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FM/DM threads Everything about FM/DM in CoD

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  #1691  
Old 05-17-2012, 10:27 AM
NZtyphoon NZtyphoon is offline
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Having found a 1942 (?) copy of R A Beaumont Aeronautical Engineering: A Practical Guide for Everyone Connected with the Aero Industry (modern reprint http://www.pitstop.net.au/view/aviat...uery/plu/23199) it's interesting to read what he says about the "four degrees (types) of boost" used by British aero engines:

(1) Take-off Boost - ...an additional amount of induction-pipe pressure....accompanied by an extra richening of the mixture which prevents an unstable combustion termed detonation...(p. 105)

(2) The Rated Boost - often known as maximum climbing boost....boost pressure is reduced to a value which permits the engine to run continuously at that particular power output...(p. 105-106)

(3)Override Boost - For the greatest possible power output for take-off or emergency, an increase in pressure above the normal take-off boost is permitted on some engines. This condition is used in conjunction with a special fuel. (p. 106)

(4) Maximum Cruising Boost....

Thus it is specifically stated that override or emergency boost was used only in conjunction with a fuel that permitted the higher boost rating.
Attached Images
File Type: jpg Types of Boost 1.jpg (154.0 KB, 10 views)
File Type: jpg Types of Boost 2.jpg (184.4 KB, 8 views)

Last edited by NZtyphoon; 05-17-2012 at 10:36 AM.
  #1692  
Old 05-17-2012, 01:08 PM
Ernst Ernst is offline
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Acctualy the SIM should be: SUPERMARINE SPITFIRE: CLIFFS OF DOVER. I almost sure the right the devs must go to BoM. At least no spitfires there. Most of data here come only from two sources: spitfireperformance.com or from Kurfurst site. I am almost sure that the DEVS had other data, maybe from URSS evaluations of the SPITS and 109s that not exactly match the data presented here.

Last edited by Ernst; 05-17-2012 at 01:27 PM.
  #1693  
Old 05-17-2012, 01:30 PM
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Crumpp Crumpp is offline
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Quote:
No, the engine couldn't run at 10.5lb boost with 87 octane fuel. The story about the pilot modding his engine with a match stick pertained to a Merlin III using 100 octane fuel and an unauthorised mod to obtain 16lb boost at low altitude Here's the some info on the use of 100 octane for development at RR:
No Seadog, it was possible as we can see from the Operating Notes. I am sure that engine was trashed after overboosting to +16lbs but it was definately possible on 87 Octane fuel.

It definately was not good but it was possible. Pulling the tit and overboosting the engine is not proof of the use of 100 Octane fuel.
  #1694  
Old 05-17-2012, 04:57 PM
Seadog Seadog is offline
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Quote:
Originally Posted by 41Sqn_Banks View Post
This is not correct. In the unmodified condition there was no restriction of the maximum boost when the boost control cut-out was used, thus the boost could be increased to about +17 lbs at full throttle at sea level.

See:
http://forum.1cpublishing.eu/attachm...1&d=1337242614
http://www.spitfireperformance.com/spit1-12lbs.jpg
Thus the boost override could not be used in the unmodded condition since it would cause almost instant engine destruction, which is a very bad thing for pilots to do during combat...It was only after 100 octane was used that the boost override became a useful adjunct to increase low altitude performance.
  #1695  
Old 05-17-2012, 05:12 PM
41Sqn_Banks 41Sqn_Banks is offline
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Quote:
Originally Posted by Seadog View Post
Thus the boost override could not be used in the unmodded condition since it would cause almost instant engine destruction, which is a very bad thing for pilots to do during combat...It was only after 100 octane was used that the boost override became a useful adjunct to increase low altitude performance.
Indeed. Though it was possible to use the cut-out without modification and without 100 octane, this was only allowed in case of failure of the boost control. It is clearly not allowed during combat situations. The Merlin engine manual is pretty clear about this and even put an emphasize on this restriction, as posted already:
  #1696  
Old 05-17-2012, 05:15 PM
Seadog Seadog is offline
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Quote:
Originally Posted by Crumpp View Post
No Seadog, it was possible as we can see from the Operating Notes. I am sure that engine was trashed after overboosting to +16lbs but it was definately possible on 87 Octane fuel.

It definately was not good but it was possible. Pulling the tit and overboosting the engine is not proof of the use of 100 Octane fuel.
read:


The above story clearly pertains to an engine that was already modded for 12lb boost (and thus using 100 octane) and the match stick mod permit boost up to 18lb, and it has already been established that Hurricanes in France were using 100 octane fuel by May 1940.

Maximum boost with 87 octane was 7lb:

http://www.spitfireperformance.com/spit2pnfs3.jpg

Last edited by Seadog; 05-17-2012 at 05:22 PM.
  #1697  
Old 05-17-2012, 05:16 PM
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klem klem is offline
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Quote:
Originally Posted by Ernst View Post
Acctualy the SIM should be: SUPERMARINE SPITFIRE: CLIFFS OF DOVER. I almost sure the right the devs must go to BoM. At least no spitfires there. Most of data here come only from two sources: spitfireperformance.com or from Kurfurst site. I am almost sure that the DEVS had other data, maybe from URSS evaluations of the SPITS and 109s that not exactly match the data presented here.
Well a key point about the spitfireperformance website is it gives us data collected at the time in reports written at the time. It is unlikely that Russian test organisations would have got any nearer to the true performance figures than the companies building the aircraft and engines and their prime user the RAF and its test organisations.
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  #1698  
Old 05-17-2012, 06:25 PM
Al Schlageter Al Schlageter is offline
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Did the Russians ever get any Spitfire Mk1s and/or MkIIs? They did get Mk Vs and MkIXs.

IvanK supplied most, if not all, of the data for the DEVS.

Great posts Seadog.
  #1699  
Old 05-17-2012, 06:49 PM
NZtyphoon NZtyphoon is offline
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Quote:
Originally Posted by Crumpp View Post
Pulling the tit and overboosting the engine is not proof of the use of 100 Octane fuel.
Wrong - there are two engine tests, one on 87 Octane and one on 100 which both ran up to 10.5 lbs boost - there was no boost override used which, as Beaumont observed, required special fuel - ie: 100 Octane - to achieve. Later Merlin engines, such as the 45 series, were capable of boost override of +18 lbs but needed, and were designed to use, 100 Octane to do so. Later still +25 lbs boost could only be achieved using 150 Octane.
  #1700  
Old 05-17-2012, 07:37 PM
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Crumpp Crumpp is offline
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Quote:
It is clearly not allowed during combat situations.
Where does it clearly say that?

It does not, the General Operating Notes clearly say he can use it.

Last edited by Crumpp; 05-17-2012 at 07:39 PM.
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