Hi folks, with all the excitment of the 777 announcement recently, I've been watching a number of youtube videos (as you do :P ) and was just wondering why, when the flaps are in the takeoff range and takeoff power/thrust is set, do the flaperons move from their drooped position back up, only to droop again?

They have a complex set of parameters to reduce wear and tear on the actuators, including a system bypass which inhibits their movement until 80 knots, some of the movement may also be due to the altered pressure over the wing (this is a guess), but I do know they have that system to reduce the wear on the actuators until the speedo gets to 80.

 

Al

Not certain, but I'd imagine it has something to do with the immense amount of thrust put out during takeoff, so they retract in order to not be damaged. Just my thought but someone with more intimate knowledge can surely give you a more accurate answer.

They have a complex set of parameters to reduce wear and tear on the actuators, including a system bypass which inhibits their movement until 80 knots, some of the movement may also be due to the altered pressure over the wing (this is a guess), but I do know they have that system to reduce the wear on the actuators until the speedo gets to 80.

 

Al

 

Thats right...they droop when initially commanded due to their weight, and then will float until airspeed reaches about 100 kts with at least one engine running. At that time, the ACEs will put the flaperon PCUs into normal mode, and they return to the droop position for takeoff.

This sounds interesting, do you have a video so I can get an impression of how it looks like?

This is also a fairly good one to see it in operation:

 

Here is an interesting topic at a.net.

 

Strange 777 Inboard Aileron Movements

 

Checkout reply #12

 

Cheers,

 

Andrej

Learned something new today. Thanks guys.

Here's what Andej found on A.net.

 

The behaviour is caused by a design feature to protect the flaperon, and particularly its actuators, from vibration damage due to engine thrust impingement loads. Where it is located it cops a lot of abuse from both mechanical fatigue due to the thrust impingement and sonic fatigue.

 

When the engines are throttled up at the start of the roll the actuators are bypassed so there is no hydraulic pressure holding them in place. The flaperon can then float so the vibration load is reduced on the actuators. This initially causes the small amount of droop, but then as the speed increases the airflow causes the flaperon to rise. Above a set speed (80 knots, I believe, but it is definitely around that number) the bypass is removed so the flaperon is commanded to its drooped position.

 

My understanding is that this problem was discovered either in flight test or early service.

 

The 787 flaperon is also bypassed in the same way for the same reason.

 

All credit goes to dynamicsguy of A.net

 

 

It may be just me but I hear a thump sound at the exact moment the flaperon shudders slightly @ 1:42. (I can only see it in fullscreen)

Could be the sound of the flaperon entering bypass mode. The engines can be heard spooling up a second later.

 

Edit: Sorry I tried to make the video start at 1:30 (&t=1m30s). Just skip ahead to 1:30 for the takeoff.

Thanks for the comments folks, interesting stuff looking forward the the 777 release

I never noticed that, I always thought that it was the PF making control inputs for crosswind, here is a video I recorded last year on my way back from NY.

 

 

http://youtu.be/zBIyzH1gm30

Here's another short video that I like, maybe the PMDG model may go to this depth

 

http://www.youtube.com/watch?v=b3fEoTfE8Hw

 

Regards

Here's another short video that I like, maybe the PMDG model may go to this depth

 

http://www.youtube.com/watch?v=b3fEoTfE8Hw

 

Regards

 

Yep it's all there on our 777, all painstakingly recreated and animated like what you see in the video. The flaperons will also have hydraulic actuators that you can only see when the flaps are fully extended. I'll be working on that this week.

 

Of course we wouldn't leave anything like this out of the model. Look at the NGX, it has all the flap actuators you can see.