Why is the Spitfire Mk IX still unstable??

[bongodriver]

Apparently the only thing difficult about flying a Spitfire is getting someone to let you do it.

 

Anyway, breathing deeply, aligning my chakras and contemplating the universe.

[Pilum]

The problem with that is, what do you call a pleasant flight? In a Chuck Yeager scale anything is a pleasant flight, while less gifted pilots would call the same experience a hell. A single sentence like that can't be any help in the module development and any of us should take those as matter of fact without further explaining what actually means a pleasant flight to the guy saying it.

 

S!

 

In addition to all the pilots accounts I'd say read the POH for the Mk9: This describes the Spitfire as "pleasant" to fly. Two points here: First, I seriously doubt the publication was written to be read by pilots of Chuck Yeager's ability and above. Second: Find me an airplane that is unstable with the pilot in direct control, i.e. without FBW, that pilots describe as "pleasant" to fly. :joystick:

 

So summing up: The only evidence suggesting Mk9 instability in this thread has been connected with fuel in the rear tank. In addition, contrary to earlier claims there seems to be no Mk9 instability report. Nor is there any other evidence suggesting that the Mk9 is unstable unless there was fuel in the rear tank. However, we do know that the designers did put ballast in the tail which reduces stability which only makes sense on an already stable plane. The result is a plane which AFAIK the overwhelming majority of all who flew it loved and if anyone can find data suggesting pilots professing love for unstable planes I'd love to see that. :)

Edited October 26, 2015 by Pilum

[Cripple]

In addition to all the pilots accounts I'd say read the POH for the Mk9: This describes the Spitfire as "pleasant" to fly. Two points here: First, I seriously doubt the publication was written to be read by pilots of Chuck Yeager's ability and above. Second: Find me an airplane that is unstable with the pilot in direct control, i.e. without FBW, that pilots describe as "pleasant" to fly. :joystick:

 

...

 

1) I'd agree with that, and take it as read that the Pilot Notes say that (haven't got them to hand). I've certainly read that in some official document recently.

2) Mrrrrrrrrrrrrrrrrrp! Nope. You have fallen in to the common fallacy (as we discussed earlier) of comparing a 2015 sensation of "pleasant" to fly with one from 1945. A plane could be unstable, but markedly less unstable (or have mitigating positive characteristics...) than the *contemporary* competition - resulting in it still being described as quoted.

 

By way of analogy, I am sure that a number of hotels described as "pleasant" in the 1940s would not be described so favourably in the early 21th century (if unchanged). I suspect the lack of Wi-Fi might be commented upon... ;)

[MiloMorai]

Had a conversation with my late uncle many years ago. Advanced flight training was done in the Harvard and then was sent to learn to fly Seafires. He said Seafires were a dream to fly compared to the Harvard.

[Ala13_ManOWar]

But that's the point, everyone who said they like the Spit say it because it's not tricky to fly, it is carefree in handling and gives plenty of warning of approaching stall.

The reason this thread exists is because the OP has a personal hatred of the Spitfire and is obsessed with trying to influence developers to make his interpretation of the FM.

 

In addition to all the pilots accounts I'd say read the POH for the Mk9: This describes the Spitfire as "pleasant" to fly. Two points here: First, I seriously doubt the publication was written to be read by pilots of Chuck Yeager's ability and above. Second: Find me an airplane that is unstable with the pilot in direct control, i.e. without FBW, that pilots describe as "pleasant" to fly. :joystick:

I don't try to influence the developers nor I think anybody around here knowing the precedents would. If somebody really thinks they can influence just posting a few "complains" he's a newbie to these forums and/or ED development process :music_whistling:.

 

That said, are the histories I've listen about the difficulties to newbie pilots in the 40's in handling the Spits false? I mean, you both are mistaking the same people did with 109, good qualities doesn't means at all you don't have to learn to fly and deeply master her first. After that of course any pilot would describe her as a pleasant flight, but firsts steps... I'm not so sure.

 

Whatever, I still think it's too soon to so much discuss about smoke yet.

 

S!

[Ala13_ManOWar]

Had a conversation with my late uncle many years ago. Advanced flight training was done in the Harvard and then was sent to learn to fly Seafires. He said Seafires were a dream to fly compared to the Harvard.

Of course they were a dream. What's better to drive, a mini cooper or a Ferrari? :lol:

 

S!

[Paradox]

Of course they were a dream. What's better to drive, a mini cooper or a Ferrari? :lol:

 

S!

 

See now this is interesting because it depends what you're doing with it.

 

A mini cooper is tremendous for small, not necessarily blisteringly fast journeys.

 

The main reason I love the Mustang in DCS so much is that it's fun to fly for long journeys, you can cruise, the visibility is great and once you're trimmed out you can think about carb heat and radiator position at your leisure.

