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.

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Paul Lamar