Allen wrote:
I think you are making this waaaay to complicated.
I know I am. I'm an engineer, it's what we do...
Anyways.

The volume of air going
through the venturi remains the same as you climb
I believe this is a good approximation -- volumetric efficiency should
not change (much) as an aircraft climbs into thinner air, and throttle
setting and RPM's approx constant.

but the amount of oxygen
(the component needed to burn the fuel) decreases.
The mass flow decreases of air (and oxygen), and therefore the amount of
fuel required decreases; I agree.

The volume of air
remains the same so the fuel drawn out of the float bowl remains the same.
This is the part I don't agree with. The mass rate of fuel drawn outta
the float bowl is driven by the pressure decrease in the venturi, which
depends on both the density and the velocity. Density goes down as you
climb. Amount of fuel drawn should not remain a constant.

If I can give a rough and poor analogy. As you climb into less dense
air, you don't achieve the same aerodynamic performance from the
airplane with a given airspeed. You will stall at a higher airspeed,
your airplanes gear and flaps can handle higher airspeeds, Vx and Vy are
higher airspeeds, and Vne is a higher airspeed. The air has to go
faster to have the same effect on the wings and other devices on the
bird. It is because of the decreased density... I'd propose that is the
same effect as is happening in the carb venturi. The air has to go
faster to have the same effect in pulling gas out.

Oh yeah, before somebody corrects me I'm particularly talking about TAS
above, I know these speeds stay roughly the same at IAS (just because
the ASI is also thus affected ).


That's my story and I am sticking to it.
And most people are satisfied with that, I'm wondering why it doesn't
stand up to a little deeper analysis.