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rob345

Flaperons behaviour at flaps 25/30

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Hi,

 

I have a question concerning a "surprising" discovery:

With flaps 25 or 30 selected the flaperons retract to their neutral position at or above ~145kts.

I find this somehow weird because flaps 20 maneuvering speed is usually above 145kts. Thus, you have to reduce speed further to 145kts or below before selecting flaps 25.

 

Is this the correct behaviour of the flaperon? Maybe a kind of load relief?

 

I have searched the web, tutorial and FCOM but haven't found an answer so far...

 

 

Thanks for clarification

 

Robert

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I have just noticed that even the official release video (on the PMDG website) shows this kind of flaperon behaviour.

 

During landing at KPHX you see that on short final the flaperons are retracted and drop down only seconds before touchdown (probably because speed reduces below the suspicious threshold of ~145kts)?!

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Is this the correct behaviour of the flaperon? Maybe a kind of load relief?

 

The flaperon - note the name, which is a portmanteau of flap and aileron - is there to both provide lift and roll the aircraft.  Part of landing is coming in with just enough lift so that you keep flying, but not so much that the plane wants to keep flying by the time you're supposed to touch down.

 

As part of the flaperon's purpose is to augment lift, do you see where I'm going here, and why it might be doing what you're seeing?

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Wow! This is indeed interesting folks. I fly very frequently on 777s. Mainly on American Airlines from DFW to SAO, DFW to LHR, and DFW to ARG. I have always observed the 777 wing behavior during all aspects of flight and I have to say.......I've never seen this flaperon behavior before. In every single occasion the 777 flaperon goes down with every notch down of the flaps and it flaps allright, but it does it all while being down at a pretty good angle. United (the airlines showcased in the video) flies 777s with PW engines and the ex-COA's fly with GEs. AA flies strictly RR, except the new 300s which feature GE engines. Would the engines maybe have something to do with this?

 

Strange! Dennis

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Would the engines maybe have something to do with this?

 

You noted that the flaperon normally deflects with the flaps when you've observed them, which is true.  Remember that there's also a trained pilot up front in these cases.  Now, based on my above post, do you see where this is going?  :wink:

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Thanks for your answer Kyle. But I am not yet completely happy with it... ;-)

 

Generally, I know what a flaperon is and what it is designed for.

What was new to me is that its deflection on the T7 seems to depends not only on the current flap setting but also on other parameters (speed, thrust or whatever).

 

Part of landing is coming in with just enough lift so that you keep flying, but not so much that the plane wants to keep flying by the time you're supposed to touch down.

 

Actually, the landing in the release video (http://www.youtube.com/watch?v=qOm1oBD6eQ0) shows the contrary: Coming in with no flaperon (neutral) and just before touchdown instant deflection (full down).

 

So, I want to come back to my inital observation in the PMDG 777 that the flaperon retracts above ~145kts with flaps 25 or 30.

As a video says more than words, I made (a lousy) one to demonstrate what I mean:

 

http://www.youtube.com/watch?v=GaApo8ARgjo

 

As Vapp is around 143kts in this example, the flaperon would continuously retract/extract during final approach.

So, is this behaviour intendend?

 

Thanks again

 

Robert

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So, is this behaviour intendend?

 

Yes...if you look a little closer and read between the lines of what I wrote you'll start to see why I've said it.

 

Watch real videos of the plane and it behaves normally.  These pilots are trained to be on point.

Watch videos of simmers at the controls and in some cases it does not behave like you'd expect.  These pilots do not have the same training and control that the real pilots do.

 

Instead of continuing to be mysterious:

The plane is trying to salvage the pilot's poor technique.

 

Extra airspeed means extra lift.  Extra lift means the aircraft will not want to settle as easily.  Extra lift can be killed by reducing the level of the flaperon.

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Thanks for your answer Kyle. But I am not yet completely happy with it... ;-)

 

Generally, I know what a flaperon is and what it is designed for.