 

My main worry about the Spitfire (in general really) is that I might not enjoy it the same way. The Spitfire was designed as a short range combat aircraft, nothing more and certainly nothing less.

 

A P-51D is like a GT car, it's powerful, fast and actually quite comfortable

 

Spitfire might be amazing for a 20 minute flight but hell if you have to go long distances?

 

Not everyone has the same standards when it comes to determining the "quality" of a given aeroplane.

[bongodriver]

I don't try to influence the developers

 

I didn't suggest you do.

 

If somebody really thinks they can influence just posting a few "complains" he's a newbie to these forums and/or ED development process :music_whistling:.

 

He joined in Dec 2014, but is a familiar character on most WWII aviation sim/discussion boards peddling the same message.

 

Whatever, I still think it's too soon to so much discuss about smoke yet.

 

S!

 

I agree completely, absolutely no need for a thread like this one to be started at all.....unless they are trying to influence someone.

Edited October 26, 2015 by bongodriver

[MiloMorai]

Of course they were a dream. What's better to drive, a mini cooper or a Ferrari? :lol:

 

S!

 

The Spit was easier to fly than the Harvard which had some quirks that killed many budding pilots.

[Cripple]

Paradox - excellent point. Someone in another thread who was claiming the F-18 was "better" than the A-10 needed reminded of that too.:music_whistling:

 

Bongodriver - ... and here was me thinking this was friendly little debate to kill time until the IX surfaces.

[Friedrich-4B]

He joined in Dec 2014, but is a familiar character on most WWII aviation sim/discussion boards peddling the same message.

As well as peddling the same theme, in one form or another, on this forum.

 

Actually, the OP would help himself were he to stop implying that other forum members, who have considerable real-world aviation experience (engineering and/or flying), are idiots who don't know what they are talking about. Unfortunately that is the OP's most prevalent MO.

[NineLine]

As well as peddling the same theme, in one form or another, on this forum.

 

Actually, the OP would help himself were he to stop implying that other forum members, who have considerable real-world aviation experience (engineering and/or flying), are idiots who don't know what they are talking about. Unfortunately that is the OP's most prevalent MO.

 

You guys are really having trouble with the concept of discussing the topic and not the people involved... knock it off.

[Ala13_ManOWar]

My main worry about the Spitfire (in general really) is that I might not enjoy it the same way. The Spitfire was designed as a short range combat aircraft, nothing more and certainly nothing less.

But that's the same trouble with 109 we already have, a short ranged fighter intended for area defence. Spitfire is a bit different of course, firstly aircraft size matters, and elliptic wing would fly quite different but still no full axis trims, so may be some troubles are slightly similar to 109. I mean, I have no fear at all to that aspects being pilot challenging further than 109 is.

 

S!

[Paradox]

But that's the same trouble with 109 we already have, a short ranged fighter intended for area defence. Spitfire is a bit different of course, firstly aircraft size matters, and elliptic wing would fly quite different but still no full axis trims, so may be some troubles are slightly similar to 109. I mean, I have no fear at all to that aspects being pilot challenging further than 109 is.

 

S!

 

Yeah definitely although the Mk IX has rudder trim I believe which will be good if we get the same trim tab settings we have for the 109

 

Could end up being quite pleasant. For me the 109 feels quite awkward to fly most of the time.

[Crumpp]

Nope, the ballast is the needle that pops your "The Spitfire Mk9 is unstable" balloon. :smilewink:

 

Your attempt to connect the ballast ONLY to the empty weight CG is the red herring. The ballast affects the CG for ALL load conditions. Since you are so fond of "maths" why don't you calculate the effects at different load conditions? You will find that in all cases the CG is moved back. Since a lot of discussion has been concerning the CG without fuel in the rear tanks I calculated that and it turns out the CG is shifted circa 0.5" back in this particular case.

 

So again, as shown in post #195, the only plausible reason they did this was to lower the stability of an already stable aircraft. However if you want to prove that the Spitfire Mk9 was unstable already without the ballast and that they added ballast in the tail to shift the CG even further back thus increasing instability even further then knock yourself out! :joystick:

 

 

Please find any Stability and Control engineering text which list's Ballasting as a method of correcting the CG limits. You cannot. Why? It does not change the limits of the CG range.

 

 

Your "ballasting theory" has nothing to do with the allowable limits of the aircraft's stability margin nor does it alter the NACA conclusions of the Spitfire series.

 

No change in the AC to rear CG limits = No change to the Stability of the aircraft.

 

Ballasting is a red herring.

