P40, A well known tune

[LFL-EightyPLUS]

Hi guys,

 

I tried searching the forum but came up short..i'd suppose i missed something and i apologize in advance.

But:

 

I was wondering if the devs are even close to considering an performance update or FM update forr the P40 Warhawk.

 

As of now, i cant really find a way to use this plane, its maneuverability is not to far off from a fully loaded IL-2. I fully understand its a very heavy plane, but if this is to be considered to be a fighter, its nothing more then a joke.

Maybe im wrong but i find it hard to believe it is truly authentic as the machine performed reasonable well everywhere in WW2.

 

I know this has been discussed over and over...but i cant help but feel very curious indeed on the thought behind this plane...

Additionally, is it just me?

Are any of you guys able to score with this machine in an Air to Air battle??

 

Thanks,

 

LFL

[6./ZG26_Klaus_Mann]

Well, at a Weight of almost 4 tons and only 1150hp and the Il-2 at 5 tons and 1650hp the two are not that far apart. The Il-2 may actually even be better. We probably have the Worst P-40 if you want a true Fighter, a P-40B or C would have been better, Or a Later Model or Merlin Powered. 

But the P-40E is quite awful with the current Engine Regimes. 

 

The Yaw-Roll Fix may bring some positive Changes for the P-40 in Terms of Un-Schröderizing it a bit but as it stands the FM seems very close to the Truth in all other Respects, 

 

As of now try Putting Yaw Trim 50% to 100% full left in Dogfight Situations to keep the Ball centered and she will be Wonderfully Stable in Turns but Quick Rolls have to be well Coordinated. 

 

I hope for the Release of a Mod that would allow to run the Engine at 56" for 5 Minutes. This would make it far more competitive. 

[ShamrockOneFive]

I am holding out some small hope that an engine upgrade is an option. P-40s were used in the Kuban battle and I'd love to see it get some use there as a fighter-bomber - surely they were running more aggressive engine setups by 1943.

[Boaty-McBoatface]

P40 is a morbidly heavy 3.8 ton airframe with low 1100hp power. It was never going to put up a fight in the online arena with these other airframes. Real life anecdotes should be put aside as they are meaningless in a computer simulation in an online arena - too many factors.

 

It is the weight of a Fockewulf 190 with power of an i-16 engine. That's an atrocious combination. 

 

56" boost was forbidden by the engine manual.

 

I think it's best to enjoy the .50 cals and take the airplane for what it really is - strong airframe, powerful, but far too heavy. 

Edited May 11, 2017 by B0SS

[DD_Arthur]

  

Edited May 12, 2017 by DD_Arthur

[Danziger]

It is the worst version of P-40. I was always hoping for a P-40B or C. For Pacific I hope for a later model.

[Riderocket]

The devs said they got the info for the earlier P-40E that was used at Moscow. So maybe they could make a new engine mod like they did with La-5, but it wouldn't effect much really.

 

Don't believe everything you hear on History Channel (or pilot diaries) they're somewhat bias.

 

People also used to claim more kills then the enemy had actually lost/got shot down, in the same way they hyped about how good their aircraft were agasint the enemy. (F4F for example)

[Gambit21]

It is the worst version of P-40. I was always hoping for a P-40B or C. For Pacific I hope for a later model.

 

Me too...and some land bases to fly it from...or to take off and shoot it down from.

Depending on my mood.

[=TBAS=Sshadow14]

Why would you dogfight with it?

Its makes for a great ground pounder.
the 50 cals tear up ground targets fine.

 

[Gambit21]

Why would you dogfight with it?

 

Its makes for a great ground pounder.

the 50 cals tear up ground targets fine.

 

 

 

Well...when you're mud moving and you get jumped then the decision isn't exactly in your hands anymore.

[19//Moach]

the p40 is the single most woefully broken plane in the game, as it is right now...

