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General Forums => Aircraft and Vehicles => Topic started by: Tilt on December 23, 2003, 03:24:18 AM

Title: Dumb questions re slats (slots)
Post by: Tilt on December 23, 2003, 03:24:18 AM
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?
Title: Re: Dumb questions re slats (slots)
Post by: Badboy on December 24, 2003, 05:29:44 PM
Quote
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.  

Quote
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.

Quote
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.


Quote
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
Title: Re: Re: Dumb questions re slats (slots)
Post by: HoHun on December 24, 2003, 06:09:35 PM
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)
Title: Dumb questions re slats (slots)
Post by: Glasses on December 24, 2003, 07:25:49 PM
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.
Title: Dumb questions re slats (slots)
Post by: GScholz on December 24, 2003, 08:06:54 PM
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! (http://www.lordpanzer.com/downloads/aerialsymphony.wmv)   (9 mb windows media)
Title: Dumb questions re slats (slots)
Post by: Flyboy on December 25, 2003, 05:26:30 AM
Quote
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! (http://www.lordpanzer.com/downloads/aerialsymphony.wmv)   (9 mb windows media)


thats a buetifull film!

what the story behind it? is it a part of a movie?
Title: Dumb questions re slats (slots)
Post by: Urchin on December 25, 2003, 08:29:46 AM
Looks like its a clip out of "Deep Blue World" to me.  Good movie.
Title: Dumb questions re slats (slots)
Post by: Tilt on December 25, 2003, 03:13:29 PM
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)
Title: Dumb questions re slats (slots)
Post by: GScholz on December 26, 2003, 12:52:39 AM
Quote
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/
Title: Dumb questions re slats (slots)
Post by: Delirium on December 26, 2003, 07:06:24 AM
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.
Title: Dumb questions re slats (slots)
Post by: Shiva on December 27, 2003, 01:40:41 AM
Quote
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).
Title: Dumb questions re slats (slots)
Post by: Badboy on December 29, 2003, 07:22:44 AM
Quote
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."
Title: Dumb questions re slats (slots)
Post by: Tilt on December 29, 2003, 12:19:01 PM
Quote
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.

(http://www.tilt.clara.net/White77/prtslatx.jpg)
Title: Dumb questions re slats (slots)
Post by: Badboy on December 29, 2003, 01:55:42 PM
Quote
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
Title: Dumb questions re slats (slots)
Post by: Tilt on December 29, 2003, 05:39:55 PM
The hinge swings around a vertical axis.........hence the slat swings forward and slightly to port or starboard. (port for a port slat)

(http://www.tilt.clara.net/White77/slat.jpg)

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.
Title: Re: Re: Re: Dumb questions re slats (slots)
Post by: Badboy on January 01, 2004, 06:20:57 AM
Quote
Originally posted by HoHun


>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)


Yep, I recall reading Eric Brown's comments but I was thinking of an anecdote quoted by a German pilot. Also there are these quotes from a report on the turning circles of the Me109, Spitfire and Hurricane, the Me109 was flown by W/C. Stainforth during this investigation. Some of the comments regarding the slats are seen in the image below:  

(http://www.badz.pwp.blueyonder.co.uk/Files/Images/Me109slots.jpg)

Badboy
Title: Re: Re: Re: Re: Dumb questions re slats (slots)
Post by: HoHun on January 01, 2004, 07:39:18 AM
Hi Badboy,

>Yep, I recall reading Eric Brown's comments but I was thinking of an anecdote quoted by a German pilot.

In fact, most German pilots seem to have liked the slats. I recall an anecdote by Erwin Leinkauf, who claimed he could out-turn Spitfires during the Battle of Britain with them. (I assume he referred to high altitude, as he mentioned that this wasn't possible any more against later Spitfire marks with more powerful engines.)

I've also read a comment suggesting that the slats on the RAE Messerschmitt were improperly adjusted so that they came out asymmetrically in a symmetrical turn, while they'd normally only come out asymmetrically due to asymmetrical air flow.

