Mixture Control

B

Bletchley

Guest
Hello All,

I have butted in on a few threads over the past months to provide some information on the different types of fuel mixture controls that the WWI aircraft of OFF had historically. So I thought it might be usefull to provide a list, here, for those who might want to fly with a more 'authentic' mixture control. I have divided up the OFF aircraft list (only P2 a/c, as have yet to receive my copy of P3) into those with no mixture control (i.e. do not use mixture control in flight, just set it to the optimum or desired level before take-off); those with mixture control (rotary engined a/c and those, mostly Allied a/c, with altitude compensating carburettors); and those with an 'automatic' mixture control (this can be set as a workshop setting in OFF, and represents the late war German a/c with high or over compressed engines that had mixture control for high altitude incorporated into the main, or as a secondary, throttle control).

This is a rather 'rough and ready' guide, as it does of course depend on engine rather on aircraft - and some had a variety of engines, some with mixture control and some without. I can check or add to the details here if anyone wants particular date-based information for any particular aircraft in OFF P2, or for any a/c in OFF P3 that are not included here.

Allied

Camel = Mixture Control
Pup = Mixture Control
Triplane = Mixture Control
SPAD = Mixture Control
DH2 = Mixture Control
Bristol Scout = No Mixture Control (Unless RNAS)
N11 = Mixture Control
N16 = Mixture Control
N17 = Mixture Control
RE8 = No Mixture Control until September 1917
Se5a = Mixture Control
Strutter = Mixture Control

German

D.II = No Mixture Control
D.III = No Mixture Control
D.V = No Mixture Control
D.Va = No Mixture Control
D.Va 200 = Automatic Mixture Control
Dr1 = Mixture Control
D.VII = Automatic Mixture Control
E.III = Mixture Control
Hannover = No Mixture Control
Pfalz D.IIIa = No Mixture Control

Bletchley
 
Bletchley said:
Hello All,

I have butted in on a few threads over the past months to provide some information on the different types of fuel mixture controls that the WWI aircraft of OFF had historically.
Bletchley
Click to expand...

Excellent list thanks Bletchley should help everyone enjoy a more authentic experience.
 
Thank you for this important list for all "full real" aviators!:applause:
 
Hello Bletchley,

thank you very much for the list - did i say i was on the brink of asking you just THIS ! :wave:

To make things perfect - how would you then fly a plane in OFF without mixture control? Let's take the Alb. D.III - would you set the OFF sim settings to automatic mixture, or rather to a fixed one like 50 percent, or maybe 15 percent?

Thanks and greetings,
Catfish
 
Thanks Bletchley, good stuff. I would be interested to see a recommendation on how best to simulate historical throttle control too within the game, particularly for the various rotaries. Maybe once you receive P3....?
 
"To make things perfect - how would you then fly a plane in OFF without mixture control? Let's take the Alb. D.III - would you set the OFF sim settings to automatic mixture, or rather to a fixed one like 50 percent, or maybe 15 percent?" Catfish

You would need to set the mixture before take-off, and then leave it alone once you were in the air. The carburettors of the Great War are generally believed to have been adjusted to give a near stoichiometric mixture at ground level - this would give something like 95% of full power. Some early carburettors were probably adjusted to give a slightly rich mixture that would give 100% or thereabouts for take-off. There is some evidence, however, that German aircraft with the Daimler Mercedes or the Benz engines were adjusted to to give a slightly lean mixture at ground level, to give something like 85%-90% of full power for take off - with the trade off that the engine would then give 100% full power at about 6000-8000 ft, and would therefore be able to reach a somewhat greater altitude before over enrichment caused it to start loosing significant power (at altitudes of over about 12,000 ft plus). This was done, probably, by replacing the fuel jet in the carburettor with one of slightly smaller diameter:

"With a fixed jet, we can then only obtain best results for one altitude. But this simple device of having a smaller jet will give considerable increase in power as soon as the aeroplane reaches a sufficient altitude. At the ground and at low altitude there will be a small drop in power...for a jet with 2.8 per cent smaller diameter...the power reaches the limiting maximum at about 2,300 m...The maximum power on the ground is reached at a greater jet diameter" H.S. Bader, in Technische Berichte vol.2 1917-18 (Air Ministry English abstract)

I am not sure how accurately CFS3 and OFF models this enrichment of mixture with altitude. If it is an accurate model, then adjusting the mixture at ground level to give 80%-90% of full power would probably give best altitude performance - do a test flight at something like this mixture setting and see how high you can get - you should be able to get up to 15,000 ft, maybe a max of 17,000 ft with some difficulty. The trade-off is slightly poorer low level performance, for improved altitude performance.

