Engine Cut-out for Spitfire Mk. V during Negative G?

[I/JG54_chuishan]

First to be clear that I do not intend to be nit-picking, Team Fusion has done a great job in modelling all the aircraft in Desert Wings.

 

I'm curious about the negative G engine cut-out feature, or the lack thereof, existed on Spitfire Mk. V. As far as I know the first RR Merlin engine installed with a Bendix Stromberg "negative-g" carburettor was Merlin 50, but most of the Spitfire Mk. V aircraft were installed with Merlin 45 & 46 engine, including those Mk. Vs modelled in Desert Wings series.

 

However as I remember none of the Mk. V model has the engine cut-out effect during negative G in Desert Wings, including the Mk. Va, which NACA claimed that there is a cut-out during negative G.

 

I'm aware that a quick solution was worked out somewhere during 1941 and 1942 to install a copper ring into the fuel valve, but that measure only deals with the risk of total flame-out when the aircraft is coming out of a negative G maneuver, preventing too much fuel flow flooding the carburettor. It cannot counter the initial cut-out when the aircraft enters a negative G maneuver.

 

The Spitfire Mk. Vb in IL-2 GB series has no engine cut-out too.

 

If there's something else that I've neglected on this issue? May be some explanations from TF? Thanks a lot! @Buzzsaw

 

 

 

[FTC_Karaya]

Very late production Mark V Spitfires had Merlin 50 series engines which were the first Merlins to feature Bendix Stromberg injection carburettors. Not exactly sure when these were put onto production machines but I suspect it wasnt before the end of 1942 or beginning of 1943.

 

Before that the RAE came up with the so called "Mrs Schilling orifice" which was a diaphragm which limited fuel flow into the engine. Neg G cutout is a 2 stage phenomenon:

 

1) First off, fuel is forced to the top of the carburettor by the negative acceleration forces, thus starving the engine of fuel (lean cutout).

2) Meanwhile fuel continues flowing into the carburettor unrectricted filling it up. When pos G are restored again, the engine will start choking on the excess fuel inside the carburettor chamber (rich cutout).

 

What the Schilling orifice effectively prevented was the rich cutout from happening as it limited fuel flow precisely to that amount which was necessary for the engine to run at full power. Even with the orifice installed the engine would however cutout due to fuel starvation in the first few seconds of the bunt.

 

From a different discussion of the matter:

Quote

There were three different setups tested in these trials one of which was the RAE Negative G carburettor (Mrs Schillings Orifice) The others Large capacity Jet wells, and another one that is a variation of the RAE version. and a combination hybrid. The test results are quite complex with varying results as a function of system used, Boost at the time of application of negative G. In the end the most effective proved to be a combination of the Large Jet wells and the RAE modifed version of Mrs Schillings orifice . This combined hybrid system was the recommendation of the test for fleet incorporation.

 

I have no idea when this was effectively introduced in the RAF fleet but as the document that reports the results is dated February 1942 I would suspect it took another month or two until service introduction.

In any case I would expect that the early variants of the Spitfire Mk.V and Hurricane Mk.II experienced the same cutout effects as the earlier Spitfire Mk.I/II and Hurricane Mk.I.

Edited November 2, 2020 by Karaya

[ZachariasX]

9 hours ago, Karaya said:

What the Schilling orifice effectively prevented was the rich cutout from happening as it limited fuel flow precisely to that amount which was necessary for the engine to run at full power.

It did thus require the engine to run at max. power, as the restricttor would calibrate to this max. fuel flow. If the engine consumes less at partial power, you can still flood the carb and case a rich cut-out.

[I/JG54_chuishan]

On 11/2/2020 at 4:49 PM, Karaya said:

In any case I would expect that the early variants of the Spitfire Mk.V and Hurricane Mk.II experienced the same cutout effects as the earlier Spitfire Mk.I/II and Hurricane Mk.I.

 

I'm totally agree with your findings Karaya, that's exactly what I've come up with.

 

So I'm very confused that neither GB nor DW has modelled it.

Edited November 3, 2020 by I/JG54_chuishan

[JV69badatflyski]

On 11/2/2020 at 9:49 AM, Karaya said:

Very late production Mark V Spitfires had Merlin 50 series engines which were the first Merlins to feature Bendix Stromberg injection carburettors. Not exactly sure when these were put onto production machines but I suspect it wasnt before the end of 1942 or beginning of 1943.

 

 

From the spit production list, we can conclude the Merlin 50series (50/55/M/MA/etc..) equipped spits started to be massively produced from end Feb43..

[Talisman]

Alex Henshaw  https://en.wikipedia.org/wiki/Alex_Henshaw  flight testing a MkV Spitfire at Castle Bromwich Birmingham 1941. This ( apart from a few brief seconds with XF) is the only known footage of Alex actually flying. The acting of the "American" is am dram at its worst, but there was a war on.

