REFLECTOR: Franklin Oil temp and flow data
Brian Michalk
michalk at awpi.com
Sat Mar 1 10:29:01 CST 2014
Yes. Your data matches mine. A stronger bypass spring *can* result in
the corresponding lower pressure at the engine.
The bypass spring *allows* higher pressure delta across the
pump-to-engine hoses (meaning, the cooler). By allows, I mean that
anything in excess of this pressure is allowed to go into the engine.
If you have a weak spring that opens at 5PSI, then the oil pump out
pressure will be up to 5PSI above the engine galley pressure. That valve
will be open most of the time, bypassing the oil cooler.
If you have a strong spring that opens at 35PSI, then the same happens,
with pump outlet pressure being up to 35PSI above engine pressure.
Here, the valve is mostly closed, forcing more oil through the cooler.
In my research with different springs, I don't see the max 35PSI drop,
because the oil cooler doesn't pose that much of a restriction. I do
see lower engine oil pressures though.
If you want more cooling, try a stronger spring. This might help, but I
doubt it with a tight engine that doesn't flow much oil.
If you want more oil pressure, use a weaker spring. You can also try
shimming the relief valve.
PZL says to place the oil temperature probe on the oil returning from
the cooler. I think this is a bad location.
Assume your pump produces 15gpm at 2500RPM. Assume your engine flows
4gpm at 2500RPM. Assume the standard spring. Assume a 50hour SMOH
engine, like mine.
You will send 11 gallons back to the sump, through the relief valve.
About two gallons will go through the cooler, then to the engine.
About two gallons will bypass the cooler, going into the engine hot.
If you have very little oil flowing through the cooler, then it comes
back very cool, and that is what you see on your panel gauge for oil
temp. I believe that we should be measuring the temperature of the oil
going into the engine. I tapped the bypass spring plug, and inserted my
oil temperature probe there. It sort of gives me what I think is a
realistic value.
Related:
I have finished the design of a new oil bypass assembly that duplicates
the Lycoming oil flow path. Now with this email, I am reminded that I
should add some tapping points for pressure and temperature. My next
step is to have it 3D printed in nylon and assembled for ground tests.
I wonder if I should spread some of the cost around with crowdsourcing
the fabrication?
The new assembly also has adjustable bypass and relief valves. No
disassembly required. Oh, and one more thing. The tapped locations are
far enough apart to be able to get wrenches on your fittings.
On 03/01/2014 08:42 AM, John Dibble wrote:
> Recently my oil temp has been creeping downward. With an OAT of 60 F,
> it's running 50 C. I let it warm to 40 C before takeoff. Sometimes
> it goes back down to near the OAT right after takeoff and then slowly
> inrcreases after a few minutes. My oil temp is measured at the cooler
> outlet. Suspecting that the bypass spring I made had gotten weaker, I
> checked it. It seemed slightly weaker. I replaced it with a stronger
> one that I calculate will give 35 psi. As I expected, the oil temp
> increased by 10 C, indicating that more oil is going to the cooler.
> What surprised me is that my oil pressure decreased by 10 psig (from
> 70 to 60). Part of that must be due to the warmer oil temp, but 10
> psig seems like a lot. Before I discovered that an oil pressure
> spring (80 psig) was installed in the bypass spot, my oil pressure was
> running 50-55 psig with oil temp at 70 C. FWIW
>
> John
>
> On 11/15/2013 12:07 PM, Brian Michalk wrote:
>> Yeah, I've been thinking about that too. The relief valve wouldn't
>> cause any additional pressure drop.
>>
>> For an experiment, I would like to put in a dummy blank filter in
>> place of my current filter. I suppose I could rearrange some hoses.
>> Removing the filter would take one variable out of the equation to
>> see if the same symptoms happen again.
