Black 6 Thu 19th Apr update re Spit II

[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.

[Kwiatek]

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.

It was cleared.

I got original manual for SPitfire MK II from July 1940 where it is emergency boost +12 boost allowed for take off or for 3 minutes.

[41Sqn_Banks]

Originally Posted by Kwiatek

It was cleared.

I got original manual for SPitfire MK II from July 1940 where it is emergency boost +12 boost allowed for take off or for 3 minutes.

"Take-off" boost is not the same as "emergency" boost. See Pilot's Note General (1st Edition, June 1941):



The description exactly applies to the Spitfire II. There was a "gate" for "take-off" boost and a "cut-out" for emergency power.

[Kwiatek]

From July 1940





and another manual (probably later)

[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.