Regards,

Henning (HoHun)
Title: Dumb questions re slats (slots)
Post by: gripen on January 01, 2004, 04:02:17 PM
HoHun,
RAE report on Bf 109E says quite same as Leinkauf; "In surprisingly large number of cases, however, the Me. 109 succeded in keeping on the tail of the Spitfire or Hurricane during these turning tests, merely because our pilots would not tighten up the turn sufficiently from fear of stalling and spinning."  RAE test also says  clearly that slots came out well before stall (about 0,5g) and " when the slots were fully open the aircraft could be turned quite steadily until very near the stall". Leinkauf and RAE are talking about same thing; skill of the pilot. Nothing in the RAE report indicates that the plane had been in bad condition.

About slots opening it should be noted that level turning is not symmetrical flying; inner slot will come out earlier due to rolling moment and slower air speed if compared to outer slot. What changed in the later Bf 109 models was that frise aileron did not snatch as slotted ailerons.

gripen
Title: Dumb questions re slats (slots)
Post by: HoHun on January 01, 2004, 06:00:33 PM
Hi Gripen,

>About slots opening it should be noted that level turning is not symmetrical flying

Not exactly, but coordinated turning, which means energy-efficient turning, is fairly close.

>Leinkauf and RAE are talking about same thing; skill of the pilot.

Well, I admit that I'd certainly expect more familiarity with flying the Me 109 on the Luftwaffe side :-)

Regards,

Henning (HoHun)
Title: Dumb questions re slats (slots)
Post by: gripen on January 01, 2004, 11:45:51 PM
HoHun,
To keep altitude constant while  turning (ie level turning) the pilot must use ailerons to bank plane simultaneously and continously while pulling elevator, rudder is used just to keep "ball in the middle" (ie to controll direction of the plane). If ailerons are not continously  used during turn, the plane will gain or lose altitude or yaw due to rudder input. Therefore you can't call anykind of turning symmetrical flying if altitude is keeped constant.

I'm pretty certain that skills of the LW pilots varied as well as skills of the RAF pilots. Anyway, RAE test pilots appear to have been quite familiar with the Bf 109; results in the simulated combats support Leinkauf's view.

gripen
Title: Dumb questions re slats (slots)
Post by: HoHun on January 02, 2004, 12:04:34 AM
Hi Gripen,

>Therefore you can't call anykind of turning symmetrical flying if altitude is keeped constant.

Strictly speaking, correct. However, how much asymmetry do you expect from a 30 ft wingspan plane in a 900 ft radius turn? I'd say that in a coordinated turn, there should be no appreciable asymmetry in slat deployment. I freely admit that I'm speculating, though :-)

>Anyway, RAE test pilots appear to have been quite familiar with the Bf 109; results in the simulated combats support Leinkauf's view.

I'm glad to find finally anything consistent in the Me 109E discussion :-)

(Many reports on the Emil don't seem to match each other, so I'm quite serious actually.)

Regards,

Henning (HoHun)
Title: Dumb questions re slats (slots)
Post by: gripen on January 04, 2004, 04:57:43 PM
HoHun,
As noted several times above: There is two factors which cause uneven opening of the slots in the turn,  (very) small speed difference between inner and outer slot and angle of the attack difference between inner and outer slot due to rolling moment caused by aileron deflection. Later is probably more important in the case of the Bf 109 but both affect to same direction.

Leinkauf and RAE test pilots saw both same phenomena. Leinkauf draw wrong conclusion while RAE draw correct conclusion.

gripen
Title: Dumb questions re slats (slots)
Post by: HoHun on January 04, 2004, 06:35:01 PM
Hi Gripen,

>angle of the attack difference between inner and outer slot due to rolling moment caused by aileron deflection.

It may be this point where I don't understand you. Do you mean the angle-of-attack difference while rolling, or the different airflow around the wing with ailerons deflected?

