Why do Spitfires turn better than Hurricanes?!

[Viper2000]

Originally Posted by Kurfurst

'Fighter' seems to make the sentence untrue, given that the supposed .89 Mach figure was measured on an unarmed photo recce aircraft (ie. aerodynamic windshield, no cannons stubs, no MG ports ruining the flow over the wing); besides the fact that the said report of the PR XI dive measured does not mention a thing about control behaviour..

I have a report of a proper Mark IX (ie. Fighter) dive trial, and it shows exactly the same symptoms of loosing control as any other fighter above 0.80 Mach. Add to that the instruments were also inaccurate at these speeds, and you have a myth liked by fans, but with very little root in reality.

I didn't claim that a Spitfire fighter was capable of Mach 0.89 in a controlled dive. You seem to have set the PR.XI Mach number up as a straw-man.

The Spitfire Pilots Notes put the dive limit at 450 mph IAS (after position error; so really it's more like CAS but without the modern compressibility correction) or what was effectively Mach 0.85, the limit being defined by a lookup table due to the absence of a Mach meter.

I would suggest that Eric Brown is probably the best reference for relative performance of fighter aeroplanes because he flew so many types.

It's fine to argue instrument error when you're talking about squadron pilots diving in the heat of battle and seeing fantastic numbers on their ASI. Indeed, I'm more than happy to offer up the alleged Mach 0.92 dive by a Griffon Spitfire in the vicinity of Hong Kong post war as likely erroneous.

However, RAE were a competent flight test organisation, and they were perfectly capable of correcting for compressibility. The same goes for NACA, though it is notable that the USAAF went to RAE for an assessment of the high speed handling characteristics of their fighter aeroplanes (See Wings on my Sleeve).

Compressibility correction for a pitot tube really isn't that hard, especially subsonic when you can just say that gamma = 1.4.

Therefore I have considerable confidence in the Spitfire PR.XI dive data showing Mach 0.89; if you look at Morgan & Shacklady you'll see that the aeroplane was rather impressively instrumented for these high speed dives. I also note that this tended to break engines due to overspeeding, resulting in several serious accidents, despite the fact that the propeller was modified to feather in an attempt to contain rpm.

So I wouldn't claim that a Spitfire fighter could be safely operated by a squadron pilot at such a high Mach number.

But I have no reason to believe that it was unsafe to operate the aeroplane within its published envelope (i.e. the lower of 450 mph after position error correction, or Mach 0.85), not least because pilots tend to get quite vocal if aeroplanes scare them within the published envelope, and I also have no reason to disbelieve the tactical Mach numbers quoted by Eric Brown in his various books.

IIRC there may be some dive test data from a Spitfire IX showing a tactical limit of about Mach 0.83 out there somewhere. This would be fairly reasonable.

AFAIK the tactical limit for the Mustang is about 0.80, Thunderbolt about 0.72, Bf-109 and Fw-190A 0.75, whilst the P-38 was only ok to about 0.68. However, my books are at home; the numbers can be cross-checked in Wings on my Sleeve, Wings of the Luftwaffe, and Wings of the Weird & Wonderful.

[Sternjaeger II]

Originally Posted by Viper2000

I would suggest that Eric Brown is probably the best reference for relative performance of fighter aeroplanes because he flew so many types.

Brown's accounts are a good read but hardly of any serious value man.. I think this is the biggest mistake: always looking for a source of comparison, but looking only into English literature on the subject.

The Germans had a lot of planes to play with, and I believe they might have produced an extensive literature on the subject, it would be interesting to hear from our German speaking friends on the matter.

[Viper2000]

Brown was at the RAE high speed flight; decision makers acted upon his views at the time. I don't think that you'll find a substantially better source.

The Germans didn't have the opportunity to test war trophies after VE day, so their literature is unlikely to be anything like as broad as that produced by the Allies, especially at the RAE; don't forget that the RAE were the world-leaders in high speed flight until the idiotic cancellation of the Miles M.52...