 

 

Edited November 3, 2020 by 56RAF_Talisman

[I/JG54_chuishan]

29 minutes ago, 56RAF_Talisman said:

the only known footage of Alex actually flying.

 

Thank you for the video Talisman! 

 

I can actually see the black smoke resulting from the engine cut-out. Also when the aircraft is flying inverted, you can tell from the sound that the engine is cut-out but not totally flame-out, and pilot can open up again when the aircraft comes out of the maneuver. That's exactly what has been simulated on Spitfire Mk. I/IIs in Clod.

[Talisman]

At 1 minute 16 seconds the female pilot in the film appears to say "WTF", but I am not an expert lip reader LOL.

 

Happy landings,

 

56RAF_Talisman

[Buzzsaw]

Miss Shilling completed her testing and the modification to the carbs, her 'Orifice' was completed in early 1941 and Miss Shilling and her team went base by base installing the mod on the Merlin carbs in service.  It was installed in all models of the Spitfire in front line service by March of 1941.

 

The Spitfire VB did not go into service till approx. May/June of 1941 so it would already have the mod.

 

The Spitfire VA was in service from mid February of 1941 but as the best available aircraft it is most likely the Squadrons equipped with this type were the first to receive the Shilling mod.  Even if they did not, there would potentially be at most a two week period prior to the mod being added when the aircraft would experience neg G cutout.

 

As it stands in the game, all types with Merlin XLV have the Shilling modification, including the Spit VA.  I am not going to create a new 'Early' type of VA model without the Shilling mod just in case for the two week period when these aircraft MIGHT not have had the mod.

 

Regarding the VA model which was tested by NACA in the U.S:

 

The RAF supplied the USAAF with two aircraft for testing purposes... both early models, the Spit VA and Hurricane IIA... both were shipped to the US by sea and likely took some time to get there... they were tested in December of 1941 long after both types were out of service with the RAF.  It is probable the aircraft sent were from among the first batch produced, therefore would not have the modification.  As I have mentioned, all aircraft in the field were converted by March 1941.

 

The actual real question is whether or not the IIB with its Merlin XII should have the Shilling mod.  As it stands now, it does not have the mod, and this engine experiences negative G cutout.

 

But in fact, the IIB did not come into service till March of 1941, so it is more than likely it came equipped with the Shilling mod.

 

So if I do any correction, it will be to the IIB, and to add the Shilling mod to it.

 

The Bendix/Stromberg injection carb won't come till the VC is added... this was generally a part of the whole package which upgraded the VC along with the new wing/gun and Hispano II's.  So players will see this with the VC and IXA if we go on to create TF 6.0 and these aircraft.

[Buzzsaw]

On 11/3/2020 at 6:29 AM, 56RAF_Talisman said:

Alex Henshaw  https://en.wikipedia.org/wiki/Alex_Henshaw  flight testing a MkV Spitfire at Castle Bromwich Birmingham 1941. This ( apart from a few brief seconds with XF) is the only known footage of Alex actually flying. The acting of the "American" is am dram at its worst, but there was a war on.

 

 

The aircraft in this video, if it is a V model, is clearly a VA.

 

And because it is at the factory, likely the mod is not installed.

[ZachariasX]

46 minutes ago, Buzzsaw said:

And because it is at the factory, likely the mod is not installed.

How come he can fly inverted without any sign of carb flooding?

 

Also, during inverted flight, there is no engine lubricarion. As soon as you approach 0 g even when pushing forward, oil pressure drops immediately. If he was to deliver this aircraft to the squadrons, he‘d be fighting for the Germans.

[Talisman]

7 hours ago, ZachariasX said:

How come he can fly inverted without any sign of carb flooding?

 

Also, during inverted flight, there is no engine lubricarion. As soon as you approach 0 g even when pushing forward, oil pressure drops immediately. If he was to deliver this aircraft to the squadrons, he‘d be fighting for the Germans.

 

Oil pressure might drop, but I would think there should remain enough lubrication for a short period without danger.

 

Happy landings,

 

56RAF_Talisman

[ZachariasX]

1 hour ago, 56RAF_Talisman said:

Oil pressure might drop, but I would think there should remain enough lubrication for a short period without danger.

 

Happy landings,

Yes, there obviously is. You could see that by the engine not quitting after the inverted flight. But if you do that in todays flying Spitfires, their owner will probably do more than just frown upon you.

