How High Do RC Planes Fly?


How High Do RC Planes Fly

RC Planes have come a long way since the first time they flew in 1938. With the rapid development in technology, RC Planes are soaring to new heights these days. The efficiency and capability of RC planes has increased with the most modern ones coming in par with the real planes.

So how high do RC planes fly? Beginner Ready to Fly RC planes can fly upto an height of 400ft on average. The height up to which an RC plane can fly is mainly dependent on its design. Among many, the major parameters determining the flight height of an RC plane are Weight, Lift, Thrust and Drag.

We did ask some of the expert RC pilots and most of them said that they did fly their RC planes between 6000ft and 7000ft. Only a very few among them claimed that they have taken their plane to an altitude close to 8000ft. The one thing they all said in common was that at that height it’s virtually impossible to see anything. So they brought down their planes from that level fast.

Before we proceed further you need to understand that we cannot generalise the heights up to which RC planes can fly. A lot of factors come together to determine how high can an RC plane can fly. In this article, we will have a look at those factors and see the role each one plays.

Let us begin with having a sneak peek into how an RC plane flies.

How does an RC plane fly?

It doesn’t matter if it is an RC plane or an actual plane, they all work based on the Bernoulli’s principle. When the aircraft is pushed forward by the engine or a propeller the aircraft moves forward and the wings cut the airflow in half.

The air that’s pushed under the wing generates lift, which makes an aircraft remain in the air. While the air that’s pushed upwards creates a partial vacuum on top of the wings that sucks the aircraft upwards.

For this upward push and pull generated by a thrust to continue, the aircraft must have a steady flow of air on its wings. This is accomplished by using a jet engine or a propeller that pushes the aircraft forwards.

Now that you have a basic idea of how an aircraft flies, let’s go a little deep.

What are the factors that determine the flight height of RC planes?

four forces of flight

As discussed in the previous section, four fundamental forces keep the aircraft in the air and flying:

  • Weight
  • Lift
  • Drag
  • Thrust

How much lift and thrust an aircraft generates clubbed with how minimum the weight and drag determine the height at which an RC plane or aircraft can fly.

Let’s begin with analyzing each of the factors individually:

 

Weight

The weight of an object is the force with which gravity pulls it downwards. So anything that flies in the air has to constantly develop a force to counter its weight. The more the weight of the airplane the more upward force (Lift) an airplane has to generate.

The most important part of an RC Airplane is its airframe which decides the core endurance of an airplane. When an RC Airplane climbs to gain altitude, it is going to experience a lot of force. A strong airframe is important when it comes to high altitude flying.

An array of electronic devices and components comes with RC planes. For instance, Batteries, Sensors, transmitters and receivers, electric motors, servos and a lot of other components.

The thumb rule in designing an RC plane is that the air-frame should weigh at least thrice the weight of all the electronic components.

How optimized is the total weight of your RC plane determines how high it can fly.

Lift

As mentioned in the earlier section, what keeps an airplane up and flying in the air is the upward force called lift. A plane accelerates upwards/climbs when the lift generated is more than its weight.

For an airplane to climb or remain in balance in the air sufficient lift is necessary.

Let us have a look into how lift is generated to determine the factors that affect the lift of an airplane.

If you have seen the wing of an aircraft, you might have observed that the surface area at the top is less than that of the bottom. When an airplane cruises through the air, this shape of the wing causes air to flow faster on the top than at the bottom. This difference in velocity on both sides is going to create a low pressure on the top and high pressure on the bottom of the wing which generates sufficient lift.

As mentioned in the previous section, the reason why an airplane can be explained using Bernoulli’s equation. According to which the lift of an aircraft is dependent on

  • The wing area
  • Square of the Velocity of the airplane
  • The density of air

Though the wing area and the velocity at which a plane can fly is purely based on the design of your RC plane, the density of air is not. As your plane climbs with every meter the density of the surrounding air decreases.

With dropping density of the air it is going to be difficult for the wings to generate enough lift to keep your RC plane balanced and flying. Again, the weight of the plane becomes a decisive factor here. The more the weight the difficult it is to generate sufficient lift at heights.

It is for the same reason why most of the commercial aircraft have a height ceiling beyond which it cannot fly. Unlike a fighter aircraft, commercial aircraft are heavy and are meant to carry passengers and cargo. Considering its weight and payload, for most commercial airlines the flight ceiling is set at 38,000ft.

In brief, how high can an RC plane also depends on how much lift can its wings generate and the density of the air.

 

Drag

The explanation of drag and its impact on the height at which your RC plane can fly is beyond the scope of this article. For now, we will have a sneak peek into the same.

The drag of an airplane is defined as a force that opposes the thrust generated by an airplane. To put it in simple words, the opposing force you experience when you keep your hand out of the window of a moving car is called drag.

The drag of your RC Plane depends on the

  1. The properties and geometry of your RC plane
  2. The motion of your RC plane through the air
  3. The properties of the air (Density, humidity, temperature, etc.)

As mentioned in the earlier section, for an airplane to climb it needs to generate more lift than its weight. The lift generated is directly proportional to the square of the velocity of the plane. Which means, the more the velocity the more the drag is going to be.

Similarly, by adjusting the angle of impact (the angle at which the plane’s wing contacts the air), it is possible to increase the lift and the rate of climb of the aircraft.

In short, drag is another important aspect when it comes to the height at which an RC plane can reach.

 

Thrust

The thrust generated by the propulsion system of your RC plane is another decisive factor that determines the height your plane can reach.

Thrust is the force that keeps the aircraft moving, opposing the drag. As discussed in the previous sections the faster the plane moves the better the lift is going to be. This means your RC plane can reach more height.

For instance, assume the case of an RC plane powered by a propeller engine that develops thrust by moving a large mass of air through a small change in velocity. With an increase in altitude the density of air decreases which means the propellers wouldn’t have enough air to develop adequate thrust to fly high.

To give you an idea, for a propeller plane to produce enough thrust at higher altitudes; theoretically, the blades must at least be a few meters long.

Apart from the low density of air, the IC engine that’s powering the propeller blades will not have sufficient oxygen to burn the fuel efficiently to generate enough power to drive the propeller blades.

In short, the thrust your RC plane can produce determines the height at which it can fly.

Apart from these four factors viz; weight, lift, thrust and drag, there are other factors such as the range of the transmitters and receivers, visibility, wind speed, terrain, etc. that determine how high can an RC plane fly.

 

Is there a formula to find the maximum height achievable by an RC plane?

No, there isn’t a formula to determine the maximum height your RC plane can reach. As mentioned in the previous sections there are a ton of factors to be considered.

From a technical point of view, your RC plane’s maximum altitude is where the thrust required is equal to the thrust available. The thrust generated by engines decreases with altitude. At some point, the aircraft will be generating just enough thrust to compensate for the drag and weight of the aircraft. You can consider this the maximum achievable height.