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Gun Boat
28 Aug 12,, 12:09
This is just a what if. All the German jet felllows meet in a bar in 1936 and decide that jets are the way to go. Hitler and Goering love it. Several ships wash up on German shores with thousands of tons of nickel, cobalt, chromium and molybdenum inside which is reserved for Jet production. How ever it happens, it happens, and the Germans develop a serviceable engine.

Say Germany fields a full squadron of He-280s and they do very well over Poland. The Me262 is nearly ready to go. The Luftwaffe decide pistons are out and jets are in.

How do you guys reckon fullscale war would affect jet development? If the war managed to carry on to 45 as historical what aircraft would be lining runways around the world?

I think the US would get to at least the Sabre.
British have to get to the Vampire.
Russians would probably have the Mig 15 (I speculate they would start there jet program from crashed and captured german types?)
Germany would probably just stay with the 262 and maybe 229.
Do you reckon we would be seeing supersonic fighters after 6 of war time development?

gunnut
10 Sep 12,, 23:41
1. Germany would be impossible to bomb without exceedingly high casualties if those jets were used as bomber destroyers.
2. Germany may not control the space over the frontline because jets back then made great bomber destroyers but may not have been good dog fighters against mature piston engine fighters.
3. There would be a crash program to get allied jets in service. P-59 and Meteors might be mass produced and pressed into service.
4. We will not see Mig-15 or F-86 as they appreared in the late 1940s. They were based on swept wing technology developed by the Germans. If war had dragged on, then we wouldn't have that German research for these fighters.

TopHatter
11 Sep 12,, 00:00
Russians would probably have the Mig 15 (I speculate they would start there jet program from crashed and captured german types?)

The MiG-15 design, besides leveraging captured Me-262's and massive amounts of Germany's aviation industry, was successful only because of the Rolls-Royce Nene turbojet.

Gun Boat
11 Sep 12,, 03:32
How long would it take the allies to:
A) Be convinced that jets are now the way to go.
B) Put into service a large jet powered bomber.

Thats where I'm going with this scenerio. How quickly do the allies come into the jet age and how far do they commit? Do they remain with the piston powered
bomb trucks and surround them with jet powered escorts. Maybe even pushing through aerial refuelling?

Or develop a large jet bomber?

And does it create a bloodier air war? Does it consume more rescourses than historical (which might would break the luftwaffe sooner due to fuel and pilots)?

I think that come VE day the Allies would be facing off against the Soviets with a vastly superior airforce at hand, I really can't see the Soviets being able to
adapt to the Jet age as quickly as the allies.

USSWisconsin
11 Sep 12,, 03:43
The P59 was pretty lousy, no faster than the P51, it was only used for training. The P-80 would probably have been the front line US jet.

http://en.wikipedia.org/wiki/Bell_P-59_Airacomet


http://en.wikipedia.org/wiki/Lockheed_P-80_Shooting_Star


Here's a cool what if aircraft
Ryan XF2R Dark Shark - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/XF2R_Dark_Shark)

A Soviet Contemporary
http://en.wikipedia.org/wiki/Sukhoi_Su-9_(1946)

gunnut
11 Sep 12,, 04:43
How long would it take the allies to:
A) Be convinced that jets are now the way to go.

Jets were not the way to go for the allies back in 1943. They didn't have enough thrust for climbing. The engines didn't last too long before overhaul. Most importantly, they drank too much fuel.



B) Put into service a large jet powered bomber.

Thats where I'm going with this scenerio. How quickly do the allies come into the jet age and how far do they commit? Do they remain with the piston powered
bomb trucks and surround them with jet powered escorts. Maybe even pushing through aerial refuelling?

Or develop a large jet bomber?

Not gonna happen until the 1950s when jet engines became more reliable and less thirsty.



And does it create a bloodier air war? Does it consume more rescourses than historical (which might would break the luftwaffe sooner due to fuel and pilots)?

Jet engines drank more fuel, but they drank cheap crap, not the highly refined aviation gasoline. In a way, this would help Germany so the Panzers don't compete with Luftwaffe for gasoline (cheap gas is still gas).



I think that come VE day the Allies would be facing off against the Soviets with a vastly superior airforce at hand, I really can't see the Soviets being able to
adapt to the Jet age as quickly as the allies.

Western allies had vastly superior air power over the Soviets on VE day already. It wasn't until the Brits "lost" the Rolls Royce design to the Soviets, the Soviets smuggled out a sample of the alloy used to make the turbine blades, and combining with German swept wing technology, did the Soviets leap frog over the west in fighter tech.