 

most unfortunately indeed, for one, they took the engine's limits from the manuals as physical tolerances, whereas those limits were published at a pre-war date with the intention of reducing maintenance costs - which meant the pilots quickly found they could run it somewhat harder than they were "allowed"

 

this is impossible here, alas - since the game is built taking the rated limits quite literally, meaning the engine cannot physically handle more than the manual says one should use... this contradicts all historical claims about how it really performed in combat - and many players have raised a wealth of material to back this up

 

 

but even with these overly restricted engine limitations, the real main issue with the P40 is really how the tail "slides out" by simply nosing over to the side ever so slightly -- this will induce an uncontrollable spin, which will end any low level dogfight before the enemy even has to fire his guns, or should you have altitude to recover, you may as well bail out, as that 109 is certainly gonna be on your tail by the time you're in control again

 

the much anticipated rudder update is the lynchpin of the community's hopes for that plane - it has a lot of potential to solve this biggest of problems it has

 

 

also, I have discovered by thorough investigation and testing that the p40 has indeed a whole hidden "layer" of performance underneath the nigh unmanageable wobbliness of that tail - the workload to achieve this, however, is currently well beyond something acceptable for a combat situation (where you need your attention on the thing trying to kill you, instead of on the turn/slip indicator)

 

 

so as it stands, the veredict for the "shittyhawk" is sadly:   not usable for combat

 

 

 

 

you can still use it in a way similar to one who rides a unicycle - not because it's good, or because it's better in any way than whatever alternative - but because you look kinda cool doing something that's dangerous and impractical just because you can...

 

you can also use it for honing your use of tactics, and practicing engagements from an advantage - it is VERY educational in that sense, since you cannot outfly anything whatsoever (even a stuka is a threat for a p40 in BoS) - so you gotta use proper tactics, because it's really all it's got (and be extremely careful with the rudder while at it, or the germans may as well go home, their job well done)

 

 

if you kill anything with it, feel free to boast openly about it - for it might as well count as five, and you're an insta-ace for pulling it off

 

and if you get absolutely murdered, then there's no need to even feel bad about it - P40s in BoS are written off as casualties as soon as they throttle up for takeoff

 

 

 

we'll see what the rudder update brings for it... hope are high, because really - the way it is right now is almost a disrespect to the brave men who flew it for reals

Edited May 12, 2017 by 19//Moach

[Inkophile]

also, I have discovered by thorough investigation and testing that the p40 has indeed a whole hidden "layer" of performance underneath the nigh unmanageable wobbliness of that tail - the workload to achieve this, however, is currently well beyond something acceptable for a combat situation (where you need your attention on the thing trying to kill you, instead of on the turn/slip indicator), so as it stands the veredict for the "shittyhawk" is sadly:   not usable for combat

 

you can still use it in a way similar to one who rides a unicycle - not because it's good, or because it's better in any way than whatever alternative - but because you look kinda cool doing something that's dangerous and impractical just because you can...

 

you can also use it for honing your use of tactics, and practicing engagements from an advantage - it is VERY educational in that sense, since you cannot outfly anything whatsoever (even a stuka is a threat for a p40 in BoS) - so you gotta use proper tactics, because it's really all it's got (and be extremely careful with the rudder while at it, or the germans may as well go home, their job well done)

To put emphasis on this, let me quote the "The Pilot Training Manual for the P-40" (unfortunately no date of print or document number for the scan):

 

 

  You're a fighter pilot now. Your fingers are itching to get at the controls of a P-51 or P-47. You may be a little disappointed that you have to spend a few weeks flying a P-40.

  Well, don't be. When you learn to fly the P-40 there won't be a fighter you can't handle. The P-40 is no cinch to fly; it's fast and skittish and responds like lightnig to controls. The savvy you pick up on the P-40 is going to make you a good pilot in any fighter.

...

  True, no more P-40's are being sent to the war theaters. Instead we are sending P-47's, P-51's, P-38's and even newer aircraft. We're sending them for a good reason: they're better aircraft than the P-40. The enemy's aircraft have been improved; ours must be even better. So the P-40 has made way for the new fighters.

...

  It is worth the sweat and study. Remember - if you're a good P-40 pilot, you're a good fighter pilot.

 

The manual goes on past the introduction to basically say that even the P-40N is a mouthful to handle because of the P-40's very touchy flying properties and tendency to stall making it easy to mess up with. Since we got the E version on that we also have the very attention-demanding engine management, so the manual's introduction certainly stays true: If you can learn to do well in the P-40, you can do well in ANYTHING.

 

It's a better school-plane than warplane.

 

(Even then though the plane does seem much too sluggish in pitch and roll. Not that it has the engine power to make good use of more responsive pitch, but at least it'd allow getting off snap shots while bleeding all the speed one would bleed anyway).

