Resolved. German jets were a waste of time and effort (1 Viewer)

[FLYBOYJ]

Hi Flyboy,

Thats right on the reason for the swept wings - but aerodynamic stability was also a factor IIRC, also it would have aided performance(?)

It did, but the designer stated the main reason was for CG considerations...

I don't thik the Me262 was maneuverable enough - not that it had to be IMO. When it got into fights with prop planes it was toast, unless it used boom-and-zoom tactics.

Nonsense - the Me 262 got into trouble on take offs, landings and trying to fight in the horizontal at speeds recips were operating at, again this boils down to tactics.

The armament had a very looping trajectory and short range, which I beleive were major flaws.

At what ranges and firing solutions?

When used to attack bombers, it performed well - but I think the guns let it down a little.

Woldermar Voight stated that one of the reasons why the 262 was picked over Heinkel was because of the guns and the design team choose the 262's armament very early in the program, again according to this interview in Arrow to the Future.

Axial flows have better performance, but centrifugals have advantages - toughness, for example.

As tough as axials could be, they are limited on how much they can put out were were eventually cast aside for aircraft. For helicopters they are perfect. Once construction methodologies were established the extra toughness was not worth the potential axials have in power and that's why they have been the standard for combat aircraft propulsion systems for over 60 years.

I think the main is, what was it? A heavy interceptor, in the vein of the Me110 (bomber destroyer), or a fighter? (like the Me109)

The Me 110 had dismal performance even as a bomber destroyer, it could barely get out of its own way and was not much faster than it's contemporaries. The Me 262 was able to and did compete with fighters, especially if you have someone who knew how to use its advantages and not fight the "recips fight."

From what you say, perhaps problems with early jets were inescapable and this threads hypothesis is correct?

No - it was an evolving new technology that was being rushed into service due to a major conflict. And even with those flaws in early jet fighters they did what they were supposed to do. Moving on with this technology was the right thing to do given the circumstances, that this includes all combatants.

I meant as a dogfighter - then, 20mm cannons might have been preferable (longer range, higher RoF and enough performance - the extra power of the 30mm being unecessary).

The 20mms might have been better as a dogfighter but at the same time the need was to take down bombers. Look at the armament of the MiG-15, it was designed for a similar role.

 

[Knegel]

Needed documents and the metric system? I don't know what you're talking about

I talk about to reproduce the 262 in england. Someone wrote "it dont got used, so it was useless", and i gave a hint why a plane itself dont got used, but still dont needed to be useless. Same like the other jet datas, mainly basing on the experiences with the 262 and 162.

The swept wings of the 262 and specialy of the 162 are clearly found to be an advanatge all over( no V wing angle needed anymore and a better high speed performence(both go particular hand in hand).

It took at least 2-3 years until the allieds did realise the advantage(after war), then all did jump onto the long time running train.

 

[FLYBOYJ]

I talk about to reproduce the 262 in england. Someone wrote "it dont got used, so it was useless", and i gave a hint why a plane itself dont got used, but still dont needed to be useless. Same like the other jet datas, mainly basing on the experiences with the 262 and 162.

The swept wings of the 262 and specialy of the 162 are clearly found to be an advanatge all over( no V wing angle needed anymore and a better high speed performence(both go particular hand in hand).

It took at least 2-3 years until the allieds did realise the advantage(after war), then all did jump onto the long time running train.

But again, that was not the main reason why the 262 had swept wings, all aside the allies realized almost immediately the advantages of the swept wings as the F-86 design team quickly incorporated this into the 86. With the XF-86 taking flight for the first time in October 1947, swept wings were incorporated into the design at least a year earlier,

 

[riacrato]

just fyi: the original me262 prototype only had the outer part of the wing swept back (further indication that high speed performance was not the reason for it?). later they continued the same angle on the part inside of the nacelles... to improve LOW speed handling. but nevertheless germans were aware of the advantages and the future projected versions of the 262 had more sweep for high speed purposes.

 

[GrauGeist]

...The swept wings of the 262 and specialy of the 162 are clearly found to be an advanatge all over( no V wing angle needed anymore and a better high speed performence(both go particular hand in hand).

The He162 didn't have a swept wing...

