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Starlionblue
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777 Flaperon Behavior On The Runway.

Tue Mar 29, 2005 8:34 am

I've been meaning to ask this question every time I step off a 777, but I keep forgetting. This time I took notes  Wink

The 777 high-speed (inboard) ailerons droop with the flaps, and are thus technically flaperons. However there are two instances when their behavior is different.
- During the take off run, up until a certain speed (80kt?) they are in line with the wing in the non-drooped center position. When the aircraft has accelerated to a certain speed, they droop again.
- During landing, when the spoilers deploy, they are again in line with the wing in the non-drooped position. They then droop again when the spoilers are retracted.

Does anyone know why they are programmed to do this?
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
dl757md
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RE: 777 Flaperon Behavior On The Runway.

Tue Mar 29, 2005 9:39 am

Your observations are generally correct. However only flap position and speedbrake lever position determine flaperon droop. Speed has nothing to do with it.

From the 777 SDS(Systems Description Section of the AMM)
The flaperons droop to 10 deg TED(Trailing Edge Down) when the flaps are at the 5 position. They droop to 20 deg TED when the flaps are at the 15 or 20 position. They droop to 31 deg TED when the flaps are at the landing position (25 or 30).

On the ground, the PFCs (Primary Flight Computers) remove the flaperon droop command in proportion to the speedbrake lever movement from 17 to 55 deg. When the speedbrake lever goes back to the down position, the flaperons gradually droop to the position commanded by the flaps.


To answer as to why they retract during rollout. The flaperon droop is a lift augmenting feature. When you touch down and the speedbrakes are deployed you want to get rid of all the lift that you can so the plane stays firmly planted on the ground. Since the logic that controls this comes from the speedbrake lever position sensor, then when the lever goes back to below 17 deg the flaperons droop again.

Hope this helps.

Dl757Md

Edit:abbr definition

[Edited 2005-03-29 01:54:03]
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Starlionblue
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RE: 777 Flaperon Behavior On The Runway.

Tue Mar 29, 2005 9:44 am

Thx for the great info DI757md. That make a lot of sense.

However, why did I notice the removal of flaperon droop during the takeoff roll? Speedbrakes are not used then. Or maybe I am imagining things. I have only noticed it once on takeoff, but every time on rollout.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
dl757md
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RE: 777 Flaperon Behavior On The Runway.

Tue Mar 29, 2005 9:55 am

Quoting Starlionblue (Reply 2):
However, why did I notice the removal of flaperon droop during the takeoff roll?

I have no explanation as to why this happened. Bottom line...It shouldn't have. If it in fact did then there was either a system malfunction or pilot error.

Dl757Md
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Starlionblue
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RE: 777 Flaperon Behavior On The Runway.

Tue Mar 29, 2005 10:02 am

Quoting Dl757md (Reply 3):
Quoting Starlionblue (Reply 2):
However, why did I notice the removal of flaperon droop during the takeoff roll?

I have no explanation as to why this happened. Bottom line...It shouldn't have. If it in fact did then there was either a system malfunction or pilot error.

Probably just seeing things. We made it safely to London so...  Wink

Thx again for the info!
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
ArmitageShanks
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RE: 777 Flaperon Behavior On The Runway.

Tue Mar 29, 2005 10:24 am

Quoting Dl757md (Reply 3):
However, why did I notice the removal of flaperon droop during the takeoff roll?

I've seen that happen twice before, too.

Someone posted videos from MAN on here and you can clearly see them drooping a few seconds into the takeoff roll.
 
dl757md
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RE: 777 Flaperon Behavior On The Runway.

Tue Mar 29, 2005 10:42 am

Quoting ArmitageShanks (Reply 5):
Someone posted videos from MAN on here and you can clearly see them drooping a few seconds into the takeoff roll.

Can you find a link to those videos?
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CCA
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RE: 777 Flaperon Behavior On The Runway.

Tue Mar 29, 2005 10:50 am

Quoting Starlionblue (Reply 4):
Probably just seeing things. We made it safely to London so...

You're not seeing things the flaperon droop is removed when TO thrust is set to reduce wear and tear on the aileron until 100kts then the airflow over and under the wing begins to have some effect and the flaperon droop is reinstated.

Rgds CCA
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dl757md
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RE: 777 Flaperon Behavior On The Runway.

Tue Mar 29, 2005 12:04 pm

Quoting CCA (Reply 7):
You're not seeing things the flaperon droop is removed when TO thrust is set to reduce wear and tear on the aileron until 100kts then the airflow over and under the wing begins to have some effect and the flaperon droop is reinstated.

