Aerodynamic Buffet of the Spitfire

[DD_Fenrir]

Research properly...Agenda??

 

Why don't you drop the theatrics and false drama please. It does nothing for the discussion.

 

The NACA and the RAE discovered the instability and not me. It is fact that lives were lost because of it just as it is fact the stick force per G gradient was increased to aid in controlling it by the RAE. It is also fact that increasing the stick force per G gradient does not fix the stability, it just shifts the curve.

 

That unresolved underlying instability manifested itself throughout the designs history. The RAE did struggle and work to resolve the issue. Their efforts suffered without a defined standard and advanced in a sporadic manner based on the individual specific knowledge of whatever team or organization undertook the particular test regiment.

 

The deep buffet zone and high energy buffet would be an undesirable characteristic in a more stable design but were essential to safe controllable flight in the Spitfire due it's defined and measured longitudinal instability.

 

Whatever Crummp.

 

I've read the report from end to end - it's interesting and for me adds detail to stuff I already knew in general form.

 

The difference being that I interpret 'neutral static stability' (Page 8 of the very report you posted by the way) as just that - neutral static stability; you're the one who bleats on about 'unstable' - you're seeing what you want to see instead of adjusting your opinion based on all the information that is available, some of it provided by me - and flagrantly dismissed on very thin grounds I might add.

 

The evidence you provide speaks for itself.

 

Your interpretation is frankly surplus to requirement. And speaks volumes about you.

[IvanK]

Here we go all over again !

[Friedrich-4B]

Here we go all over again !

 

The subject of the Spitfire's "bad" flight characteristics, and the apparent inferiority of the entire British aeronautical establishment of WW2, cf the German and American equivalents, seems to be an obsession;

 

http://forum.1cpublishing.eu/showthread.php?t=33245

http://forum.1cpublishing.eu/showthread.php?t=33245&page=94

 

:yawn:

Edited January 1, 2015 by Friedrich-4/B

[Yob]

 

Apparently the majority of Britain's test pilots, RAE staff, the Air Ministry and those who designed the Spitfire were a bunch of ignorant, ill advised nincompoops who didn't know much about aerodynamics, and couldn't think their way out of a paper bag.:dunno: :helpsmilie: We should all just sit back, relax and learn. :smartass:

 

Yea as were supposed to believe that they where a bunch of bumbling idiots, who couldn't organize a booze up in a brewery. :megalol:

 

No worries; all that's happened (predictably) is that this thread has become an impromptu series of lectures dealing with how bad the entire British aero-establishment of WW2 was, compared with those of Germany and America.

 

I Have in fact learnt so much first EAS Now this... I went away and did research and look EAS just as bongo said.

Sorry bongo and JTD for that misunderstanding

 

Yes, this thread has really been a fascinating lecture and I have thoroughly enjoyed reading it and learning so many new things! For example, I always thought that the British Royal Aeronautical Establishment knew what they were doing but based on new insights gleaned in this thread it now seems I need to revise that opinion.

 

On the subject of lectures, I noticed that the entertaining series on turn performance and correct usage of Equivalent Air Speed (EAS) have been halted for some reason. I wonder why?

 

 

No matter, this forum will no doubt also next year be blessed with new insights and interesting lectures on the subject of aerodynamics and flight mechanics and it's all for free as well!

 

Happy New Year! :holiday:

 

As a aircraft engineer i am surprised you enjoyed the lecture :P

Almost like i am in a class room listening to my professor go on about how, Oh wait he uses facts, that are proven. and then doesnt use a quote out of context from Yo-Yo.

 

Interesting how self proclaimed professors use there facts. :doh:

 

Research properly...Agenda??

 

Why don't you drop the theatrics and false drama please.

 

Crump,

 

Have a reality check please. EVEN IF WE WHERE ALL WRONG. Which i higly doubt. But how long have you been on this forum, please just stand back, stop making topics that incite hatred and personal tiffs between every one vs u and kurfust.

 

And please, for the love our every ones sanity. GET along with every one. There are some people on this forum that are annoying and hated by a lot of people. So please stop trying to make your self one.

 

Settle down and relax.

 

And does it really matter in every day life about this.

 

And honestly i would believe a BBMF pilot over any report, that leaves inconclusive information about the weight bobs.