 

It does not effect the CG limits and is used only to prevent adverse loading conditions from developing when the CG changes in flight for specific load conditions. Permanent ballast is used to bring the empty weight CG back to the same position it was before the equipment or configuration was changed.

 

The whole ballasting thing is just white noise that has little to do with the conversation.

 

EWCG = Empty Weight Center of Gravity

 

I told you this back on page 20, Pilum.

[Crumpp]

 

None of the stuff you just quoted appears in the AAN for the MkIX you just linked to, you are just making stuff up now.

 

Manufacturing tolerances were a concern to the RAE and Supermarine engineers in regards to the longitudinal stability of the type and were critical to the design.

 

 

http://www.spitfireperformance.com/Spitfire_IX_ML-186_Handling.pdf

[Crumpp]

I don't try to influence the developers nor I think anybody around here knowing the precedents would. If somebody really thinks they can influence just posting a few "complains" he's a newbie to these forums and/or ED development process :music_whistling:.

 

That said, are the histories I've listen about the difficulties to newbie pilots in the 40's in handling the Spits false? I mean, you both are mistaking the same people did with 109, good qualities doesn't means at all you don't have to learn to fly and deeply master her first. After that of course any pilot would describe her as a pleasant flight, but firsts steps... I'm not so sure.

 

Whatever, I still think it's too soon to so much discuss about smoke yet.

 

S!

 

Exactly. Like many Bf-109 fans, there seems to be this perception that stability is fixed and does not change in an aircraft. The lateral instability of the Bf-109 is a good example.

 

Flying qualities of an aircraft change with velocity and condition of flight. It is not a single characteristics under all conditions. It changes and is linked to loading, configuration, load factor, velocity/Coefficient of lift, drag changes, etc...

 

 

Crumpp says:

Flying qualities is Coefficient of Lift dependent. As speed increases, our coefficient of lift decreases. Lets look at the slope of the static longitudinal stability curve of the Spitfire and see what happens.

 

When the curve is moved up or down, the point it intersects the 0 line is our trim speed.

 

In this case the red line approximates the curve shifted up to represent the aircraft trimmed for a speed of 250mph IAS. Forgive my not so good line shifting....it is not meant to make specifics only to show the concepts.

 

The slope of the Spitfires stability curve gets larger the lower the coefficient of lift. Our stability increases and at 250mph IAS, the aircraft has good static longitudinal stability and with the light stick forces, I would certainly agree it is not only satisfactory at this speed but it must have been quite pleasant to fly around.

 

That does not have anything to do with the weak static longitudinal stability experienced elsewhere in the envelope or the dynamic longitudinal neutral to unstable found at normal to aft CG.

 

http://forums.eagle.ru/showpost.php?p=2528533&postcount=166

[Pilum]

Please find any Stability and Control engineering text which list's Ballasting as a method of correcting the CG limits. You cannot. Why? It does not change the limits of the CG range.

 

 

Your "ballasting theory" has nothing to do with the allowable limits of the aircraft's stability margin nor does it alter the NACA conclusions of the Spitfire series.

 

No change in the AC to rear CG limits = No change to the Stability of the aircraft.

 

 

 

EWCG = Empty Weight Center of Gravity

 

I told you this back on page 20, Pilum.

 

You miss the point Crumpp: I never said the ballast changes the CG limits or that it was added for this purpose. Ballast in the tail is added to shift the CG rearwards to DECREASE the stability of the plane.

 

I’m not at home now so I don’t have my notes but I calculated the CG of the Mk9 sans rear fuel and it’s around 6.3” from the datum without ballast. Now apparently, the boffins at Supermarine thought this was too far forward so they add 17.5 lb ballast to shift the CG back to circa 6.8” in this configuration. If memory serves me right the rear limit is at 9” so it’s still well within the allowable range.

 

So no, they did NOT add the ballast to change the CG range. They added the ballast to shift the CG of the plane which affects ALL load conditions from empty to fully loaded.

 

The concept I’m trying to explain is that the CG is still within the range and they did not have to add the ballast. However, adding ballast shifts the CG backwards for ALL load condition, making the plane more unstable in ALL load conditions. Now ask yourself, from which state does it make sense to increase instability? On a plane that is stable or on a plane which is already unstable?

 

As I have a life outside these forums, don’t expect another reply until tomorrow evening CET. Me and the missus are going to the theatre. It's a deal we have: She get's to watch some unstable actors, I get to fly some stable planes in DCS! ;)

[Crumpp]

Nope, the ballast is the needle that pops your "The Spitfire Mk9 is unstable" balloon. :smilewink:

 

Your attempt to connect the ballast ONLY to the empty weight CG is the red herring. The ballast affects the CG for ALL load conditions.

 

The entire purpose of permanent ballast is to RESTORE the Empty Weight CG when a design has been altered. End of Story.

