Spoiler / Speed Brake Quest.

[B767PL]

From what I have read in the past, the difference between a speedbrake and a spoiler is that the speedbrake is mounted onto the fuselage and is used to slow the aircraft while not having a direct affect on the aircrafts altitude. While the spoiler is mounted on the wing, to slow the aircraft, and spoil lift, make it descent.

Is this true? If so, then why in most flightdecks I see, are the spoiler levers marked as "Speed Brake". I am a bit confused by this, and this leads me to believe I may be a little mixed up in this, anyone care to explain? Thank you! :)

Edit : Spelling error

[LOMCEVAK]

One personal thought is that spoilers are control surfaces which are used for roll control when extended on just one wing. Therefore, the word "Speedbrake" is used to denote a function i.e. increasing drag, rather than the extension of a specific control surface. To a pilot, it should not matter how the extra drag is created and on the F-18E/F it is achieved by clever deflections of the normal flight control surfaces.

[Genghis the Engineer]

For that matter, I believe that on the old Folland Gnat it involved lowering the maingear didn't it?

G

[FE Hoppy]

Typically on modern airliners the speed brakes are spoilers however if you look at the apeedbrakes on some older types they extended on arms so as not to spoil the lift. This can be seen on the comet and Vulcan.

[mymymy]

Pertaining to B767....

The spoiler/speedbrake system uses the same flight control surfaces to perform two functions. The system operates the surfaces as spoilers to provide lateral control of the airplane in conjunction with the ailerons. The system also operates the surfaces as speedbrakes to increase drag and reduce lift in flight and during landing


;)

3m

[Old Smokey]

B767PL,

Why are Thrust levers still called Throttles? Why do pilots talk of Power in jet aircraft when the engines produce Thrust directly? - Because old habits die hard, and what's in a name?

To the specifics of your question - Speedbrakes produce drag without any direct influence upon the lift. Spoilers fulfill the dual purpose of speedbrakes and spoilers by (1) Applying a little of their own 'form' drag, (2) Spoiling lift, wonderful on landing for making braking more effective, and, (3) In flight, necessitating an increase in angle of attack to regain the lift lost, thus causing an increase in drag. This latter AoA increase contributes far more drag than the lesser drag provided by their form.

[Romeo Tango Alpha]

As Old Smokey stated.

Look at speedbrakes as spoliers deployed symmetrically across the wing, so that even drag is produced, causing a retardation.

Spoliers on the other hand essentially spoils lift. Spoilers are used as a roll control device, and operate ASYMETRICALLY.

In the abscence of high speed ailerons on some jet aircraft, the inboard spoilers act as the high speed ailerons.

On some aircraft spoilers are THE ONLY form of roll control- B1 "lancer" bomber, F-111 bomber, F-14 and other similar aircraft. These are "swing wing" aircraft, or to use the correct term, variable geometry. At high speed, the elevator (ALWAYS an all-moving stab elevator) is used asymetrically, so that roll is acheived through differential elevator. At low speed, the wings extend, and the stab functions merely as pitch control, and the spoilers are the ailerons...

Speedbrake can also be stand-alone, like on the BAe 146 (the tail cone - it also has spoilers on the wings!), as well as fighter aircraft - doors that open on the side of the aircraft face on into the relative airflow, creating significant drag due to form drag, and accompanying eddy formation. The Hawker Hunters ventral fuselage mounted brake is a significant one, and can only be PARTLY opened on the ground (also acts as a high speed dive brake). The F-111's brake is the mainwheel gear door, and can be opened indepednatly to the gear, but LAWAYS comes down WITH the gear.

Interesting topic aerodynamics!

[B767PL]

Thanks for all your replies guys! Appreciated.:ok: