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Piper Arrow electric fuel-pump



 
 
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  #1  
Old May 29th 04, 11:58 PM
MC
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Default Piper Arrow electric fuel-pump

Anybody know how for long the electric fuel-pump
in a fuel-injected Piper-Arrow IV can be
operated for.?
indefinitely ? or intermitantly ?

The POH is somewhat vague as it says that the
electric pump can be turned-off in cruise and
I haven't spotted a limitation in the POH yet.

The reason I ask, is that I normally turn it off
when in mid climb, but on a recent long trek
I had some adrenalin surges when the engine
started getting rough.
The fuel-pressure was low and varying, hence
causing excessive leaning, thus rough running.
Turning on the electric pump got the fuel
pressure back to normal values and 'ops normal'

After some experimenting in-flight, I determined
that the the problem only happened when I was
using the right-tank, which implies that there's
some obstruction in that fuel line or in the
fuel selector.

So., any views on how long the electric fuel
pump can/should be run for ?
  #2  
Old May 30th 04, 02:06 AM
Ben Jackson
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Default

In article ,
MC wrote:
Anybody know how for long the electric fuel-pump
in a fuel-injected Piper-Arrow IV can be
operated for.?
indefinitely ? or intermitantly ?


All I know for sure is that the one in my plane (PA-24 Comanche) is
shockingly expensive so I only have it on for takeoff, tank changes,
approaches and landing.

With the engine driven pump operational I don't see any indication on
the fuel pressure gauge when I turn it on/off.

So., any views on how long the electric fuel
pump can/should be run for ?


Besides wearing it out you should also look at a fuel system diagram and
see how it works. Early Comanches pumped around the engine pump, leading
the engine driven pump to overheat and possibly vapor lock when you
switch the electric pump off after a long use. Later ones pump through
the engine driven pump and avoid that problem.

--
Ben Jackson

http://www.ben.com/
  #3  
Old May 30th 04, 02:33 PM
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Posts: n/a
Default

Aside from wearing the pump out prematurely, there's nothing significant about
running it for long periods of time. Of course, if you left it on indefinately, you'd
get no indication about one of the pumps failing.

I had a similar experience in my Cherokee 180 on the right tank. About 400'
AGL after takeoff on the right tank, the engine sputtered to a stop. No fuel
pressure, and the boost pump was already on. Switching to the left tank fired it back
up. Took about 3 seconds to diagnose, act on, and get the engine running again, but
felt like 3 hours. I had noticed a drop in fuel pressure at high flow conditions
(full rich takeoff) on the right tank before that time but didn't think much of it.
After that incident, we tore into the fuel system and found a paper wasps' nest in the
right tank fuel line after removing the tank. I'd suggest any discrepancy like that
to be looked into and the problem found.

Also, just as a data-point. The Cherokee (not sure about the later Arrows)
line has an extremely *marginal* electric boost pump stock. We ended up installing
the Petersen autofuel STC on our plane which requires replacing the stock pump with
two (only one at a time) replacement pumps. Rather than pumping around the engine
pump, they can (individually) pump through it now. Before the upgrade, I never saw
much difference between the pump being on or off. Now, in full-power climbout, I see
5 psi with either boost pump, or about 2 psi when I turn them off. According to
Petersen, the fuel pump swaps were necessary when the stock pump, "failed to meet
miniumum flow requirements." A euphamistic way to say Piper's original design sucked
and wouldn't pass ceritification requirements today.

-Cory

MC wrote:
: Anybody know how for long the electric fuel-pump
: in a fuel-injected Piper-Arrow IV can be
: operated for.?
: indefinitely ? or intermitantly ?
:
: The POH is somewhat vague as it says that the
: electric pump can be turned-off in cruise and
: I haven't spotted a limitation in the POH yet.

: The reason I ask, is that I normally turn it off
: when in mid climb, but on a recent long trek
: I had some adrenalin surges when the engine
: started getting rough.
: The fuel-pressure was low and varying, hence
: causing excessive leaning, thus rough running.
: Turning on the electric pump got the fuel
: pressure back to normal values and 'ops normal'

: After some experimenting in-flight, I determined
: that the the problem only happened when I was
: using the right-tank, which implies that there's
: some obstruction in that fuel line or in the
: fuel selector.

: So., any views on how long the electric fuel
: pump can/should be run for ?

--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************

  #4  
Old May 30th 04, 08:57 PM
MC
external usenet poster
 
Posts: n/a
Default

Ben Jackson wrote:

Anybody know how for long the electric fuel-pump
in a fuel-injected Piper-Arrow IV can be
operated for.?
indefinitely ? or intermitantly ?