[Sternjaeger II]

Originally Posted by Viper2000

Brown was at the RAE high speed flight; decision makers acted upon his views at the time. I don't think that you'll find a substantially better source.

questionable.. he wasn't the only pilot, only the one that bothered writing a somehow interesting (albeit incomplete and biased) text on his experience. RAE had to make a lot of compromises in their testings, so if you're looking for an accurate testing, look somewhere else.

The Germans didn't have the opportunity to test war trophies after VE day, so their literature is unlikely to be anything like as broad as that produced by the Allies, especially at the RAE; don't forget that the RAE were the world-leaders in high speed flight until the idiotic cancellation of the Miles M.52...

Brown's tests of our interest were mainly made during war years, the postwar years were more devoted to jet planes (he's claimed as the only Allied pilot who flew a Komet, but in fact he only glided in it).

The Luftwaffe had an extensive testing of captured planes (they even bothered to install a DB601 on a Spitfire to check its performance!).

I found some literature of interest:

"Luftwaffe Test Pilot, Flying captured Allied Aircraft of World War 2" Published in German in 1977 and English in 1980. Author: Hans-Werner
Lerche.

1. Strangers in a Strange Land Vol. 1 (Squadron Signal pub) by Hans Heiri Stapfer. Usually available on the web for
$ 10 - $ 15 used condition. A number of photos and color drawings are included as well as interesting discussions on specific aircraft that were captured.

2. Fremde Vogel unterm Balkenkreuz I have scanned photos from this book, but haven't been able to find a copy for sale.....it contains a number of photos of captured
aircraft in Luftwaffe service organized by country of origin. This book was published in the early 1980s I think.

3. Il Ricco Bottino (The Rich Booty) by Hans Werner Neulen. Excellent book on captured Italian aircraft in Luftwaffe service. around $ 18.

4. The Luftwaffe from Training School to the Front (Chapter 10) by Meyer and Stipdonk. Chapter 10 provides a number of photos of captured aircraft.

5. Foto Archiv Band 8. Although several Band in this excellent publication include at least one or two photos of captured aircraft..Band 8 includes by far the most with
several types I not seen elsewhere. You can order this one online at the following site:
www.stormbirds.com/flugzeug/ (http://www.stormbirds.com/flugzeug/)

Flugzeug magazine and Jet & Prop magazine, also available at this web address, have published excellent articles on this subject. Included are: Fiat G-12; Bloch SO 161;
Hopfner Ha 11/33; Brequet Br 521 Bizerte (2 parts); SM-75/SM 82; Rechlin September 1943 display; SE 200 etc.

6. Luftwaffe Fledglings 1935 - 1945. by Ketley and Rolfe. Although not exclusively about captured aircraft, this book nevertheless contains quite a bit of interesting
information, photos and drawings concerning captured aircraft used as trainers.

7. Modell Fan magazine ran a series of articles in the late 1970s and early 1980s entitled 'Sie Flogen mit dem Balkenkreuz' there were at least 13 or 14 articles in this
series, maybe more.

8. The Czech magazine REVI has published comprehensive articles by Igor Mrkvanek on captured Czech aircraft in Luftwaffe service. Very informative.

9. Flypast has published at least two very interesting articles on captured British aircraft in Luftwaffe Service.

10. Luftwaffe Codes, Markings and Units (Barry Rosch) contains quite a bit of information on captured aircraft organized by Luftwaffe unit. Some photos and drawings of
captured aircraft are included throughout the book.

11. The Luftwaffe Verband Journal has published several articles on aircraft evaluated at Rechlin or operated by Versuchsverband.

[Sternjaeger II]

uh and "KG 200 - The True Story" by Peter Stahl

[Viper2000]

Originally Posted by Sternjaeger II

questionable.. he wasn't the only pilot, only the one that bothered writing a somehow interesting (albeit incomplete and biased) text on his experience. RAE had to make a lot of compromises in their testings, so if you're looking for an accurate testing, look somewhere else.

Having met the man a few years ago I must say that I found him convincing, and most impressive.

The biggest problem with his books is the fact that the typist doesn't understand engine power settings and therefore incorrectly converts between psi boost and ata throughout the text, littering it with parenthetical errors which were obviously absent from the original manuscript.

