risingsunfitnes
Topic Author
Posts: 32
Joined: Sat Sep 03, 2011 5:59 am

Spoiler Question...

Wed Nov 16, 2011 11:20 am

Hi All,

I flew on a Jetstar A320 today, sitting 13A, so right over the wing. I noticed when we started our descent, spoilers were deployed to slow down as usual. So far, all would agree is normal.... What happened today, which i maybe haven't noticed before, is not all of them came up ? I know, obviously, there are varying degrees of how much, for want of a better word, you can deploy the spoilers... but it seemed odd to to me that of the 6, only three lifted slightly, and of those three, one was lower than the other two.

So my question is, have i just missed this previously in all my flights, and depending on the landing config, not all spoilers deploy in a given situation ?

PS Very good friend of mine was the FO, she was PIC for landing, great crosswind land at SYD...and forgot to ask her...muppet!   

thanks in advance
 
Goldenshield
Posts: 5017
Joined: Sun Jan 14, 2001 3:45 pm

RE: Spoiler Question...

Wed Nov 16, 2011 11:28 am

There are two type of spoilers on a transport airplane: ground spoilers, and flight spoilers.

In the case of the former, as their name implies, they are only used on the ground. For the latter, they are used to supplement. or even replace, roll control during flight; however, they will open fully on the ground to assist the ground spoilers.

As for why they are aligned differently, it's just how they are rigged.
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Fabo
Posts: 1151
Joined: Tue Aug 16, 2005 1:30 am

RE: Spoiler Question...

Wed Nov 16, 2011 4:44 pm

Quoting risingsunfitnes (Thread starter):
great crosswind land at SYD

I think this might be the key - if you were observing them shortly before landing (as in seconds, maybe tens of seconds) - this might be a result of a crosswind landing technique that calls for roll "into the wind", that might just have been big enough to cause spoilers to go up assiting ailerons. (Spoileron setup, is it called?)
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pilotpip
Posts: 2825
Joined: Fri Sep 19, 2003 3:26 pm

RE: Spoiler Question...

Wed Nov 16, 2011 4:57 pm

Many jets have multifunction spoilers. They serve as speed brakes and roll assist in the air, and on the ground as lift dump spoilers. I can only comment on the aircraft that I fly (the 170) but there are many similarities between the FBW system on that and the airbus.

The spoilers on the 170 are controlled by the FBW computers. The outboard 3 are multifunction and the inboard 2 are only lift dumps. When used as speedbrakes the computer figures out how far to put them up based on speed and altitude. Full at cruise isn't the same as full at 5,000 feet. When used as a roll assist the computer figures out the roll rate I'm requesting at the yoke and will add spoiler to assist the ailerons. At higher speeds it takes very little aileron deflection to roll the airplane so the most common place you'll see them helping with roll is on takeoff and landing.
DMI
 
dhawald3
Posts: 16
Joined: Tue Jun 28, 2011 3:10 pm

RE: Spoiler Question...

Wed Nov 16, 2011 6:23 pm

The A320 has 5 spoilers on each wing, numbered from inboard to outboard 1-5.

They are used as follows.

1 to 5: Ground spoilers- for reducing speed after the aircraft touches down.
2 to 5: Roll spoilers - assist the aileron in rolling, also used in rolling if there is failure of aileron.
2 to 4: Speed brakes- for speed reduction when airborne.

This Image explains it clearly.
flight control A320
 
risingsunfitnes
Topic Author
Posts: 32
Joined: Sat Sep 03, 2011 5:59 am

RE: Spoiler Question...

Wed Nov 16, 2011 9:29 pm

Thank all for the explanation !
 
Goldenshield
Posts: 5017
Joined: Sun Jan 14, 2001 3:45 pm

RE: Spoiler Question...

Wed Nov 16, 2011 10:06 pm

Quoting dhawald3 (Reply 4):
2 to 4: Speed brakes- for speed reduction when airborne.

It should be noted that the spoilers themselves don't actually do the act of slowing you down. Rather, it's the combination of aerodynamic lift lost from opening the spoilers, which causes the airplane to start descending, coupled with the pilot slowly increasing the pitch attitude of the aircraft, which is, in effect, sacrificing airspeed to maintain altitude.
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tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Spoiler Question...

Thu Nov 17, 2011 4:23 am

Quoting Goldenshield (Reply 6):
It should be noted that the spoilers themselves don't actually do the act of slowing you down.

That's not entirely true. Although the spoilers do force you to a higher AoA to maintain lift (increase induced drag, Cdi), they also generate drag on their own (increased form drag, Cd).

Tom.
 
Goldenshield
Posts: 5017
Joined: Sun Jan 14, 2001 3:45 pm

RE: Spoiler Question...

Thu Nov 17, 2011 10:36 am

Quoting tdscanuck (Reply 7):
Although the spoilers do force you to a higher AoA to maintain lift (increase induced drag, Cdi), they also generate drag on their own (increased form drag, Cd).

Aye, but the amount of added drag is pretty marginal compared to lift lost since the spoiler is relatively streamlined with the airflow. Now, when you compare them to the drag that airbrakes on the likes of the BAE-146, or dive brakes on dive bombers and gliders produce, that's a whole different story.  Smile

[Edited 2011-11-17 02:55:41]
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bonusonus
Posts: 228
Joined: Thu Nov 05, 2009 3:49 pm

RE: Spoiler Question...

Fri Nov 18, 2011 11:08 pm

Quoting dhawald3 (Reply 4):
1 to 5: Ground spoilers- for reducing speed after the aircraft touches down.
2 to 5: Roll spoilers - assist the aileron in rolling, also used in rolling if there is failure of aileron.
2 to 4: Speed brakes- for speed reduction when airborne.

Wow, great explanation and diagram. I had no idea that speed brakes, spoilerons and spoilers overlapped in function like that.
 
474218
Posts: 4510
Joined: Mon Oct 10, 2005 12:27 pm

RE: Spoiler Question...

Sat Nov 19, 2011 1:21 am

Quoting Goldenshield (Reply 1):
There are two type of spoilers on a transport airplane: ground spoilers, and flight spoilers.

In the case of the former, as their name implies, they are only used on the ground. For the latter, they are used to supplement. or even replace, roll control during flight; however, they will open fully on the ground to assist the ground spoilers.

Not really!

Look at the picture of the A320 "dhawald3" provided in Reply 4:

There are ten (10) spoiler panels, five (5) on each wing.

All Ten (10) are used as ground spoilers.

Six (6) are used as speed brakes (in flight).

Eight (8) are used for roll control (in flight).

So of the ten (10) spoiler panels eight (8) have more than one function.

The inboard most spoiler on each wing has one function ... ground spoiler.

The next three spoilers on each wing function as ... ground spoilers, speed brakes and as roll control.

The outboard most spoiler on each wing functions as a ... ground spoiler and as roll control.
 
Goldenshield
Posts: 5017
Joined: Sun Jan 14, 2001 3:45 pm

RE: Spoiler Question...

Sat Nov 19, 2011 4:10 am

Quoting 474218 (Reply 10):
Not really!

Look at the picture of the A320 "dhawald3" provided in Reply 4:

The only thing I really failed to mention in my original post was that the flight spoilers as a whole were used to help slow the aircraft, but that's only because I would assume that most all people on this forum know that doing such is their primary purpose. Regardless, though, my post pretty much implies that they are multi-purpose to begin with.

I refuse to call them speed brakes. I'll take "lift dumpers" as the brits call them, but not "speed brakes."

[Edited 2011-11-18 20:23:39]
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