12/23/2003 01:13:34 PM,
Serialize complete at 12/23/2003 01:13:34 PM
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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