Zyzygie’s Mumbles and Rambles

[swampyankee]

I think that for whatever the reason, high build quality for the Me262 was going to be the exception rather than the rule. As Koopernic says:

"...The other is airframe tolerances. If one wing is slightly different to the other it will reach critical Mach ahead of the other and cause stability issues. Precision and high tolerances is essential in jets as are airfoils that have a high critical mach."

Germany's use of maltreated, underfed slave labor did little to improve build quality, but treating the peoples of invaded countries well was contrary to nazi ideology.

 

[Kevin J]

Germany's use of maltreated, underfed slave labor did little to improve build quality, but treating the peoples of invaded countries well was contrary to nazi ideology.

I believe the top speed of the Me 262 ranged from 485 to 540 mph depending on build quality.

 

[Zyzygie]

I'll quickly handle your responses.
1 Galland was spending a lot of time flying combat missions in Me 262A1 fighters he championed. He was certainly not keeping an eye on development in the Me 262A2 bombers such as TSA 2D toss bombing sights or integration of radar based blind bombing he had strenuously argued against and that led to his demotion. He had a side to take and he is interested in finding and emphasising the worst. He was right at the time, wrong in the long run.

2 Neither the Meteor I nor the XP80A had air brakes. Split flap style Air Brakes were introduced with the Meteor III which entered service in Jan 1945 We had to wait for conversion from Welland to Derwent Engines, from the release of the Derwent from thrust restrictions and no less than two engine nacelle upgrades (more to come). for the Meteor to be combat ready The P-80A was much the same as the YP-80A which preceded it, differing only in minor details. The P-80A introduced under-fuselage dive brakes which opened forward at the wing join.

Hence Dive Brake, eg Me 410 style split dive brakes, could have been fitted to the Me 262 as they were to the P80 and Meteor. As it stands sustained dives of greater than about 20-25 degrees were probably problematic but this was within the capability of the TSA.

3 You said " The 'acceleration control valve' was never going to fix the engine problem. Carbon steel flame tubes and what is essentially stainless steel turbine blades were hopeless. I wouldn't go down the "if only" track. The Allies can do that too:

You realise that all of the data and information you are providing relates to the Meteor IV or Meteor F8. The Meteor IV missed the war entirely. It missed 1945 entirely. It didn't fly till 1946 and wasn't in service till 1947 (in Argentina not the UK). What the UK had at the end of the war was the Meteor III with nacelles modified yet again and derated Derwents. The speed was 495mph. Before the nacelles were modified speed was 480mph. After the war the derating was lifted and speed improved to 515. So by all means keep this entirely before May 1945 because the Me 262A1 will be 45mph or 72km/hr faster with 2-3 times the roll rate than the Meteor III.

I'm keeping it to developments which were running but had not seen service.

Below is the entry to the diary of the Chief Luftwaffe Technical Intelligence officer for March 16 1945. It says the accelerator cotrol valves were expected in early April 1945 which is 3 weeks before he was writing the diary and 6 weeks before the war ended.

KTB-TLR part 8
109 - 004 (ie Jumo 004, koopernic)
Vorschau am Monatsanfang 1000, am Monatsende 900, geliefert 876. (planed production previous month 1000, actually delivered 876, koopernic)

Mehrfache Forderung eines Einbaues eines Beschleunigungsventils, (= intensive expedition of accelerator control valve) welches die Aufgabe hat, unzulässige Überheizung des Triebwerks bei plötzlichem Gas geben zu vermeiden. (=which has the purpose of preventing impermisable overheating of the jet propulsion system during acceleration, koopernic) Einführung bei der Truppe und soweit vorhanden in der Serie bis Anfang April 1945 vorgesehen. (=Introduction to the troops scheduled in the begining of April 1945, koopernic)

Fehlen von Ersatzteilen 004 macht sich bei der Truppe störend bemerkbar. General Kammler befiehlt, daß Ersatzteile unmittelbar zum Klarmachen von Einsatzflugzeugen, ohne Rücksicht auf Serienbelange, zu liefern sind. (=Missing spare parts deliveries to the troops are notably disruptive, General Kammler inists that in service aircraft are to be prioritised)

Me-262: Future in light of engine development

Here some observations from Eric Brown:

Regarding the brakes he wrote on page 245 :"After lining up the aircraft on the runway, the engines were opened up to 8500 rpm on the brakes, and a check was made that the Zwiebel (onion), as the exhaust cone had been dubbed, was protruding from each orifice.

