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Gumtree
01-24-2011, 08:41 PM
G'day all,

What I was wondering is, does any one know if BOB will deal with engine neg G better than IL2 does currently?

I keep reading that Mrs Shilling's orifice was installed on all operation fighter by March 1941. This means that we will have a Hurricane and Spitfire that suffer from neg G fuel starvation (which is as it should be.

What I want to know is why does the IL2 Merlin cut out entirely when what I have read states that the engine would miss a beat (lose power for a brief period not stop running).

is this a limitation of the game engine or will this be modelled similarly in BOB?

WTE_Galway
01-24-2011, 10:55 PM
Originally posted by Gumtree:
G'day all,

What I was wondering is, does any one know if BOB will deal with engine neg G better than IL2 does currently?

I keep reading that Mrs Shilling's orifice was installed on all operation fighter by March 1941. This means that we will have a Hurricane and Spitfire that suffer from neg G fuel starvation (which is as it should be.

What I want to know is why does the IL2 Merlin cut out entirely when what I have read states that the engine would miss a beat (lose power for a brief period not stop running).

is this a limitation of the game engine or will this be modelled similarly in BOB?


Which Spitfire are you talking about?

The SU equipped merlins absolutely did stop when under sustained neg G ... and that is with or without the Tilly Orifice.

All the Tilly Orifice did was restrict the maximum rate of fuel flow to the float chamber and hence reduce the rate of flooding and resultant over rich mixture cut-out in the SU carbs fitted to early Merlins. (The needle valve was also modified.)

It absolutely did NOT eliminate the problem just made it more manageable.

Eliminating the problem completely was impossible without using a totally different type of carb or going to fuel injection ... the neg G cutout issue was "built in" to the float chamber based SU carb design.

Of course the onset of neg G flooding and cut out was much later in a Tilly/Shilling Orifice equipped Merlin than with a standard SU allowing brief excursions into neg G ... but the problem remained and sustained inverted flight was still impossible.

From 42/43 onwards Bendix and later Rolls Royce pressure carburetors were fitted and these actually DID eliminate the problem altogether. A pressure carb outfitted Merlin should not cut out.

Here is some info on just how the cutout occurred (note an initial loss of power followed by complete cutoff) :


http://www.absoluteastronomy.c...Shilling%27s_orifice (http://www.absoluteastronomy.com/topics/Miss_Shilling%27s_orifice)

(the early merlin) engine came equipped with a SU carburettor. When the aeroplanes equipped with such an engine performed a negative g force manoeuvre (pitching the nose hard down), fuel was forced upwards to the top of the float chamber of the carburettor rather than into the engine, leading to loss of power. If the negative g continued, the fuel would collect in the top of the float chamber, forcing the float to the floor of the chamber. This would in turn open the needle valve to maximum, flooding the carburettor with fuel and drowning the supercharger with over-rich mixture. This would lead to a rich mixture cut-out, which would shut down the engine completely, a serious drawback in combat.

K_Freddie
01-24-2011, 11:02 PM
Swig...swig... BBBUuurrrpp!!
Crunch.. munch ..munch..!
http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

WTE_Galway
01-24-2011, 11:10 PM
Also I assume we are talking Mk V here as the Mk I and Mk II are not official 4.10 flyable aircraft.

To clarify, correct behavior should be a temporary power loss (temporary fuel starvation) after which if Neg G is sustained an eventual flooding and mixture cutout.

If the neg G situation is removed the Merlin by accounts would restart eventually without pilot intervention. This self restarting could actually cause serious issues in twin engine aircraft if the throttle on the dead engine was not closed.

JtD
01-24-2011, 11:45 PM
This is a short pdf I made to help me understanding the mechanics of a float type carburettor under neg g. (http://mitglied.lycos.de/jaytdee/tillyshort.pdf)

Maybe worth checking before getting all excited about "fuel starvation" under neg g - as that wasn't a problem. The sketches roughly illustrate the proper workings, and also show that I'm not an artist.

Hope it helps.

M_Gunz
01-25-2011, 02:50 AM
As Oleg stated officially about the IL2 '1941' Spit V, it was mislabeled and is really a mid-1942 Spit V. He didn't say what kind of carb it uses.

However try nosing down hard in an I-16 some time.

Gumtree
01-26-2011, 04:48 AM
Galway,

As you state the neg G caused an initial loss of power that if continued would cut the engine. What I am saying is that the game as it is now practically stops the engine as soon as you go into neg g, this is not as it was described by the pilots.

As to the temporary fix, the flow restricter allowed pilots to run neg g for a short period.

What the restrictor did was metre out the fuel flow to a point where the plane could be kept at neg g for a short period of time to allow extraordinary manouvres in combat.

I have not made any claims about the fix removing the problem, what I asked was does any one know if the new game engine handle / simulate this better?

As to the plane well I am talking about the new game (COD) so I am refering initially to the mk 1 / 11.

Gumtree
01-26-2011, 04:54 AM
Please note I am talking about the game engine (COD) and not the dynamics of a flooded engine!

My opinion is that IL2 has never correctly simulated neg g on the engine. It is to abrupt.

Woke_Up_Dead
01-26-2011, 12:07 PM
Originally posted by Gumtree:

My opinion is that IL2 has never correctly simulated neg g on the engine. It is to abrupt.

I think the latest patch addressed that issue, now when you put I-16s and early Hurricanes in a negative-G maneuver their engines smoke and lose power as if their fuel mixture was set incorrectly.

thefruitbat
01-26-2011, 12:25 PM
Originally posted by Woke_Up_Dead:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Gumtree:

My opinion is that IL2 has never correctly simulated neg g on the engine. It is to abrupt.

I think the latest patch addressed that issue, now when you put I-16s and early Hurricanes in a negative-G maneuver their engines smoke and lose power as if their fuel mixture was set incorrectly. </div></BLOCKQUOTE>

+1

its much improved in 4.10

Gumtree
01-26-2011, 02:23 PM
Sounds sweet will have to try it out and see.