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Getting Started on RC Helicopters – Part 6 (Learning to fly)

May 10, 2010 Leave a comment

In this (very long) post, i will go through the several stages of learning to pilot a RC helicopter. I can tell you it will not happen without practice and time, so keep your anxiety controlled. But, if you follow these guidelines, you should be able to progress in your skills and soon will be flying like Tareq Al Saadi!

Level 1 – The hover

This first step into flying model helis is probably the hardest part to learn, mainly because you have to do it yourself. Of course an instructor can hover your model and show you the basic controls, he will make it look very easy but at least you know that if he can do it, the model must be okay. On your first attempt at hovering you might wonder what you have got yourself into as it seems almost impossible, don’t worry, its like riding a bike and once you can hover there is no going back.

You will need to fit a training under carriage, there are two types, crossed sticks with balls on the end or crossed sticks with a standard hula-hoop attached, either type is okay and they are usually fitted using cable ties.

Whatever radio you use make sure you have the best gyro you can afford as this will make control of the tail a lot easier. If you can get your hands on a good simulator it will help considerably, and at around £100 if you have a PC, it will be money well spent.

Try to choose a day with little or no wind and make sure you keep the model pointing into wind as this will help to keep the tail straight, all you are trying to do at this stage is to keep the model hovering on the spot at about 1 to 6 inches (25mm to 150mm) high, if it gets any higher, lower the throttle, land and try again. Just keep practising for as long as it takes, it will probably take several visits to the flying field to perfect the tail in hover.

So you can hover tail in and land fairly smoothly. Do not remove your training under carriage; it will still be useful for the next step, which is hovering side on. You can do this by hovering diagonally and gradually turning the model side on as you progress, make sure you practise on both sides of the model, it is very easy to get handed and once you have got the habit of hovering only your favoured side it is hard to get out of.

All the above will take many hours of practise to perfect so take your time and don’t remove your training under carriage until you feel you are ready to do so, you may want to move directly on to learning the nose in hover while you have it on, or you can leave nose in hovering until you can fly circuits when you can gradually fly the model towards yourself until you can stop and hover, which way you do this is up to you as I have seen it done both ways.

Remember, the most important things you will need to become an RC Heli pilot are patience and determination.

Level 2 – First Circuits

Before we get into the flying, set your lower pitch to about minus 2 degrees with 5 to 6 degrees in the hover position and 8 to 9 degrees at the top. It is also useful to set up the radio so that the throttle trim gives you tick over in the middle, idle up at the top and engine cut at the bottom. You should be able to achieve this using the travel adjustment (not the throttle curve) on the transmitter, if not you will have to adjust the throttle servo arm as required. You should now fly the model with the throttle trim at the high position; this will keep the engine revs up when in negative pitch there-by giving more control. As with learning the hover it is a good idea at this stage to get an experienced pilot to fly the model and adjust the trims as required, this will make it much easier for you.

Start with the model tail in, facing into wind, at a height that you are happy with, then hover over to your left side, back to the middle and then to the right side, keep practising this with the tail in then gradually turn the tail to follow the direction of the model and without stopping in the middle. The turns are initiated by applying lateral cyclic (aileron) to produce a bank, together with tail rotor (rudder) to make the tail follow the turn. The amount of aileron and rudder applied will vary according to the forward speed of the model and whether you are turning upwind or downwind. With practise this will eventually become a figure eight with the turns at both ends away from you and at the same height all the way round.

Do not be tempted to fly the model in a circuit around yourself; this is bad practise as most flying sites will not permit you to do this, so all flying should be in front of the pilot and anyway, you will not learn much from this as the model is in the same situation relative to you, all the way around.

Some pilots find the transition from forward flight to the hover quite difficult and avoid this manoeuvre by stopping the model at height and lowering the model vertically to land. This looks very untidy and if you are ever going to fly in a scale like manor you will have to approach at 45 degrees, you will also need to be able to do this to learn autorotations.

To return the model to hover from forward flight reduce power and apply back cyclic, adjust the amount of each control to achieve a 45 degree approach. Ideally the approach should be into wind but make sure you practise from the left and right to avoid getting handed.

