AT From United States of America, joined Jul 2000, 863 posts, RR: 0 Posted (5 years 3 weeks 2 days 2 hours ago) and read 3478 times:
I have been watching a number of videos on the likes of jetvideos and flightlevel350.com and have noticed a number of cases where the spoilers on the wing seem to rise (though not fully) during takeoff.
Why is this? Isn't the sole purpose of the spoilers to kill lift upon landing? If so, that seems counter productive.
767driver From United States of America, joined Feb 2008, 103 posts, RR: 0 Reply 2, posted (5 years 3 weeks 2 days 2 hours ago) and read 3439 times:
On most large aircraft, spoilers are also used to assist the ailerons in turns. Therefore, if you turn right, the right aileron will raise along with several of the spoiler panels on the right wing. Since you would have right aileron in during a crosswind takeoff (xwind from the right), this would explain the spoiler action you are seeing in the videos
PhilSquares From , joined Dec 1969, posts, RR: Reply 5, posted (5 years 3 weeks 1 day 19 hours ago) and read 3135 times:
Quoting Pilotpip (Reply 4): The spoilers would be up a bit if the pilot were adding proper crosswind correction.
From the 744 FCTM Limit control wheel input to
that required to keep the wings level. Use of excessive control wheel may
cause spoilers to rise which has the effect of reducing tail clearance. All of
these factors provide maximum energy to accelerate through gusts while
maintaining tail clearance margins at liftoff.
A properly executed x-wind takeoff should be accomplished without spoiler activation. Generally, there is enough lateral control using just ailerons alone. On the 744, at low speeds or with the flaps out of the up position, both inboard and outboard ailerons will be available.
474218 From United States of America, joined Oct 2005, 6340 posts, RR: 10 Reply 6, posted (5 years 3 weeks 1 day 18 hours ago) and read 3120 times:
On most large transport aircraft additional roll control is required when the flaps are extended. Therefore spoilers are mixed with the ailerons to provide this roll control. When the control wheel (or side stick) is moved to input aileron movement spoilers on the up aileron wing also move. Normally this movement is on a one to two basis (5 degree aileron would equal 10 degrees spoiler). Spoilers on the down aileron wing remain stowed. Without this feature roll control would be very sluggish as the lift created by the flaps cancels out some of the ailerons effectiveness. When the flaps are fully retracted this function is nulled as is the outboard aileron on some aircraft.
767driver From United States of America, joined Feb 2008, 103 posts, RR: 0 Reply 9, posted (5 years 3 weeks 1 day 7 hours ago) and read 2983 times:
Quoting PhilSquares (Reply 5): From the 744 FCTM Limit control wheel input to
that required to keep the wings level. Use of excessive control wheel may
cause spoilers to rise which has the effect of reducing tail clearance. All of
these factors provide maximum energy to accelerate through gusts while
maintaining tail clearance margins at liftoff.
A properly executed x-wind takeoff should be accomplished without spoiler activation. Generally, there is enough lateral control using just ailerons alone. On the 744, at low speeds or with the flaps out of the up position, both inboard and outboard ailerons will be available.
The 767/757 FCTM says the exact same thing, however "excessive control wheel deflection" is not defined. In a strong crosswind, I do what is necessary to keep the wings level, but I'm sure there is slight spoiler activation. It's not excessive, but it does exist.
The 757 is more susceptible to spoiler activation during a strong xwind takeoff since we don't have inboard ailerons.
PhilSquares From , joined Dec 1969, posts, RR: Reply 10, posted (5 years 3 weeks 1 day 6 hours ago) and read 2959 times:
Quoting 767driver (Reply 9): The 767/757 FCTM says the exact same thing, however "excessive control wheel deflection" is not defined.
Excessive control wheel deflection is defined as continuous spoiler activation. On the 400 with the outboard aileron unlocked, there is usually enough of control authority to do a cross wind takeoff with no problems.
Point8six From United Kingdom, joined Apr 2008, 94 posts, RR: 0 Reply 11, posted (5 years 3 weeks 1 day 5 hours ago) and read 2943 times:
Control-wheel deflection should only be sufficient to keep the wings level during a cross-wind take-off. Even max. cross-wind should not require control-wheel deflection that extends the spoilers significantly. The tendency is often to deflect the wheel according to the reported wind, rather than deflect it to counter the wing-drop caused by the actual wind, thereby inducing a degree of 'over-controlling'.
474218 From United States of America, joined Oct 2005, 6340 posts, RR: 10 Reply 13, posted (5 years 3 weeks 1 day 5 hours ago) and read 2902 times:
Quoting 767driver (Reply 12): Exactly. The key word here is "significantly". Spoilers (at least on the 767/757) will be slightly extended during a strong xwind.
What make the spoilers extend during a strong cross wind and do they extend asymmetrically?
767driver From United States of America, joined Feb 2008, 103 posts, RR: 0 Reply 14, posted (5 years 3 weeks 1 day 4 hours ago) and read 2897 times:
Quoting 474218 (Reply 13): What make the spoilers extend during a strong cross wind and do they extend asymmetrically?
They extend as a function of aileron displacement. As you turn the yoke, the ailerons move along with proportional extension of the spoilers. Example, you turn the yoke to the right, the right ailerons will first move up, then the more you turn the yoke, the spoilers on the right wing will begin to extend to aide in turning the airplane (creating more drag on the right wing)
474218 From United States of America, joined Oct 2005, 6340 posts, RR: 10 Reply 15, posted (5 years 3 weeks 1 day 4 hours ago) and read 2889 times:
Quoting 767driver (Reply 14): They extend as a function of aileron displacement. As you turn the yoke, the ailerons move along with proportional extension of the spoilers. Example, you turn the yoke to the right, the right ailerons will first move up, then the more you turn the yoke, the spoilers on the right wing will begin to extend to aide in turning the airplane (creating more drag on the right wing)
I said that exact same thing in reply 6, but people kept talking about cross wind takeoffs and got me confused. The only reason the spoilers are up on a cross wind takeoff (or landing) is because the ailerons (aileron) on the same wing are up.
Also the up aileron/spoiler takes away lift and the down aileron creates more lift, both effect the drag. It is the differential lift that aids in turning, not drag.
Vc10 From United Kingdom, joined Nov 2001, 1382 posts, RR: 17 Reply 16, posted (5 years 3 weeks 1 day 2 hours ago) and read 2839 times:
Quoting 474218 (Reply 15): Also the up aileron/spoiler takes away lift and the down aileron creates more lift, both effect the drag. It is the differential lift that aids in turning, not drag.
I always thought there was a thing called differential aileron where the up going aileron moved more than the down going aileron, so there was less drag on the down going aileron side [ sorry about all the downing and uping]
474218 From United States of America, joined Oct 2005, 6340 posts, RR: 10 Reply 17, posted (5 years 3 weeks 22 hours ago) and read 2798 times:
Quoting Vc10 (Reply 16): I always thought there was a thing called differential aileron where the up going aileron moved more than the down going aileron, so there was less drag on the down going aileron side [ sorry about all the downing and uping]
While some aircraft may have differential aileron travel, none of the on the aircraft I worked on (Lockheed/Douglas/Convair) did. On all of them aileron travel was the same on th up wing and the down wing.
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