What was new to me is that its deflection on the T7 seems to depends not only on the current flap setting but also on other parameters (speed, thrust or whatever).

 

 

Actually, the landing in the release video (http://www.youtube.com/watch?v=qOm1oBD6eQ0) shows the contrary: Coming in with no flaperon (neutral) and just before touchdown instant deflection (full down).

 

So, I want to come back to my inital observation in the PMDG 777 that the flaperon retracts above ~145kts with flaps 25 or 30.

As a video says more than words, I made (a lousy) one to demonstrate what I mean:

 

http://www.youtube.com/watch?v=GaApo8ARgjo

 

As Vapp is around 143kts in this example, the flaperon would continuously retract/extract during final approach.

So, is this behaviour intendend?

 

Thanks again

 

Robert

 

What sea textures are you using? they look great!

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What sea textures are you using? they look great!

 

These are REX Essential textures with the theme "Wonderous" selected + shader 3 mod.

 

More pictures of these settings can be found on the homepage of my freeware FSX weather program FSXWX: http://www.plane-pics.de/fsxwx/

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According to Boeing the pilot is supposed to add at least 5 knots to Vref on approach, depending on wind etc. So why does the flaperon go up at Vref+5?

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These pilots are trained to be on point.

Watch videos of simmers at the controls and in some cases it does not behave like you'd expect.  These pilots do not have the same training and control that the real pilots do.

 

Instead of continuing to be mysterious:

The plane is trying to salvage the pilot's poor technique.

 

I don't see any "poor technique" or "not being on point" by being stable on approach at Vref+5? ... but the flaperons continuously go up and down nonetheless.

And btw: It also happens during autoland. So, does the autopilot control the airplane "poor", too...? ;-)

 

 

So why does the flaperon go up at Vref+5?

 

Thanks for understand my initial question correctly! That's exactly the point I don't understand.

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Have seen the same and wondered about it. When i select flaps 30, flaperons go back in its neutral position. Thats definitly not a pilot thing. It happens all the time. Never seen it on a real 777 before. The flaperons should stay in a flaplike down Position.

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Just to add to this, if you look at the flaperon when the spoilers deploy on landing, the flaperon will go 'level'. Why? Adding to the above explanation; the flaperon goes level to reduce the lift and therefore add to the effectiveness of the spoiler deployment upon landing.

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Looks like he had an left aileron crosswind correction,observe the outboard aileron.

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Could this be Landing Attitude Modifier in action? The PMDG pilot mentioned this feature rather proudly in one of his pre-release screenshot posts on this forum. A previous poster got it right I think, reduction in flaperon deflection promotes a nose up attitude to correct for the higher speed. Perhaps you can experiment with a steady flight at the correct approach speed in the right configuration, and see how the flaperon behaves.

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These are REX Essential textures with the theme "Wonderous" selected + shader 3 mod.

 

More pictures of these settings can be found on the homepage of my freeware FSX weather program FSXWX: http://www.plane-pics.de/fsxwx/

 

Thanks, your weather engine looks great. I had no idea REX worked with the shader 3 mod. Do all their water textures work with the new shader?

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Hi,

 

I have a question concerning a "surprising" discovery:

With flaps 25 or 30 selected the flaperons retract to their neutral position at or above ~145kts.

I find this somehow weird because flaps 20 maneuvering speed is usually above 145kts. Thus, you have to reduce speed further to 145kts or below before selecting flaps 25.

 

Is this the correct behaviour of the flaperon? Maybe a kind of load relief?

 

I have searched the web, tutorial and FCOM but haven't found an answer so far...

 

 

Thanks for clarification

 

Robert

 

 

Try landing with the autothrottle engaged so that you maintain Vref + 5 accurately and you shouldn't see this happen.

 

RSR described this flaperon behaviour in a post a while ago. They retract when you're fast to reduce lift; this prevents you from pushing the nose forward to maintain glide path and smacking the nose into the runway.

