Aerodynamic Buffet of the Spitfire

[Friedrich-4B]

Since they were bending airplanes at a consistent rate in the Mk IX on pull outs from bombing runs, it sounds like the design needed more work in the longitudinal stability and control department.

 

Yep, the poor old Spitfire IX just didn't have the longitudinal stability or control needed for a bomber and bent under the strain because it was so fragile. It was a sad state of affairs that an aircraft originally designed to be a short range interceptor couldn't hack it as a fighter-bomber engaged in intensive operations over hostile territory. :no_sad:

 

 

(Morgan and Shacklady - Spitfire: the History)

Edited December 31, 2014 by Friedrich-4/B
deleting quote from deleted post

[Crumpp]

(Morgan and Shacklady - Spitfire: the History)

 

Thanks for posting that! Read it carefully please.

 

There are also several investigations on the Mk IX tied to solving the wrinkling issue in the same book. It is a good read and is in my collection.

[bongodriver]

on reading carefully it really makes no suggestion at all of a stability issue, failing to pull out of a vertical dive would really give some severe skin wrinkling though, I believe the 109 was adept at that demonstration :music_whistling:

[Friedrich-4B]

Thanks for posting that! Read it carefully please.

 

There are also several investigations on the Mk IX tied to solving the wrinkling issue in the same book. It is a good read and is in my collection.

 

There is exactly one investigation (not several) into the wrinkling issue mentioned in the book; I provided the full description while several pages later M & S provide a condensed summary (below), with the serial numbers of the Spitfires tested.

 

 

As it is, only one Spitfire unit, 125 Wing, is mentioned in connection with the problem.

 

on reading carefully it really makes no suggestion at all of a stability issue, failing to pull out of a vertical dive would really give some severe skin wrinkling though, I believe the 109 was adept at that demonstration :music_whistling:

 

Not to mention the radical escape manœuvers, and the ways pilots trimmed, or failed to trim the Spitfire. This in an aircraft not designed to be a dive or glide bomber.

Edited December 30, 2014 by Friedrich-4/B
add M&S

[Crumpp]

Actually I spot at least 5 trials and investigation related to the longitudinal control issues of the design in the Mk IX series.

Edited December 30, 2014 by Crumpp

[bongodriver]

Se also clutching at straws.

[MiloMorai]

Actually I spot at least 5 trials and investigation related to the longitudinal control issues of the design in the Mk IX series.

 

And these are ...............

[Crumpp]

Yes...and? 1946 test? Relevant how?

 

Yep, that is part of looking for longitudinal stability issues. There was also in March 1944 high speed trials, March 1944, High speed trials - effect of mach number on dive, march 1944 Handling with wing bombs, 25 June 1944 Handling trials with wing bombs, November 1944 Acceleration records Vg testing.

 

It was the very first production Mk IX that exhibited the trim change with ordinance as discussed on page 313, 1st column, third paragraph.

 

You understand that is all longitudinal stability issues? They first noticed it in the very beginning of Mk IX series production but did not really solve it in the design.

 

I do not have a good explanation for why they did not solve it except to say their methods are sometimes questionable especially in the transonic realm of flight and stability and control investigations. Some of the reports are just babbling opinion without anything of any value being quantified but they are published as stability and control investigations. Other things are measured and some areas quite sophisticated.

 

I included a sample of the kind of official stability and control reporting found. Look at the data on rolling velocity. It does not include the most basic requirement of aileron angle or input force. Look at the set up of the test. No equipment to measure input force and no equipment to measure aileron deflection. They just adjusted the aileron droop and sent some poor pilot officer out to record time to angle of bank. It is just a big waste of ink and the fact it was taken seriously shows the depth of knowledge on stability and control issues. It really seems to have run the entire gamut and I am not surprised Gates ran into so much resistance to adopting a stability and control standard for the Air Ministry.

 

I am sure somebody read the report on the effect of clipping wings and thought it was a great expenditure of man hours to advance the war effort.

 

I think the Air Ministry kind of rested on their laurels after World War I in some areas. In fact, their leading stability and control engineer, Gates did not publish to the British aerodynamic community the discovery of the movement of the AC in transonic flight until 1949! Think about that, the RLM is issuing patents to Junkers for Area Rule in 1944 while the Air Ministry still does not realize the stability margin changes in transonic flight.

 

AC movement was common knowledge at the RLM and the NACA during the war. I guess Gates was not privy to everything going on at the NACA on his whirl wind tour! Kind of underhanded if you ask me as Gilruth adopted Gates stick force per G criteria. :smilewink:

 

I think if the Air Ministry had been more savvy to the need for stability and control engineering and listened to Gates, lives would have been saved and the RAF would have had an even better fighter in the Spitfire.

 

But that is just my opinion based on what I know.

