Flaps

[Cthulhu]

Fowler flaps have been around since the early-mid 30's I think. Lockheed's designs like the Super Electra had them.

The British planes usually will have split flaps.. panels extending from the bottom of the wing... 'splitting' the airfoil. Spitfires, Hurricanes, Tempests even Lancasters have these flaps. Some other US planes have them like P-40's and P-39's.

But not all of the flaps will be identified visually. The F4U Corsair has slotted flaps (flaps with a space between the leading edge of the flaps and trailing edge of the wing) and the P-51 has plain flaps but you won't notice the space in between the Corsair's flaps and wings visually. This special slotted flaps is also used by the P-47 line. The narrow space between the flap and the wing allows air to move from the bottom of the wing through the space, pressurized via Venturi principle and shot out over the top of the flap. Remember, the faster the air moves at the top of an airfoil compared to the air at the bottom usually will mean extra lift is afforded. This is probably the most logical reason as to why a P-47 will gain a 40% turn radius decrease (just an estimate) while the P-51 with plain flaps, will gain about a 30% decrease in turn radius.

Pappy, you're correct about the higher velocity (and hence lower pressure) airflow the slot produces over the top of the flap. It does increase lift. But I think we also need to mention that one big advantage of slotted flaps is that the introduction of high velocity (read that: high energy) air over the top of the flap delays flow separation at the trailing edge and precludes stall, effectively lowering the stall speed. If I recall, it does this by maintaining laminar flow, delaying the onset of turbulent flow in the boundary layer.

If this is what you meant to say, I apologize. It's boring here at work.

[Kuhn]

To expand on what Gian said:
Leading edge flaps and slats are two different things. As an example, the F-16 has leading edge flaps, whereas Messerschmitt's fighters had slats. Flaps serve to shift the entire CL/Alpha curve upward (with a corresponding increase in drag), whereas slats extend the curve, allowing the wing to pull a few more degrees alpha before stalling.

Oh, and 190's have split flaps too. Another reason to never get slow and turn-fight in a 190.

(EDIT)
And since we're on the subject:

B-17: split flaps (Ho-hum)
B-24: fowler flaps (Impressive  )

The La5 has split flaps and they do help some in the slow turn, but it seems they induce a stall much quicker than say a P51s flaps. So it seems that split flaps offer the least advantage in a slow turn fight.

[Cthulhu]

The La5 has split flaps and they do help some in the slow turn, but it seems they induce a stall much quicker than say a P51s flaps. So it seems that split flaps offer the least advantage in a slow turn fight.

Split flaps are mainly useful for landing because of less pitching moment (not as drastic an effect on trim) compared to plain flaps, but they produce significant drag at small deflections, and really aren't very impressive in the lift department. Like you say, in a turn fight they're marginally useful at best, and because of the drag they might actually do more harm than good. That's certainly how it feels sometimes in the Dora. 

[Pkun]

many japanese fighters in WW II have fowler flap.
KI-43, Ki-44(with manual flap for dogfight)
Ki-83
ki-84 series(Ki-106, Ki-113 ki-116, may be Ki-117)
J2M
N1K series(include Rex) and A7M(with automatic flap for dogfight)
J7W
may be Ki87, ki94, J4M.

Japanese fighters having split flap in WWII are few(ex A6M Ki-45, Ki-61, Ki-100, J8M).

but I don't know some prototype planes (ex J5N, J6K).

[AirFlyer]

Split flaps are mainly useful for landing because of less pitching moment (not as drastic an effect on trim) compared to plain flaps, but they produce significant drag at small deflections, and really aren't very impressive in the lift department. Like you say, in a turn fight they're marginally useful at best, and because of the drag they might actually do more harm than good. That's certainly how it feels sometimes in the Dora. 

How I feel in my A6M5b, I reserve them for landing purposes and slowing quickly only.

