1C Home   |   Register   |   Today Posts   |   Members   |   UserCP   |   Calendar   |   Search   |   FAQ

Go Back   Official 1C Company forum > 1C Publishing > IL-2 Sturmovik: Cliffs of Dover > Technical threads > FM/DM threads

FM/DM threads Everything about FM/DM in CoD

Closed Thread
 
Thread Tools Display Modes
  #1  
Old 05-06-2012, 12:53 PM
Osprey Osprey is offline
Senior Member
 
Join Date: Jan 2010
Location: Gloucestershire, England
Posts: 1,255
Default Bug 174 on 12lbs boost. Review please.

I'm about to update bug #174 on the Merlin 100 octane issue. I have re-written the bug for Artist as requested and would like a review. Kurfurst and Crumpp will be ignored, I am interested in ratification from one or more from Glider/Banks/NZTyphoon/Robo/lane. If this is ok I'll post the update, if there is anything I can add such as a good graph or table or test please post. Thanks.

Description
Presently if the Automatic Boost Control (ABC) is pulled on Spitfires and Hurricanes and full throttle applied there is no increase in boost above 6.25lbs even when the ABC is enabled. This results in reduced and inaccurate performance of RAF fighter aircraft.

During the BoB all frontline fighters had been modified to use 100 octane fuel in their Merlin II and III engines which allowed the engine to achieve 12lbs boost under strict limits. The Merlin XII engine fitted to the Spitfire II was designed to use this fuel from the factory. The approval and introduction of these changes gave the RAF fighters a performance boost in top speed, acceleration and rate of climb up to the Full Throttle Height (FTH) of about 18,000ft. At sea level a Spitfire was about 30mph faster when the ABC was enabled.

Merlin II and III (fitted to Spitfire Ia and Hurricane Ia)
The Merlin engines have a mechanical supercharger and can deliver up to 20lbs of boost at S.L. with the throttle valve fully open using either 87 or 100 octane fuel however this would cause serious engine damage by pre-detonation in the cylinders. Because of this the Merlin II and III have a boost controller fitted which limits the boost to only 6.25lbs. With modification to use 100 octane fuel the pilot could achieve 12lbs boost by pulling the Automatic Boost Control increasing the ‘safe’ power that the engine could produce. When the pilot applied the ABC on the Spitfire a thin wire was broken to indicate to the ground crew that ABC had been used and to make necessary checks. The Hurricane had a valve which was pulled (“pulling the tit”)

Merlin XII (fitted to Spitfire IIa)
The Merlin XII did not require modification in order to use 100 octane fuel. It had a slightly different throttle system and used a ‘gate’ on the throttle control. This allowed the pilot to achieve 12.5lbs boost on takeoff and is allowed up to 1000ft when he moved the throttle past the gate. Up to the gate 9lbs boost was achievable up to the FTH of 17000ft and later clearance was granted to use 12lbs boost (see pilot notes) There are lots of combat reports supporting this.

Here are the engine power ratings for given boost vs altitude
http://www.spitfireperformance.com/merlin3curve.jpg

Spitfire Ia prop tests using 6.25lbs boost and 87 octane
http://www.spitfireperformance.com/spitfire-I.html
It contains information on the clearance and usage of 100 octane fuel including this graph for the Spitfire Ia using 12lbs boost
http://www.spitfireperformance.com/s...-rae-12lbs.jpg

Here is the performance test for the Hurricane Ia using 100 octane fuel and 12lbs boost
http://www.wwiiaircraftperformance.o...rricane-I.html

Here is the performance for the Spitfire IIa
http://www.spitfireperformance.com/spitfire-II.html
Note that the boost for the tests is 8.8lbs, that is up to the ‘gate’ and this falls away from 17,500ft, the FTH.

Pilot notes for the Spitfire IIa indicate the limitations
http://www.spitfireperformance.com/spit2pnfs3.jpg

This report is evidence for the approval of 12lbs/100 octane prior to the Battle of Britain start
http://www.wwiiaircraftperformance.org/ap1590b.jpg

This is supported by lots of evidence of its use in combat reports (supplied by others in this bug report)

These reports not only supply data on the speed per altitude but also rate of climb and acceleration, plus some information of spin characteristics, dive ability and rate of turn. This should all be used to improve the current flight models for RAF types.