Edited May 12, 2017 by Inkompetent

[19//Moach]

yes, there are a number of things that require attention on the P40 which more modern planes will take care of by themselves

 

the most important thing, is the manifold pressure regulator, and the crucial fact that there isn't one

 

 

while later planes would self-adjust to keep man. press. steady at the level set by the throttle handle, the earlier P40 relies on the pilot to continuously adjust the throttle in order to maintain a constant boost throughout varying RPMs, altitudes and speed (yes, the game does model ram air pressure on the intake)

 

 

the manuals clearly state that caution is very much needed in order to avoid overboosting, especially on takeoff and in dives - the engine does have limits, however higher they would be than those arbitrarily decreed by the game... the engine won't protect itself

 

 

nevertheless, what NONE of the manuals even hint towards, is the possibility of departure from controlled flight being initiated by a minor rudder error alone - even though it says intentional spins are prohibited, as those are reported to have been quite erratic and violent, all manuals indicate to this being so only after a wing or two has stalled

 

in BoS, the tail will stall, however, before either wing does (of course they soon follow when that happens) - and that is what makes the P40 enter what has come to be known as The Death Slide™

 

 

now, it doesn't take an aerodynamicist to figure that a tractor prop airplane with a fuselage and tail configuration such as the P40 should be very well immune to such a phenomena (it can happen to jets, and other non-p40-like aircraft in some conditions)

 

the layout of the fuselage, should normally ensure that the propeller slipstream cannot separate even in zero-airspeed situations - a P40 thus, could not possibly encounter a rudder stall, as long as the fuselage remains located between the propeller and the rudder (not ruling out that it could perhaps be rearranged, with the help of german engineering)

 

 

but - until someone comes and removes the tail from the plane, there is basically no logical reason why the vertical stabilizer would stall - let alone do it BEFORE either wing

 

many experiments have been performed with the P40 in game - including deliberately entering spins just like the manual says not to - these have revealed that a spin induced by means of a snap-roll is noticeably a much different event, which a pilot can readily counter should he react to it in time

 

the much deadlier Death Slide™ has thus been ruled out as a form or result of asymmetric stalls - it stands apart as an independent phenomenon, which of course, not actually supposed to happen

 

one would expect such a dangerous aspect of a plane's behavior to be described in the manuals, right? - well, there's not even a hint on them to suggest, let alone warn, that "slightly too much rudder causes death"

 

 

 

many far less dangerous things, such as actual spins, are prohibited by those same manuals... at the very least, if this behavior was indeed present in the real aircraft, you'd find pilots forbidden from using the rudder as well

Edited May 12, 2017 by 19//Moach

[AndyJWest]

...

in BoS, the tail will stall, however, before either wing does (of course they soon follow when that happens) - and that is what makes the P40 enter what has come to be known as The Death Slide™...

 

I'd like to see evidence for this. Verifiable evidence, not just an opinion that it is occurring....

[JtD]

Actually, the devs say that in the P-40 description: P-40 is unstable in yawing. At 12° sideslip angle it departs. In real life, if you look into NACA documents, at 12° the rudder forces go down, but the plane still reacts normally, i.e. stable, to changes in rudder angle. In game it doesn't, it matches the description given by the devs.

 

The devs have stated they are aware of some issues with the P-40, but they are lacking time to do a full review of the FM (like they for instance did with the Fw190A3 couple of months ago). Maybe we have a chance for a rudder fix when they look into the yaw-roll coupling.

 

All this has already been discussed here:

 

https://forum.il2sturmovik.com/topic/25323-p-40-turn-rateflight-model-check/page-25

 

EightyPLUS, might be the topic you want to browse through. Not much that hasn't been said there.

[Inkophile]

As for rudder causing stall; Well, what I've seen in manuals they do suggest it being an issue. Although none of the pilot manuals give any specific numbers they do mention that the plane is very sensitive to uncoordinated flight and must be flown in well-coordinated turns or the plane will stall to shit.

 

The effect is still exaggerated in the game since it is too easy to get into that state compared to IRL (where it was still easy if not paying attion, but not IL-2 levels of easy), but JtD lines that out pretty well.

Edited May 12, 2017 by Inkompetent

[19//Moach]

you'd think if it really did that IRL there'd be at least a bit of non-ambiguous documentation about it... 

 

what has been found is mostly about "instability"* but none of the sources mentions any major danger resulting from it - what we have here is a plane that's VERY dangerous, and any mistake can lead to an unstoppable spin unto doom... that's the kind of thing you'd expect to find written somewhere - but nope

 

the manuals only warn about the tail wagging side to side (no mention of spins as consequence) when flying at low speeds, and there is documentation of it requiring good coordination when performing controlled stalls to avoid them becoming spins

 

 

 

*some sources have described a problem with the tail known as "force reversal" - this is not to be read as implying that the rudder would start acting backwards (as the ingame behavior might even have one suppose) - it actually means that the force on the pedals could reverse, see...

