Zyzygie’s Mumbles and Rambles

[Koopernic]

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..."

Just a note as to why the first Whittle Engines had such a large diameter. Whittle was very concerned by shaft alignment and vibration and wanted the turbine disk and shaft fabricated in one piece. He was a very good engineer. Therefore he used double reverse flow combustion chambers to keep the distance between turbine and compressor short. This was the one idea von Ohain copied from Whititles patent thought he used an annular reverse flow combustion chamber for the HeS 003. When Rolls Royce became involved they got rid of the reverse flow feature to reduced the engine diameter and used their resources to ensure there was no shaft alignment issue.

The diameter issues disappeared by making outsized engine nacelles, as engines became more compact overall and of course the Americans fixed it by just putting a big engine inside the P80. In a way deHaviland did the same with the Vampire/Goblin.

In some photographs (Anthony Kay's book) has a photograph of a sort of bird cage basket over Jumo 004 engined intakes. These were to protect ground crew but it was found that flight was uneffected and combat missions were conducted with no effect on performance with the baskets on. They were flown in combat to protect against combat FOD. All up the Jumo handled intake disturbance better than they expected. Kay's book has a photo of a Jumo 004 with a 10ft stove pipe intake extension to simulate an air intake duct for the Messerschmitt P1011. It worked well with only 3% loss in thrust.

 

[Zyzygie]

German jet rivalry - Flight

 

[Zyzygie]

Just a note as to why the first Whittle Engines had such a large diameter. Whittle was very concerned by shaft alignment and vibration and wanted the turbine disk and shaft fabricated in one piece. He was a very good engineer. Therefore he used double reverse flow combustion chambers to keep the distance between turbine and compressor short. This was the one idea vin Ohain copied from Whititles patent thought he used an angular reverse flow combustion chamber. When Rolls Royce became involved they got rid of the reverse flow feature to reduced the engine diameter and used their resources to ensure there was no shaft alignment issue.

The diameter issues disappeared by making outsized engine nacelles, as engines became more compact overall and of course the Americans fixed it by just putting a big engine inside the P80. In a way Dehviland did the same with the Vampire/Ghost.

In some photographs (Kay's book) has a photograph of a sort of birdcage basket over Jumo 004 engined intakes. These were to protect ground crew but it was find that flight was uneffeced and combat missions were conducted with no effect with the baskets on. They were flown in combat to protect against combat FOD. All up the Jumo handled intake disturbance fairly well. Kay's book has a photo of a Jumo 004 with a 10ft stove pipe extension to simulate an air intake duct for the Messerschmitt P1011. It worked well with only 3% loss in thrust.

Further to ruggedness of military jets. An extract from Flight 1950:

 

[BiffF15]

"...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..."

I'm very familiar with the MiG-29s system to include the louvers on top of the fuselage (have fought these guys many times) however not the Su-27s version. Do you have any sources you could pass / post?

Cheers,
Biff

 

[Zyzygie]

The Swallow in the forest:

 

[Zyzygie]

The de Havilland Goblin of "hailstone gobbling"
fame:

 

[Zyzygie]

Graph of theoretical specific fuel consumption (SFC) vs pressure ratio relationship, superimposed with actual values for the Derwent and JUMO 004. The JUMO figure was probably affected by the need to bleed off some air for blade cooling.

Parasitical losses if you like.

 

[Zyzygie]

I'm very familiar with the MiG-29s system to include the louvers on top of the fuselage (have fought these guys many times) however not the Su-27s version. Do you have any sources you could pass / post?

Cheers,
Biff

Sorry Biff, only modeller sites seem to reference intake grills for the Flanker:

 

[Zyzygie]

Me 262 - new detailed original commentary, Clean film footage

 

[Zyzygie]

Allied jets of World War 2:

 

[FLYBOYJ]

Further to ruggedness of military jets. An extract from Flight 1950:

View attachment 566619

You've posted a lot of good links and information on here but having worked on a few turbine engines, I think the above comments about birds and being ingested into an engine and causing no damage is completely false. Back in the day there may have been some who "thought" no damage was sustained but then again there was little guidance to address these types of occurrences and what to do in the aftermath.

 

[Zyzygie]

You've posted a lot of good links and information on here but having worked on a few turbine engines, I think the above comments about birds and being ingested into an engine and causing no damage is completely false. Back in the day there may have been some who "thought" no damage was sustained but then again there was little guidance to address these types of occurrences and what to do in the aftermath.

This may be a case of "how long is a piece of string?" The question in this case is "how big is the bird."

"Patrick Smith, a US pilot and author of the book Cockpit Confidential, adds: "As you'd expect, aircraft components are built to tolerate such impacts. You can see web videos of bird carcasses being fired from a sort of chicken-cannon to test the resistance of windshields, intakes, and so forth." "

" "I've personally experienced several strikes, and the result was, at worst, a minor dent. When a bird flies, or is sucked into, the engine of a plane, the poor critter usually disintegrates. However, in incidents with larger birds there can be extensive damage to the engine..."

How common are bird strikes – and could they bring down a passenger jet?

I take on board your point that there may be no apparent damage on visual inspection, but when properly checked out with state of the art crack detection methods, it may be a very different story. Back in those days they didn't have the technology to do that.

 

[FLYBOYJ]

How common are bird strikes – and could they bring down a passenger jet?

I take on board your point that there may be no apparent damage on visual inspection, but when properly checked out with state of the art crack detection methods, it may be a very different story. Back in those days they didn't have the technology to do that.

Exactly - I would also go on to say that many of these early stories hardly ever follow up to say if the engine made TBO or what was found when the engine was finally torn down.

 

[Zyzygie]

F2 Meteor fitted with Metrovick axial jets.

"...[The Metrovick F2] axial flow jet first powered a Gloster Meteor in November 1943, outperforming contemporary models from Power Jets. In spite of this excellent start, it was considered unreliable and never saw use during the war. In the post-war era, a number of engines provided much higher performance, and interest in the F.2 waned."

"The potential of the engine and the investment did not go to waste, however; the design was passed from Metropolitan-Vickers (MetroVick) to Armstrong Siddeley when MetroVick left the gas turbine business. Armstrong Siddeley produced a larger version as the successful Sapphire..."

Wikipedia

 

[Zyzygie]

 

[Zyzygie]

Me 262 replica testing.

 

[Ascent]

I used to work on the RB199 in the RAF and if you were lucky something small like a sparrow going down the bypass instead of the core would do no damage. But even a small bird, even if it did no physical damage to the blades, could clog cooling holes on the turbine blades causing blade failure.

 

[Zyzygie]

Melancholia... Lacrimosa

 

[Zyzygie]

Early "tail dragger " Me 262 prototypes:

 

[Zyzygie]

The legacy of war


"...While in the United States the Boeing B-17 Stratofortress and the B-29 bombers were still assembled by riveting individual shaped sheet metal parts together, Germany made light and strong magnesium and aluminium structural components. To produce these components, the Third Reich engineers built a 33,000-ton hydraulic press and two smaller 16,500-ton machines to produce the first Messerschmitt Me 262 jet fighters. The latter two machines were requisitioned by the United States, while the first ended up in the hands of the Soviet Union. Fearing that this technological disadvantage would result in a military disadvantage, the US launched the Heavy Press Program with the intention of building the world's largest forging presses..."

The world's largest hydraulic presses | Gasparini Industries