Black 6 Thu 19th Apr update re Spit II

[klem]

Originally Posted by Moggy

Is that in case the pilot fail to report using the boost klem?

As a 'tell tale' the ground crew would know it had been used. I'm fairly sure I have read of that being the case but I would have to trawl through about 20 autobiographies

This page
http://www.spitfireperformance.com/spit1vrs109e.html
refers to 'breaking the wire' but I can't put my hand on definitive data.

[IvanK]

Klem the "Gate" it would appear only came in to use with the SPIT II. The Throttle Quadrant on the MKI didn't have a Gate.

Camber thanks for reminding us of that thread and your summary. Great reading.

[Moggy]

Originally Posted by klem

As a 'tell tale' the ground crew would know it had been used. I'm fairly sure I have read of that being the case but I would have to trawl through about 20 autobiographies

This page
http://www.spitfireperformance.com/spit1vrs109e.html
refers to 'breaking the wire' but I can't put my hand on definitive data.

No need for that klem, it makes perfect sense what you're saying.

[JG5_emil]

Ivan/Banks
"up to the rated altitude this will increase boost (about 12lb./sq.in. at sea level)."

It looks to me that 12 Lb boost is only possible at or close to sea level and that the amount of boost decreases with altitude, which makes sense to me. Is this correct or wrong?

[fruitbat]

Originally Posted by JG5_emil

Ivan/Banks
"up to the rated altitude this will increase boost (about 12lb./sq.in. at sea level)."

It looks to me that 12 Lb boost is only possible at or close to sea level and that the amount of boost decreases with altitude, which makes sense to me. Is this correct or wrong?

To quote 'The Spitfire Story' by Alfred Price,

Re 100 octane fuel and boost,

Although this gave no improvement at or above the 16,500 foot full throttle height of the merlin II and III engines fitted to spitfires, below that altitude the maximum boost pressure could be raised from 6 1/4 pounds to 12 pounds without causing detonation in the cylinders; the resultant extra power increased the maximum speed by a useful 25 mph at sea level and 34 mph at 10,000 feet.

[41Sqn_Banks]

[ATAG_Bliss]

It'll be interesting to see how the new FMs fly. They can show us all the graphs they want, but I still think it's a little premature to argue over the picture until we've experienced new FMs 1st hand.

Good bit of info though.

[fruitbat]

Originally Posted by ATAG_Bliss

It'll be interesting to see how the new FMs fly. They can show us all the graphs they want, but I still think it's a little premature to argue over the picture until we've experienced new FMs 1st hand.

Good bit of info though.

Agreed, but i'm already resigned to seeing our Mk I spits on 6 1/4 boost and 87 octane fuel performance unfortunately.

[camber]

Originally Posted by JG5_emil

Ivan/Banks
"up to the rated altitude this will increase boost (about 12lb./sq.in. at sea level)."

It looks to me that 12 Lb boost is only possible at or close to sea level and that the amount of boost decreases with altitude, which makes sense to me. Is this correct or wrong?

Hi Emil, it is Fruitbat said, a bit of extra info:

The supercharger can deliver about +20psi at sea level with throttle valve fully open, so the boost controller quietly (without moving the pilot handle!) moves the throttle valve to give +12psi if the red cutout is on. When altitude has increased to where the supercharger maximum output is +12 psi, the boost controller cannot control any more (both the pilot's throttle handle and actual throttle valve are at 100%), and the boost will drop from then on.

This will happen a bit earlier than if the boost controller was on +6 1/4 boost, so the full throttle height is lower for +12psi than +6 1/4 psi. It is still >15000 feet though.

The gate system is different though because it gives a set throttle valve position...it will give the higher boost at takeoff, then decay quite rapidly to the lower controlled value (and stay there) as you climb. I think the system should act exactly the same if you are through the gate or not, above a few 1000 feet.

camber

[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.

High Banks,

Just to clarify, are you suggesting that the RAF introduced a new MkII version of the Spitfire in the middle of the battle that did not have emergency operational power for combat and thus was slower in combat than the Spit MkI with operational emergency boost engaged?

The Spit MkII test data states the following vs the Spit MkI (N.3171):

4.0 Level Speeds.

.......The top speed of this aeroplane is the same as that of N.3171 but is reached at 17,600 feet, 1400 feet lower than the Mk.I Spitfire. Consequent upon this and the increase in power of the Merlin XII over the Merlin III below full throttle height the aeroplane is about 6 - 7 miles per hour faster at heights less than 17,000 feet and about 4 - 8 m.p.h. slower at heights above 20,000 feet. It should be noted that though the boost pressure on the Merlin XII is +9 lb. per sq.inch as against +6 1/4 lb. per sq.inch on the Merlin III there is little difference in the engine power at heights of 16,000 feet and above.

So, if the Spit MkI is 6 to 7 mph slower at heights less than 17,000 ft, then to my mind the data indicates that the level speed of the Spit MkI at 1,000 ft was 287 mph ( Spit II, 294 mph at 1,000 ft minus 7 = 287). If the Spit I pilot then engages operational emergency boost, he then gets an extra 25 to 30 mph, giving a speed of 312 mph (287 + 25) at 1,000 feet on 100 Octane fuel.

So, with the Spit MkI at 312 mph on emergency boost at 1,000 feet and the Spit Mk II at 294 mph without emergency boost, it is slower in combat than the Spit MkI unless the Spit MkII has emergency boost available. Or am I missing something? Surely the Spit MkII had emergencey power operational boost available to provide and extra 25 to 30 mph for operational emergency, just like the Spit MkI.

For me, the test data shows how the Spit MkI can be bench-marked against the Spit MkII in terms of performance for the CloD dev team. What do you think?

The fact that the CloD sim provides a Spit MkI that only makes approx 240 mph level speed at 1,000 feet, rather than the historic record of approx 287 mph (312 mph with emergency boost on 100 Octane fuel) is very disappointing from a historical accuracy perspective.

Also, surely the boost dial on the Spit Mk II in the CloD sim should read over 8lbs.

Talisman