[Stoney]

The F4U Corsair has slotted flaps (flaps with a space between the leading edge of the flaps and trailing edge of the wing) and the P-51 has plain flaps but you won't notice the space in between the Corsair's flaps and wings visually. This special slotted flaps is also used by the P-47 line. The narrow space between the flap and the wing allows air to move from the bottom of the wing through the space, pressurized via Venturi principle and shot out over the top of the flap. Remember, the faster the air moves at the top of an airfoil compared to the air at the bottom usually will mean extra lift is afforded. This is probably the most logical reason as to why a P-47 will gain a 40% turn radius decrease (just an estimate) while the P-51 with plain flaps, will gain about a 30% decrease in turn radius.

Don't forget the broader chords of both the Jug and Hog flaps.  At the low speeds at which flaps are capable of being deployed, the Reynolds number falls off, and gets lower.  Broader chord flaps will maintain a higher overall Reynolds number relative to the narrower chords of the P-51, for example.  The Cl at the same AoA is relative to the Reynolds number, so that a higher Reynolds number has a higher Cl at the same AoA.  Both of those aircraft had high percentages of flapped area compared to the P-51 as well.  Slotted or Fowler flaps aren't necessarily more efficient than Split or Plain flaps, it depends on many other factors than simply the flap configuration.

[bozon]

The point in slotting the flaps is not to add lift directly. I think it actually lowers the lift compared with the non-slotted flap given same conditions. What it does is to allow reaching higher angle of attacks before stalling the wing. Thus, the maximum lift coefficient is increased. The added drag associated with ALL flaps is usually a welcomed feature to facilitate its main function - to assist with landings.

In order to benefit from the potential extra lift to maneuver, the plane has to be able to handle the extra drag - either by making the flap more efficient (adding less drag, but still adding) or by exploiting the extra power of the engine to offset the drag penalty (basically converting thrust to lift). Thus the potential gain from flaps in slow maneuvering is largest for high wing-loaded planes with good power/weight ratio, almost regardless of the type of flaps. Larger area flaps will gain you nothing in terms of maneuvering if you don't have the power to spare, or that you can't control the torque at that speed (hence, can't use the available power). This is why comparing kinds of flaps on different planes is not very accurate to say the least.

The physical speed limitation on the use of flaps comes from the concern of bending the flap mechanism. The more lift generated, the greater the stress on the flap. Lift is proportional to G (for a given weight). However, even at 0G, there is still some stress on the flap due to the drag it adds. Numbers you see in pilot manuals (max velocity in this or that settings) refers to level flight - 1G, NOT FOR MANEUVERING. Since lift is also proportional to the velocity squared, I'd estimate that the safe-use speed for higher G load is lower by a factor ~sqrt(G). That is, if the stated safe speed to use certain flap setting is 200 mph, it will be only about 140 mph when making 2G maneuver and 115 for 3G. Thus, flaps are safe to use only in really slow maneuvering where you can't pull much higher G anyway. Definitely not extending at 400mph and pulling 6G like some planes can do in AH. This is a very rough estimate, but I think it explains why maneuver flaps were not "must have". Simply, in order to extend the envelope of save usage, the flaps had to be so sturdy and heavier that it was not worth the effort. They were useful in a very limited way. That is my opinion anyway.

[Cthulhu]

The point in slotting the flaps is not to add lift directly. I think it actually lowers the lift compared with the non-slotted flap given same conditions. What it does is to allow reaching higher angle of attacks before stalling the wing.

Exactly. This was my point earlier.

... big advantage of slotted flaps is that the introduction of high velocity (read that: high energy) air over the top of the flap delays flow separation at the trailing edge and precludes stall, effectively lowering the stall speed. If I recall, it does this by maintaining laminar flow, delaying the onset of turbulent flow in the boundary layer.

Although in my haste I got laminar and turbulent flow reversed. I'm surprised Stoney didn't jump on this.

[Stoney]

Although in my haste I got laminar and turbulent flow reversed. I'm surprised Stoney didn't jump on this.

I must be getting soft...

[SgtPappy]

If this is what you meant to say, I apologize. It's boring here at work.

Ha, no prob Cthulhu. It's always good to learn something new. And speaking about slotted flaps, I have 2 NACA tests on my comp.. both test the P-51B but one states that the P-51B has slotted flaps, the other; plain.

[Stoney]

...I have 2 NACA tests on my comp.. both test the P-51B but one states that the P-51B has slotted flaps, the other; plain.

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