Paul

 Any words of advice about the Revmaster?
 http://revmasterautomotive.com/revmasteraviation/?p=206 One per
 rotor required. This seems like a very simple device and works on
 very low pressure.Dan F

 Oops! I meant the Aerovee, as it has larger
 outlet.http://www.aeroconversions.com/products/aerocarb/index.html

 Dan F

 I have no idea. I can't even find the diameter of the throat on
 the web site. Just a lot of BS. Perhaps somebody knows how
 big it is :)

 It appears to be a strictly gravity feed device.
 That means to use it with a fuel pump you need to
 have a header tank very close to the carb with a return
 fuel supply to the main tank. I suspect these super low
 pressure carbs may be subject to vapor lock.

 Paul Lamar

 After not getting very far with the MIKUNI round slide carbs, I decided
to
give the Aerocarb a shot. Performance turned out to be really good.
Manifold pressure at WOT is generally running at less then one inch
below
atmospheric. This is with the 35mm size on the 12A based single rotor.
Mixture control seems to be very sensitive. My set up on the test stand
 is
with a pressure regulator set to 2psi. Being a very simple device,
there
are some very peculiar handling procedures required. Since there is no
float or diaphragm, fuel flow has to be manually shut off when the
engine
is not running. For starting, fuel can not be opened until the engine
is
turned with the ignition on, otherwise it will flood immediately. Which
gives a starting sequence like -crack the throtle, turn on the ignition,
push the starter switch while opening fuel flow in pushing mixture
 control
to full rich. As it looks now, I am going to use it in the airplane in
 the
same way.

FWIW

Richard Sohn
N2071U

Richard

 Thanks for your info, just what I was hoping for! For my single rotor
 the 38mm size is rated 125 to 160hp (planned 130hp). In response to the
 apparent small ID's the web site says the throat size is a "perfect flow
 passage" , which I take to mean very smooth transitions between
 diameters with laminar flow. Your results show they know what they are
 talking about. :)

 Dan F

 Is it 35 mm or is it 38 mm?

 2.76 square inches for a 1.875" (47.6 mm) diameter runner used on
 a p-port 7500 RPM 250 HP 2 rotor. Half of that is 125 HP for
 a one rotor 13B p-port.

 We used a dual 50 mm Weber on the 13B p-port 250 HP
 dyno engine. We did not measure the pressure drop.

 A p-port 12A at the same RPM should put out 230 HP.
 Half of that should be 115 HP. One inch below 29 inches
 is 28/29 times 115 HP or 111 HP in theory.
 What RPM are you running Richard?

 Only 1.77 square inches for a 38 mm (1.5 inch) diameter runner.
 That certainly is remarkable performance.
 Seems a bit small to me.

 Paul Lamar

These numbers are from 6000 RPM WOT. My intake runner is 25" at this time.
Plans are to go to 21" finally. Runner diameter is 1.5" or 38mm . BTW, the
35mm AeroCarb had to be set to its lowest fuel flow for reaching a
manageable mixture ratio. EGT is close to 1500F.

Richard Sohn
N2071U --

What brand of pressure regulator are you using Richard?

One cubic foot of fuel is 53 pounds.

Therefor 12 inches of fuel is .36 psi.
One inch is about .03 psi.

2 psi divided by .36 psi is 66 inches of fuel head.
That translates to a big airplane with high wing tanks.

I think you would be better off with less pressure.
The only way is to lower the pressure regulator setting.

How far above the carb are your wing tanks? If less
than 66 inches you would be better off by
doing away with the regulator and the fuel pump
if used.

The trouble with that is the fuel pressure
is then going to be a function of deck angle as the tanks
are well above and well behind the carb. This is the
perennial problem with these kinds of super low pressure
carbs and high wing tanks. As far as I can tell, other
than a very expensive and accurate pressure regulator
in the 0 to 1 psi range, one will have serious problems.

Aero V does not talk about this high wing problem.

I first heard about it from Steve Bennett at Great Plains
aircraft. Every year he gives a talk at Sun n Fun in
the engine tent on the subject of carbs.

