Spoileron movements when spoilers deployed

[maple-syrup 40]

Those are pictures of a 737 Classic 300-400-500, but yeah same idea...

[Capt. Windh 3]

FYI

 

Had to change settings on my video in order for PMDG support to view it.

 

https://vimeo.com/74512274

 

password: pmdg

[Capt. Windh 3]

The answer from PMDG support:

 

"I reviewed your video and I don't see anything out of the ordinary.  The Spoiler Mixer in the wheel interacts with the Aileron quadrant to add or remove spoiler input exactly as illustrated in your video.  We created the Spoiler mixer operation after reviewing numerous Boeing Maintenance documents and with advice from the Tech Team of 737NGX Captains and Maintenance personel.  What specifically is it that you think should be happening and can you provide technical references to back up these findings?"

 

I don't have any solid references as of now, except for the Classic material provided in the thread, which really does not goes into Ground Mode.

 

We all agree that this is a fault in the modelling, I just need to find solid proof now. If anyone else finds something, please post it here!

 

Realism FTW!

 

 

J

[kevinh 409]

 

 

We all agree that this is a fault in the modelling, I just need to find solid proof now. If anyone else finds something, please post it here!

You could try telling tell PMDG support that the roll spoilers should not fully retract for a small wheel movement, they should move towards closed proportionately with wheel movement.  Fixing this would go a long way to improving the visual appearance in your video.  I have proof of this for the 737 Classic, but not the NG.  PMDG don't think this is wrong behaviour, it's how they've designed the simulation, but it is.

 

It may also be true that, as Matt says, the roll spoilers should not operate differentially at all when on ground.  However this is much more debatable.  It wasn't the case with the 737 Classic.  PMDG have certainly got the way the speedbrake and spoilers interact in flight wrong.

[Capt. Windh 3]

OK Kevin, I'll tell them that. 

 

And by the way, I'm a little baffled that not many more has discovered this. Does everybody who use pedals just let go of the yoke, the second the aircraft touches ground? By all means, the aircraft is still very aerodynamically responsive at this part of the landing. Either that or people just never thought of to have a look at their landing from outside.

 

[Spin737 102]

I've been trying to find something in my manuals that backs up what I said, but I can't so I can't be 100%. I don't often see people really deflecting the yoke much after touchdown, anyway. It's not a Cessna, but the FCTM does state that we should use the yoke to keep the wings level.

[Capt. Windh 3]

I've been trying to find something in my manuals that backs up what I said, but I can't so I can't be 100%. I don't often see people really deflecting the yoke much after touchdown, anyway. It's not a Cessna, but the FCTM does state that we should use the yoke to keep the wings level.

Sure. And as you can see in my video, no large input at all is required to make the spoiler ins react. Very very little in fact.

[Capt. Windh 3]

Johan-

 

The 737 is also modeled correctly.

 

When the spoilers are deployed and the yoke is moved outside of the neutral band (i think 7 degrees... but it may be slightly larger/smaller as it has been 4 years since I coded this) the up-side wing spoilers lay flat.

 

This is true of all boeing airplanes.

 

Robert S. Randazzo

Technical Support

PMDG Simulations, LLC

 

 

 

:Shame On You:

[Vagabondo 23]

 

 

My understanding of the aircraft system is that on ground with speedbrake extended fully, the flight spoilers deflect partially and should still modulate with wheel input, as they do in flight. However the ground spoilers go to full deflection and are not affected by wheel position.

On this point are correct for the standard NG. However, try deselecting Short Field Package in the CDU equipment options. Now you should see the flight spoilers partially extended on the ground. We're not given any specific details, but one of the features of the SFP is extended flight spoiler deflection on the ground.

 

With regards to spoiler movement vs control wheel displacement. I don't know for sure, but I imagine that on the ground with the ground spoilers deployed, flight spoiler response would have to be exaggerated compared to in flight to ensure sufficient roll control during cross wind landings. Difficult to know for sure to be honest, but it doesn't seem particularly wrong.

[kevinh 409]

 

:Shame On You:

Indeed, Robert is wrong about that I'm afraid. I have Boeing data which shows otherwise.

On this point are correct for the standard NG. However, try deselecting Short Field Package in the CDU equipment options. Now you should see the flight spoilers partially extended on the ground. We're not given any specific details, but one of the features of the SFP is extended flight spoiler deflection on the ground.

 

With regards to spoiler movement vs control wheel displacement. I don't know for sure, but I imagine that on the ground with the ground spoilers deployed, flight spoiler response would have to be exaggerated compared to in flight to ensure sufficient roll control during cross wind landings. Difficult to know for sure to be honest, but it doesn't seem particularly wrong.

I don't know much about the short field package, but you are wrong about normal flight spoiler operation on ground with wheel input. There is no reason to exaggerate their movement, if that was the case why not exaggerate the aileron movement too. It would make it much harder for a pilot to control if as soon as the aircraft touched down his crosswind control inputs were suddenly increased. Similarly it would be odd if they suddenly disappeared.

[Vagabondo 23]

I don't know much about the short field package

Increased flight spoiler extension on the ground, winglets, two position tail skid, reduced idle thrust on the ground and sealed slats increase takeoff weight reduce landing distances. The SFP option is the reason different people see different behavior in NGX.