All I know for sure is that the one in my plane (PA-24 Comanche) is
shockingly expensive so I only have it on for takeoff, tank changes,
approaches and landing.


Like many things in aviation g

So., any views on how long the electric fuel
pump can/should be run for ?


Besides wearing it out you should also look at a fuel system diagram and
see how it works. Early Comanches pumped around the engine pump, leading
the engine driven pump to overheat and possibly vapor lock when you
switch the electric pump off after a long use. Later ones pump through
the engine driven pump and avoid that problem.


The arrow (from what I can deduce from the one-page diagram) has
a 'through the engine-driven pump' system.
  #5  
Old May 30th 04, 09:12 PM
MC
external usenet poster
 
Posts: n/a
Default

wrote:

Aside from wearing the pump out prematurely, there's nothing significant about
running it for long periods of time. Of course, if you left it on indefinately, you'd
get no indication about one of the pumps failing.

I had a similar experience in my Cherokee 180 on the right tank. About 400'
AGL after takeoff on the right tank, the engine sputtered to a stop. No fuel
pressure, and the boost pump was already on. Switching to the left tank fired it back
up. Took about 3 seconds to diagnose, act on, and get the engine running again, but
felt like 3 hours. I had noticed a drop in fuel pressure at high flow conditions
(full rich takeoff) on the right tank before that time but didn't think much of it.
After that incident, we tore into the fuel system and found a paper wasps' nest in the
right tank fuel line after removing the tank. I'd suggest any discrepancy like that
to be looked into and the problem found.


Yeah.. I'm sure it's an obstruction, but at the moment I'm a lonnnnng way away
from any reasonably equiped repair shop.

Also, just as a data-point. The Cherokee (not sure about the later Arrows)
line has an extremely *marginal* electric boost pump stock. We ended up installing
the Petersen autofuel STC on our plane which requires replacing the stock pump with
two (only one at a time) replacement pumps. Rather than pumping around the engine
pump, they can (individually) pump through it now. Before the upgrade, I never saw
much difference between the pump being on or off. Now, in full-power climbout, I see
5 psi with either boost pump, or about 2 psi when I turn them off. According to
Petersen, the fuel pump swaps were necessary when the stock pump, "failed to meet
miniumum flow requirements." A euphamistic way to say Piper's original design sucked
and wouldn't pass ceritification requirements today.


It may be just my combination of equipment, but with the electric pump on, the
fuel pressure stays fairly stable, but the engine-driven pump has never given
a constant reading, it fluctuates from minimum to about mid range on the gauge.
  #7  
Old May 31st 04, 12:53 PM
external usenet poster
 
Posts: n/a
Default

MC wrote:
: It may be just my combination of equipment, but with the electric pump on, the
: fuel pressure stays fairly stable, but the engine-driven pump has never given
: a constant reading, it fluctuates from minimum to about mid range on the gauge.

At different power settings/attitudes, right? Fuel pressure gets awfully low
on mine if I turn off the electric pump in a full power/rich power-on stall
attitude... probably 1psi. As I said befo marginal.

-Cory

--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************

  #8  
Old June 3rd 04, 02:50 AM
MikeremlaP
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Posts: n/a
Default

Hi All:

If we're talking about the Facet "beer can" style pump, the pump can be left on
indefinitely. (Have taken one apart. Nothing to them.) There's no heat
limitation. Depending on your plumbing (parallel or series), it might affect
your mixture very slightly in flight. (Carburetor.)

The right tank problem could be due to deteriorating fuel / vent lines in the
wing. Light Plane Maintenance did an article on pulling the tanks and
replacing these hoses. They're rubber hoses with a life limit and the usual
breakdown deterioration. You're looking at a tedious job. (If you can get a
337, I'd replace with a longer life hose. Maybe an AQP style.)

Aircraft Spruce sells Facet replacement pumps.

At different power settings/attitudes, right? Fuel pressure gets awfully
low on mine if I turn off the electric pump in a full power/rich power-on

stall attitude... probably 1psi. As I said befo marginal.

Cory's problem is probably endemic to the Piper vent system. I suspect, during
the stall attitude, you're pulling a slight vacuum on the vents.

On our Glasair, we had similar low pressures in climb attitude. Turns out the
vents didn't protrude far enough below the wing. I extended the vent tubes
another inch and a half, and that solved the low pressure on climb out problem.

Hope this helps,

Mike Palmer
Excellence in Ergonomics





 




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