>>
>> On 11/15/2013 12:01 PM, John Tvedte wrote:
>>>
>>> Brain,l
>>>
>>> I am not understanding why you would be concerned about a filter
>>> that has a relief valve. That relief valve works on the pressure
>>> difference across the filter media. Primarily for cold starts, but
>>> effective also for the unthinkable clogged filter media. The oil
>>> filter assembly won't block the flow of oil. An oil filter bypass
>>> operates at a reasonably low pressure difference of a few psi -- and
>>> so it would not 'rob' the circuit pressures of any more than those
>>> few psi.
>>>
>>> John
>>>
>>> *From:*reflector-bounces at tvbf.org
>>> [mailto:reflector-bounces at tvbf.org] *On Behalf Of *Brian Michalk
>>> *Sent:* Thursday, November 14, 2013 8:28 PM
>>> *To:* Velocity Aircraft Owners and Builders list
>>> *Subject:* Re: REFLECTOR: Franklin Oil temp and flow data
>>>
>>> On the data I sent out, right after engine start, the engine surged
>>> to 1500RPM. The oil pressure coming out of the engine was 117PSI,
>>> the oil pressure returning to the engine was 98PSI. It wasn't that
>>> cold. 70F.
>>>
>>> I am measuring the galley pressure where PZL says to measure it,
>>> which is off the port on the bypass plate. I measure the pump
>>> pressure right at the oil cooler, which is after about three feet of
>>> -10 stainless braided hose.
>>>
>>> I am logging 46 unique channels on the airplane. I am logging more
>>> parameters than that, but don't count them, like I count fuel counts
>>> and fuel flow as one unique signal.
>>>
>>> The more I think about this, the more I am suspecting the oil
>>> filter. I am using the K&N HP-3002, and in looking back at my
>>> manual, I had selected the HP-2002. They are both 550PSI burst
>>> pressure, but the 3002 has a PSI relief valve, bypass valve and
>>> anti-drain back valve. The 2002 has none of those. I probably
>>> picked up the 3002 because they didn't have any 2002's on the shelf.
>>>
>>> On 11/14/2013 06:54 PM, John Dibble wrote:
>>>
>>> On 11/14/2013 1:29 PM, Laurence Coen wrote:
>>>
>>> Brian,
>>>
>>> There are two valves in the "bypass plate" and they perform
>>> independent functions. The pressure regulator valve sets
>>> the oil pump pressure at 80PSI. That is the maximum
>>> pressure that can exists anywhere in the system and is also
>>> the maximum pressure that the oil cooler can see.
>>>
>>> Well, with the 80 psig spring in the cooler bypass location, at
>>> start up on cold days I would see 99 psig at the cooler outlet
>>> (99 is the max reading for my RMI monitor, so it could have been
>>> higher). Seems like the pressure going to the cooler would have
>>> been higher yet.
>>>
>>> John
>>>
>>>
>>> Please note that this has nothing to do with the external loop
>>> bypass valve. Your data would indicate that your statement that
>>> no oil flowed for nine minutes is incorrect. I don't how you
>>> are measuring oil flow or where but the fact that there is a
>>> differential pressure at the output of the oil cooler and the
>>> galley is only possible if there is flow through the cooler. In
>>> a hydrostatic system (no flow) where two points are connected
>>> the pressure will be the same. Your graph shows a differential
>>> pressure at opposite ends of a tube connecting the oil cooler
>>> and the oil galley. This indicates oil flow through the cooler
>>> from start up to shut down.
>>>
>>> Functionally, the Franklin set up works the same as the pressure
>>> regulator/"Vernatherm" in a Lycoming. In a Lycoming, when the
>>> oil is cold, The Vernatherm opens a bypass on the oil cooler
>>> loop. When the oil gets hot the Vernatherm closes the bypass
>>> forcing the oil to flow through the oil cooler. On the Franklin
>>> the fact that cold oil is thick when cold causes a large drop in
>>> pressure through the external loop. This in turn opens the
>>> bypass just like the Vernatherm on the Lycoming. When the oil
>>> is hot, the pressure drop in the external loop decreases
>>> allowing the bypass to close, just like the Vernatherm did in
>>> the Lycoming. In both cases the pressure regulator simply sets
>>> the output pressure of the oil pump.
>>>
>>>
>>>
>>>
>
>
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