Bug 174 on 12lbs boost. Review please.

[Kurfürst]

Originally Posted by bongodriver

which logic dictates are lesser in terms of level flight.

Yes. Which is why they let you use 3000 rpm instead of 2850 rpm in level flight with the same boost.

Like I said, the names were somewhat arbitrary, iirc in British manuals 'climb' rating was previously referred to as 'normal' (or the other way around?).

Back on new 100 octane models, the two things I wonder about:

1, What will be the new FM's be based on? There's not a single flight tests for +12 lbs performance. How are climb, turn etc. times are derieved - will they be estimated?

2, How will aircraft with a cooling system designed for ca. 900-1000 HP (+6.25) will cope with thermal loads occuring at 1100-1300 HP (+12 lbs). I would expect that temperature management will be more challanging at higher boost and power. Are there any radiator suitability figures available for the Spit/Hurri I?

[SlipBall]

2850 level seems an very extreme high number to me, but I have not flown that model much to have any real practical knowledge in game...

[41Sqn_Banks]

Originally Posted by Skoshi Tiger

This posses the questions, were there any modifications to the merlin XII engine that allowed it to work at the higher boost for the extended periods in 1941?

Or was it a decision based on accepting reduced engine life to keep the aging MKII competitive in air combat?

Or were the 1940 limits too conservative so they were increased?

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

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.
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.

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

[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".

[bw_wolverine]

Originally Posted by Kurfürst

This is a correct description IMHO for 1941. It is not a correct description for 1940.

It depends on what timeframe you are looking at.

With all due respect, the thing being modelled is the equipment, not the time period. If the IIa that was cleared for 9 lbs continuous is the same basic piece of equipment that was used in 1940, then we should have it.

If you want to model the orders from FC, then convince the various RAF squadrons to impose 6.25 lbs continuous on their pilots.

Otherwise, you should also be campaigning for the reduction in the 109 fuel tank to help simulate the time spent in France before heading over the channel and reducing fuel load, or whatever other things.

Simulate the tools, let us play with them as we see appropriate.

[Osprey]

Originally Posted by Osprey

Yes it was inevitable that "the worst person on the forum to answer his question" would do so and bend it against the RAF. His argument is of course about 'official clearance' in the manual, which is nonsense in RL combat and what actually happened. Indeed, a different throttle with a gate, 9lbs continuous hence the flight tests @ 9lbs (8., recommended 12lbs through the gate for takeoff power to 1000ft however this could still be used below the FTH (about 17k ft) anytime but for limited periods.

Predictably it took only about 3 more posts in the thread before........

Originally Posted by Kurfürst

This is a correct description IMHO for 1941. It is not a correct description for 1940.
............
It's only later, amended manuals (presumably from 1941) that are clearing +12 lbs for combat, too. <------ HA HA
............
Should 1C decide to introduce a post-BoB 1941 variant (doubtful), a +12 lbs version would be feasible, of course.[/b]

I love this.....

Originally Posted by Kurfürst

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.

max·i·mum (mks-mm)
n. pl. max·i·mums or max·i·ma (-m)
1.
a. The greatest possible quantity or degree.
b. The greatest quantity or degree reached or recorded; the upper limit of variation.
c. The time or period during which the highest point or degree is attained.
2. An upper limit permitted by law or other authority.

That would be 12 then.

Originally Posted by Kurfürst

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.

Yes I'm struggling to see why anybody would try to save their life if it meant breaking a sanction.

Originally Posted by Kurfürst

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.

You aren't reading the reports then. They do frequently say this but others say 'pull the tit' or 'through the gate', which means to operate the ABC therefore use 12lbs, otherwise it would be 6.25 or 9. It's RAF slang from the time.

Originally Posted by Kurfürst

"I call it wishful thinking".......

......."My assumption"......blah, 109 never beaten, blah...."Its quite likely"......lie, make something biased up

"Its only logical"......

More opinion.

Originally Posted by Kurfürst

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

Maybe it's because the engine would blow up after a while?? Jeez.......

Originally Posted by Kurfürst

....come up with whatever fantasy we may like.

We hear you Kurfurst. You think that 12lbs is 'fantasy' lol This thread is going to be locked, I can see it already.

[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.