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FM/DM threads Everything about FM/DM in CoD

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  #71  
Old 09-23-2011, 10:43 PM
IvanK IvanK is offline
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The 12Lb Boost lines and +16Lbs are computed projections of performance I believe. 12lbs we know was available on the MKI. 16Lbs was not available/used in the MKI. I think the first operational use of +16Lbs was on the Spit MKV with Merlin 45
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  #72  
Old 09-24-2011, 12:23 AM
Al Schlageter Al Schlageter is offline
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It does say Boscome (Aeroplane and Armament Experimental Establishment), so I would say it was from testing done there.

The source for the graphic is on the graphic.
http://www.spitfireperformance.com/
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  #73  
Old 09-24-2011, 01:58 AM
Seadog Seadog is offline
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Quote:
Originally Posted by TomcatViP View Post
*Fake (or very highly suspicious) !

pls refer to my earlier post if ever needed regarding power increase Vs speed

Quote:
Originally Posted by IvanK View Post
The 12Lb Boost lines and +16Lbs are computed projections of performance I believe. 12lbs we know was available on the MKI. 16Lbs was not available/used in the MKI. I think the first operational use of +16Lbs was on the Spit MKV with Merlin 45
Here's actual flight data from the Hurricane using 6 and 12lb boost:



Note how closely the performance increases match the previous data for the Spitfire I at 6 and 12lb boost.

I haven't read of the Spitfire I/II using 16lb in combat, but they must have run the Merlin III at 16lb boost to certify it for the Sea Hurricane, and those tests are just as easy to do in a Spitfire with a Merlin III.
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  #74  
Old 09-24-2011, 02:18 AM
lane lane is offline
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The following passage from Wing Commander Royce Wilkinson's book is interesting and germane to the discussion.

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  #75  
Old 09-24-2011, 02:30 AM
Blackdog_kt Blackdog_kt is offline
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Wow, nine aircraft in ten days?

Probably these guys flew quite a lot during those days, let's take a guess and say 3 to 5 sorties per day (depending on distances/time flown), this gives us nine "busted" engines for 30 to 50 sorties total for these 10 days.

Now, divide the amount of engines used up by the sorties and you get a per-sortie engine failure rate of 18% to 30% for going above the limits. In other words, almost one in five to one in three sorties results in a busted engine, not exactly a trivial risk.

Pretty interesting reference there to get a feel of how easy it was to break an engine under operational conditions, thanks for linking it.
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  #76  
Old 09-24-2011, 02:51 AM
lane lane is offline
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Originally Posted by Blackdog_kt View Post
Pretty interesting reference there to get a feel of how easy it was to break an engine under operational conditions, thanks for linking it.
Sure, no problem. 18 lbs., 3200 rpm clearly exceeded approved limits and as mentioned was hard on the engines. +12 lb., 3000 rpm on the other hand was approved and could be used operationally in emergencies without damage to the engine.



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  #77  
Old 09-24-2011, 03:56 AM
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Crumpp Crumpp is offline
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Quote:
without damage to the engine.
That is an entry in a Squadron logbook. The man who wrote that is not a technical expert in engines. He is an operator not an engineer.

The engineers clearly disagree with this operator in the instruction under entry number 11 for AP 1590B/J.2-W Merlin II and III Use of +12lbs Boost Pressure - Alterations and Precautions.

Paragraph 11 clearly states:

The use, in an emergency, of this high boost pressure is a definite overload condition on the engine....

Last edited by Crumpp; 09-24-2011 at 03:59 AM.
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  #78  
Old 09-24-2011, 03:33 PM
Viper2000 Viper2000 is offline
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Quote:
Originally Posted by 41Sqn_Stormcrow View Post
If however I well understood, the boost cut out was put because this high pressure was damaging to the engine in the long run and therefore its use was limited to real emergency cases.
ABC was introduced in order to prevent pilots from breaking engines by overboosting them below FTH.

I suspect that the cutout was originally provided in case the ABC failed, so that the pilot would still have access to direct throttle control.

The cutout modification was basically a hack which allowed the cutout to function as a combat power detent without extensive modification to the rest of the cockpit.

Later Spitfires didn't have a boost control cutout, but were instead fitted with a gated throttle which allowed the independent setting of the various engine ratings, including the combat rating. They also had double-acting ABC instead of single acting ABC, which meant that the throttle behaviour was a bit different. This is explained in the relevant AP from the period (I forget the number now, but it's been linked to in quite extensively in this forum).
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  #79  
Old 09-24-2011, 03:48 PM
Viper2000 Viper2000 is offline
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Quote:
Originally Posted by Crumpp View Post
Only after significant modification to handle such pressure, modifications that did not exist in 1940. Your document clearly separates it from the earlier Merlin II and III engines.
The Sea Hurricane was a special case; it was used on CAM ships and could not be recovered. The pilot would either parachute out or ditch when he ran out of fuel, as CAM ships had no way of accepting the aeroplane back for landing.

As such, both engine and airframe life were expected to be no more than one sortie, and it was therefore perfectly reasonable to give them a Viking funeral.
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  #80  
Old 09-24-2011, 04:18 PM
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Crumpp Crumpp is offline
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As such, both engine and airframe life were expected to be no more than one sortie
You know I read that part about one sortie life span. Thanks for pointing that out. Makes perfect sense to put your obsolete motors and so extremely over-boost them in a disposable airplane. Even then I would like to see what the engine was approved for at the boost. I would think it was just to get off the CAT.

Even a disposable fighter is worthless if it cannot fly to a target and fight.

Last edited by Crumpp; 09-24-2011 at 04:21 PM.
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