 

that is to say: the rudder, unlike our sim-pedals, has no centering spring - on this particular case, conditions are such that the centering force provided by airflow may "reverse", such that the pedals would pull away from the center

 

so the effect of the rudder on the plane's attitude would not itself reverse - it's only the control forces that might do that - which is indeed quite dangerous by itself, especially to an inexperienced pilot - this has led to many redesigns of that tail in subsequent variants

 

yet, this is not at all the same phenomena being experienced in the sim - it's actually very difficult to simulate this without a force-feedback set of pedals (if such thing even exists) - this is actually one rare case in which there's no choice but to give out on realism for practicality

 

 

now, I've tried this multiple times in the sim, and when an asymmetric stall occurs, it is marked by a sharp wing drop, and a loud rumbling as you'd expect - it can also be prevented from developing further with a simple instinctive countering with the controls - no big deal

 

 

I then tried slipping further to the sides making sure the wings did NOT stall -- what happens then is most befuddling:  upon a critical point-of-no-return, the tail virtually ceases to exist - the behavior is very similar to that of the IL2 when the vertical fin gets blown completely off - this is most unnatural and extremely difficult to counter, often resulting in several rounds of tumbling before it can be picked up straight again (or a crater)

 

this is the infamous Death Slide™ - and it's distinctively unlike an uncoordinated stall, with no sign of buffeting, or any other form of warning before it starts turning on its own - it takes just under one second after point-of-no-return for the low wing to actually stall

 

also, unlike a normal spin, this can happen at any time, regardless of loadout, AoA , altitude, speed, etc.  whereas the manuals describe yaw instability as a concern only when the aft fuselage tank is full, and/or flying at low speeds (below 200mph)

 

 

 

 

so yes, even if there's any truth to it - it's most certainly very exaggerated indeed - but there are no sources we could find online to verify that it actually ever took place in the real aircraft (yes, variants were very thoroughly checked for this)

 

more suspiciously - no other plane in the sim (or any other sim I've flown) exhibits this kind of treacherous vice.... curiously enough, a historical account of the kittyhawk specifically describe it as "having no vices" 

 

 

it all points to "it didn't do that" - also, I really don't believe a plane which did would ever have passed certification, let alone be put into frontline service

 

 

the rudder fixes seem quite like the very kinda thing that just might do the trick and fix it - and for that, we're very eagerly waiting

Edited May 12, 2017 by 19//Moach

[6./ZG26_Klaus_Mann]

I then tried slipping further to the sides making sure the wings did NOT stall -- what happens then is most befuddling:  upon a critical point-of-no-return, the tail virtually ceases to exist - the behavior is very similar to that of the IL2 when the vertical fin gets blown completely off - this is most unnatural and extremely difficult to counter, often resulting in several rounds of tumbling before it can be picked up straight again (or a crater)

 

 

This is a Phenomenon caused by a Combination of Tail-Heaviness, Short Tail and undersized Stabilizer and to me normally only happens with a filled Rear Tank. 

 

 What I think happens is that the the High, Slab Sided Airframe basically allows for too much Airflow over the Top of the Vert. Stab. flowing over the Nose and basically Stalling it. Since the Aircraft is quite Tail heavy and has a lot of Inertia keeping/pushing it even further. The Rudder may just experience a Total Stall with only One Wing partially Stalled. The Result is the dreaded "Steilspirale" in which the Aircraft is still mostly under Control, it feels like a Spin but you are gaining Speed quickly. 

 

I know Control Reversal in the Rudder in a Slip, it's something I absolutely Love IRL in a K-13 because I'm heavy and it won't go any further. The Rudder basically sucks itself into the Limits and stays there until you apply some Force to get out of the Slip. 

Some of the Light Girls at the Flying Club have however told me Horrorstories that the Aircraft can enter a State where they aren't stalled, but uncoordinated and describe exactly that Feeling as if the Rudder wasn't there anymore until they gained some Speed. 

 

Anyways, I think the Curtiss Engineers seem to have been quite aware of this Issue which is why on the P-40K they brought this Rudder Extension in order to Lessen the Effect of Seperation over the Fuselage. 

 

What I'm trying to say is that the Changes will make things Better, but it will probably never be as "Stable" as you hope for. And this Phenomenon of the Tail "ceasing to exist" is something Real. 

