109G6 vs Spit 9, 14, Tempest 5, and P-51

[PJ_Godzilla]

What charge is talking about is the high propensity for the FW-190 to tip stall due to a combination of planform (slight) and airfoil thickness (high) taper.  Deploying flaps would exacerbate this situation as the inboard portion of the wing near the root would fly much further into a tip stall than when flaps were not deployed.  Interestingly enough, almost all WWII fighters suffered from tip-stall tendencies as a result of thickness taper, since the thinner airfoils do not perform as well at the higher AoAs, and are also exposed to lower Reynolds numbers due to the planform taper.  The 15% root/9% tip thickness profiles were very common among the FW-190's peer aircraft.  The FW-190 airfoil will still be able to achieve the same angles of attack as most other WWII fighters, but its resulting lift coefficient at the same AoA would be less, due to the much smaller wing area and resulting high wing-loading.  Therefore, it will always suffer from higher stalling speeds compared to its peers, even with the same airfoil and thickness ratios.  All of these characteristics would be exacerbated at high g-loads, or when operated at low dynamic pressure.  While the washout should help alleviate some of these tendencies, its my understanding that the FW-190 suffered from the wing tips' tendency to flex/twist, which in essence, removed the washout from the wing. That it should be very maneuverable about the roll axis and a pig in the turn is, from an aerodynamic standpoint, very easy to explain.  

As we've said many times before, defining exactly what "out-turn" means in these reports is extremely difficult, because there is never any quantitative data (such as degrees per second, etc.) in the report.  They always rely purely on the test pilots' annecdotal statements.

I buy your Reynolds number argument (lesser characteristic length  -chord here - at the tips) and your wing torsional flex argument - center of pressure on the section would tend to cause reduced geometric washout since load resolves to something like quarter chord...

But, can you answer my question about the F-dubs outboard airfoil section? Because, if it is as posited, it strikes me as a bit dumb to have a lower max alpha on the outboard section, even if re-oriented w/r freestream with geometric washout.

As for Thorsim, I think he just reiterated what I posited about data fits - but I seriously doubtr HTC used some anecdotal basis for relative fits.

[Saurdaukar]

But I'm speculating. Why can't we get HiTech to weigh in on this one? Don't be afraid to hit us with something complicated, Dale. Many of us are technical people, it seems. Remember the old joke about engineers and wrestling with pigs...

Patented or not; I don't think HTC would be well served by revealing the method by which they simulate aircraft performance on a public message board.

Just a guess.

[PJ_Godzilla]

Patented or not; I don't think HTC would be well served by revealing the method by which they simulate aircraft performance on a public message board.

Just a guess.

I'm only looking for a broad-brush treatment here. There's nothing especially secret about doing simulations. Like I said, I was doing ADAMS models (that's all Lagrangian dynamics -  a method I seriously doubt they'd use for this, unless computing power has gotten way ahead of my estimates) for about 10 years. You get valuable after 3, really useful after 5. Thus, the barrier to entry is high enough, the incentive to copy low enough, that I doubt anyone's going to take too much notice - unless they're dying to compete in a market that draws about 5000 complaining WWII air combat geeks of elevated self-regard (I can't exclude myself here)...

What, do you think if he tips his hand a little WB is going to eat his lunch? I've got a subscription over there. I never use it. Those guys suck.

But you're probably right that he considers the info highly proprietary. I'm just interested in a word or two on methodology.

[Stoney]

I buy your Reynolds number argument (lesser charactersitic length  -chord here - at the tips) and your wing torsional flex argument - center of pressure on the section would tend to cause reduced geometric washout since load resolves to something like quarter chord...

But, can you answer my question about the F-dubs outboard airfoil section? Because, if it is as posited, it strikes me as a bit dumb to have a lower max alpha on the outboard section, even if re-oriented w/r freestream with geometric washout.

As for Thorsim, I think he just reiterated what I posited about data fits - but I seriously doubtr HTC used some anecdotal basis for relative fits.

