Leading edge slot behavior

[HagarTheHorrible]

I was enjoying flying around in the La 5 one pleasant evening, flying in VR is quite a novelty and pleasure. 

 

I noticed the slats popping back and forth, often not at the same time, but apart from the visual I wouldn't have known they'd deployed or retracted at all.

 

i know what the purpose of the slats are and I'm sure they work to that end but I was a little surprised that I didn't see any noticeable effect on my speed, riding the edge between in and out, or any aerodynamic wobbles as they deployed, particularly when they did so asymmetrically. 

 

Are there any downsides to having slats fitted, in BoX  ?

 

 

 

 

Please, please, please, please try to be civil, stick to the point, be constructive and don't wander off topic and start ranting.  All I'm after is to know if there should be reasonably obvious physical indications that the leading edge slats have deployed or undeployed.

[busdriver]

Well...in the F-16 there was no noticeable feeling when the Leading Edge Flaps (functionally the same purpose as slats) deployed symmetrically. Asymmetrical deployment, the airplane would roll unless you applied countering stick. In the F-4E with Leading Edge Slats, guys would notice a difference especially in close formation (or on the boom of the tanker), so the generally accepted technique was to lock them in place for those cases. On the Airbus 319/320 I didn't feel the slats deploy, except there is definite nose down movement as your AoA decreases.

 

I would expect to notice a rolling moment in BoX airplanes with asymmetric slat extension. Without force feedback, I don't notice slat deployment in game. It's only when I watch the wing do I realize what has happened.

 

YMMV

 

[HagarTheHorrible]

I think I would have expected a yawing motion as well with asynchronous deployment, caused by the slightly higher drag of the deployed slat ?

 

It must feel a bit odd (brain befuddling) if the nose pitches down when the slats deploy and what you're trying to do is maintain a consistant turn rate. I don't know if this pitching down is general behaviour or just particular to the Airbus ?

[Wulf]

Well, according to Eric Brown, the asymmetrical opening of the leading edge slats, on a Bf 109, resulted in "aileron snatching".

 

EB notes that in mock attacks in a 109 G on a Lancaster and a Mustang "the slipstream of these aircraft caused the intermittent operation of the slats so that accurate sighting became impossible."

 

Was the La-5 much the same?  I would imagine so.   

[busdriver]

I think I would have expected a yawing motion as well with asynchronous deployment, caused by the slightly higher drag of the deployed slat ?

 

It must feel a bit odd (brain befuddling) if the nose pitches down when the slats deploy and what you're trying to do is maintain a consistant turn rate. I don't know if this pitching down is general behaviour or just particular to the Airbus ?

 

Well for game purposes and RL air-to-air, your eyes are outside the cockpit whilst maneuvering so I wouldn't expect to notice any yawing motion. These days I tow gliders with a 160 HP Super Cub at 65 MPH, and I really notice yawing when the glider I'm dragging around "boxes the wake" or works recovering from a slack line.

 

Ref the Airbus, the only time I'd notice the nose down pitch when going to Flaps 1 (or Config 1 for some airlines) was in level flight. I liked to fly with the Autopilot and Autothust disconnected whilst flying visual approaches. If turning or descending when going to Flaps 1, I honestly couldn't detect the pitch down moment.

[andyw248]

When the Blue Angels flew the A-4 Skyhawk in the 70's they locked the slats because they would deploy asymetrically on the A-4 and that would negatively impact flying in tight formation.

[HagarTheHorrible]

i think if the slots asimetrical deployement didnt have functionality theyd be linked together

 

i guess or is this asimetrical deployment an idea like the downwards ejection

That's not quite how it works, they work by air pressure rather than mechanically. Linking them would have over complicated a simple idea and probably introduced other issues plus a weight penalty amongst other things. For most general flying asymmetrical deployment wouldn't have been much of an issue anyway, it's only in the rarified air of combat that undesirable traits become problematic. A slight roll or other noticeable side effects are no more than a mild, easily corrected, irritant for most aviation situations.

 

I suppose, given that BoX is a physics based flight model, that deployment of the slots doesn't appear to be noticeable on the physics apart from the benefit of allowing a higher AoA ( and maybe delayed wingtip stall ?).

[HagarTheHorrible]

The other thing to note, and my observations of the La 5 might be different to other aircraft, is that the deployment seems to be quite lazy. 109 pilots talked of a bang, that could sometimes even be heard over the noise of the engine, that suggests deployment was quite sharp.

