some clarifications on slats

[Sternjaeger]

I feel there's still a bit of confusion on the whole slats thing i.e. how/why they work/deploy/retract and the benefits they bring, so I thought I'd give my 2p worth of experience on the matter to clarify this possibly once and for all.
 
So what are slats? As per Wikipedia's definition: "Slats are aerodynamic surfaces on the leading edge of the wings of fixed-wing aircraft which, when deployed, allow the wing to operate at a higher angle of attack. A higher coefficient of lift is produced as a result of angle of attack and speed, so by deploying slats an aircraft can fly at slower speeds, or take off and land in shorter distances. They are usually used while landing or performing maneuvers which take the aircraft close to the stall, but are usually retracted in normal flight to minimize drag."
 
The deployment of slats can be of two kinds: manual, where the pilot controls the deployment by means of a lever or other mechanism; automatic, where the combination of the airflow and angle of attack will cause the deployment of the slat. Slats are not to be confused with slots, which generate the same effect as slats, but are fixed in an opened position.
 
The video below shows the effect of a manually deployed slat: note that this is NOT an automatic slat, and this video is just intended to demonstrate how the airflow behaves on your wing when your slat is deployed. Please observe how the stagnation point (which is the bit where the airflow splits between upper and lower airflows, and which is characterised by a zero airspeed and high pressure area), moves on the leading edge as the angle increases.
 
http://youtu.be/q_eMQvDoDWk?t=8m52s
 
So what's the difference with an automatic slat? The automatic slat deploys itself when two conditions are met: as your angle of attack increases, your stagnation point, which normally sits on the leading edge, will move slightly under the leading edge itself, causing a reduction of pressure on the leading edge and air to flow under the slat itself, deploying it. 

The angle of deployment is right before the stall angle, thus ensuring that the necessary airflow to generate lift is blown on the upper surface through the slat before reaching the stall angle itself, extending also the efficiency of the ailerons.

It is important to remember that the mechanism which allows the slat to be deployed is a deliberately loose, so that the deployment of the slats is as undisturbed as possible.
 
 What does it look like in real life?

http://youtu.be/C2fUZQMf8dw?t=54s

 

[Finkeren]

Good info, though I knew most if it already.

 

The first video was not only very illustrative but downright beautiful.

 

One thing I'd like to know: The slats that were fitted on the LaGG-3 from series 35 onwards and from very early on in the La-5 development, were they automatic or manual, or were they in fact fixed "slots" and not slats at all?

[Sternjaeger]

LaGGs were fitted with automatic slats from the Series 35, but the Finnish modified their captured ones (Series 4) with wing slots going through the wing (visible here)

 

[Finkeren]

Ah ok, thanks.

 

So the series 35 slats were in fact just as advanced as the 109s. Do you know if it did anything to alleviate the problems of the pointy Soviet wing design stalling unevenly? I think it was more of a problem on the Yak, but is supposed to be present on the Lavochkin and Mig designs as well.

[Sternjaeger]

I will have a look at what my publications say later, but if memory serves the Russians were very unimpressed with the stall behaviour of the Lagg, and the Finnish modification was aimed at addressing that instability in the best possible way.

 

It would be interesting to find some witnessing of Finnish pilots flying the modified LaGGs to see how/if things were improved with their design solution.

 

The adoption of automatic slats from the series 35 was again aimed at curing the temperamental behaviour of the aircraft, but again if I remember correctly it didn't quite work as expected.

 

My conclusion on the LaGG is that, like majority of the early Russian aircraft of the time, it was an intrinsically bad design, but also a testbed which taught the Russians a lot, yet because of the urgency of war it was produced and sent into combat, with the idea of updating it as the war progressed. 

Edited January 14, 2014 by Sternjaeger

[Finkeren]

Can't say, I agree with the 'intrinsically bad design' part. Didn't it take less redesign of the airframe to turn the LaGG-3 into the La-5FN, than it took to make a Yak-3 out of the Yak-1? The LaGG airframe might not have been the most weight efficient construction, but once it was fitted with a proper engine, it was more than just airworthy.

 

I might agree to calling many of the early 1939-41 designs 'initially' bad, but not 'intrinsically'.

Edited January 14, 2014 by Finkeren

[DD_bongodriver]

Thought I'd add another video of slats in action, this time on an actual 109, found this particularly interesting as it shows the slats extending when the 109 makes a simple break away from formation, it's a 109 E so has the earlier swing arm design I think.

 

http://www.youtube.com/watch?feature=player_detailpage&v=BzUUlO6ihwE#t=250

Edited January 14, 2014 by DD_bongodriver

[Sternjaeger]

Can't say, I agree with the 'intrinsically bad design' part. Didn't it take less redesign of the airframe to turn the LaGG-3 into the La-5FN, than it took to make a Yak-3 out of the Yak-1? The LaGG airframe might not have been the most weight efficient construction, but once it was fitted with a proper engine, it was more than just airworthy.

 

I might agree to calling many of the early 1939-41 designs 'initially' bad, but not 'intrinsically'.

The LaGG went just plagued with poor performance, it also had stability issues that werre never fully cured. In addition to that, there was the craftsmanship issue, with aircraft assembled badly and/or with poor quality materials.

Thought I'd add another video of slats in action, this time on an actual 109, found this particularly interesting as it shows the slats extending when the 109 makes a simple break away from formation, it's a 109 E so has the earlier swing arm design I think.