Regards,

Henning (HoHun)
Title: Dumb questions re slats (slots)
Post by: gripen on January 05, 2004, 03:41:22 AM
HoHun,
I don't know how to explain this better than I have allready done? If a plane is in a continous and steady level banked turn then ailerons must be used to keep bank constant. Without this the plane will start to gain altitude while the amount of bank decrease if the g load is keeped constant with elevator. If the altitude is keeped constant then g load will decrease due to decrease of the bank. Basicly there is a small difference between angle of the attack between outer and inner wing tip due to this rolling moment needed to keep bank constant. This is excatly the same phenomena claimed by Eric Brown when he said that deployment of the slots ruined accurate sighting while maneuvering.

gripen
Title: Dumb questions re slats (slots)
Post by: HoHun on January 05, 2004, 11:10:31 AM
Hi Gripen,

>Basicly there is a small difference between angle of the attack between outer and inner wing tip due to this rolling moment needed to keep bank constant.

This small difference is only going to lead to asymmetric slat deployment when you're exactly bracketing the angle of attack for deployment with it.

There's both a large part of the envelope where both flaps do not deplay in a term, and a large part of the envelope where they both deploy in spite of the difference.

Do we agree so far?

Regards,

Henning (HoHun)
Title: Dumb questions re slats (slots)
Post by: gripen on January 05, 2004, 05:44:26 PM
HoHun,
I am just pointing out physical reasons why slots does not  work simultaneously at speeds where they come out  assuming that otherwise slots are identical (and wing is in optimal condition etc.). Even on these ideal conditions exactly simultaeous opening of the slots would be a rarity because fully symmetrical flying condition is a rarity as well. In the RAE  test "slots opened almost simultaneously" when they tested stall speeds for determination of the Clmax.

In practice there are many other things which affect (condition of the plane, manufacturing tolerances etc.).  I have seen films of the Bf 109 and the La-5 where uneven opening is clearly visible on maneuvering plane. Therefore it's quite safe to say that uneven opening of the slots was a standard "feature" on Bf 109. But it should be noted as allready said above that later models of the Bf 109 had frise type ailerons which did not snatch as badly as slotted ailerons of the Bf 109E.

gripen
Title: Dumb questions re slats (slots)
Post by: Tilt on January 05, 2004, 06:35:17 PM
Quote
Originally posted by gripen
I have seen films of the Bf 109 and the La-5 where uneven opening is clearly visible on maneuvering plane.


You have seen film of an La5?
Title: Dumb questions re slats (slots)
Post by: gripen on January 05, 2004, 11:53:57 PM
Tilt,
Yes,  there is a russian company which sells video copies of original training films. I've seen this kind of film on DB-3, Po-2, Pe-2, La-5 and several other planes including film on captured Fw 190.

gripen
Title: Re "uneven" opening
Post by: VO101_Isegrim on January 06, 2004, 09:17:32 AM
Some little addition to the uneven opening of the L.E. slats. I tend to believe that the RAE`s report is referring to the uneven opening of one slat, and not to the assymetric opening of both on the two wings depending on AoA etc., which should be nothing of news value, being quite natural. And perhaps due to my lack of understanding in  aerodynamics, I don`t see why would this lead to aileron snatching...

Thus I believe itthe phenomenon they talking about was actually the uneven opening of one slat in turn, if the pilot was not keeping the ball centered, for example the slat`s inner portition came out first in a turn, and the outer one only later, which of course meant that the lift was chaning unevenly over the wing area AND the ailerons, resulting the ailerons being twisting/snatching slightly under different pressures.

As Dave Southwood described on Bf 109G :

Quote
One interesting feature is the leading edge slats.  When these deploy at low speeds or in a turn, a 'clunk' can be heard and felt, but there is no disturbance to the aircraft about any axis.  I understand that the Bf109E rolled violently as the slats deployed, and I am curious to know the difference to the Gustav that caused this.