Full power of 8700 rpm was then applied and a quick check was made on the jet pipe temperature, burner pressure, and fuel pressure."

Regarding handling characteristics he wrote on page 252:" The normal range of flight characteristics from aerobatic manoeuvres to the stall revealed the Me 262 as a very responsive and docile aeroplane, leaving one with a confident impression of a first class combat aircraft for both fighter and ground attack roles. Harmony of controls was pleasant, with a stick force per 'g' of 2.72 kg (6lb) at mid-CG position and a roll rate of 360 degrees in 3.8 seconds at 645 km/h (400 mph) at 1525m (5000 ft)."

Regarding the 'snaking' he wrote that the German engineers managed it better to tame it, during the war, than i.e. Gloster engineers with the Meteor I, which had the same problems.

So we have, for the Me 262 a roll rate of 360 degrees/3.8 seconds or 95 degrees second at 400mph. This is quite fast, Faster than the very fast rolling P-51B/D which at that 400mph speed rolled at 85 degrees per second and faster than the 80 degrees second of the long wing Meteor F.4 (I am assuming the normal British/US practice of 60lbs stick force, I do not have short wing meteor F.4 roll rate). The Me 262 had a telescoping joy stick to allow more leverage of the joy stick. I've seen turn rate charts which show that Me 262 turned faster (in degrees/second) than the P-51 though the P-51 could still turn inside the Me 262.

The poor handing refers to snaking at 350mph IAS. At 25000ft 350 mph IAS = 305 knots IAS which becomes 457 knots TAS or 525 mph TAS!. Hardly an impediment considering the P-80, Meteor III barely reached this speed. I have variously heard that the onset of snaking was 460mph, 480 mph or that it could be cured by methodical trim tab adjustments.

In other words the Me 262 was 45mph faster than the Meteor III and rolled faster than the Meteor IV hence it was vastly faster than the Meteor III which was very bad in this area.

Manoeuvring begins with rolling. An Me 262 jumped by a Meteor III would use its superior roll rate to jink or out turn the Meteor and then use its speed to escape. About 50 seconds gets it 1000m away.

Note, the link https://apps.dtic.mil/dtic/tr/fulltext/u2/a800524.pdf you provided to an aircraft is clearly in bad shape. Its listed as having a maximum speed of 460mph. I think we can discount it.

4 "...The stabilizer angle could be varied with an electric motor activated by the pilot to provide rapid changes in trim with speed. This highly desirable feature was used on many later jet fighters. A deficiency in the aircraft was the lack of a speed brake, which is important for speed control in high-performance aircraft..."

Speed brakes are essential for jets. No argument there. However the Me 262 was useable without air brakes.

The proper solution to the Mach Tuck problem required some electronics. A Mach Meter needed to be installed with an electronic output. When the aircraft reaches critical Mach, say M0.8 the electric all moving stabiliser is progressively moved. For instance 0.1 degrees at Mach 0.81 and 0.5 degrees at Mach 0.85. This ensures the aircraft allways has enough pitch authority and also ensures the aircraft wont overstress as it slows down. These were in development.

Further to the engines the Germans had 4 relatively quick ways forward
1 the accelerator control valve to stop fuel overdosing
2 the Me 262 had thermocouples to measure EGT exhaust gas temperature. These thermocouples needed some electronics and to operate a bypass valve if the temperature became too high but also to damp down its rate of temperature increase. Easy for electronics to do.
3 the Jumo 004 had automatic control for the exhaust gas nozzle. Its purpose was to keep the pressure in the system (turbine, combustion chamber, compressor) approximatluy constant. It needed some improving.
4 duplex nozels to atomise fuel at low flow rates. A standard feature on the HeS 011 and planed for the Jumo 004.

The Me 262 does have a problem developing at the end of 1945 because both the US and UK are introducing 4000lb to 5000lb thrust engines. To this the Germans can answer only with 3000lbs.

Jumo 004B4 880kg (1980lbs)
Jumo 004C 950kg (2095lbs) some sources claim 1000kg
Jumo 004D (1030kg) 2270lbs) some sources claim 1100kg
HeS 011A 1300kg (2900lbs) (benching 1153kg in Feb 1945, meant to be ready for Ta 183 first flight in June 1945)
HeS 011B 1500kg
HeS 011C 1700kg

All these engines could be fitted to the Me 262
Development of an 1800kg/4000lb thrust Jumo 004H had started as a scaled down Jumo 012 with parts or mock-up beginning.