CCA Im curious as to where you found this information. It sounds good, but looking in the AMM, WDM, SDS, and SSM, I couldn't find anything about this. The SDS says that The PFC's software includes the flight control laws. The PFCs calculate control commands for:
The ailerons, flaperons, and spoilers for roll control.
The ailerons and some spoilers for lockout during cruise.
The ailerons and flaperons for droop control during flap extension.

The PFCs use N1 speed card info for flight envelope protection in regards to thrust asymmetry compensation. But that is a rudder control function. I could find no relation between the engine settings or airspeed and the flaperons.

Perhaps this is a software option that Delta chose not to order and therefore is not in Delta's manuals.

Dl757Md
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CCA
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RE: 777 Flaperon Behavior On The Runway.

Tue Mar 29, 2005 2:18 pm

Dl757md,

I saw what Starlionblue said on a CX 777 flight, so went and looked it up. Delta use Rollers as well, is that correct? thought it may be a Roller only thing.

I looked it up in the MM on CDROM but may have found it as you said somewhere other than Flight Controls, also may have been in a wiring/flow diagram with AND/OR gates that show: TO thrust set and <100kts.

I'll go look it up again and get back to you.

Rgds CCA

[Edited 2005-03-29 06:21:12]
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Newark777
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RE: 777 Flaperon Behavior On The Runway.

Tue Mar 29, 2005 2:37 pm

Look here, you can clearly see them drooping during the takeoff roll:

http://www.flightlevel350.com/public_viewer.php?cat=75&pic=2251

Harry
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CCA
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RE: 777 Flaperon Behavior On The Runway.

Tue Mar 29, 2005 3:30 pm

Newark777,
Thanks for that.

At :30 you can see the flaperon drooped inline with the outboard flaps, at :48 as power is applied you can see them droop even more due to the low pressure being created on the lower surface of the flaperon (velocity increase=pressure decrease) then at :58 you can see it undroop and finally at 1:11 during the takeoff as Newark777 said they droop again.

Rgds CCA
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mhsieh
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RE: 777 Flaperon Behavior On The Runway.

Thu May 13, 2010 8:48 pm

With takeoff thrust, until reaching 80kts, the flaperons are in BYPASS mode so they droop all the way down due to gravity, then upon reaching 80kts, power to actuator is restored and they resume the preset drooped position. There is another post by a mechanic on this topic.
 
787atPAE
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RE: 777 Flaperon Behavior On The Runway.

Thu May 13, 2010 11:44 pm

Quoting CCA (Reply 7):
the flaperon droop is removed when TO thrust is set to reduce wear and tear on the aileron until 100kts

Correctimundo. The flaperon takeoff bypass is there to reduce the fatigue on those silly actuators when the thrust right in front of that surface is rather large. The flaperons will float as the lift on the wing increases.

On landing the speedbrake function will cause the flaperon surfaces to go trailing edge up to dump lift (along with all the other main surfaces).

The 787 should have a similar effect on both sides of the flight (bypass on take off run then speedbrakes on landing).
 
dynamicsguy
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RE: 777 Flaperon Behavior On The Runway.

Fri May 14, 2010 9:03 am

Quoting mhsieh (Reply 12):
With takeoff thrust, until reaching 80kts, the flaperons are in BYPASS mode so they droop all the way down due to gravity, then upon reaching 80kts, power to actuator is restored

Wow, you've just gone back to a 5 year old thread to provide the correct answer. Maybe I should find that thread from 3 years ago in which someone said that the 787 does not have flaperons and was never corrected.

The flaperon cops a hiding from thrust impingement, so the bypass mode is there to reduce the fatigue damage. 787atPAE is correct - the 787 flaperon is also bypassed.
 
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Starlionblue
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RE: 777 Flaperon Behavior On The Runway.

Fri May 14, 2010 9:24 am

Quoting dynamicsguy (Reply 14):
Wow, you've just gone back to a 5 year old thread to provide the correct answer.

Yeah I was really surprised. I was like, "did I start a new thread in my sleep or something?" 
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Tristarsteve
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RE: 777 Flaperon Behavior On The Runway.

Sat May 15, 2010 9:58 am

Quoting Dl757md (Reply 8):
Quoting CCA (Reply 7):
You're not seeing things the flaperon droop is removed when TO thrust is set to reduce wear and tear on the aileron until 100kts then the airflow over and under the wing begins to have some effect and the flaperon droop is reinstated.

CCA Im curious as to where you found this information. It sounds good, but looking in the AMM, WDM, SDS, and SSM, I couldn't find anything about this.

B777 AMM Pt 1 27-11-00 Page 56.

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