I don`t think the Frise ailerons on 109 G (and F, K) would be the major reason for the improvement. Then it would be an improvement, while it is clear that the phenomenon found on the 109E just disappeared. I think the reason for that lays within the fact that the slat`s mechanism was changed on late Fs and all Gs, being operated by 2 rollers/slat (late F/G/K) instead of 2 swing arms/slat as on previous models. If I got it right the latter would allow by their nature the slat open unevenly along the leading edge, while rollers would make it even all the way, as there`s no "play" between the operating of the two, they move in perfect syncron forward and aft, opening and closing the slats neatly. As a result, the slats will always make their appearance felt over the wing or the ailerons on the trailing edge right in their aerodynamic shadow at the same time, hence no disturbance in any flying axis.

BTW, what type of slat operation the Lavochkin series had ? Swingarm or rollers?

As for the British pilot`s skill with the 109s, I find that very doubtful. Perhaps a very few of them were familiar with it, and managed to push it to the edge in turning, but the overwhelming majority of them give the impression they fly a plane with leading edge slats for the first time in their life, hence the almost childish curiosity display towards the operating of the slats.  It was just all new, unfamiliar to them. Besides, how much time they did have on those rare flyable models ? Eric Brwon, probably the most skilled pilot of all of them, and certainly the most often qouted, logged in about a single hour into the Bf 109G-6/U2/R-6 he flew. That`s about 1/30 of the time a German rookie spent in the type as late as 1944...... it speaks for itself, even if we take Brown`s great general flying experience, he hardly had more than a single sightseeing run with the type instead of a proper training under the hands of a skilled instructor. Certainly such an unfamiliarity on the part of British test pilots with the plane`s major asset for horizontal manouveribilty contributed to such surrealistic result such as :

Quote
Turning Circle

The Tempest is slightly better, the Bf.109G being embarrassed by its slots opening near the stall.


Well at least they made the reason clear: the pilot`s were being embrasssed by opening of the leading edge slats, which happened a good 20-30 km/h above the stall speed itself. Of course trying to turn about 25 km/h over stall speed, with the maximum lift coefficient of the wings isn`t even realising would hardly improve the turning circle. I remember reading Tobak`s book, a 109s pilot who`s clealry remembered his instructor`s most common advice during the training with Bf 109s: Ziehen, noch ziehen!. Or pull it, pull it more. In other words, the 109 was a plane that like being pulled hardly on the stick in turns, the slats allowed for high angles of attack at which un-slatted types would stall due to loss of airflow.
Title: Dumb questions re slats (slots)
Post by: Tilt on January 06, 2004, 10:28:50 AM
Quote
Originally posted by gripen
Tilt,
Yes,  there is a russian company which sells video copies of original training films. I've seen this kind of film on DB-3, Po-2, Pe-2, La-5 and several other planes including film on captured Fw 190.

gripen


How do i contact them?
Title: Re: Re "uneven" opening
Post by: Tilt on January 06, 2004, 10:45:22 AM
Quote
Originally posted by VO101_Isegrim

BTW, what type of slat operation the Lavochkin series had ? Swingarm or rollers?

 


Swing arms however I can personally attest to the fact that the motion was rigidly parrallel to the wing...........


see picture above...............
Title: Dumb questions re slats (slots)
Post by: HoHun on January 06, 2004, 12:15:08 PM
Hi Gripen,

>I am just pointing out physical reasons why slots does not work simultaneously at speeds where they come out

I'm not suprised by the slats deploying unevenly, but that is just a transitional effect that shouldn't affect sustained turns.

The British report quoted by Badboy suggests that this makes it impossible to tighten the turn, and I don't see the physical reasons for that.

Regards,

Henning (HoHun)
Title: stuff about slots & slats
Post by: joeblogs on January 06, 2004, 03:26:05 PM
Slots were invented and patented by Handley Page in UK and almost simultaneously by a researcher in Germany, who obtained a patent in that country. A very profitable cross licencsing agreement was reached.

HP came up with the idea of the automatic leading edge slat and used them on large passenger planes in the early to mid 1920s. As has been mentioned, the slats deployed when air pressure over the front of the wing reached a certain point.

The EFFECT of the slat is to allow a plane, holding constant its air speed, to attain a higher angle of attack before a stall sets in. In a turn that would mean that more elevator can be applied...

