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In a message dated 11/28/2002 1:11:31 AM US Eastern Standard Time, lors01@msn.com writes:
While I've been playing with the cooling system measurements, I decided to
look into a nagging symptom that I've had since building the airplane. The
cooling system has never remained completely topped off and seemed to loose
a small amount of coolant (~ 2 oz) on every flight. This didn't seem to be
a problem because the cooling system works OK until its about two quarts low
and I check and top off the system long before that happens.
I have a one quart overflow bottle which is about the only size the
aftermarket brands offer (I used Moroso) so I assumed this was adequate for
any installation. To test this, I ran the hose from the overflow port on
the overflow bottle to the cockpit and connected it to a second bottle.
Sure enough, when the engine got up to full operating temperature, the hose
puked a couple of ounces into the second bottle. When the engine cooled to
room temperature, it recovered all the coolant in the first bottle then
sucked in a bit of air.
Moral of the story: Use a coolant recovery bottle larger than 1 quart. I
just installed a 1.5 liter bottle. Will flight test this setup tomorrow.
I also noticed that cooling was noticeably better when the system was
completely full of liquid with absolutely no air in it. Even a few ounces
worth of air in the system caused the coolant temp to go up about 5 - 7
degrees. The amount of air did not seem to affect it much. Anything from 3
oz to 60 oz of missing coolant has the same effect on temperature. I don't
know the exact cause of this temp increase. More than 60 oz missing causes
the temps to rise rapidly (I think the pump starts sucking air at this
level).
Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com
I have a recovery bottle from an RX-2 connected between the water outlet and the radiator. Once I have heat cycled the engine a few times, I keep adding coolant until I have the bottle 1/4 full. After that there is no loss of fluid. I have a catch tank connected to the outlet on the RX-2 bottle but it never gets anything in it. I have the hose connection to the catch tank near the top so it cannot recover any dumped coolant. This way I can look into the catch tank and be sure all is well without opening my pressurized system. I have a Shrader valve installed in the RX-2 recovery bottle so that I can pressurize the coolant before I start the engine. The Stant 16 pound lever cap on the recovery bottle will hold pressure for weeks on end so long as the cap and seat are in good condition. The coolant pressure inside the engine will be dependent on a number of conditions in the coolant loop. The pumps are oversized so as to perform well in the worst case situation. Unrestricted, the pump can circulate an enormous amount of coolant through the system. If there is no thermostat or restrictor in the exit from the block, there will be high flow rate and the radiator(s) will be the restriction. High pressure will exist between engine out and radiator in. The top hoses will be very hard at full RPM. The suction side of the pump my drop below 1 bar and some cavitation may occur. Dissolved gasses may be liberated on the suction side of the pump and may not be reentrained quickly on the pressure side. Then you have a bit more pressure than your pressure cap will contain. On shutdown, the gasses are reabsorbed and all is well, less the small amount dumped into your catch tank. The pressure generated by the pump can be well above what even a 22 pound racing cap can contain. So, the location of the connection between the system and the recovery bottle can cause a problem. Between the engine and the radiator will be the highest pressure in the system. It is also the most popular location for this connection. As in the case where a car radiator has the pressure cap on the radiator tank. But cars have thermostats in them. In addition to being a temperature actuated valve, a thermostat is also a restrictor. A sharp edged hole with a sharp edged disc hovering above it. Very bad for flow. So even when wide open it creates a terrible flow restriction that raises the pressure in the block, (all good news) and lowers pressure in the upper radiator hoses and in most cases pressure going to the recovery bottle. (more good news).
I do run a thermostat in cool weather. I have a plate welded over the water outlet casting on top of the water pump. All of the water that cools my race engine must pass through a 5/8" sharp edged hole in this plate. My connection to the recovery bottle is down stream from the 5/8" restriction. I have no cooling problems at all since I started racing rotaries in 1980. My engine does not overheat and does not dump coolant into my catch tank. My recovery bottle has a 16 pound Stant lever cap.
For airplane use I would go to 22 pounds just to be sure. Lynn E. Hanover
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