"I would be interested to see a recommendation on how best to simulate historical throttle control too within the game, particularly for the various rotaries." 77Scout

Gnome: Full power/No power only, no mixture control

Gnome Monosoupape: Full power/no power, with mixture control

Le Rhone/Clerget/Bentley/Oberursel: power limited to 6,8,0 on keyboard, or no power, with mixture control

"How about DFW C.V please?" von Chlum

I think this had the Benz Bz IV: early versions of this engine had no mixture control. The later (overcompressed for high altitude) version of thgis engine (1918) had an altitude compensating carburettor that appears to have been similar to that of the overcompressed Daimler Mercedes, to give a mixture control for high altitude that was integrated into the throttle movement and engaged by pressing a button to override a 'gate' aimed at preventing inadvertent use at low altitude. In OFF this could be done by asigning Automatic Mixture Control in workshop settings.

I hope this helps :)

Bletchley
 
Great job again Bletchley

Perhaps you would consider reposting your synopsis of the FLAK, for WWI.

Cheers,

british_eh
 
Thats awesome Information, since i always wondered how to operate those Engines in OFF for maximum realism. :)
 
Hello Bletchley,
thanks for posting this - great stuff.

I do as well not know how OFF internally handles the settings, but:

Flying the Alb. D.III or V. in phase 2 seemed to (!) show no difference in mixture control. I usually adjust the control settings to more simple keyboard command (thus avoiding pressing three buttons to in- or decrease mixture), like one key for "mixture off", "full", and one key step up, resp. one step down.

Now what i found out there are 70 "steps" in the Fokker E.III, and appx. 120 for the Albatros types from full fat mixture to cut the mixture altogether, and vice versa.

In the Albatros i am able to start the engine with say full mixture, and then i lean the mixture manually by some 110 steps hacking away on the keyboard lol. So from the number of steps this would be appx. 11 percent of full mixture, and the engine is short before cut-off. But it still runs at some 1380 rpm, and it will do so at maximum altitude. I am able to lean it even more 2 or three strokes at very high altitude, but only then will the engine die as soon as i descend.
So it is obvious the 110, or 70 strokes do not represent a mixture of 100 percent, and you cannot adjust it percent-wise.

I do not know whether this represents percents of mixture on the vanilla WWII CFS3 planes, but maybe this could be adjusted for OFF ?

Did anyone understand what i wrote lol ?

Greetings,
Catfish
 
Bletchley said:
"How about DFW C.V please?" von Chlum

I think this had the Benz Bz IV: early versions of this engine had no mixture control. The later (overcompressed for high altitude) version of thgis engine (1918) had an altitude compensating carburettor that appears to have been similar to that of the overcompressed Daimler Mercedes, to give a mixture control for high altitude that was integrated into the throttle movement and engaged by pressing a button to override a 'gate' aimed at preventing inadvertent use at low altitude. In OFF this could be done by asigning Automatic Mixture Control in workshop settings.

I hope this helps :)

Bletchley
Click to expand...

Thanks Bletchley, I´ve been thinking, if isn´t mixture control of DFW C.V differently than in reality.Thanks for all that.
 
Superb info!

Essential information for the survivor of said... fracas!

But if I may,
Is "stoichiometric", terminology that was prevalent under canvas?

I am only equipped with a modern form of certification, so.....
Do you think this would be "field speak" or drawing board jargon?
Just how well equipped were the lads at the aerodromes?
One cant help but ponder, the state of the workbenches. :faint:
Most appreciated, thx!
CheerZ to P3!
 
"Perhaps you would consider reposting your synopsis of the FLAK, for WWI." british_eh

I could probably dig it up again, if there is still interest (?)