Originally Posted by Sternjaeger II

Brown's tests of our interest were mainly made during war years, the postwar years were more devoted to jet planes (he's claimed as the only Allied pilot who flew a Komet, but in fact he only glided in it).

Actually he illicitly flew it under power in 1945; see the latest edition of Wings on my Sleeve. He also tested a number of piston engined types post war, most notably the Ta-152 (albeit with neither MW50 nor GM1) and Do-335.

Originally Posted by Sternjaeger II

The Luftwaffe had an extensive testing of captured planes (they even bothered to install a DB601 on a Spitfire to check its performance!).

I suspect that they did this after an engine failure in order to make the best possible use of a rare captured airframe; there might also have been some political purpose (both internal, so that DB could demonstrate their good works to their masters) or external (IIRC they were quick to suggest that the DB engine was an improvement).

Originally Posted by Sternjaeger II

I found some literature of interest:

"Luftwaffe Test Pilot, Flying captured Allied Aircraft of World War 2" Published in German in 1977 and English in 1980. Author: Hans-Werner
Lerche.

Got it somewhere. It's interesting, though rather less technical than Brown's books. I seem to recall that quite a lot of emphasis was placed upon taking captured aeroplanes to German fighter squadrons so that they could see them up close. His observation that the B-17 was only fast due to its turbochargers is obviously correct, but of course all's fair in love and war!

I don't recall as much interest in tactical Mach numbers as was displayed by the Allies, because in the late war period the Germans often found themselves climbing into battle, whilst the Allied escort fighters were diving from on-high.

Originally Posted by Sternjaeger II

1. Strangers in a Strange Land Vol. 1 (Squadron Signal pub) by Hans Heiri Stapfer. Usually available on the web for
$ 10 - $ 15 used condition. A number of photos and color drawings are included as well as interesting discussions on specific aircraft that were captured.

2. Fremde Vogel unterm Balkenkreuz I have scanned photos from this book, but haven't been able to find a copy for sale.....it contains a number of photos of captured
aircraft in Luftwaffe service organized by country of origin. This book was published in the early 1980s I think.

3. Il Ricco Bottino (The Rich Booty) by Hans Werner Neulen. Excellent book on captured Italian aircraft in Luftwaffe service. around $ 18.

4. The Luftwaffe from Training School to the Front (Chapter 10) by Meyer and Stipdonk. Chapter 10 provides a number of photos of captured aircraft.

5. Foto Archiv Band 8. Although several Band in this excellent publication include at least one or two photos of captured aircraft..Band 8 includes by far the most with
several types I not seen elsewhere. You can order this one online at the following site:
www.stormbirds.com/flugzeug/ (http://www.stormbirds.com/flugzeug/)

Flugzeug magazine and Jet & Prop magazine, also available at this web address, have published excellent articles on this subject. Included are: Fiat G-12; Bloch SO 161;
Hopfner Ha 11/33; Brequet Br 521 Bizerte (2 parts); SM-75/SM 82; Rechlin September 1943 display; SE 200 etc.

6. Luftwaffe Fledglings 1935 - 1945. by Ketley and Rolfe. Although not exclusively about captured aircraft, this book nevertheless contains quite a bit of interesting
information, photos and drawings concerning captured aircraft used as trainers.

7. Modell Fan magazine ran a series of articles in the late 1970s and early 1980s entitled 'Sie Flogen mit dem Balkenkreuz' there were at least 13 or 14 articles in this
series, maybe more.

8. The Czech magazine REVI has published comprehensive articles by Igor Mrkvanek on captured Czech aircraft in Luftwaffe service. Very informative.

9. Flypast has published at least two very interesting articles on captured British aircraft in Luftwaffe Service.

10. Luftwaffe Codes, Markings and Units (Barry Rosch) contains quite a bit of information on captured aircraft organized by Luftwaffe unit. Some photos and drawings of
captured aircraft are included throughout the book.

11. The Luftwaffe Verband Journal has published several articles on aircraft evaluated at Rechlin or operated by Versuchsverband.