With some aerodynamic refinement eg the area ruling humps in my other post a 1945 Me 262 should be able to propel itself to 560mph Mach 0.85 and remain controllable as well as accelerate at high speed.

Many thanks for keeping it brief Koopernic.
I don't think I could have digested the full version...

Your deep conviction on the matter brought to mind aphorism #630 in Friedrich Nietzsche's "Human, All Too Human"...

 

[Zyzygie]

Re Galland and the idea of the "Schnellbomber," we'll have to agree to disagree. But Messerschmit seemed to think the ideal configuration for a bomber should be nearer the Meteor in terms of cockpit location:

Re the automatic throttle, you may be interested:

The German jets were extremely heavy, and hence had low thrust to weight ratios. This wasn't going to change with further development.

The proposed future development JUMO engines all had a thrust to weight ratio of 1.4 to 1. Half that of the Derwent V.

Re maneuverability:

The Meteor had a much higher service ceiling than the Me 262: 13,000 vs. 11400 metres.

 

[Snautzer01]

not to bad or as good ad the Fw190

 

[GrauGeist]

The German jets were extremely heavy, and hence had low thrust to weight ratios. This wasn't going to change with further development

The Jumo 004 series were heavy, others like the BMW 003A were lighter at 1,375 pounds with a max. thrust of 1,760 lbf., HeS8 at 838 pounds with a max. thrust of 1,300 lbf. and the HeS30 at 860 pounds with a max. thrust of 1,896 lbf.

 

[Zyzygie]

The Jumo 004 series were heavy, others like the BMW 003A were lighter at 1,375 pounds with a max. thrust of 1,760 lbf., HeS8 at 838 pounds with a max. thrust of 1,300 lbf. and the HeS30 at 860 pounds with a max. thrust of 1,896 lbf.

Very interesting. But unfortunately just more "if only" sagas. Also apart from the HeS 30, fairly low thrust to weight ratios:
"...Helmut Schelp, in charge of engine development at the RLM, refused to give Heinkel a production contract, an event Hans von Ohain claims brought Ernst Heinkel near tears. Schelp noted that while the design was excellent, BMW and Jumo were so far ahead they simply did not need another "Class I" engine – something that would prove ironic in another two years when both of those engines were still not operational. It also appears he had some misgivings about the compressor arrangement, but if this was the case it was never official. He also cancelled von Ohain's Heinkel HeS 8 at the same time."
"Instead of yet another Class I engine, Schelp asked Heinkel to continue work on a Class II engine of about 1,300 kg thrust, which would be needed for reasonably sized single-engine fighters, and as a useful addition to twin-engine bombers. Thus work on the HeS 30 and HeS 8 ended, and Heinkel turned, grudgingly, to the Heinkel HeS 011, which would not enter production before the war ended. The remains of Müller's team were then moved to the Heinkel-Hirth plants to work on the new engine..." Wikipedia

It looks like it held some promise, but never got beyond the prototype stage. We don't have any details of performance in combat conditions: What was it like in terms of durability? Reliability? Controllability? Specific fuel consumption? Surge resistance?

All of these were the Derwent's strengths.


JUMO bench tests - deterioration with time:

Creep was inevitable with the alloys they were using.

The development of Nimonic was crucial to making gas turbines practical:

Corrosion was also a big problem. Mild steel highly stressed and exposed to hot (~ 700C) oxidizing gas was not going to last long. That was medium cherry red hot.

 

[GrauGeist]

Very interesting. But unfortunately just more "if only" sagas. Also apart from the HeS 30, fairly low thrust to weight ratios:

However, the of the Jumo engine list you posted, only the 004, 004A and 004B were ever used the rest were either in the test phase or they were paper projects.

The HeS8 as not allowed to be developed, like the HeS30 and keep in mind that they didn't have remarkable thrust, but they weighed a fraction of a 004, greatly reducing the weight penalty.

The He280 performed remarkably well as a fighter with the HeS8 and would have been relentless with the HeS30...when they installed 004s on it, the He280 could barely get off the ground...

 

[Zyzygie]

However, the of the Jumo engine list you posted, only the 004, 004A and 004B were ever used the rest were either in the test phase or they were paper projects.

The HeS8 as not allowed to be developed, like the HeS30 and keep in mind that they didn't have remarkable thrust, but they weighed a fraction of a 004, greatly reducing the weight penalty.