"Flying the Alb. D.III or V. in phase 2 seemed to (!) show no difference in mixture control" Catfish

They Alb. D.III and D.V had the same engine, a Daimler Mercedes D.IIIa

"In the Albatros i am able to start the engine with say full mixture, and then i lean the mixture manually by some 110 steps hacking away on the keyboard lol. So from the number of steps this would be appx. 11 percent of full mixture, and the engine is short before cut-off. But it still runs at some 1380 rpm, and it will do so at maximum altitude. I am able to lean it even more 2 or three strokes at very high altitude, but only then will the engine die as soon as i descend. So it is obvious the 110, or 70 strokes do not represent a mixture of 100 percent, and you cannot adjust it percent-wise."

The fuel/air ratio must be within 0.06 and 0.08, for modern aviation fuel (which generally has a higher octane than that used for aviation fuel in WWI). Somewhere below this ratio there will be a 'lean cut' of the engine, where there is not enough fuel to support combustion. Somewhere above this ratio there will be a 'rich cut' where there is too much fuel (the one you experience when descending from a higher altitude). A fuel/air ratio 0.074 to 0.08 will give a slightly over-rich mixture for 100% power; a ratio of 0.067 is stoichiometric (in theory, supports complete combustion, but in practice some fuel remains unburnt) for about 95% power; a ratio below 0.067 will give a 'lean economy' setting of between 85%-95%. So there is only a small range of settings that will keep the engine running, not 0% to 100%. The actual range might have varied considerably due to variations in the quality of the fuel (anything from about 50 octane up to around 70 oc, although 'octanes' were unknown then - there is an interesting discussion on WWI fuel over at The Aerodrome forum, if anyone wants to read more information on this) :)

I did an OFF test flight (P2 still) in a Alb. D.III last night, accepting the default mixture settings at 2500 ft, to see how high I could get before I experienced a 'rich cut' at altitude. Up to 5000-6000 ft the engine was fine. Above 6000 ft there was a slight drop in rpm. Above 8000 ft the engine started to sound rough, and there was a further drop in rpm. I managed to get up to above 10,000 ft, with rpm down to 1300 and a rough sounding engine. Above this, progress was very slow and I was eventually bumped off the computer (at around 11,000 ft) by my daughter, who needed it for her homework (the PC, not the Alb. D.III). I would guess from this that the mixture effects might be somewhat overmodelled in CFS3/OFF, and that to get historical performance at altitude some fiddling will have to be done with the mixture settings - tonight, I will try another test flight by reducing the mixture setting to just above a 'lean cut' at 2500 ft, and then see how high I can get on that setting. If that works, then it will just be a case of experimenting with settings between 'lean cut' and 'default stoichiometric' to find the 'sweet spot' where the a/c can reach high altitude without too much loss of power at low level. As I said in my earlier post, there is some evidence that carburettors were adjusted in this way as the war in the air progressed and there was a need to reach the higher altitudes (but it was supposed to have been done by the engine manufacturers, SPUD, not by mechanics in the field. The maintenance manuals for WWI engines that I have seen all give instructions to air mechanics NOT to tamper with the fixed fuel jets in the carburettor: which means, of course, that they most probably did, or could, as this instruction would otherwise be unneccesary).

Edit: Here is an example, SPUD, from the British manual "Hispano-Suiza Engines: Notes for Squadrons in the Field", Feb/Sept. 1918 (I don't have any German maintenance manuals, unfortunatley, just the English language 'capture' reports of German and Austrian engines, but I would expect them to have a similar instruction).

"The Zenith D.C. carburettor for 200 h.p. Hispano. The standard size of jets and choke tubes should not be altered, long experience having shown that they meet all the requirements"

Bletchley
 
I have been experimenting further with the mixture control, using the Alb. D.III in quick flight as my test bed. One oddity of the mixture control system in CFS3/OFF that I hadn't noticed before: having manually leaned the mixture, any movement of the throttle down and then back up to fully open will 're-set' the mixture back to the default 'balanced' setting.

This means that there is not much point in adopting a mixture setting less than the default, if you are going to use a 'no mixture control' approach to these German aircraft. On the plus side, however, if you do want to adopt this 'historically accurate' approach to engine control, then the standard or default setting will get you up to 14,000-15,000 ft, with a bit of a struggle, which seems reasonable to me (I looked up Peter Gray's profile of the D.III, Profile Publication no.127, and the altitude data only goes up to 13,120 ft or 4000 m, which suggests that the operational ceiling of the D.III wasn't much above this).

