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Hello Capt Lim,
I just discovered your site today and what a wealth of information you have compiled here! As is the case with many of your readers, I am a Boeing 777 enthusiast. It is IMHO, the best commercial aircraft in the industry and I imagine you must really enjoy flying that wonderful machine. I got my pilots license back in *93 and am currently flying a Cirrus SR22G2.
My question is: When the spoilers of the 777 are automatically deployed upon touching down on the runway (assuming spoilers were armed during approach), do the spoilers automatically retract at a certain speed during deceleration or must they manually be retracted?
Best Regards,
Jeff Willwerth
Livermore, CA
Hi Jeff,
Yes, spoilers are very useful to pilots of jet planes. Ask any pilots who fly these planes! They can get you out of a very difficult position, such as, when caught high and fast! Another thing - they are also incredibly effective for landing too. Forgetting to arm or select them for landing in a short and wet runway will see the plane crashing out at the end!
Having said that, if the spoilers are armed - they would not automatically retract after landing. Instead, the pilot would have to manually retract them after landing. However, if the pilot decides to reject the landing after a touch down - advancing the thrust levers again will automatically retract the spoilers.
For others who do not know what spoilers are - here is a brief description: (I have taken the photo below while sitting as a passenger - not flying for a change - from New York to Stockholm on a Boeing 777 on New Year Day 2006)
Spoilers are basically small hinged flat plates on the top of both sides of the airplane wings. Their main function is to slow down the plane or to assist a plane to descend rapidly. When the pilot deploys the spoilers, you can feel the sudden deceleration followed by some vibrations. As a rule of thumb, it takes about a mile to decelerate about 10 knots. For instance, if I were 300 knots at 40 miles from the runway, selecting the spoilers would reduce the speed to 200 knots by the time I am 30 miles away - slow enough to start extending flaps (they have limiting speeds for extension) - or just about over a minute to cut down 100 knots (115 mph) in the air.
How it works? Well, when activated, the plates flip up and disturb the airflow - just like you would suddenly thrust your flat palm out of the car window at 100 mph! The drag of the wing is increased and the lift is decreased. In other words, it "dumps" lift and assist the plane to descend more rapidly, or to slow it down sufficiently in preparation for a landing.
When armed for the landing, they deploy automatically; if not, the pilot does it manually to kill the lift - this keeps the plane to settle on the runway firmly in order for the brakes to work more efficiently. The frictional force between the tires and the runway surfaces is dependant on the "normal" force - which is the airplane weight minus any lift. The lower the lift, the better the brakes would work!
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