The He280 performed remarkably well as a fighter with the HeS8 and would have been relentless with the HeS30...when they installed 004s on it, the He280 could barely get off the ground...

Hmmm... sorry, but this looks like another "if only" story:

"...The German Air Ministry eventually forced airplane makers towards the newer, more advanced HeS 011 series turbojet engine due to ongoing issues with the HeS8 and HeS 30 turbojet models. However, the advanced nature of this new engine was equally problematic for engineers. This is where pulsejets allowed at least some further development to take place regarding the He 280 prototypes. Similarly, the BMW 003 and Junker Jump 004 turbojets were options."

"Due to all of its inherent limitations, the Messerschmitt Me 262 "Schwalbe" twin-jet-powered fighter was selected ahead of the He 280 to become Germany's first jet fighter in the war. As such, the He 280 was canceled in full on March 27th, 1943, and Heinkel was forced to concentrate on German bomber production and development for the remainder of the war..."

https://www.militaryfactory.com/aircraft/detail.asp?aircraft_id=220

I note that the Germans were also working on a sort of hybrid centrifugal-axial engine? The Heinkel HeS 011.
It would be interesting to see what their rationale was there...

General characteristics

• Type: Turbojet
• Length: 3450 mm (11 ft 3¾ in)
• Diameter: 875 mm (34½ in)
• Dry weight: 950 kg (2,094 lb)

Components

• Compressor: Diagonal + three stage axial
• Combustors: 16 chambers
• Turbine: Two stage axial.

Performance

• Maximum thrust: 12.7 kN (2,900 lbf) at 11,000 rpm.
• Thrust-to-weight ratio: 1.29

Heinkel HeS 011 - Wikipedia

 

[Koopernic]

I believe the top speed of the Me 262 ranged from 485 to 540 mph depending on build quality.

Lockheed P-80 Shooting Star vs. de Havilland Vampire

Walter J Boyne's book "The Best of Wings" quotes Me 262 test pilot Gerd Lindner pilot as saying it could achieve 565mph at 16,400ft (that would have been 925kmh at 5000m). He was a professional test pilot, not a factory acceptance pilot or a fighter pilot. He's paid to be technically accurate. Smooth surface, maybe filled in, well aligned airframe, well aligned engines, good pair of engines.

Lindner also notes he nursed a pair of engines to 60 hours on the wing. The official Jumo MTBO was 25 hours and on the basis of spare parts production the Germans expected 4 x 25 hours life out of the engines. The Luftwaffe maintenance crews, the blackbirds were possibly pulling them early to be safe. It is also important to note that the more reliable hollow air-cooled blades of the Jumo 004B4 only reached the front in December 1944 or so and so air cooled blades were likely quite rare.

Poor Airframe build tolerances & quality was not due to the quality of the labour, which was quite capable, but the fact that Me 262 were being built in the open air in Forrest factory lines on wooden rails without jigs. The Jumo 004 also suffered from unauthorised martial substitution.

The 25 hour overhaul involved replacing the 6 carbon steel combustion chamber cans and the turbine. Turbine was to be inspected at 25 and run till 37.5 if ok, I thunk this was seldom done.

 

[GrauGeist]

"If only"?

The He280 was further developed than the Me262, flying under it's own power roughly two years ahead of the Me262 - it was the slow development of the engines (ALL makes) that plagued the jet fighter program.

The HeS8 and HeS30 were not allowed to be developed further like the 004 and 003 were - both of which were never fully developed by war's end and the HeS series were less problematic than the Jumo/BMW engines.

Instead of looking at their total thrust output, look closely at their Thrust to Weight ratio.
HeS8: 1.61
HeS30: 2.20
Jumo004B: 1.25
BMW003A: 1.13

 

[Zyzygie]

Note, the link https://apps.dtic.mil/dtic/tr/fulltext/u2/a800524.pdf you provided to an aircraft is clearly in bad shape. Its listed as having a maximum speed of 460mph. I think we can discount it.

I don't follow...

It gave a normal CRUISE speed of 465 mph?

As I read it, the maximum measured speed was 568 mph at 20,000 ft.

Hans Fey gave the following:

As for roll rate:

 

[Kevin J]

I don't follow...

It gave a normal CRUISE speed of 465 mph?

As I read it, the maximum measured speed was 568 mph at 20,000 ft.