 

I myself enjoy the P-40 as a faster Option to the Il-2 I love that it flies like on Rails once Cruising. It is the most Relaxing Aircraft I know. And in a Dogfight I think it's absolutely adequate in Manouvering, good Enough to Hold my own but too Outclassed in Performance. 

The "Death Slide" is only very Rarely an Issue for me as it happens only when flying really rather badly. 

 

Edited May 12, 2017 by 6./ZG26_Klaus_Mann

[6./ZG26_Klaus_Mann]

It seems to have been quite Common for American Designers to add these Tail-Fences due to Stability Issues, the P-51 and P-47 had similar Trouble:

 

 

 

[Barnacles]

I know this may have been said before but, and I caveat what I suggest by recognising it may be a gross oversimplification...

 

The quoted maximum take off weight for a 109G4 is 3303kg. (achievable with bombs and 100% fuel etc.)

The Quoted wieight for an empty P40  with 10% fuel is 3264.2kg.

 

Combat power in p40 is1150hp.

 

If you knew what throttle setting 1150hp was equivalent to in the 'G4 it'd be interesting to fly the two around each other in a mock dogfight at that the above weights and both at 1150 hp and see how they match up in game.

 

Without any aeronautical educational background, but with a fair amount in physics, I'd expect the large surface area and generally large wings to give the p40 some sort of advantage in some flight regimes over the 109 at that power and weight in real life, but being pessimistic I reckon the g4 will still fly rings around the p40 in this game.

 

Could anyone answer the following...

 

What is 1150hp on the G4?

 

Is the above experiment worth doing/considering, I know it won't prove anything outright one way or the other?

[LFL-EightyPLUS]

Thanks for the info guys, i truly appreciate it...

Still the Number one question is why the hell would the devs waste so much time on an airplane that truly doomed to fail? Its not good as a ground pounder since we are well supplied with IL-2's and it under powered as a fighter...What to do?

[6./ZG26_Klaus_Mann]

Thanks for the info guys, i truly appreciate it...

Still the Number one question is why the hell would the devs waste so much time on an airplane that truly doomed to fail? Its not good as a ground pounder since we are well supplied with IL-2's and it under powered as a fighter...What to do?

The Community had the Choice of either a P-40 or a Hurricane. I voted Hurricane. 

 

It's (the P-40's) Top Speed matches the 109E so it isn't all that Bad, and in many Ways it's more of a Competitor for the 110E rather than Single Engine Fighters. It's Bombload Matches the Il-2, it's Firepower is overwhelming as well. 

I think enabling 56" for 5 Minutes would already do a Ton to improve it. 

Edited May 12, 2017 by 6./ZG26_Klaus_Mann

[xDeadMan]

You guys are way too smart for me. Is this still a videogame?

[6./ZG26_Klaus_Mann]

You guys are way too smart for me. Is this still a videogame?

[-=PHX=-SuperEtendard]

I think enabling 56" for 5 Minutes would already do a Ton to improve it. 

 

Those nearly 1500 HP would suit it very well really. The Tomahawk was acknowledged as an agile plane, which could compete or even be a bit better than Bf 109 in horizontal turning fights, the Tomahawk is around 300/400 Kg lighter than the P-40E, but it also has a bit less powerful engine (that comparing combat settings, don't know how much it has in emergency power).

 

Between taking less guns and less fuel I guess you can make the P-40 some 300 Kg lighter? and see how it compares while having similar weight to the Tomahawk.

Edited May 13, 2017 by -=PHX=-SuperEtendard

[19//Moach]

yes, lifting the engine limitations to a higher-than-rated 5 minutes without unpredictable powerplant self-destruction (as should be per historical accounts) would go a long way in addressing the unsurmountable ineptitude of the p40 in BoX 

 

currently, the il2 is an overwhelmingly more fit alternative to ANY use a p40 might have - yes, even as a fighter it can hold its own much better, for it remains stable at low speeds where it can outturn an attacker, and has enough firepower to shred anyone daft enough to go in front of its guns

 

so if you need a capable ground-attack fighter, you take an il2 - if you wish to die (often without help from the enemy) accomplishing little to nothing, you take a p40

 

 

what we have here is a truly useless airplane, which in MP, is often jokingly said to welcome the company of an il2 or pe2, to give it fighter cover -- yet this notion has more truth than jest to it

 

having done a lot of research about this model, the vast majority of its veterans seem to agree that it was extremely underrated and ill-portrayed in history, the claims about it from those who flew it include:

 

 

 - it was the best turning of all american fighters, with a smaller turn radius than the much more acclaimed p51