[Ribbon]

Ref the Airbus, the only time I'd notice the nose down pitch when going to Flaps 1 (or Config 1 for some airlines) was in level flight. I liked to fly with the Autopilot and Autothust disconnected whilst flying visual approaches. If turning or descending when going to Flaps 1, I honestly couldn't detect the pitch down moment.

I guess it is cos of wings/flaps position relation to the position of the center of weight/gravity, so it is noticable in level flight while in turns and descending center of weight moves on plane's axis according to it which makes it less or not noticable.

Also in turns rudder trim comparator unit might prevent those effects. Didn't work on these planes so i can't tell for sure.

Edited May 3, 2017 by redribbon

[BlitzPig_EL]

Because the purpose of leading edge slats is to increase lift, one would think that in game an asymmetric deployment would induce a fair amount of roll.   This may not be working correctly for the same reason that proper side slipping of the aircraft cannot be done in the sim.

 

Maybe after that fix for airflow over control surfaces is released the behavior of the leading edge slats will be more in line with the real world.   It's odd though that the roll coupling of the rudder is so pronounced, yet roll for slats isn't.

Edited May 3, 2017 by BlitzPig_EL

[Ribbon]

Because the purpose of leading edge slats is to increase lift, one would think that in game an asymmetric deployment would induce a fair amount of roll. This may not be working correctly for the same reason that proper side slipping of the aircraft cannot be done in the sim.

 

Maybe after that fix for airflow over control surfaces is released the behavior of the leading edge slats will be more in line with the real world. It's odd though that the roll coupling of the rudder is so pronounced, yet roll for slats isn't.

it just helps enough to create wanted roll and stability while doing it, on the other hand it can prevent from unwanted or uncontroled amount of roll.

About impact on jaw it can only help cos increased drag on upper wing will prvent aircraft nose to go down acting like rtcu.

[=TBAS=Sshadow14]

its stall prevention technology and a stalled wing makes more drag than those slats.
so as the wing is about to stall slats extend trading 1 form of drag for another.
 

[69th_chuter]

Asymmetric slat opening is only going to happen while yawing or rolling during high AoA maneuvers as these two conditions will change the relative AoA of the left and right wings (assuming the wings have dihedral).  So, for instance, a high AoA yaw to the left could pop out the right slat (and not the left) increasing lift (drag) on the right wing BUT the right wing was already creating more lift due to the yaw (dihedral effect) so I imagine it might be difficult from the cockpit to parse out the specific contribution of the slat to the overall roll and yaw experience.  The less dihedral the aircraft has the less asymmetric slat operation one will typically experience.

[HagarTheHorrible]

I would have assumed the La 5 slats would have worked the same way as 109 slats, spring resistance and air pressure. If that were the case though, why aren't they open on the ground, do not hey have a locking mechanism ?

[Guest deleted@83466]

Well, according to Eric Brown, the asymmetrical opening of the leading edge slats, on a Bf 109, resulted in "aileron snatching".

 

EB notes that in mock attacks in a 109 G on a Lancaster and a Mustang "the slipstream of these aircraft caused the intermittent operation of the slats so that accurate sighting became impossible."

 

Was the La-5 much the same?  I would imagine so.   

 

I came across these other quotes about the BF-109 on this (http://www.pilotfriend.com/flight_reports/reports/33.htm):

 

With flaps up the ailerons snatch while the slots are opening, and there is a buffeting on the ailerons as the stall is approached.. With flaps down there is no aileron snatch as the slots open, and no pre-stall aileron buffeting.

 

Loops must be started from about 280 mph when the elevator is unduly heavy; there is a tendency for the slots to open at the top of the loop, resulting in aileron snatching and loss of direction.

 

I'm not sure exactly how "aileron snatch" appears to the pilot.  I have read somewhere some German BoB pilot that the 109 could turn with a Spitfire, but that a lot of pilots were afraid of the slots coming out, because of buffeting,so they didn't tend to push it.  Is this simply the pre-stall buffet, or is it the actual "aileron snaching" that is causing the vibration that the German pilots didn't like?

Edited May 4, 2017 by Iceworm

[Wulf]

I would have assumed the La 5 slats would have worked the same way as 109 slats, spring resistance and air pressure. If that were the case though, why aren't they open on the ground, do not hey have a locking mechanism ?