Bletchley

Still waiting for P3..... :)
 
Mixture Control - Phase 3

Hello All,

I have received and installed Phase 3 now, so I have been able to compare the altitude effects and update the list of aircraft:

"One oddity of the mixture control system in CFS3/OFF that I hadn't noticed before: having manually leaned the mixture, any movement of the throttle down and then back up to fully open will 're-set' the mixture back to the default 'balanced' setting". Good news: this is no longer the case - perhaps it never was there in Phase 2 either. It may just have been my flight stick getting old and cranky :)

I thought that altitude effects in OFF Phase 2 might have been very slightly over-modelled, but the effects on the Alb.D.III (Daimler Mercedes D.IIIa) seemed to me to be essentially correct - as, without touching the mixture control, I found that the altitude effects started around 6000 - 8000 ft, and I could get up to around 14000 - 15000 ft with a bit of a struggle. This appears to match the historical data that I have seen fairly closely :)

But in Phase 3 the altitude effects seem to have been amplified such that I notice the altitude effecting the engine from as low as 3000 - 4000 ft, and if I do not touch the mixture control I find an effective ceiling now for the Alb.D.III of around 10,000 ft. :(

Has the altitude effect been tweaked in Phase 3 to make mixture control more of a feature? Or is this a bug? I also noticed that full throttle rpm in Phase 2 was about 1380, but in Phase 3 it is now about 1300 (the nominal rpm for the D.IIIa at full throttle was 1400). I also tried the Alb.D.V (it had the same engine) in case the effects were specific to just the Alb.D.III, but found that the altitude effects were identical and the full throttle rpm even lower at about 1200 rpm.

Does everyone else find the altitude effects on fuel/air mixture amplified? (I notice that there has been some concern over the FE2b ceiling, in another recent P3 thread).

If so, using 'historically correct' mixture control for the various OFF aircraft will probably not be practical now, as the loss of power and low operational ceilings become too restrictive: but here they are anyway, for those who might still be interested, or in the event that the altitude effects can be tweaked back to the Phase 2 levels at some future point:-

Yes = Mixture Control; No = No mixture control; Aut. = Automatic

Allied

Airco DH2: YES
Bristol F2b: YES
Bristol Scout: NO
RAF FE2b: NO
Nieuport 11: YES
Nieuport 16: YES
Nieuport 17: YES
RAF BE2c: NO
RAF RE8: NO (YES from September 1917)
SE5a: YES
Sopwith Strutter: YES
Sopwith Camel: YES
Sopwith Pup: YES
Sopwith Triplane: YES
SPAD VII: YES
SPAD XIII: YES

German

Albatros D.II: NO
Albatros D.III: NO
Albatros D.V: NO
Albatros D.Va: NO
Albatros D.Va 200: Aut.
DFW C.V: NO
Fokker Dr.1: YES
Fokker D.VII: Aut.
Fokker E.III: YES
Halberstadt D.II: NO
Hannover C.III: NO
Pfalz D.IIIa: NO
Roland C.II: NO

Bletchley

I am enjoying Phase 3 very much, and hope that the above is not regarded as just negative criticism of a very good product. It may be this 'problem' is caused by some peculiarity of my PC set-up, but if not then it might be put on the list of things to tweak for a future patch - but it is not really of vital importance, as I guess that very few people would have been using my 'no mixture control' approach anyway :)
 
Is there a thread that talks about optimal mixture settings?

I checked search but did not have luck, I am flying a Spad XIII in P3 and it seems that I am not really seeing anything different when I play with the mixture controls at different settings and altitudes.

usually I can do with playing it on auto but I wanted to keep the 100 realism going.
 
With manual mixture control selected as a workshop setting, the default mixture setting for take-off is the one that will give you the best power or performance. You then only have to 'lean' the mixture as you gain altitude, keeping an eye on the rpm and listening to the sound of the engine: if you notice that rpm has dropped slightly, or the engine starts to sound a bit 'rough' then 'lean' the mixture [Ctrl + -] until the rpm rise again (although if you then lean the mixture too far, rpm will drop again - it needs a bit of fiddling with to find the correct setting). There is really no other guide than the rpm dial and the sound of the engine. Most German non-rotary engines would have been 'automatic' from about March 1918 onwards, so selecting Automatic Mixture Control for these in the workshop setting should be the historically correct option for these types from about March 1918 onwards.

Bletchley
 
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