Last & Best of the Piston Engine Fighter Aircraft.

[J.A.W.]

In another thread, Tommy Cookers put forward the Martin-Baker MB 5 as an exemplar of the thread topic breed..

The MB 5 was powered by a R-R Griffon V12 SOHC 4V mill of ~36 litre capacity, this was one of the big 3 final Brit piston jobs.

Other fighter aircraft powered by the R-R Griffon included the Supermarine Spitfire/Seafire/Spiteful/Seafang sister types,
the Australian Commonwealth Aircraft CA 15 'Kangaroo' & the Hawker Fury - the latter both prototypes, like the MB 5.

The Hawker Fury, perhaps uniquely, also flew with the other two big Brit piston mills, the Bristol Centaurus & Napier Sabre.
The Hawker Fury prototype performed best ( naturally enough) when powered by the most powerful of 'em, the 3,000+ hp Sabre.

R-R's earlier, & smaller capacity ( 27 Ltr) V12 Merlin mill also powered several contenders, several of the lightweight P-51 variants, & the twin engined P-82 Twin Mustang/British DH Hornet long-range fighters.

There were US contenders, mostly powered by the big Pratt & Whitney R-2800 radial, such as the P-47, F4U, F8F,
& prototypes of the P-47 flew with the Chrysler V16 & huge P & W R-4340, the last also being tried in the Corsair..

[Tommy Cookers]

10 pre-production 4360-engined Corsairs were built, Cook Cleland got permission to buy one (for $1250) and so won the Thompson Trophy Race
he used 100 gallons of ADI, causing a cg position that gave huge problems early in the race
4500 hp for 41 mins, much of that in 5g turns
also it lost some races with induction explosions from slow combustion of special high-Triptane 1??/200 fuel

similarly the war-winning 8th AF Mustangs of course had severe cg issues from their use of rearward fuel tankage
so the Mustang was then produced with a longer fuselage so that the range could be used without flight limitations
and the lightweights were not produced, in part because they were all designed down to a lower structural strength (RAF 6g load factors)

many engines could be fiddled in flight for increased power, without involvement of ground crew
often the pilot was simply told to restrict his throttle movement to some 'book' reading on the manifold pressure gauge eg even at takeoff
in such cases there was apparently no discretion allowed, although the discreet concept of an overboosted takeoff did exist in some heads
and in other ways eg B-25 users said in dire situations they selected high blower at low altitude (the boost went off the 55" clock)
a US Mustang pilot has written of holding down the high blower (ground check) switch in flight at low altitude and getting a lifesaving 97"
(this switch was deleted in supplies to the RAF)
legitimately, some Allison engine was flown on ADI at 108" - '3 yards of mercury'

ground propellor adjustment to mandated rpm controlled flight power of the many unfiddleable (automatic boost controlled) engines
using only certified tachos
but mysteriously the squadron leader's plane always had a little extra power ?

fining-off the prop pitch ground-settings increased rpm and so increased power even under automatic boost control
and outside the auto regime (above rated altitude for the blower ratio) the rpm increase would increase the boost, further contributing to power
Don McVicar wrote about doing this with a Mosquito for the Bendix race

planes with turbochargers could easily be operated beyond the 'book' boost, and some have now written of this eg in P-38s

and the 'book' boost also varied with different fuel qualities where such were used
most early WW2 engines were made for 80/87 fuel, but 100/130 was soon available, (later 115/145 or sometimes 120/150)
so eg the absolute 'boost' could in principle be raised in proportion to these numbers eg by 130/87 times
ie some engines in use today can give far more than 'book' power simply by moving the throttle to give a boost higher than 'book'
unless or until the CHT becomes excessive, eg causing detonation
so the P&W Wasp 1340 was tested close to 1000 hp on 98 Octane c1935, the 'book' power being 550-600 hp
much later P&W rated one test model of the Wasp at 750 hp, then it reduced to 720 hp
the power taken by the supercharger increases, but much of this power is recovered as engine forward gas-pressure increases
and mep and in-cylinder power increases without increased frictional power
the racers before WW2 did this, they added TEL and had maybe 100/108 fuel
and flew by ear ie throttling up to the point of detonation - this being unmistakeable
as on occasion did many early WW2 pilots in the USAAC/USAAF (having no automatic boost control, unlike the USN/MC planes)
and the RAF flew sweeps across France in 1942 in Allison-engined Mustangs
when necessary they ignored the 62"? boost limit and went WOT - they officially reported seeing 75"


