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

[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.

[ICDP]

Originally Posted by Seadog

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 am not saying the engines should suffer from major overheating issues if pushed for a few minutes but they should and did overheat if pushed to high for too long. The Spitfire Mk Vc had a larger radiator and had better cooling than a Mk I and Mk II, so while it is very relevant it is not a perfect example. I know these engines could take more punishment than just a few minutes at full power, but they weren't immune to breaking if pushed. Definately more punishement than a mere admin warning. I also know that cooling on the ground and cooling in flight behave differently, I am just pointing out the fact that CoD does not model overheating on the ground very well. I can sit indefinately with the radiator open on the ground at 1200 rpm, something that couldn't be done in real life in a Mk I Spitfire.

Originally Posted by Seadog

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.

I know these planes ran at +12lb boost, I have no problem with that. My only issue is with the fact that you seem to be advocating they should run without problems at +12lbs boost until the fuel ran out. ALL of the scenarios you refer to would not require +12lbs boost for more than a few minutes. In reality it would be unlikey that someone would follow your full power dive for more than a few minutes. I know if I was in a Spitfire Mk Ia in 1940 I would not dive after a 109E in a full power dive for very long, especially considering that in a few short minutes I would most likely be flying over France at low altitude with an engine starting to run hot.

In the Mk Vc full power test you linked to the radiator temperature reached 124 C at 12.000ft after 3 minutes, OAT was +5 C. This is already 4 C higher than the recommended maximum, at 130 C the Merlin had to start venting to reduce coolant pressure (small hole on right side of engine cowling just behind the prop). If this test had been done at lower altitude in the hotter air then it would almost certainly have overheated without pilot intervention. It was easier to keep these planes cool at 12,000 or 24,000 ft than it was at SL.

Originally Posted by Seadog

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.

See my response above. I do not want unrealistically hard overheating modelling for any of the aircraft. What I do want is the fact that sometimes if you push too hard for too long that there MAY be repurcussions that go beyond an admin reprimand. Apart form the ground cooling issues CoD seems to do quite well in this regard.

[Seadog]

An aircraft might fail if run too long at 12lb/3000rpm, but then again it might not, and failure is not an automatic consequence, and in fact unless the engine has suffered battle damage it probably won't fail if run until fuel exhaustion, but of course running out of fuel is likely to ruin your day, in any event.

Regarding the Spit Vc test:

.A.A.878 is fitted with a temperate type cooling system. The engine oil inlet and coolant outlet temperatures were measured on two climbs to 24,000 ft. This takes considerably longer than the 3 minutes for which the combat power may be used, a concession for test purposes. The observed temperatures are therefore likely to be higher than would normally be obtained in a 3 minute period at the same outside temperature. Even so, the oil inlet temperature is within requirements (100 deg C) for temperate summer conditions and does not exceed the emergency maximum temperature of 105 deg.C when corrected to tropical summer conditions.

The observed oil inlet temperature has been corrected to temperate summer and tropical summer conditions of A.D.M.491 by adding 70% of the difference between the appropriate standard and the observed air temperature.



.......Under tropical summer conditions, the oil inlet temperature exceeded the maximum permissible (100 oC) above 15,000 ft. and rose to 105 oC at 22,000 ft., and remained at this figure to 24,000 ft. with no tendency for the temperature to fall. The temperature exceeded 100oC for about 4 minutes.

You will note that the test made allowances for increased temps during English and Tropical (IE Egypt) summers.

Dowding did take his pilots to task for probably abusing the use of 12lb boost:
http://www.spitfireperformance.com/dowding.pdf
but this was only one facet of abuse that could lead to engine failure, as Dowding's memo points out, but RAFFC had lots of spare aircraft and engines, and I doubt that pilots felt that they were using 12lb boost unnecessarily.

[ICDP]

Originally Posted by Seadog

An aircraft might fail if run too long at 12lb/3000rpm, but then again it might not, and failure is not an automatic consequence, and in fact unless the engine has suffered battle damage it probably won't fail if run until fuel exhaustion, but of course running out of fuel is likely to ruin your day, in any event.

Exactly, pushing too far for too long COULD lead to consequences a pilot would not like to face. That is what I want modelled, not some arbitrary limit of say 5 minutes = bang, conversely I do not want it modelled that I can run at +12lbs boost constantly without some potential consequneces. Your whole point seems to be that a Merlin could run at +12lbs boost until the fuel ran out. No pilot in real life WOULD EVER do such a thing from take-off until landing.

Originally Posted by Seadog

Regarding the Spit Vc test:

You will note that the test made allowances for increased temps during English and Tropical (IE Egypt) summers.

Read what I said again. My point was that at 12,000ft or 24,000ft it is easier to keep an engine cool than at SL. Had the test been done at SL the temperatures would have been much higher. Or to put it another way, flying full power +12lbs boost without taking circumstances and consequences into account is not possible. It is silly to assume there would be no potential issues running +12lbs boost until the fuel runs out.

Originally Posted by Seadog

Dowding did take his pilots to task for probably abusing the use of 12lb boost:
http://www.spitfireperformance.com/dowding.pdf
but this was only one facet of abuse that could lead to engine failure, as Dowding's memo points out, but RAFFC had lots of spare aircraft and engines, and I doubt that pilots felt that they were using 12lb boost unnecessarily.

OK, where did I say we shouldn't be allowed to use +12lbs boost? Also what use is a spare engine sitting in a workshop when you are 12,000ft over enemy territory? Like it or not the pilot notes have engine limitations for a reason, yes they may be conservative numbers but it doesn't mean they could be ignored.

These engines required carefull attention, not constant but they certainly weren't balls to the wall and forget about the consequences.

[TomcatViP]

Give them back their Starwar cruise ship and let's end this discussion. They won't give up until they got back their 25lb spit. Years of stupid mods have to get a 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.