As you gain confidence with flying circuits try to gradually make them higher and faster. The height will be useful later when you attempt new manoeuvres, giving you more time to correct a mistake before the ground comes up! Also don’t be afraid to fly on a windy day, I have seen many pilots build up a fear of the wind and you can’t let the weather stop you flying, particularly if you live in the UK.

Remember, the only way to learn is stick time and lots of it.

Level 3 – Autorotation

There are many pilots who advance to quite a high level of flying yet never bother to learn autorotations (autos), a comment often heard is “why stop an engine that is going perfectly well”, fair comment I suppose but what if your engine cuts, chances are you will panic and crash the model. So there is one good reason to learn autos, the other reason being the shear satisfaction of landing your model time after time with no engine power. I having gone through many stages of learning to fly but I found the autorotation the most rewarding of all.

During autorotation the negative pitch will control the glide angle of decent, this will be about minus 3 degrees but will vary according to wind conditions, blades, and forward speed during the auto. I always set my negative pitch to about minus 5 degrees and then adjust the pitch with the stick to get the ideal decent angle.

Before you start, you will need to set your throttle hold switch so that it gives a reliable engine tick over when operated. If your tail is driven during autos you should set the tail blades with no pitch when the hold switch is operated, as there is no torque from the rotor head during autorotation the tail does not need any counter acting pitch. You must be able to perform a 45 degree approach and landing before any attempt at autos. Also make sure you are familiar with the throttle hold switch position on the transmitter, you will need to find it quickly while practising.

To give you an idea of how much power is in the rotor head with no engine power, from the ground, raise the throttle until the model is light on the skids, switch to throttle hold and gently add pitch, the model will hover for a short time.

Start by flying your normal circuits at a safe height, when flying into wind hit the hold switch and apply negative pitch, the forward motion of the model should keep the tail straight, if the tail kicks to the left or right return the hold switch to normal and land the model, adjust the tail trim and try again. Once you are happy with the tail trim keep practising autorotation descents but only down to a height that will give you time to abort (return the hold switch to normal). After hours of practise you will be able to descend at 45 degrees, apply back cyclic to flair (stop the forward speed) and add pitch to land. The difficult part is the timing of all this, if you add to much pitch to early (to high) you will use up the inertia in the rotor head and will not have enough to land. If you add pitch to late the result is obvious.

Autorotations are easier with a 60 size model due to the extra blade power but wither it’s a 60 or 30 size model, the type and weight of the blades will have a major effect on auto performance, use glass/carbon blades like SAB or TG for best performance.

Keep practicing, but remember – it is supposed to be fun!

Level 4 – Setup for Aerobatics

Most transmitters will have three flight modes available via the flight mode switch (sometimes called the idle up switch), this will give you three pitch and throttle curves, one for normal hovering, one for aerobatics like loops and rolls, and the third one can be set for more extreme 3D type flying.

Throttle Curve 1 - Normal

Throttle Curve 1 - Normal

Throrrle Curve 2 - Stunt 1

Throrrle Curve 2 - Stunt 1

Throrrle Curve 3 - Stunt 2

Throrrle Curve 3 - Stunt 2

During aerobatic manoeuvres negative pitch is used during the inverted sections so the throttle curve is set so that it will not drop below 50%, while you have full pitch control. These high throttle curves should only be switched in when flying and not before take off as the engine will over rev in this situation.

Pitch Curve 1 - Normal

Pitch Curve 1 - Normal

Pitch Curve 2 - Stunt 1

Pitch Curve 2 - Stunt 1

Pitch Curve 3 - Stunt 2

Pitch Curve 3 - Stunt 2

The main difference in pitch curves will be in the negative section where up to minus 8% may be used for inverted flight, where as for the hovering mode minus 1 or 2% will be ideal. It is also useful, in the hovering mode, to flatten out the curve at the centre point to make the model less sensitive.

Revolution Mixing

This is available on most transmitters and is quite simply a mixer, which adds pitch to rudder to correct tail swing on adding power. However it is not always easy to set up and if you have one of the latest piezo gyros with heading hold, you probably wont need it.

Cyclic to Throttle Mixing

Some transmitters have dedicated mixers for aileron to throttle and elevator to throttle but you can use any free mixers, try about 20% throttle to start with and if possible only on flight mode 3 for more extreme manoeuvres. Be aware that if your throttle is already flat out, the mix will try to add more throttle and could overdrive the servo, some transmitters (like the JR PCM10) take account of this and therefore will not overdrive the servo.