to takeoff and land in a practical distance all planes have wings that are too big for best speed in flight
the reason why most race-modified fighters had drastically clipped wings
as did non race-modified fighters ie the MkIII (rebuilt as MkXIIs) Spitfires (clipped much more than subsequent 'clipped' Spits)
ie the Spit was briefly being remodelled in emulation of the 109
later in WW2 plane designs were allowed more runway length, and jets were allowed much more runway length
so used 'smaller' wings (ie smaller relative to the aircraft weight)
one might think that their apparently better performance was due to this benefit (the Yak-3 designer maybe thought so)
(further, natural 'jet thrust' of piston engines exhaust can be up to 20% of prop thrust at 400 mph eg Corsair and 30% at 500 mph eg P-47J)
regarding wing size, there was debate before WW2, eg US air racers suggested that a fighter only needed 100 sq ft wing area
and Republic so design-studied the first AP-4 with Allison engine, also eg the P-46 had less wing than the P-40
Sir Richard Fairey said WW2 did not increase aircraft efficiency at all, presumably he had this factor in mind

[J.A.W.]

Here is a period appraisal of the M-B 5 from 'Flight' http://www.flightglobal.com/pdfarchive/ ... 02359.html

Perhaps it could've made a good racer, since the M-B design basics did rather resemble the race planes of the piston era.
Wing section appears a little dated - by comparison to the 'laminar flow' types then in vogue..
Interesting too that it utilizes a contra-prop set-up of M-B's own design too.

[J.A.W.]

While post-WW 2 airforces were jet-bent, & didn't want any new piston powered fighters, the last of the breed were still impressive performances, see here : http://www.flightglobal.com/pdfarchive/ ... 01660.html

Note the graph with the line marked 'standard Tempest 6' showing a speed of 418 mph at sea-level.
The Tempest with its Napier Sabre increasing boost from +9lb to +17lb enabled a sea-level speed increase of ~40mph..

The RAF flew its Tempests up 'til 1955 in the role of target tugs for realistic gunnery jet-fighter training exercises..
& then, unforgivably scrapped the whole bloody lot..

The final Hawker piston engine fighters were the Fury & Sea Fury, of which - some of the radial powered jobs survive.
Too bad Hawker themselves didn't hang on to their last & best, VP 207, shown here below:

http://www.aafo.com/hangartalk/showthre ... otypes-3-4

Tested in mil-spec trim to be capable of 457 mph at 8,000 ft ( Reno race height) it might've been a natural , as a racer..

[J.A.W.]

Check the fine aero-slick detail design of this rare P-51H Mustang, https://www.youtube.com/watch?v=HfPOVWOIL8M
- this the final production model, & a significant 'lightweight' revision.. running an ADI equipped hi-po factory Merlin.

At up to 90" ( +30lbs) boost in mil-spec WEP , for 2,200hp, it would do 400mph @ sea-level, & 428mph at 8,000ft (Reno race height),
- as performance was graphed here: http://www.wwiiaircraftperformance.org/ ... fig16a.jpg

