Radio Control Model World - Feb '95

by STAN YEO

INTRODUCTION

All too often over the years I have seen modellers arrive at the flying site full of enthusiasm with a new, untried, model only to depart a few minutes later in bitter disappointment. Post-mortems reveal three main reasons for the failures:

1. Full pre-flight checks were not carried out prior to leaving home.

2. The conditions / site were unsuitable for the model

3. The modeller did not have the experience necessary to fly the model on that occasion.

The purpose of this article is to provide a simple checklist / advice on navigating your way from building board to successful maiden flight with the minimum of aggravation. The article is geared towards slope soaring simply because it is my specialisation but the majority of the advice is applicable to all forms of fixed wing radio control flying.

PREPARING FOR FLIGHT

This is the last phase of the building operation and probably the most important. If the model is not correctly set-up it WILL NOT fly properly and, will in all probability, be more difficult to fly. Included in this phase of construction is the installation of the radio equipment. Servos should be mounted securely on balsa bearers or if you prefer non-flexible self adhesive tape. Controls should be connected as per the plan with full and free movement. Bowden cables should be supported every 10cms, avoiding sharp bends and with the minimum of slack. The Receiver battery should be installed as far forward as possible so that it does the minimum of damage in a crash and reduces the nose weight required to get the Balance Point correct. If you are in any doubt as to how to install the radio equipment or set up the controls etc. please seek advice from a more experienced modeller or purchase and read a radio control primer book.

When hinging the ailerons seal the gap with trimmed down 6mm sq. soft self adhesive Draft Excluder, available from most D.I.Y. stores. Sealing the ailerons makes a considerable difference to both the performance of the wing and the response of the ailerons. Fit the hinges to the rear spar before fitting the Draft Excluder. Use a new scalpel blade to trim the down to size.

Below is a list of some of the items that should be checked as part of your pre-flight preparation:

1. Check wing for warps (see notes below).

2. Check the wings and tailplane are at the correct angle (incidence) to each other and the fuselage.

3. Check the controls operate in the correct sense i.e. moving the Rudder control to the Right moves the Rudder to the Right, Down Elevator moves the Elevator Down and Right Aileron moves the Right Aileron Up.

4. With the trim in neutral, the servos and the control surfaces should also be in neutral.

5. Check the range of movement of the control surfaces agrees with the plan.

6. Balance the wings (spanwise) by adding weight to the tips as required.

7. The position of the 'Balance Point' (Centre of Gravity). Point' (CofG) is as shown on the plan or slightly forward but NOT aft. Mark where it should be on the underside of the wing with a 'permanent' pen.

8. Check structural integrity i.e. everything is securely attached.

9. Range check the installed radio equipment. In the absence of specific instructions expect a range in excess of 100 metres with approximately 150mm of aerial extended.

WARP REMOVAL

If the wing has a warp (twist) it must be removed before the model is flown. With a built-up wing this is best achieved by pinning the wing to your building board with a small amount of warp in the opposite direction. The covering is then, either softened using a thin coat of dope if it is a doped finish, or is re-shrunk to it's new position if it is covered in heat shrink film. The wing is then left to settle for a few days before removing from the building board. The procedure is similar for a foam veneer wing except that a cradle is built to accept the warped wing panel. Set the anti-warp component to approximately the amount of warp you wish to remove. Thoroughly heat the wing using a heat gun. Get the wing as hot as you dare without damaging the wing or covering. Once again leave to settle for a few days before removing from the jig. If the above is not successful try again but this time increase the anti-warp factor. My experience is most wings are recoverable.

BALANCING

Balancing the wing is one of the last operations that should be carried out on the model prior to flying. The method I use is to insert a Map Pin into the wing leading and trailing edges at the wing centre. The wing is then suspended by these pins and weight is added to the wing tip of the high wing until it balances. This weight is then 'buried' in the wing tip and the finish restored.

After balancing the wing the model must be balanced. A rough balance point can be found by balancing the model, on your fingers, under the wing near the wing root. For a more accurate method make a simple balancing cradle (see diagram) to support the model. Mark the position of the Balance Point on the wing, at the root, either side of the fuselage. Suspend the model in the cradle with the cradle pivot aligned with the balance point marks. Add weight to the nose or tail as required until the model is balanced with a slight nose down attitude.

TEST FLYING

Unless you have experience with a similar or higher performance model to the one you are about to test fly I strongly recommend that you seek the help of someone who has the necessary experience. This particularly applies to ab initio pilots and those graduating to an aileron model for the first time. Newcomers to Slope Soaring will find it very difficult at first. The chances of an inexperienced pilot test flying a new model successfully are poor. I know because I learnt that way, not through pig headedness but through a lack of experienced slope pilots (it was in the mid sixties!).

