# What are the differences between air brakes, spoilers and lift dumpers?

So many people use these words interchangeably, but after a little searching on Google, I found they are not quite the same thing. All the links I read explain things in a misleading way which pushed my confusion even further.

I'm looking for a simple explanation on the effect of these parts on The Four Forces of Flight

• A short answer, from what I understand, is that air brakes are designed to create drag while spoilers are designed to destroy lift. In a lot of ways though, the end result (for the pilot flying) is the same in that it helps to slow down or increase the rate of descent. The only lift dump that I am familiar with is only used on the ground and as the name implies, it kills lift, but is much more effective than a spoiler. – Lnafziger Nov 1 '15 at 17:48

Air brakes increase drag with little change in lift. The following image shows the air brake being used in BAe 146

"Eurowings bae146-300 d-aewb arp" by Adrian Pingstone - Own work. Licensed under Public Domain via Commons.

Spoilers both increase drag and reduce lift- basically, they change the lift-to-drag ratio. Sometimes, they are also used as control surfaces in lieu of ailerons. This image shows a Boeing 777 spoilers being used in flight.

The lift dumpers are basically ground spoilers that are used to 'dump' lift, especially immediately after landing, where you want rapid reduction in lift. The following image shows lift dumpers being used in BAe 146.

• Don't the manufacturers themselves even use these terms interchangeably? – TomMcW Nov 1 '15 at 19:33

In my mind these terms all refer to the same thing with 'Lift Dumper' being a more British/European term. But to help illustrate the source of the confusion a quote from the A300 AMM

The lift dumping function is achieved by control surfaces on the upper surface of each wing. In flight, the speedbrake function is achieved on each wing by :

• Two inner speedbrakes
• Two outer speedbrakes

On the ground, the lift dumping function is achieved on each wing by :

• The two inner speedbrakes
• The two outer speedbrakes
• Three spoilers.

The spoilers are also used in roll control, when they complement the action of the ailerons.

The A320 AMM

Five spoilers numbered 1 thru 5 inboard to outboard are provided on the rear upper surface of each wing. The spoilers are used for:

• Roll function
• Speedbrake function
• Ground spoilers function

So really, the spoiler is the component, while lift dump and speedbrake refer to function the spoiler is providing.

Speed brakes or air brakes is the same word and has the same meaning, mainly is used only in the air. Once the pilot decide to use them 3 or 4 of the spoilers on the wing will deflect little bit but not fully extend. purpose of using it is to 1. Reduce the IAS ( indicated air speed ) 2. To increase rate of descent beacause it will ad ( drag ) when you use them.

Spoiler of also called ground spoilers is only deployed and fully extended once the airplane weight is on the wheel which basically is on landing or when rejecting takeoff. They work by deflecting all spoilers on the wing in an angle that kills lift thus having weight and it helps the airplane decelerate cause you have the whole airplane weight on the wheels

• Do you have any references for these definitions? They seem to contradict a bit with the first answer posted. – fooot Nov 2 '15 at 17:54
• I fly airbus and these definitons are straight out of airbus manuals. in the begining you should know that the surface that controls everything is called spoilers. In the air spoiler deflection will be called speed brakes used to slow down the aircraft speed or to incrase rate of descent. On the ground it will be called ground spoilers. It will kill lift. Its basic aerodynamic but diff words – Hmb Nov 2 '15 at 18:42
• Its the same surface but with two functions dependend on where you will use it it will determine the number of spoilers deflected. For example in airbus you have 5 spoilers. When you use speed brakes it uses 3 spoilers when you land and you get the ground spoilers deployed you get all 5 spoilers deployed. In airbus in a turn the airplane uses ailerons and 4 spoilers for turn – Hmb Nov 2 '15 at 18:45
• Ok thanks for clarifying, that makes more sense. Might be good to edit your answer to clarify that this applies to Airbus, and that the surfaces are all spoilers but the different names refer to the different uses. – fooot Nov 2 '15 at 18:49
• This is similar on all manufacturers, for instance on the MD-80 the inboard spoiler is called a GROUND SPOILER and the two outboard are called FLIGHT SPOILERS. On a 737NG, the most outboard and most inboard spoilers are GROUND SPOILERS and the remaining spoilers are FLIGHT SPOILERS. – Sports Racer Nov 2 '15 at 20:28

I don't believe there is any industry standard term for these parts; they're often used interchangeably. However in general:

Airbrakes and speedbrakes are interchangeable terms; just large reinforced panels which can be extended out from the aerodynamic envelope, creating a lot of parasite drag.

Spoilers and Lift Dumpers are, again, interchangeable terms. These are just speed brakes mounted on the upper wing surfaces, in general, about 1/2 to 2/3 the length of the chord line. In addition to creating parasite drag, they induce flow separation over the top of the wing and, as mentioned above, greatly increasing induced drag in the process as the lift is 'dumped' off during deployment. Large transports will use spoilers to increase braking effectiveness and decrease the length of the landing roll.

Another function of spoilers is roll authority, particularly in fly by wire aircraft, but sometimes seen in other types of mechanically controlled aircraft e.g MU-2, TBM, etc. They will be used in conjunction with other control surfaces such as ailerons, all-moving tailplanes, etc.