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# RC Airplane Series-2
In the previous part (RC Airplane Series -1) , We learnt about the wings of the aircraft and what is the reason behind the generation of Lift for the airplane. Now that we have learnt to take the airplane into the air, it’s time to control the aircraft. So, in this part, we are going to learn how are the control surfaces used in order to control the aircraft properly.
TOPICS TO BE COVERED :
- What are different control surfaces in aircraft ?
- Different dimensions of movement
- Aileron
- Elevator
- Rudder
- Flaps
1. Different Control Surfaces
For the controls part, we have them divided into two parts : Primary and Secondary Control Surfaces
- Primary : Ailerons, Rudder, Elevator
(These are the necessary ones! Like Air, Water and Food for us)
- Secondary : Flaps
Fig. Positions of Ailerons, Rudder & Elevator
2. Dimensions of Movements :
There are basically 3 axes about which movement of the aircraft happens :
- Longitudinal : It goes from nose to tail of the aircraft
- Lateral : It goes from wingtip to wingtip and is perpendicular to the longitudinal axis
- Vertical : It is mutually perpendicular to both, longitudinal and lateral axis
Fig. Movements exhibited by an aircraft
- Pitch : It is the rotational motion of the aircraft about the Lateral Axis (Nose – Up and Down)
- Roll : Rotation about longitudinal axis is Roll. During this, the aircraft tilts its wing up and down
- Yaw : Rotation about vertical axis is Yaw. Basically, moving right and left in the plane itself
Fig. How it exactly happens?
3. Ailerons :
– Ailerons are the control surfaces situated on the wings and are responsible for the ‘Roll’ motion of aircraft.
- There are mainly 2 types of Ailerons (in Trainer Aircraft mostly) : Strip Aileron and Normal Ailerons
Strip Ailerons are the ones which span over the entire half wing and have a width = 1/8 of chord length
In normal ones, the length = 1/4 of wingspan and are situated towards wingtip and have a width = 1/4 of chord length
Working of Aileron :
For example, we need our airplane to roll towards right. For this to happen, the Right Wing should get lowered while the Left wing should be lifted up (when viewed from tail)
I will try to explain this in a very simple manner. Just remember that,
“Obstruction causes velocity to decrease“
(This is applicable for all control surfaces)
Fig. Right Aileron is raised up while Left Aileron is lowered down
- Now, we want to Roll our aircraft towards right. So we control the Aileron with the help of transmitter (in case of RC Airplane), steering wheel in case of real aircrafts.
On giving the signal, the right Aileron is raised while the left Aileron is lowered down. For the moment, let’s focus on the Right Aileron. The control surface here as been moved up & now, this causes Obstruction for the Air !!
- Because of this obstruction, the velocity of air in the upper part decreases and hence Pressure in the upper part increases. (refer RC Airplane Series-1) and this causes the Right wing to go down and left wing goes up and as an overall effect, we get the Roll towards right.
4. Elevator :
Elevator is connected to the horizontal stabilizer. The elevator is responsible to control the pitch of the Aircraft.
Working of Elevator :
Consider an example where we need to pitch up the plane (make the nose up !). In this case, when the signal is given, the elevator is deflected upwards. Now, again the air flow in the upper region feels an obstruction which lowers the velocity of air in upper region. This causes the Pressure in the upper region to get bigger.
This results in the ‘pressing‘ of the horizontal stabilizer downwards. Due to this the nose of the aircraft (front part) rises up.
(Just consider a pencil and hold it somewhere
Fig. Elevator is deflected upwards
- The process is the same for all, whether its the aileron, elevator or the rudder
Consider an example of pencil. It’s CG (center of gravity) is marked. So when we apply a pressure on the back side (FigP(a)), the front part (part which is ahead of CG) rises up (which we say here as ‘pitch up’) as it rotates about the lateral axis passing through CG (FigP(b))
FigP(a). Pressure is applied at the back end of pencil FigP(b). Result of the application of pressure (Nose Rises)
5. Rudder :
Rudder is attached to the Vertical stabilizer. It is responsible mainly for the Yaw motion of the aircraft. Basically, Yaw is like moving right and left in your plane itself !
Working of Rudder :
Consider that we need to move shift to left while being in the plane of the aircraft (i.e. just try to give nose a different direction)
- When the signal is given such that you want your nose of airplane to move towards left, then the rudder also deflects towards left. Now the rudder acts as a obstruction to the airflow on that side. Hence velocity decreased. Therefore, pressure increased. The higher pressure causes the front part to move to left (in the geometric plane)
Fig. Rudder
6. Flaps :
Flaps are the Secondary Control Surfaces which help the pilot to have a stronger control and stability over the airplane. Flaps are situated besides the Ailerons. Sometimes, the Ailerons itself work as Flaps as well (in case of single servo for each Aileron **). In this case, we call those control surfaces as ‘Flaperons’ (Flaps + Ailerons)
You must have hear pilots saying “FLAPS ON !!” or “FLAPS DOWN”. This tells that the Flaps are to be deflected downwards.
Fig. Positioning of Flaps
We are very well aware of the Lift generated because of the Flaps getting deflected downwards. (Same as Ailerons getting deflected downwards) but there is an important factor to consider, which is ‘DRAG’
DRAG :
– There is lift, but there is also DRAG developed due to downward deflection of flaps. Since, due to this, the contact between the airflow and the surface gets broken.
– This Drag causes the wing speed to decrease
- For Landing, we need the plane to be slow moving since ofcourse it’s easier to handle a slow moving car than an fast one. So the drag component takes care of reducing the speed of aircraft while on the other hand we also have the Lift generated which combinedly gives a slow and controlled descent.
- From takeoff point of view, we need Lift to be generated at lower speeds itself and hence Flaps are essential in this case as well.
Note that : “FLAPS UP” implies the retracting of flaps to the original position (no deflection)
The amount of deflection can be controlled based on the need with the help of control stick !!
Conclusion :
Through this article, We discussed about the Controlling of the Aircraft. Go through it slowly and try to visualize by yourself. You will definitely get it. In this Series, we will keep going step by step and gradually make the whole basic RC Airplane model. I hopw you enjoy this Series !!
Keep Learning !!
RC Airplane Series – All Articles (You are at Part – 2 !)
- Part-3 : Designing your Airplane !!
- Part-4 : Motor and Propeller Selection
- Part-5 : How to choose LiPo Battery ?
- Part-6 : ESC Calculations and Electronics Connection
- Part-1 (Previous) : What’s in the Wings ?
