Does Lycoming make any sense?

The pressure drop across the nozzle orifice is the absolute pressure into
the nozzle less the absolute pressure in the manifold. I don't have a
system diagram here, but I believe the factory fuel flow gauge is a
differential pressure gauge referenced to manifold pressure.

"Capt.Doug" wrote in message
...
"Stan Prevost" wrote in message
I don't think so, at least not very much decrease. I think the fuel will
divide among the functioning injector nozzles. This is why the pressure
increases when one is blocked, the fuel is forced through a fewer number
of
orifices, causing a greater pressure drop across them.

If we are talking about the OEM 'flowmeter', how many transducers does it
have? It would need two to measure a pressure drop. It needs only one to
measure the pressure near the spider. If it has only one transducer near
the
spider, and a nozzle clogs, the remaining nozzles won't flow enough to
relieve the increased pressure and the result will be an increased 'flow'
indication.


But I believe they flow all the metered fuel (or nearly all of it) as long
as the fuel pump provides sufficient pressure. Do you think the fuel flow
out of the fuel injector body (fuel servo) decreases if one nozzle clogs?
Once there is enough restriction to flow so that the "back pressure" from
the spider approaches the fuel pump pressure, then flow will reduce, but
until then, I think the servo maintains the flow it wants.

"Robert M. Gary" wrote in message
ups.com...

Stan Prevost wrote:
I don't think so, at least not very much decrease. I think the fuel will
divide among the functioning injector nozzles. This is why the pressure
increases when one is blocked, the fuel is forced through a fewer number
of
orifices, causing a greater pressure drop across them.

But there is noticable change in pressure, just in flow. The flow is
very high. I could see that if 1 nozzle was plugged that the other 3
would have increased flow but I can't see that the total amount of fuel
delivered would be double. Fuel flow is measured by a spinning wheel
and is not pressure related.


I assume you meant that there is *no* noticeable change in pressure. But
I'm not sure we are talking about the same thing. You measured fuel
pressure out of the fuel pump and found that it doesn't change. My question
was whether the "flow" indicated by the pressure-based factory flowmeter
changes. This is related to fuel pressure after the fuel servo, which is
not the fuel pressure you measured, I don't think. If the indication of the
factory fuel flow gauge, actuated by fuel in the fuel distribution lines,
has not changed, but the true flowmeter indication has greatly changed, then
I think you have one of two problems: The true flowmeter is broke, or you
are spewing fuel out of the system somewhere before the fuel servo, or in
it. But since the high fuel flow indication is accompanied by poor engine
performance, I think it is fuel spewing inside the servo.

If I remember right, one thing that can happen in a fuel servo is that an
internal problem can cause fuel to spew out of one of the ram air sensing
ports in the venturi, and get sucked up into the manifold, making the
mixture way too rich. The nozzles might have reasonably correct flow, but
the total flow will be too much. If this is happening, you can see blue
fuel stains in the venturi section, and maybe dripping fuel. Also you would
experience high true fuel flow. And ye$, thi$ doe$ call for overhaul of the
$ervo.

Stan

Stan Prevost wrote:
"Robert M. Gary" wrote in message
ups.com...
I assume you meant that there is *no* noticeable change in pressure. But
I'm not sure we are talking about the same thing. You measured fuel
pressure out of the fuel pump and found that it doesn't change. My question
was whether the "flow" indicated by the pressure-based factory flowmeter
changes.

I don't have a pressure-based flow indicator.

-Robert

"Robert M. Gary" wrote in message
ups.com...

Stan Prevost wrote:
"Robert M. Gary" wrote in message
ups.com...
I assume you meant that there is *no* noticeable change in pressure. But
I'm not sure we are talking about the same thing. You measured fuel
pressure out of the fuel pump and found that it doesn't change. My
question
was whether the "flow" indicated by the pressure-based factory flowmeter
changes.

I don't have a pressure-based flow indicator.


Oh. Sorry for the confusion. You said you had a JPI fuel flow transducer,
so I assumed that was an add-on sensor operating with an add-on instrument
and that the original factory "flow" indicator was still present. I was
assuming a certified aircraft, and you might be talking about an
experimental.

Still, a measurement of fuel pressure at the spider would be a useful clue,
as would an inspection of the venturi for fuel stains.

Stan

Stan Prevost wrote:
"Robert M. Gary" wrote in message
ups.com...
Oh. Sorry for the confusion. You said you had a JPI fuel flow transducer,
so I assumed that was an add-on sensor operating with an add-on instrument
and that the original factory "flow" indicator was still present. I was
assuming a certified aircraft, and you might be talking about an
experimental.

No, Mooney just never installed any type of flow indicator. The only
thing Mooney gave us is pump pressure. It usually drops slightly at
high power vs. low power but almost too little to notice. From my
previous Bonaza flying I understand what you are talking about though.

-Robert