Hans Fey gave the following:

View attachment 566422

As for roll rate:

View attachment 566423

IIRC, according to Kurfurst, the performance tolerance of new production German fighters at the end of WW2 was +-5%. So if median speed was 510mph then for Me 262, say 484-535mph, then a cleanup that you wouldn't do in the field should give you maybe an extra 5%. So max speed 562mph?

 

[Zyzygie]

Very interesting. But unfortunately just more "if only" sagas. Also apart from the HeS 30, fairly low thrust to weight ratios:
"...Helmut Schelp, in charge of engine development at the RLM, refused to give Heinkel a production contract, an event Hans von Ohain claims brought Ernst Heinkel near tears. Schelp noted that while the design was excellent, BMW and Jumo were so far ahead they simply did not need another "Class I" engine – something that would prove ironic in another two years when both of those engines were still not operational. It also appears he had some misgivings about the compressor arrangement, but if this was the case it was never official. He also cancelled von Ohain's Heinkel HeS 8 at the same time."
"Instead of yet another Class I engine, Schelp asked Heinkel to continue work on a Class II engine of about 1,300 kg thrust, which would be needed for reasonably sized single-engine fighters, and as a useful addition to twin-engine bombers. Thus work on the HeS 30 and HeS 8 ended, and Heinkel turned, grudgingly, to the Heinkel HeS 011, which would not enter production before the war ended. The remains of Müller's team were then moved to the Heinkel-Hirth plants to work on the new engine..." Wikipedia

It looks like it held some promise, but never got beyond the prototype stage. We don't have any details of performance in combat conditions: What was it like in terms of durability? Reliability? Controllability? Specific fuel consumption? Surge resistance?

All of these were the Derwent's strengths.


JUMO bench tests - deterioration with time:

Creep was inevitable with the alloys they were using.

View attachment 566376

The development of Nimonic was crucial to making gas turbines practical:
View attachment 566379
View attachment 566381

Corrosion was also a big problem. Mild steel exposed to hot (~ 700C) oxidizing gas was not going to last long. That was medium cherry red hot.
View attachment 566383

Myth Busting the Me-262 - Kaiserslautern American

Mythbusting the Me 262 - Kaiserlautern American

"The prototype Galland flew was powered by the first model of the Jumo 004, the Jumo 004A. This engine had been constructed with the highest quality materials available — notably nickel, cobalt and molybdenum — and as a result functioned reasonably well."
"Unfortunately, it was impossible to produce the Jumo 004A in large quantity because Germany did not have enough of these raw materials, and the production version, the Jumo 004B, was built with inferior materials."
"All of the "hot section" components were changed to aluminum-coated steel, and the turbine blades were also produced from different materials than those used in the Jumo 004A. The engine was easier to mass produce, but it was much less reliable and it required a complete overhaul every 10 hours. It also required delicate throttle movements in flight — difficult in combat."

 

[Zyzygie]

Junkers JUMO 004 B

 

[Zyzygie]

Gas turbine fuel flow control:

 

[Zyzygie]

IIRC, according to Kurfurst, the performance tolerance of new production German fighters at the end of WW2 was +-5%. So if median speed was 510mph then for Me 262, say 484-535mph, then a cleanup that you wouldn't do in the field should give you maybe an extra 5%. So max speed 562mph?

Hans Fey stated that they were only allowed 10-15 minutes at maximum speed.

Higher speeds than normal could sometimes be achieved but at the expense of overheating the engine hot components. Hence a correspondingly much higher risk of incurring catastrophic engine failure.

IIRC the engines were required to be overhauled if taken above full load for more than 10 minutes.

Extract from The Jet Race and the Second World War.

Extract from The Messerschmitt Me 262 Jet Fighter | Defense Media Network

The Me 262 Stormbird: From the Pilots Who Flew, Fought, and Survived It
By Colin D. Heaton

 

[Zyzygie]

 

[Koopernic]

Hmmm... sorry, but this looks like another "if only" story:

"...The German Air Ministry eventually forced airplane makers towards the newer, more advanced HeS 011 series turbojet engine due to ongoing issues with the HeS8 and HeS 30 turbojet models. However, the advanced nature of this new engine was equally problematic for engineers. This is where pulsejets allowed at least some further development to take place regarding the He 280 prototypes. Similarly, the BMW 003 and Junker Jump 004 turbojets were options."