The biggest difference that I can see is strategic bombing against Germany industrial heartland would be far more costly to the allies had German jets been used as bomber destroyers starting in 1943. This extra cost would make the allies hesitant to bomb Germany. More German resources would be available to the war effort, be it people, materiel, or production capacity. That in turn would mean more vehicles and soldiers on the frontline to fight the allies.

Germany would still lose. Could be 1947. Maybe even as late as 1948. But eventually Germany would be overwhelmed by the US industry. Quantity really has a quality all its own.

TopHatter
11 Sep 12,, 05:28
Germany would still lose. Could be 1947. Maybe even as late as 1948. But eventually Germany would be overwhelmed by the US industry. Quantity really has a quality all its own.

Indeed. In fighters alone, the U.S. produced nearly 100,000 machines, the Soviet Union another 63,000 and the U.K. nearly 50,000.

Germany's output was 55,000+

Gun Boat
11 Sep 12,, 06:51
Not gonna happen until the 1950s when jet engines became more reliable and less thirsty.

Do you think that the luftwaffe fielding jets early would push them to move quicker? i'm thinking 1941 luftwaffe almost exlusively jet in this little day dreaming what if.


Jet engines drank more fuel, but they drank cheap crap, not the highly refined aviation gasoline. In a way, this would help Germany so the Panzers don't compete with Luftwaffe for gasoline (cheap gas is still gas).

Didn't think of that. Would that allow the German sythetic fuel plants to produce more fuel due to not having to refine the product as heavily?


Western allies had vastly superior air power over the Soviets on VE day already. It wasn't until the Brits "lost" the Rolls Royce design to the Soviets, the Soviets smuggled out a sample of the alloy used to make the turbine blades, and combining with German swept wing technology, did the Soviets leap frog over the west in fighter tech.

Would the Soviets have feared more an allied jet airforce that completely out classed their own? Historically the Soviets may have dreamed that they were at least in the game in regards to their airfleet.


The biggest difference that I can see is strategic bombing against Germany industrial heartland would be far more costly to the allies had German jets been used as bomber destroyers starting in 1943. This extra cost would make the allies hesitant to bomb Germany. More German resources would be available to the war effort, be it people, materiel, or production capacity. That in turn would mean more vehicles and soldiers on the frontline to fight the allies.

Germany would still lose. Could be 1947. Maybe even as late as 1948. But eventually Germany would be overwhelmed by the US industry. Quantity really has a quality all its own.

Thats what i'm trying to work out. Whether or not the airwar would be completely different or if it would just be as historical except with jets instead of piston engined aircraft.

I'd say the big show would be the Battle of Britian. Using the historic production figures for Germany and converting those to Jets lets say that by January 1940 the Luftwaffe has around 1500 Jets adding another 4500 in 1940. (I just converted yearly production figures from wiki of fighters and twin engined bombers)

Thats a fairly decent jet force that is going to knock about the Brits and let them and the US that the jet age is here.

USSWisconsin
11 Sep 12,, 15:57
Range is still a showstopper at this point - these thirsty jets are ideal for defense - still lousy for long range attack - similarly, the Soviets aren't going to be too threatened by aircraft that can't reach their cities or even the rear of their deep defenses.

They would allow Germany to maul the Allied air campaign, and they would also help in the V1 attacks against Britain (if the UK had jets in the same fashion).

I don't believe anyone would need to capture the German aviation industry to figure out swept wings - a few captured aircraft and even pictures of the German aircraft would be enough to pick up on this idea.

TopHatter
11 Sep 12,, 17:37
Basically unless the Germans are able to render their airfields (and the approaches to same) relatively invulnerable, the same historical event will happen again: Roving squadrons of the hottest Allied piston-engined fighters will bounce Luftwaffe jets at their most vulnerable point.

USSWisconsin
11 Sep 12,, 17:45
Historically the Soviets may have dreamed that they were at least in the game in regards to their airfleet.

They had the Yak-3 which was in the game (late war Polish fighter squadrons preferred it over the P51 or the latest Spitfires) - it was just as good as the P-51 in combat (though it had range more equivalent to a Spitfire). The Soviet front line piston fighters and attack aircraft were formidable even at the end of WWII - though they were not generally long range aircraft like the P51 or P38.

gunnut
11 Sep 12,, 20:15
They had the Yak-3 which was in the game (late war Polish fighter squadrons preferred it over the P51 or the latest Spitfires) - it was just as good as the P-51 in combat (though it had range more equivalent to a Spitfire). The Soviet front line piston fighters and attack aircraft were formidable even at the end of WWII - though they were not generally long range aircraft like the P51 or P38.

They were formidable because they were powered by high grade avgas supplied by the US. :biggrin:

gunnut
11 Sep 12,, 20:32
Do you think that the luftwaffe fielding jets early would push them to move quicker? i'm thinking 1941 luftwaffe almost exlusively jet in this little day dreaming what if.

Probably. We could be looking at late 1940s for reliable jet engines there didn't need to be overhauled after 30 min of use. But they would still be thirsty and therefore limited in range.



Didn't think of that. Would that allow the German sythetic fuel plants to produce more fuel due to not having to refine the product as heavily?

In my uneducated opinion and guess, yes. Germany wouldn't have to refine so much avgas and the cheap kerosine could power their state-of-the-art jet fighters. More gas would be avaiable to the Panzer divisions.



Would the Soviets have feared more an allied jet airforce that completely out classed their own? Historically the Soviets may have dreamed that they were at least in the game in regards to their airfleet.

Jets were better as bomber destroyers back then, with their incredible speed at high altitude. Their acceleration and climb rate weren't that much better than piston engine fighters, sometimes worse. Their range was terrible. Allied jets wouldn't make it deep into Soviet air space.



Thats what i'm trying to work out. Whether or not the airwar would be completely different or if it would just be as historical except with jets instead of piston engined aircraft.

I'd say the big show would be the Battle of Britian. Using the historic production figures for Germany and converting those to Jets lets say that by January 1940 the Luftwaffe has around 1500 Jets adding another 4500 in 1940. (I just converted yearly production figures from wiki of fighters and twin engined bombers)

Thats a fairly decent jet force that is going to knock about the Brits and let them and the US that the jet age is here.

German jets would have the same problem as the Bf-109 in the Battle of Brittain. They lacked endurance to escort German bombers. They would be over southern England for about 15 min and then needed to turn around.

Early jets were better as bomber destroyers, not dogfighters.

They would wreak havok on the allied air offensive over Germany. First by making bomber lost rate too high to endure. Then when the escort fighters show up, making their lives much more difficult. German jets could just skip the fighters and make high speed passes at the bombers. German piston engine fighters could fly cover for the jets taking off and landing. Any allied fighter going after German jets during landing would have to expose itself to legacy fighters like the Bf-109.

Of course these are just my uninformed musings...

Stitch
11 Sep 12,, 21:38
Not gonna happen until the 1950s when jet engines became more reliable and less thirsty.

Just to back that up, the commercial aviation industry, which values range & efficiency for their aircraft above all else, were STILL using piston-engined airliners well into the '60's; not until the advent of the DeHavilland Comet/Boeing 707 were jet airliners practical enough to compete with piston engines in terms of range & efficiency.

Gun Boat
12 Sep 12,, 07:37
With the Luftwaffe fully committed to a jet powered airforce the allies will adapt.

Range doesn't seem to be an issue when you look at the 262 and Arado 234. Both around a 1000 miles. Although I think these ranges don't really reflect
what would happen in combat when the engines are pushed to their upper limits. I'd say a jet engine hanging around full power will use a great deal more fuel
than its piston brother. If you start adding drop tanks into the equation things look a lot better.

As far as the eastern front is concerned I would think the Luftwaffe would quickly adapt the slash and burn tactic (Hellcats did this to the Zeroes in the Pacific?)
ie make slashing attacks on the enemy formations and quickly climbing away. A single 30mm shell could mission kill a fighter and a few more would turn it into air borne
debri. But then you have to consider the types of airfields available. although I don't see this being a major hurdle to overcome.

As far as the allied bombing campaign is concerned I think the 8th would end up being pushed into night time area bombing runs with the Brits. I think that after a
few years, innovations would enable them to start hitting selected targets with a certain degree of accuracy.

How far forward can the B29, B36 and the B47 be brought forward in their development timelines? And what programs would the allies have to sacrifice to achieve this?

I'm certain that there would be a lot of captured material available to the allies, especially after BOB, that would enable the allies to quickly catch the Luftwaffe jet tech.

TopHatter
12 Sep 12,, 14:59
They were formidable because they were powered by high grade avgas supplied by the US. :biggrin:

A "reverse" of that case was the late war Japanese "hotrods" like the Nakajima Ki-84 "Gale", which managed 387 mph under Japanese wartime testing, but when high-octane fuel was added and tested by the U.S., it could do 426 mph!

Chogy
12 Sep 12,, 16:10
Don't forget the P-80 which was introduced in 1944. The P-80 proved to be an outstanding jet once the teething was over. I believe it could have held its own with anything Germany produced, especially when it came time for quantity production.

I still remember the T-33/P-80 actively flying at Tyndall AFB circa 1986, a testimony to the basic design.

Jet fuel is garbage stuff compared to avgas - just kerosene with additives. They can be modified to run on just about any crummy hydrocarbon, including fuels of vegetable origin. This would favor Germany, as the allies had plenty of high-octane avgas.

Stitch
12 Sep 12,, 18:22
As far as the eastern front is concerned I would think the Luftwaffe would quickly adapt the slash and burn tactic (Hellcats did this to the Zeroes in the Pacific?)
ie make slashing attacks on the enemy formations and quickly climbing away. A single 30mm shell could mission kill a fighter and a few more would turn it into air borne
debri. But then you have to consider the types of airfields available. although I don't see this being a major hurdle to overcome.

That's exactly what the Germans ended up doing; it took them a little while to develop effective tactics for the Me262, they simply had never flown anything that fast before. What they ended up doing is approaching bomber formations from the rear at high speed, too fast for the escorting fighters to catch them, and doing a "roller coaster" manuever before attacking the bombers from below and behind. They would have about two seconds to fire off a few rounds of 30mm before they had to peel away.



How far forward can the B29, B36 and the B47 be brought forward in their development timelines? And what programs would the allies have to sacrifice to achieve this?

The B-36 was actually designed very shortly after the B-29, and the initial plan was to have the B-36 operational by 1944 since there was a chance that Britain would lose the BoB, and we would need an intercontinental bomber to bomb occupied Europe. However, Britain survived BoB, the B-36 got put on the back burner, and the resources that were freed up were diverted to increased development and production of the B-29. So it's entirely possible the B-36 could've been operational by 1944-45.

kato
12 Sep 12,, 20:21
I want a few 10,000 Vampires in this.

zraver
12 Sep 12,, 23:18
By 1946 without the input of German engineering, GE had modified the Whittle into an axial flow engine that would see military service into the 1960's (J35 turbojet) and the immediate follow on the J47 turbojet introduced in the late 40's flew till 1978. While early US jet engines were not fuel sippers by modern standards, they were much better than German engines and US airframes also tended to be larger with more on board fuel.

The Me-262 generated just under 4000lbs of thrust on 2 engines which weighed a total of 3284lbs and the plane weighed a max of 15,720lbs with a top speed of 559mph, a rate of climb of 3900 feet/min and a range of 1050 miles. The P-80 with 1 engine which weighed 1790lbs generated 5900lbs thrust and the plane itself was 1850lbs with a maximum speed of 600mph, and a rate of climb of 4580 feet/min and a range of 1200mi.

zraver
13 Sep 12,, 03:26
if Germany had pushed jet interceptors early and in larger numbers,the massed bomber fleets would be out the window until allied jet escorts and bombers like the B-36 were available. This would in turn leave the Luftwaffe's legacy fighters free to remain in the East. It also means Overlord is on hold for at least another year which means very bad things for the Soviets who need a gutted Luftwaffe to make truly large gains like they did in Bagration. If the German's have another year of plentiful panzer reserves in the east and good air cover plus another year of increased production the balance tips against the Soviets and tilts very much towards stalemate. How this impacts the West-Soviet alliance is up in the air.

However, once the P-80 and B-36 do arrive, and with Japan already finished and the US fielding nukes Germany's odds plummet. US production and the generally superior P-80 means the Luftwaffe's jet fighter force is in a bind. They will know that a lone bomber can kill a city which means they have to get every lone bomber, every solo recon plane because they won't know the specifics of the bomb itself. Will it fit in a Douglas invader or Mosquito? Can the B-36 fly higher than the German radar can detect? Did a nuclear armed bomber leave a conventional bomber stream in the middle of a cloud of window foil?

Its also a political problem for the Nazi regime. If a bomber gets through and nukes a city the natural Nazi impulse and need for a scapegoat will demand high ranking officers heads. But, throwing various generals under the bus will weaken the loyalty of the military to the regime, especially if the generals figure its all over but the crying.

Chogy
13 Sep 12,, 15:22
The XP-86 was on the drawing boards around 1945 or so, although in a non-swept variant. Assuming North American aerodynamicists acted upon battlefield intel and possibly shoot-downs of the swept Me-262, and adopted the wing sweep, the F-86 could have been flying over Europe by late 1946.

