Max CL and its effect on performance

[Angus]

Surprized?
Naaaaa

[pasoleati]

Well, the problems caused by slats seem to be overrated. As far as the 109 goes, the  Finnish AF test report has no mention of any difficulties caused by slats. As for the La-7, Eric Brown who is one often quoted source for that slat problem in the 109 flew also an La-7, yet found no adverse effects caused by slats. And I have never read that the slats were any problem in the SB2C. And no one has ever complained about Me 262´s slats.

Though many land based a/c had bad accelerated stall, in landing condition the Corsair seems to be the worst of major American fighters. This I conclude from Dean´s book.

[bozon]

m is mass.
I was suggesting that comparing the wing load - mass over wing area (m/S) may be less meanningful than (m/(S*CL)).
The logic is that if you slap two barn doors to a plane, they are going to be less effective than two proper wings of the same area.

If you want even better, you can use effective area, instead of real area.

Bozon

[F4UDOA]

Bozon,

What is the benifit of Lift loading compared to span loading? Is  that the same thing?

pasoleati,

Most of the information I have read on the problems with slats have been accounts of 109's having them open at bad times during dogfights causing them momentarily loose control (for lack of a better term) in a dogfight. Clearly the technology existed at the time but the Germans and the Russians seemed to prefer them on their fighters where the Brits and Americans did not.

As far as the F4U stall when compared to the P-51D, F6F-5 and P-47D by a Modern group of military test pilots in 1989 the F4U stall was described as having "adaquate stall warning and docile behaivior at the stall". The worst of the bunch was the P-51D. Indeed the F4U had a bad stall by 1943 carrier standards but it also had the best performance.

AHT numbers to a large degree are based on the numbers from the Fighter conferance. Especially the stall data. Mr.Dean is the guy who was responsable for having that report published.

I wish I had the Elgin AFB reports as well. Some of the Elgin report is in Boone Guytons book.

[HoHun]

Hi F4UDOA,

>I have never been a fan of the outer wing slats such as the ones on the 109 or La-7. They seem to have caused more of a problem than anything else during combat maneuevers.

Actually, the disadvantages have been painted larger than life by a number of books.

Originally, the Me 109's slats were designed to be locked while the flaps were retracted, and to be released at about 10° flap deflection. They wouldn't have "interfered" with combat flight at all. In 1936, Messerschmitt conducted an extensive (and, at 2 million Reichsmark, epensive :-) series of test flights for evaluating the effects of free slats, and found them to be favourable through the entire flight envelope. As a result of these tests, the locking mechanism was deleted from the Messerschmitt's slats.

>It was harsh for a Navy A/C of the time but when compared to it land based contemporaries it was considered gentle in that respect.

Well, the land based aircraft didn't have to be put down on a boat, so that's double-edged praise ;-)

Regards,

Henning (HoHun)

[Crumpp]

m is mass.
I was suggesting that comparing the wing load - mass over wing area (m/S) may be less meanningful than (m/(S*CL)).
The logic is that if you slap two barn doors to a plane, they are going to be less effective than two proper wings of the same area.

If you want even better, you can use effective area, instead of real area.

Interesting.  Might do up a little excel spread sheet to compare different planes.

Crumpp

[Angus]

Many experienced 109 Pilots (Such as Rall) did not favour the Slats. Reason: They could clonk out and affect balance shortly during delicate moments, such as setting the enemy up for a shot.
British test pilots did not particularly favour them (flying captured 109's) except in the landing procedure.

I belive that some expert pilots though, such as Marseille, did learn the slats to the end, and benefit for it.
All a question of choice.

BTW, some LW pilots are told to have their slats fixed as shut.
(field mod)

[Crumpp]

Many experienced 109 Pilots (Such as Rall) did not favour the Slats.

True.

I have also heard from several 109 pilots that "The real manuvering did not begin until the slats deployed".

Crumpp

[HoHun]

Hi Angus,

>Many experienced 109 Pilots (Such as Rall) did not favour the Slats. Reason: They could clonk out and affect balance shortly during delicate moments, such as setting the enemy up for a shot.

Well, where's Rall's quote? Who are the "many"? Not that I don't believe you, but I've seen books printing generalizations where they shouldn't have, and I guess this particular Rall quote might be just one URL away :-)

I've not yet found a believable explanation why the slats should negatively "affect balance" at any time.