 

Once more ballasting does not effect the CG limits nor does it effect the the fact that at any CG location the stability margin of the Mk IX equals the stability margin of the NACA Spitfire Mk V.....

 

The stability characteristics are the same given the same stability margin. End of Story.

 

25 pages to realize that fact is ridiculous.

 

That is how it works, Holtzauge.

 

At 31.4% MAC the Spitfire Mk IX will act just like the NACA Spitfire Mk IX.

 

The rear CG limit for a normal ie without rear fuselage tanks Spitfire Mk IX is ~36.3% MAC and the Take OFF WT

CG is ~33.8%MAC.

 

That is 33.8%MAC - 31.4%MAC = 2.4% AFT of the NACA Spitfire Mk V.

 

:thumbup:

 

Yo-Yo says:

The only one, short, natural and the right way to determine Mk IX stability having EXACT data for Mk V, that is, for sure, obvious for you, is:

Answer the question if 9 has the same wing (planeform and airfoil), stab area and its arm relatively to the wing MAC.

If so, the neutral point of the airframe is the same, and we are able to create the airframe model having stability charachteristics exactly as Mk V using measured data.

Changing CoG position corresponding the Mk IX docs.

Get it as is... , profit.

And i am really amazed how many letters were typed during the discussion...

 

So, i very much appreciate your battle proving the engineering way of thinking!

 

http://forums.eagle.ru/showpost.php?p=2528059&postcount=150

[JtD]

The rear CG limit for a normal ie without rear fuselage tanks Spitfire Mk IX is ~36.3% MAC and the Take OFF WT CG is ~33.8%MAC.

 

Please show or at least name the manual you got these figures from. Thanks.

[bongodriver]

Manufacturing tolerances were a concern to the RAE and Supermarine engineers in regards to the longitudinal stability of the type and were critical to the design.

 

 

http://www.spitfireperformance.com/Spitfire_IX_ML-186_Handling.pdf

 

it does not necessarily suggest that there was an issue with manufacturing tolerances, I'm sure now and again a complete lemon was made.....and shipped to the states so NACA could test it :harhar:

it really just says that accuracy in manufacture is fairly critical....well duh!, at least we know the elevator itself is not responsible for the Stability of the design but more the controllability, be realistic, if it was already known that elevators needed to be made well and Spitfires were suffering for it then something would have been done to ensure quality.

Ultimately even your linked report suggests the worst case is simply a limitation to the aftmost CG limits on production aircraft, limits that Spitfires were very unlikely to reach in combat, they only needed to burn half a rear tank worth of fuel and they were just fine for combat and well within the CG limits.

 

The entire purpose of permanent ballast is to RESTORE the Empty Weight CG when a design has been altered. End of Story.

 

25 pages to realize that fact is ridiculous.

 

Absolutely correct, the MkIX with a bigger engine had it's CG shifted forward (empty) and this means that loading it with fuel, ammo and a pilot did not shift the CG rear enough to maintain satisfactory handling qualities, therefore ballast is added to the rear to bring the CG in to the desireable range when loaded and ensure it doesn't shift too far forward with consumption of fuel and ammo.

25 pages and you still don't get it is even more ridiculous.

[Crumpp]

Please show or at least name the manual you got these figures from. Thanks.

 

I already showed the conversion and the proof. Without the rear tanks, the Spitfire Mk IX Aft Cg limit is 9 inches aft of datum.

 

(-9-21.89)/85 = .3634 * 100 = 36.3%

 

http://forums.eagle.ru/showpost.php?p=2527236&postcount=113

 

If you need a Spitfire Mk IX weight and balance sheet I can post that for you too.

[Crumpp]

Here:

 

[bongodriver]

I already showed the conversion and the proof. Without the rear tanks, the Spitfire Mk IX Aft Cg limit is 9 inches aft of datum.

 

(-9-21.89)/85 = .3634 * 100 = 36.3%

 

http://forums.eagle.ru/showpost.php?p=2527236&postcount=113

 

If you need a Spitfire Mk IX weight and balance sheet I can post that for you too.

 

but your linked report already shows that is not true, even in the worst case it's shown to be a reduction from 12.6 to 7.4 if all rear fuel is burned and that includes the weight of the empty tanks + plumbing.

[Crumpp]

but your linked report already shows that is not true, even in the worst case it's shown to be a reduction from 12.6 to 7.4 if all rear fuel is burned and that includes the weight of the empty tanks + plumbing.

 

Run the math....Run the math...

 

You are lost in the sauce, bongo.

 

I solved for the LEMAC the NACA was using and compared their datum point to the RAE/Supermarine datum point so I could correct evaluate the CG locations.