After WW2 ended, the immense pressure to speed up development ended, and the original XP-86 flew in 1947. Sped up, I think they could have deployed it before that date.

The NACA and other development agencies in the USA were not slouches when it comes to advanced aerodynamics. They developed the NACA radial engine cowling shapes that permitted the draggy radial engines to not only match, but even surpass, inline engines when it came to drag. The cowling and airflow actually created thrust, much like the radiator of the P-51 added something like 300 lb of thrust to the system.

With the F-86 over Europe, the USA would have a world-beater, assuming the war went on that long. While Germany has traditionally been viewed as a leader in aerospace development in the war years, I think that has been overstated, and too much emphasis placed on post-war German data.

gunnut
13 Sep 12,, 18:33
You guys are assuming the Germans were standing still. They would have follow up designs to the Me-262 as well, just like we had the P-86 after the P-80.


The NACA and other development agencies in the USA were not slouches when it comes to advanced aerodynamics. They developed the NACA radial engine cowling shapes that permitted the draggy radial engines to not only match, but even surpass, inline engines when it came to drag. The cowling and airflow actually created thrust, much like the radiator of the P-51 added something like 300 lb of thrust to the system.

Can you elaborate on that? I never understood how that extra thrust worked or where it came from.

Stitch
13 Sep 12,, 18:55
The caveat to that is the Germans also had some pretty advanced designs in the pipeline, although I'm sure most of them weren't very practical from a production standpoint. One of the more advanced designs that may have caused the Allies some real problems was the Horten Ho 229, commonly called the Go 229, a flying-wing design with a top speed of 607 mph and a service ceiling of 52,000'; assuming the Germans could've come up with a reliable powerplant for it (the Jumo 004 only had a service life of about 25 hours on a GOOD day!), it would've been a real thorn in the Allies side, especially against bombers.

zraver
13 Sep 12,, 22:28
You guys are assuming the Germans were standing still. They would have follow up designs to the Me-262 as well, just like we had the P-86 after the P-80.



Can you elaborate on that? I never understood how that extra thrust worked or where it came from.

Hitler's interference only delayed the Me-262 program for a few months, the real hangup was the redesign of the Jumo 004 to use less strategic materials and not blow apart in testing due to vibrations. The 004 wasn't ready for full scale production until early 1944. Assumign we speed every thing up by a year and get rid of Hitler's micromanaging late 43, early 44 is when we could expect to see squadron service but only in limited numbers, not enough to stop the bomber streams, but enough to alert the allies. However by the middle of 44 there might be enough jets to shut the bombers down and cancel Overlord.

TopHatter
13 Sep 12,, 22:45
You guys are assuming the Germans were standing still. They would have follow up designs to the Me-262 as well, just like we had the P-86 after the P-80.


The caveat to that is the Germans also had some pretty advanced designs in the pipeline, although I'm sure most of them weren't very practical from a production standpoint.

The problem with the German designs wasn't one of sufficiently advanced design. In fact Stitch touched on it already: It was putting them into full-scale production in sufficient numbers.

There was also the bane of many German weapons of the war: Over complex and difficult to maintain in the field.

Next, you've got craftsmanship. How many weapons systems were sabotaged by the slave labor that Germany had to resort to?

Then there's lack of high-quality strategic metals like zraver mentioned.

Finally you've got the penchant of the Third Reich for over-duplication of effort and rivalries between companies, which only hindered design and production.

USSWisconsin
14 Sep 12,, 00:07
You guys are assuming the Germans were standing still. They would have follow up designs to the Me-262 as well, just like we had the P-86 after the P-80.



Can you elaborate on that? I never understood how that extra thrust worked or where it came from.

Some cowling designs had a cooling fan, which could add some modest thrust. The venturi effect also increased the outlet velocity.

Gun Boat
14 Sep 12,, 01:17
A "reverse" of that case was the late war Japanese "hotrods" like the Nakajima Ki-84 "Gale", which managed 387 mph under Japanese wartime testing, but when high-octane fuel was added and tested by the U.S., it could do 426 mph!

What did they do to the engine to achieve that? I'm pretty sure that simply feeding higher octane fuel to an engine designed to run on low octane fuel will show little or no difference in output. You either have to
raise the compression ratio or advance the ignition timing.

zraver
14 Sep 12,, 01:47
What did they do to the engine to achieve that? I'm pretty sure that simply feeding higher octane fuel to an engine designed to run on low octane fuel will show little or no difference in output. You either have to
raise the compression ratio or advance the ignition timing.

