Flap Type and Efficiency

[Charge]

"It would be interesting to see what a fowler design would have on say a spitfire. I still feel as if it would be an enhancement over a split design or a plain flap.."

While I do not agree fully with Stoney this quote seems to verify his assumption.

having a Fowler flap in a Spit could be problematic since if you consider the drag that big wing causes, say, at 13 deg AoA if you add the drag effect of Fowler to that the plane could run out of engine power to benefit from increased wing area in anything but landing situation. And even without Fowler the Spit has a tendency the flare quite long so a Fowler would probably not add anything but weight to the design.

Why it works in Ki84 then? Smaller wing area and less weight from wing structure and less drag with AoA so that with Fowler depolyed the drag does not become overwhelming while the lift is increased.

Maybe it would be more interesting what a Fowler flap design could give to a high wing loaded designs, e.g. to FW190s.

-C+

[Waffle]

Might be moot, but here's some food for discussion on fowler flaps....from the summary:

"Of the three flaps tested, the Fowler flap had the lowest drag coefficient at high lift coefficients."

I'm not aeronautics geek, but low drag with high lift sounds good to me.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930085051_1993085051.pdf

[Captain Virgil Hilts]

See Rule #4

[thorsim]

i think it would depends on what you want from your flaps.  the spitfire for example always was a good turning aircraft so why add the weight and the drag (assuming the wing would need to be thicker to allow for the mechanism) of adding  a fowler flap system to improve the turn rate of a plane that already turned as well or better than all it's primary adversaries. 

also the part of the turning process where it may have suffered vs. it's opponents was in its roll rate which is why the wings were clipped in some models. 

in the case of the bigger or higher wing loaded planes, i suspect the designers foresaw the need to possibly close up a turn a bit vs. a projected opponent and since the weight battle was already lost they may have figured the cost/benefit was in favor of having a device to improve the turn.

i.e. sitting over the design table looking at the spit you would be thinking "iffin it ain't broke ... don't break it"

sitting over the design table looking at the 38 you might be thinking "wow this thing is gonna need a little turn assistance" because you had a good idea it's adversaries would be able to turn better. 

i know that is all projection but it's fun to think about. 

+S+

t



 

[Stoney]

Might be moot, but here's some food for discussion on fowler flaps....from the summary:

"Of the three flaps tested, the Fowler flap had the lowest drag coefficient at high lift coefficients."

I'm not aeronautics geek, but low drag with high lift sounds good to me.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930085051_1993085051.pdf

There is no doubt in my mind that a Fowler system is the most beneficial design of the different flap families, taken by itself.  However, it is not helpful for anything aerodynamic to be considered a panacea.  Saying that the flaps on an aircraft are "the most efficient" is like saying that elliptical wings are the most efficient, or that laminar flow airfoils are the most efficient, or that water cooled engines are the most efficient, or that high aspect ratio wings are most efficient.  When you isolate any one component of the aircraft, and compare it out of context to another component on another aircraft, you run the risk of making some false comparisons.  For aircraft, the flap system is a means to reduce landing speed--one of the reasons the Corsair has such a monstrously efficient flap system--big heavy plane that needs to fly extremely slow to land on a carrier.  Why didn't it use Fowler flaps?  Surely it had more need than a USAAF P-38?  Perhaps the designer decided the tradeoff wasn't worth it, or that he had enough flapped area that a slotted flap was going to be sufficient for him to hit his design criteria.  Perhaps the P-38 has the most efficient flaps in the game, but its because the flap system is most efficient, and not simply because the flap design uses a Fowler system.  

