Mosquito and negative load

[peter]

Hello.  Just got the Mossie and jumped right into instant action.  The first thing i noticed is that when i put a negative G load on the aircraft the engines nearly die until i pull positive G's again.  What am I missing?  Are there fuel pumps that should be on?  I thought that everything would be configured correctly in an instant action setup.  Or, is this a bug or characteristic of the mosquito?

 

I'm not new to DCS, i have just never seen behavior like this with and other piston module.

 

Thank you.

[Rudel_chw]

5 minutes ago, peter said:

What am I missing?  Are there fuel pumps that should be on? 

the Merlin engines are carburetor equipped, a device that is sensitive to negative-G:

 

http://www.griffonmerlin.com/2010/09/30/why-did-rolls-royce-merlin-have-a-carburettor-when-the-daimler-benz-had-fuel-injection/

[peter]

So every time you push on the stick in the mosquito we have to deal with choking engines?  I have flown several piston driven aircraft and have never experienced this.

[DD_Fenrir]

1 minute ago, peter said:

So every time you push on the stick in the mosquito we have to deal with choking engines?  I have flown several piston driven aircraft and have never experienced this.

 

Yes. As explained above.

[bell_rj]

Today's patched has tuned the behavior - it'll still exist but will take longer to trigger apparently.

[peter]

Thank you bell_rj

[Richard Dastardly]

21 hours ago, bell_rj said:

Today's patched has tuned the behavior - it'll still exist but will take longer to trigger apparently.

It sputters a bit rather than cuts totally with a gentle pushover, it's more of a warning now.

 

The Merlin like everything else was the usual British mix of genius & frustrating mediocrity - the Spit & the Mustang don't suffer because the ones we have came after there'd been time to sort the details like carbs out. One might argue there was plenty of time to do that earlier, but well, I live here & I can understand it perfectly...

[DD_Fenrir]

28 minutes ago, Richard Dastardly said:

The Merlin like everything else was the usual British mix of genius & frustrating mediocrity - the Spit & the Mustang don't suffer because the ones we have came after there'd been time to sort the details like carbs out. One might argue there was plenty of time to do that earlier, but well, I live here & I can understand it perfectly...

 

You forget that even in the 1930's there was a school of thought that held that dogfighting was now impossible because of the speeds of modern aircraft.

 

The Merlin's were designed without negative-g tolerance partially because no-one foresaw the requirement to engage enemy fighters; the RAF doctrine could not predict the fall of France and were thus expecting hordes of German bombers from Germany, where no fighter aircraft could possibly accompany the bombers - not from just over the Channel with clouds of escorting 109s.

 

Add to this the already pointed out fact that fuel injection is not a catch all panacea - there are other compromises and complications that come with choosing it as the method to get fuel into the cylinder; RR chose the solution they a) had most experience in and b) could harness, tune and exploit most advantage from.

 

Too many glib opinions round here are based on hindsight and no appreciation of context or chronology.

 

[grafspee]

On 9/22/2021 at 3:07 PM, peter said:

So every time you push on the stick in the mosquito we have to deal with choking engines?  I have flown several piston driven aircraft and have never experienced this.

Piston engine does not care at what G is operated under. Most aerial engines use dry sump oil system so oil starvation is not instant.

It is fuel distribution system. S.U carb which is instaled in merlin 25 despite that is extreemly complex and very advanced, it uses float chamber. Main thig which allow this carb to work is gravity. So fuel sits at the bottom of the float chamber. As soon fuel is pushed up this carb stops working. Modern aerial piston engines dont use this tech anymore

Edited September 23, 2021 by grafspee

[Richard Dastardly]

3 hours ago, DD_Fenrir said:

 

You forget that even in the 1930's there was a school of thought that held that dogfighting was now impossible because of the speeds of modern aircraft.

 

The Merlin's were designed without negative-g tolerance partially because no-one foresaw the requirement to engage enemy fighters; the RAF doctrine could not predict the fall of France and were thus expecting hordes of German bombers from Germany, where no fighter aircraft could possibly accompany the bombers - not from just over the Channel with clouds of escorting 109s.

 

Add to this the already pointed out fact that fuel injection is not a catch all panacea - there are other compromises and complications that come with choosing it as the method to get fuel into the cylinder; RR chose the solution they a) had most experience in and b) could harness, tune and exploit most advantage from.

 

Too many glib opinions round here are based on hindsight and no appreciation of context or chronology.

 

 

You can *see* if dogfighting was now impossible by just trying it. The problem in a dogmatic - and bomber-focused - institution like the inter-war RAF and it's interface with government is making your voice heared. If you've ever had to deal with the government here then you'll likely know it's still exactly the same now. Britain had a whole empire to defend, it wasn't just about Germany.