[Sternjaeger II]

Originally Posted by Viper2000

Having met the man a few years ago I must say that I found him convincing, and most impressive.

don't get me wrong, the man is a LEGEND! I met him last year or two years ago at Duxford and I was honoured to shake hands with him! but as you pointed below..

The biggest problem with his books is the fact that the typist doesn't understand engine power settings and therefore incorrectly converts between psi boost and ata throughout the text, littering it with parenthetical errors which were obviously absent from the original manuscript.

de facto making it an interesting read, but not quite the reliable reference that we need

Actually he illicitly flew it under power in 1945; see the latest edition of Wings on my Sleeve. He also tested a number of piston engined types post war, most notably the Ta-152 (albeit with neither MW50 nor GM1) and Do-335.

now that's interesting! I have the older version, bugger!
The thing that you point about the Ta-152 happened with other planes as well: the incorrect use (or lack) of fuels meant that they were more general handling tests instead of performance ones.

I suspect that they did this after an engine failure in order to make the best possible use of a rare captured airframe; there might also have been some political purpose (both internal, so that DB could demonstrate their good works to their masters) or external (IIRC they were quick to suggest that the DB engine was an improvement).

apparently it was just a genuine performance test to see whether they could improve the handling of their 109s, have a look at this interesting article
http://www.unrealaircraft.com/hybrid/spitfire.php

Got it somewhere. It's interesting, though rather less technical than Brown's books. I seem to recall that quite a lot of emphasis was placed upon taking captured aeroplanes to German fighter squadrons so that they could see them up close. His observation that the B-17 was only fast due to its turbochargers is obviously correct, but of course all's fair in love and war!

I don't recall as much interest in tactical Mach numbers as was displayed by the Allies, because in the late war period the Germans often found themselves climbing into battle, whilst the Allied escort fighters were diving from on-high.

this proves though that surely there are other tests that have been made and data has been collected, sourcing it is another story though..

[Viper2000]

Originally Posted by Sternjaeger II

de facto making it an interesting read, but not quite the reliable reference that we need

It's pretty easy to untangle the typographical errors because the conversions are in parentheses, obviously added by the typist after the fact. You can just ignore them and then it's all good. In any case, the conversion errors tend to be glaring - provided that you know roughly what the correct answer should be, it's pretty easy to weed them out.

The main advantage of Brown's test results is that they are internally consistent; it's the same guy flying all the aeroplanes, so you get a real comparison between aeroplanes rather than a comparison between pilots.

This is especially important when you come to consider handling, since it was strength limited in large parts of the envelope, particularly at high speed.

His tests of German aeroplanes are especially good because of course his German was good enough that he understood the captions in the cockpit, could interrogate pilots & ground crew, read manuals if available etc.. This means that there's considerably less risk of under-performance due to poor technique than might otherwise be the case.

Originally Posted by Sternjaeger II

now that's interesting! I have the older version, bugger!

I think that he decided that the statute of limitations had expired for the latest edition... AFAIK he just flew the thing for the heck of it, on the basis that the fuel was going to be disposed of and the aircraft scrapped, so why not? (Other than the obvious health & safety issues of course).

Originally Posted by Sternjaeger II

The thing that you point about the Ta-152 happened with other planes as well: the incorrect use (or lack) of fuels meant that they were more general handling tests instead of performance ones.

This sort of thing applies to all captured aeroplanes; you have to read the small print very carefully so that you know what you're actually comparing.

The lack of MW50 & GM1 doesn't necessarily fatally compromise the Ta-152 tests, since you can calculate the additional power which they would have provided and hence deduce what the maximum performance would have been. Of course, to do this properly you need to have enough other test data to infer the shape of the drag polar, but you only really need this information for a relatively narrow range of CL. It's really amazing how much you can deduce about aircraft performance from quite limited data. In fact, some people make careers of it.

For example, one of the main reasons for scrupulously fitting exhaust nozzle blanks to shiny new fighter jets when they're in the static park at an airshow is that if I know the nozzle throat area then an experienced observer estimate the engine thrust with rather better accuracy than the layman might expect.

