Black 6 Thu 19th Apr update re Spit II

[Talisman]

Originally Posted by 41Sqn_Banks

I'm not sure if the emergency boost was cleared for the Merlin XII at that time, e.g. for the Merlin XX it was cleared in November 1940, see http://www.wwiiaircraftperformance.o...xx-15nov40.jpg.

There is a link at the bottom of the trial data web page to the pilot manual (1940) which shows 12lbs boost available. It is in very small print.

Talisman

[41Sqn_Banks]

Originally Posted by Talisman

There is a link at the bottom of the trial data web page to the pilot manual (1940) which shows 12lbs boost available. It is in very small print.

Talisman

I'm sure you are referring to this page.
Note the header where it reads "Amended in Vol. I by A.L. 31 and P.N. by A.L./L". This means the content of the page was changed at a later date.
Judging from the date of the previous A.L. 30, which was issued December 1943, I would guess it is from early 1944 if not later.

The page without amendments looks like this: http://forum.1cpublishing.eu/attachm...9&d=1332086948

Note the "List of Contents" page from June 1940. Para 1 of Section 2 didn't contain "Engine data" but "Introductory notes".

http://forum.1cpublishing.eu/attachm...7&d=1332086792
http://forum.1cpublishing.eu/attachm...8&d=1332086871

See this post for more details: http://forum.1cpublishing.eu/showpos...&postcount=677

Of course this doesn't mean that +12 "Emergency boost" was cleared not before early 1944. I would guess it was cleared in November 1940 at the same time as the Merlin XX.

[Talisman]

Originally Posted by 41Sqn_Banks

I'm sure you are referring to this page.
Note the header where it reads "Amended in Vol. I by A.L. 31 and P.N. by A.L./L". This means the content of the page was changed at a later date.
Judging from the date of the previous A.L. 30, which was issued December 1943, I would guess it is from early 1944 if not later.

The page without amendments looks like this: http://forum.1cpublishing.eu/attachm...9&d=1332086948

Note the "List of Contents" page from June 1940. Para 1 of Section 2 didn't contain "Engine data" but "Introductory notes".

http://forum.1cpublishing.eu/attachm...7&d=1332086792
http://forum.1cpublishing.eu/attachm...8&d=1332086871

See this post for more details: http://forum.1cpublishing.eu/showpos...&postcount=677

Of course this doesn't mean that +12 "Emergency boost" was cleared not before early 1944. I would guess it was cleared in November 1940 at the same time as the Merlin XX.

Thanks for posting. Wikipedia says:
Merlin XII (RM 3S)
1,150 hp (860 kW); fitted with Coffman engine starter; first version to use 70/30% water/glycol coolant rather than 100% glycol. Reinforced construction, able to use constant boost pressure of up to +12 psi using 100 octane fuel; Used in Spitfire Mk.II.[76] First production Merlin XII, 2 September 1939.[18]

First production Merlin XII Sep 1939 and trial data from the link is dated May 1940, so I would hope RAF pilots were provided with an emergency boost capability, and other improvements, by the time the first Spit Mk II sqn was fully operational later in the year, or they would have had less capability than the Spit MkI. Amendments to RAF Air Pubs show a vertical line in the margin to mark the place the amended information has been inserted on the pages that are effected; I do not see any vertical lines on the page for the latest amendment. Still perhaps someone will be able to clarify the point you raise. Perhaps some combat reports from Spit MkII sqns will help if any of them mention operating the boost cut-out.

Talisman

[Kwiatek]

Originally Posted by 41Sqn_Banks

Of course this doesn't mean that +12 "Emergency boost" was cleared not before early 1944. I would guess it was cleared in November 1940 at the same time as the Merlin XX.

Not true see my post above with engine settings from Spit Mk II manual from July 1940 not November or later time.

[41Sqn_Banks]

Originally Posted by Kwiatek

Not true see my post above with engine settings from Spit Mk II manual from July 1940 not November or later time.

The July 1940 page only allows +12 boost for "take-off". As said, "take-off" boost is not the same as "emergency boost". "Take-off" boost was only allowed below 1,000 feet or for 1 minute whichever applies first. It was activated by a gate at the throttle. Pilot's Notes General actually says it is not effective up to any considerable height.

"Emergency boost" was allowed for 5 minutes and was effective up to FTH and was activated by the boost control cut-out, but this is nowhere mentioned in the Spitfire II manual, except for the posted page which is dated after December 1943. Of course it doesn't mean it was introduced after December 1943, it only shows that it wasn't cleared in June 1940.

Please see the relevant pages from the Spitfire II manual.

[IvanK]

It is my belief that that the Boost cut out "lever/catch" actually prevents the the throttle from being pushed past the gate. So if you want +12lbs be it for take off or in flight you still need to operate the Boost Cut out catch, this uncovers the gate and allows further throttle movement forward. With the catch in place the the Gate limits the throttle movement so max boost is the rated value (+9Lbs for the Spit MKII and +6.25Lbs for the MKI).

The division of Take off use and in flight use in the engine limitations section of the notes does not imo amount to much other than stipulating the desired 1 min take off limitation.
In other words Take Off Boost and Emergency boost are two different sets of limitations but the mechanism is the same. .... i.e. activate boost cutout to enable +12Lbs to become the max limited Boost.

Jpg below is from Spit MKI pilots notes dated June 1940

As can be seen this indicates removal of the Boost Cutout catch allows further forward throttle movement to achieve up to +12Lbs boost.

looking in the MK I manual to the same fuel system schematic as Banks illustrated above shows no gate per see in the MKI quadrant. As does the Throttle drawing in the MKI notes:




So a change in quadrant design seems to have occurred between the MKI and MKII. This commensurate with the increase in rated boost to +9Lbs in the MKII (as against 6.25in the MKI). However I don't believe this makes any real difference how you get +12Lbs boost in either case Boost Cut out switch needs to rotated forward.

