Bug 174 on 12lbs boost. Review please.

[Kurfürst]

Originally Posted by 41Sqn_Banks

A higher "emergency" boost than the rated +9 was definitely used from 21 August 1940 on, there are combat report and ORBs that proof this.

http://www.wwiiaircraftperformance.o...3aug40-orb.jpg
http://www.wwiiaircraftperformance.o...1aug40-orb.jpg
http://www.wwiiaircraftperformance.o...g40-orb541.jpg
http://www.wwiiaircraftperformance.o...-21aug40-1.jpg
http://www.wwiiaircraftperformance.o...-21aug40-2.jpg

Note that none of these papers ('proof') specify any kind of boost rating. They merely say they used max. power. And max. power was +9.

Kurfürsts has the theory that the whole squadron called the regular climbing/rated boost of +9 boost in this instance "emergency boost". However he didn't came up with an explanation why they would do this.

Because that was the maximum allowed for the Spitfire II as demonstrated.
Its no more than an awfully silly theory that when pilots made reference to emergency power, they meant using an emergency power far above the sanctioned limits for emergency power.



In contrast 41Sqn_Banks has the theory that a reference to emergency boost *MUST* refer to +12 lbs, even though +12 lbs is not listed anywhere, not referred to by any pilot, report or manual.

I'd like to see the reasoning why it is so certain that a reference to the emergency rating refers to a higher than +9 lbs boost. I call it wishful thinking.

What he didn't came up is an explanation why would the Spitfire II manual lists +9 lbs as maximum combat boost (whereas the Spitfire I manual lists +12 lbs.)

Note that this reports explicitly mention "emergency boost" and don't mention "emergency power", the later could be interpreted as the normal "All out" setting of +9 and 3000 RPM, which was only allowed for emergencies. But as this is not the case it's clear that a boost higher than +9 was used in this instance.

All this is playing with the words, assuming a random rating which is not listed anywhere.

It's simply your assumption that the mention of emergency boost or cut out refers to +12 lbs.

My assumption is that emergency boost simply refers to the +9 lbs combat limit, which is underlined by the fact that this is the limit specified by the manual.

You are welcome to prove that emergency boost allowed for greater than +9 lbs, in the summer of 1940.

There are also other reports from November 1940 that show the use of the boost control cut-out. The use of the cut-out only makes sense to increase boost beyond the rated +9 or when there is a failure in the boost control.

http://www.wwiiaircraftperformance.o...son-2nov40.jpg
http://www.wwiiaircraftperformance.o...en-30nov40.jpg

Problem is the maximum rating allowed was +9 lbs.

There's a logical failure in your assumption that the boost cut-out would increase boost beyond +9 lbs. Its quite likely in fact that the pilots obtained +9 by using the boost cut-out, as on the Spitfire I.

Fact is that the Spitfire I manual of the era lists +12 as the limit, obtainable with the boost cut-out. When Spitfire I pilots refer to using the boost, they sometimes specify the boost used as well (+12).

Its only logical that since the the Spitfire II manual of the era lists in contrast only +9 as the limit, it would mean that when Spitfire II pilots refer to using the +9 boost, w/o specifing the boost used and referring it in vague terms like 'emergency boost'.

P.S. Curious, isn't it, that there's not a single hint or tests for +12 Spitfire IIs isn't it.

But if we are going down the road of fantasy boosts that are much higher than the limits listed in the engine/aircraft manuals, I want my 1.7 ata 109E, too. Even though if the manuals say something completely different. Hell if official limits are to be ignored on Spitfires, we might as well ignore them on Messerschmitts as well, and come up with whatever fantasy we may like.

[41Sqn_Banks]

Kurfürst I'm not saying it was +12 boost, only that the boost must have been higher than +9, as it wouldn't make sense to use the cut-out without getting any benefit. I don't think there is so far any definite proof for the exact emergency boost value of the Spitfire II in 1940. However the fact that earlier (Merlin III), similar (Merlin XX) and later (Merlin 45) engines had +12 emergency boost in 1940 (the Merlin 45 of course in 1941), and the fact that +12 boost is documented for the Merlin XII for 1942(?) is a strong indicator that +12 boost was the emergency limitation of the Merlin XII.

BTW in RAF terminology "All-out" is not equal to "emergency". This can be seen in the Spitfire V test report: http://www.spitfireperformance.com/aa878.html

Max. for all-out level flight (normal rating)(5 minute limit) +9
Max. for all-out level in special emergency (prior to increase to +16) +12
Max. for climb and level flight (combat rating)(3 min. limit) +16

Of course this is not a Merlin XII engine but it shows that there could be different boost limitations for "all-out normal rating" and "all-out emergency".

[camber]

Originally Posted by Kurfürst

There's a logical failure in your assumption that the boost cut-out would increase boost beyond +9 lbs. Its quite likely in fact that the pilots obtained +9 by using the boost cut-out, as on the Spitfire I.

