Ken Welter has been flying a Weber for a few years on his Coot. I
think he
is tricking the float chamber by using dynamic air pressure to lower the
fuel level.
The Weber uses a accelerator pump jet. The carb will pull through that
jet at low altitudes & WOT. Similar to the Holley power-valve. At high
alts. there wouldn't be vacuum enough to draw through that jet. Mild
automatic leaning. The Weber is a complicated device. It won't be easy
to duplicate, even just one circuit. My bet would be that when finished
the duplicate would cost twice as much as the original. You can't make
10 parts and get any economies of scale. There are at least 10 tunable
circuits on a Weber. They wouldn't make the carb that complicated if
they could do it simpler. I think it would be folly to go into the task
of making a carb. Buying a available unit is a vastly safer course. I
understand why everyone would like to make a custom unit. It may work, I
just don't think it would be cost effective. As much as everyone has had
some difficulties getting started I really believe Tracy's unit or
another EFI will end up being the easiest in the long run. If not that
buy a standard carb, and adapt a electronic ignition. My $.02 worth.
Bill Jepson
Bill there is a world of difference in the operation of a car and
an airplane engine. I am not trying to duplicate a Weber.
I'll be happy with the mixture anywhere in the range of 10:1 to 20:1.
The AC engine runs at constant RPM and load for 99% of the time.
The pilot sets the mixture as needed.
Klaus ran his engine with a small hole into the intake manifold connected
to a gravity feed tank. No venturi. No other parts. Nada. Nothing.
Klaus has also tried EFI. He took it off. He gets 50 MPG at 180 MPH
with a carb. He went 254 MPH in the Dayton to OSH 500 mile race with
a carb.
Many people have had trouble with EFI. Its not worth it. 99% of the airplanes
out there have trouble free carbs and every mechanic knows how to work
on them.
Paul Lamar ...No rotor no motor.
Hi Paul,
FWIW, I support Bill' s sentiment.
A right and proper carb is a complex animal and will be extremely
difficult to develop. By your own words, you state you'd be happy with a
mixture from 10 to 1 to 20 to 1----- the rotary already suffers poor
fuel economy, but at this time it's tolerable, what will 10 to 1 do to
the BSFC ? Will that still be tolerable?
As for the 99 % of the time, that other 1 % is called a go-around and
that is not the time to have a carb decide to stop your engine.
Your talents and vision are much appreciated, but in his instance you
are trying to reinvent the wheel to save a couple bucks. If the
difference of a couple hundred dollars between a "new" carb and an
existing proven / slightly modified carb is a purse breaker, then
perhaps that person should rethink his/her hobby options.
I believe you were on the right track developing the turbocompound. This
technology does not exist in present day hardware and will take a proven
engine to a new level of performance and economy. Consider this: if you
knock heads with Larry and develop a turbocompound that will increase
rotary efficiency 15 % what do get in return? At 12 GPH and $3.50per
gal, 100 hours of flying costs $4200-------15 % off that is $630. That
equals one carb. After the second hundred hours, the other carb is paid
for. After the third hundred hours, you need to take your wife somewhere
nice! The real benefit here is the turbocompound will keep giving back
in economy whereas the lower cost carb only saves you money once, at the
time of purchase.
I'm not pro carb or pro EFI, I just think as a group we can use your
brain to better advantage and would like to hear opinions of
others. Thanx, Dave M
The fuel burn is a function of the mixture. The pilot sets the mixture and
leans the engine at cruise and it stays there for the majority of the flight.
This is the major factor on fuel burn. Other things like atomization
of the fuel has minor effects at high engine power.
This could be done with a petcock and gravity feed. Nothing else is needed
in cruise mode. This is exactly what the Wright Brothers did.
Aircraft carbs do not have accelerator pumps.
Because of this your instructor told you set the mixture full rich in the pattern.
He also told you not to move the throttle lever rapidly.
One of our problems is there are no side draft aircraft carbs available
for aircraft engines as far as I can find out. The rotary is a side
draft engine.
Paul Lamar
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