I surmise that the inclusion of the gate in the MKII simply provides the pilot an additional tactile feedback for Rated (+9lbs boost in the Spit II) throttle position. So that if he has the the Boost cutout catch rotated forward then the Gate provides a tactile stop to +9lbs rated position.
In combat the pilot might enter the fight with Boost Cutout switch already rotated forward ready to go, so he doesnt have think about finding and pushing the cutout switch forward in the heat of combat. Then he can easily get +12 by simply rocking the throttle past the gate and pushing it all the way forward. If not in dire straits then he knows pushing the throttle to the gate will give him rated +9lbs boost.

Getting back to limitations these are not Instant failure values but rather wear and tear values on the engine.

[41Sqn_Banks]

Hello Ivan, I strongly disagree.

The division of Take off use and in flight use in the engine limitations section of the notes does not imo amount to much other than stipulating the desired 1 min take off limitation.

It's clear that they are two different mechanisms. Both increase the boost (and deactivate the boost control) but the "take-off" boost additionally uses "excessively rich mixture":

As can be seen this indicates removal of the Boost Cutout catch allows further forward throttle movement to achieve up to +12Lbs boost.

The Spitfire I manual states that "and so open full throttle at the carburretor at any time". It's not speaking about the throttle lever but the throttle valve, which can't be opened at any time when the boost control is enabled.

In combat the pilot might enter the fight with Boost Cutout switch already rotated forward ready to go, so he doesnt have think about finding and pushing the cutout switch forward in the heat of combat. Then he can easily get +12 by simply rocking the throttle past the gate and pushing it all the way forward. If not in dire straits then he knows pushing the throttle to the gate will give him rated +9lbs boost.

As soon as the switch is rotated the boost control is deactivated and and at low altitudes almost any throttle lever setting will give +12 boost.

Also looking at the throttle control drawings it don't see how the switch would prevent the throttle from moving to the most forward position or through the gate.

If both things were the same, how was it possible that in the updated Spitfre II manual take-off boost is given as +12.5 and emergency as +12?

[IvanK]

Greetings Banks. Good snippets in para IV excerpt especially.

These are however from the Generic or Pilots Notes General (AP2905) so arn't specific to the Spitfire installation. Though I do see your point there. I am trying to find these sections in my copy of the AP2095 (2nd addition dated April 1943) but so far cant... I guess thing s changed between the early and second versions.

Same goes for the discussion of excessive rich mixture for Take off boost its a generic statement. In short I believe it a discussion on Mixture use versus Boost but not an indication of a specific systems design.

Reading the Spit II notes I see what you are saying about 2 systems. The manual states in the take off section that max boost can be obtained by pushing past the gate no mention is made of the Boost Cutout switch in this circumstance. So I agree with you here and I was incorrect. So the gate gives +9Lbs. Pushing past the gate on Takeoff will give you +12.5Lbs but with ABC still operative. In Flight however as you said Boost cutout (ABC now not operative) gives you only +12Lbs ... so there is still something limiting you to +12Lbs .. (The mod driilled Bleed holes in the ABC I presume ?). What would happen say at 2000Ft if you simply pushed full throttle past the gate +12.5Lbs or +12Lbs ? Why this diff between +12.5Lbs and +12lbs ... no idea. I need to do some more homework here.

I will delve into the Merlin manuals and the various early Spit maintenance manuals to see if there is anything more specific.

Of note is the Spit II Merlin XII throttle system is different to the Spit MK I Merlin II/III system

What manual is the last jpg from the one with the line drawings ? This is dealing with a 2 speed supercharger running MS and FS gear (file name implies Merlin XX) , its not relevant to the Merlin XII or II or III as fitted to the Spitfire I and or II.

[NZtyphoon]

There could be a reason for the difference; read #1219. I know that there is a set of Spitfire II notes on Scribd; these show that there have been no amendments and it is possible that the operational limits for the Merlin XII were originally set at +9 lbs boost, later pushed to +12 1/2 lbs. (Paragraph 4 of the attached document does state that the Merlin XII was cleared for this boost.) It is possible that on operational units an amendment slip specifying +12 1/2 lbs was issued with the notes.

There is a small possibility of printer error, for example on p3 it describes the Spitfire II as being "powered by a Merlin III..."

Correction: This particular set of notes does incorporate some amendments, on top of page 6 and 19 "Amended by A.L.No.6" - interesting; this indicates they could have been republished later than July 1940.

[41Sqn_Banks]

Originally Posted by NZtyphoon

There could be a reason for the difference; read #1219. I know that there is a set of Spitfire II notes on Scribd; these show that there have been no amendments and it is possible that the operational limits for the Merlin XII were originally set at +9 lbs boost, later pushed to +12 1/2 lbs. (Paragraph 4 of the attached document does state that the Merlin XII was cleared for this boost.) It is possible that on operational units an amendment slip specifying +12 1/2 lbs was issued with the notes.

There is a small possibility of printer error, for example on p3 it describes the Spitfire II as being "powered by a Merlin III..."

Now that's a interesting find. The page without amendments only give +12 boost for take-off, but the 1939 documents states +12.5 boost for take-off.

However it's still clear from the June 1940 "List of content" that the page that contains the +12 emergency boost was not contained at that date and was added later and at that date only the page without +12 emergency boost was contained.

IMHO the easiest would be to get the combat reports of the "units concerned" (pun intended ) to find one that proofs the use of +12 in a Spitfire II or search in the National Archives for a similar doc like the one that clears the use of +12 emergency boost for Merlin XX.