Last edited by Osprey; 05-07-2012 at 04:47 PM.
  #2  
Old 05-06-2012, 01:28 PM
Glider Glider is offline
Senior Member
 
Join Date: Jun 2011
Posts: 442
Default

looks good to me
  #3  
Old 05-06-2012, 02:25 PM
41Sqn_Banks 41Sqn_Banks is offline
Senior Member
 
Join Date: Oct 2007
Posts: 644
Default

- IIRC ABC stands for "automatic boost control" and not the cut-out.

- Spitfire II had "gate control" for fixed take-off boost (it gave a fixed throttle valve setting) and "boost control cut-out" like the Spitfire I, see this thread: http://forum.1cpublishing.eu/showthread.php?t=31319
  #4  
Old 05-06-2012, 02:28 PM
fruitbat's Avatar
fruitbat fruitbat is offline
Approved Member
 
Join Date: Jan 2010
Location: S E England
Posts: 1,065
Default

I think 1C will be as stubborn about this as they were about the FW190 bar in il2.
  #5  
Old 05-06-2012, 03:49 PM
41Sqn_Stormcrow
Guest
 
Posts: n/a
Default

Could you add any indications of the duration for which running at 12lbs / 12.5 lbs was allowed? They would have to model engine damage if the time was exceeded and is essential for any correct FM/DM
  #6  
Old 05-06-2012, 04:48 PM
Glider Glider is offline
Senior Member
 
Join Date: Jun 2011
Posts: 442
Default

The official limit was 5 mins but there was nothing to stop pilots going for a lot longer than that. Dowding issued a memo to all pilots that warned them of overusing the boost. In some of the combat reports you sometimes see words along the line of switched guns to fire, lowered the seat and pulled the plug.
  #7  
Old 05-06-2012, 04:52 PM
Osprey Osprey is offline
Senior Member
 
Join Date: Jan 2010
Location: Gloucestershire, England
Posts: 1,255
Default

@Banks: Thanks.
@Stormcrow: Pilot notes specify the limits.
  #8  
Old 05-06-2012, 05:56 PM
Bonkin's Avatar
Bonkin Bonkin is offline
Approved Member
 
Join Date: Aug 2011
Location: Yorkshire
Posts: 55
Default

Wow. That's a wealth of information that you have accumulated there Osprey.

I have an original Air Publication 1565A "The Spitfire I Aeroplane Merlin II Engine" manual which I thought might be useful - but I think those references you have must cover it all. I went through it specifically looking for performance charts but unfortunately there are none. There are change bars around the fuel and pitch sections though... and it states:

Fuel ....... Specification D.T.D.230
Note:- 100 octane fuel may be used, if the engine has been suitably modified.


Under the Automatic boost control it does mention +12lb/sq.in at sea level but does not tie this to 100 octane fuel.
__________________
Intel® Core™ i5-2500K CPU @ 3.30GHz
ASUS P8P67 Rev3
EVGA 1280MB GeForce GTX 570 HD Superclocked
8 GB DDR3-1600-Corsair Vengeance
750W Corsair Enthusiast 750TXV2UK PSU
Microsoft Windows 7 Professional 64 bit
Microsoft Sidewinder 2 FFB and NaturalPoint TrackIR3
  #9  
Old 05-06-2012, 09:02 PM
Osprey Osprey is offline
Senior Member
 
Join Date: Jan 2010
Location: Gloucestershire, England
Posts: 1,255
Default

Just had a speed test in the Rotol Hurricane. Couldn't get more than 230mph ASi out of it, trimmed, level flight, at various RPm (best 2650). According to this:

http://www.wwiiaircraftperformance.o...rricane-I.html

I should get 261mph with the Rotol which is 290mph TAS.
  #10  
Old 05-06-2012, 09:18 PM
Biggs Biggs is offline
Senior Member
 
Join Date: Feb 2008
Location: United States
Posts: 351
Default

i have a feeling as well that we will not have correct speed performance for these engines for a while.

I applaud the efforts of you and others to try and keep this issue near the forefront... 1C needs to get it right.
Closed Thread

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 03:45 PM.

Based on a design by: Miner Skinz.com

Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright © 2007 1C Company. All rights reserved.