[Tommy Cookers]

an outstanding read (some have this already, no doubt)
http://www.enginehistory.org/members/ar ... Sleeve.pdf

a reference book source that some have used shows Sabre VII ? rated as high as 3500hp/3850 rpm at 20" on ADI
comparison with the same engine at other pressures and with ADI suggest to me that it's a typo for 3300 hp or 3250 hp

to me the Tempest/Sabre is the BRM H16 car and eg the MB5 is the Lotus 49/DFV
the Spitfire rather skimped on stability for improved performance (ensuring startup orders when the Hurricane was already established)
the Hurricane, Typhoon, and Tempest had good stability (helping gunnery) and good control
the Fury/Sea Fury had reduced stability (shorter fuselage ?) and repairability, for improved performance
some test pilot school graduates and other opinion-formers lobbied for one approach, some for the other
lots of development was necessary to make Spitfire and Sea Fury stability and control acceptable (though Spit 21s were impossible)

ok one sort of lightweight Mustang (the H) went into production (about 500) for eg anti-kamikaze/V1 work, it was never used in war
as it was built to a lower (British) load factor it was left on the bench for the Korea war (unlike the old D and K)
(about 100 Spit 9s were lost with structural failures before control cable bobweights were used to increase stick force per 'g')
this H was 2' longer and had more tailfin, so could fly properly with the fuselage tank (unlike the D/K)
and an improved aerofoil - presumably that already from the start of P-63 and A-26
which in tunnel tests had more zero-lift drag, but actually gave less drag on real wings in real-world conditions
Lee Attwood said the (WW2 Mustang's) low drag was due to the radiator duct not the wing
some showed in WW2 that propwash turbulence anyway prevented the low tunnel-measured drag occurring on a real wing
also greater screen slope than on the Spitfire gave much less drag there (Bill Waterton said that vision for gunnery was an RAF obsession)
the race Mustang 'Beguine' ultimately had one wing clipped more than the other - to behave like stagger on an oval car
unsurprisingly in the race it crashed in a turn and killed a houseful of people, so that racing was banned

http://www.crazyhorseap.be/Mustangs/His ... 51H_02.htm

[J.A.W.]

T-C the 3,500hp take-off rated Sabre7 specs are listed in Wilkinson's 1947 tome, Aircraft Engines of the World, see here:
http://www.wwiiaircraftperformance.org/ ... _Sabre.pdf

Scroll down the list & you can see the steady increase in boost/power development, from +9lbs to +20lbs, as I noted, earlier.

That sleeve valve analysis article you cited requires a proper editing, as the author show some basic misapprehension when it
comes to engine construction technicalities, which results in flawed conclusions. Such as not appearing to comprehend why
a more powerful twin crankshaft 24 cyl mill will naturally weigh more than a V12 of lesser output, even if of similar capacity,
& even the basics listed in Bristol ads, such as no overhead valve gear to fettle, or leak & provide bulk & wear complexities.

That he also uses such non-technical terms as "one would suspect" in his ( incorrect) assumption that sleeve-ports will
offer lower flow efficiency than poppet valves, due to the "nozzle" effect, & missing the fact that the poppet head tends
to obtund flows in practice, tends to reduce the validity of his thesis..

The low-drag 'laminar-flow' wing ( which the M-B 5, lacked) was also used by the British Tempest/Fury & Spiteful/Seafang,
& as direct comparison with Typhoon/Spitfire using the same power showed, it was worth in the order of ~20mph.

The M-B 5 also required the same increase in tail/rudder surface area as the rest of the up-powered/long-nosed piston-engine fighters, but missed out on that low-drag wing/speed advantage.

The P-51H was not by any means 'fragile' compared to the earlier iterations, nor was it restricted in speed/manoeuvres, the reason the earlier D/K model went to Korea was basic logistics, given that several thousand of the earlier models were available,
& in the event, the total number lost in ops there, nearly reached the total number of H variants available, altogether.

The H model also had very little spares commonality with the D/K, & was still wanted by the USAF Strategic Air Command
for duty in Alaska where its long-range abilities to counter Soviet (B-29-type) Tu 4 incursions, was still unmatched by the jets of the day.

Edit: added cited article critique.

[J.A.W.]

