Van's Air Force
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Over Cooling in Winter
- Thread starter jsharkey
- Start date
Here's one way of doing it - I have no experience with this personally.
https://www.rvplasticparts.com/product-page/rv9-cowl-winter-air-dam
jsharkey
Well Known Member
MacCool
Well Known Member
I had over-cooling problems...rarely could get above 130° F in the winter, rarely above 150°F in the summer. I tried taping off the back of the oil cooler, didn't do near enough. I ended up having my A&P install an Anti-Splat shutter with a Bowden cable in the cockpit...problem solved. It was a pretty simple installation.
It's a typical parallel valve issue.
A cold vernatherm is retracted, resulting in an open bypass port, which allows some oil to flow directly from the pump to the filter, rather than from pump to cooler to filter. Note flow exists through the cooler even when the bypass port is open, i.e. when the oil is cold.
The most effective way to raise oil temperature is to stop flow to the cooler. Larry Vetterman seems to be the best known pioneer of the method in RVs, removing the vernatherm, installing a viscosity valve piston and spring, and placing a pilot controlled ball valve in one of the flex lines to or from the cooler. The potential downside goes to the reason Lycoming maintained some cooler flow when cold; with zero flow and very cold conditions, it's possible to congeal the oil in the cooler passages and block flow if subsequently desired in flight.
Not quite as effective, but arguably more practical is to stop airflow through the cooler. It can be as simple as duct tape on its inlet face. Better is a pilot controlled shutter, the previously mentioned Anti-Splat being an example.
Blocking the oil cooler air path will raise upper cowl Cp, so CHT may be reduced. If it is also too cool, the same cure is applied...reduce airflow. The long standing best practice is a pilot controlled variable cowl exit (aka a cowl flap); the exit is the system throttle. It allows cooling air control year round, particularly when climb and slow flight requirements are compared to cruise.
It is also possible to throttle mass flow by blocking the inlet. It's inefficient, but easily applied, which has a lot of merit.
A cold vernatherm is retracted, resulting in an open bypass port, which allows some oil to flow directly from the pump to the filter, rather than from pump to cooler to filter. Note flow exists through the cooler even when the bypass port is open, i.e. when the oil is cold.
The most effective way to raise oil temperature is to stop flow to the cooler. Larry Vetterman seems to be the best known pioneer of the method in RVs, removing the vernatherm, installing a viscosity valve piston and spring, and placing a pilot controlled ball valve in one of the flex lines to or from the cooler. The potential downside goes to the reason Lycoming maintained some cooler flow when cold; with zero flow and very cold conditions, it's possible to congeal the oil in the cooler passages and block flow if subsequently desired in flight.
Not quite as effective, but arguably more practical is to stop airflow through the cooler. It can be as simple as duct tape on its inlet face. Better is a pilot controlled shutter, the previously mentioned Anti-Splat being an example.
Blocking the oil cooler air path will raise upper cowl Cp, so CHT may be reduced. If it is also too cool, the same cure is applied...reduce airflow. The long standing best practice is a pilot controlled variable cowl exit (aka a cowl flap); the exit is the system throttle. It allows cooling air control year round, particularly when climb and slow flight requirements are compared to cruise.
It is also possible to throttle mass flow by blocking the inlet. It's inefficient, but easily applied, which has a lot of merit.