 

The subject of the Spitfire's "bad" flight characteristics, and the apparent inferiority of the entire British aeronautical establishment of WW2, cf the German and American equivalents, seems to be an obsession;

 

http://forum.1cpublishing.eu/showthread.php?t=33245

http://forum.1cpublishing.eu/showthread.php?t=33245&page=94

 

:yawn:

 

Oh so i am not the only one to notice the two argument inciters on many forums. Very funny

[MiloMorai]

The Spitfire had horrible control forces harmony. That did not make it unstable or hard to fly.

 

In fact Werner Molders called the Spitfire "Childishly easy to fly".

 

It was very honest airplane that gave it's pilot ample warning when it was near the edge of it's envelope.

 

IMO the Spitfires handling characteristics, which are totally different from it's performance characteristics, are what kept the RAF pilots alive in the early days of WWII.

 

The RAF was forced to send pilots with very little Air-to-Air Combat training into the fray early in the war. Gentle handling allowed them to fly at the edge, survive, and learn.

 

When the situation was reversed in 1944 and the Luftwaffe was forced to send under trained pilots into combat things were different. Neither the 109 nor the 190 had gentle handling. The 190's especially were not an "honest" airplane. It could fly right up to the edge of its envelope with no warning as to how close a pilot was to stalling. Its vicious stall ensured fledging combat pilots did not "push" the plane. Since they could not "fly at the edge" many of them died in their initial combats with no chance to learn.

 

The Spitfire's performance was good on top of it's gentle handling. IMO it was the premier angle fighter in the European Theater.

hummm guess who

[Crumpp]

So your saying I got through 6 years of education...two at graduate level earning a MAS (Aero Sciences) with a 3.9 GPA and don't understand EAS?

 

 

 

Why is it so difficult for people to accept verifiable facts? Fortunately the devs do understand the measured data even if many readers do not. It is a shame emotionalism is substituted for reason.

[Crumpp]

i will post some last reports when I get home. The ignore list will just have grow.

[Crumpp]

hummm guess who

 

 

Great find and thank you. Definative proof that we do learn in life and the power of measured data vs anecdotes!!

 

The anecdotes very much depend on what conditions and which variant the aircraft was flown.

[Pilum]

So your saying I got through 6 years of education...two at graduate level earning a MAS (Aero Sciences) with a 3.9 GPA and don't understand EAS?

 

Why is it so difficult for people to accept verifiable facts? Fortunately the devs do understand the measured data even if many readers do not. It is a shame emotionalism is substituted for reason.

 

Crumpp: It is really interesting to hear about your Msc.in aeronautics: I think you mentioned this before as well but IIRC without many details but I'm sure there are many of us here in this forum who would like to know more so it would be great if you could share some of your work experience with us:

 

When did you graduate and what fields did you specialize in? What did you do as masters thesis? How many years have you been in the aviation industry? What aeronautical companies have you worked for and on which projects/aircraft?

 

I'm especially interested since it seems we are colleagues:

 

I got my MSc. in 1986 from the Royal Institute of Technology in Stockholm, Sweden. I specialized in aerodynamics, flight mechanics and structural engineering. My masters thesis was a computer program for predicting the impact on flight performance of external stores on fighter aircraft. It is a derivate of this program I now use to predict WW2 aircraft performance and sometimes post results from here. I have left the industry now but before that I worked for more than ten years at various companies owned by SAAB and Ericsson such as Ericsson SAAB avionics, Ericsson Microwave systems etc. I have worked mainly with countermeasures systems, both tactical and training systems for the JA37 Viggen and JAS39 Gripen fighters.

 

I know you like to tell us and share freely about your experiences as a private pilot in these forums and now that you brought up the subject of education and work experience yourself it would be great if you could share that with us as well.

 

I'm really looking forward to hearing this Crumpp because you have a high profile in these forums and it would therefore be really interesting to know what similar lasting contributions you have made in the aeronautical industry.

[Friedrich-4B]

i will post some last reports when I get home. The ignore list will just have grow.

 

Let's just cut the entire, laborious process of posting irrelevant reports shall we?

 

Why is it so difficult for people to accept verifiable facts? Fortunately the devs do understand the measured data even if many readers do not. It is a shame emotionalism is substituted for reason.