Like the M-B 5, powered by the R-R Griffon - yet the high speed wing form of the Supermarine Spiteful gave more speed.
As noted here: http://www.flightglobal.com/pdfarchive/ ... 01321.html - the Mk XVI prototype made 408 mph at sea-level..

(& those wings were adopted for an unusal 'tail-dragger' jet the Attacker, which was good for 590 mph)..

[Tommy Cookers]

T-C the 3,500hp take-off rated Sabre7 specs are listed in Wilkinson's 1947 tome, Aircraft Engines of the World, see here:http://www.wwiiaircraftperformance.org/ ... .pdfScroll down the list & you can see the steady increase in boost/power development, from +9lbs to +20lbs, as I noted, earlier.

The low-drag 'laminar-flow' wing ( which the M-B 5, lacked) was also used by the British Tempest/Fury & Spiteful/Seafang,
& as direct comparison with Typhoon/Spitfire using the same power showed, it was worth in the order of ~20mph.
The M-B 5 also required the same increase in tail/rudder surface area as the rest of the up-powered/long-nosed piston-engine fighters, but missed out on that low-drag wing/speed advantage.
The P-51H was not by any means 'fragile' compared to the earlier iterations, nor was it restricted in speed/manoeuvres, the reason the earlier D/K model went to Korea was basic logistics

ok one could believe (or disbelieve) 3500 hp at 20 lb with ADI
belief suggests a response disproportionate to abs 'boost', maybe possible for reasons as I suggested earlier re the Wasp response to boost
the data is a compliation of multiple years
(interestingly including earlier model Sabre TO rating at 4000 rpm - and notes about automatic timing change with ADI on eg Sabre VIIs)
so what flew, when, and on what fuel at 20 lb ? ..... and .....
is 20 lb even available at heights above a sea level takeoff ie could 3500 hp ever have been used in combat ?
Lallemant wrote that inflight 'boost' had an air of mystery, and he only used it in combat once (in pursuit at low level)


the Tempest/Fury/Sea Fury aerofoil/wing was not the so-called laminar flow
ie its Cd at small AoA was not outstandingly low (as the Mustang's was)
like Spitfires the Tempest wing was a particularly 'aerodynamically thin' (very low t:c ratio) aft-loaded high-speed aerofoil (Spit's came from Republic)
very low t:c ratio gave, crucially, an unusually high critical Mach no. - which surely also means a lower drag coeff at high Mach than otherwise
the v low t:c ratio, despite the rather large root and midspan chord, rather limited spar depth

the Mustang wing was not 'aerodynamically thin'
its t:c ratio was not very low and so it allowed a deeper spar than the Spit's
its Cd at small AoA was outstandingly low (but deteriorated in service), ie it was fast at most altitudes
but its critical Mach no. was not as high - which surely also means a higher drag coeff at high Mach than the Spit or Tempest wing

simply, the Mustang wing had a lower critical Mach no. than a Spitfire wing (because this was thinner both aerodynamically and absolutely

the Spiteful/Seafang/Attacker wing was so-called laminar flow type and was found to have a lower critical Mach no. than the Spit's
so surely a higher drag coeff at high Mach than the Spit's

and I thought the M-B 5 used the Mustang type wing


T.O.No 1F-51D-1 says the 51D accelerometer safe to 8g @ design gross weight and ASI safe to 505 mph/Mach 0.77 ('g' suit standard)
what are the equivalent values for that thin-skinned 51H ?

btw the Bearcat was also designed around the anti-Kamikaze role (ie lower load factors)
its negative 'g' limit is rather low, and so structural failures have occurred in civil use (rolling etc)

[J.A.W.]

T-C, aero-engine 'rating' figures are established by type-test, scientifically, so whether you "believe" as such, does not enter into it.

If you wish to read the linked data, (which is obviously factory/Air Min sourced) relevant specifics such as - fuel type - are listed.

