Bug 174 on 12lbs boost. Review please.

[Kurfürst]

Originally Posted by 41Sqn_Banks

The use is reported on:
- 21 August 1940 http://forum.1cpublishing.eu/showpos...postcount=1441

Only mentions "emergency boost", at 4000 feet, does not specify boost used/obtainable.

- 2 and 30 November 1940 http://forum.1cpublishing.eu/showpos...8&postcount=55

Only mentions "boost cut-out", at 4500 feet, does not specify boost used/obtainable.

The page from the Pilot's Notes is from June 1940. Spitfire II entered service on 13 August 1940.

And the point is?

+12 lbs boost was only usable for take off and at low altitudes, and it fell of rapidly, in contrast to Spitfire I pilot notes which notes its effective up to rated altitude. There was no 'two different' sytems on the Spitfire II during BoB.

See:

[41Sqn_Banks]

Originally Posted by Kurfürst

There was no 'two different' sytems on the Spitfire II during BoB.

AP 1565B, Vol I, Section 8 was issued in August 1940 and mentions the "two different" systems. "6. The quadrant plate has a ... gate for the throttle lever in the take-off position". And in paragraph 7 mentions that the "red-painted thumb lever can be pushed forward in emergency".

[Kurfürst]

Originally Posted by 41Sqn_Banks

AP 1565B, Vol I, Section 8 was issued in August 1940 and mentions the "two different" systems. "6. The quadrant plate has a ... gate for the throttle lever in the take-off position". And in paragraph 7 mentions that the "red-painted thumb lever can be pushed forward in emergency".

They are the same. The throttle had a section for takeoff gate postion, and the "Red painted thumb lever" covered that position as safety switch, physically preventing the throttle to be pushed into the take off position until it was pushed forward.

Hence the confusion. The manual itself does not describe any two different systems.

[41Sqn_Banks]

Originally Posted by Kurfürst

They are the same. The throttle had a section for takeoff gate postion, and the "Red painted thumb lever" covered that position as safety switch, physically preventing the throttle to be pushed into the take off position until it was pushed forward.

Hence the confusion. The manual itself does not describe any two different systems.

Please explain how the red painted thumb lever was able to physically prevent the throttle to advance into the gate position.

[Kurfürst]

Originally Posted by 41Sqn_Banks

Please explain how the red painted thumb lever was able to physically prevent the throttle to advance into the gate position.

In the override position...?

Use your imagination a bit where that little thing just above the "Push" sign goes when the red painted thumb lever is rotated back. Yup, it prevents the throttle from being pushed into the takeoff gate.

[41Sqn_Banks]

Originally Posted by Kurfürst

In the override position...?

Use your imagination a bit where that little thing just above the "Push" sign goes when the red painted thumb lever is rotated back. Yup, it prevents the throttle from being pushed into the takeoff gate.

Both positions of the red painted lever are shown in the drawing. I painted red lines into the drawing to show that the lever doesn't obstacle the gate position in any of the two positions.

[klem]

Originally Posted by Kurfürst

In the override position...?

Use your imagination a bit where that little thing just above the "Push" sign goes when the red painted thumb lever is rotated back. Yup, it prevents the throttle from being pushed into the takeoff gate.

The 'little thing' above the Push sign is the actuator for the 'throttle closed warning' horn switch. Look closely.

Also examine the boost page that you yourself published here
http://forum.1cpublishing.eu/showpos...9&postcount=66

It says COMBAT 5 MINS LIMIT. 3,000 rpm +12lbs

The Merlin XII was able to use constant boost pressure of up to +12 psi using 100 octane fuel

With +12lbs available it would have been used whenever the pilot felt he needed it. There was no air ministry beaurocrat sitting in the cockpit to slap his wrist. Engine life/wear may have been a consideration but the Merlin XII was built nore strongly than the Merlin III for just that reason.

This has been hammered out again and again and you constantly come back with red herrings. Give it up.

[Buzpilot]

You have just posted the August 1940 manual of the Spitfire II, what engine limitations does it show? It would settle the matter quickly, wheter there was any change compared to the June/July manual, which clearly states +9 lbs for all out.

Is it possible, that the June/July manual was written for 87 octane?

[JtD]

+12 lbs boost was only usable for take off and at low altitudes, and it fell of rapidly, in contrast to Spitfire I pilot notes which notes its effective up to rated altitude.

Now how would they technically do that, make the boost of 12" drop off quickly instead of having it follow the outside pressure? What did the automatic boost control cut out do on the Spitfire II if not disable automatic boost control?

[Kurfürst]

Originally Posted by JtD

Now how would they technically do that, make the boost of 12" drop off quickly instead of having it follow the outside pressure? What did the automatic boost control cut out do on the Spitfire II if not disable automatic boost control?

As I understand, the cut out as its name suggest disabled to automatic boost control and gave direct control to the pilot over the boost. Maximum forward position on the throttle was set to open the cross section for +12 lbs at SL, and naturally this fell off with altitude; the pilot would have to open even further to compensate, which was however physically impossible - the throttle could not be pushed even further, it was already in the end position.

This graph suggest (see boost falling) that +12 fell back to +9 within about 2500 feet. This would also suggest that using the boost cutout was quite useless above that altitude, since it gave you the same performance as not using it at all.

http://www.spitfireperformance.com/p7280-speed.jpg

Come to think of it, it seems to work exactly the same as the 109E's 1-minute rating, altough that latter was automated.