 

Crumpp, do you have any definitive reports, whether from NASA or any other such organisation, proving that the Spitfire IX was longitudinally unstable: Yes/No?

If you have, could you please post it or them; all anyone has to go on is your speculation/allegations - a lot of the so-called "emotionalism" would be saved if you would simply provide good evidence for your claims.

 

Apart from that, no-one is interested in your opinions about the competence or otherwise of the British aeronautical industry during WW2, so is there any good reason why you have to continue with your crusade?

Edited January 1, 2015 by Friedrich-4/B

[Yob]

So your saying I got through 6 years of education...two at graduate level earning a MAS (Aero Sciences) with a 3.9 GPA and don't understand EAS?

 

 

 

Why is it so difficult for people to accept verifiable facts? Fortunately the devs do understand the measured data even if many readers do not. It is a shame emotionalism is substituted for reason.

 

I was not saying you where wrong was i?

 

I was saying that i shoundt automatically assume that EAS is sea level.

 

No lets start to act like adults before we all get banned.

 

And on what Frederic said, if you can show us proper proof not just a discussion on how it might be unstable. WE Will all believe.

 

And another thing if you are an aero engineer. You should know that things that are said on paper, some times are wrong.. Bare that in mind.

[Pilum]

IIRC then the later Spitfires (like the late Me109's) had ballast added in the tail to compensate for the increased engine installation weights in the later marks. When did this start to be incorporated? Was it already in the Mk9's or was it with the later Griffon variants?

 

It would be reasonable to assume that no more ballast was added than necessary since any added weight to an airplane by definition is bad unless it serves a purpose, in this case to reduce excessive tail loading caused by nose heavyness.

 

So on the Spitfire marks where ballast was added, it stands to reason that no more was added than needed, i.e. the airplane would have been on the stable side since adding more ballast than that would move the airplane towards instability which makes no sense really.

 

Addendum: From Morgan & Schacklady page 323: Weight and loading Spitfire Mk IX AB197: "Tare (includes 5 x 17.5 lb ballast weights in tail) .....".

 

Don't know if that was just AB197 or if other MkIX flew with ballast. Anyway, adding ballast in the tail would not be something you would want to do in an unstable aircraft.......

Edited January 2, 2015 by Pilum
Added reference to MkIX AB197

[Pilum]

More Spitfire MkIX ballast info from Morgan and Schacklady: Page 334 shows a loading plan and here table 2 details two ballast weights in tail: One standard at 17.5 lb and one additional one at 5 lb.

 

However, even though the table is in the Mk IX chapter of the book, there is also a figure of a MkXVI on same page so it's not totally clear that the loading plan is for the MkIX.

 

So seeing ballast is added in tail, this would point to the aircraft being stable since adding ballast otherwize makes no sense.

 

This table also details the moment of arm which is 175 inches.

 

So maybe AB197 did not have 5 x 17.5 lb weight in tail after all but flew with 5 lb with a moment arm of 175 inches and this was interpreted as 5 x 17.5 lb....

 

Anyway, irrespective of if it was 5 lb or more ballast: You don't add weight in the tail of an already unstable aircraft .......

[Crumpp]

Ballasting only keeps the load within the CG limits. It does not correct the basic instability. The basic stability characteristic is a function of the relationship of the CG limits to the Aerodynamic Center of the design.

 

Increasing a CG range means changing the aerodynamic center of the design. That is an enormous undertaking that generally impossible without a complete redesign of the aircraft.

 

As an engineer you should know this......

[bongodriver]

Ballasting only keeps the load within the CG limits. It does not correct the basic instability. The basic stability characteristic is a function of the relationship of the CG limits to the Aerodynamic Center of the design.

 

Increasing a CG range means changing the aerodynamic center of the design. That is an enormous undertaking that generally impossible without a complete redesign of the aircraft.

 

As an engineer you should know this......

 

nobody has said that the ballast was for correcting stability, in fact pilums last posts make that very clear.

in fact you have evaded entirely what his last posts really mean in quite a bizarre fashion.

[Crumpp]

It might be helpful to explain what defines the physical limits of the CG.

 

The forward CG is defined the elevators ability to raise the nose of the aircraft at landing speeds in order to flare the airplane for landing.

