Effect of boost control cutout prior to +12 psi boost modifications

[Seadog]

The Merlin XX played only a small part in the BofB, but it was approved for 12lb boost during emergencies in Nov 1940:


and, since 12lb boost was available during TO right from its introduction, any pilot, at his discretion could use 12lb boost at any time or any altitude where it was possible, and there was no physical lockouts in the cockpit engine management system to prevent a pilot from doing this.

[TomcatViP]

Lol

- The XX was a post BoB product hence as a fighter eng it shld hve beneficed of the former improvements
- If 12lb MS is indicated it EXCLUDE any use of this level of boost above s/c alt

Sry but your statement does not match any engineering rules and is contradicted by the submitted text.

Let me explain : Supercharging put strain on your eng (300HP at recovering s/c alt)
If at low alt a boost level is restricted it certainly can't be achieved at alt !!

To give an exemple, my car has a turbocharger at 1.4 bar of boost (nearly 1.4 atm)

I once had a friendly race against a motorbike in a mountainous road from 1K up to 3K meters. My boost is electronically regulated. My turbo s/c is capable of much higher boost value to be reliable in a series car. The higher we went the better was my engine against the motorbike naturally aspirated engine (same boost same HP for me- Lowering boost for him) up to the point that my 1.4t cars "matched" his much lighter vehicle. BUT the temp went to high as did the strain and (hopefully) the electronic module give it away before I blew the eng.

That's what you risk with super/turbo charging. The lower the outside pressure is, the more the strain on the engine (mechanical or thermal respectively) will be.

If a limit is settled at low alt, it means that it can't be superseeded at high alt otherwise the limit would be put at s/c alt (but as it was difficult to have accurate pressure measurement at alt in a moving ac at the time they might have choose to rely on a low alt limit).

Baaah forget it I know that I am certainly loosing time writing this

[Seadog]

Originally Posted by TomcatViP

Lol

- The XX was a post BoB product hence as a fighter eng it shld hve beneficed of the former improvements
- If 12lb MS is indicated it EXCLUDE any use of this level of boost above s/c alt

Sry but your statement does not match any engineering rules and is contradicted by the submitted text.

The Hurricane/Merlin XX was introduced to combat in August 1940, but not given the designation Hurricane II until Sept 1940.

The text specifically allows 12lb boost in M gear for short periods of time during combat and during TO. It states the the boost override will provide 12lb boost up to 8500 ft after which it will gradually decline (to 9lbs at about 13000 ft):

3. The increased boost pressure will be effective up to approximately 8500 ft, above which the boost pressure will fall with increase of height.

However, as I've stated there is no physical interlock preventing a pilot from using the boost override in S gear, and using the Boost Override in S gear will provide additional power up to about 19000ft. Yes, this is an overload on the engine and cooling system but every pilot flying a Hurricane II always had the option to engage the boost override at any altitude and in either M or S gear.

[Blackdog_kt]

I think that getting near-unlimited use of war emergency power settings should only be allowed if

1) we are forced to fly with the same virtual aircraft, damage carrying over between missions and so on: i push it on one sortie, i do it on the next, i keep doing the same thing, it dies on me mid-channel on the 10th sortie or so...happy swimming back to Dover

2) this also applies to multiplayer along with an incentive to keep our aircraft alive (the usual IL2 server conditions where losing all your aircraft means you lose the mission, along with public stat-tracking so that everyone on the server can see who's the points maniac that's depleting all the team's aircraft), instead of having everyone over-boosting and "recycling" them by deliberately crash-landing worn-out airframes

3) it applies to all aircraft, 109s running a constant 1.45 Ata for example

and then we have IL2:1946 all over again

[Seadog]

"I had to return from Nuremburg in a Wellington II on one engine and used maximum boost and revs on a Merlin X for five hours with no sign of distress..." = +10lbs at 3000rpm.
The Merlin in Perspective,p25.

If COD is to have accurately reproduced flight and engine characteristics then the use of 12lb boost must be allowed with pilots only facing administrative penalties for doing so. The Merlin cooling and lubrication system could cope with 12lb boost and 3000rpm for long periods of time, but of course above 17750ft the Merlin III was no longer able to provide more than 6.25lb boost at 3000rpm.

[ICDP]

Originally Posted by Seadog

If COD is to have accurately reproduced flight and engine characteristics then the use of 12lb boost must be allowed with pilots only facing administrative penalties for doing so. The Merlin cooling and lubrication system could cope with 12lb boost and 3000rpm for long periods of time, but of course above 17750ft the Merlin III was no longer able to provide more than 6.25lb boost at 3000rpm.

