How can gliders fly without propulsion | The most complete explanation

Gliders or sailplanes are a kind of aircraft that differ from the rest

by their ability to fly great distances without the need for an engine

or propulsion of any kind

even gaining altitude during their flight

but, how is this possible?

That is what I will answer today in this video.

Welcome to Joyplanes RC 2.


Personally, gliders are my favorite aircraft

because they don't need an engine to fly

and because of the long impressive wingspan they have

but their long wings have a reason to be.

Let's start with the basics

we know that an airplane can fly or glide without an engine

but in the process it will gradually lose altitude and depending on its weight

aerodynamics and other physical facts it can go down faster

this happens with every airplane

regardless of whether they are gliders or not

without an engine it is possible to fly for some distance and land

as long as a constant speed and descent rate is maintained

to be in a stable flight

but the gliders are designed to take full advantage

of this balance of forces

the gliders are made with lightweight materials

and the weight is distributed at strategic points

in an efficient manner to improve air penetration

and the configuration of their wings allow them to have

more lift with less aerodynamic drag

as a result their glide ratio is one of the most efficient

among all airplanes

The glide ratio is the distance that the aircraft can travel

in respect to the lost altitude

for example a Cessna 172 has a glide ratio of 9 or 9: 1

which means that if its engine stops working

it can fly from 100 meters of height for about 900 horizontal meters

in modern gliders this gliding ratio

can be between 40: 1 to 70: 1

which means that if a glider has a 50: 1 ratio

then it could fly for 50km if it starts at 1km high

making it capable of covering long distances in this way

Still it is impossible to gain altitude for an aircraft

that moves through a static atmosphere

without the use of propulsion of some kind

luckily our atmosphere is not static at all

to gain altitude

gliders can take advantage of various atmospheric phenomena

There are three main phenomena

the ridge lift


and wave lift

Thermals are the most mentioned way

to gain altitude in a glider

these are columns of hot air that is generated by a surface

heated by the sun

this air becomes less dense

than the surrounding air

and begins to rise rapidly

the glider when entering a thermal

can begin to fly in a circular pattern

to stay inside it and gain altitude

until the thermal disappears or weakens

the other way to gain altitude is with the ascending

currents of air on the slopes of the mountains

this is simply air that is forced to climb the mountain

and a glider can take advantage of this current

to gain or maintain altitude

the closer to the slope the stronger the climbing rate

the last form is the use of air waves that are generated

after the air passes through the mountain

these waves extend for several kilometers

and are invisible waves

similar to the waves of the sea

Using these strategies to gain altitude

a glider can stay in flight for many hours

this is totally free and clean energy

that glider pilots gather and manage

to get the most out of it


to make a glider take off

you need an airplane

that will tow it to an acceptable altitude

where the glider can start by itself

another way is to take off with a tow winch from the ground

but the altitude that it gains is not as much

as that of the first method

hopefully on a sunny day the glider can take a thermal

that makes it fly longer

others Wways to take off a glider is from a mountain

with a system of elastic ropes on a hillside

or by having a retractable propulsion system

integrated into the glider that is only used to take off

or gain the altitude needed

Why long and thin wings?

the thin wings

generate less induced aerodynamic drag

than the common wings that are seen in self-propelled airplanes

this way the glider can pass through the air with less difficulty

obtaining the same lift and losing less speed than other airplanes

another factor that helps for better Aerodynamics

is the design of the fuselage

making everything as smooth

thin and aerodynamic as possible

which is why the pilot enters the cockpit

in much the same way as a Formula 1 driver in his car

(almost lying down).

the wings are also measured by aspect ratio

glider wings have a high aspect ratio

and war airplanes wings have a low aspect ratio

war or acrobatic aircraft wings generate

more induced drag than thin wings of gliders

but because they are short wings

they are more maneuverable

maneuverability is a priority in warplanes rather than fuel efficiency

in the case of gliders it isn’t necessary to make quick maneuvers

so priority is given to efficiency sacrificing maneuverability

The wings end up being naturally long

because a large wing area is required

with the restriction of a reduced cord wing

to minimize drag

Gliders are built to be very light but strong at the same time

they even become so light

that you have to put more weight on the wings

to improve their penetration and speed characteristics

this is done by filling the glider with water ballast

in special tanks inside the wings

the total weight of this ballast can be even higher than the pilot's weight

the water can be drained during the flight

in case the thermals are not so strong

and must also be drained before landing

In the beginning gliders were made out of wood with fabrics or metal

and then the use of composite materials


carbon fiber and kevlar was introduced

achieving a huge resistance with a very light weight

Flight instruments

Gliders are equipped with the basic instruments

that can be found on any other aircraft

except for flight instruments associated

with the use of an engine

the most used and necessary instruments

are the anemometer



and compass

You can also find a turn coordinator

Sometimes an accelerometer

and tools such as a radio

and a GPS

One of the most basic indicators

that are still used even in high-performance gliders

is the yaw string

it is a small string that is placed on the outside

in front of the pilot that indicates the wind direction

in regarding to the glider flight

if the string is not centered

it must be corrected using the rudder

and that way the pilot makes sure that he is flying efficiently


that means that the fuselage is off

by some degrees in respect to the flow of air

and that generates a lot of drag

It is important to be aware of the speed at all times

since if the glider gets to slow than recommended

it is possible to lose some control and go into a stall

also depending on the design

there is a specific speed in which the glider

has the maximum efficiency between descent and distance traveled

to measure the speed at which the glider goes with respect to the wind

the anemometer is used

the airspeed is different from groundspeed

the variometer indicates the speed of climb and descent

this instrument is super important

to know when the glider is beginning to climb

usually when it enters a thermal

and thus stay within the thermal

the gliders are equipped with a system that generates a sound

depending on the speed of ascent or descent

with this sound you can more easily identify

if the glider is going up or down

without having to look at the indicator all the time

as you have already seen in this video

gliders are a very interesting type of aircraft

especially because they don’t burn any type of fuel

to stay in flight

only the natural energy available in air currents

nowadays gliders are used for sports and recreational purposes

I give special thanks to Stefan Langer

who is a glider pilot

you can see his channel in the description of this video

Making the animations

the editing and post production in general of this video

has taken me a couple of months

it would be great if you could support me

through a small donation

link in the description

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for now I will see you in the next project