This in contrast with certain types of flap which lower a plane's stall speed, holding constant its angle of attack. This is done by increasing the camber of the wing (imagine bending a plastic straw more and more). In principal, this would allow a plane to engage in a sustained turn at a slower speed and thus a tighter turn...

Other flaps simply increase drag, increasing the rate of descent of planes on approach.

In fighters, well designed slots are preferred to combat flaps because they significantly increase the performance envelope with less drag. But, as has been pointed out, the slots might not deploy or retract in exactly the same instance...

-Blogs
Title: Dumb questions re slats (slots)
Post by: Badboy on January 06, 2004, 06:22:40 PM
Quote
Originally posted by HoHun
Hi Gripen,

>I am just pointing out physical reasons why slots does not work simultaneously at speeds where they come out

I'm not suprised by the slats deploying unevenly, but that is just a transitional effect that shouldn't affect sustained turns.

The British report quoted by Badboy suggests that this makes it impossible to tighten the turn, and I don't see the physical reasons for that.

Regards,

Henning (HoHun)


Hi HoHun

The claim made in the report was that since the slots opened unevenly there was a "flick" and "slowing down of the rate of turn" I can only assume that the effect was severe enough to warrant those comments.

However, I must agree that it should have only been a transient effect, and once the slots were open, the aircraft should have flown normally for the changed wing configuration. A configuration that should have enhanced the turn, not degraded it.

But there is the possibility, that after the "flick" and subsequent reduced rate of turn mentioned above, an inexperienced pilot may have momentarily reduced the back pressure on the stick, reducing the angle of attack allowing the slots to close again, so that when the pilot tried to tighten the turn again, the whole process would have simply repeated, which would have destroyed the benefit of the slats, and the validity of the test.  But of course that is pure speculation on my part.

Badboy
Title: Dumb questions re slats (slots)
Post by: gripen on January 06, 2004, 07:19:01 PM
Isegrim,
The difference between the slotted and the frise type aileron is that  slotted type aileron let airflow go through the gap all the time and some airflow is actually directed to the gap, therefore any kind change in the airflow around wing will affect to it. In the frise type aileron gap is nearly closed when aileron is centered and no airflow is directed to it so changes in the airflow affect less.  Mechanical differences between slots of the Bf 109E and later models had quite little to do with uneven opening of the slots. Otherwise I don't know if you are a right person to talk about surrealism.

Tilt,
I have no idea how to contact them, my friend got those VHS tapes from a local modeling shop here in Finland. Try google. IIRC that serie contained also types like Li-2, Il-2 and Fw 189 and some more but can't remember.

HoHun,
As quoted above, the RAE report concluded that when slots were out the Bf 109E behaved well in the turns and also in stalls. Badboys's quote appears to be opinion of one pilot (possibly unexperienced on type) and RAE results do not support his view. "Even in a very tight turn the stall was quite gentle, with no tendency for the aircraft to suddenly flick over on it's back and spin".

gripen
Title: Dumb questions re slats (slots)
Post by: gripen on January 06, 2004, 07:26:40 PM
Tilt,
Look here (http://wingstv.ru/war2_eng.html)

gripen
Title: Dumb questions re slats (slots)
Post by: VO101_Isegrim on January 07, 2004, 06:47:33 AM
Gripen, I am very well aware of the difference of Frise and plain type aileron`s centre of rotation and their effect. The effect however is gradual, and should not completely cease the described phenomenon. I guess it`s just another case when you have set your mind into stone, and outright dismiss and ignore anything and everything else. Speaking of surrealism, I am a bit surprised that you actually believe the Tempest could actually outturn the Bf 109G-2/trop, whereas it could not show any real advantage in turns vs. FW 190A-4 in the same tests... I guess tunnelvision has it`s own negative effects to get the whole picture.
Title: Dumb questions re slats (slots)
Post by: gripen on January 07, 2004, 08:17:39 AM
Isegrim,
The Bf 109E had slotted type ailerons, later models had frise type. AFAIK none production Bf 109 had plain type ailerons.