[thorsim]

There is no doubt in my mind that a Fowler system is the most beneficial design of the different flap families, taken by itself.  However, it is not helpful for anything aerodynamic to be considered a panacea.  Saying that the flaps on an aircraft are "the most efficient" is like saying that elliptical wings are the most efficient, or that laminar flow airfoils are the most efficient, or that water cooled engines are the most efficient, or that high aspect ratio wings are most efficient.  When you isolate any one component of the aircraft, and compare it out of context to another component on another aircraft, you run the risk of making some false comparisons.  For aircraft, the flap system is a means to reduce landing speed--one of the reasons the Corsair has such a monstrously efficient flap system--big heavy plane that needs to fly extremely slow to land on a carrier.  Why didn't it use Fowler flaps?  Surely it had more need than a USAAF P-38?  Perhaps the designer decided the tradeoff wasn't worth it, or that he had enough flapped area that a slotted flap was going to be sufficient for him to hit his design criteria.  Perhaps the P-38 has the most efficient flaps in the game, but its because the flap system is most efficient, and not simply because the flap design uses a Fowler system. 

i think you touched on it in the purposes stoney, as you pointed out the hog being an aircraft carrier intended plane a lot of drag in the flap system was i am pretty sure seen as a desired effect.

the 38s needs were different obviously, so increasing lift without reducing speed was the priority.  

i wonder if in a lot of the planes the flaps were explored for turn improvement as sort of a "byproduct" of the ability to adjust the wing for better landing speeds.  

as in that report i posted it sort of seemed like they were really looking for the reasoning for dropping flaps to improve turn performance, almost like that was not the design intent of the flaps at all.

[Stoney]

i think you touched on it in the purposes stoney, as you pointed out the hog being an aircraft carrier intended plane a lot of drag in the flap system was i am pretty sure seen as a desired effect.

the 38s needs were different obviously, so increasing lift without reducing speed was the priority.  

i wonder if in a lot of the planes the flaps were explored for turn improvement as sort of a "byproduct" of the ability to adjust the wing for better landing speeds.  

as in that report i posted it sort of seemed like they were really looking for the reasoning for dropping flaps to improve turn performance, almost like that was not the design intent of the flaps at all.

Well, like you said in another post, the P-38 was a very heavy aircraft as well.  I don't know what the design requirement for landing distance and landing speed issued by the USAAC was, but given the engine/boom positions, the amount of flapped area was going to be small, relative to the entire wingspan.  Perhaps the Fowler design was chosen purely to maximize that limited area.  Whereas the Corsair had the benefit of the bent wings providing more flapped area, and the ability to use more of the overall wingspan for flaps.  I don't know, just spit-balling...  One thing to remember though is that flaps are used to increase the camber of the wing, and therefore increase lift.  A higher Cl created by the flap extension is what lowers the landing speed, not the drag.  The heavier the airplane, the higher the required Cl to hit a target landing speed.  Lower landing speeds mean shorter runways and less need for extremely rugged and heavier landing gear.  The drag that results from flap extension is a by-product of flap use, not a primary purpose.  Spoilers are used to purposefully create drag, for example.

[Karnak]

Nakajima seems to have chosen Fowler flaps for its fighter products so as to enable an effective combat flap.  Mitsubishi did not, though its fighters were, like the F4U, the carrier based fighters, excepting the J2M series.

[bozon]

It really depends on what you want to gain from the flaps and you overall plane design.

Flaps first function is landing. This has two faces: drag and lift. Drag is GOOD for landing in most planes. If you plane has low drag for its mass you need an air brake or you will run out of runway. For this purpose, there is no reason to use a complicated flap. Lift is important if your plane is very high wingloaded - it helps to reduce the stall speed, hence the landing speed. Lower landing speed need less added drag to stop you in time. P-38 which is fairly heavy and has no torque, hence can safely fly with high power near stall speed, is a prime candidate to have one.

Then there is the overall plane design. Surprisingly, planes are not built to have the "best" possible performance. There are many other considerations that have nothing to do with how the plane flies that end up having greater effect on the air-war. Making the plane cheaper, easier & quicker to manufacture, easier to maintain, more reliable and safer, can have far reaching consequences - much more than improving an insignificant corner of the flight envelope. Could the mosquito be "better" had it had more metal and less wood? Perhaps yes, but it would be much more expensive and could not be built by the piano makers when no one was buying pianos. Likely it would not have been built at all. The P-38 was a great fighter, but it was very expensive and required almost twice the maintenance that a single engine plane needed. You could use these engines to get two mustangs instead. The F4U had a more advanced design and many performance tweaks over the F6F. However, the F6F was more reliable, faster to manufacture, cheaper and safer on the flight deck. The F6F was fighting all the decisive battles when the F4U was fighting technical problems and deck qualifications.