In any case, the handling is generally more interesting than the kinematic performance, since it's far easier to calculate kinematic performance than it is to calculate handling characteristics, especially at transonic speeds.

[QUOTE=Sternjaeger II;281235]apparently it was just a genuine performance test to see whether they could improve the handling of their 109s, have a look at this interesting article
http://www.unrealaircraft.com/hybrid/spitfire.php

I think I might have come across this before at some point. The comparison argument is a strange one, because firstly it's irrelevant to combat, and secondly no two installations are alike in any case.

Since the Germans weren't stupid, my best guess is that:

1. They expected engine failure, and therefore opted to premptively replace the engine.
2. They realised that the Spitfire V was obsolete, but since they didn't have high performance fuel they couldn't investigate its development potential by over-boosting the engine; therefore the only way to investigate the aircraft's ability to handle extra power was to add the next generation of DB engine instead.

In the latter instance, this would imply that they were yet to capture a flyable Mark IX or XII.

It's worth noting that the RAE, with access to high grade fuels, took the former route with their early captured Fw190s, handily exceeding rated boost (and possibly rpm, though I'd have to check my copy of Wings of the Luftwaffe). I suppose this might technically be called the fly it like you stole it approach...

Originally Posted by Sternjaeger II

this proves though that surely there are other tests that have been made and data has been collected, sourcing it is another story though..

I have no doubt that the Germans collected vast amounts of data on a myriad of subjects, since that is their nature, but I suspect that a lot of it either went up in smoke some time in 1945 or else was carted off by one or other of the victorious Allies (most likely the USSR or the USA; the British mission essentially consisted of whatever Sir Roy Feddon could beg or borrow, and much of what he obtained was instantly stolen at gunpoint by the yanks...).

However, it's important to remember that the Germans were under no obligation to (for example) use the same standard atmosphere assumptions as us, or to test their aeroplanes according to the same methodology. So if you want to make a really satisfactory comparison it's not sufficient to just perform a unit conversion and overlay the data; you've got to actually drill down to find out what the assumptions underlying the test results were, and then correct everything to a common standard.

Otherwise it's apples vs oranges.

I think I went into this in my flight testing thread.

Hopefully in a few patches time, when things are sufficiently stable for serious testing, we will have amassed enough of this underlying information on assumptions to allow everything to be converted to modern ISO standard conditions so that fair comparisons can be made.

However, since I don't have a great deal of German data on test methodologies, German standard atmospheres and so on, I'm very much reliant upon the wider community to fill in the gaps.

[Kurfurst]

Originally Posted by Viper2000

I didn't claim that a Spitfire fighter was capable of Mach 0.89 in a controlled dive. You seem to have set the PR.XI Mach number up as a straw-man.

No straw man here, the PR.XI PR Mach number is just happens to be the most commonly referenced.

Originally Posted by Viper2000

But I have no reason to believe that it was unsafe to operate the aeroplane within its published envelope (i.e. the lower of 450 mph after position error correction, or Mach 0.85), not least because pilots tend to get quite vocal if aeroplanes scare them within the published envelope, and I also have no reason to disbelieve the tactical Mach numbers quoted by Eric Brown in his various books.

IIRC there may be some dive test data from a Spitfire IX showing a tactical limit of about Mach 0.83 out there somewhere. This would be fairly reasonable.

AFAIK the tactical limit for the Mustang is about 0.80, Thunderbolt about 0.72, Bf-109 and Fw-190A 0.75, whilst the P-38 was only ok to about 0.68. However, my books are at home; the numbers can be cross-checked in Wings on my Sleeve, Wings of the Luftwaffe, and Wings of the Weird & Wonderful.

What is a 'tactical limit'?

Basically I think the Mach 0.85 dive limit is arbitrary, ad hoc, ex stomach etc. - a bold guesswork that was set well before they would test the actual capability, just like many of the era's limits, though a bit bolder..

But, personally I believe the behaviour shown by fighter Mark IX BS 310 was certainly no greatly different - better or worse - than just about any WW2 fighter: controls functioned normally up to about .70 Mach, then all sorts of anomalies began to appear.. and at 0.815, there's already a longitudal pitching motion - and 0.85 is still rather far away..