High octane= more resistant to detonation but less power per volume. This means you can turn up the boost on the supercharger/turbo (manifold pressure) and generate a lot more power.

Chogy
14 Sep 12,, 15:40
Can you elaborate on that? I never understood how that extra thrust worked or where it came from.

Any time you take compressed air, add heat to it in any form, either radiator (liquid cooled) or cylinder heads (radial engine), then allow it to expand aft, you create a crude form of carnot cycle. (http://en.wikipedia.org/wiki/Carnot_cycle) Wikipedia has a decent entry on the NACA cowl. (http://en.wikipedia.org/wiki/NACA_cowling)

Gun Boat
15 Sep 12,, 18:30
How the bloody jebuz do you just 'turn the boost up' on a Japanese fighter powerplant? Did the Japanese fighters have that level of adjustment built into them or what? If the engine is over-boosting and is equiped with a waste gate I can unstersand. But I'm pretty sure the Japanese motors were tuned to run on the fuel available.

You turbo-supercharge any engine you have to set the comp ratio to facilitate the given boost. There is very little adjustment available once the comp ratio is set. Not trying to argue, but fair dinkum, for that Japanese engine to put out an additional 40mph there would be a lot of re-tuning required.

I've just been to an over 28s nightclub. And also watched the pies beat west coast. I'm excited and possibly a little er-neeb-re-ated. Love you. But still, boost, compression, Bigfella is a lefty. Love you.

Gun Boat
15 Sep 12,, 18:39
Uh oh. Out of line. Please let the ban be swift and short... Sorry.

USSWisconsin
15 Sep 12,, 19:06
These fighter aircraft engines were normally supercharged to achieve good performance at higher altitudes - yes they may have needed to do some tuning to increase the boost - though it might have been a fairly simple adjustment, since they would normally run less boost at low altitude and increase it at higher altitude, cylinder head temp was an indicator of how much pressure the engine could take.

They wouldn't have needed to change the static compression of the engine. Many Japanese engines were derived from American designs and probably had similar supercharger controls. Water-Methanol injection was another way to to support increased manifold pressure, many WWII aircraft used this too (it had limitations due to the supply of water methanol mixture - the methanol served primarily as an antifreeze, since pure water would freeze up at altitude).


Two-stage and two-speed superchargers
In the 1930s, two-speed-drives were developed for superchargers. These provided more flexibility for the operation of the aircraft, although they also entailed more complexity of manufacturing and maintenance. The gears connected the supercharger to the engine using a system of hydraulic clutches, which were manually engaged or disengaged by the pilot with a control in the cockpit. At low altitudes, the low-speed gear would be used in order to keep the manifold temperatures low. At around 12,000 feet (3,700 m), when the throttle was full forward and the manifold pressure started to drop off, the pilot would retard the throttle and switch to the higher gear, then readjust the throttle to the desired manifold pressure.

Another way to accomplish the same level of control was the use of two compressors (also known as stages) in series. After the air was compressed in the low-pressure stage, the air flowed through an intercooler radiator where it was cooled before being compressed again by the high-pressure stage and then aftercooled in another heat exchanger. In these systems, damper doors could be opened or closed by the pilot in order to bypass one stage as needed. Some systems had a cockpit control for opening or closing a damper to the intercooler/aftercooler, providing another way to control temperature. The most complex systems used a two-speed, two-stage system with both an intercooler and an aftercooler, but these were found to be prohibitive in cost and complicated. In the end, it was found that, for most engines, a single-stage two-speed setup was most suitable.
Supercharger - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Supercharger#Two-stage_and_two-speed_superchargers)

Gun Boat
15 Sep 12,, 19:32
So 'two speed' superchargers means that they're geared right? I've never fully understood how that works. When you engage the 'second stage' do you infact change gears in the supercharger? And does that involve a clutch of some sort or is it up to the pilot to judge the change and 'mesh' the cogs?

USSWisconsin
15 Sep 12,, 19:47
Yes, they were centripetal types (normally on the back of the engine) with planetary gear drives and clutches - they were shifted by the pilot or by automatic controls on some more advanced engines. We had a cool cutaway P&W R2800 in Madison - it was very impressive.

zraver
15 Sep 12,, 22:13
How the bloody jebuz do you just 'turn the boost up' on a Japanese fighter powerplant? Did the Japanese fighters have that level of adjustment built into them or what? If the engine is over-boosting and is equiped with a waste gate I can unstersand. But I'm pretty sure the Japanese motors were tuned to run on the fuel available.