 

[schwarzpanzer]

Hi Flyboy,

So the Me262s failings were due to poor tactics? True, but I think the best tactic would be to just avoid dogfights - but thats not always possible?

I'm not sure of ranges, best I can get right now is this:

Although there were drawbacks with the MK 108, such as an insufficient flat trajectory (the shell "arced" too much due to the low muzzle velocity)

- From: Rheinmetall-Borsig MK 108 30mm cannon Luft '46 entry

and this:

The resulting low muzzle velocity was the MK 108's main shortcoming, with the result that its projectile trajectory was seriously affected by bullet drop after a comparatively short range—41 m (135 ft) of drop in the first 1,000 m (3,300 ft) of range. The long time of flight and curved trajectory strongly reduced the usefulness of the MK 108 against maneuvering targets like fighters; it was designed for use against bombers. Even against these, attacks had to be pressed home to close range, which was particularly challenging for fast fighters like the Me 262, which risked colliding with the target if their approach speed was too high.

- which is unfortunately from Wikipedia, and unsourced.

Woldermar Voight stated that one of the reasons why the 262 was picked over Heinkel was because of the guns and the design team choose the 262's armament very early in the program, again according to this interview in Arrow to the Future.

Was that just because they thought 30mm would obviously be better than 20mm? IIRC the Me262 prototype had MK103s?

I dont know much about helo engines, but its someting I wish to research. I always thought Centrifugals would suit the Mi-24.

Once construction methodologies were established the extra toughness was not worth the potential axials have in power and that's why they have been the standard for combat aircraft propulsion systems for over 60 years.

Centrifugals are easier though - for example, the Soviets couldnt grasp the Jumo 004, but got to grips with the Nene easily enough.

You make a good point on the Me262 being able to take on fighters, but I think this should not have been made a habit of?

I suppose then, that the question is, what shouldve been done with jets? I'm tempted to say 'testbench only', or at least spend more time there. Then bomber destroying only. Only later to be used as fighters ( recon before that). Dunno about bombers... Certainly not fighter-bombers though!

The 20mms might have been better as a dogfighter but at the same time the need was to take down bombers. Look at the armament of the MiG-15, it was designed for a similar role.

The Migs armament was flawed too - IMO the 37mm shouldve been dropped, as the 23mm was more than enough to deal with a B-29 (but maybe not a B-17).

 

[The Basket]

The only real fault with the Me 262 was it ran out of time.

The Gnat thing again...

remember in 1953, the RAF had to rush buy the Canadair Sabre Mk 4

The Gnat didnt fly until 1955 and if it was available earlier then maybe the Sabre would have been Gnats...

 

[FLYBOYJ]

Hi Flyboy,

So the Me262s failings were due to poor tactics? True, but I think the best tactic would be to just avoid dogfights - but thats not always possible?

Had they had the numbers, training and tactics available to them in in 1943, the Luftwaffe would have prevented the strategic daylight bombing of Germany from ever developing...

Was that just because they thought 30mm would obviously be better than 20mm? IIRC the Me262 prototype had MK103s?

Don't know - that was the comment from the designer of the aircraft.

I dont know much about helo engines, but its someting I wish to research. I always thought Centrifugals would suit the Mi-24.

That helicopter was one of the few exceptions

Centrifugals are easier though - for example, the Soviets couldnt grasp the Jumo 004, but got to grips with the Nene easily enough.

And as soon as they developed better axial flow engines they too cast aside centrifugal engines. As a matter of fact the only warsaw pack aircraft to be powered by a centrifigual flow engine in later years (after the MiG-17 and MiG-17) was the Czech L-29.

You make a good point on the Me262 being able to take on fighters, but I think this should not have been made a habit of?

It shouldn't have as it was the bombers they needed to deal with.

I suppose then, that the question is, what shouldve been done with jets? I'm tempted to say 'testbench only', or at least spend more time there. Then bomber destroying only. Only later to be used as fighters ( recon before that). Dunno about bombers... Certainly not fighter-bombers though!

Again hindsight is 20/20

The Migs armament was flawed too - IMO the 37mm shouldve been dropped, as the 23mm was more than enough to deal with a B-29 (but maybe not a B-17).

See above...

Actually the Soviets were also preparing to deal with the B-36 as well.