 

You can't really wash away every opinion as "it's easy now with hindsight" - too many forgotten lessons from WW1 had to be relearned in WW2, and honestly far too much doctrine across all services was based on wishful thinking rather than intelligence gathering & practical tests.  The pressure carb just needed someone to see there was a problem first, there were people intelligent enough to devise it, if only someone important enough had asked or if only someone at Rolls had sat down and looked at the problem from a bit further away. And no, I don't believe german-style mechanical fuel injection was necessarily the best solution at the time, it's not the simplest.

 

Too many people assume glibness when someone doesn't want to write an essay, so enough of that thanks.

Edited September 23, 2021 by Richard Dastardly

[Bremspropeller]

14 hours ago, Richard Dastardly said:

The problem in a dogmatic - and bomber-focused - institution like the inter-war RAF and it's interface with government is making your voice heared. If you've ever had to deal with the government here then you'll likely know it's still exactly the same now.

 

That is a fundamental cronstraint that applies to any country.

Ze Germans had the exact same issues with "making voices heard".

[DD_Fenrir]

On 9/23/2021 at 6:42 PM, Richard Dastardly said:

 

You can *see* if dogfighting was now impossible by just trying it.

 

 

To what end? When there was a widely held belief that fighters were purely a defensive weapon and that attacks would only involve fleets of bombers? Why dogfight?

 

I'm sure it was noted that bunting caused a momentary loss in power but at the time it's effect would well have been deemed a passing nuisance. One didn't spend much time inverted as engine oil systems didn't take well to that kind of behaviour either, and bunting heavily is (a) highly uncomfortable (b)not considered part of the doctrine (ref. Fighter Area Attacks); it's only in the crucible of actual combat against actual enemy fighters that this suddenly becomes an altogether more critical issue.

 

You can dress your disdain up as much as you like and call your reasoning as superior to those in authority at the time, but your judgment is absolutely and inherently hindsight driven, it can’t not be. Your arguments DNA is based upon "they should have known"; that is the absolute epitome of hindsight.

 

By the way, if dogfighting was impossible with float carburettors how were so many Spitfire Mk I and Hurricane Mk.Is able to engage in so many over the UK in the summer of 1940?

 

Me thinks you overstate the case.

 

Edited September 25, 2021 by DD_Fenrir

[DD_fruitbat]

On 9/23/2021 at 6:42 PM, Richard Dastardly said:

 

The pressure carb just needed someone to see there was a problem first, there were people intelligent enough to devise it, if only someone important enough had asked or if only someone at Rolls had sat down and looked at the problem from a bit further away. And no, I don't believe german-style mechanical fuel injection was necessarily the best solution at the time, it's not the simplest.

 

 

I have just had a quick flick through to see if I could quickly find the relevant passage in 'Spitfire The History' by Morgan and Shacklady, which is the definitive tome on everything Spitfire, and by extension the Merlin development. However Its a thick book, so go educate yourself (Amazing book).

 

Anyway, It was a conscious decision in the original design and is documented in said book, to have a float carburettor rather than other options, as it enhanced straight line performance in the Merlin engine design, by about @20mph iirc, at sea level they concluded.

 

Shocking I know, that people had a better understanding back then of engines they were making rather than you, I mean that's crazy right??????

Edited September 25, 2021 by DD_fruitbat

[Morat]

This is grim reading overall - but the points made about the negative G behaviour of a Merlin being fixed by the Mark 25 are relevant to this discussion.

https://assets.publishing.service.gov.uk/media/542301dce5274a1317000b69/dft_avsafety_pdf_501355.pdf

[Skewgear]

On 4/4/2023 at 9:49 PM, Morat said:

This is grim reading overall - but the points made about the negative G behaviour of a Merlin being fixed by the Mark 25 are relevant to this discussion.

https://assets.publishing.service.gov.uk/media/542301dce5274a1317000b69/dft_avsafety_pdf_501355.pdf

Not sure they were fixed as much as temporarily worked around with Miss Shilling's Orifice.

Here's the master of all things Merlin writing about carb development and operation at detail and length, complete with Merlin carb diagrams. https://www.calum-douglas.com/article-1-rolls-royce-merlin-carburettor-development/

What I take from that is our Mosquito should be susceptible to rich/negative G cut-outs under sustained -G, bearing in mind the fuel flow restrictor was not a complete cure for the problem. That only happened with the 60-series Merlins and their Bendix-Stromberg pressure carbs (which is why our Spitfire doesn't cut out under negative G).

The other point of note is carb icing should definitely affect our Mosquito with its Merlin 24/25 engines and their SU AVT40 carbs, at least until the engine oil temp is up within minimum operating limits.

[Morat]

Frustratingly, Douglas doesn't seem to say what carburettors were fitted to the Merlin 25. The anti-g carbs (not the pressurised Bendix carbs which came later) were able to cope with both the lean and rich cut conditions and were definitely fitted to G-ASK which was the FB mkVI discussed in the report I linked above. Of course, that could have been a WW2 refit or a post-war modification.

Edited April 21, 2023 by Morat