 

The stability margin is greatest and the airplane is at its most stable at the forward CG.

 

The rearward CG limit is defined by the location of the aerodynamic center. The stability margin is at it smallest at the rearward limit meaning the airplane is at its least stable.

 

The aerodynamic center is a point fixed by the design which for all intensive purposes it does not move in subsonic incompressible flow without a configuration change to the aircraft such as a camber change like flaps for example. Compressibility effects also move the AC as well effecting stability.

[DD_Fenrir]

Evasive? Crummp? Never.... ;)

 

So we summarise: the Spitfire across all marks had narrow limits for CoG position; it depended on the mark and it's equipment loading as to where this margins lay and whether an individual aircraft was within them; less of an issue on the Mk.I & IIs, a much greater factor with the Mk.V, and pretty much sorted with the new elevator on the Mk.IXs and variants thereafter.

 

These narrow CoG limits led to an aircraft that was neutrally statically stable, but the washout leading to root stall first gave excellent feedback to the pilot as to airflow state allowing them to ride the stall. Downsides were increased drag and concurrent airspeed drop (30-35mph over 2 seconds loss during the buffet state at anything over 3g @ 170mph IAS), and effect buffeting had on involuntary control movement, making the aircraft less effective as a gun platform during buffet.

 

The neutral static stability could - note 'could' as we have no conclusive proof otherwise in accounts or data - be problematic during non-buffet conditions when pitching the nose on to target as pilots would likely have to manually settle the nose and the low stick forces and sensitivity of the elevator control mean over control is likely; however, I would add, as long as the behaviour is consistent it would be predictable and a pilot familiar with his aircraft should be able to anticipate and compensate accordingly - THIS LAST IS SIMPLY MY OPINION AND BASED ON MY ALBEIT LIMITED EXPERIENCE FLYING GLIDERS AND LIGHT POWERED AIRCRAFT AND FEW 1000S OF HOURS IN FLIGHT SIMS, I WOULD LIKE TO SEE DATA TO VERIFY OR DISPROVE IF ANY ONE HAS IT.

 

Pretty much everything - except my last which is conjecture, but I feel a reasonable supposition - seems to confirm everything I've read in around 25 years of amateur study of the Spitfire. Responsive, sensitive, good control feedback, joy to fly, not the best gun platform but there's the trade-off.

 

What's your point Crummp?

Edited January 2, 2015 by DD_Fenrir

[Crumpp]

Holtzauge says

 

Anyway, adding ballast in the tail would not be something you would want to do in an unstable aircraft.......

 

Anyway, irrespective of if it was 5 lb or more ballast: You don't add weight in the tail of an already unstable aircraft .......

 

In English, the statement about not adding ballast to an unstable airplane is implying adding ballast has an effect on stability.

 

Adding ballast has nothing to do with the stability margin.

 

There is absolutely nothing evasive about my answer. It is clear, direct, simplified, and correct.

 

:music_whistling:

Edited January 2, 2015 by Crumpp
Added Holtzauge quotes from first post

[Crumpp]

Permanent Ballast (fixed ballast). A weight permanently installed in an aircraft to bring its center of gravity into allowable limits. Permanent ballast is part of the aircraft empty weight.

 

http://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/media/faa-h-8083-1a.pdf

 

 

Answers such as "adding ballast to affect the stability" is confusing from my point of view, people.

 

It is like going to car mechanic and telling him to change the hood ornament because the tires are flat.

 

 

Of course the poor car mechanic would wonder what the hood ornament has to do with the flat tires!

 

:doh:

Edited January 2, 2015 by Crumpp
Changed "fix" to affect as it is more precise. Fixed ballast does not effect stability

[Friedrich-4B]

I ask again:

 

Crumpp do you have a definitive report or reports that prove that the Spitfire IX was longitudinally unstable? Yes/No

[Crumpp]

Crumpp do you have a definitive report or reports that prove that the Spitfire IX was longitudinally unstable? Yes/No

 

Yes. And I ask again......have read what is already posted AND understood the information. It is not a dig on you as I doubt you had to take aircraft stability and control in college.....trust me it is a class to be avoided if your GPA is borderline.

 

It is a serious question. If you do understand it, please explain that understanding so we are not looking at hood ornaments instead of tires!!

