The Secret Horsepower Race - WW2 Aero Engines in detail
Discussion
Yertis said:
It's easy to forget that the Germans were feeling their way as much as everyone else with regard bomber tactics in the early part of the war. I don't think they ever expected the 109 to be flying escort missions. The BoB was the first time they'd come up against and serious opposition, and their dedicated 'escort fighter' the Me110 was completely outclassed by the Hurricane and Spitfire.
Yeah, pre-war German doctrine seems to have focused quite heavily on treating the Luftwaffe as an assistant to the Wehrmacht, in support of fighting on the ground as an integrated part of Blitzkrieg, rather than as an independent strategic force. I also think that Hitler was half-hoping not to have to fight Great Britain at all, hoping we'd be content with our Empire and let him have control of the Continent.samoht said:
I also think that Hitler was half-hoping not to have to fight Great Britain at all, hoping we'd be content with our Empire and let him have control of the Continent.
He was. He didn't feel he had a fight with Britain and just couldn't understand why they seemed to be wanting to pick a fight with him.Simpo Two said:
aeropilot said:
They didn't have any to use, as hadn't been developed for the E at that time.
Hmm, you think they might have invented one! Can't have been very hard compared to the other stuff they were doing.The Luftwaffe had to take on a much more strategic role in the Battle of Britain and lacked much of the training and equipment to do it. Drop tanks were the least of their worries.
samoht said:
Another example were the photo-reconnaissance Mosquitos and Spitfires which could snap away over Germany with near-impunity, whereas the Germans had much less ability to do so, contributing to their failure to see the Normandy landings coming.
I believe they had special Ju88s which were pretty damn fast.Simpo Two said:
samoht said:
Another example were the photo-reconnaissance Mosquitos and Spitfires which could snap away over Germany with near-impunity, whereas the Germans had much less ability to do so, contributing to their failure to see the Normandy landings coming.
I believe they had special Ju88s which were pretty damn fast.I recall reading elsewhere that there was work on higher-altitude Mosquitos specifically to intercept these German PR planes, but they stopped after the Germans gave up coming over. So sounds like they were able to for a period, but then lost that capability.
The Ju86Ps were special pressurised developments of the basic Ju86. They could fly very high by WW2 standards and it took a bit of an effort for the British to come up with an answer to them.
The ultimate answer would have been the Westland Welkin (also Merlin powered) which was designed specifically for high altitude interception. However, the Ju86 threat disappeared (as described above) and by the time the Welkin was ready, it wasn't needed. It was a lovely looking plane though -
The ultimate answer would have been the Westland Welkin (also Merlin powered) which was designed specifically for high altitude interception. However, the Ju86 threat disappeared (as described above) and by the time the Welkin was ready, it wasn't needed. It was a lovely looking plane though -
samoht said:
Simpo Two said:
samoht said:
Another example were the photo-reconnaissance Mosquitos and Spitfires which could snap away over Germany with near-impunity, whereas the Germans had much less ability to do so, contributing to their failure to see the Normandy landings coming.
I believe they had special Ju88s which were pretty damn fast.I recall reading elsewhere that there was work on higher-altitude Mosquitos specifically to intercept these German PR planes, but they stopped after the Germans gave up coming over. So sounds like they were able to for a period, but then lost that capability.
Eric Mc said:
The Ju86Ps were special pressurised developments of the basic Ju86. They could fly very high by WW2 standards and it took a bit of an effort for the British to come up with an answer to them.
The ultimate answer would have been the Westland Welkin (also Merlin powered) which was designed specifically for high altitude interception. However, the Ju86 threat disappeared (as described above) and by the time the Welkin was ready, it wasn't needed. It was a lovely looking plane though -
Like a Whirlwind on steroids.The ultimate answer would have been the Westland Welkin (also Merlin powered) which was designed specifically for high altitude interception. However, the Ju86 threat disappeared (as described above) and by the time the Welkin was ready, it wasn't needed. It was a lovely looking plane though -
Eric Mc said:
Yes - followed the basic shape but a very different aeroplane.
Both the Whirlwind and Welkin were designed under Teddy Petter. He left Westland to join English Electric where he designed the Canberra and the P1, which became the Lightning.
And after that, he went Folland, and designed the Gnat.Both the Whirlwind and Welkin were designed under Teddy Petter. He left Westland to join English Electric where he designed the Canberra and the P1, which became the Lightning.
'Welkin' has to be about the worst name for an a/c ever.
