without crashing!

THE SKILLS

The three basic skills I have identified as the most crucial and the ones that must be mastered before attempting a solo landing are:

1. Being able to 'drive' the model forward in a shallow dive and at the same time steer it in a straight line.

2. Be able to execute tight, well co-ordinated, turns including flat 'eights'.

3. Fly towards yourself and instinctively move the controls in the correct direction i.e. be able to reverse the rudder (aileron) control when the model is coming towards you.

Perhaps a forth one should be included, that of being able to fly along the ridge, close in, in light conditions using the wind to maintain position relative to the slope.

1. Driving Forward

This is important because in general flying it is often necessary to drive the model forward against the wind to make contact with the best area of lift after launching, after an aborted landing attempt or after being blown back during a turn or aerobatic manoeuvre. It is also important during the final landing phase when the model is turned into wind. Often at this critical moment the nose rises, presenting the underside of the model to the wind and throwing it into a deep stall from which there is seldom a recovery. It is also important when building up speed to perform aerobatics. Here the optimum dive angle must be maintained if speed is going to be built up efficiently without too much loss of height.

One reason that some flyers find this difficult, particularly Mode2 flyers (those who fly with the primary controls on the right hand stick) is that the elevator stick is being held in a position against the stick springs whilst at the same time moving the stick along the rudder axis. Until the technique is perfected the elevator control is inadvertently moved every time the rudder control is moved. The technique here is to start off with the model pointing into wind and put it into a very shallow dive and at the same time gently steer it left and right. To terminate the exercise face the model into wind and slowly release the down elevator until the model resumes it's normal flying attitude. If the elevator is released too quickly the excess speed will cause the model to stall. If this starts to happen re-apply the elevator. This is all part of the skill in driving forward. As stated previously, start with a very shallow dive, this will minimise the speed build-up and make it easier to end the drive forward. As you become more proficient increase the dive angle. On a boxy rudder elevator model the optimum dive angle will be around 30 degrees for maximum horizontal forward speed. On a sleeker machine this angle will be nearer 15 degrees, any steeper, and whilst the model may be going faster it is not going forward any quicker. In fact the forward speed will start to decrease the steeper the dive becomes.

2. Tight Turns

Like the drive forward the tight turn is best built up to gradually i.e. start with gentle turns that do not require any elevator input to maintain level stable flight. With a good well co-ordinated rudder elevator trainer it should be possible to initiate a gentle turn, return the controls to neutral and watch the model complete 90% of the turn without requiring further control input. Always start at a safe height and a safe distance away from the slope. Tighten the turn and see what happens. The nose starts to drop and the model builds up speed (it is in a shallow spiral dive!). Stop the turn and the model will go into a zoom climb due to the excess speed built up. If this climb is not corrected in time with a dab of down elevator the model will go into a deep stall. This often results in complete loss of control for the raw beginner with the inevitable results unless of course you have taken your guardian angel with you.

Before discussing the solution lets discuss the problem. The first action when applying the rudder to initiate a turn is to cause the model to bank. For the purposes of this article why and how this happens is not relevant only that it does. The amount of bank is dependant on the amount and how long the rudder is applied and secondary by the wing dihedral angle. This is mentioned as very few novice flyers relate rudder effectiveness to dihedral angle. As the model banks the resultant lift develops a horizontal component and it this component that 'pulls' the model around in a turn. Unfortunately as the model banks the rudder starts to function as an elevator. This has the effect of causing the nose to 'dig in' in the turn i.e. put the model into a spiral dive. We all know that when an aeroplane is in a dive it descends and gathers speed. The model will continue in this dive as long as the rudder is applied and the model banked. Neutralise the rudder, level the wings and the model suddenly has excess flying speed, hence the zoom climb.

To stop the zoom climb we must stop the speed building up in the first instance by:

1. As soon as the rudder starts to take effect gradually reduce the applied rudder.

2. At the same time slowly feed in a small amount of up elevator, just sufficient to maintain the fuselage in its normal flying attitude.

The secret lies in being able to recognise the normal flying attitude of the fuselage, irrespective of the angle at which the model is being viewed (orientation). You must build up a data bank in your memory of the model in all sorts of attitudes so that you can automatically recognise any one of them and maintain / make the appropriate control inputs. This skill is only acquired by experience (stick time) and in the early stages is often helped by mentally reminding yourself during the manoeuvre what it is you are doing. Sounds silly I know but when the model is coming towards you in an unfamiliar attitude panic often sets in and raw instinct takes over invariably resulting in the wrong control input.

Back to the turn! Start practising with gentle turns and gradually build up to very tight, highly banked, multiple turns. You should aim to be able to complete consecutive full rudder, flat eight turns and exit them without having to take recovery action!! Be responsive to the airspeed of the model. In a tight turn the wings have to work harder to produce the lift required to keep the model in what we perceive as the normal flying attitude. If the model starts to mush reduce the up elevator and open out the turn because if you do not there is a danger of going into a spin or stalling into a spiral dive. Always practice the turns at a safe height and distance and initially under supervision. There is no substitute for height and a forward position when recovering from an errant manoeuvre. As a bonus you will find that being able to throw the model around will increase your confidence no end which is why I introduce aerobatics very early on when teaching someone to fly.

3. Flying Towards Yourself

Learning to fly towards yourself takes a little longer with a slope soarer than a flat field model. Not because it is more difficult but simply because, except for landing and ridge hugging in light lift the model is invariably flying away from you. The first step in developing this skill is to work out a strategy for automatically reversing the steerage controls in your mind whenever the model is flying towards you and practising it at home, preferably with the help of a sympathetic friend! Remember it is only the steerage controls (rudder and ailerons) that need to be reversed. Not the pitch (elevator) control!

How you remind yourself that left is right and right is left is up to you but the mnemonics must be foolproof. One method used to pick up a dropped wing is to move the control stick in the direction of the down-going wing. Another for turning when flying towards yourself is simply to repeat left is right or right is left.

The best way to practise is to fly the model as far away from the slope as possible and then fly downwind directly towards yourself, initially just keeping the wings level but later incorporating a series of 'S' turns. Always decide well in advance where and in which direction your turn back into wind will be. The biggest danger in making this turn is not normally in the direction of the turn but in making the turn too late. I am often heard to say when giving tuition on this aspect of flying "I don’t care what decision you make but please make one!" Naturally on these occasions there is usually some emphasis in my voice! Flying a slow floater, in light lift, is an ideal way to learn this skill. Benign conditions with plenty of thinking i.e. time to correct mistakes, is the order of the day.

SUMMARY

In writing this article I have deliberately avoided the aerodynamic theory in an effort not to confuse the target reader. All this article has attempted to do is help the ab initio pilot acquire, with a little understanding, the three most basic skills needed before attempting a solo landing. Practise the control inputs at home and set flying targets on the slope. Remember practise makes perfect.

FOOTNOTE

Should you be interested and have access to back issues of this magazine (if not they are available from Traplet Towers) a number of other associated Prepare articles have been written, namely Prepare - to Fly (Feb 95) to Land (Jul 94) for Lift-off (Apr 94) for Slope Aerobatics (Nov 95)