 

 

 

but you are wrong about normal flight spoiler operation on ground with wheel input. There is no reason to exaggerate their movement, if that was the case why not exaggerate the aileron movement too.

I don't know. Taking into account the fact the ailerons on a 737 aren't particularly effective in any phase of flight (anyone who has experienced manual reversion can probably attest to this), then at less than flying speed on the ground they'd be even less effective. Perhaps also it there are wing structural considerations. Perhaps aerodynamic considerations. Perhaps the engineering solution of controlling roll through controlling spoiler extension means less parts, less weight and less maintenance. Who knows the answers to these things except the people to made the original design compromises.

 

You say you have data, what data do you have? Perhaps that would stop this pointless conjecture

[Capt. Windh 3]

I'd also love to see some numbers on this, to show to PMDG.

 

And I wouldn't say this is a pointless discussion at all. It is about realism. The NG by iFly and even the NG for FS9 did not respond this way on control input.

[kevinh 409]

I don't know. Taking into account the fact the ailerons on a 737 aren't particularly effective in any phase of flight (anyone who has experienced manual reversion can probably attest to this), then at less than flying speed on the ground they'd be even less effective. Perhaps also it there are wing structural considerations. Perhaps aerodynamic considerations. Perhaps the engineering solution of controlling roll through controlling spoiler extension means less parts, less weight and less maintenance. Who knows the answers to these things except the people to made the original design compromises.

 

 

 

You say you have data, what data do you have? Perhaps that would stop this pointless conjecture

 

 

Unfortunately the data is Boeing proprietary so I can't share it here. This data is for the 737-3/4/500.  However although the spoiler panel configuration is different for the -6/7/8/900 I would be very surprised if the way the panels moved as a result of wheel and speedbrake lever inputs is changed in any significant degree.

 

The data shows how the wheel and speedbrake controls are combined in the spoiler mixer unit to position the flight spoilers.  Firstly there is no difference between on ground and in flight situations, apart from the fact that in flight the speedbrake lever can't move as far, thus preventing the ground spoilers extending. Secondly, with the flight spoilers deflected symmetrically by the speedbrake lever, any wheel input will deflect the spoilers either up or down in the same direction as the ailerons. So the spoilers on the up going wing (aileron down) don't simply retract (as modelled by PMDG), they move down by a similar amount as the spoilers on the down going wing move up.

 

If the speedbrake is down the spoilers on the down going wing don't start to deflect until the aileron gets to around 2-3 degs, so small wheel inputs don't cause the spoilers to extend in that case.  This is modelled correctly in the NGX.

 

The effect of speedbrake lever and wheel on flight spoiler position is non-linear.  But broadly speaking the speedbrake lever is commanding the flight spoilers to move symmetrically, the wheel input is commanding them to move asymmetrically (like the ailerons) and the spoiler mixer unit sums these two inputs together.  The resulting panel position is limited between the minimum position (faired flat to the wing surface) and the maximum deflection position.

[Vagabondo 23]

Thanks Kevin,

I don't disagree, perhaps PMDG's animations are a bit out in relation to the control wheel movement. The only further comment I have is regarding the following.

 

Firstly there is no difference between on ground and in flight situations, apart from the fact that in flight the speedbrake lever can't move as far, thus preventing the ground spoilers extending...The resulting panel position is limited between the minimum position (faired flat to the wing surface) and the maximum deflection position.

I think there are definitely some differences between ground and air with both SFP and non SFP versions of the NG. For example the maximum deflection position is different, something like 30 degrees in the air and 60 degrees on the ground. Taking that maximum deflection into account, on the ground with the speedbrake lever past the flight detent, full aileron will move one side of flight spoilers from 30 degrees up to full deflection (60 degrees) and the other from 30 degrees to retract - I presume to try to maintain the total weight on wheels during braking.

[kevinh 409]

 

 

I think there are definitely some differences between ground and air with both SFP and non SFP versions of the NG. For example the maximum deflection position is different, something like 30 degrees in the air and 60 degrees on the ground. Taking that maximum deflection into account, on the ground with the speedbrake lever past the flight detent, full aileron will move one side of flight spoilers from 30 degrees up to full deflection (60 degrees) and the other from 30 degrees to retract - I presume to try to maintain the total weight on wheels during braking.

Firstly I was talking about the non-SFP versions, which is by far the majority.  With those, the only difference on ground is that the speedbrake lever can move further, beyond the flight detent, allowing more deflection for the flight spoilers and also fully deploying the ground spoilers.  Without the SFP, if you deploy the speedbrake on ground to the flight detent the flight spoilers will behave exactly as they do in the air.

 

With the SFP the flight spoilers deflect even further, but I don't think the maximum mechanical deflection limit is changed.  In that case there might not be any additional movement up available if the wheel is turned.  There could still be retraction on the opposite wing but as that would begin from a larger initial deflection angle it would be even less likely to have them lie flat at full wheel.  The additional symmetric panel deflection of the SFP on ground does not increase the asymmetric deflection of the wheel, as you imply.