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First Model – High Wing Trainer

April 30, 2010 Leave a comment

On previous post, i talked about the basics to get you started, but when advising about a first plane, the reference was just to a generic high wing trainer… Well, as much as it says, there are so many high wing models in the market that it seems not helpful enough… until now!
On this post, i will share with you my experience on the first models and will suggest a particular one with which i learned to fly for real and still think it is one of the most beautiful high wing models due to it’s smooth, docile and forgiving flight characteristics. It is also very strongly built and will not break the bank as the price is very reasonable.

To cut to the chase quickly, i will introduce you the model right away.  And the first good news is that it is a well sized ARF model (1.6 meters wingspan), covered in strong, light, very resistant and durable Oracover film and there are two manufacturers offering this model, so you have two different color schemes to choose from.
Let’s start first with the Rainbow EP, a electric ARF version that comes in transparent orange and green. This color scheme is great, giving the model that “vintage” feeling, looks great and provides great visibility of the model in the air. This was my choice because when i bought it i was not aware of the next model availability.

Phoenix Rainbow EP
Phoenix Rainbow EP

The next one is the Graupner Electro-Kadett, the exact same ARF model with just a different brand name and color scheme – this one comes in a more consensual blue and yellow scheme. Initially i would go this color scheme if i had the choice, but now i just developed a passion for that “vintage” look of the Rainbow… Anyhow, it is just a matter of taste.

Graupner Electro-Kadett
Graupner Electro-Kadett

There is a great review and build log on RCGroups on the Graupner model. If you decide to go with the Rainbow, you can still refer to this to help you in your build as they are virtually identical.

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!