REFLECTOR: Franklin Oil temp and flow data
Brian Michalk
michalk at awpi.com
Thu Nov 14 13:45:21 CST 2013
Thanks for replying. I was hoping you would join in on this.
I disagree with your analysis somewhat. The cooler bypass will cause a
delta pressure across the cooler, even if there is no flow across the
cooler. That delta will be caused by the cooler bypass valve being
pushed open by the oil. This could be caused by not allowing oil to
flow across the cooler (perhaps by a clogged oil filter). My point is
that there could be a pressure delta, but no flow. I do agree that a
pressure delta must exist for there to be flow.
I believe my data is correctly showing the state of the oil flow. The
temperature data backs it up as well, because once the flow meter began
registering flow, the oil temps began to stabilize.
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. 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.
>
> *From:* Brian Michalk <mailto:michalk at awpi.com>
> *Sent:* Monday, November 11, 2013 11:12 AM
> *To:* Velocity Aircraft Owners and Builders list
> <mailto:reflector at tvbf.org>
> *Subject:* Re: REFLECTOR: Franklin Oil temp and flow data
>
> From my notes, and diagrams I made, my understanding of the system is
> that the bypass is there to ensure that the cooler is not over
> pressurized. There are two regulators.
> 1) oil bypass, which causes a pressure differential across the cooler.
> 2) Galley bypass, which prevents overpressure on the engine.
>
> The oil cooler will see an absolute pressure of galley pressure, plus
> cooler bypass pressure. Absolute pressure does not imply oil flow.
> Only delta pressure across the ports to the cooler makes oil flow, and
> that's provided by the bypass.
>
> If one looks at the bypass plate, you can see two spring loaded valves.
>
> * Increasing spring stiffness on the left valve sets the bypass
> pressure (delta pressure oil cooler) higher.
> * Increasing spring stiffness on the right side sets the max galley
> pressure higher.
>
> The oil pump is a constant volume pump, not constant pressure. These
> valves are "relief" valves, meaning that above a set point, they will
> allow oil to bypass the circuit. If the oil pressure is below the set
> point, then no oil is bypassed. In other words, cranking up the
> spring pressure does not necessarily mean you get higher oil
> pressure. If the pump is only making 50PSI, setting the bypass at
> 80PSI is not going to get you more pressure.
>
> That said, I do not know if the cooler bypass is bypassing. If it is,
> then adding a stiffer spring there will cause more oil to flow to the
> cooler.
>
> http://wiki.velocityoba.com/images/8/8e/Sevice_Letter_No_PZL-F_1_98_page_2_%28F6%29.jpg
>
> On 11/11/2013 9:57 AM, Grover McNair wrote:
>>
>> Has anyone ever just bypassed the oil bypass valve to allow oil to
>> flow to the cooler constantly? I realize it would take longer to warm
>> and could potentially cause temps to be too low.
>>
>> Just curious.
>>
>> Grover McNair
>>
>> *McNair Performance Inc.*
>>
>> 6404 Westgate Rd.
>>
>> Raleigh, NC 27617
>>
>> 919-781-3604
>>
>> *From:*reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]
>> *On Behalf Of *John Dibble
>> *Sent:* Monday, November 11, 2013 8:46 AM
>> *To:* Velocity Aircraft Owners and Builders list
>> *Subject:* Re: REFLECTOR: Franklin Oil temp and flow data
>>
>> On 11/10/2013 8:19 PM, Brian Michalk wrote:
>>
>>
>>
>> It was about 70F today, not that cold. The oil flow is just very
>> strange. It didn't start flowing until nine minutes into the
>> flight, and I don't think it's a sensor problem because the
>> coolant temp leveled off after it started flowing. If this data
>> is correct, I'm not getting enough oil through my cooler. The
>> specs on the cooler are for 7gpm, and I'm barely half there.
>> Yes, I'm having high oil temp problems.
>>
>>
>> After my engine rebuild, my oil now takes 10 minutes to warm up. It
>> used to take 4-6 minutes. The reason for so much time is because
>> when the oil is cool, there is a high pressure drop across the
>> filter/cooler and nearly all the oil bypasses until the oil in the
>> sump, which warms faster, gets warm enough to reduce the pressure
>> drop. The reason mine took less time before is because the bypass
>> spring was the wrong one. It was the same as the oil pressure
>> regulating spring, which means there would be 80 psi across the
>> filter/cooler, before it would bypass. That means the pressure off
>> the pump could get as high as 160 psig. YIKES, but it ran without
>> incident for 1100 hours. I couldn't get one of the special bypass
>> springs for the Franklin, so I made my own from a spring from the
>> hardware store that I calculated would give 20 psi pressure. My oil
>> runs 10 C cooler after the rebuild and I attribute most of that to
>> new bearings. New bearings have a smaller space between the bearing
>> and crankshaft, so less oil passes through and therefore doesn't pick
>> up as much heat. That reduces the oil cooling requirement. Also,
>> with more oil now bypassing the cooler, there is less oil to cool and
>> that contributes to a lower oil temp (leaving the cooler) as well. I
>> should point out that I have a larger oil cooler than the standard.
>> My CHTs are 10 C lower as well and I attribute that to the lower oil
>> temp. My oil pressure runs 10 psig higher, also due to the lower oil
>> temp. One trick I use to warm the oil with less idling is to runs
>> for 2 minutes, then shut down for 10-15 minutes. When I start back
>> up, the oil warms up in 2 minutes. This way my CHTs are still low.
>>
>> John
>>
>>
>>
>>
>>
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