"Due to all of its inherent limitations, the Messerschmitt Me 262 "Schwalbe" twin-jet-powered fighter was selected ahead of the He 280 to become Germany's first jet fighter in the war. As such, the He 280 was canceled in full on March 27th, 1943, and Heinkel was forced to concentrate on German bomber production and development for the remainder of the war..."

https://www.militaryfactory.com/aircraft/detail.asp?aircraft_id=220

I note that the Germans were also working on a sort of hybrid centrifugal-axial engine? The Heinkel HeS 011.
It would be interesting to see what their rationale was there...

General characteristics

• Type: Turbojet
• Length: 3450 mm (11 ft 3¾ in)
• Diameter: 875 mm (34½ in)
• Dry weight: 950 kg (2,094 lb)

Components

• Compressor: Diagonal + three stage axial
• Combustors: 16 chambers
• Turbine: Two stage axial.

Performance

• Maximum thrust: 12.7 kN (2,900 lbf) at 11,000 rpm.
• Thrust-to-weight ratio: 1.29

Heinkel HeS 011 - Wikipedia

The HeS 011 had a 4 stage compressors. Stage 1 is the interesting stage. It is often referred to as a diagonal flow compressor or a mixed flow compressor. On the surface it looks like a centrifugal radial compressor but the key difference is a carefully curved design that directs the outgoing air in the axial direction instead of radial. The air is directed on to a stator vane which achieves considerable compression. This is followed by 3 normal axial stages, an annular combustion chamber and a two stage air-cooled turbine.

The mixed flow (centrifugal/axial) first stage compressor ensured combat ruggedness and the ability to ingest turbulent air. Hence aircraft concepts with the HeS 011, such as the Me 262 HG III often are shown with the engines in the wing root area or even buried in the wing rood ingesting air through slits in the leading edges.

The first German jet engines not only had radial single sided compressors they had radial inflow turbines which are just radial compressors running in reverse. von Ohain chose these because they tend to self balance the compressor and turbine.

In order to keep the diameter down (which the von Heinkel and Ohain worried about more than Whittle Rover RR) von Ohain added a single stage fan ahead of the radial compressor (without stator). Because they couldn't get enough compression and airflow to achieve performance goals they started to add axial stages after the radial compressor. This eventually evolved into the HeS 011A.

Part of the reason was that although the German air ministry had bet on axial jets they wanted to keep developing centrifugal gas turbines.

 

[Zyzygie]

The HeS 011 had a 4 stage compressors. Stage 1 is the interesting stage. It is often referred to as a diagonal flow compressor or a mixed flow compressor. On the surface it looks like a centrifugal radial compressor but the key difference is a carefully curved design that directs the outgoing air in the axial direction instead of radial. The air is directed on to a stator vane which achieves considerable compression. This is followed by 3 normal axial stages, an annular combustion chamber and a two stage air-cooled turbine.

The mixed flow (centrifugal/axial) first stage compressor ensured combat ruggedness and the ability to ingest turbulent air. Hence aircraft concepts with the HeS 011, such as the Me 262 HG III often are shown with the engines in the wing root area or even buried in the wing rood ingesting air through slits in the leading edges.

The first German jet engines not only had radial single sided compressors they had radial inflow turbines which are just radial compressors running in reverse. von Ohain chose these because they tend to self balance the compressor and turbine.

In order to keep the diameter down (which the von Heinkel and Ohain worried about more than Whittle Rover RR) von Ohain added a single stage fan ahead of the radial compressor (without stator). Because they couldn't get enough compression and airflow to achieve performance goals they started to add axial stages after the radial compressor. This eventually evolved into the HeS 011A.

Part of the reason was that although the German air ministry had bet on axial jets they wanted to keep developing centrifugal gas turbines.

Sometimes contemporary turbines use centrifugal in series with axial compressors, but always put the centrifugal after the axial as it's more effective at the high pressure end. On the other hand, as you say, the centrifugal gave "combat ruggedness and the ability to ingest turbulent air." In a combat situation, straightforward technical considerations may be less important than resistance to damage from flying shrapnel or other loose battlefield material. The Russians have taken that very seriously, see Foreign object damage - Wikipedia
"...The Russian Mikoyan MiG-29 and Sukhoi Su-27 fighters have a special intake design to prevent the ingestion of FOD during take-off from rough airfields. The main air intakes could be closed with mesh doors and special inlets on the top of the intakes temporarily opened. This would allow enough airflow to the engine for take-off but reduced the chances of the engine sucking up objects from the ground..."