You turbo-supercharge any engine you have to set the comp ratio to facilitate the given boost. There is very little adjustment available once the comp ratio is set. Not trying to argue, but fair dinkum, for that Japanese engine to put out an additional 40mph there would be a lot of re-tuning required.

I've just been to an over 28s nightclub. And also watched the pies beat west coast. I'm excited and possibly a little er-neeb-re-ated. Love you. But still, boost, compression, Bigfella is a lefty. Love you.

All engines are over engineered to an extent. There is room to play with, thus turning up the boost. The fact the Japanese fighter managed higher speeds with higher octane is proof positive of that excess capability to re-tune.

Lets say the Japanese fighter normally runs 20lbs of boost on 80 octane fuel- detonation limited. Adding 100 octane avgas means you cran really crank up the boost to be closer to the physical capability of the motor. As far as I know, all turbos have a waste gate either external or internal and all can be manipulated to control the amount of boost they allow. You can further control detonation by playing with the timing advancing or retarding as needed.

Finally, most Japanese fighters were dumbed down in production. The lack of a skilled technical base meant fine tuning in the field simply wasn't possible so setting had to be set conservatively by the factory to compensate.

zraver
15 Sep 12,, 22:17
Water-Methanol injection was another way to to support increased manifold pressure, many WWII aircraft used this too (it had limitations due to the supply of water methanol mixture - the methanol served primarily as an antifreeze, since pure water would freeze up at altitude).

OT side note, blue colored windshield washer fluid is an almost perfect mix for a meth-injection system. Try to a tell a red neck that and he asked me what I was smoking so I had him read the ingredients- methyl alcohol and water.

USSWisconsin
16 Sep 12,, 02:02
They were formidable because they were powered by high grade avgas supplied by the US. :biggrin:

It appears that the improvements in octane had a lot to do with the growth in power. Perhaps it helped decide a few battles too?



Effects of fuel octane rating
Until World War II all automobile and aviation fuel was generally rated at 87 octane or less. This is the rating that was achieved by the simple distillation of "light crude" oil. Engines from around the world were designed to work with this grade of fuel, which set a limit to the amount of boosting that could be provided by the supercharger, while maintaining a reasonable compression ratio.

Octane rating boosting through additives was a line of research being explored at the time. Using these techniques, less valuable crude could still supply large amounts of useful gasoline, which made it a valuable economic process. However, the additives were not limited to making poor-quality oil into 87-octane gasoline; the same additives could also be used to boost the gasoline to much higher octane ratings.

Higher-octane fuel resists auto ignition and detonation better than does low-octane fuel. As a result, the amount of boost supplied by the superchargers could be increased, resulting in an increase in engine output. The development of 100-octane aviation fuel, pioneered in the USA before the war, enabled the use of higher boost pressures to be used on high-performance aviation engines, and was used to develop extremely high-power outputs – for short periods – in several of the pre-war speed record airplanes. Operational use of the new fuel during World War II began in early 1940 when 100-octane fuel was delivered to the British Royal Air Force from refineries in America and the East Indies.[14] The German Luftwaffe also had supplies of a similar fuel.[15][16]

Increasing the knocking limits of existing aviation fuels became a major focus of aero engine development during World War II. By the end of the war, fuel was being delivered at a nominal 150-octane rating, on which late-war aero engines like the Rolls-Royce Merlin 66[17][18] or the Daimler-Benz DB 605DC developed as much as 2,000 hp (1,500 kW).[19][20]
Supercharger - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Supercharger#Two-stage_and_two-speed_superchargers)

Chogy
17 Sep 12,, 15:26
Interestingly, the technology behind advanced turbo & superchargers lends itself well to gas turbines... especially the turbocharger, which requires advanced materials, bearings, and lubrication so as to deal with extreme temperatures and speeds. As gas turbine development began aggressively in the 1940's, companies like GE were well-positioned due to their earlier research and development.

zraver
17 Sep 12,, 18:06
Interestingly, the technology behind advanced turbo & superchargers lends itself well to gas turbines... especially the turbocharger, which requires advanced materials, bearings, and lubrication so as to deal with extreme temperatures and speeds. As gas turbine development began aggressively in the 1940's, companies like GE were well-positioned due to their earlier research and development.

Ya, you don't want a turbo flying apart under boost....

Stitch
17 Sep 12,, 20:50
Interestingly, the technology behind advanced turbo & superchargers lends itself well to gas turbines... especially the turbocharger, which requires advanced materials, bearings, and lubrication so as to deal with extreme temperatures and speeds. As gas turbine development began aggressively in the 1940's, companies like GE were well-positioned due to their earlier research and development.