As for the measured relationship between boost/hp/speed gains shown graphically, here is an example from
earlier in Tempest development: http://www.spitfireperformance.com/must ... t-fig2.jpg
- compare with the chart in the article linked earlier above of the later Mk 6 , at +17.25lbs..

The ability of the Sabre to run hard was a major feature, appreciated by its pilots, such as F/O Ron Dennis, who with a
wingman ran his Tempest WFO for ~50 miles in hot pursuit of an Me 262 jet, before shooting it down, & he reckoned..

"The engine loved tough handling, & never objected to maximum revs or boost for extended periods."

His compatriot, top RNZAF ace & 122 Wingco flying, Evan Mackie agreed, saying:

" The harder you flew them, the better they went... they could be thrown around the sky like a piece of paper. "

& he'd turned down the opportunity to introduce the Meteor jet into the 2nd TAF, prior to war's end,
preferring the Tempest, (after trying the jet).
He also preferred the Tempest to the Spit, even though he had 800+ hours on them.

While the Spitfire used an earlier mid '30s NACA wing profile, ( & incidentally the US Navy F4U/F6F/F8F types
all used the same NACA profile as the FW 190) the Tempest/Fury used a "...special high speed section
developed by Hawker's, the thickness chord ratio at the root being 14% & at the tip 10%.
The maximum thickness is at 37.5% of the chord. The aircraft is thus able to fly & dive at very high speeds
without any adverse effect on stabilty or control" - ( Hawker factory specs).

USN aircraft designed for carrier ops are built to be robust enough, although the early F8F had a silly wing-tip shedding
feature incorporated ( & deleted when it proved fatal in practice), so I don't know what you mean exactly by suggesting that
"British" ultimate G-load factors were somehow "light", ( Tempest rated 13.9G, - quite robust) , perhaps you meant
constructional techniques, which in the case of the Spitfire, did need work to make the Seafire a practicable carrier plane.

The original Spitfires, even in the improved Mk XIV variant, were limited to Vne/diving speed of 470 IAS, & also did not
accelerate in the dive as quickly as the 109/190, let alone the US fighters, or the Typhoon/Tempest/Fury.

The Mustang did have a low drag wing, with its maximum chord set back (similar to the Tempest) & this was a major
contribution to being significantly faster, both in cruise & maximum speed than the Spitfire, indeed the Spitfire
required the fitting of the big Griffon V12 to keep pace, but even then could not cruise as fast as either P-51, or Tempest.

[J.A.W.]

Here are a couple of references from period 'Flight' mags that give some Sabre power/boost data, & in application.

http://www.flightglobal.com/pdfarchive/ ... 02284.html - this shows that 'combat' power, &
take-off power were close, & the relative ratio between boost increase & power gain, with various settings.

http://www.flightglobal.com/pdfarchive/ ... 01455.html - ADI installation on Tempest Mk 6.

AFAIR, Neville Duke, Hawker test pilot wrote something about flying the Sabre-powered Fury prototypes,
which even if unwanted by the jet-bent RAF, made for lively piston engine machines, none-the-less..

[Tommy Cookers]

......As for the measured relationship between boost/hp/speed gains shown graphically, here is an example from
earlier in Tempest development: http://www.spitfireperformance.com/must ... t-fig2.jpg
- compare with the chart in the article linked earlier above of the later Mk 6 , at +17.25lbs..

the Tempest/Fury used a "...special high speed section developed by Hawker's, the thickness chord ratio at the root being 14% & at the tip 10%.
"British" ultimate G-load factors were somehow "light" ?? ...... ( Tempest rated 13.9G, - quite robust)
The original Spitfires, even in the improved Mk XIV variant, were limited to Vne/diving speed of 470 IAS

where to start ?
the Spitfire wing was only 13% thick at the root and 6% at the tip - yes, too thin for any practical benefit but a landmark aerodynamically
and I have never said or implied that its drag (Cd) was lower than others except near critical Mach