 

[vanir]

I think the USAF made it pretty clear to the Soviets that in any full scale conflaguration the Russians would be facing large numbers of heavily armed/escorted bombers over their home territories, it was the primary battle doctrine.

Also remanufactured Jumo's were used in the Yak-15 and progressive derivatives for the Yak-17 and 19, which the Russians seemed to have a fine handle on (they were noted for reliability, Yak-17 trainers remained in service into the 60's). The Nene base was chosen for the MiG-15 I think because of its altitude performance. Perhaps once fighters started using afterburners altitude just became a matter of airspeed, I suppose you can get more air through an axial more quickly than a centrifugal and have streamlining bonuses.

 

[Shortround6]

Shooting at 1000meters is a pipe dream. for a shell to drop 135ft it has to have time of flight of something over 2 seconds. In just over 2 seconds a bomber flying at 250mph will have moved over 750ft. A 350mph bomber will move just under a 1/4 mile in 2.5 seconds.

THe centrifugal vs axial compressor thing and it is compressors because the burner cans/combustion chambers aren't that different and the turbine sections aren't much,if any, different either.

The Centrifugal compressor was lighter (if fatter) and better understood at the time but the centrifugal compressor has pressure limits. About a 4 to 1 pressure ratio was good at the time for a single centrifugal compressor. at the time in question it took about 7-9 axial stages to get the same pressure ratio. the Axial compressor was obviously longer, if skinner, heavier and more difficult/expensive to make.

People have "stacked" axial compressors in jet engines and made two stage compressors but this means an even larger diameter or much longer engine as the air has to be routed from the outer edge of the compressor housing to the central inlet of the next stage.
Designers could stack more stages on an axial compressor easier. As more knowledge was gained about axial compressors and the pressure ratio of each stage went up the overall pressure ratio ratio of the compressor went up by leaps and bounds. While modern centrifugal designs have gotten a bit better there was nowhere near the improvement of the axial.
The pressure ratio is important because it is a good indicator of the overall efficiency of the engine. The higher the pressure ratio the less fuel is needed for a given thrust rating. Like high compression car engines give better gas mileage than low compression engines.
this also affects engine choice in aircraft. Helicopters need very light but powerful engines even if they are not the most fuel efficient. Since ranges are short (mostly) the combination of a light engine/s and a bit more fuel may be lighter than heavier more efficient engines with less fuel.
Most fixed wing aircraft need the more efficient engines because of their longer range or flight times. Amount of fuel carried can easily exceed the weight of the engines.
Some engines have combined the two compressors. Adding an axial stage or two or three is an easier way of upgrading an existing centrifugal design than adding an extra centrifugal stage or building a whole new engine.

 

[FLYBOYJ]

I think the USAF made it pretty clear to the Soviets that in any full scale conflaguration the Russians would be facing large numbers of heavily armed/escorted bombers over their home territories, it was the primary battle doctrine.

Also remanufactured Jumo's were used in the Yak-15 and progressive derivatives for the Yak-17 and 19, which the Russians seemed to have a fine handle on (they were noted for reliability, Yak-17 trainers remained in service into the 60's). The Nene base was chosen for the MiG-15 I think because of its altitude performance. Perhaps once fighters started using afterburners altitude just became a matter of airspeed, I suppose you can get more air through an axial more quickly than a centrifugal and have streamlining bonuses.

Agree

THe centrifugal vs axial compressor thing and it is compressors because the burner cans/combustion chambers aren't that different and the turbine sections aren't much,if any, different either.

Actually they were different in the way they were designed to accept airflow coming at them and this is from the fat single compressor. Centrifugal burner cans are generally longer and the turbine blades are more aligned with the longitudinal axis of the engine.

The Centrifugal compressor was lighter (if fatter) and better understood at the time but the centrifugal compressor has pressure limits. About a 4 to 1 pressure ratio was good at the time for a single centrifugal compressor. at the time in question it took about 7-9 axial stages to get the same pressure ratio. the Axial compressor was obviously longer, if skinner, heavier and more difficult/expensive to make.