So your model is now set up for aerobatics!

Rotor Head & Vibration

The main enemy in any model heli is vibration; this can be split into two types; high frequency and low frequency.

High frequency vibration usually stems from the engine, fan or clutch area and cannot easily be seen until cracks appear in the side frames or servos and other radio parts start to fail. All you can do is balance fan and clutch and all should be okay.

Low frequency vibration stems from the rotor head and normally shows as vibration of the tail boom and sometimes on the landing gear. Blade tracking is the first thing to check. Stick a strip of tape to the end of each blade, a different colour each end is required, as you bring the head speed up and looking at one side of the rotor disc you will be able to see if one of the blades is higher than the other (out of track) the different colour tape will tell you which one is high or low so it can be raised or lowered by adjusting the pitch control link.

The blades that came with your heli are probably wooden and will need balancing, how to do this is normally explained in the manual, however, I would try to use quality carbon/glass blades, I know they are more expensive but they do come ready balanced and their performance is far beyond that of wooden blades. I have used SAB, TG and NHP blades and have never had a set out of balance. I have not used any other make so I can’t comment.

Other sources of vibration can be the flybar, paddles and feathering spindle. Damper rubbers should be lubricated with silicone grease when fitting and the flybar must be centered with paddles of equal weight.

If your model has been crashed then the main shaft, feathering spindle and sometimes the tail rotor shaft will probably be bent and must be replaced. The feathering spindle can sometimes be straightened but for how much it costs it’s just not worth it. The main shaft must always be replaced as it could be weakened if straightened.

The rotor head speed on a model heli can vary from 1100 rpm to 2000 rpm at the extremes. Generally speaking the higher head speeds help stability, but things will wear more quickly, on the other hand if your head speed is to low the model will be unstable and sometimes the nose will nod up and down. The manufacturer should be able to tell you the maximum head speed permitted but good quality blades are recommended at higher head speeds. In my experience head speeds tend to vary from club to club as everyone sets up their model to sound like other models in the club, resulting in every member having a similar head speed wither its high or low. I run my Raptor 30 at about 1450 rpm in the hover, 1650 rpm in flight mode one, and 1800 in 3D mode.

So run a head speed no higher than you need to and don’t fly with any vibration and your model should perform well for a many hours.

Scale Helicopters

After several years flying model helis I was getting a little bored with throwing it around the sky at great speed and wanted something different. So scale was the way to go with so many skills required it was bound to be interesting.

There are three main ways into scale helis :

1.Buy a complete kit, which includes all scale parts as well as the mechanics. (i.e.Hirobo Lama or JR Ergo Robinson R22).

2. Buy a pod and boom model, which is also designed for use in scale fuselages (i.e. Vario or Graupner/Heim).

3.Buy a fuselage and fit your chosen heli into it.

Option 1 is the simpler and cheaper one although there will be less choice of models. Option 3 will require a higher degree of design and skill to build. Option 2 is I think the best option as once you have the pod and boom model you can fly it for some time to test and get used to it before putting it into a fuselage also there are plenty of scale fuselages to choose from.

Your choice of subject for scale might be your local police helicopter or a military helicopter or maybe one that you have seen on film, like the Airwolf, or it could be one that you just like the shape of. Whatever you choose remember that a full fuselage will always restrict access to the mechanics where as models like the Robinson R22 or Hughes 300 will be more accessible. This may not be a problem to you, but worth bearing in mind.

Three, four and five blade rotor heads can be fitted for more realism though they are expensive and have different flying characteristics to the standard two blade and flybar.

Also available from Vario are models like the EC 135, which has an enclosed (Fenestron) type tail rotor and the Notar which has no tail rotor but uses vectored air instead.

Flying a scale model is quite challenging and requires a great deal of accuracy to make it look realistic. Smooth hovering, slow climb outs and circuits, and nice 45 degree approaches are all part of scale flying. I prefer a model which flies well and looks realistic in the air rather than one which is accurate in every detail but is not flown due to the pilot being afraid of a possible crash, maybe the pilot lacks the confidence or has spent to long on all that detail!

