100-octane fuel in the RAF in 1940

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More comparison data here:


Comparisons of Spitfire I's with DH and Rotol props and bullet proof windscreen found top speeds to be similar with N.3171 obtaining 354 mph and R.6774, 355 mph. By comparison, Spitfire I K.9793 with a DH two-pitch prop and original windscreen reached 367 mph.


While costing speed, the bullet proof windscreen did prove its worth.
 
more interesting if the different wings were noted. or do we take the assumption? would explain more of the Mk2s speed?
 
I let things calm down a little, and take that for a genuine remark. These paragraphs are pretty interesting and I don't dispute their conclusion.

But a document lacking date, from / to, and context is of little-to-no relevance.

(Having to remind history method 101 keeps puzzling me)
 
It seems there has been plenty of documentation shown with dates included.
Yet you dont seem to want to believe what they are saying ?
 
The document specifically states that it was giving the operational situation up to the end of June 1940, which is relevant to the Battle of Britain generally stated to be from July to October. It explains in part why Park had a Hurricane as his transport, whatever he used had to run on 100Octane fuel.
 
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Hi,
Just a couple of words about the German VDM WW2 propellers. Possibly, before WW2 VDM took out some licensing on Hamilton Standard V.P. Props or patents? However, the VDM V.P props fitted during the wartime period were quite different. Generally, the VDM props were remotely electrically actuated, with pitch change by a differential co-axial geartrain and blade root wormgear. The early Bf 109 E versions started pre-war with a simple instrument panel Coarse/Fine selector. This was a simple V.P prop and had no automatik function.
Then a Throttle lever thumbswitch control was fitted to the Bf 109 which allowed propeller control with hand on throttle. The propeller position was still physically indicated on a "clock" type scale and this indicated blade angle. Approximately, during the BoB period the Automatik version of propeller pitch control was added. The Automatik version had engine rpm control by the propeller pitch, linked directly to throttle position, unlike most Allied systems that developed with an engine speed lever, that could be set independently from throttle position. The Automatik VDM system could still be operated in the original "Hand" or manual method, just by selecting the desired method on an electrical switch.
The earliest reference I have to the VDM Automatic control is 1938, but it does seem that system was not properly introduced until 1940.

Eng
 
Juha3 said:
Hello Engineman
Thanks a lot for the correction and very useful info.

Thankfully
Juha
Click to expand...
Thanks.
It is also worth considering the German foresight in the development of their engines and propellers. In around 1933, the RLM specified that the new fighter engines should have features that included engine mounted cannon and fuel injection. The early development engines took a little while to get F.I sorted out but, from the start, the DB 600 and JuMo 210 engines had an integral blast tube and gun mount on their prop shaft, with the supercharger moved to the side flank of the engine.
The VDM propeller was developed with the requirement to allow the propshaft blast tube from the start.
The Bf 109 had difficulties with integrating the motor-mounted gun, and development with such weapons was slow, not really making full progress until the Bf 109 F in late 1940, although the engine itself and the propellers had been ready before that.

Eng
 

I wonder to which extent the decision to make room for a motor cannon constrained German supercharger development during the war? Looking at the two-stage intercooled supercharger on the Merlin 61+ for comparison, it's a rather big piece of kit. How would you fit something like that on the side of the engine without a huge bulge in the airframe?
 
This is quite a complicated subject. Overall, the rear flank position is not a bad place for the blower, it can be quite well fitted into the required cross section, and there can be less direction change of the airflow. Also, the German DB engines were not throttled before the impellor. Additionally, the later DB superchargers were quite efficient and, it has to be remembered that losses in a 2-stage supercharger are multiplied. Furthermore, the principle German engines were larger capacity than the Merlin and running a lower MAP, so the need for really high supercharge was not as great. That said, these and many other factors did make multi-stage supercharging important even to the Germans at the end of the war and there were the multi-stage DB 605 L and DB 603 L engines coming into service at the end of the war, still quite well streamlined into their aircraft, still providing effective supercharge and engine mounted cannon feature.

Eng
 

Further comment about fitting the rear flank mounted superchargers to accommodate the engine cannon, particularly on the DB 605/603 and JuMo 211/213 families of engines is possible. If you study the RR Merlin superchargers, you see that the inline positioning of the supercharger drive(s), the supercharger itself and the intake elbow/carburetor/throttle body all add to the engine length, despite very careful design.
Study of the DB and JuMo supercharger drives shows how the driving systems of gears are arranged across the rear of the engine, thereby not adding much to the length of the engines. The German engines have some very attractive detail design in these systems, despite the differences in the particular types.
Ultimately, the late Bf 109 versions with the larger supercharger AS and D engines did have to bulge the cowling around the larger supercharger, but at the same time they did incorporate the MG 131 bulges into the smoother new cowlings and the aerodynamics of that detail improved.
The Germans did admire the RR Merlin 2-stage supercharger and the later DB 605 L / DB 603 L probably benefitted from consideration of the 2-stage Merlin.

Eng
 
For interest, here is a Rolls-Royce Merlin engine manual published in Polish, for the Polish pilots in the RAF: the instructions for the 100 Octane setting are outlined and translated



 
Lees direction change? Its still a 180 degree change in direction from the air intake to the intake manifold for both engines. You seem to be implying that DB superchargers were more efficient than RR which I don't believe is true. Also the DB 603Ls and 6035Ls did not have an intercoolers which hurts performance.
 
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"
 
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
 
Inter-coolers in fighters was always something of a question. While they are not heavy they add bulk and drag.
A German engine running at 1.42 Ata is running at about 6lbs of boost if I have done the math right. At 1.8 Ata it is running about 12lbs of boost.
Now with superchargers the heat problem is the amount of compression that is being done. So at 20,000ft our 1.42 Ata engine is compressing the air about 3.09 times.
A Merlin running 12lbs of boost is compressing the air about 3.92 times.
Even if the two superchargers have the same efficiency the Merlin is going to be dealing with much hotter air in the intake system. A two stage Merlin needs an inter cooler if you want to get the performance you paid for with the fancy supercharger.
The German engines have tougher decision to make balancing the extra power the intercooler will give vs the bulk/drag the intercooler will cost. They aren't going to get the same boost in performance but they are not going to pay the same bulk/drag cost either. The higher the plane has to fly and the more boost it uses the more important the intercooler gets.
 
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