This is contradicted by the July 1940 Spit II manual which you are quoting. 30 minute climb rating is +9psi, 30 minutes, 2850rpm. The boost cutout description is listed as EMERGENCY override of automatic boost control, sealed against inadvertant use. 30 minute climb is not an emergency, thus clearly +9psi is available on normal throttle operation (also +9psi is typically referred to as rated boost in Spit II publications).

It does beg the question, what kind of boost control override installation is being described in the July 1940 Spit II manual? An original type, which gives full throttle plate control in the event of controller failure and is unsuitable as a combat boost? Or the modified type, which is not really a cutout but an increment for the boost control setpoint (to +12psi)?. The July 1940 manual does not let us know.

It seems commonsense that the Spit II boost cutout was the +12psi type, and use of it as combat boost was approved and occurred during the BoB (although not in the July 1940 manual). This is considering the use of +12psi Spit I's during the same period and combat reports as above. But specific documents appear to be lacking.

camber

[Zachariasx]

Originally Posted by camber

This is contradicted by the July 1940 Spit II manual which you are quoting. 30 minute climb rating is +9psi, 30 minutes, 2850rpm. The boost cutout description is listed as EMERGENCY override of automatic boost control, sealed against inadvertant use. 30 minute climb is not an emergency, thus clearly +9psi is available on normal throttle operation (also +9psi is typically referred to as rated boost in Spit II publications).

It does beg the question, what kind of boost control override installation is being described in the July 1940 Spit II manual? An original type, which gives full throttle plate control in the event of controller failure and is unsuitable as a combat boost? Or the modified type, which is not really a cutout but an increment for the boost control setpoint (to +12psi)?. The July 1940 manual does not let us know.

It seems commonsense that the Spit II boost cutout was the +12psi type, and use of it as combat boost was approved and occurred during the BoB (although not in the July 1940 manual). This is considering the use of +12psi Spit I's during the same period and combat reports as above. But specific documents appear to be lacking.

camber

I think too that makes logical sense. Kurfürsts document mention 3 min +12 lbs take off power which translates into "it was physically possible to increase power to +12lbs". I would think now this is the case whether the landing gear is up or down. Now lets say, you fly down on the deck and a 109 is after you. Would you say "oh my, it is VERBOTEN to use +12 but MAYBE it's gonna save my sorry ass for some minutes and go to +12, or stay with the book that says "well, factory gives clearence only for +9 lbs while in flight, but then up to 30 mins". Or does the engine kinda know you're cheating and it just won't let you go to +12 because "it's not right"?

I also think it yould be strangeif one called something an "emergency boost" that you can use for 30 mins?

Zach

[41Sqn_Banks]

Originally Posted by Kurfürst

There's a logical failure in your assumption that the boost cut-out would increase boost beyond +9 lbs. Its quite likely in fact that the pilots obtained +9 by using the boost cut-out, as on the Spitfire I.

This is not correct. The "early" manual states that +9 is obtained when the throttle lever is at the rated gate position, see attachments.


Sorry for OT, maybe one of the moderators can move the posts into FM subforum.

[lane]

Here's a couple more RAF Hurricane squadron Operations Record Books that mention 100 octane fuel.

[II/JG54_Emil]

Originally Posted by lane

Here's a couple more RAF Hurricane squadron Operations Record Books that mention 100 octane fuel.

Which says that it was tested and later that it wasn´t avaiable...

[ATAG_Snapper]

Hmmmm, no 100 octane at Shawberry. Shawberry!!!!! Well, there you have it, then. (He misspelled "octane" as well, another indicator that this whole 100 octane thing is a hoax).

Good catch!

[lane]

When viewed in context the picture is clearer. Other units and stations at the time were clearly doing quite a bit more than "tested" 100 octane:

151 Squadron


611 Squadron


74 Squadron


605 Squadron left Hawkinge on 28 May 1940 where 100 octane was obviously present enroute to Drem, also which obviously had 100 octane. For some reason they stopped over at Shawbury, which I understand was a Flying Training School and apparently didn't stock 100 octane ("unavailable"). It's interesting that it was determined that the Squadron was unable to proceed further without the 100 octane fuel. This suggests that once having converted to 100 octane, whatever fuel the flying school was using (87 octane?) was unsuitable.

610 Squadron Spitfire Mk I at Hawkinge in early July 1940. Note the petrol bowser marked for 100 octane fuel.


100 octane was required at Drem, 605 Squadron's destination, as well as Debden where 504 Squadron was based.



Obviously Drem was stocked with 100 octane fuel by February 1940

602 Squadron


Fighter Station, With the Spitfires in Scotland. Flight, No. 1631 Vol. XXXVII, March 28, 1940 (602 Squadron at Drem)

111 Squadron

[Kurfürst]

Originally Posted by BlackSix

· Added new Hurricane Mk I and Spitfire Mk I variants with constant speed propellers and fuel tanks filled with 100-octane fuel. Older 87-octane variants also remain available. (Please note that the new planes use existing cockpits, so the boost indicator gauge shows new extrapolated values)
[/FONT][/B]

End of story.

(reminds me awfully of the 150 grade tale )