Spoilers, no spoilers?

On Feb 8, 9:25*am, Peter Clark
wrote:
On Fri, 8 Feb 2008 07:40:33 -0800 (PST), "F. Baum"
wrote:



. If there truly was a physical reason why
spoilers should not come out in the air, it would have been an
engineering requirement to systematically disable their mechanism
unless, say, the gear is down and the wheels rolling.

Actually, this is the way it works. Only some of the spoilers deploy
inflight (Either through the spoiler handle or the Aileron/Spoiler
mixer ). The rest of the spoilers will not deploy until the plane is
on the ground.

Or an airspeed lockout. *If memory serves they won't deploy, even for
roll assistance, above a certain speed either.

Not too sure on this. On all the jets I have experience with, the
boards are usable to VMO/MMO. On some some of the older ones, like the
727 they will blow down a bit as you approach the pole.


*Don't they also
deflect at different angles depending on what system is activating
them? *Highest angle off the wing is for full in-flight spoiler handle
(and some don't even come up for that), inboard segments deflect at a
greater angle than outboards for roll assistance (which is about 1/2
the angle off the wing compared to full spoiler), and everything comes
up at full for weight-on-wheels spoiler system?

They deploy proportionate to the roll or spoiler input. On several of
the newer airliners there is a flight detent and full range for ground
deployment. Exceeding the flight detent results in buffeting. As an
interesting side note, on the Boeings, if you have the boards about
half way extended and then try a turn, you get a dramatic increase in
the roll rate.

Amine wrote:
On Feb 7, 3:35 pm, Dudley Henriques wrote:
Go around.


Well, let's play the devil's advocate... What if you can't go around?
(E.g. because of engine failure or in a glider). I mean, I understand
why you don't want to deploy spoilers if you're below minimums or if
you're flirting with stall speed. But if you're well above minimums,
with no risk of stalling, I don't see any reason why you shouldn't use
spoilers to bleed the extra momentum/altitude. The only disadvantage
would be that the final approach will be steeper and thereby would not
have the elegance of the perfect glide slope. But that's seems to be
more a matter of taste (and possibly performance) than an actual
safety issue.

After all, the "no-spoiler-in-midair"dogma isn't built in the design
of the pilot interface. If there truly was a physical reason why
spoilers should not come out in the air, it would have been an
engineering requirement to systematically disable their mechanism
unless, say, the gear is down and the wheels rolling.
The "go around" comment was meant as a general rule for any approach
situation that has the aircraft too high and fast for the runway.
Naturally, any approach situation ending with an accident assumes
something went wrong somewhere.
In the case of spoiler use, I can't speak directly to the DC8 scenario
as I'm not DC8 type rated, but obviously in this case, a spoiler
deployment scenario that had the POTENTIAL for problems had been noted
prior by the Captain (at least this is my understanding anyway).
In such a situation, with the first officer making the approach, the
scenario for an in-flight deployment error on the spoilers having been
noted, it would seem obvious to me that a go around call rather than ANY
attempt to use spoilers to save the approach would have been the prudent
call by the first officer.
I'm sure there is more to the story. There always is.
:-)

--
Dudley Henriques

On Feb 7, 1:20*am, Amine wrote:
How come the first officer (with over 5500 hrs
with that type of aircraft) made such a decision to deploy spoilers
while still in the air? What else, when full flaps and idle power
aren't enough, can a pilot use to handle a too high/too fast final
approach if not deploy spoilers?

Dudley got this one right (Go Around), but it is kinda a loaded
question because you cannot use flight spoilers or airbrakes beyond
certain flap settings . So if you had landing flaps, spoilers are not
an option. In the older jets you would get a warning horn if you had
any flaps deployed. The best thing to do when you are to high is to
get into the landing configuration early because this will cut the
ground speed and give you the best decent rate over a given distance.

As a side question, what is the functional difference between spoilers
and airbrakes?

Nothing. The current Boeing manuals make a distinction between
airbrakes and ground spoilers because not all of them deploy in
flight. Some only deploy on the ground during landing rollout or RTO.
As a side note the flight spoilers augument roll control when you pass
10 degrees of aileron deflection (This makes Xwind takeoffs
interesting). Hope this helps,
FB

On Feb 7, 8:40*am, "F. Baum" wrote:
As a side question, what is the functional difference between spoilers
and airbrakes?

Nothing. The current Boeing manuals make a distinction between
airbrakes and ground spoilers because not all of them deploy in
flight.

Oops, should have said Flight spoilers and ground spoilers.