The flaps on a plane’s wings help generate lift for the plane during take-off and generate drag during landing.

Flaps help planes both with landing and taking off, but they’re more important during take-offs.

While useful, wing flaps aren’t absolutely necessary for most planes.

In fact, not having flaps just means that a plane has to travel on more runway before it can successfully take off or land.

So, flaps only help with landing and taking off, and most pilots can just as easily land or take-off without them.

Flap failure is also not considered a huge emergency by most airliners for that reason. 

What Do Flaps Do on Planes During Take-off?       

The flaps help the aircraft produce lift during take-off.

Pilots often fully or partially raise flaps during take-offs to increase lift and help the aircraft rise into the air.

The advantage of higher lift is that it reduces the distance a plane has to travel on the runway to take off.

At the same time, raising the flaps also means a decreased climb rate during take-offs.

Overall, it’s advantageous for pilots to raise flaps during take-offs to get into the sky faster. 

What Do Flaps Do on Planes During Landing?      

Wing flaps help reduce stall speed during landing along with allowing the plane to land at a steep, but controlled angle.

Airplanes require a controlled stall for safely landing, since airplanes can’t land while producing lift.

A controlled stall decreases a plane’s altitude and speed, which allows the plane to land on the runway. 

How Do Flaps on Planes Work?                     

Wing flaps change the airplane wing’s shape by diverting air around the wing.

The flap’s setting can normally be changed between 5 and 15 degrees, depending on the plane’s needs.

The flap’s setting is changed for increasing lift during take-offs or decreasing lift during landings.

Once the flaps are up, the plane’s camber is positioned so that the wings produce higher lift.

The wing flaps completely retract once the aircraft has taken off.

What Types of Flaps Do Planes Have?                     

Planes have the following 4 main types of flaps.

Some planes will also have multiple types of flaps. 

1. Plain Flaps 

Plain flaps are made using the edge section of the airplane wing’s airfoil.

So, a plain flap is when the whole edge of the plane is a flap. 

2. Split Flaps

In a split flap, only a section of the bottom half of the airplane wing goes down, but the top section of the wing remains in its place.

Split flaps are most commonly used when the wings contain other structures that prevent them from moving.

For instance, some twin-engine planes have parts of their engine nacelle in the wing’s edge section. 

3. Slotted Flaps 

Slotted flaps have air-producing airfoils, so they let air flow over their top and bottom, which lets them generate greater lift than most other flaps. 

4. Fowler flaps 

With fowler flaps, the edge section of the lower half of the plane’s wing travels down the wing tip and extends at the bottom.

As a result, this flap actually increases a plane’s total wing area to create lift.

Fowler flaps are quite common on airliners. 

Are Flaps Always Used During Take-off?                            

Most planes can take off without flaps, but they’re very useful for taking off faster.

Without flaps, airliners would have to generate more speed during take-off.

Some airliners, like the Airbus A300 and the Boeing 767 are designed to take off without using their flaps.

But, they’d be able to take off faster and easier with flaps than without them.

Are Flaps Always Used During Landing?                      

Flaps can be useful during landings, but they’re not always used or always needed.

For instance, it could be dangerous to use flaps during crosswinds or flap failure.

For example, flaps could make it difficult to land lightly wing-loaded planes during strong crosswinds.

Flaps also potentially increase the likelihood of airplanes experiencing a loss of direction, or suffering from less effective brakes. 

Can You Land a Plane Without Flaps?         

You can land most aircraft without flaps.

A no-flap landing would only require the pilot to fly a few knots faster on landing.

A pilot might also need to use several hundred more feet of runway before coming to a stop.

So, flaps only make landing easier, though they’re not absolutely necessary to land. 

What Happens if the Flaps on a Plane Fail?              

Flaps are retracted during flap failure.

The plane then lands with a higher landing airspeed, which depends on the plane’s weight.

The higher landing speed causes longer landing rolls, for which the pilot needs more runway.

In some situations, pilots will find alternative airports if the original landing runway doesn’t have a long enough runway to compensate for flap failure. 

At What Altitude Do Pilots Retract Flaps?         

Pilots usually retract a plane’s flaps at an altitude of 3,000 feet, since most planes achieve a positive rate of climb at that height. 

In conclusion, the flaps on airplane wings only help the plane generate lift during take-off and drag during landings.

Generating lift and drag helps the aircraft take-off and land, but flaps aren’t strictly necessary for either process.

Most aircraft can safely land or take-off without using flaps, but they’d require more runway and a higher airspeed.

It’s not considered a dangerous emergency if flaps fail, either, since it would only require the pilot to fly the plane faster and use more runway.

Michael Price - Aviation Expert
Aircraft Engineer

Michael is an aircraft engineer and aviation expert with an insatiable passion for all things aviation-related.

With decades of experience and knowledge under his belt, Michael is an authority on the intricacies of private, commercial, and military aircraft.

Michael has been quoted or mentioned in major publications, including Business Insider, The Observer, Next Big Future, HowStuffWorks, CleanTechnica, Yahoo, UK Defence Journal, 19FortyFive, as well as referenced on Wikipedia.