But the logic I presume is thus:
Definition of welkin
1a : the vault of the sky : FIRMAMENT
the sun of heaven … made the western welkin blush
— William Shakespeare
b : the celestial abode of God or the gods : HEAVEN
2 : the upper atmosphere
https://www.merriam-webster.com/dictionary/welkin
But the logic I presume is thus:
Definition of welkin
1a : the vault of the sky : FIRMAMENT
the sun of heaven … made the western welkin blush
— William Shakespeare
b : the celestial abode of God or the gods : HEAVEN
2 : the upper atmosphere
https://www.merriam-webster.com/dictionary/welkin
The Bf109E's technical superiority with fuel injection over the British planes' carbs is often talked about - and just as often overstated.
What doesn't seem to get as much covering was the Bf109's (well, really the DB601 engine's) supercharger drive. At the time the Merlin in the Spitfire and Hurricane used a simple single-speed, single-stage supercharger with automatic boost limit but no other form of control.
The DB601 drove its single-stage supercharger through a hydraulic coupling which allowed infinite gradation of drive ratios between the minimum and maximum available. This meant that at low altitudes the supercharger was only driven slowly, drawing less power from the engine which meant more could go to the propeller. Meanwhile the Merlin drove its supercharger at maximum at takeoff RPM, absorbing a fair chunk of power generating boost which was then 'thrown away' at the partially-closed throttle plate without getting anywhere near the cylinders.
So the DB601 made way more power at takeoff than the Merlin (something like 1050 v. 850) and because it's supercharger gearing wasn't a single compromise it was at least equal at altitude - the DB was limited in how much compression the supercharger could deliver by the maximum acceptable intake temperature (one of the disadvantages of its direct fuel injection since the Merlin's carb delivered a significant charge cooling effect thanks to the stream of fuel vapour) and the overall boost that could be put to both the mechanicals of the engine and the fuel it was running on.
The variable supercharger drive also gave an early advantage against British aircraft with the Merlin's using two-speed supercharger drives. These gave a 'saw tooth' power/altitude curve as power at the prop increased with climb until critical altitude when the throttle plate was fully open, then declined as boost dropped with further climbing, then spiked up again as the supercharger kicked into its fast gear, then slowly increased until the throttle was opened again then slowly dropped until the service ceiling. With the hydraulic drive the DB601's curve was basically flat at full throttle until it reached the critical altitude with the supercharger at its fastest speed (direct drive).
German pilots soon cottoned on to the altitude that British engines kicked into fast gear and tried to engage just below it, so the RAF planes would be stuck in the the 'valley' on the back of their slow gear power curve. The Brits got around that by giving pilots a manual override switch so they could select fast gear on demand.
Since a powerful engine is nothing without a good propeller, mention should also be made of the Bf109E's infinitely variable pitch propeller, replaced on later E variants with a constant speed prop. Meanwhile the height of RAF propeller technology in the spring of 1940 was a two-speee variable pitch prop and Hurricanes fought in France with WW1-style fixed-pitch two-blade wooden props. For the Battle of Britain there was a rush in-the-field upgrade program to convert the two-position props to constant speed operation, but some Spitfire Mk1s still fought with the older type.
What doesn't seem to get as much covering was the Bf109's (well, really the DB601 engine's) supercharger drive. At the time the Merlin in the Spitfire and Hurricane used a simple single-speed, single-stage supercharger with automatic boost limit but no other form of control.
The DB601 drove its single-stage supercharger through a hydraulic coupling which allowed infinite gradation of drive ratios between the minimum and maximum available. This meant that at low altitudes the supercharger was only driven slowly, drawing less power from the engine which meant more could go to the propeller. Meanwhile the Merlin drove its supercharger at maximum at takeoff RPM, absorbing a fair chunk of power generating boost which was then 'thrown away' at the partially-closed throttle plate without getting anywhere near the cylinders.
So the DB601 made way more power at takeoff than the Merlin (something like 1050 v. 850) and because it's supercharger gearing wasn't a single compromise it was at least equal at altitude - the DB was limited in how much compression the supercharger could deliver by the maximum acceptable intake temperature (one of the disadvantages of its direct fuel injection since the Merlin's carb delivered a significant charge cooling effect thanks to the stream of fuel vapour) and the overall boost that could be put to both the mechanicals of the engine and the fuel it was running on.
The variable supercharger drive also gave an early advantage against British aircraft with the Merlin's using two-speed supercharger drives. These gave a 'saw tooth' power/altitude curve as power at the prop increased with climb until critical altitude when the throttle plate was fully open, then declined as boost dropped with further climbing, then spiked up again as the supercharger kicked into its fast gear, then slowly increased until the throttle was opened again then slowly dropped until the service ceiling. With the hydraulic drive the DB601's curve was basically flat at full throttle until it reached the critical altitude with the supercharger at its fastest speed (direct drive).
German pilots soon cottoned on to the altitude that British engines kicked into fast gear and tried to engage just below it, so the RAF planes would be stuck in the the 'valley' on the back of their slow gear power curve. The Brits got around that by giving pilots a manual override switch so they could select fast gear on demand.