[Talisman]

Having read the book written by Alex Henshaw https://www.amazon.co.uk/s?k=sigh+for+a+merlin&i=stripbooks&adgrpid=51995124183&gclid=EAIaIQobChMIj6r8wrXu7AIVRLDtCh1k3QjkEAAYASAAEgKrvfD_BwE&hvadid=259129823222&hvdev=c&hvlocphy=9046066&hvnetw=g&hvqmt=e&hvrand=7167761480572751148&hvtargid=kwd-299637634279&hydadcr=11438_1787607&tag=googhydr-21&ref=pd_sl_6jidvqcg5a_e

about his time testing Spitfires, his accounts of "showing off the Spitfire", as he calls it, are even more hairy than the video film above, which is rather tame in comparison.  The book is a great read and I recommend it.  Also, his accounts of dive testing the Spitfire are awesome.  No one in their right mind would fly a Spitfire today like they were tested and flown in WWII.  We stand on the shoulders of giants.

 

Happy landings,

 

56RAF_Talisman

[I/JG54_chuishan]

19 hours ago, Buzzsaw said:

Shilling mod

 

Thank you for your reply, Buzzsaw!

 

I think there is a common misunderstanding about the effect of the Shilling mod, which leads people to believe that it can prevent engine cut-out in negative G conditions. I would like to make a clear-up on that.

 

First, engine cut-out happens when fuel is forced to the top of the carburettor by the negative acceleration forces, while the entrance of the needle valve (which fuel should flow in) is located at the bottom of the carburettor. So at this time no fuel flow is exiting the carburettor to mix with the air, thus cutting the engine.

 

Second, the Shilling Mod limits the fuel flow enters the carburettor, but it cannot prevent the fuel already in the carburettor coming to the top, leaving empty space down at the entrance of the needle valve.

 

So the conclusion is, with Shilling mod installed, no fuel flow can exit the carburettor, the engine will still cut-out.

 

Finally, as to what the Shilling Mod really does. It actually limits fuel flow entering the carburettor precisely to the amount which is necessary for the engine to run at full power. So that when the aircraft is coming out of a negative G condition, the fuel flow coming out of the needle valve will not be too rich, so that the fuel will not flood the mixture chamber and cause a total flame-out.

 

Many sources on the Internet claim that the Shilling mod prevents engine cut-out, I'm afraid they are incorrect. This video has explained it just fine: 

 

 

 

 

Edited November 6, 2020 by I/JG54_chuishan

[Sokol1]

... 

 flight testing a MkV Spitfire at Castle Bromwich Birmingham 1941.

 

Curious is the footage of early model cockpit in this video, showing old fuel cock out model and control for extend landing light, removed for latter models.

Comment in Youtube, explain:

 

This wasn't filmed at CBAF, this is Eastleigh airfield, the home of the Supermarine Aviation Works near Southampton. The ferry Spitfires are a Mk.Ia R7157 and a Mk.IIa P7961. Some of the footage of R7157 was shot later when the aircraft had left 12 Maintenance Unit and had been issued to 124 Sqn. You can clearly see the ON-* code in the take off segment.

 

..."the aerobatic display was mostly filmed at Ratcliffe. [/quote]

 

This footage was used in the movie "The First of the Few" released in September, 1942 and is a mix of several footage. Some of the "Ferry Pilot", 1941 documentary (dramatized).

 

 

 

[Buzzsaw]

Hello Chuisan

 

Sorry, but to suggest the Shilling modification did not solve the problem of negative G cutout is incorrect.

 

It did not solve the problem 100%, but to all intents and purposes, it provided the fix which was required for combat.

TF has all the Royal Aircraft Establishment documents which detail the tests of this mod.

 

While we are not claiming the current modeling is 100% correct, it is not inaccurate to the point of being an issue.

 

We have always been planning to add some negative G effects to improve the functioning of other carburetor types... and when we do so, we may tweak the Rolls Royce version with the Shilling orifice, but most players will probably not notice the difference unless they prefer to fly upside down.  ?

 

Last comment on this subject.

[I/JG54_chuishan]

5 hours ago, Buzzsaw said:

Hello Chuisan

 

Sorry, but to suggest the Shilling modification did not solve the problem of negative G cutout is incorrect.

 

It did not solve the problem 100%, but to all intents and purposes, it provided the fix which was required for combat.

TF has all the Royal Aircraft Establishment documents which detail the tests of this mod.

 

While we are not claiming the current modeling is 100% correct, it is not inaccurate to the point of being an issue.

 

We have always been planning to add some negative G effects to improve the functioning of other carburetor types... and when we do so, we may tweak the Rolls Royce version with the Shilling orifice, but most players will probably not notice the difference unless they prefer to fly upside down.  ?

 

Last comment on this subject.

 

Thank you Buzzsaw. 

 

Then I shall give you guys all my trust on this subject. I apologize if there's any damage to the authenticity of your work because of my doubt. 

 

I am looking forward to the new negative G effects you mentioned and please continue your effort. ♥️