Yes, it was a relatively small step to go from high-speed, high-temperature turbines for turbo-superchargers to a gas turbines; I know that GE was one of the few companies in the world that had the necessary technology to build turbo-superchargers for the P-38.

zraver
18 Sep 12,, 00:14
Yes, it was a relatively small step to go from high-speed, high-temperature turbines for turbo-superchargers to a gas turbines; I know that GE was one of the few companies in the world that had the necessary technology to build turbo-superchargers for the P-38.

Its a rather big step, jet turbine blades and turbo compressor wheels are not at all alike and operate on different freqs. However the research into high temp high strength metallurgy and advanced bearings was a big head start.

USSWisconsin
18 Sep 12,, 02:32
Its a rather big step, jet turbine blades and turbo compressor wheels are not at all alike and operate on different freqs. However the research into high temp high strength metallurgy and advanced bearings was a big head start.
early jets did use centripetal compressors and turbines (very much like modern turbos) - the Germans pioneered the axial jets we are familiar with today.

Another interesting development was the Paxton type centripetal supercharger with a belt driven compressor, some of these operate at turbo like speeds due to a step up gear drive in the supercharger itself. They're still around, I've seen them on some funny cars putting out huge horsepower.

Imagine how far they might have gone with piston airplane engines if the jet didn't come out as soon as it did...

Chogy
18 Sep 12,, 16:04
Imagine how far they might have gone with piston airplane engines if the jet didn't come out as soon as it did...

In the mid to late 1940's there were some piston-engine monsters on the drawing board.

The Lycoming XR-7755 (http://en.wikipedia.org/wiki/Lycoming_XR-7755) - 36 cylinders, 5,000 HP.

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Wright R-2160 - never flew...
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There were a number of so-called "Hyper" engines that were rendered obsolete overnight by the gas turbine. The complexity is staggering, maintenance would have been a nightmare, and their power to weight ratio is quite pathetic next to a jet engine. But they are amazing examples of a technology we'll never see again, real jewels of mechanical design.

FJV
18 Sep 12,, 17:40
Maybe this site is appropriate.

Luft '46 - WWII German aircraft projects (http://www.luft46.com/)

USSWisconsin
18 Sep 12,, 17:44
Imagine that R-7755 beast with turbos, intercoolers and all the other power additions that the final production engines got - probably a bomber engine for the likes of the B-36. I bet 7500 HP would have been pretty straight forward, maybe even 10,000 HP.

TopHatter
18 Sep 12,, 19:43
Imagine that R-7755 beast with turbos, intercoolers and all the other power additions that the final production engines got - probably a bomber engine for the likes of the B-36. I bet 7500 HP would have been pretty straight forward, maybe even 10,000 HP.

By comparison, the Wasp Major for the B-36 could crank out "only" 4,300 HP

Chogy
19 Sep 12,, 15:16
To provide an example of jet engine vs piston engine power to weight ratios...

One of the most highly refined piston engines ever, the PW R-4360 71.5 L 28-cylinder supercharged Radial engine:

1.83 kW/kg 1.11 hp/lb


Compared to a modern, high-bypass turbofan, the GE90-115B, Boeing 777 engine:

10.0 kW/kg 6.10 hp/lb; equal to 112,000 hp.

The gas turbine produces almost 6X as much power per unit weight, and does so with no reciprocating motion.

When I was on the Boeing 777, I was in awe at the powerplant, in my case a Rolls-Royce Trent, equivalent to the GE engine. You could walk inside the engine casing; the fan blades were simply enormous. Here it is on a test pod on a B-747, compared to the normal 747 engine on the left.

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Large twin-engine aircraft like the 777 must by law be certified to fly at maximum gross weight on ONE engine. This means a fully-loaded 777 taking off for Japan could lose an engine on rotation, and still get into the air on the remaining engine. And it did so with authority. It peaked around 100,000 lb of thrust, equivalent to FOUR F-15 engines in full afterburn. Awesome technology.

USSWisconsin
19 Sep 12,, 16:42
This example makes it very clear why the jets replaced reciprocating engines. :)

gunnut
19 Sep 12,, 20:33
When I was on the Boeing 777, I was in awe at the powerplant, in my case a Rolls-Royce Trent, equivalent to the GE engine. You could walk inside the engine casing; the fan blades were simply enormous. Here it is on a test pod on a B-747, compared to the normal 747 engine on the left.

The engine nacelle of the B777 has almost the same diameter as B737's fuselage...