 - its engine could take a surprising amount of punishment, grossly exceeding the stated limitations when the situation called for it

 - it was a stable, reliable gun platform - with excellent firepower which it could deliver very precisely

 - it could take heaps of damage and shrug it off (this is more or less true of the ingame model, except for engine damage, which usually means guaranteed death)

 - it had no tricks or vices in handling, and was very easy and a joy to fly

 

it did have the known shortcomings of a single-stage supercharger, which made it unsuitable for high-altitude roles - which made it "bad" by western front standards - it's top speed was also not very competitive against the later 109s, though it was said to be capable of out-diving them - it was supposedly capable of holding out very well against those in a turn fight, where its lower wing loading gave it an edge and allowed it to outstall the messerschmitts (this is extremely difficult ingame, due to wobble induced death slides at those speeds)

 

the russians found it somewhat better suited in their front, as most aerial combat there took place in close support of ground forces (no strategic bombing from the stratosphere) - the p40 was then hailed as "much better than the "I-16"

 

now - this sounds like a wonderful airplane, right?

 

 

 

what we have instead is the single most deadly airplane in the game - not for its enemy, but for the poor masochistic victim who dares try it

 

it can be outturned by just about everything - 110s can run circles around the "Shittyhawk" with not much sweat

 

many pilots will quickly choose the LaGG-3 or the I-16 over it in multiplayer, quote them:  "because I'd rather not die"

 

 

 

this is not historically correct in any way shape or form - the plane depicted in this game is absurdly incapable against anything else in the sky, but most commonly that isn't the way off its doom, for the enemy needs only fly a pair of circles around it, and the p40 will "slip", then crash without a shot being fired by either side

 

even engagements from a tactical advantageous position AND with numerical advantage have met the same fate - if Chennault said one p40 against one zero was outnumbered 3 to 1, then in BoX a P40 is a negative quantity, for it more readily kills its own pilot than lets the enemy do it for him

Edited May 13, 2017 by 19//Moach

[Stig]

The RAF promptly transferred the P-40 as far away from British airspace as possible.

The VVS turned their P-40's over to the PVO and wanted more P-39's instead.

The USAAF had to use what was an hand at the time, but replaced P-40's with P-47's and P-51's as they became available.

 

Curious how the major operators all seem to have missed the boat when it comes to the P-40   

Edited May 13, 2017 by Stig

[Caudron431]

It seems to have been quite Common for American Designers to add these Tail-Fences due to Stability Issues, the P-51 and P-47 had similar Trouble:

 

 

 

Most of these modifications were made after the transition to tear drop canopies, perhaps the original design had no critical stability problems as you seem to say. My guess is that these "tail fences" were less usefull in combat than in cruising tight strategical formations. Those high precision formation flights would last hours, making them easier by increasing stability and visibility (tear drop) makes sense when you have to escort heavies over Berlin and back. At the time these types entered service the Luftwaffe was already becoming a rarity in the european skies, the fight was already won by the older types which were apparently stable enough?.

Edited May 14, 2017 by Caudron431Micha

[JtD]

In case of the P-51, the tail fin was added for structural reasons, not for aerodynamic reasons.

[ZachariasX]

In case of the P-51, the tail fin was added for structural reasons, not for aerodynamic reasons.

And that is why they would bolt it on to ealirer batches as well? Even "Razorback" variants? This is the first time I hear this. Can you elaborate?

[JtD]

Re-reading the documents, I withdraw my case.

 

It was added to address structural failures caused by control issues. Rudder forces were too light and tails kept coming off in extreme manoeuvres. The fin did not make the tail stronger, it (together with other measures) increased control forces so that the load on the tail from aerodynamic forces would be reduced.

 

However, what I read sounded to me more like a control sensitivity issue than an instability.

[Holtzauge]

From an aerodynamic angle dorsal fins help both to increase the stall sideslip angle and they are also useful to combat rudder lock, i.e. that at a high sideslip angle the rudder control forces can suddenly reverse and the rudder gets "locked" at full deflection. This can happen both on larger and smaller airplanes and can be quite troublesome on larger planes where the pilot might find it difficult to overcome the forces and get the airplane back on track. Don't know if this was the reason it was added on the P-51 though because it obviously also increases the structural integrity but I do recall reading about a number of examples where it was added for aerodynamic reasons. IIRC then the excellent book by Abzug, Airplane Stability and Control had some good IRL examples of rudder lock and dorsal fins but I returned it to the library and its so damn expensive that its not been added to the bookshelf yet.