DASH 8 400 Spoilers extended before T/O
 

A few days ago, behind a Dash8 400 ready to takeoff, I told him "XXX you have some spoilers extended"... just in case.

Is it normal, maybe for the first flight of the day? some sort of test?

We saw the spoilers retract upon T/O power application.

Just curious. Thanks

For some odd reason it is normal practice to put the spoilers up prior to every departure. I fly the thing and I'm not really sure what the point is.?!!!

Its frequent that people mention it as we line up so its great to see people are looking out for us!!!

Another odd 'dashism' !!!

It's normal on every flight.

Basically, there is a ground/flight switch on the flight deck, weight on wheels sensors and a Power Lever Angle (PLA), basically a microswitch, which all control the position of the spoilers.

In ground mode the WoW sensors are overridden and the spoilers stay retracted. If you exceed the PLA, about 12 degrees I think, in ground mode (rare as you don't need that much power whilst taxying) the switch will move to flight mode, but the spoilers remain retracted as you are now above the required PLA.

If however, you manually select flight mode with weight on wheels and a PLA of less than 12 (as we do when we line up) the spoilers will extend. This is why you see the spoilers extended prior to take off. And, as you pointed out, they retract on power application as you've now passed the 12 degree PLA microswitch.

When you land, the switch is at flight, you will get weight on wheels AND only when you've reduced past the PLA of 12 the spoilers will extend.

A bizarre system I know but does that make sense?

Not familiar with flying this type but I would imagine it also aids the possibility of a RTO and saves the flightdeck one less task of setting spoilers???

Got it,thanks!
I would imagine the crew has to check for their retraction with a callout or flight controls page?...

Clear4to, yep that's another reason.

Paolo, yes, there is a powered flying controls indicator permanently on the captains MFD. There is no call as such, but it's SOP to check they go down as they should, but the config warning would (hopefully!) sound if they stayed up. There is a "spoilers" call on landing. We do the full and free check with the spoilers in ground mode as they're also used as roll spoilers.

Flew Dash 7's in the early 1980's. Had the same procedure.

I believe there was a Dash 7 crash in S. America that had spoiler deployment inflight. During training they explained the procedure as "we check the system every flight now. If they don't retract at high power you abort."

Vnav, I'd tend to agree with you. Coming from the 146, as I did, it was a habit of mine to put a lot of into wing aileron in (swept wing and narrowish track undercarriage). On the Dash (Q400) it's not necessary to have the roll spoilers deployed, for the reasons you've stated. And you're also increasing the drag on the upwind wing, enhancing the weathercock effect. I still put a bit of aileron in but not that much.

With the wide track of the Dash, no into wind aileron is required during the t/o roll. Even taking off in maximum allowable crosswind, there is no tendency for a wing to lift.

WRT into wind aileron/spoiler, rather than put the aileron/spoiler into wind at the commencement of the take-off roll, because that's the way it's always been done, why not just keep the wings level during the take-off roll? In other words, just enough aileron deflection is used to keep the wings level.

Simply because it's easier to keep a wing down than it is to get it back down if it's lifted. That's why.

Sorry to show my ignorance but...

One microswitch failure and the spoilers don't retract or?

I never thought much of this practice, and at my previous employer one crew found themselves airborne with one panel stuck up (and no horn). It is not normally that big of a deal if they do not deploy on landing; it is a big deal if they do not all retract on takeoff.

As for why this is done, the story I was given by a test pilot at Downsview was that it had to do with...office politics. I guess that the flight test folks are not free of it either.

As for crosswind technique, is the airplane heavy and performance limited? Or perhaps the runway braking action is less than good? One must adjust technique to fit the situation.

XWind Take Off
 

This statement is correct. There is no requirement to put any imput on take off roll. Having been a Dash 8 test pilot for deHavilland, I can assure you this is the method used during testing and certification by senior test pilot on Dash 8 (all models). You will of course require imput once rotation ocurrs so be ready for it.

Erm...never thought of that! I don't know how the system really 'thinks' but I assume that's the reason for us to check they are retracted during the power application.

The situation that 742 describes shouldn't ever happen!

The spoilers should retract as soon as the power levers are advanced (1 switch) but if they don't you will get the takeoff warning horn (separate switch). If you did continue the takeoff and the aircraft lifted off, the spoilers would retract as soon as any weight on wheels switch sensed off the ground. It is pretty safe.

This topic, control input early or late, never goes out of fashion. The answer I've always heard, beyond technique discussions, is that the a/c aren't certified that way. If you're doing this in a balanced field condition your performance will be worse than demonstrated.

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XWind Take Off
Quote:
Originally Posted by reptile http://www.pprune.org/forums/images/...s/viewpost.gif
With the wide track of the Dash, no into wind aileron is required during the t/o roll. Even taking off in maximum allowable crosswind, there is no tendency for a wing to lift.

This statement is correct. There is no requirement to put any imput on take off roll. Having been a Dash 8 test pilot for deHavilland, I can assure you this is the method used during testing and certification by senior test pilot on Dash 8 (all models You will of course require imput once rotation ocurrs so be ready for it.

Fine. No need to shout.

That must be type specific.

Just trying highlight his comment and not shout it out.

"Type specific"? I just emailed a guy that should be able to get the answer from a leading manufacturer. If he gets an answer I'll post it.

The question -

Curiuos if you could ask the flight test guys how a/c are certified for crosswind takeoff's, specifically the use of ailerons to prevent the upwind wing from raising.

Do they start with full control input prior to the start of takeoff roll, feed in aileron to keep the wing level as they accelerate, or don't use any aileron input until rotation starts?

The answer -