And please do not  make assumptions on my opinions about  AFDU tests, so far I have not presented any comments on them. If you want to find some kind of surrealism, check your own theories on aileron snatch above.

gripen
Title: Dumb questions re slats (slots)
Post by: Tilt on January 07, 2004, 10:05:54 AM
Quote
Originally posted by gripen
Tilt,
Look here (http://wingstv.ru/war2_eng.html)

gripen



Thanks:aok
Title: Dumb questions re slats (slots)
Post by: VO101_Isegrim on January 07, 2004, 12:40:59 PM
Quote
Originally posted by gripen

And please do not  make assumptions on my opinions about  AFDU tests, so far I have not presented any comments on them. If you want to find some kind of surrealism, check your own theories on aileron snatch above.


Gripen,

Yes indeed you have commented on the AFDU tests, and critized me for calling them surreal. Just let`s see:

Isegrim :

Certainly such an unfamiliarity on the part of British test pilots with the plane`s major asset for horizontal manouveribilty contributed to such surrealistic result such as :

Quote

Turning Circle

The Tempest is slightly better, the Bf.109G being embarrassed by its slots opening near the stall.


and Gripen`s comment on that:

Otherwise I don't know if you are a right person to talk about surrealism.

And now:

If you want to find some kind of surrealism, check your own theories on aileron snatch above


OK, let`s put it straight as it is: stupid, primitive insult of destructive nature as a response to a comment. So I guess that means you on your hand don`t find the AFDU turning circle results surreal, or otherwise why the response that sounds like this comment hit a nerve ? Or is it just your usual self ? Having seen some of your replies, I tend towards the latter, it`s always the same pattern: Gripen tells the One and Only Truth, To Which There Are No Alternatives, then if any conflicting opinion is presented, the reaction is :
a, insulting the poster
b, ignoring, dismissing everything else
c, parrotting endlessly the same until everyone bored of it and leaves it alone... Which is sad IMHO, you have a lot of information at your hands, it`s only that tunnel vision and inability to discuss it in a constructive manner that prevents very interesting discussion to happen. Over and out.
Title: Dumb questions re slats (slots)
Post by: gripen on January 07, 2004, 01:11:09 PM
Isegrim,
The AFDU tests have quite little to do with the subject (slots). I'm just pointing out that only surrealistic part of this thread is your theories on aileron snatch. Stay on subject please. Your last post contained nothing on subject, it's just a personal attack.

gripen
Title: Dumb questions re slats (slots)
Post by: VO101_Isegrim on January 08, 2004, 09:26:13 AM
Gripen,

I do not wish to waste my time on such silly exchange of words. Mind you, I didnt start it...

Now, please tell why aileron snatching could not possibly a result of uneven extension of a leading edge slat that changes the airflow assymetrically over the aileron area.
Title: Dumb questions re slats (slots)
Post by: gripen on January 08, 2004, 12:29:28 PM
Isegrim,
Well, you announced a BS theory on aileron snatch so basicly you started this.

The aileron snatch means that force balance between ailerons (say left and right, other combinations are also possible) somehow suddenly changes. When combined with control input the pilot gets a feeling that ailerons "snatch" ie ailerons try to reach new balance point which might be higher or lower deflection than current input by pilot (which can be anything between full and none). In the case of Bf 109E  this is reported to happen when slots came out uneven ie airflow around other aileron suddenly changes. If a slot comes out  somehow uneven along it's span the result will be just a bit softer snatch because airflow change is not as sudden as in the case of even opening of a slot. In reality a slot came out fast so even if there is some sort of  "uneven extension" the result was hardly noticeable. Basicly your theory is total nonsense and when combined with your comments  on plain type ailerons (which had nothing to do with the Bf 109) I can only conclude that you have no idea what you are talking about. BTW differences between Bf 109 slotted and frise type ailerons are presented in one of your regular sources.

gripen
Title: Dumb questions re slats (slots)
Post by: VO101_Isegrim on January 08, 2004, 01:50:56 PM
Isegrim,
Well, you announced a BS theory on aileron snatch so basicly you started this.


