Dumb questions re slats (slots)

[Tilt]

At approx 210/220 km/hr IAS the wing slats on lavochkins came out. They were self actuating being "sucked out " by the air flow against some sort of counter balance.

I am aware that they extended the period of lift as the speed decreased and the AoA increased. (i think)


However..........

I assume they would also come out during other manouvers where the "in line" IAS was circa 210/220km/hr but these manouvers may not be high AoA manouvers (just slow ones)

Loops..... would they tend to pull the nose down at the top of a loop?

Wing overs.......(slow high yo yo's, particularly when "apexing" with full rudder)..........could one wing only gain lift as it slowed whilst the other (outboard) wing  still had slats closed?


I think what i am asking is given they clean the air over the wing in high AoA flight (and extend the lower speed/lift curve) do they also add "wing" and lift in slow manouvers where AoA is not a factor?

[Badboy]

Originally posted by Tilt
At approx 210/220 km/hr IAS the wing slats on lavochkins came out. They were self actuating being "sucked out " by the air flow against some sort of counter balance.

I am aware that they extended the period of lift as the speed decreased and the AoA increased. (i think)

However..........

I assume they would also come out during other manouvers where the "in line" IAS was circa 210/220km/hr but these manouvers may not be high AoA manouvers (just slow ones)

That’s not a good assumption, because the movement of automatic slats depends on the pressure distribution around the wing, and that depends on AoA not airspeed. At low AoA there is enough positive pressure on the leading edge to keep them in, while at higher AoA there is enough of an increase in negative pressure over the slat’s upper surface to cause a forward force component to pull them out. That pressure distribution depends on the AoA not on airspeed.

Having said that, if the airspeed is so low that the aerodynamic forces are too small to either pull the slats out or push them in, then the slats will go in or out only depending on the orientation of the aircraft, i.e they either fall in or fall out of their own accord due to their own weight. But if the airspeed was that low, it wouldn’t make any difference if they were in or out anyway.  

Loops..... would they tend to pull the nose down at the top of a loop?

Yes, but only if the AoA was such that they were open, and then only if you increased the AoA even farther to take advantage of the increased lift in the extended AoA range.

Wing overs.......(slow high yo yo's, particularly when "apexing" with full rudder)..........could one wing only gain lift as it slowed whilst the other (outboard) wing  still had slats closed?

That one isn’t so easy to answer because theoretically it is possible to have one wing above the AoA required for the slats to open while the other is below it, but good pilots didn’t roll the aircraft at high AoA in a way that would cause that to happen because of that and other risks. It has always been good practice to unload slightly before rolling, to avoid all such risks. However, I have heard of it happening anyway, either because the slats were iced up and one released before the other, and I’ve heard of it happening due to damage. There is also one account of it happening to an Me109 pilot who described an occasion where the slats opened differentially in a hard turn during combat, but I don’t recall the source off hand.

I think what i am asking is given they clean the air over the wing in high AoA flight (and extend the lower speed/lift curve) do they also add "wing" and lift in slow manouvers where AoA is not a factor?

Nope, the AoA has to be a factor.

Hope that helps

Badboy

[HoHun]

Hi Badboy,

>Having said that, if the airspeed is so low that the aerodynamic forces are too small to either pull the slats out or push them in, then the slats will go in or out only depending on the orientation of the aircraft, i.e they either fall in or fall out of their own accord due to their own weight.

On the other hand, slats could be spring-loaded to enforce a certain status under low-speed conditions. Slats could also be locked down to prevent their operation outside of low-speed operations. The Me 109 for example originally unlocked its slats only when the flaps were lowered.

>Yes, but only if the AoA was such that they were open, and then only if you increased the AoA even farther to take advantage of the increased lift in the extended AoA range.

Well, slat extension actually seems to increase the effective wing area according to my aerodynamics book, increasing lift at constant angle of attack. I'm not quite sure of what to think about that.

>That one isn’t so easy to answer because theoretically it is possible to have one wing above the AoA required for the slats to open while the other is below it

Unless the slats were interconnected, which seems to have been a design philosophy rivalling with individually free slats for a while at least.

Generally, I agree with all your comments on slats, but as I'm not sure that the La-5 family didn't deviate from the standard slat configuration in some point, I'll just say you're "most probably" right about the Lavochkin :-)

>There is also one account of it happening to an Me109 pilot who described an occasion where the slats opened differentially in a hard turn during combat, but I don’t recall the source off hand.

It was RAE test pilot Eric Brown :-)

Regards,

Henning (HoHun)

[Glasses]

From my understanding the  Slats on the 109 were used to increase its lateral control at lower speeds and high AoA. Increasing the wing area and the speed of which the  air passes through the wingtip area  delaying the effects of a stall or when the aircraft is about to enter it.

[GScholz]

About 1/3rd out in this movie you'll see a cockpit shot of a 109 rolling over a smoking Spit. The camera is filming the 109's wing as well and you can clearly see the slats pop out at what seems to me as a rather low G turn/AoA.

Arial Symphony!   (9 mb windows media)

[Flyboy]

Originally posted by GScholz
About 1/3rd out in this movie you'll see a cockpit shot of a 109 rolling over a smoking Spit. The camera is filming the 109's wing as well and you can clearly see the slats pop out at what seems to me as a rather low G turn/AoA.

Arial Symphony!   (9 mb windows media)

thats a buetifull film!

what the story behind it? is it a part of a movie?

[Urchin]

Looks like its a clip out of "Deep Blue World" to me.  Good movie.

[Tilt]

Thanks Badz

I think your explanation is one that helps it all make sense to me. (ie I can understand it........I think)

I have played with the slats on the La7 at Prague.

