Bing, altitude, & mixture

by Karl Kleimenhagen in General Tech Discussion 7 years ago

As I understand it, the Bing is semi-compensating for altitude and has no mixture adjustment. Can one optimize it for the altitude and power you fly at most often, or is there little adjustment? Can you over-optimize it, leading to the engine cutting out in other conditions?

Comparing the 912S to the 912iS, it seems the Bing is always running rich. Some Rotax spec sheets, though, indicate it should be within 10% at 75% power.

Karl

Re: Bing, altitude, & mixture

by Karl Kleimenhagen » 7 years ago

Karl Kleimenhagen

5 10 0

I see others are thinking about this, too: How well does the HACman mixture control work on a 912S? I haven't read through all the information on it, but it sounds like a pneumatic solution (and will work two carbs at once). I gather one can lean out for cruise and then turn it off to let the carb handle descent and climb. There seems to be a "gotcha," in that if used aggressively at the wrong power setting you can get detonation.

My curiosity about mixture control was piqued on seeing the ancient O-235 with the equally ancient MA carb can deliver the same cruise bsfc as the 912iS with all its electronic wizardry.

Of course, the 912iS is constantly adjusting mixture for you while monitoring the EGT, and it will never ice up. It automatically selects an optimum mixture from start up to shut down and will deliver the better trip economy, but in cruise the Lycoming can do at least as well and perhaps better.

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Re: Bing, altitude, & mixture

by Roger Lee » 7 years ago

Roger Lee

128 5.28k 4.98k

Hacman has been around quite awhile, but most who use them usually remove them to. It isn't a good option. If you live and fly out of higher elevations and altitudes then you can adjust the clip on the main jet needle, but doing so without an understanding of what's really going on in the engine or deciding to fly at much lower altitudes could be an issue. Even outside air temps will affect this. Where you engine gets its air will affect this. Outside cool air or someone using inside the cowl hot air.
The Bing should be a tad rich for high or max rpms. This is what may keep the engine safe and you from an off field landing and buying a new engine. I know people that have flown to 18K ft with a factory setup. The engine has been doing well and has had good longevity since its inception. For most this may be better left alone. I've seen several detonated engines and I don't think it's worth it to try and over tweak it.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Bing, altitude, & mixture

by Karl Kleimenhagen » 7 years ago

Karl Kleimenhagen

5 10 0

For most this may be better left alone.

I figured as much, but I'm just starting to learn about the 912S series. All I know for sure is it can fly nicely.

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Re: Bing, altitude, & mixture

by Karl Kleimenhagen » 7 years ago

Karl Kleimenhagen

5 10 0

My curiosity about mixture control was piqued on seeing the ancient O-235 with the equally ancient MA carb can deliver the same cruise bsfc as the 912iS with all its electronic wizardry.

Methinks I've been deceived. I was basing bsfc on Cessna POH data for the 152. Looking at their data for the 150 I see their bsfc numbers are at least 10% lower than what Continental claimed in some old dynamometer charts I found on the web.

Let's just say those older engines weren't half bad.

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Bing, altitude, & mixture

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