The Secret Horsepower Race - WW2 Aero Engines in detail

[samoht]

I've always been interested in the piston engines used in WW2 aircraft. They're close enough to our car engines to be relatable and relevant, and yet many of them used technologies such as direct injection, forced induction, four-valve heads and water/methanol/nitrous injection, that only arrived in road cars much later.

The other fascination is that during the war additional horsepower was worth more than bragging rights or quarter-mile times, it was literally a matter of life or death. If the other guy can do 400mph and you can do 410, then you've little to fear from his guns; vice versa and you could be shot down. This pushed the combatants into intense competition, each needing to respond to the others' advances. The closest peacetime analogy I can think of is F1.

I've read a bit about the Merlin and how it was developed during the war, Stanley Hooker's autobiography of how he realised that the existing supercharger design was mathematically incorrect, and redesigned it giving the Spitfire a crucial mid-war boost, then followed up with the two-stage supercharger for more power at high altitudes. However it's been harder to find real detail about the German efforts.

Anyway, I just finished reading The Secret Horsepower Race, written by a former Toyota Motorsport engineer who's spent years crawling through archives, and it more than fills this hole. It's a real treasure trove of archive photos, performance charts and cutaways of US, British and especially German engines, telling how the far-sighted Helmuth Sachse laid down the template for German engines as being inverted-vee, single stage supercharged and fuel injected, before he was 'retired' from the air ministry to BMW for being insufficiently enthusiastic a Nazi. Then how the Germans had to battle against shortages of crucial materials for bearings and valves, and for high-octane fuel, while bringing improved engines to production, before being crushed by allied bombing.

The book isn't perfect, but issues are mainly ones of omission, based on lack of available original documents to back up areas such as the ongoing workarounds the British implemented to make carburettors work under negative g conditions. But it provides a great overview and fantastic original detail of the areas it does cover, especially although not exclusively the German side.

Did you know that post-war, Garrett turbochargers employed as head of research the wonderfully named Werner von der Null, a German aristocrat with duelling scars who had been a key figure in aircraft super and turbocharger development during the war?

Basically, if you're interested in aero engines, or arguably any piston engines, I'd highly recommend seeking out a copy - I found it absolutely fascinating.

[Simpo Two]

Thanks, I'll add that to my list.

Another I can recommend is 'And The Engines Were Rolls Royce' by Ronald Harker: https://www.amazon.co.uk/Engines-Were-Rolls-Royce-...

[jet_noise]

Does it mention specialist fuels such as synthetic or 150(!) octane?

[Krikkit]

Sounds like a good read, I've ordered a copy!

[samoht]

jet_noise said:

Does it mention specialist fuels such as synthetic or 150(!) octane?

Probably the best answer I can give to that is "yes", see index sections below:





I'd had no idea the extent to which the Germans synthesised avgas from coal with hydrogenation and de-hydrogenation, the fact that German high-octane fuel was different from Allied high-octane due to high aromatic content, the fact that fuels have a different octane rating at 'lean' and 'rich' mixtures, etc. The German high-octane fuel programme in particular, blending various different exotic hydrocarbons, reminds one of nothing more than the turbo cars of 1980s F1. It seems that they were able to produce high octane ratings, but not always able to do so in the high volumes that the Allies could.

[jet_noise]

samoht said:

jet_noise said:

Does it mention specialist fuels such as synthetic or 150(!) octane?

Probably the best answer I can give to that is "yes", see index sections below:





I'd had no idea the extent to which the Germans synthesised avgas from coal with hydrogenation and de-hydrogenation, the fact that German high-octane fuel was different from Allied high-octane due to high aromatic content, the fact that fuels have a different octane rating at 'lean' and 'rich' mixtures, etc. The German high-octane fuel programme in particular, blending various different exotic hydrocarbons, reminds one of nothing more than the turbo cars of 1980s F1. It seems that they were able to produce high octane ratings, but not always able to do so in the high volumes that the Allies could.

!

[Simpo Two]

There may be some hertiage from the Schneider Trophy there, where fuel was equally important for wringing the last bit of power from an engine. After the contest was won, the Macchi-Castoldi MC72, with its remarkable 'double' Fiat engine and potion from British fuel expert Rod Banks, achieved 440mph in 1934 - a record for a piston engine seaplane that still stands.

[samoht]

Simpo Two said:

There may be some hertiage from the Schneider Trophy there, where fuel was equally important for wringing the last bit of power from an engine. After the contest was won, the Macchi-Castoldi MC72, with its remarkable 'double' Fiat engine and potion from British fuel expert Rod Banks, achieved 440mph in 1934 - a record for a piston engine seaplane that still stands.