on 5 Feb 1952 F Lt Ted Powles was in a PR19 doing a met flight from Hong Kong (ie had recording barographs and oat gauges etc)
at a true 51550' (tropical atmosphere) altitude entered an emergency descent due to failing cabin pressure and went beyond critical Mach
he recovered around 3000', official reconstruction of the flight apparently showed a peak tas of 690 mph and 0.94 Mach
(and of course W Cdr Martindale reached 0.89 Mach in research dives in a Spitfire X1 in 1944)
both were PR planes, ie no guns to degrade the aero or mechanical properties of the wings (and deeper noses maybe reducing transonic drag)
officially (an expert told me) a Spitfire went in at Dunkirk with a sonic boom, also did a P-47 in the US later, this according to the book 'Heelicopter'
lots of 109s went in also beyond their (lower) critical Mach, but afaik no boom was reported

the Spitfire was built to Specification No. F.7/30 - this called for load factors thus .....
6g with most rearward CoP, 4.5g at max speed horizontally, (-) 4.5 g inverted, and 1.75g in a tv dive
(as today, there would be a 50% margin on this before real structural failure)


the Sabre VII 3500 hp TO @ 20lb with ADI is definitely unthrottled MS gear and so unobtainable in flight eg at military rating height of 2250'
and unobtainable (and unuseable anyway by any prop) for TO as the plane's autothrottle is definitely set to 17.25 lb at sea level
at 2250' a max 17.25 lb is obtainable (unthrottled), giving the 3055 max hp that is always quoted even in enthusiastic forum posts

yes I can believe it (checking, other engines show a similarly disproportionate response to boost), but it's hard to explain all of the response
the TO 'ratings' seem rather exact multiples of 100s of hp - since the aircraft never ran unthrottled at sl are they really (flight) ratings as such ?

[J.A.W.]

T-C, Wilkinson defines the various ratings, such as:

"Take-off rating, or the maximum hp which is permissable to use at sea-level & at low altitudes."
&,
"Military (combat) rating, or the maximum hp which it is permissable to use for military purposes at low altitudes."

Obviously, the Sabre was strong enough to accept these ratings, whereas certain other engines could only accept
'unthrottled' maximum hp ratings at 'rated altitudes', albeit, some of this was a function of the supercharger set-up,
with the likes of US turbocharged aero-engines allowing a 'flat' or sea-level pressure/hp to be maintained up to high altitudes, if intakeair/detonation temps &/or cylinder head temps allowed for it.

The airframe too might have a bearing on take-off power settings, as shown in 'Pilots Notes' ,
& the Griffon Spitfires ( with a narrow track undercart originally designed for 1/2 the available power)
were capable of pulling the tyres off their rims with the torque application - if due care was not given.

The high Mach characteristics you noted for the Spitfire wing were incidental, & while many pilots survived
such out of control descents, some of the airframes were over-stressed & had popped rivets, others fell apart..

In any instance, it was of no use in combat, nor in racing, since the drag rise was too high for level flight,
& a long high dive was necessary, the Spit having a tendency to 'hang', while the 109/190s slipped away below.

The Mustang was ( unlike the P-38/P-47 which required 'dive flaps' to regain control in 'terminal' dives) quite
benign up to its limiting Mach, not 'tucking', but eventually reaching a structural failure vibration period.

Tiny test pilot Eric Brown relates doing research dives in a Tempest, reaching Mach 0.87 - whereupon the
strength required to pull-out nearly fatally exceeded his physical capability, but that the robust Tempest was unfazed..

The ability of the the Sabre to tolerate 4,000+ rpm in dives was another point, the Centaurus radial was not so forgiving..

[J.A.W.]

T-C, Napier also ran fairly sophisticated engine management systems for the day, while most big aero-mills ran fixed ignition timing,

Napier though, provided for both automatic fuel de-enrichment/ignition timing adjustment when operating ADI/high boost.