People have "stacked" axial compressors in jet engines and made two stage compressors but this means an even larger diameter or much longer engine as the air has to be routed from the outer edge of the compressor housing to the central inlet of the next stage.
Designers could stack more stages on an axial compressor easier. As more knowledge was gained about axial compressors and the pressure ratio of each stage went up the overall pressure ratio ratio of the compressor went up by leaps and bounds. While modern centrifugal designs have gotten a bit better there was nowhere near the improvement of the axial.
The pressure ratio is important because it is a good indicator of the overall efficiency of the engine. The higher the pressure ratio the less fuel is needed for a given thrust rating. Like high compression car engines give better gas mileage than low compression engines.

true...

this also affects engine choice in aircraft. Helicopters need very light but powerful engines even if they are not the most fuel efficient. Since ranges are short (mostly) the combination of a light engine/s and a bit more fuel may be lighter than heavier more efficient engines with less fuel.

Because the turbine engine is not physically powering the helicopter (turbine engine driving either a direct shaft or a non coupled impeller) the loss of fuel efficiency is made up from the main rotors.

Most fixed wing aircraft need the more efficient engines because of their longer range or flight times. Amount of fuel carried can easily exceed the weight of the engines.
Some engines have combined the two compressors. Adding an axial stage or two or three is an easier way of upgrading an existing centrifugal design than adding an extra centrifugal stage or building a whole new engine.

And that's been the norm since the 1950s

 

[Shortround6]

Actually they were different in the way they were designed to accept airflow coming at them and this is from the fat single compressor. Centrifugal burner cans are generally longer and the turbine blades are more aligned with the longitudinal axis of the engine.

Different in detail but if a company/country could design one they could probably design the other and there shouldn't be any great difference in reliability or "ruggedness"

Because the turbine engine is not physically powering the helicopter (turbine engine driving either a direct shaft or a non coupled impeller) the loss of fuel efficiency is made up from the main rotors.

Not sure what you mean by this. while the main rotors may be a more efficient way of transmitting the power of the engine than direct jet thrust at helicopter speeds or lift it would be more efficient for both the centrifugal and axial engine types.

Basic point is that in the period between 1943 and 1947 or so the axial compressor was thought to better in theory but but people were having a hard time putting the advantages into practice so the centrifugal was a viable alternative. As the Axial improved in practice and fulfilled it's theoretical advantage it came to dominate the fixed wing arena.
But to base claims of superiority in 1944-45 on what the axial was capable of in 1950-55 seems a bit out of touch. I am not suggesting this last is your position FlyboyJ.

 

[FLYBOYJ]

Different in detail but if a company/country could design one they could probably design the other and there shouldn't be any great difference in reliability or "ruggedness"

For the most part true. There might l be some minor engineering and manufacturing issues that differ from the two engine configurations.

Not sure what you mean by this. while the main rotors may be a more efficient way of transmitting the power of the engine than direct jet thrust at helicopter speeds or lift it would be more efficient for both the centrifugal and axial engine types.

The lift generated by the rotors are more efficient than the kinetic energy coming from the engine, especially in helicopters like the A Star.

Basic point is that in the period between 1943 and 1947 or so the axial compressor was thought to better in theory but but people were having a hard time putting the advantages into practice so the centrifugal was a viable alternative. As the Axial improved in practice and fulfilled it's theoretical advantage it came to dominate the fixed wing arena.

Agree

But to base claims of superiority in 1944-45 on what the axial was capable of in 1950-55 seems a bit out of touch. I am not suggesting this last is your position FlyboyJ.

No but the potential was there, that's my point and designers knew it and its evident by such engines as the J35 and J47 that emerged in the post war years. The Brits developed some magnificent engines even though their axial flow engines served well in the post war years.

 

[red admiral]

Peak efficiency for the 004 compressor was 78% whilst for the Whittle types (W2 etc) it was 79%. Highest I'm aware of for the period was 86% for the Metrovick F2.

To get more power you generally need to increase diameter to get higher flow rates, which leads to very large diameter centrifugal engines like the dH Ghost.

Increasing pressure ratio to get reduced fuel consumption is relatively easier with axial compressors, adding more stages, but this leads to efficiency dropping off, surging, and stages stalling when starting. This leads into multi-spool engines. Adding centrifugal stages is simpler but reduces efficiency by around 4% each time because of the 180° turn the flow has to negotiate from the edge of the first compressor to the eye of the second.

