View Full Version : Questions about adjusting mixture

03-09-2005, 09:43 AM
I've spent the past couple of weeks learning CEM and I love it. Its' so much more fun to have full control of the a/c.

The last piece of the puzzle for me is the altitudes at which to adjust the mixture. I usually fly RAF and USAAF a/c, which don't require manual adjustment, but I occasionally jump into VVS a/c which have manual mixture control and I have yet to see any reference as to how to determine when to lean.


Is there a way to tell from the instrument panel that it's time to lean?

Are all a/c alike in terms of the various altitudes at which you need to lean the mixture?

How do mixture and supercharger stage relate to one another, if at all? In other words, if I reach an altitude that requires 60% mixture, and this happens to coincide with the recommended altitude to change supercharger stage, do I change both at the same time?

Any guidance on this is appreciated.

03-09-2005, 04:17 PM
I guess this amounts to an auto-bump. Does anybody have any advice on this?

03-09-2005, 04:37 PM
I never fly high enough to bother with mix, but in other sims, I use the tachometer to tweak the mix. As the mix gets where it should be, RPM will increase. It will dip again as mix goes beyond its optimal setting.

03-09-2005, 06:23 PM
Probably manifold pressure is a better indicator of when to adjust fuel mixture. It will drop off as you lose power, signalling a required mixture adjustment. However(!) your question about superchargers is excellent, manifold pressure also naturally drops off as your altitude increases (thats why we need superchargers), so be sure you know the specific altitude/supercharger relationship of your aircraft. A general rule of thumb is ~3000m, below which is low-supercharger-gear and a steadily decreasing manifold pressure until it shifts, and ~6000m, at which your 'average' supercharger no longer can keep up with the thin air (this of course does not include turbosuperchargered aircraft, or dedicated highaltitude aircraft such as Ta-152 or P-51).

03-10-2005, 03:45 AM
Thanks Lignite - I was hoping you might respond http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif I'll watch my MAP gauge and see what happens as I lean. I get the distinct impression that putting mixture on a HOTAS slider would be a good idea - but I'm all out of sliders at the moment. Somebody should make a WWII propsim throttle with mixture and pitch levers. Probably won't happen but that would do the trick.

03-10-2005, 05:04 AM
Excellent question.

For Corsair and Hellcat fans, supercharger shift altitudes are 5,000 and 15,000 feet according to the training films.


03-10-2005, 06:14 AM
Generally speaking, as also ZG77_Lignite said, the best thing to do in order to check if you're using the optimal compressor stage and mixture, is to look at the manifold pressure gage. This instruments measures the air pressure that is between the carburetor and the cylinders. This pressure is a function of: throttle opening, altitude, mixture and, if it is present, pressure provided by the compressor. At a given altitude, with constant throttle, try switching the compressor and the mixture. The combination which gives you the highest manifold pressure is the best one, and corresponds to the max power at that altitude and throttle opening. Moreover, at a given power (depending on throttle, altitude and RPM), the richest the mixture, the cooler the engine, the higher the fuel consumption.
This is in RL.

On FB-AEP-PF, unfortunately, this is not well modeled http://forums.ubi.com/groupee_common/emoticons/icon_frown.gif. In fact, it seems that changing the mixture has no significant effect on manifold pressure, consumption and engine temperature at any altitude. Except of course if it's too rich (black smoke and lost of RPM and power) or too lean (coughs and lost of RPM and power).

For F6F and F4U, in order to get max manifold pressure, you should switch to compressor stage 2 at around 800-900 m (less than 1500 m = 5000 ft suggested by the real flight manual) and to stage 3 at about 4-5000 m. Mix control 120% has not detectable effect and should not be used above 200-300 m, otherwise the engine gets killed and makes black smoke Mix control on those 2 aircraft is not at all well modeled, IMHO, since in RL it has 4 positions: idle cut-off (maybe 60%?), auto lean (80%?), auto rich (100%?) and emergency rich (120%?).

For La-5 to 7 and Yaks, more or less it's the same story. Switch to stage 2 at around 2500-3000 m. Mix should progressively decrease as altitude increases, since at around 5000 m with 100% mix the engine starts to do black smoke and loses power and RPM. At high altitude (>8000 m) mix should be less than 60%. Anyway, if it's too rich you have the black smoke/loss of power warning. I have no clue about the mix control of these airplanes in RL.

The same of Las and Yaks can be said for all the other aircraft in FB-AEP-PF that have active manual mix control (all of them should have that control: even in the all-automatic FW.190s and Bf.109s mix control could be bypassed manually).