Since a powerful engine is nothing without a good propeller, mention should also be made of the Bf109E's infinitely variable pitch propeller, replaced on later E variants with a constant speed prop. Meanwhile the height of RAF propeller technology in the spring of 1940 was a two-speee variable pitch prop and Hurricanes fought in France with WW1-style fixed-pitch two-blade wooden props. For the Battle of Britain there was a rush in-the-field upgrade program to convert the two-position props to constant speed operation, but some Spitfire Mk1s still fought with the older type.
I didn't know that there were still Hurricanes using two blade Watts propellers during the Battle for France.
Later Spitfires (the MkVIII, IX onwards - ignoring the Griffon powered Spitfires) were fitted with two stage superchargers which improved their performance a lot. They also had four blade propellers.
Later Spitfires (the MkVIII, IX onwards - ignoring the Griffon powered Spitfires) were fitted with two stage superchargers which improved their performance a lot. They also had four blade propellers.
Eric Mc said:
I didn't know that there were still Hurricanes using two blade Watts propellers during the Battle for France.
When Eric Mc tells me I've taught him something I go and check my facts...I was wrong in as much as Watts-propped Hurricanes never actually fought in France. They were deployed to France with the two-blade props but all were upgraded to the DH two-position 3-blade ones during the Phoney War. The Watts was no longer in service by the time the bullets started flying.
samoht said:
According to wikipedia "Ju 86P-2 photo-reconnaissance aircraft. Those operated successfully for some years over Britain, the Soviet Union and North Africa. In August 1942, a modified Supermarine Spitfire V shot one down over Egypt at an altitude of some 14,500 m (49,000 ft); when two more were lost, Ju 86Ps were withdrawn from service in 1943. "
I recall reading elsewhere that there was work on higher-altitude Mosquitos specifically to intercept these German PR planes, but they stopped after the Germans gave up coming over. So sounds like they were able to for a period, but then lost that capability.
My recollection is that the Ju86P threat to mainland UK was ended following a successful interception by a modified Spitfire IX of the High Altitude flight. This was an RAF unit formed to combat this type of incursion, the aircraft were modified but not pressurised. Although the 86 was not shot down the interception at 42,000 feet by P/O Prince Emmanuelle Gallitzine effectively ended these operations by the Luftwaffe.I recall reading elsewhere that there was work on higher-altitude Mosquitos specifically to intercept these German PR planes, but they stopped after the Germans gave up coming over. So sounds like they were able to for a period, but then lost that capability.
(this is from memory by the way the full story is in Alfred Price's 'Spitfire at War III' (I think)
Mark V GTD said:
My recollection is that the Ju86P threat to mainland UK was ended following a successful interception by a modified Spitfire IX of the High Altitude flight. This was an RAF unit formed to combat this type of incursion, the aircraft were modified but not pressurised. Although the 86 was not shot down the interception at 42,000 feet by P/O Prince Emmanuelle Gallitzine effectively ended these operations by the Luftwaffe.
(this is from memory by the way the full story is in Alfred Price's 'Spitfire at War III' (I think)
Pretty much.(this is from memory by the way the full story is in Alfred Price's 'Spitfire at War III' (I think)
Although it wasn't technically a production Mk.IX Spit, it was one of two existing Mk.V that was then specially converted by Rolls Royce to the then just about to go into production, MK.IX spec Merlin 61 engine configuartion.
One can only imagine the consternation of the Ju86P crew when they suddenly saw a few cannon shells whizzing past them making contrails....
No wonder they never ventured back over the UK again.
Edited by aeropilot on Tuesday 17th November 14:07
Early MkIXs were actually Mk V airframes fitted with Merlin 61s. The plan for the two stage Merlin was that it would be fitted to a new airframe which was designated the MkVIII. It turned out that the 61 fitted just as well to the basic MkV airframe so it was decided to concentrate on this rather than the VIII.
A couple of hundred VIIIs were made, most of them ending up in the Australia/Borneo/New Guinea theatre. The MkVIII had a retractable tailwheel whereas the IX retained the fixed tailwheel of the V.
A couple of hundred VIIIs were made, most of them ending up in the Australia/Borneo/New Guinea theatre. The MkVIII had a retractable tailwheel whereas the IX retained the fixed tailwheel of the V.
Eric Mc said:
Early MkIXs were actually Mk V airframes fitted with Merlin 61s. The plan for the two stage Merlin was that it would be fitted to a new airframe which was designated the MkVIII. It turned out that the 61 fitted just as well to the basic MkV airframe so it was decided to concentrate on this rather than the VIII.
In fact they were all ordered originally as Mk.III's...!Such was the pace of the wartime development that the last batch of that production order ended up being Mk.IX's
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