Dakota123 From United States of America, joined Aug 2006, 116 posts, RR: 0 Posted (8 years 11 months 5 days 20 hours ago) and read 4912 times:
Hello,
was recently on a B777, seated near the wing's trailing edge. When the crew cycled the flight controls prior to takeoff I was amazed at the speed with which the inborad ailerons ('flaperon', actually) moved full-up to full-down. Even in flight it moves very quickly and with large movements.
The question I have is how is the actuator arranged on that particular device? Is it a single device? How often does it (or they) need to be renewed/changed out? It looks like it gets a major workout!
TristarSteve From Sweden, joined Nov 2005, 4287 posts, RR: 32
Reply 1, posted (8 years 11 months 5 days 20 hours ago) and read 4894 times:
There are two linear jacks on each flaperon, inboard and outboard.
When the flaps are down for takeoff, the flaperons are affected by the flow from the engines. So when an engine is near take off, the controls are disconnected and the flaperons actually flap in the airstream. So watch them durii´ng take off next time. They will come down with the flaps, then float up at the start of the take off roll. About 30secs later at a certain airspeed, they willl be reenergised and move down to their original position.
Dakota123 From United States of America, joined Aug 2006, 116 posts, RR: 0
Reply 2, posted (8 years 11 months 5 days 19 hours ago) and read 4878 times:
Quoting TristarSteve (Reply 1): When the flaps are down for takeoff, the flaperons are affected by the flow from the engines. So when an engine is near take off, the controls are disconnected and the flaperons actually flap in the airstream. So watch them durii´ng take off next time. They will come down with the flaps, then float up at the start of the take off roll. About 30secs later at a certain airspeed, they willl be reenergised and move down to their original position.
Thanks for the additonal tidbit, I was wondering about that aspect as well.
OldAeroGuy From United States of America, joined Dec 2004, 3806 posts, RR: 66
Reply 3, posted (8 years 11 months 5 days 11 hours ago) and read 4773 times:
Quoting TristarSteve (Reply 1): So when an engine is near take off, the controls are disconnected and the flaperons actually flap in the airstream.
The flaperon controls are never disconnected. When takeoff power is selected with no airspeed, the flaperon control system drives the flaperon to the neutral position. This is done to get the flaperon out of the engine exhaust plume, which expands widely when there is no forward airplane velocity. If the flaperon were extended to sit in the expanded engine exhaust, the exhaust turbulence would cause the flaperon to buffet. The buffeting tends to fatigue the flaperon support structure. After the airplane reaches a speed of about 80 kts., the slip stream reduces engine exhaust expansion and the controls move the flaperon down to align with the inb'd/outb'd flaps.
Any "flapping" you might see is in response to pilot inputs as the retracted flaperon still functions as an aileron.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
TristarSteve From Sweden, joined Nov 2005, 4287 posts, RR: 32
Reply 4, posted (8 years 11 months 5 days 7 hours ago) and read 4732 times:
Quoting TristarSteve (Reply 1): When the flaps are down for takeoff, the flaperons are affected by the flow from the engines. So when an engine is near take off, the controls are disconnected and the flaperons actually flap in the airstream.
Quoting OldAeroGuy (Reply 3): When takeoff power is selected with no airspeed, the flaperon control system drives the flaperon to the neutral position. This is done to get the flaperon out of the engine exhaust plume,
From my B777 training notes...
Flaperon Bypass Logic
The flaperon bypass logic gets signals from the left and right
engine running status and the position of the left and right thrust
resolver angles. The logic also gets the CAS signal from the
ADIRU and the air/ground signal from the WOW cards.
The logic operates on the ground with at least one engine
running and its thrust resolver angle near the takeoff position.
With the airspeed less than 85 knots, the logic sends a
command signal to all four ACEs to put the flaperon PCUs in
bypass mode. This decreases the flaperon actuator fatigue
cycles caused by the engine exhaust on the flaperons.
At low airspeed with the flaperon PCUs in bypass mode, the
weight of the flaperon may cause the flaperons to move down to
the PCU stops. The exhaust flow of the engines may cause the
flaperons to flutter. As the airspeed increases during takeoff
roll, the airloads may cause the flaperons to float to the neutral
position.
When the airspeed is approximately 100 knots, the logic stops
operation and sends a command signal to the ACEs to put the
flaperon PCUs in the normal mode. The flaperon PCUs then
gradually move the flaperons to the commanded position.
The flaperon bypass logic is inhibited for 30 seconds after an air
to ground transition. This prevents the flaperon PCUs to be in
bypass during touch and go operation of the airplane.
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