[bongodriver]

But testing the effects of ordinance, retro fitted aft fuel tanks and high trans sonic speed regimes are not indications of any inherent stability issues, they do however indicate a diligence on the part of the British for testing stability and control.....it really doesn't reflect the theory you try to push about British stability and control standards and methodology.

It is rather unsurprising that the British were less advanced in aerodynamic research than the Germans, the Germans had decided they wanted to murder large portions of the world population many years before and spared no expense in inventing ways to do it.

[DD_Fenrir]

Anybody who claims to be presenting any information regarding Spitfires would do well to read cover to cover, and then re-read Jeffrey Quill's book 'Spitfire' ISBN 0-09-937020-4. He covers the whole gamut of stability, bob-weights and the redesigned elevator thoroughly and to those approaching this issue without agenda would find some of the apparent issues here raised by our renowned Spitfire bashers a little stretched.

 

Quill regarding stability in the MkI:

 

page 231: "I remarked, however, that the stability margin was tight"

page 231: "The aeroplane was on the borderline of instability..."

 

Quill regarding the Mk. V Issue:

 

Page 232: "...a fair amount of additional of additional operational equipment had gradually crept into the aircraft."

Page 233: "Therefore for each sub-variant of the Mk.V (and there were Va, Vb and Vc)detailed instructions for the correct loading of the aircraft were issued to squadrons to ensure that the centre of gravity remained within the limits set down."

Page 233: "However, the importance of these loading instructions was not generally appreciated in squadrons in the daily round of operational activities they tended to be disregarded."

 

He goes on to report that he and another production test-pilot who had both been flying correctly loaded MkVs had the chance to fly some line aircraft and found that those flying on the squadrons to be almost dangerously unstable - so to summarise more accurately, the bob-weights were introduced as an emergency measure more to counter the effects of poor following of procedure at squadron level than some inherent design flaw of an unstable aircraft.

 

As for the revised elevator:

 

"The 'Westland elevator' [an experimental type not fitted operationally - DD_Fenrir], as it became known , demonstrated the way forward; but our aerodynamicists at Hursley Park thought that an even more effective answer could be obtained by enlarging the horn balance of the standard elevator and this we did by stages. The effect was astonishing. At last a way had been found to improve the basic static stability margins of the aeroplane..."

 

So we have an aircraft that is not inherently unstable; it just has a small range in which the CoG can reside before the aircraft becomes unstable. We have bob-weights introduced as an overarching policy to Mk.V aircraft only (certainly not required on aircraft whose loading instructions have been correctly followed) to mitigate the repercussions of incorrect loading, and an elevator design that renders the bob-weights superfluous - all before the Mk.IX variant we are reputed to be having in game saw service.

 

You know, with the slightly longer nose and the increased weight of the supercharger, this increased moment forward of the CoG could well hint that the Mk.IX was a more stable aircraft than a Mk.V anyway, even before the improved elevator.

Edited December 31, 2014 by DD_Fenrir

[Crumpp]

Let's examine the Air Ministries receptiveness to new ideas. Take Frank Whittle and the Jet Engine.

 

In Germany, the idea was embraced. With major finacial backing from Heinkel, Hans von Ohain engine was not only the first operational jet engine design, it flew in an airplane days before the war even started.

 

Whittle had a much different experience suffering two nervous breakdowns before the end of the war trying to give the Air Ministry the gift of the Jet Age.

 

He tried to persuade the Air Ministry to try it. But they took the advice of the Royal Aircraft Establishment at Farnborough which was wedded to things with propellors. ‘Impracticable’ was the official verdict in 1929.

 

:doh:

 

The British Government refused to exercise its right to keep the thing secret, on the grounds it wasn’t important enough.

 

:huh:

 

n the aftermath of World War II, copies of Whittle’s patents would be found in research labs all over Germany.

 

:doh:

 

The money was chickenfeed compared with the sums being spent in Germany, now fast re-arming and desperate to take the lead in this pioneering field.

 

:(

 

Over the subsequent years, Whittle’s story was one of constant ingenuity thwarted by sluggish bureaucrats and devious businessmen.

 

:mad:

 

He received a knighthood for his troubles, but he wanted people who would help him turn his ideas into machines. And after Britain surrendered its commanding lead in the very jet industry which Whittle had created, it was hardly surprising when he ended up moving to America.

 

:megalol:

 

British aviation innovations were supposed to come from the old Royal Aircraft Establishment at Farnborough, not a junior RAF officer. Whittle was an embarrassment because he left Farnborough standing,’ says Nicholas Jones. ‘They consistently undermined him and that Farnborough mindset persists to this day among some historians.’

 

http://www.dailymail.co.uk/news/article-1379807/Frank-Whittle-Jet-engine-inventor-genius-shrank-globe.html

 

The idea of a stability and control standard was not invented at the RAE and therefore, in the RAE tradition, had no place in it.

