Thermostat or radiator shutters

[cap01]

after a couple of years of flying in a cold cockpit I finally tried the duct tape on the radiator and finally some heat . Now for a more permanent fix , thermostat or shutters . Not too sure about a thermostat without some kind of bypass but also not sure of how affective shutters would be on the back side of the radiator . Maybe some of the guys up in the real cold country would have some thoughts on this ? Thanks

[jamesmil]

we used a in line thermostate from" highwing llc" it works well summer or winter. we can have some 95' days in the summer and the temps are fine.
on those real cold days around 40' the water temp is around 190'

[Dorsal]

Two concerns I have about the inline thermostats is;

- Restricting flow and increased pressure. They are certainly used in other Rotax applications so perhaps not an issue though some models use a by-pass.
- Restricting flow to the cabin heater as I think the heater T is down stream from the likely location of the thermostat. This might keep the coolant temps up but not provide more cabin heat.

For these reasons I went with AL tape on half the radiator, seems to work OK but I liked the idea of the coolant thermostat better. I use a thermostat on the oil and it works great. If others know why my concerns above are silly please chime in

[Dave S]

I theory, like the idea of a coolant thermostat, primarily for the sake of maintaining a constant healthy temperature for the engine.

In practice, I have not installed one simply out of wanting to keep the system as simple as possible.

I.C. (internal Combustion) engines operate most efficiently with as high an operating temperature as the materials the engine is made of and the oil will tolerate. An inline thermostat serves that purpose; and, provides the side benefit of a more effective heater. (same idea with oil thermostats...keep the temp up to a decent operating level)

My first concern with any kind of liquid or air restriction device like a thermostat or radiator shutter in my airplane is failure mode operation. A liquid thermostat has two failure modes...stuck open or stuck shut...(or something in between). The first is not an operational problem; however, stuck shut means the engine has to be shut down in time to prevent damage or it will shut itself down due to overheating...either way...no power. Having said that, I can't say how common that kind of a failure is with Rotax in line thermostats...I know I have had stuck shut thermostats in cars and you are all done pretty quick.

I have thought about a shutter designed so failure mode would blow the vanes open....although, control systems on certified aircraft (throttle, ICO, Carb Heat, cowl flaps) have no fail safe mode...they count entirely on the system not failing...so maybe failure mode concerns are over-rated.

I am pretty cautious about things like this.....my luck is best explained in terms of a contest I was in once....with 200 door prizes......There were 201 entrants including myself.....and I don't need to even say who didn't get a door prize........

I am leaning towards some kind of shutter system on the back side of the radiator as a more fool proof system; but, the fact that all is running well and the cabin is comfortable....oh well.

Dave S
KF7 Trigear
912ULS Warp Drive

[HighWing]

There is one other option for you guys with the in cowl radiator fed by the NACA duct. The 5 Outback with Series 7 FWF, I helped finish, has a "Door" on the NACA Duct opening that consists of the cowl skin cut along the curved sides and aft but with the short forward edge uncut to act as a hinge. A fiberglass "joggle" provides a seat for the door. and foam stiffeners were bonded to the door for rigidity. To avoid having to unhook the control cable when removing the cowl, we designed a mechanism that reversed the pull on the cable at the cowl firewall interface to a push motion. Fail safe was a spring set-up that would open the door in the case of cable failure. Pulling on the cable in the cockpit pushed the door closed through the nesting push fittings. Three photos attached.
Lowell

[farmboy]

I had my first flight today after installing a oil Thermostat,oil temp held at 158 degrees outside temp was 11 degrees farenheit. Before installation I was running 128 degrees.

Do I understand this correct that the 912 needs a bypass inline when a coolant thermostat is installed? I have a cabin heater so I want full heat and do not want too much pressure in system when thermostat is closed. Sorry if this has been discussed before but just want to do things right. Thanks for the help!

Series VI 912s