There is no altitude compensation with the standard Bing/ Rotax setup.
It is possible to lean the mixture by bleeding air into the balancing pipe
between the carbs but this is not an approved modification. You would do
this at your own risk and would certainly invalidate any guarantees
(including any airworthiness certificates).
The fact is that most installations do not fly high enough for this to be a
problem but if you fly in an area of high altitude you could compensate by
changing the needle settings and possibly the main jet but you would need to
take advice from Rotax on this.
----- Original Message -----
From: <irampil@notes.cc.sunysb.edu>
Subject: Europa-List: Bing 64 Carb and Altitude Compensation
>
> Greetings All,
>
> Can someone explain the theory, oft stated by salespeople, that
> Rotax engines with Bing carbs compensate for the lack of a mixture
> control. I have sought wisdom and counsel from a variety of sources,
> but have not found an answer. I've looked through our archive and several
> others. I read Mark Wilksch assertion that the Bing is not altitude
> compensation
> and I tend to believe it since many others (not all on the web) complain
> about
> decreasing efficiency and increasing fuel flow at high altitudes.
>
> This weekend I even asked the founder and former owner of Mattituck
> Airbase (now Teledyne
> Mattituck), an engine expert if ever there was one (plug:) (while touring
> his most
> excellent automotive museum at 21N!). Even he could not speculate on why
> constant
> vacuum (or constant depression for the UK folks) would lead to proper
> mixture
> at altitude. These carbs maintain constant downstream vacuum head despite
> throttle
> setting (compensating for the jet nozzle variably plugging the throat as I
> understand it.
> I don't think the venturi vacuum stays constant when ambient density
> changes.
> If true, the constant vacuum should prevent reduction in venturi suction
> head
> pressure with throttle and therefore lead to increased gas flow and too
> rich a mixture at altitude.
>
> I admit to being backwards about mechanicals (from time to time), so come
> on and tell us all how the Bing
> works for us and why Rotax would choose this device for an aircraft
> engine.
>
> Has anyone considered replacing the carbs or just adding a mixture
> control?
> Since I can get nitrous oxide cheaply, I was thinking about flowing some,
> say 10-20 l/min,
> into the 912S airbox. It would only be a few percent of engine air intake,
> but would lean the
> mixture a bit and I could watch the EGTs. One of my tanks holds about
> 1600 l of nitrous whereas
> the same oxygen tank would hold only 660.
>
> Better yet, is Nigel or somebody else persuing Rotax Fuel injection?
> Despite reports of
> Teal Rain efforts (www.vectorsite.net/twuavc.html ), it seems even the
> USAF Predator
> while having multistage turbos are not yet fielding fuel injection.
>
> Happy Holidays
>
> Ira N224XS Building Finished!! Testing and Tearing Down to commence
> Soon!
>
>
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