Thanks for the video Bongo, the E and F had swing arms, but to be honest with you I'm not 100% sure that's what they used for this restoration: warbirds receive a lot of big and small upgrades to make them safer. In any case that video also shows the slats pretty well.

[Finkeren]

The LaGG went just plagued with poor performance, it also had stability issues that werre never fully cured. In addition to that, there was the craftsmanship issue, with aircraft assembled badly and/or with poor quality materials.

Might be, but AFAIK those stability issues were common to all the "pointy wing" designs of the VVS, it was considered a tradeoff in return for increased agility IIRC. The poor worksmanship and overall quality of production really has little to do with the design itself.

[Sternjaeger]

Guess you didn't get the memo: we sold Southampton to France 

 

It's the Bf109E video, the yellow nose one that flies in the US (and is now up for sale apparently!).

[DD_bongodriver]

Blocked in my country. Damn Disney Corporation.

 

weird, I'm from the UK too.

[Sternjaeger]

Might be, but AFAIK those stability issues were common to all the "pointy wing" designs of the VVS, it was considered a tradeoff in return for increased agility IIRC. The poor worksmanship and overall quality of production really has little to do with the design itself.

 

I'll read what it says on my books later and will transcribe it, never been a huge fan of Russian design, I regard their stuff like their guns: crude, but they do the job. 

The poor quality was a combination of design choices (when I say "design" I mean the engineering of course, not just the lines of the aircraft) and bad materials/craftsmanship. The Russians were super impressed with the quality of the German aircraft they captured, and their design bureaus surely learned a great deal from them.

[Finkeren]

never been a huge fan of Russian design, I regard their stuff like their guns: crude, but they do the job.

It's funny, I'm actually a fan of Russian design for the exact same reason

[DD_bongodriver]

It's funny, I'm actually a fan of Russian design for the exact same reason

 

+1, it has a soul

[Sternjaeger]

+1, it has a soul

 

lol yeah right, until you have to fly with them: I had a ride on an An-2 some years ago, and I haven't sat in a Russian-made (or designed) aircraft ever since..

Edited January 14, 2014 by Sternjaeger

[VO101_MMaister]

lol yeah right, until you have to fly with them: I had a ride on an An-2 some years ago, and I haven't sat in a Russian-made (or designed) aircraft ever since..

 

Hehe, the good old lady. At least you could sit! I was standing in one while it was doing some low alt demo flying over our airfield:) I almost bent the grab bar while I was trying to hold myself:)

[DD_bongodriver]

lol yeah right, until you have to fly with them: I had a ride on an An-2 some years ago, and I haven't sat in a Russian-made (or designed) aircraft ever since..

 

Thoroughly enjoyed a go in a Yak-52, my respect to anybody that can bolt together some iron girders and make them fly.

 

Just like when I had a go on an AK-47 and an AR-15, the 15 broke in no time, the AK would have gone all day.

Edited January 14, 2014 by DD_bongodriver

[Finkeren]

Don't get me wrong: If my life depended on it, I would only choose Russian technology in a few specific cases. For instance I'd take a PPSh over any other period submachine gun any day.

[DB605]

Don't get me wrong: If my life depended on it, I would only choose Russian technology in a few specific cases. For instance I'd take a PPSh over any other period submachine gun any day.

 

I would rather take proper Suomi-smg than any cheap copy of it

[Sternjaeger]

Thoroughly enjoyed a go in a Yak-52, my respect to anybody that can bolt together some iron girders and make them fly.

 

Just like when I had a go on an AK-47 and an AR-15, the 15 broke in no time, the AK would have gone all day.

 

I was offered a ride on a Yak*, but politely refused.. there's a whole long story about Yak drivers, one day maybe... 

As for the guns, the AK-47 is legendarily sturdy, but beyond 100 yards you wouldn't hit a house even if you aimed at it. The AR-15 is surely more delicat, but breaking?! What did you do to it?!?!

 

Don't get me wrong: If my life depended on it, I would only choose Russian technology in a few specific cases. For instance I'd take a PPSh over any other period submachine gun any day.

 

PPSh were used by the Germans mainly because they had a larger magazine and were ideal for house to house fighting in cities. Never shot with one unfortunately, but I handled both the PPSh and the MP-40, and I remember being surprised about how the former is considerably heavier: you could probably still use the buttstock as an offensive weapon if you ran out of rounds!

 

 

*it would really sound awkward in any other context, wouldn't it? LOL

Edited January 14, 2014 by Sternjaeger

[DD_bongodriver]

I was offered a ride on a Yak*, but politely refused.. there's a whole long story about Yak drivers, one day maybe... 

As for the guns, the AK-47 is legendarily sturdy, but beyond 100 yards you wouldn't hit a house even if you aimed at it. The AR-15 is surely more delicat, but breaking?! What did you do to it?!?!

 

Don't get me wrong, loved the AR-15, felt good, but the extractor broke, the AK is not an innacurate firearm, it's just not as accurate but if you want range then I'd take 7.62 over 5.56.

[Finkeren]

I would rather take proper Suomi-smg than any cheap copy of it

The Suomi is a great gun, but it is not as simple and a little less tough than the PPSh. The PPSh is quite a bit lighter, has an even higher rate of fire and fires the 7,62mm Tokarev, which may have slightly worse stopping power than the 9mm Parabellum, but has much higher muzzle velocity, awesome penetration for a pistol round and can be effective out to 200m when fired from a longer barrel like on the PPSh.

 

I'd take the Soviet weapon over the Finish that inspired it.