[Viper2000]

Originally Posted by Kurfurst

No straw man here, the PR.XI PR Mach number is just happens to be the most commonly referenced.



What is a 'tactical limit'?

I'm using the nomenclature adopted by Eric Brown, which is that the tactical Mach number is the maximum Mach number at which the aeroplane may be used tactically, whilst the Critical Mach number is the maximum Mach number at which the aeroplane may be controlled. I am personally of the view that tactically in this context probably means offensively, because you can obviously frustrate an enemy's gun solution after having departed from controlled flight...

Obviously, with manual controls, both of these Mach numbers depend upon pilot strength.

Limits in the Pilot's Notes are there to protect the airframe and engine from harm, so they will tend to correlate more closely with what Brown would call the critical Mach number than with what he would call the tactical Mach number.

N.B. - This nomenclature is inherently confusing the aerodynamicists, who would tend to think of the critical Mach number as the lowest freestream Mach number at which sonic flow is seen around whatever shape they're examining. Therefore, for example, you can't look up aerofoil critical Mach numbers in Abbot & Doenhoff and compare them with flight test reports.

Originally Posted by Kurfurst

Basically I think the Mach 0.85 dive limit is arbitrary, ad hoc, ex stomach etc. - a bold guesswork that was set well before they would test the actual capability, just like many of the era's limits, though a bit bolder..

I am inclined to disagree, because Henshaw et al routinely conducted dive tests to the limiting CAS as part of their production testing at Castle Bromwich. This actually involved diving to 470 mph IAS because the instrument error was assumed to be 20 mph IAS. So there was no great shortage of knowledge as to the behaviour of the aeroplane at the placarded limits of its envelope.

Originally Posted by Kurfurst

But, personally I believe the behaviour shown by fighter Mark IX BS 310 was certainly no greatly different - better or worse - than just about any WW2 fighter: controls functioned normally up to about .70 Mach, then all sorts of anomalies began to appear.. and at 0.815, there's already a longitudal pitching motion - and 0.85 is still rather far away..

By Mach 0.70 a P-38 would already have departed from controlled flight...

I'd say that it's probably reasonably safe to place the tactical Mach number of the Spitfire at approximately 0.80, perhaps higher for the Griffon Spitfire due to its longer nose and correspondingly higher fineness ratio.

Additionally, comparison with the P-51D is interesting:

http://www.wwiiaircraftperformance.o...-divetest.html

http://www.wwiiaircraftperformance.o...-27-feb-45.pdf

IMO the Spitfire comes out of this comparison looking pretty good.

Originally Posted by Kurfurst

Do you have the rest of this report? It's interesting stuff.

Note, however, that it's a somewhat different animal from the PR.XI tests. The PR.XI tests were aimed at getting the highest possible Mach number on the clock. They therefore involved dives from about 40000', the maximum Mach number being reached at about 29000' with the aeroplane unloaded; recoveries were pretty gentle at about 2 g.

Meanwhile, your report appears to be an attempt to investigate the effect of Mach number upon CLmax; it talks about 5 g recoveries, which is pretty brave out at the edge of the envelope; the Mustang dive tests emphasise the risk of structural failure unless extremely gentle recoveries are made from high Mach number dives.

It's hardly surprising that the maximum Mach number at which you can really throw the aeroplane around would be lower than that which can be reached if gentle flying. I'm actually quite surprised that the Spitfire would tolerate this sort of handling at such high Mach numbers; there's no mention of rivets popping, things bending, breaking or falling off etc. I can't think of any other WWII fighter that would repeatedly tolerate >5 g at M>0.80 without complaint.

So I suppose that a lot of this stuff is in the eye of the beholder, but if I had to spend my time at the top right hand corner of the envelope for real in a WWII fighter then I'd pick a Spitfire to do it in.

The caveats regarding date collection in the report are important; it's quite hard to work out exactly what the uncertainties are with this sort of test. They might easily be as high as +/- 0.03 M.