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Beginners’ Guide

April 30, 2010 Leave a comment

First Model

Some people consider a glider as the obvious choice for the first model. Although a glider normally flies slower and is supposed to be more forgiving, I think that’s just a matter of taste. Being a skilled glider pilot doesn’t necessarily mean being also a skilled powered aircraft pilot and vice-versa.

Assuming that a powered model was chosen, the beginner is advised to start with a so-called trainer. This type is usually a high wing aircraft model with nearly flat bottom airfoil that produces high lift, permitting slow landing speeds without stalling. It also has some dihedral angle to give a good lateral stability.

However, a flat bottom high wing with dihedral is more sensitive to crosswind gusts, so the first flights should be done during calm weather. A beginner should avoid wings with too sharp leading edges, as it will worsen the stall characteristics.  A well-rounded leading edge is therefore preferable, as it better conveys the airflow onto the upper wing surface allowing higher angle of attack at low speed.

A trainer model should not be too small, as it would be difficult to assemble and maintain and would be more sensitive to strong winds.  It should not be too large either,  as it would be difficult to transport, require a larger flying field and
would be more expensive. A reasonable size is about 150cm wingspan (60 in) with a high aspect ratio, which means the wingspan being about 5.5 times the wing chord. A square wing is advisable, as it distributes the weight of the aircraft evenly over the entire surface of the wing. In order to allow a reasonable low landing speed without stalling, the wing
loading
should not be greater than about 60g/sq.dm (19-oz/sq. ft). Wing loading is the aircraft’s weight divided by the wing area. Some degree of wing washout also improves the stall characteristics.

The basic parts of a trainer model:

Engine – provides the power to rotate the propeller.
Propeller – (also Prop) is attached to the engine’s shaft to convert rotational motion into thrust and speed, which depends on the Prop’s diameter, pitch and the Engine’s power.
Spinner – streamlined part that covers the end of the Prop shaft.
Fin – (also Vertical Stabiliser) provides directional stability (stability in yaw).
Rudder – movable part fitted to the Fin’s trailing edge, is used to change the aircraft’s direction.
Stabiliser – (also Horizontal Stabiliser or Stab) provides longitudinal stability (stability in pitch).
Elevator – movable part fitted to the Horizontal Stabiliser’s trailing edge, is used to make the aircraft climb or dive.
Ailerons – movable parts on both sides of the wing, are used to make the aircraft roll about its fore – aft axis. When one aileron moves up the other moves down.
Wing – provides the aircraft’s main lifting force.

One may build a model aircraft based on drawings (plans). This requires some building skills and also time and effort to find out and gather the materials needed for the construction. An easier approach (albeit more expensive) is buying a kit of parts. There are many kits on the market with different levels of prefabrication depending on their price.
The cheaper kits have most of parts included, but some pieces come either pre-cut or printed on sheets of wood, so the builder is expected to do some extensive job, such as to cut out the fuselage formers and wing ribs, glue the parts together, apply the covering material, etc.
For those who are not so keen on construction, there are almost ready to fly (ARF) kits with an extensive re-fabrication, requiring one or two evenings to assemble. There are also ready to fly (RTF), which normally come complete with the power plant and some of them even with the radio pre-installed.

First Flight

It’s highly recommended to have an experienced instructor beside you during your first flight. However, it is not impossible to get succeed by doing it alone. Maximum wind speed recommended is 5-8 Km/h (3-5 mph) including gusts.

Check your plane’s CG location with empty fuel tank (if you are using a combustion model) or with batteries (if using an electric model) by supporting the model with your fingertips underneath the wings. Find the position where the fuselage gets level or its nose is pointed slightly downwards. Remember a golden rule: a plane with a CG a bit forward to it’s ideal location will fly badly, but a plane with a CG aft it’s ideal location will fly once… So, if you are not sure about how to exactly put your CG, just make sure it is more forward than aft. Within the first flights when you try to fly leveled you will notice by it’s flight characteristics and you can make small corrections on each new flight.

Transmission range check should be performed on the ground before the flight. This is usually done with the Transmitter aerial collapsed (this is not applicable for 2.4Ghz radio systems). The control surfaces should respond without glitch at a distance of about 80 meters (263ft). This distance is only an approximately guide line, as the actual range may vary depending on the environment.
The effective range may only be half of this value if located at mountain bowl site or close to a public radio transmitter, radar station or similar. The range may suffer adverse effects if the receiver aerial is close to metal parts or model components reinforced with carbon fiber. Some transmitters allow the aerial to be totally collapsed inside a metal case (again not applicable to 2.4Ghz radio systems), which also may reduce the radiation. In this case the lower section of the aerial should be extended during the test. The check should be repeated with the power system running, alternating the throttle setting between idle and full-throttle.

