wardialer
Posts: 1144
Joined: Fri Sep 14, 2001 1:08 pm

Spoiler Activation On Long Runways

Tue Oct 01, 2002 2:39 am

Is it really necessary to activate the spoilers on long runways? I watch airplanes land on 25L which is 11,096 feet at KLAX Airport and each time they land the spoilers come up and they even activate the reverse thrust especially on the B737, and A-320s. The runway should be long enough for them to stop without spoilers.
 
bragi
Posts: 212
Joined: Sun May 27, 2001 5:17 am

RE: Spoiler Activation On Long Runways

Tue Oct 01, 2002 4:14 am

There might be many reasons for this. For example, at a busy airport like KLAX they are probably hurrying to vacate the runway so another aircraft can use it.
Most airlines also want to save wear and tear on the engines, and therefore they want to make more use of spoilers to slow down the aircraft in stead of using reverse thrust.

I hope that answers your question. Big grin
Muhammad Ali: "Superman don’t need no seat belt." Flight Attendant: "Superman don’t need no airplane, either."
 
Rick767
Posts: 2613
Joined: Sun Jan 30, 2000 8:11 pm

RE: Spoiler Activation On Long Runways

Tue Oct 01, 2002 5:53 am

I think you have a misconception as to what the spoilers are actually for. Many people believe they exist to provide aerodynamic braking. In fact that is not their primary function (it is quite a negligable effect).

What the spoilers do is literally "spoil" the airflow over the wing, dumping the lift force. The wing goes from creating much lift to simply being two big bits of heavy metal.

The spoilers therefore allow all the aircraft weight to be supported by the wheels, increasing friction and allowing the wheels to grip better and therefore maximise available braking. Remember that when a transport aircraft touches down it is still at least 1.2 times the stall speed, still perfectly capable of flight, and the wings are still creating significant lift.

On most aircraft the speedbrakes deploy automatically on touchdown (provided the pilot selects the function in advance) and many aircraft will extend the spoilers automatically on application of reverse thrust.

The use of Reverse Thrust as a standard operating procedure has been discussed recently on the forum, in my airline we always engage it to maximum by procedure on every landing, except in a few defined cases. Many aircraft you see will only be engaging reverse "idle".
I used to love the smell of Jet-A in the morning...
 
Guest

RE: Spoiler Activation On Long Runways

Tue Oct 01, 2002 11:00 am

Rick is absolutely correct, spoilers have very little to do as speed brakes by generating drag... Speed brakes is the name given (generally) by Boeing...
xxx
At times I criticize the terminology used in England about some aircraft components - "undercarriage" - for gear, is one example - but often, England uses much more accurate terminology... example, spoilers (or speed brakes) are often referred to as "lift dumpers", love that wording, as it really means what they do. Most of the drag comes from flaps rather than spoilers.
xxx
Rick, what I often do on long runways on the 747, is NOT TO ARM spoilers before landing, to get that "smooth landing" which impresses so much passengers as to this superior "master pilot"... arming speed brakes makes that touch down so hard on the 747 (deploy with gear geometry position) whereas the spoilers in manual deploy with the thrust reverser levers... and all landings are extremely smooth... try it, if your old man allows that  Wink/being sarcastic
xxx
I assume it is equivalent in your 767...?
Happy contrails
(s) Skipper
 
Rick767
Posts: 2613
Joined: Sun Jan 30, 2000 8:11 pm

RE: Spoiler Activation On Long Runways

Tue Oct 01, 2002 5:37 pm

Skipper,

Yes the "speedbrake" logic is the same on the 757/767. If armed (which is our SOP on all landings) provided both tilt sensors detect ground contact and both thrust levers @ idle, they will deploy automatically. This ruins what could be a very gentle landing in many cases, like you said.

It is also the case that even with the speedbrakes in the DOWN detent, with either reverse thrust lever raised to the interlock the speedbrake lever will move to the up position and all will deploy.

Because we use full reverse or reverse idle on pretty much all landings that means your idea would also work, getting a nice smooth touchdown on the deck then applying reverse thrust. Worth a try I think... I also find the autobrakes can be a bit jerky upon touchdown so having those off as well could give a really smooth landing.

It would have to be a long runway though to do both those things, if you're not going to follow the SOPs then the last thing you need is to whizz off the end @ 60 knots! Our company does allow discretion with autobrake (non-)usage on long dry runways though.
I used to love the smell of Jet-A in the morning...
 
HAL
Posts: 1743
Joined: Tue Jan 15, 2002 1:38 am

RE: Spoiler Activation On Long Runways

Tue Oct 01, 2002 5:41 pm

Skipper,
You are right about the 767. I've been with captains that do that (not arm spoilers) and it does help smooth out the landing, although not as much as it did on the DC-10. I don't know if it is the short stroke of the landing gear pistons, or the gear geometry, or who-knows-what, but it seems harder to make a greaser on the 767 than the DC-10.

Possibly, it may be since the -10 had a higher wing loading, the landing spoilers killed a lot more lift, causing the plane to really thump in if the pilot wasn't careful. Landing without the spoilers really did make a difference, but like I said, I haven't seen it help smooth things out as much on the 767.

HAL
One smooth landing is skill. Two in a row is luck. Three in a row and someone is lying.
 
erj-145mech
Posts: 305
Joined: Tue Oct 02, 2001 4:21 am

RE: Spoiler Activation On Long Runways

Tue Oct 01, 2002 6:27 pm

On the ERJ's, with the weight on wheels sensors (WOW) sense ground contact, and the brake pedals are depressed, the ground spoilers are activated by the brake control unit (BCU) when the ground speed is greater than 25 kts, this is generated by the 4 wheel speed transducers.

Dave
Continental Express
QC Inspector
TYS
 
Guest

RE: Spoiler Activation On Long Runways

Wed Oct 02, 2002 9:36 am

Dear Rick - Dear Hal -
xxx
I assumed your birds were the same as mine, looks exact equivalent...
xxx
Have to admit I only do that, on long runways - 10,000+ft, dry conditions, if anything less than ideal, I go by the book... but try it if your captains are civilized persons...
xxx
Never have problems stopping 2/3 down the runway doing this... I practiced this a lot in my days flying Air Force E-3s and E-4s, result is, for me doing "aerodynamic braking" is superb, and smooth as well... the whole cabin is "clapping their hands"... you may be the worst pilot in the airlines, but if you land smooth, passengers have the highest regards for your abilities...
xxx
 Wink/being sarcastic
(s) Skipper
 
Rick767
Posts: 2613
Joined: Sun Jan 30, 2000 8:11 pm

RE: Spoiler Activation On Long Runways

Wed Oct 02, 2002 6:29 pm

"you may be the worst pilot in the airlines, but if you land smooth, passengers have the highest regards for your abilities..."

Skipper,

Isn't it funny how, despite your hard work for perhaps 9 or 10 hours in getting the aircraft safely from A to B, the passenger perception of a "good" flight or "good" pilot is all based on that last few seconds of flight... the touchdown.

As my base training captain told me, "a firm touchdown at the aiming point is a better landing than a greaser outside the touchdown zone". Very true, but the passengers would probably disagree!
I used to love the smell of Jet-A in the morning...

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