Yeah, it's interesting how the Schneider Trophy race turned into effectively a biannual weapons test for the competing nations. I have fond memories of seeing one of the Supermarine winners in the Science Museum. There's a chapter on the Schneider Trophy in the book also, as you say it was a significant prelude to the aircraft of WW2. I hadn't realised that surface cooling was used to avoid radiator drag, nor that on average one pilot was killed at each event, so hairy were the racing planes, nor that the Germans were banned under Versailles restrictions (although it makes sense).

[Simpo Two]

samoht said:

Yeah, it's interesting how the Schneider Trophy race turned into effectively a biannual weapons test for the competing nations. I have fond memories of seeing one of the Supermarine winners in the Science Museum. There's a chapter on the Schneider Trophy in the book also, as you say it was a significant prelude to the aircraft of WW2. I hadn't realised that surface cooling was used to avoid radiator drag, nor that on average one pilot was killed at each event, so hairy were the racing planes, nor that the Germans were banned under Versailles restrictions (although it makes sense).

My info came from here, which I read earlier this year: https://www.amazon.co.uk/Schneider-Trophy-Aircraft...
More detail than you can shake a stick at.

[Yertis]

I enjoyed reading (in Jeffrey Quill’s book) about the ‘race’ set up during the war to demonstrate the speed advantage the Typhoon had over the FW190 and Spitfire, which was won by the Spitfire.

This book looks like another good read

[Piginapoke]

It's an interesting subject. My understanding is that the Spitfire Mk 1 and Messerschmitt 109 were close in enough in performance that the pilot and tactical situation were the defining factors, rather than another 10mph top speed. Is that right?

(Later Spitfire marks becoming much more dominant over the 109, including the G model)

[Simpo Two]

Piginapoke said:

It's an interesting subject. My understanding is that the Spitfire Mk 1 and Messerschmitt 109 were close in enough in performance that the pilot and tactical situation were the defining factors, rather than another 10mph top speed. Is that right?

There are many factors, only one of which is speed (level, dive or climb?), and they all combine. Otherwise, the a/c that was 10mph faster would always win and the other one would always get shot down.

[aeropilot]

Piginapoke said:

My understanding is that the Spitfire Mk 1 and Messerschmitt 109 were close in enough in performance that the pilot and tactical situation were the defining factors, rather than another 10mph top speed. Is that right?

As said, more than just a speed issue.
They were pretty much even overall, if both pilots were of comparable skill level, and one had the advantage in some areas of the flight envelope, and the other one in other areas.....
The 109E had a significantly better roll rate, and could bunt with neg g, and dive faster (smaller size and frontal area helped, as did the much bigger engine)
Spit had a much better turn rate, and was much easier to fly and fight by a less experienced pilot than the 109, which was the real telling factor in the BofB, as was the limited range of the 109, meaning they really had very little time over the UK before having to break off and head back over the channel.

Piginapoke said:

(Later Spitfire marks becoming much more dominant over the 109, including the G model)

By then though, that was as much about number advantages of the Allies combined with far more young and inexperienced Luftwaffe pilots being sent up against such a numerically superior force, than any significant superiority in machine capability.

[Simpo Two]

aeropilot said:

as was the limited range of the 109, meaning they really had very little time over the UK before having to break off and head back over the channel.

Why didn't they use droptanks for the outward leg? Speed wasn't critical (like it was for us) because they had time to assemble.

[aeropilot]

Simpo Two said:

Why didn't they use droptanks for the outward leg?

They didn't have any to use, as hadn't been developed for the E at that time.

[Simpo Two]

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.

[aeropilot]

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.

They had no reason to up to that point. They didn't really see a need for it, until they got well into the BofB and began to realise it wasn't going the way they thought it was going to go. They had developed a centre rack for a bomb of course by mid BofB, so it was a matter of designing a tank (may have been an adaption of a 110 aux tank) to use the rack and design the plumbing for it, which they had done by the end of 1940/early 1941, by which time the BofB as such had been lost.

[Yertis]

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.

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.

[Eric Mc]

Yes - drop tanks only started to emerge as the war progressed. All sides eventually developed them. I think the Japanese might have been the first when they fitted auxiliary tanks to their Zeros.

[samoht]

Piginapoke said:

It's an interesting subject. My understanding is that the Spitfire Mk 1 and Messerschmitt 109 were close in enough in performance that the pilot and tactical situation were the defining factors, rather than another 10mph top speed. Is that right?

Yeah, that's my understanding also - when both pilots wanted to fight each other, the aircraft were pretty equal and pilot skill and initial conditions were most significant.

However, there were also cases where e.g. a German pilot would run for home, or a German bomber would be too high/distant for a British fighter to reach before they hit their target. In these cases the relative top speeds of each aircraft were crucial.

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.