This is from his web site.
http://www.greatplainsas.com/iposa.html
====================================================
A few facts to consider

1" of fuel head is equal to .022 psi

46.17" inches of vertical fuel column is equal to 1 psi

Fuel boils at 170 degrees F

An average engine will consume between .435 and .450 lb. of fuel per hp
per hour.

Cowling air typically runs 60 F warmer than outside ambient air
temperature, with isolated hotter spots.

A fuel system must have an adequate fuel vent.

Types of carb are float bowl, diaphragm, and float less.

Aircraft carbs, Zenith, Bing, Weber, Solex are examples of float bowl
carbs. These carbs can operate on gravity feed or usually up to 4 psi of
fuel pressure. Most of these have a float bowl well vent to prevent vapor
lock.

Tillitson, Ellison, Zama, are types of diaphragm carburetors. These carbs
usually require some fuel pressure to operate correctly.

POSA, Lake Injector, Revflow and Aero Carb are floatless, diaphragm less
carburetors. These carbs do not operate well on more than .5 lbs of fuel
pressure; yes that is less than pound of fuel pressure. These carbs do not
vent any fuel vapor that may form in the body to the venturi as there is
no float bowl well or diaphragm vent.

If a vapor lock forms in the body of the carb or the fuel line preceding
the carb, the engine will start to surge and eventually quit if the vapor
lock cannot be moved through the carb. It requires the absence of heat to
remove the vapor lock from POSA style carbs as fuel pumps are not used.

The fuel in the tank should be full. This is because a full tank of fuel
will make the carb run richer and an almost empty tank will run leaner.
Remember that you are operating on .022 pound of pressure per inch of
vertical fuel column. So if you have 12" of vertical fuel drop, (this is
from the top of the tank to the carb, not from the top of the tank to the
bottom of the tank) with a full tank this is .022 x 12 = .265 psi or a
little over " lb of fuel pressure. For simplicity say our tank is only 6"
tall. If we have used a half a tank of fuel we now have used 3" of fuel
and have a 9" drop to the carb. So, 9 x .022 = .198 lbs of fuel pressure.
Less than a quarter of a pound.

===============================================================================

Paul Lamar

The pressure regulator I am using is a HOLLEY 12-804. Get it through
Amazon.com for $31.35 .

Richard Sohn
N2071U

I suspect that is set too high Richard or it is not accurate
enough. 2 psi is the absolute upper limit.
That is why the mixture control seems to be very sensitive
Are your tanks in the wings or in the cowl?

Paul Lamar


The aero V carb looks a lot like the old Posa carb made prettier.
Ellison took the same concept and developed a nice device.

The main difference between the Ellison and the Posa/aero-v is the way
the fuel is delivered into the sliding throat.

The Ellison also uses a pressure regulator and delivers the fuel into
the airstream via the brass tube with the holes in it. The wider open,
the more holes and when almost all the way open, there are more holes to
deliver the appropriate fuel. I have already talked about the mixture.

The AeroV, if it is like the Posa, which I am almost sure it is, has a
tapered needle fixed probably to the slider. This needle slides into a
jet in the body of the carb  so that when the throat  is closed, the
needle being wider at the base allows a small amount of fuel to be
delivered into the low pressure area (due to the venturi). As the slide
opens, admitting more air, more of the needle is exposed and thus since
it is tapered, more fuel can flow to feed the hungry pumpers. The posa
had various needles available and tuning was a matter of selecting the
right needle. I don't know about the V. One of the problems with the
posa/V was the fact that mixture between cylinders was not consistent
because of the fact that the fuel was not evenly dispensed in the
throat. One solution was to use a "swirl plate" just downstream of the
carb to cause a swirling of the air/gas and liquid gasoline mixture and
somewhat even it out. For rotaries, I don't know if that is a
significant factor, but it would seem that the more homogeneous the
mixture going into the intake part of the cycle, especially with PP
since it is straight through, the better. With a 4 banger and 4 runners,
it was very important.

The Ellison is a much more sophisticated unit, based on similar concepts.

Rich