Well, remember that NACA's airfoil research, presented in NACA report 824, was pretty revolutionary.  No one, even aircraft manufacturers/designers had conducted anything like this before.  When these aircraft were being designed, we were only 35 years removed from Kitty Hawk.  Aircraft introduced 2 years later than another then represented leaps in technology that we would consider generational today.  Everything was changing all the time--powerplants, materials, design.  What NACA 824 did to the industry though, was paint it, almost in its entirety, into a corner, attempting to achieve the "mythical" elliptical lift distribution through airfoil taper and planform design.  You see it in everything designed and introduced in the 30's--those curved and rounded wing tips, horizontal and vertical stabs, etc.  Almost all of the most famous designs possessed thickness taper.  F6F, F4U (to a lesser extent), P-47, Spitfire, P-51 etc. all suffered from the same airfoil thickness taper issue.  You see a lot of bad planform designs especially, during this period.  Look at the T-6 Texan planform and consider that it was supposed to be a trainer.  It introduces wing sweep, planform taper, and thickness taper all in the same package, which truly made it more of a handful than it could have been.  Also, the 23000 series airfoils are probably one of the worst airfoil designs that have ever been produced in quantity.  That airfoil was probably used on more designs in the 30s-40s than any other, all because designers thought that a zero-pitching moment airfoil was the most important characteristic.

So, short answer is that they just didn't know any better.  The presence of washout in most of these designs shows that they were aware, but obviously, not very concerned.  Most of the washout in these designs did little more than add drag to the wing.  The German and Russian slat designs are the only evidence I've seen of designers trying to truly combat the tip stall tendencies, even if they did make them useful by designing poor planforms--especially the Russians with their extreme planform tapers.

I believe that HTCs modelling of these aircraft is probably as accurate as you can get with a vector-based approach, with the exception of what I perceive in their trim mechanic--but I understand why its modeled the way it is.

[PJ_Godzilla]

Interesting take on the matter...

Going to the Abbott and Von Doenhoff on the olde bookshelf, I note that they characterize the leading edge slat to be worth approx. 8 degrees of alpha above the alpha max w/o slats. Kudos to Herr Messerschmitt for recognizing this.

I also verify, in the section data herein, that the 23015 has a max alpha of about 18 degrees - the man didn't lie.

As for the outboard section of the 190 wing, this site seems to verify the assertion for at least the d-9: http://www.ww2aircraft.net/forum/aviation/fw-190-dora-9-vs-p-51d-mustang-3151.html

This lends credence to your theory.

The 23009 foil I cannot find in A &vonD but, based on his record, I'd say it's probably correct as posited. So, it may be as you say - KT might've done a dumm thing. How can this be? Everyone says he's a genius... 

As for the planforms...

I always postulate two schools of thought here. I think the British went for the elliptical planform as a means of getting the magic elliptical lift distribution- and the induced drag benefit of same. It looks ike the German school of thought recognized the significance of aspect ratio... Either one has a tradeoff, the former in manufacturing, the latter in efficiency.

Bottom line: your opinion appears to have a factual basis. 

[Stoney]

KT might've done a dumm thing. How can this be? Everyone says he's a genius... 

I think he was, and this single design aspect doesn't mean he wasn't.  He was doing the same thing every designer in the world was doing--using airfoil taper.

As for the planforms...

I always postulate two schools of thought here. I think the British went for the elliptical planform as a means of getting the magic elliptical lift distribution- and the induced drag benefit of same. It looks ike the German school of thought recognized the significance of aspect ratio... Either one has a tradeoff, the former in manufacturing, the latter in efficiency.

Bottom line: your opinion appears to have a factual basis. 

Well, I personally think aspect ratio is moot for fighters at the dogfight level.  The Ta-152 aspect ratio had a singular purpose, and that was high-altitude performance, where the extreme low dynamic pressure insured that a high aspect ratio wing would combat the high induced drag, and give it a performance advantage.  At low altitude, high aspect ratio only contributes to drag and lessens roll performance (generally speaking).  The Dora still had the stock FW-190 wing, so it was going to have to rely on power to give it performance at altitude versus the wing planform.  And, ultimately, I think the Spitfire wing-loading had more to do with its performance than "near elliptical" lift distribution.  The compounded its design by building in drag with washout as well.  They look really cool though, and in my book, that's almost as important...   

[PJ_Godzilla]

I think he was, and this single design aspect doesn't mean he wasn't.  He was doing the same thing every designer in the world was doing--using airfoil taper.