Which is better? You need to look at a term called specific speed, which deals with the flow rate, pressure ratio and efficiency. For the fairly low power developed by the period engines, the centrifugal comes out better. The axial compressor isn't as efficient at low flow rates when small in size. Leakage around the tips is a real problem (not so much today with micro turbines with blisks 1" diameter spinning at 100,000rpm+).

 

[Shortround6]

The lift generated by the rotors are more efficient than the kinetic energy coming from the engine, especially in helicopters like the A Star.

this is quite true but my original position was that the axial type engine with it's lighter weight per shaft HP might be better suited for helicopter use than an axial engine even though it has a higher specific fuel consumption.
Both engine types get the benefit of the higher efficiency of the rotors.

This is a similar situation to WW I aircraft were the rotary engine competed against the inline water cooled. The rotary was much lighter per horsepower but used much more fuel per hp/hour. Which was better?

It depended on how long your planned mission was. 1 to 2 hr fighter mission (WW I remember or 4-8 hour bomber or flying boat mission.

 

[FLYBOYJ]

Which is better? You need to look at a term called specific speed, which deals with the flow rate, pressure ratio and efficiency. For the fairly low power developed by the period engines, the centrifugal comes out better. The axial compressor isn't as efficient at low flow rates when small in size. Leakage around the tips is a real problem (not so much today with micro turbines with blisks 1" diameter spinning at 100,000rpm+).

That sums it up right there

this is quite true but my original position was that the axial type engine with it's lighter weight per shaft HP might be better suited for helicopter use than an axial engine even though it has a higher specific fuel consumption. Both engine types get the benefit of the higher efficiency of the rotors.

This is a similar situation to WW I aircraft were the rotary engine competed against the inline water cooled. The rotary was much lighter per horsepower but used much more fuel per hp/hour. Which was better?

It depended on how long your planned mission was. 1 to 2 hr fighter mission (WW I remember or 4-8 hour bomber or flying boat mission.

Agree but in turbine helicopter considerations you're strapped with weight and engine size considerations and for the most part you're going to only need to extract just a portion of the energy from the engine, and even there you're still limited on how much energy you can take from the turbine and transmit to the main rotor shaft(s).

 

[drgondog]

The hairiest 'arcane art' in helicopter design teams is the Transmission (or in case of V-22 the Mixing box) Group.

Just the inherent 'probable' location of the helicopter engine (close to rotor shaft/cg of airframe) seems to always dictate an axial flow rather than centrifugal type engine...

 

[red admiral]

Just the inherent 'probable' location of the helicopter engine (close to rotor shaft/cg of airframe) seems to always dictate an axial flow rather than centrifugal type engine...

I'm not sure I follow that line of thought. Helicopter engines are pretty low powered giving fairly small engines compared to the size of the aircraft. Space isn't a big factor for hanging things on the outside.

Engine design is a complicated issue, one of the things raised here is the lower sfc offered by axial types. That only comes with higher pressure ratios, and then you need to increase temperature as well. IR signature is a major driver in recent designs. Helicopter engines are operating at much lower temperatures than contemporary turbofans. You could change the materials and cooling arrangements to bring about a couple of hundred hp extra (even quite a bit more than that in some cases) but IR signature balloons (radiation proportional to T^4).

Current operations in Iraq and Afghanistan require you to put a lot of sand and dust through your engine every time you touch down. Axials don't tend to like that very much and it's driving a lot of future requirements - as well as the power drop for hot/high operations.

That sums it up right there

Probably useful to point out that axials are more finnicky to manufacture as well. The UK was still having problems in the early 1950s manufacturing enough quality blades to limit axial production. The German wartime press/fold method leads to rather dodgy quality blades.

 

[DerAdlerIstGelandet]

Current operations in Iraq and Afghanistan require you to put a lot of sand and dust through your engine every time you touch down. Axials don't tend to like that very much and it's driving a lot of future requirements - as well as the power drop for hot/high operations.

We installed filters on our Blackhawks because of the and and particals flying into the engines. They worked fine...

We had 0 incidents or accidents or lost any aircraft because of engine problems or failure caused by the injesting of sand or particles.

 

[bobbysocks]

they learned a big lesson in desert ops and the effects of sand when they tried to rescue the us embassy hostages in iran...1979.