Just out of curiosity, do many people use a carb setup on their
aviation Wankel's? Figured I'd ask since I've seen a few questions
regarding the standalone ecu for fi and not much regarding getting
a carb on the 13B (assuming most people use 13B's.)

Vlad

Not many. There may be one or two. The fact is an aviation carb
is as much money as a fuel injection system. I think Ken Welter
uses a 48 mm Weber carb. Webers cost over $1000 and are not easily leaned.
Two 48 mm Mikunis might be had for less than about $750 total.

Paul Lamar


This is going to sound ignorant but I have to ask anyway.
Why not use auto carbs? Last I checked Edelbrocks were
about $300 shipped from Summit/Jegs.
Vlad

Well you can but they cannot be leaned at altitude.
That is essential for low fuel burn.
For awhile there there was a remote leaning kit available for
Holly  four barrel carbs. I don't know if that is still
available.

Paul Lamar

Hi Paul,
Just an off-the-wall thought for your comments. Can a standard
auto carb sit atop a pipe with an adjustable window downstream
of the carb? Similar to the way a propane oven burner or bar-b-que
burner mixes air with the propane gas. At sea level the window
is closed, and all air goes into the engine thru the carb and the
venturi does it's thing. At altitude, the window in the pipe
downstream of the carb is progressively opened allowing air to
enter, thus less air thru the carb. Less air thru the carb would
equal less gasoline sucked in by the venturi and a leaner mixture
arrives at the engine. This approach would "lean" the mixture by
admitting more air rather than less gasoline. I'm probably missing
something obvious, if this were so simple it would have been done
years ago by aeroengine manufacturers  : )  Any thoughts?   Dave M


------------------------------------------
Yes that might work but you might also loose fuel through the window
as the pressure in the intake pipe goes below and above atmospheric pressure
on a regular basis per rev.

Ken Welter was fooling around with dynamic pressure effect
leaning. I never really figured out how his idea worked.

Unlike a car an airplane is always going at least 100 MPH so dynamic
pressure will be above static atmospheric pressure. If you feed
that from a forward facing scoop through a pipe and some sort of
valve into the intake pipe below the carbs that MIGHT work with
no loss of fuel. At 100 MPH at sea level dynamic pressure is
.18 psi. Not much compared to the pressure variations in the intake
manifold that are probably on the order of  +/- several psi above and below
atmos.. You would need a rather long pipe from the scoop to retain the
fuel vapor on average. It might also screw up the tuning if it were
beyond a certain size. A very short non tuned manifold like Ken was
using may have helped.

Another possibility is to just bypass the carb to the carefully designed
and sealed ram air box so any accumulated raw fuel drains
back through the the carb into the engine. That may or may not lean the
engine. It would be interesting to fool around with this.

Unfortunately our main man doing R&D making automotive carbs
work in aircraft was Don Dunbar. Recently deceased God rest his soul.
His plan was to copy Revmaster and remove the float bowl from the
bottom of a Mikuni carb and control the pressure of the fuel at the needle
valve orifice with a manual valve. It works for Revmaster. Dave McCandless
might be taking up the quest for his Rotec radial in his Funk.

RevMaster/Mikuni 40 mm carbs are a bit small for a rotary so the larger
motor cycle 48 mm Mikuni could be modified in the same way.

Paul Lamar


I looked into the Revmaster carbs and $330-380 is really not that bad
a price. One question though Mr. Lamar, when you say that the 40mm
carbs a a bit small for the rotary, do you mean a single is too
small or even twins?
Vlad


Yes even two are too small.

Two 48 in a p-port would yield around 250 HP.

40 squared is 1600

48 square is 2300

Power would be 1600/2300 X 250 or about 170 HP max with the 40 mm.

Paul Lamar