If using quotes to backup your agenda at least make sure the plane in question is a Spitfire. The cooling system on a Wellington II was very different than that of a Spitfire Mk I, Hurricane, Defiant or any other plane with a Merlin. Finding one quote stating a Merlin could run at +10 lb boost for five hours does not mean they ALL could. Adequate cooling in the early Spitfires was a problem that was not overcome until the extra radiator was introduced on the Mk IX. Even then the issue wasn't totally cured. The problem was not so severe in the Hurricane because its radiator was directly in the prop wash. Have a read of this, this is taken from the chief pilot of the BBMF. They fly both Hurricanes and Spitfire as well as a Lancaster bomber.

http://www.key.aero/view_feature.asp...ection=airshow

Note the very large radiators directly under each ungine for the Mk II Wellington.
http://upload.wikimedia.org/wikipedi...ington_Mk2.jpg

[Seadog]

Originally Posted by ICDP

If using quotes to backup your agenda at least make sure the plane in question is a Spitfire. The cooling system on a Wellington II was very different than that of a Spitfire Mk I, Hurricane, Defiant or any other plane with a Merlin. Finding one quote stating a Merlin could run at +10 lb boost for five hours does not mean they ALL could. Adequate cooling in the early Spitfires was a problem that was not overcome until the extra radiator was introduced on the Mk IX. Even then the issue wasn't totally cured. The problem was not so severe in the Hurricane because its radiator was directly in the prop wash. Have a read of this, this is taken from the chief pilot of the BBMF. They fly both Hurricanes and Spitfire as well as a Lancaster bomber.

Fighters, by definition cannot run for more than about 40 - 50 minutes at 12lb boost/3000rpm because of fuel limitations, and yet if a fighter could only be flown for a few moments at 12lb/3000rpm then there would be no need to point out the increased fuel consumption at 12lb/3000rpm (see point 4 in AP1590G above at 12:27PM)

Cooling on the ground and cooling in the air are two separate issues. This is a test of a Spit V at the normal and combat ratings, and the plane was flown repeatedly to its service ceiling at 16lb boost:
http://www.spitfireperformance.com/aa878.html
and the aircraft was specifically tested for cooling suitability at 16lb boost and was found acceptable for English summer conditions and this required considerably more cooling than at 12lb.

I don't have any "agenda" other than historical accuracy. Every Hurricane and Spitfire in RAFFC could use 12lb boost, and there was no 'magic' limit after which the engine caught fire or blew up or seized up. Using 12lb boost simply increased the wear and tear on the engines and probably kept the ground crews up late at night doing engine checks but this probably caused little concern to pilots whose lives and/or aircraft were saved or who ensured kills by "pulling the plug" and going all out. It is quite telling that the Merlin III could be modded to accept 16lb boost on the Sea Hurricane I with essentially identical engines and cooling as per BofB Hurricanes.

If COD is going to be an accurate simulation then it has to allow 12lb boost at the pilot's discretion, and then factor in some kind of admin penalty for using it without justification.

[lane]

Originally Posted by Seadog

The Merlin XX played only a small part in the BofB, but it was approved for 12lb boost during emergencies in Nov 1940:


and, since 12lb boost was available during TO right from its introduction, any pilot, at his discretion could use 12lb boost at any time or any altitude where it was possible, and there was no physical lockouts in the cockpit engine management system to prevent a pilot from doing this.

Hmmm, it comes to mind that the publication date of 20 March 1940 for A.P. 1590B/J.2-W, Merlin II and III – Use of + 12 lb./sq.in. Boost Pressure followed actual unit conversion to 100 octane/+12 in the field in some cases; see for example 602 Squadron Operations Record Book, 151 Squadron Operations Record Book, 111 Squadron Operations Record Book & 74 Squadron Operations Record Book - Fwiw.

[ICDP]

Originally Posted by lane

Hmmm, it comes to mind that the publication date of 20 March 1940 for A.P. 1590B/J.2-W, Merlin II and III – Use of + 12 lb./sq.in. Boost Pressure followed actual unit conversion to 100 octane/+12 in the field in some cases; see for example 602 Squadron Operations Record Book, 151 Squadron Operations Record Book, 111 Squadron Operations Record Book & 74 Squadron Operations Record Book - Fwiw.

Remember your linking to info on the Merlin II and III, the document Seadog is linking to is for a Merlin XX. The Merlin XX was not used by fighters during the Battle of Britain so its boost rating is irrelevant since we don't have any flyable plane in CoD with a Merlin XX.

[lane]

Originally Posted by ICDP

Remember your linking to info on the Merlin II and III, the document Seadog is linking to is for a Merlin XX.

Oh, I certainly got that, sorry if I didn't communicate the point effectively. The issue I was addressing was that the operational use of a modification may precede, or follow for that matter, the official Air Publication document announcing the clearance or mod. Since Merlin III's were modified to operate at +12 lbs at the unit level before the publication date of the mod, it follows that the Merlin XX may also have been operated with +12 lbs emergency at the squadron level prior to the 15 November 1940 publication date.

For example:
16 February 1940 Operational conversion to the modification

20 March 1940 Publication of the modification

Originally Posted by ICDP

The Merlin XX was not used by fighters during the Battle of Britain so its boost rating is irrelevant since we don't have any flyable plane in CoD with a Merlin XX.

I agree that the Merlin XX has little to do with anything with respect to Viper’s initial subject or the sim FMs. Try telling that to TomcatVip though I’m less certain about your position on introduction into service of the Hurricane II with Merlin XX. See Seadog’s post #40: "The Hurricane/Merlin XX was introduced to combat in August 1940, but not given the designation Hurricane II until Sept 1940." McKinstry writes of the Hurricane II: "The first models emerged from the Langley works in September 1940, going into service initially with 111 'Treble One' Squadron and then replacing other Fighter Command units over the coming months."