 

Gates ran into that, I think!

[Crumpp]

the bob-weights were introduced as an emergency measure more to counter the effects of poor following of procedure at squadron level than some inherent design flaw of an unstable aircraft.

 

Do you really believe this and think that is what happened?

 

To me it does not make any sense to add bobweights when you can just say.....

 

Follow the published weight and balance sheets.

 

Much cheaper and much more effective solution that ruining the stabilty and control of an aircraft design.

 

Didn't Oleg say, "Close this book and never open it again..."

[DD_Fenrir]

Do you really believe this and think that is what happened?

 

To me it does not make any sense to add bobweights when you can just say.....

 

Follow the published weight and balance sheets.

 

Much cheaper and much more effective solution that ruining the stabilty and control of an aircraft design.

 

Didn't Oleg say, "Close this book and never open it again..."

 

Wow.

 

So flippant your disregarding the Spitfire Test Pilots own words there Crummp. Yes, Crummp, I said Test Pilot. Spitfire. From prototype to the the Seafire F47. Bravo. So I'm going to take your hackneyed and biased observations over the chap who's been there and done it? Riiiiiiiiight.

 

If you choose to ignore the words of the fellow who was actually there at the time and actually doing it - not just sitting on his butt interpreting charts and cherry picking evidence to suit his own agenda 70 years later - then more fool you.

 

Yes it would be simpler to follow the instructions, I couldn't agree more, but these had been issued and disregarded in some cases; in order to save valuable pilots and aircraft the bob-weights were pushed as an attempt to mitigate the effects of poor loading when the documentation had been ignored or misinterpreted.

 

You claim to be an aviation enthusiast but for someone interested in WW2 aircraft not to have read the Quill book is frankly astonishing. It almost sounded like you didn't know who Jeffrey Quill was.

[DD_Fenrir]

Let's examine the Air Ministries receptiveness to new ideas. Take Frank Whittle and the Jet Engine.

 

In Germany, the idea was embraced. With major finacial backing from Heinkel, Hans von Ohain engine was not only the first operational jet engine design, it flew in an airplane days before the war even started.

 

Whittle had a much different experience suffering two nervous breakdowns before the end of the war trying to give the Air Ministry the gift of the Jet Age.

 

 

 

:doh:

 

 

 

:huh:

 

 

 

:doh:

 

 

 

:(

 

 

 

:mad:

 

 

 

:megalol:

 

 

 

http://www.dailymail.co.uk/news/article-1379807/Frank-Whittle-Jet-engine-inventor-genius-shrank-globe.html

 

The idea of a stability and control standard was not invented at the RAE and therefore, in the RAE tradition, had no place in it.

 

Gates ran into that, I think!

 

What the hells this got to do with anything in this thread?!?

[Crumpp]

Here is what the RAF Pilots Notes General says about CG limits and who is responsible for maintaining them.

 

It also includes a pretty good very basic primer on stability in the Pilot's Notes General.

 

So, that entire line of thinking that the bobweights were added because the squadrons were not following procedure just does not make sense.

 

It is much cheaper to send simply enforce the standard than go thru the danger and expense of testing to arrive at bobweights.

 

Now stranger things have happened and the basic premise is the RAF was not doing what they were supposed to anyway.

 

So just because the instructions say to do it one way is not solid proof.

 

 

 

What is solid quantifiable proof the instability was not due to a hooligans not following the rules is the fact the CG the aircraft was flown at is published in the NACA report on Flying Qualities of the Spitfire. It is clearly within the normal CG range. It is not even close to the aft CG limit.

 

While I have no doubt as to Mr Quill sincerity in his belief, the measured data just does not support this conclusion.

 

 

hat the hells this got to do with anything in this thread?!?

 

It estabilishes the Culture and mindset of the RAE, the folks responsible for such things as stability and control research.

 

British aviation innovations were supposed to come from the old Royal Aircraft Establishment at Farnborough

 

Gilruth, an american engineer pioneered the necessity for a stability control standard. Gates and him were very good friends and much of Gilruths work was shared in 1942 when Gates was a guest of the NACA.

 

It is a fact that Gates received considerable resistance to the adoption of a stability and control standard at the RAE. He was not successful in convincing the RAE of the need for it until the postwar years. Long after most other nations had a standard in place.

 

You ever wonder why we do not see any reports like the NACA flying qualities reports from the RAE or the Air Ministry??

 

Because they did not do any such things except piecemeal investigations to try and solve a specific issue. Ever heard the expression, "missed the forest because of the trees"?

Edited December 31, 2014 by Crumpp

[Crumpp]

ow the thread has degenerated into utter nonsense about how bad the Spitfire was

 

You really believe this? I can tell you it is not true and I have not said anything "bad" about the Spitfire.

