100-octane fuel in the RAF in 1940

Engineman · Sep 17, 2024

Of course, the Merlin always benefitted from charge-cooling to some extent by the fuel carburettor/injection into the inlet airflow. Sir Stanley Hooker listed the cooling effect as 25 degrees C reduction.
The reality is that the Germans were fighting an uphill battle with shortages of high grade materials and high-Octane fuels, remember that the DB 605 did not even get back to it's
basic 1.42ata rating until about autumn 1943.
The 60 series Merlin was already amazing the Germans when they first saw them in 1942. The RLM and Daimler Benz had hoped to head the 2-stage Merlin off with engines like the
2-stage DB 628, but those, and similar developments, did not mature and the best that could be done was the big supercharger DB 605 AS in late Spring 1944!
The 2-stage DB 605 L and DB 603 L were developed, but hardly reached production before endex.

Eng

pinehilljoe · Sep 17, 2024

SaparotRob said:
I think that line is in the book version of the movie Battle of Britain too. Taka taka taka.

The movie is back on Prime Video, Prime seems to cycle it on and off.

MikeMeech · Sep 17, 2024

pinehilljoe said:
In With Wings Like Eagles, Michael Korda quotes Dowding in saying, "if Chicago gangsters can have bullet proof glass for their cars, why can't I have it for my Spitfires"

Hi
To avoid any confusion that the bullet proof glass was a BoB decision, it was being decided on during 1938 to give some protection for fighters from the return fire of enemy bombers. This and other matters were being discussed during the deliberations of the Air Fighting Committee between June and December 1938, extracts appear in 'Knights of the Skies, Armour protection for British fighting aeroplanes' by Michael C Fox, some pages below:

Firing trials were also undertaken:

Mike

Reluctant Poster · Sep 17, 2024

Engineman said:
You are mistaken, the rear mounted Merlin supercharger required an additional 90 degrees of intake airflow direction change compared to the flank mounted superchargers.

I wrote, "Additionally, the later DB superchargers were quite efficient and, it has to be remembered that losses in a 2-stage supercharger are multiplied." I state that, I do not imply they were more efficient, later DB superchargers were quite efficient and multi-stage supercharging does suffer from multiplication of efficiency losses.
On the point of which superchargers were the more efficient, I make no claims because that is a very specific point. However, data in Calum Douglas' superb co-authored book Turbo/Supercharger Compressors and Turbines (TSCT) does have a lot of detail on this and I recommend it to anyone who is interested.
As regards charge-cooling, the various high supercharged German engines, including DB 605 L and DB 603 L, used ADI or Intercoolers as they saw fit, although their actual use of the intercooling option was generally very late in the War.

Eng

The airflow in the Merlin comes from the air intake, does a 90 degree turn into the carburetor, followed by a 90 degree turn into the eye of the impeller, followed by a 90 degree turn into the intake manifold
The DB605 comes from the air intake, does a 90 degree turn into the eye of the impeller, followed by a 90 degree turn to the centerline of the engine, followed by a 90 degree turn into the intake manifold.

Its obviously more nuanced than that. The discharge elbow of the DB 605 is rolled 45 degrees or so to allow the third 90 to become a 45. Unfortunately this benefit is negated by a change in the elevation of the pipe which requires a 2nd 45. On the other hand the beautiful sweeping pipe on the Merlin from the supercharger discharge to the intake manifold would provide a very low pressure drop. The air intake to the DB supercharged is quite abrupt and would cause a pressure loss. There are turning vanes in the intake to help straighten the flow into the supercharger somewhat but this is a palliative not the best solution.

Overall I would say the Merlin intake system is better from a pressure drop perspective but without knowing the pipe sizes and without drawings to calculate the actual pressure drop this is just my opinion.

Engineman · Sep 17, 2024

Reluctant Poster said:
The airflow in the Merlin comes from the air intake, does a 90 degree turn into the carburetor, followed by a 90 degree turn into the eye of the impeller, followed by a 90 degree turn into the intake manifold
The DB605 comes from the air intake, does a 90 degree turn into the eye of the impeller, followed by a 90 degree turn to the centerline of the engine, followed by a 90 degree turn into the intake manifold.

Its obviously more nuanced than that. The discharge elbow of the DB 605 is rolled 45 degrees or so to allow the third 90 to become a 45. Unfortunately this benefit is negated by a change in the elevation of the pipe which requires a 2nd 45. On the other hand the beautiful sweeping pipe on the Merlin from the supercharger discharge to the intake manifold would provide a very low pressure drop. The air intake to the DB supercharged is quite abrupt and would cause a pressure loss. There are turning vanes in the intake to help straighten the flow into the supercharger somewhat but this is a palliative not the best solution.

Overall I would say the Merlin intake system is better from a pressure drop perspective but without knowing the pipe sizes and without drawings to calculate the actual pressure drop this is just my opinion.

It isn't a matter of opinion. The basic difference between the intake flow path available to a flank mounted centrifugal supercharger and a rear mounted rear entry centrifugal supercharger is that the rear mounted supercharger needs at least one extra 90 degree bend. So, we do not need to even consider the nuances as the point was raised WRT the
position of the supercharger and the provision of a Motor Cannon.

Eng

100-octane fuel in the RAF in 1940

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Engineman

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