In a gunnery pass, they could deploy when you tighten up your turn, but that's one bang, and that was it.

Any "delicate" gunnery pass would have to take place at a fairly constant Cl, there'd be one transition at best, either slats going out or slats retracting.

Regards,

Henning (HoHun)

[Angus]

Rall's quote is actually from a TV inteview. A friend of mine has that on a VHS.
I must confess, I sometimes throw out some strings from memory only, but only when I am fairly safe it is correct.
Now, since I met Rall and spent a day with him, there may have been something he said there also. Anyway, there is something sitting in the back of my head as this:
"The slots would not always deploy equally, thus yawing the aircraft for a moment, that was quite strong enough to throw you off your gunsight"
(My wording)

Anyway, I will check out and see what I can find out more.
Might be some days though.

BTW, the basic slats on the 109 were a British design, - Handley-Page

(Again from memory)

[Crumpp]

"The slots would not always deploy equally, thus yawing the aircraft for a moment, that was quite strong enough to throw you off your gunsight"

I have heard that as well.  I understood though, it only occurred in an uncoordinated turn.  

Crumpp

[HoHun]

Hi Angus,

>I must confess, I sometimes throw out some strings from memory only, but only when I am fairly safe it is correct.

I actually think you're correct, since I seem to remember something like that as well :-) Still, it would be nice to have the actual quote.

Here are a couple of quotes regarding slats:

http://www.virtualpilots.fi/hist/109myths/#slats

>BTW, the basic slats on the 109 were a British design, - Handley-Page

>(Again from memory)

Correct again :-)

They were invented at Handley-Page by the German engineer Gustav Lachmann who held a patent for slatted wings in Germany, which had been the reason for his recruitement. Lachmann actually stayed with Handley-Page, who were closely cooperating with Messerschmitt during the test flights I mentioned. (Lachmann seems to have been an aircraft designer with Handley-Page at that time - I've seen him mentioned as creator of the Handley-Page Hampden.)

Regards,

Henning (HoHun)

[joeblogs]

The HP patent dates from WWI or just after. A German engineer came up with the same idea at about the same time and obtained a patent in Germany. The two cross licensed and these slats were quite popular on European designs in the early 1920s.

-blogs

Originally posted by HoHun
Hi Angus,


>BTW, the basic slats on the 109 were a British design, - Handley-Page



Henning (HoHun)

[Kurfürst]

Originally posted by F4UDOA

Most of the information I have read on the problems with slats have been accounts of 109's having them open at bad times during dogfights causing them momentarily loose control (for lack of a better term) in a dogfight. Clearly the technology existed at the time but the Germans and the Russians seemed to prefer them on their fighters where the Brits and Americans did not.

Most of such information is based on the single RAE report on that 109E the french had captured after it belly landed, had a bent fusalage, and then passed over to the Brits who seen the thing for the first time and didn`t like the slats they never seen before on the fighters they trained with. I don`t know if they had trouble with the particular, damaged and badly maintained aircraft, but it can`t be ruled out.

What is appearant though, that the same problems was not felt on the 109G, which would mean it`d be hardly a problem on the similiar F and K:

"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."

Besides, the slats open only if one of the wings begin to stall. On an aircraft with no slats, when this happens the wing will drop and the firing solution is gone to hell; on aircraft with slats the slats will open, restore the airflow over the wing, and instead of a violent roll, there may be some disturbance - or no disturbance at all, as the qoute shows. Another good thing about slats is that they enable the pilot to fire very high deflection shots - normal wings simply can`t support so high AoA that is required for those !

As for why the Soviet/German designs employed it, and US/UK ones not, it`s fairly simple, all the latter relied on wing mounted guns, not having an fighter engine I can think of that would enable them to mount fuselage weapons, being normal Vee ones, with rear mounted compressors.. and so the wing guns took the space away in the leading edge required for slats. And BTW, if the slats would be bad, they wouldn`t be on 95% of the modern Mach 2 jet fighters today...

[Angus]

Ooff, from memory again.
The slats sometimes had the habit of opening up when hit by rough at high speed. (On the 6 of an enemy plane it was often a tad rough)
The high deflection shots are worth looking into, - most kills were made at very low deflection.
Now, a pilot who definately benefitted from the slats to get him into a good position was Marseille, - while one of the finest deflection shooter of them all, Rall, did not prefer the slats in combat.

Todays fighter jet slats are deployed how?