Obviously, more adventurous power-testing could be more safely done on the dyno' than in a single-engined aircraft,
but even the twin-engine Warwick flight test-bed got a lively ride, being pushed up to max allowable speed/ shedding its
fabric skinning under the urging of Sabre power.

Oddly, the Corsair retained a significant degree of fabric airframe covering too.

Here is the mil-spec test data for the Corsair powered by the massive P & W R-4360 'corncob' engine,
with 3,000hp at sea-level pushing it to 399mph (clean, but with fixed/capped ordnance pylons).
http://alternatewars.com/SAC/F2G-2_Supe ... Tommy).pdf

It was found that the later developments of the R-2800 engine fitted to the F4U-4/5 offered a better allround performance.

[Tommy Cookers]

.....Griffon Spitfires ( with a narrow track undercart originally designed for 1/2 the available power)
were capable of pulling the tyres off their rims with the torque application
The high Mach characteristics you noted for the Spitfire wing were incidental, & while many pilots survived
such out of control descents, some of the airframes were over-stressed & had popped rivets, others fell apart
In any instance, it was of no use in combat, nor in racing, since the drag rise was too high for level flight,
& a long high dive was necessary, the Spit having a tendency to 'hang', while the 109/190s slipped away below.
The Mustang was ( unlike the P-38/P-47 which required 'dive flaps' to regain control in 'terminal' dives) quite
benign up to its limiting Mach, not 'tucking', but eventually reaching a structural failure vibration period.
The ability of the the Sabre to tolerate 4,000+ rpm in dives was another point, the Centaurus radial was not so forgiving..

thousands of 109s etc trying to dive away from Spits didn't 'slip away', but went in, often without bullets being fired
and eg W Cdr Allen etc argued for Spits replacing the cannon with 6x.50cal and wing tanks for high cover of long range bombers
those high speeds were of course better survivable in a Spit than in anything else
and diving GCI attacks on V1s were viable, as were similar autonamous attacks by eg NF Mosquitos
(anyway by far the most V1s were shot down by the innovative use of proximity-fused predictor-directed AAA)


slower planes will break up in flight at quite slow speeds eg about 200 mph for eg the basic 2 seat light aircraft
this is speed(dynamic pressure)-related and independent of load (wings will flutter and break or the back end will break from excess stabiliser load)

our subjects won't, but reaching critical Mach means they will (typically) develop an uncontainable 'downwards' pitching moment
ie dive more steeply and go in (as did many 8th AF P-38s, causing the 8th via the range-limited P-47 to demand the Mustang and its Merlinisation)
this is Mach-related and relatively independent of dynamic pressure and load
some will be recoverable at low altitude as they will then be below critical Mach (Mach speed rising with temperature)
this applies to our airliners even today, of course
some of our subjects eg Tigercat and others, develop a large or uncontainable 'upwards' pitching moment (eg P-39 needed trimming into the dive)
so cannot be dived steeply, this is militarily disadvantageous, but 'safe'

officially permitted over-rev % of the Merlin (Spit 9) was 20%/3600 rpm, so that Sabre figure seems a low % (though fair enough in context)
the tyre problem (that I revealed) was a Mk 14 Spit problem, eliminated in subsequent Griffon Spits
afaik concussion bursts due to all the weight being on 1 wheel, not eg directional factors
many pilots spoke well of narrow gear (as easier to keep straight 'tail-up' ?), and certainly the Typhoon and Tempest were not docile on takeoff

as apparently I am the first person anywhere/ever to post about the 3500 hp appearing in 1 edition of Wilkinson's book ......
an absence of any pilot's notes etc seems to confirm that it was never released and official
also never released and official were the manual overboosts used successfully maybe a million times before everything was made automatic

the Sabres smaller bore and much shorter stroke would seem ideal for poppet valves (given the fuel quality revolution)
Sabre funding was maintained both to keep a sleeve-valve foot in the liquid-cooled door, and a reserve engine for the Vulture