Well, I personally think aspect ratio is moot for fighters at the dogfight level.  The Ta-152 aspect ratio had a singular purpose, and that was high-altitude performance, where the extreme low dynamic pressure insured that a high aspect ratio wing would combat the high induced drag, and give it a performance advantage.  At low altitude, high aspect ratio only contributes to drag and lessens roll performance (generally speaking).  The Dora still had the stock FW-190 wing, so it was going to have to rely on power to give it performance at altitude versus the wing planform.  And, ultimately, I think the Spitfire wing-loading had more to do with its performance than "near elliptical" lift distribution.  The compounded its design by building in drag with washout as well.  They look really cool though, and in my book, that's almost as important...  

\\

Wingloading is another matter entirely. Here I think you deal with the obvious tradeoff between speed and handling at a given power level.
I like this description: Aircraft with low wing loadings tend to have superior sustained turn performance because they can generate more lift for a given quantity of engine thrust. The problem with low wingloading is the other component of drag - Cd0.

 The other big thing about aspect ratio is its impact on climb performance - because of the shrinking denom of the CDi ( decreasing dynamic pressure) as you noted, and the fact that climb is all about thrust in excess of drag. The guys at Supermarine got both climb and turn because they have minimized induced drag with their planform (remember the form factor K - 5-10 percent higher for non-elliptical) AND a low wingloading AND a reasonable AR in the denom. It looks like they give up a little top end in the trade, though.

I suspect the Germans optimized around their needs: quick time-to-alt (for interception purposes) a strong top end (same reason), and big firepower (snapshots and bomber kills) and gave up a little on yank and bank. By most accounts, the vast bulk of kills happened as a result of the quick swoop and boom anyway, not as a result of long 1v1 battles. The FW is wellsuited to this tactic. In AH we've got perfect knowledge, mostly, and the Icon (a red billboard, imj). That kind of buzzkills things for F-dubber - and is probably something WORTH complaining about. Even so, I saw one of my squaddies get vaporized by an A-8 the other day. I got as far as, Look out, Short, there's an A-8 <BOOM>.

As for Tank - he was, likely, some kind of genius  - I look at his mechanical systems, though, rather than his aero work. Consider this: Komandogerat. Innovative, undeniably...

[Charge]

"While the washout should help alleviate some of these tendencies, its my understanding that the FW-190 suffered from the wing tips' tendency to flex/twist, which in essence, removed the washout from the wing."

I saw this claim first time in D. Lednicer's analysis of WW2 airfoils and already then the claim looked a bit suspicious. Let me elaborate my suspicions a bit:

If we consider the structure of 190's wingspar to be very rigid and also the source of much of the design's weight I'd say that the 80% of the span was very rigid compared to other contemporary designs. After all that was also one of the factors, along with aileron design, which made it so phenomenal in roll performance. At wing redesign phase from A6 onwards the structure was changed so that it became a bit lighter, although I have no information how this was done or what kind of effects it had in handling but, AFAIK, there was none to mention. The outer 20% section was a separate part from the "box" which formed the inner wing spar but the amount of riveting does not suggest that it lacked in density compared to inner wing. Also the much less span and size of the wing, when compared to allied counterparts, does in fact make it less prone to such behavior in my mind, since the loading momentum might actually be smaller than in a large wing due to its inability to force its way through the air due to weight/wing-area distribution.

I think that the idea of excessive flexing would originate from test reports where the reasons for sudden departures were speculated, mainly because they did not know that 190 was very sensitive of its aileron adjustment which could induce an uneven stall behavior when left unadjusted. My understanding is that while different to Spitfire the approach of stall was somewhat similar, if the ailerons where adjusted correctly, with a difference that Spit could ride the stall awhile, where as in 190 the buffeting was a sign of imminent stall which would happen as a very sudden "flick" that would rotate the plane even more than 180 degrees in its roll axis if pulled a slightly more after the onset of buffeting.

Interesting theory would be that the rigidness of the wing was the factor that made 190 different in stall warning from Spitfire, since while having a larger and less rigid wing the Spitfire could ride the stall due to increasing washout because of wing flexing in hard turns. That would be because the airstream tends to bend the wing tip to less AoA due to loading momentum the airstream poses especially to wingtip in turns since the momentum of the wing possibly moves outboards in high AoA flight, especially at the onset of inboard stall of the wing.