 

Anybody that knows stability and control design will see the same issues.

 

Why do you think Yo-Yo made the statements he did?

 

You think he hates the Spitfire too? Probably not. He just understands the engineering and reaches the same conclusions the NACA, the RAE, and everyone else involved in the design.

 

So what makes more sense to you?

 

Now I do speculate some because there is no other plausible explanation I see for why it went on for so long in the design other than just plain ol stubbornness to adapt to new ideas. It is fact that Gates ran into that very same trait in his career at the RAE.

 

That is not bashing the Spitfire, it just offering a reasonable explanation as to why the facts are what they are.....

[Crumpp]

Friedrich-4/B...Why are there not any measured flying qualities investigations performed by the RAE on British Designs?

[Crumpp]

Gates work in developing the stick force per G criteria was critical to the NACA's adopted standard.

 

Guess he is a Spitfire hater too?

 

That evaluation of the stick force per G being "rather too light" is from Gates report Longitudinal stability criteria.pdf posted earlier in this thread.

 

Included is a history of Stability and Control engineering as presented at the 7th Von Karmen Lecture hosted by the AIAA.

[Friedrich-4B]

What the hells this got to do with anything in this thread?!?

 

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.

 

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:

 

Happy 2015! :holiday::beer::clap_2:

Edited December 31, 2014 by Friedrich-4/B
It is now 2015!

[Pilum]

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:

[DD_Fenrir]

I say again, what the hell has the bureaucratic inertia of the RAE or the Air Ministry got to do with this discussion on Spitfire buffet?

 

Who cares if there was no standard specification laid to 'acceptable' stability characteristics by the Air Ministry/RAE?!?!?

 

The level of understanding of the theories of stability characteristics and those factors which affect them was well in evidence in the British Aeronautical Engineering Industry at the time in question, it would appear the instruments to measure to detail the physical manifestations of these stability effects were not available or not perfected. Quill covers this - if you've read the book.

 

The prototype was deemed safely flyable by ordinary squadron pilots by Humphrey Edwardes-Jones, a qualitative judgement but a sound one.

 

No-one claims the Spitfire was the perfect fighter, I certainly don't claim it should kick the butt of every thing in the sky, but you rolling in here like you've found the holy grail on how apparently dangerous the Spitfire was because of some inherent instability in the design, when the rest of us who research properly, without agenda already know about the marginal stability, the parameters under which it became dangerous and the fact that others more knowledgeable than you deemed the aircraft safe.

 

Your barking up the wrong tree Crummp.

 

By the way you do know the Spitfires maximum permissible IAS was 450mph? I make that 0.75 mach. Why on earth are you talking about movement of stability margins at transonic speeds when the transonic range does not begin till 0.8 mach?

[gavagai]

By the way you do know the Spitfires maximum permissible IAS was 450mph? I make that 0.75 mach.

 

At sea level in dry air at 20 degrees C? At higher altitudes in colder air 450mph IAS can be much more than 0.75 mach.

[DD_Fenrir]

Yes Gav but Crummps argument is related to dive bombing, specifically regarding 2nd TAF Mk.IXs, the start alt at which dive bombing attack commences is at 6,000ft according to 2nd TAF documents, and 6,000-8,000ft according to Raymond Baxter who flew dive-bombing ops against V2 sites in Holland. Pretty difficult to hit 0.8 mach at those alts.

[Crumpp]

I say again, what the hell has the bureaucratic inertia of the RAE or the Air Ministry got to do with this discussion on Spitfire buffet?

 

Who cares if there was no standard specification laid to 'acceptable' stability characteristics by the Air Ministry/RAE?!?!?

 

The level of understanding of the theories of stability characteristics and those factors which affect them was well in evidence in the British Aeronautical Engineering Industry at the time in question, it would appear the instruments to measure to detail the physical manifestations of these stability effects were not available or not perfected. Quill covers this - if you've read the book.

 

The prototype was deemed safely flyable by ordinary squadron pilots by Humphrey Edwardes-Jones, a qualitative judgement but a sound one.

 

No-one claims the Spitfire was the perfect fighter, I certainly don't claim it should kick the butt of every thing in the sky, but you rolling in here like you've found the holy grail on how apparently dangerous the Spitfire was because of some inherent instability in the design, when the rest of us who research properly, without agenda already know about the marginal stability, the parameters under which it became dangerous and the fact that others more knowledgeable than you deemed the aircraft safe.

 

Your barking up the wrong tree Crummp.

 

By the way you do know the Spitfires maximum permissible IAS was 450mph? I make that 0.75 mach. Why on earth are you talking about movement of stability margins at transonic speeds when the transonic range does not begin till 0.8 mach?

 

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.

[MiloMorai]

How was the Spitfire when fitted with the auxiliary fuselage tank ever able to fly?