They could be pulled out easily with one finger. There seemed to be nothing other than the hinging mechanism behind them.

Any pictures of an la5 or 7 (on the ground) you see the slats closed.

The La's were built with the fuselage in the horizontal and pictures of la's under production show the slats then fully extended under their own weight.

The La7 at Prague has its tail wheel on a small plinth and the slat is slightly extended from its fully seated position.


The above would lead me to believe that the suction and pressure forces around that edge of the wing far exceed any weight or mechanical dynamic in the slat its self.

I have two texts that refer to AoA creating the inverse pressure to pull them out.

I have two texts also refering to the speed at which this should happen (210>220Km/hour). I was puzzled that the speed was so specific as i would expect it to differ with what ever AoA the AC was trimmed to.

However one of the references to the 210>220km/hr was during a climbing trial. Where for a "std test" such a figure would have been Known against the std trim  and AoA adopted for such trials.

( infact the reference was due to a slat sticking open and prejudicing that particular trial)

[GScholz]

Originally posted by Flyboy
thats a buetifull film!

what the story behind it? is it a part of a movie?

Yes, Dark Blue World it is. Beautiful film. If you haven't seen this award winning Czech gem, you're missing out on a great movie experience.


Here: http://us.imdb.com/title/tt0244479/

[Delirium]

I saw an ad for it in a magazine here in the US, but never heard a single thing since. I'm certain it never made movies, but maybe the rental video place has it.

Who says a body of water can't isolate you? I'll pick it up this weekend, until G's post I couldn't even remember the name of the movie.

[Shiva]

Originally posted by Tilt
The above would lead me to believe that the suction and pressure forces around that edge of the wing far exceed any weight or mechanical dynamic in the slat its self.

I have two texts that refer to AoA creating the inverse pressure to pull them out.

Most automatic slats were designed to have spring mechanisms pushing the slats open; at high speeds the pressure of the air against the slat would keep it pushed in, while at slow speeds or high angles of attack, the reduced air pressure would allow the springs to extend the slat.

Slats could also be operated entirely by aerodynamic forces. On an airfoil, there is a 'static point' where the airflow divides between going over the upper and lower surfaces of the airfoil. This point is, under normal flight conditions, slightly below the axis of motion of the airfoil; as the angle of attack increases, this point moves further to the underside of the airfoil. A freely-floating slat can be designed to be an airfoil in itself, such that when the static point moves below a certain point on the wing, it will have moved to a point where the lift generated by just the slat itself exceeds the force on the slat pressing it in, and the slat extends.

If the design of the airfoil is known, and the parameters of the aircraft are known, the airspeed of the aircraft at the point at which it attains that required angle of attack can be calculated. However, this is a very finicky calculation; spring-loaded automatic slats provide more consistent deployment (although are more vulnerable to asymmetric deployment).

[Badboy]

Originally posted by Shiva
Most automatic slats were designed to have spring mechanisms pushing the slats open; at high speeds the pressure of the air against the slat would keep it pushed in, while at slow speeds or high angles of attack, the reduced air pressure would allow the springs to extend the slat.

There is some helpful information on the design and construction  of the slats used on the Me109 at this location.

http://109lair.hobbyvista.com/techref/systems/control/slats/slats.htm

Badboy

Edit:

This quote from the site may be of particular interest.

"A common question asked regarding the 109 is "Should the slats be in or out when the aircraft is parked?"  The answer is "yes".   The slats are free-moving devices, and are commonly seen extended in many wartime and contemporary photos; however, if manually pushed back into the wing, the slats would remain there until the aircraft moved, at which time they would extend of their own volition.  This action was confirmed by Günther Rall when questioned by Lair visitor Erik Whipple some time back; according to Gen. Rall, it was common practice at their field to push the slats in once the aircraft were secured so that no dust or debris would accumulate in the traveling tracks.  Evidently at least one new pilot was lost due to faulty operation of the slats when taking off, which led to this practice."

[Tilt]

Originally posted by Badboy
There is some helpful information on the design and construction  of the slats used on the Me109 at this location.


Badboy

Seems identical to my reading and observation on the La7 except for what its worth the La7 slats seem to extend further.

[Badboy]

Originally posted by Tilt
Seems identical to my reading and observation on the La7 except for what its worth the La7 slats seem to extend further.

Nice photograph. That slat appears to be a simple sheet metal profile, did you notice if it had any ribbing or inner skin to strengthen it?

Also, judging by the lack of clearance between the upper wing surface and slat, gives the impression that the holes for the connecting arms are excessively large. No doubt when the slats were opened under aerodynamic pressure the slats would be held hard against the upper edge of those large holes, thus providing the correct clearance to the upper wing surface. I first thought those holes might be worn, or that they were created large due to poor workmanship, but it is hard to imagine that those slats could jam due to the large clearances involved, so maybe it was quite deliberate. After all, I’ve read several accounts of problems with the German slats, particularly on the E model, but none for the Russian slats… That photograph may well explain why.

Badboy

[Tilt]

The hinge swings around a vertical axis.........hence the slat swings forward and slightly to port or starboard. (port for a port slat)



You see that the actuating lever hits a hard stop.

I think the slat is "tuned" by adjusting its  angle to the wing by use of the clamping pivot (elbow) which forms part of the two piece actuating lever.

This same elbow seems to have an adjustable screw to set the fine adjustment against the hard stop.  You may have some hinges using a similar principal in your kitchen


The hole thru which the lever swings may have to be large to facilitate access for repair and replacement of the assembley. the wing remember is a glued wooden composite bolted to a steel spar.