In this respect the PR.XI data is better because an auto observer was used AFAIK, and of course the aeroplane was quite heavily instrumented and modified in other respects as well. So I'm quite confident that their quoted Mach 0.89 is +- a rather small error (though I don't make any particular claim as to the applicability of this figure to an operational aeroplane on a squadron, beyond the qualitative implication that the basic airframe was selected for dive tests by the high speed flight because it had the best high Mach number characteristics available off the shelf).

However, it's important to make the distinction between the uncertainty due to observational difficulties, those due to lack of instrumentation, and those due to instrument errors.

For example, if the ambient conditions (especially static temperature) aren't recorded, there might be a considerable error in Mach number due to differences between the test day and standard atmosphere conditions. Not much can be done about this, because even a couple of hours later the weather can and probably will have changed.

OTOH, it's much easier to go back a few weeks later and correct for instrument error by careful calibration of the instruments used during the test, and measurement uncertainly can be reduced by repeating the tests and applying statistics.

I point this out because there is a tendency for certain sections of the community to suggest that just because some reported dive is considered bogus (usually a combat report for their favourite aeroplane citing 600 mph IAS or something) that all dive testing is bogus. The reality was of course that it was merely difficult to get good data in the 1940s; serious flight test organisations could do it, whereas the average fighter pilot could not, because nobody had seen fit to give him the necessary tools to do so.

///

Tomcat et al, conventional elevators work by modifying the camber of the tail section.

Moving the relatively small control surface therefore affects the CL of the entire tail.

The force required to do this is set by the hinge moment.

At high freestream Mach number you get sonic flow over the tail. The control surface cannot affect the pressure distribution over the tail surface upstream of the sonic line. So the control effectiveness suddenly dramatically declines.

Since the control deflection was limited by pilot strength, the effect that the pilot perceives is a nose down pitching moment, because he's pulling as hard as he can, and the stick stays in the same place. But what's really happened is that the elevator effectiveness has declined, which is equivalent to reducing the absolute camber of the tail.

This means that high Mach number departure was often a 2 stage phenomenon. First the aeroplane starts wanting to pitch down due to shock formation on the wing changing the downwash angle over the tail. Then at some higher Mach number the effectiveness of the elevator fades away and the nose down pitching tendency gets worse. A lot of aeroplanes wouldn't really get into this second regime because they'd either break or start slowing down and getting into warmer air first.

Obviously, an all moving tail doesn't have this elevator problem because it just changes alpha rather than translating its lift curve slope with camber changes.

It has other problems due to the force required to actuate it, possible overbalance etc. But you can fix most of them by just throwing massive irreversible screwjacks at it, although it is advisable to combine this with Q feel so that the pilot doesn't inadvertently break the aeroplane when flying fast...

Yeager suggests that keeping the flying tail secret allowed the F-86 to have a technological lead over British and Russian aeroplanes of the period, but really this is an oversimplification because the idea of the all moving tail was not new. The rather more mundane reality is that getting the enabling technologies in the rest of the control system to work wasn't a trivial problem in the 1940s, and in Britain almost all of the funding for such work evaporated in 1945, whereas in America it kept on flowing. Meanwhile the Russians had slightly different priorities, but it's probably fair to say that the kill ratio achieved by the UN in the Korean war was probably more a function of pilot skill than aircraft performance differences (though the F-86 was superior at high Mach number, it was certainly far from perfect).

BTW, the first generation X-1 wasn't as clever as the M.52.

AFAIK the M.52 had no elevators and just moved its entire horizontal tail for pitch control "out of the box".

The X-1 had elevators for pitch and an all moving tail for trim (rather like a Bf-109, except that the X-1 moved the tail electrically, and the control was a coolie hat on top of the stick).

The elevators became ineffective somewhere in the transonic regime (0.9ish) and the workaround was to hold the stick still and control pitch with the trimmer.

I assume that the 2nd generation aeroplanes ditched the elevator...

Of course, despite its aerodynamic sophistication, it's not entirely certain that the M.52 would actually have been supersonic in level flight as drawn because this would have been asking an awful lot of its engine.

But now we're waaaaay OT.