[Stoney]

Nakajima seems to have chosen Fowler flaps for its fighter products so as to enable an effective combat flap.  Mitsubishi did not, though its fighters were, like the F4U, the carrier based fighters, excepting the J2M series.

Zeros didn't weight 12,000 lbs when they landed either.  I don't know this, merely guessing, but I'd bet that Nakajima didn't choose the Fowler design for combat--they chose it for landing, or, perhaps to acheive a certain landing speed.  If you need the plane to "turn" better in combat, you'd design the wing differently in the first place.  By that, I mean to say that if I'm the designer and the requirement is for the plane to have a turn radius of X, I'm not going to design the plane to give me a radius of Y and then let the flaps get me the rest of the way to X.  I'm going to build the plane to hit X without flaps from the start.  I don't think period aircraft had those types of design requirements--wingloading perhaps, but not radius--but hopefully you understand what I'm getting at.

[Stoney]

Dbl post

[Karnak]

Maybe, but as I understand it all the Nakajima fighters have a "combat" setting for their flaps.

Personally I think the deployment speed for the combat setting has simply been lost to time and what we have in AH are the landing speeds for the combat setting and the landing setting.

[Ack-Ack]

I'm familiar with this.  All things being equal the same flapped area, using a Fowler design can be more efficient.  But, there are considerations beyond simply the aerodynamic function of the things.  The mechanism is a lot more complicated and usually, much heavier.  It is conceivable that there could be Fowler designs that, while aerodynamic marvels, create such a weight penalty that they lose their efficiency to simpler designs.  There are other situations where the designer has a limited flapped area to use for the system, and chooses a fowler design to maximize the limited space.  The disclaimer at the bottom of that chart states as much.

My point in beginning this thread was to express my dismay when I hear people say "its flaps are more efficient because they're fowlers".  For the P-38, the most oft used example, the flaps may be more efficient, but its because its a more efficient design overall, not merely because its a fowler design. 

The P-38 actually uses a hybrid flap system, Fowler Flaps and the conventional hinged flap system.


ack-ack

[Krusty]

The bold print above is just typical Krusty BS. Another bogus assumption with little basis in fact. Another attempt by Krusty to justify a Krusty whine.

People who have never played this game, but are well versed in aircraft design know Fowler flaps are efficient, possibly even the most efficient flap design.

Nice attempt at flamebaiting, Hilts, but you fail.

Posted on an AH forum, where a lot of folks seem to chime in with "Oh, the plane is such a great performer because of the fowler flaps!" comments, my post was a commentary on the AH populace.

It's directly applicable to the original post:

Why is it everyone thinks Fowler flaps, as a flap design type, are more efficient than all other flaps?  For what its worth, you could design a Fowler Flap that was less efficient than a Split Flap, depending on how its designed.  The type of flap, taken by itself, has no bearing on how efficient a flap system is on a particular airplane.

90% of the so-called elite will go on giving tips and hints on how to out-turn anything with flaps in this game, including on this sub-forum. Most of the discussions helping new pilots involve "Use this plane's flaps, they're fowlers, and will make you turn super tight!"

Quite relevant, and on-topic.

[Saxman]

90% of the so-called elite will go on giving tips and hints on how to out-turn anything with flaps in this game, including on this sub-forum. Most of the discussions helping new pilots involve "Use this plane's flaps, they're fowlers, and will make you turn super tight!"

Quite relevant, and on-topic.

Same thing comes up with the Corsairs. "Dump speed and get the flaps out immediately!" (personally, I think the rudder is just as if not MORE important).