100-octane fuel in the RAF in 1940

[Mike Williams]

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.

 

[Clean32]

More comparison data here:
View attachment 738345

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.
View attachment 738346

While costing speed, the bullet proof windscreen did prove its worth.
View attachment 738348

more interesting if the different wings were noted. or do we take the assumption? would explain more of the Mk2s speed?

 

[PAT303]

This graph if nothing else shows just how much an improvement the MkIII was over the MkI/II/V not excluding everything else in the air in 1940, such a missed opportunity.

 

[Mori]

I hope we can all go home now, this appears to be pretty categorical proof that "all operational fighter and bomber stations" were not only stocked with aircaft "approved" for use with 100 grade (which we already knew), but that also, the only way it could be stored was the REMOVAL of the old 87 remaining. This was it says complete by the end of June 1940. View attachment 738005

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)

 

[rochie]

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 ?

 

[pbehn]

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)

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.

 

[rochie]

Any more snide comments and i will delete this thread

 

[DerAdlerIstGelandet]

Any more snide comments and i will delete this thread

Start with thread bans young padawa. Lets not punish the posters interested in learning without all the snide remarks and BS.

 

[Engineman]

The idea of CS propeller was that it changed its pitch automaticly. I cannot say on the early Rotols from top of my head but IIRC the VDM propellers (licenced Hamilton Standard type) used by Germans were CS but at least in those used later in Bf 109Gs had also a manual use option.
Pilot could not do anything with a fixed pitch propeller either but he had to change pitch with a two position variable pitch propeller. Take off and climb used one setting and level flight another. One could kill himself and/or wreck his plane by taking off with wrong setting and had to watch his engine speed while diving for not to ruin his engine by overspeeding (too high rpm)

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]

Hello Engineman
Thanks a lot for the correction and very useful info.

Thankfully
Juha

 

[Engineman]

Hello Engineman
Thanks a lot for the correction and very useful info.

Thankfully
Juha

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

 

[z42]

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.

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?

 

[Engineman]

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

 

[Engineman]

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?

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

 

[NZTyphoon]

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

CHARGE PRESSURE LIMIT
of 12 f/inch² / only on certain types of aircraft/.
Special spark plugs and 100-octane fuel must be used to enable this high charging pressure.
In order to increase the performance of the aircraft in level flight /in exceptional cases/, the charging pressure regulator has been modified so that after adjustment of the cut-off lever, a charging pressure of approx. 12 f/inch² is achieved with the throttle fully open.
Under no circumstances must the increased charging pressure be used to test the engine on the ground and for take-off, and the engine must be running at no less than 2,300 rpm when climbing. >>>

Try to limit the use of boost pressure to periods of 5 min.
If it is necessary to use the limiting charging pressure, slightly reduce throttle, move the cut-off lever and apply full throttle.
To return to normal charging pressure, close the throttle and move the cut-off lever to the normal position.

 

[Reluctant Poster]

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

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.

 

[pinehilljoe]

More comparison data here:
View attachment 738345

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.
View attachment 738346

While costing speed, the bullet proof windscreen did prove its worth.
View attachment 738348

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"

 

[Engineman]

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.

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

 

[Shortround6]

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.

 

[SaparotRob]

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"

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