 

 

It is my understanding that the slats are activated by aerodynamic forces alone.  I don't think springs are used at all, at least not on the 109. 

[Wulf]

I came across these other quotes about the BF-109 on this (http://www.pilotfriend.com/flight_reports/reports/33.htm):

 

With flaps up the ailerons snatch while the slots are opening, and there is a buffeting on the ailerons as the stall is approached.. With flaps down there is no aileron snatch as the slots open, and no pre-stall aileron buffeting.

 

Loops must be started from about 280 mph when the elevator is unduly heavy; there is a tendency for the slots to open at the top of the loop, resulting in aileron snatching and loss of direction.

 

I'm not sure exactly how "aileron snatch" appears to the pilot.  I have read somewhere some German BoB pilot that the 109 could turn with a Spitfire, but that a lot of pilots were afraid of the slots coming out, because of buffeting,so they didn't tend to push it.  Is this simply the pre-stall buffet, or is it the actual "aileron snaching" that is causing the vibration that the German pilots didn't like?

 

 

Also interesting to note that, according to your reference report and the reports prepared by Eric Brown, the elevator on the Bf 109 was pretty much locked solid at 650 kph which isn't something we see in the game.  In the game you have good elevator authority well out past 700+ kph.

[HagarTheHorrible]

It is my understanding that the slats are activated by aerodynamic forces alone.  I don't think springs are used at all, at least not on the 109.

 

Springs push them out, air pressure pushes them in ? There has to be some counterbalancing resistance, they don't just flop about. I'm interested too, like Iceworm, how would aileron snatch appear to the pilot ?

[novicebutdeadly]

Also interesting to note that, according to your reference report and the reports prepared by Eric Brown, the elevator on the Bf 109 was pretty much locked solid at 650 kph which isn't something we see in the game.  In the game you have good elevator authority well out past 700+ kph.

Eric Brown is talking about the 109E (why they have what looks like a G6 imagine I have no idea),

 

Aileron snatching was common on the 109E (I don't fly the E in game, but if it isn't modelled in game and it's possible it should be), but not from the F series onwards PROVIDED that the slats had been installed and adjusted correctly (please note that I have just read that the E and F series used the same system for the slats, it was changed on the G to a more reliable set up, but I have not been able to confirm this).

 

In regards to the elevator the report fails to mention the stab trim setting whilst in the dive, or if he had tried to use the stab to help reduce the stick forces (and also while maneuvering).

 

The tailplane was also redesigned in the F series compared to the E which improved the elevator and stick forces to a degree (the tailplane was moved forward and down)

 

 

Are you able to send me the link in regards to Eric Browns mock attacks using a 109G

 

I found a useful site that explains how the slats work: http://www.boldmethod.com/learn-to-fly/aircraft-systems/leading-edge-slat-lift-device/

 

 

 

 

 

 

 

 

 

[Wulf]

Eric Brown is talking about the 109E (why they have what looks like a G6 imagine I have no idea),

 

Are you able to send me the link in regards to Eric Browns mock attacks using a 109G

 

I found a useful site that explains how the slats work: http://www.boldmethod.com/learn-to-fly/aircraft-systems/leading-edge-slat-lift-device/

 

 

 

 

 

 

 

 

 

 

No, he wasn't referring to the "E" model at all.  He was talking about a 109G.

 

Here's a direct quote from this book.  "Inevitably a Gustav reached us at Farnborough.  To be precise it was a Bf 109G-6/U2 which had landed at Manston in error on 21  July 1944."

 

 

The reference to the G6 "mock attacks" is contained on page 155 of Wings of the Luftwaffe.

Edited May 5, 2017 by Wulf

[=TBAS=SkyWalker77]

The only odd thing about them in the sim is on the 110 the right one will stay down long after the left has retracted its odd think its a bug.

[novicebutdeadly]

No, he wasn't referring to the "E" model at all.  He was talking about a 109G.

 

Here's a direct quote from this book.  "Inevitably a Gustav reached us at Farnborough.  To be precise it was a Bf 109G-6/U2 which had landed at Manston in error on 21  July 1944."

 

 

The reference to the G6 "mock attacks" is contained on page 155 of Wings of the Luftwaffe.

 

The link that someone provided is talking about the 109E

 

 

I knew that you were not as you had said that it was a 109G that Eric Brown used in the mock interception and dogfight, which is why I was curious to read it.