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Date: Wed, 02 Oct 2013 07:51:02 -0400
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Subject: Re: [LML] Re: Engine surging
From: Charles Brown <browncc1@verizon.net>
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OK well if your MP and rpm stayed steady (and I think ordinary =
instruments are responsive enough to display any significant variations =
-- this is not an aliasing problem), then I'll stick to my assessment =
that you have irregular fuel flow causing mixture variations causing =
power variations that are being soaked up by prop pitch adjustments and =
appear as fluctuating thrust.  It sure sounds like your boost pump is =
producing irregular flow and maybe some simple diagnostics are in order =
before removal/overhaul:

1.  Do your fuel flow and fuel pressure (panel instrumentation) =
fluctuate when you turn it on, with a period similar to the surging =
period?

2.  Dumb but very fundamental question:  does fuel press go UP like it =
should or does it go DOWN when you turn on the pump?  (wild thought, but =
worth verifying).

3.  Ground test -- check the boost pump fuel flow by pumping through the =
system and out of the fuel filter, with the filter outlet disconnected =
from the engine and streaming into a bucket/catchbasin -- is it steady?

4.  Other quick check -- is the fuel filter clean?  (is there anything =
that could get stirred up, like water, even, at higher flows driven by =
the boost pump?

Those are all my ideas.  If you do these diagnostics you may find a =
smoking gun.  If not, I'd swap the pump out.  And, here's a free =
opinion, I'd regard a boost pump that causes surging as an unreliable =
backup and consider that you're now flying with a single point of =
failure (the mechanical pump) that could force a landing any time.  =
Strictly speaking your airplane is airworthy, but you've peeled off a =
big safety layer.

On Oct 1, 2013, at 1:57 PM, Art Jensen wrote:

Charley,
The surging was first noticed after take-off with low boost ON at about =
800 feet AGL leaned for altitude 2500 RPM WOT. Being under the KFTG TCA =
climbs were in steps to 9500 MSL where I leveled off to try to =
understand what's going on and see how changes in operation affected =
what I was seeing and feeling. I reduced power and went LOP same =
results. Then turned off the low boost and the surging stopped. The =
engine ran very smooth. Turned the low boost back on and the surging =
came back. Again I turned it off and it went away. I determined I had =
found the cause (fuel pump) but still don't understand why (what is =
beginning to fail) or the connection (how it plays a roll to create the =
results I experienced).

Still looking for the expert who can put it all together so that I can =
come up with a plan of action for repair.=20

Called Lancair to price a new Dukes Fuel Pump, $3350, might be a bargain =
tomorrow but at that price I'm not going to R&R as a test. Haven't =
checked a price for overhaul assuming my problem is in fact the pump.=20

Any and all advice appreciated.=20

Art

Sent from my iPhone; Art Jensen

> On Oct 1, 2013, at 1:30 AM, Charles Brown <browncc1@verizon.net> =
wrote:
>=20
> Just a thought ... if there wasn't any rpm change, and you heard or =
felt surging, it could be a torque increase that causes a pitch =
increase, and increased thrust.  And if MP was constant, then the only =
thing *that* leaves is mixture.  If you're running lean of peak, power =
depends significantly on mixture.
>=20
> The thing is, this sounds backwards.  If it's worse when you turn the =
boost pump ON, then it sorta seems that you were running so far rich of =
peak that additional fuel pressure degraded power?  I'm not aware that =
the engine can even produce a mixture that overrich, except at very low =
power settings.
> Charley
>=20
> On Sep 30, 2013, at 7:58 AM, Art Jensen wrote:
>=20
> Looking for thoughts from the collective minds of the LML.  Last =
flight in my IO-550 normally aspirated legacy, I noticed surging in the =
engine with the low boost pump on. I did not notice any surging when I =
turned the boost pump off. Also did not notice any fluctuation in RPM. =
Nor did I see any fluctuation in RPM when I downloaded the engine data. =
The obvious question would be what are the possible causes and does it =
make the airplane unsafe for flight as there is no surge when the boost =
pump is off. I don't understand how I could feel and hear surging in the =
engine yet see no fluctuation in RPM, so I'm stumped. Any ideas would be =
appreciated, thank you.=20
> Art
>=20
> Sent from my iPhone; Art Jensen
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>=20
>=20
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