When you are ready to test fly your model ensure that the radio equipment is fully charged and serviceable. Wait for a day when the weather is suitable (how many times have you been told that?). Do not be tempted to test fly your new model in marginal conditions. It is a recipe for disaster. If you are a newcomer to radio control flying please establish contact with the local model flying club that specialises in gliding / slope soaring. Find out as much as you can about the local slopes i.e. the most suitable wind strengths and directions and perhaps, more importantly, take out third party insurance before you fly (BMFA and ASP Insurance are both sufficient and reasonably priced, see modelling magazines for details).

On the day of the test flight take your current model along and fly that FIRST to get yourself attuned both to flying and the conditions. If you need a more experienced modeller to test fly your model insist that he/she has a flight with their own model first for the same reasons. Carry out the usual pre-flight checks i.e. the model is correctly assembled, your frequency is clear before switching on your transmitter, all controls are connected and operate in the CORRECT sense and trims are neutral (the controls should have been set up with the trims in neutral). Ask a competent modeller to launch the model for you just in case a panic response is required immediately the model is launched. Finally before launching the model check the whereabouts of other flyers' models. Launch the model gently but firmly into wind with a slightly nose down attitude. Do NOT give it a tremendous 'heave'. It is not necessary. It will only cause the model to climb violently, due to the excess airspeed, and stall into the ground unless you are lucky enough to recover in time. If the model has been properly built and prepared it should fly 'straight off the board' as they say with the minimum of trim adjustments. Be prepared for different flying characteristics and if you are moving up to a higher performance model be prepared for an increase in flying speed and control response. Take care when slowing the model up, particularly near the slope just in case it enters a spin. Get to know the model by trying out different manoeuvres but please allow a greater safety margin just in case things do not work out as you intended.

TRIMMING FOR PERFORMANCE

The control set-ups given on the plans are often conservative. The reason is that two conflicting groups of flyers have to be catered for, namely the inexperienced and the experienced. Consequently control responses are often set mid range and can be changed a small amount if desired. Despite meticulous setting up it is still possible that the model will require further trim adjustments. This could be for a number of reasons i.e. prevailing weather conditions, flying site constraints or simply personal preference. If the model does require further adjustments only make one adjustment at a time and keep notes for future reference. Below are a few notes to help with the adjustment of the Balance Point. The model will not necessarily exhibit all the symptoms mentioned.

Centre of Gravity too far forward.

1. Requires excessive up trim

2. Flies faster than normal or expectation.

3. Prone to diving.

4. Sluggish elevator response.

5. Requires a lot of up elevator when flying inverted.

6. Reluctant to spin.

7. Restricted aerobatic performance.

Centre of Gravity too far Back

1. Requires excessive down trim.

2. Model gets 'blown back' easily (poor penetration).

3. Unstable in pitch i.e. cannot find suitable elevator trim position.

4. Prone to diving (result of a flat stall).

5. Twitchy elevator response.

6. Has a tendency to enter a spin when slowed down in a turn.

It is imperative that the elevator control is set-up correctly as an over / under sensitive elevator can make flying the model very difficult. Too much elevator movement can result in the tailplane being stalled during aerobatics. A tailplane stall often manifests itself as a flick roll in the pull up for a loop or a slow roll at the bottom of a bunt on the application of more down elevator. Both can be very disturbing if you are not expecting it.

LANDINGS

Landing is the most difficult manoeuvre in slope soaring and requires alot of simulated practise plus good basic flying skills. If you are inexperienced ask an experienced flyer to land your model for you. If you are going to land yourself PLAN your circuit. Think about what you will do if the model is HIGH or LOW in the circuit. Start your circuit with the model in the RIGHT place and DO NOT go back behind the hill (you can always go around again). Practice imaginary landings in front of the slope before committing yourself to a landing, you may find the model (or is it the pilot?) behaves differently when close to the ground! Familiarise yourself with the model's behaviour when close to the stall and learn to recognise the symptoms that precede a stall or spin. The more you know about the model's flying characteristics the more confidence you will have and the better the chance of making a safe landing. Landing with reduced control responses i.e. with rates selected, may help to overcome the tendency to over control in pressure situations. Also if it is a basic trainer type model a small amount of down trim will not only increase the speed slightly and reduce the risk of stalling but it will also reduce the buffeting caused by the turbulence close to the ground. Landing and landing techniques is a complete article in itself and has been covered in the July '94 issue of RCMW.

SUMMARY

In a short article like this it is only possible to take a cursory look at the topics covered. Most paragraph headings could be expanded into complete articles if supporting theory is added. In my travels around the country visiting model flying clubs, delivering talks on various aspects of modelling, it is my experience that few modellers are interested in the nitty gritty theory. The majority rely heavily on trial and error and just want to know the basics needed to get the optimum performance from their models hence the abscence of theorems in my articles.

Required To Support The Article

1. Photographs of typical slope soarers models.

2. Diagram of balancing Jig.

3. Wind flow over a hill. (copy from previous article)