So let`s see, I presented an alternate opinion, which fact alone is just soooooo damned unacceptable for you (HOW DOES HE DARE TO DISAGREE WITH [bME ?!!!!!), that you see it as valid reason to insult me being "surrealistic" (3 times), and my theory "BS", "total nonsense", yada-yada-yada. Massively ridiculus to blame it others, when the problem is with your attitude..  :rolleyes:  



The aileron snatch means that force balance between ailerons (say left and right, other combinations are also possible) somehow suddenly changes. When combined with control input the pilot gets a feeling that ailerons "snatch" ie ailerons try to reach new balance point which might be higher or lower deflection than current input by pilot (which can be anything between full and none). In the case of Bf 109E this is reported to happen when slots came out uneven ie airflow around other aileron suddenly changes. If a slot comes out somehow uneven along it's span the result will be just a bit softer snatch because airflow change is not as sudden as in the case of even opening of a slot. In reality a slot came out fast so even if there is some sort of "uneven extension" the result was hardly noticeable.

Did you just say/admit that in some truly miraculus way, there might be aileron snatching because of uneven opening of one slat along the leading edge?

You are definietely wrong in this, I have just read from someone who knows all and better then everyone that it`s a surrealistic, total nonsense, bull***** idea. Completely impossible, even in it`s smallest details... :cool:


Basicly your theory is total nonsense and when combined with your comments on plain type ailerons (which had nothing to do with the Bf 109) I can only conclude that you have no idea what you are talking about.

LOL, your typical self. :D

I would like to express that I fully agree with you. Yes, I have no idea of what I am talking about, and I would like to add, nobody else here other than You have. You are the light that leads us in our eternal darkness.
That`s what you want to hear, isn`t it ? Fine, there it is. Pleased now?

And for the note, I never said plain type ailerons had anything to do with the 109. That`s your own little surrealistic version, which you keep parrotting like mad, peppered with some derogratory comments. An attitude/behaviour I do not wish to comment on.


BTW differences between Bf 109 slotted and frise type ailerons are presented in one of your regular sources.

And the point?
Title: Dumb questions re slats (slots)
Post by: gripen on January 08, 2004, 03:03:24 PM
Isegrim,
Well, if your theory is nonsense should I not tell it to you?

The form of opening of a slot (even or what ever) did not  cause snatching phenomena.

Why did you start to talk about plain type ailerons?

The point in the source for data on frise/slotted type ailerons is that it's available. There is no need for theories like you presented above.

gripen
Title: Dumb questions re slats (slots)
Post by: Badboy on January 10, 2004, 01:42:46 PM
Quote
Originally posted by Badboy


But there is the possibility, that after the "flick" and subsequent reduced rate of turn mentioned above, an inexperienced pilot may have momentarily reduced the back pressure on the stick, reducing the angle of attack allowing the slots to close again, so that when the pilot tried to tighten the turn again, the whole process would have simply repeated, which would have destroyed the benefit of the slats, and the validity of the test.  But of course that is pure speculation on my part.

Badboy


I need to correct myself. I was never comfortable with the explanation I proposed above, because it paints a picture bordering on incompetence, on the part of the pilot flying the tests. However, despite lack of experience in the type, the tests were flown by highly skilled test pilots and the following quote indicates that I was almost certainly wrong.

This quote on the fighting qualities of the Me.109 in dog-fights with Spitfire and Hurricane:

Quote
Mock fights were staged between the Me.109 and a Spitfire, both flown by pilots of the R.A.E. In addition a number of fighter pilots, all of whom had recent experience of operational flying, visited the R.A.E. with their Spitfires and Hurricanes in order to practice combat with the Me.109; during these fights the Me.109 was flown by an R.A.E. pilot who had completed the handling tests described earlier in this report, and was thus thoroughly familiar with the aircraft and could be expected to get the best out of it.


I don’t believe such a statement would have been made without a very high degree of confidence in its veracity. I stand corrected.

Badboy