 

This could be a reason anyway.

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Thanks, your weather engine looks great. I had no idea REX worked with the shader 3 mod. Do all their water textures work with the new shader?

 

Sorry, I don't know if all their water textures work with the shader 3 mod.

And oh, these water textures also might be the ones from Orbx FTX Wales (the video is taken near EGFF) because I don't know which parts of water areas are covered with their own ones.

 

Here is video of a full autoland which looks pretty much "being on point" to me. A/T engaged, Vref+5.

http://www.youtube.com/watch?v=ZiNC7SgvJP0

 

It seems that the position of the flaperons only can be neutral or full down. Nothing inbetween.

Btw: As long as it only affects the animation not the actual flight model, I don't care if they behave odd by going up and down...

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Would be interesting if someone who really knows the system logic  - and not just tries to let us know that we are not trained... - could explain this.

 

 

@ Robert - good catch! 

 

 

Cheers,

Berni

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*sigh*

 

Okay, so, because I clearly don't know what the system logic is, I guess the following will be of no use, but I'll post it anyway:

 

Flaperons:

What do flaps do?  Enhance lift.

What do ailerons do?  Effect roll.

Put those two together: what do flaperons do?  Enhance lift and effect roll.

 

The flaperons are part of a very involved system that looks at several things at once to determine where these things should be placed.  Part of the system determines if a deflection is necessary to roll (the flaperons are actually the primary roll device at cruise - ailerons are locked out in this phase).  Part of the system determines if a deflection is necessary to follow flap extension.  Part of the system determines if flaperon retraction is necessary to augment the lift to remain within an acceptable range (you're welcome to think I'm not knowledgeable for not knowing what the range is specifically, but I challenge you to find it).

 

So, assemble all of those parts and you get your answer:

The flaperons are behaving the way they are to get the best of the situation.

 

They will retract if there is too much lift being developed in the given situation, regardless of who (or what) is controlling the plane.  Without seeing an AoA indicator in either video, I can't really get a clear idea as to why they're behaving like that.  Sure, speed has a correlation to lift, but AoA is a better direct correlation.  As to what drives the flaperon decisions, I can't quite say, because there are multiple sources for the flaperon commands, to include the ADIRU, airspeed sensor (specifically, calibrated), flap position, roll commands, and so on.

 

As Jordan mentioned, RSR noted this feature in one of the early preview posts.

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Kyle, I really do appreciate your answer! And at no time, I said you "clearly don't know what the system logic is".

And of course your general description about flaps and aileron = flaperon is correct.

 

But as PMDG claims high standards, I do too regarding the correct implementation of those things! ;-)

 

 

Part of the system determines if flaperon retraction is necessary to augment the lift to remain within an acceptable range (you're welcome to think I'm not knowledgeable for not knowing what the range is specifically, but I challenge you to find it).

 

Ok, here we go. I found following description (no garantuee of correctness):

 

The landing attitude modification (LAM) logic decreases the flaperon droop when the airplane is in an overspeed approach with flaps at the 25-unit or 30-unit position. The PFC calculates the reduction of flaperon droop proportionally to the overspeed increment. Full flaperon droop removal occurs when the airspeed is 20 knots more than the approach landing speed shown in the airplane flight manual.
When the LAM logic is active, it reduces wing lift and causes an increase in angle-of-attack. This increases the nose gear ground clearance.

 

So that's the way I would expect the flaperons to work! From an engineering/aerodynamic point of view it absolutely makes sense to adjust the droop proportionally (and this is also the way you see it in hundreds of youtube videos)!

But that's not the way PMDG have implemented it. Like I said above and what is clearly visible in the video (and of course you can try it yourself if you miss the AoA), the flaperon only alternates between full up or full down.

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And at no time, I said you "clearly don't know what the system logic is".

 

You didn't, and I didn't quote you as saying so.  I was alluding to the post immediately above mine.

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