 

:smilewink:

Edited January 2, 2015 by Crumpp

[Crumpp]

South American FOD has conspired to keep me away from home and given me the opportunity to practice V1 cuts outside the simulator. It will have to wait a few days until I get off work and go home.

 

In the mean time do you mind explaining without the emotional sensationalism exactly why you think "fixed" the stability in the Mark IX? I am not being condescending so please do not take it that way. It is just important we are on the same page.

 

Cut me a break please and try to step in my shoes for a moment.

 

I look at what is posted so far and see the design changes and with what I know, there is no question. I do not know what makes you think differently.

 

We know they improved the controllability but explain what fixed the instability, please.

Edited January 2, 2015 by Crumpp

[Crumpp]

I have Gates calculations on the coeffient of moment and Report addressing the longitudinal instability. It is what prompted the controllability improvements.

[bongodriver]

http://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/media/faa-h-8083-1a.pdf

 

 

Answers such as "adding ballast to affect the stability" is confusing from my point of view, people.

 

It is like going to car mechanic and telling him to change the hood ornament because the tires are flat.

 

 

Of course the poor car mechanic would wonder what the hood ornament has to do with the flat tires!

 

:doh:

 

it's confusing for you? despite the fact CoG has a direct effect on aircraft stability?

 

From the very document you linked:

 

Stability and Balance Control

Balance control refers to the location of the CG of an

aircraft. This is of primary importance to aircraft stability,

which determines safety in flight.

The CG is the point at which the total weight of the aircraft

is assumed to be concentrated, and the CG must be located

within specific limits for safe flight. Both lateral and

longitudinal balance are important, but the prime concern

is longitudinal balance; that is, the location of the CG

along the longitudinal or lengthwise axis.

An airplane is designed to have stability that allows it to

be trimmed so it will maintain straight and level flight with

hands off the controls. Longitudinal stability is maintained

by ensuring the CG is slightly ahead of the center of lift.

This produces a fixed nose-down force independent of

the airspeed. This is balanced by a variable nose-up force,

which is produced by a downward aerodynamic force on

the horizontal tail surfaces that varies directly with the

airspeed.

If a rising air current should cause the nose to pitch up, the

airplane will slow down and the downward force on the

tail will decrease. The weight concentrated at the CG will

pull the nose back down. If the nose should drop in flight,

the airspeed will increase and the increased downward tail

load will bring the nose back up to level flight.

As long as the CG is maintained within the allowable

limits for its weight, the airplane will have adequate

longitudinal stability and control. If the CG is too far aft,

it will be too near the center of lift and the airplane will

be unstable, and difficult to recover from a stall. [Figure

1-2] If the unstable airplane should ever enter a spin, the

spin could become flat and recovery would be difficult or

impossible.

If the CG is too far forward, the downward tail load will

have to be increased to maintain level flight. This increased

tail load has the same effect as carrying additional weight;

the aircraft will have to fly at a higher angle of attack, and

drag will increase.

A more serious problem caused by the CG being too far

forward is the lack of sufficient elevator authority. At slow

takeoff speeds, the elevator might not produce enough

nose-up force to rotate and on landing there may not be

enough elevator force to flare the airplane. [Figure 1-3]

Both takeoff and landing runs will be lengthened if the CG

is too far forward.

Now we all know tail ballast is going to change the CoG and push it rearward, we also know that a forward CoG is beneficial to stability, so why add weight to shift a CoG rearward on an unstable aircraft?......unless of course the aircraft is not really unstable and has plenty of static margin in order to put ballast to correct a forward CoG from a heavier engine.

[DD_Fenrir]

My thoughts precisely Bongo.

 

Ballast alters the CoG in relation to it's aerodynamic limits; how the blazes can you, a self professed expert, claim it's unrelated?!?!?! I've had no more experience in aerodynamics and CoG positions than flying radio controlled a/c, but dear lord, even I know this!

 

Your 'credentials' get more and more equivocal by the minute mate.

 

So, last chance Crummp me old china, money where your mouth is: let's see this report on the Mk.IX - and btw if it's anything to do with serial MK210 then I'm gonna blow whatever tired and flawed argument you have with that out of the water also.

 

Hoping for better but expecting more manure....