The range will be much higher when the model is in the air, normally about 1Km or as far as one can see the model.

Take-off:

If you hand launch your model, throw it against the wind horizontally and straight ahead, not up.
If you take-off from the ground, taxi the model towards the wind and let the model gain ground speed before applying elevator. Once in the air try to climb at a very small angle, not abruptly upward, which would cause loss of airspeed and stall.

The model is more sensitive to the motor torque effect during the relatively low take-off speed and may begin to turn left (or right). Use the rudder or ailerons to prevent the model from turning during the climb stage, otherwise the model may initiate a spiral dive.

Don’t try any turns until the model has gained speed and reached a “safe altitude”. Be very gentle with the controls and practice gentle turns high in the air before you try to land. To prevent losing altitude when turning the model, just give little up elevator at same time you make a turn.

Try to keep the model in sight and do not fly too high or too far away. You may reduce the throttle while high in the air so you may get an idea how the model behaves at low speed – try to glide it while high and use just a bit of elevator to keep the nose leveled – even thought initially you will feel it is too slow and it may fall, just keep doing it so you have a real feel of how slow it can fly (as you have the model high in the air with slack to recover if something happens). This will give you an idea of the kind of speed you will use when approaching for a smooth landing (which will NOT happen on the first times… – you have been warned).

To prevent getting confused about which way to turn when the model flies towards you, turn your back to the model slightly while keeping watching it, so you can imagine “right” and “left” from the model’s point of view. At this stage, you should have already practiced with a good computer flight simulator and you should be already comfortable with this situation. If not, better to spend a few more hours on the simulator if you don’t want to crash your expensive plane.

Some trimming may be needed in order to reduce or eliminate roll, bank and/or pitch tendencies. A flat bottom wing often tends to “balloon” up into the sky, keeping climbing when full throttle is applied. This may be reduced during the flight by adjusting the elevator trim or by reducing the throttle. In worst cases it may be needed to increase the motor’s down-thrust angle and/or decrease the main wings incidence angle.

Landing:

Reduce throttle to about half or even less (depending on the power and torque of your power plant) so you have to slightly pull up the elevator to keep the altitude. Turn the model towards the wind and let the model sink gradually towards the landing area by easing the elevator.

During the last fifteen to twenty meters (45 to 60 feet) of descent, (which depends on the model’s characteristics) you should idle the throttle. The model will start sinking at a higher rate now. Try to keep the model in a shallow dive and don’t use the elevator to gain altitude or to prolong the flight at this stage, otherwise stall is likely to occur.
Just keep a slightly downward attitude throughout the final approach in order to maintain the airspeed.
The higher the wing loading, the steeper the approaching angle may be. However, it is not recommended approaching angles greater than 45 degrees.
If you notice that the model is sinking too fast or is too low to reach the landing field – just increase the throttle first before applying elevator to maintain or gain altitude to prolong the flight or to repeat the landing approach.
Pull up the elevator slightly about 30-60cm (1-2 ft) before the touch-down so that the propeller or nose gear don’t hit the ground.

Be prepared to repeat unsuccessful landings several times, since it’s often a matter of trial and error before one gets used with how the model behaves. If you are using a flying field with grass around the track (highly advisable), on the first tries just worry about the landing approach. Don’t try to land in a specific spot, avoid turns when the model is flying low or at low speed. Just let your model glide into the ground straight-ahead. With time and more experience, you will get better and better an soon will be landing exactly where you want. Even experienced pilots sometimes have hard landings, as this is the most difficult maneuver.

Avoid the proximity of buildings, roads and electric power lines. Don’t fly close to or towards people and animals.
The bigger the field for your first flight, the greater will be your chances for success. And remember, if the weather conditions are not adequate for your first experiences, control your excitement and come back later when the weather is better. This is a great way to prevent mistakes that will cost you a lot of money in repairs.

It’s also advisable to join the nearest model aircraft club there you may meet experienced fliers who can provide lots of useful tips and hints.

Good luck!