That would mean that 190 would have needed even more wash-out to its wing tip but -2 degrees was considered a sensible limit, and rightly so, since any more would have adverse effects on load distribution and the effects of high wingloading would still have been present all the same.

Just a theory though.

-C+

[Krusty]

I've only skimmed through the thread. Seems similar to some from before. One thing pops out at me.

The 190 wing may have had greater possibility to tip-stall, but are you all taking into account that the wings were built with a twist? The wingtips didn't flex, but rather were built with the tips at a lower angle than the root, so that during stalls they (or the wing?) would stall more evenly.

Just curious if folks are forgetting that, or if they are already taking into consideration?

EDIT: -2 degrees on the wingtips, I think?

[PJ_Godzilla]

I've only skimmed through the thread. Seems similar to some from before. One thing pops out at me.

The 190 wing may have had greater possibility to tip-stall, but are you all taking into account that the wings were built with a twist? The wingtips didn't flex, but rather were built with the tips at a lower angle than the root, so that during stalls they (or the wing?) would stall more evenly.

Just curious if folks are forgetting that, or if they are already taking into consideration?

EDIT: -2 degrees on the wingtips, I think?

That's the clear diff b/w geometric washout and aerodynamic washout. I'm not sure what the geometric w/o was on the 190 - I guess I'd ask you to cite source here for the 2 degree figure.

Mr. Krusty, I'm still disappointed that you haven't responded to the story of Muto in his N1K2... Like I say, I think he's the guy on which all this latewar uberhikoki bullsh*t is based.

[Krusty]

I haven't responded because I haven't seen it. Sorry.

IMO doesn't matter where it started, it's a common occurence. Sorry to hijack this thread.

End of hijack.

As for the 2 degrees, I can't cite that just now, going from memory. Might have been more (hence the question mark), but I've read in a number of places that the 190 wing had "washout" built in. It's even been mentioned on these forums before. You can even see it in some pictures, such as the new 190A-8N (the one they built a couple years back based on original plans) in some photos like this:

[Stoney]

Just curious if folks are forgetting that, or if they are already taking into consideration?

Yes, if you read the details, we did discuss the 2 degrees of washout built into the wing.  The best description I've found of the FW-190 wing design is from David Lednicer's CFD analysis he performed.

[PJ_Godzilla]

I haven't responded because I haven't seen it. Sorry.

IMO doesn't matter where it started, it's a common occurence. Sorry to hijack this thread.

End of hijack.

As for the 2 degrees, I can't cite that just now, going from memory. Might have been more (hence the question mark), but I've read in a number of places that the 190 wing had "washout" built in. It's even been mentioned on these forums before. You can even see it in some pictures, such as the new 190A-8N (the one they built a couple years back based on original plans) in some photos like this:

(Image removed from quote.)

Well, looking back, Stoney cites 2 degrees of geometric washout but, as we noted earlier in the thread, the aerodynamic washout is negative - since they go to a section with a lower alpha max (from 18 degrees inboard to about 15-16 outboard). The net impact would be something like a wash, so to speak - and likely not mitigating the tip stall effectively.

[Stoney]

Well, looking back, Stoney cites 2 degrees of geometric washout but, as we noted earlier in the thread, the aerodynamic washout is negative - since they go to a section with a lower alpha max (from 18 degrees inboard to about 15-16 outboard). The net impact would be something like a wash, so to speak - and likely not mitigating the tip stall effectively.

Exactly, and the bottom line is that washout is a poor technique for combating tip stall.  From a manufacturing standpoint, retarding planform taper, which would create a longer tip chord is easier to manufacture than washout, which creates the need for precise jigs to set up the washout.  For the most part, at this point in aerodynamic technology, they hadn't figured out that the airfoil thickness issue was compounding the problem, nor that they were using one of the worst airfoils in existence, with respect to stall behavior.  In my opinion, washout does nothing but add drag and compensate for poor wing design.  There are many who would disagree with me.  

Ironically, if the FW-190 stays in a conventional "interceptor" envelope, washout excepted, the wing design works well.  Keeping the wing area as small as possible, relative to the desired landing speed, minimizes drag, and increases top speed.  Just don't try to pull a lot of alpha with it, especially in low dynamic pressure conditions (slow and/or at high altitude).