FWIW,
When I was rebuilding my Renesis, I had planned to install the jets. I purchased them from Atkins against their recommendation. I bounced it off Tracy, and he concurred with Atkins. Their contention was that the jets were more for auto racing applications (very high rpm’s).
Bryan
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Jeff Whaley
Sent: Tuesday, October 06, 2009 3:45 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Seepage, no more. Oil system
Hi Lynn, with regards to your high-lighted comment about the check balls in the crank – that is one item Bruce Turrentine suggested be removed in an overhaul for aircraft applications, replacing the balls with a carburetor jet to allow oil flow right away and continuously. So, I did install carburetor jets in my e-shaft during rebuild. Any comments? Anybody else out there do the same thing? Just curious as I’m fighting high oil temps.
Jeff
Plus, the rotary is cold blooded. The big bearings stress the oil film to no great extent, and the major source of oil temperature is rotor cooling. At low speeds and idle, the check balls in the crank don't even open to allow cooling oil to spray into the engine. Those balls operate as a function of RPM not temperature.
On the other hand, you will get a water temperature increase within one minute of startup. A water based coolant has very low viscosity and flow to a distant heat exchanger will be immediate. Like the rear heater in my school bus.
Lynn E. Hanover
OK here you go...... The rotary has problems with unburned hydrocarbons at all RPMs. The reason is the area of cooled combustion chamber available to the fuel air charge. The mixture tends to condense back into droplets and that reduces the area of the total number of gasoline molecules available to latch on to an oxygen molecule so more than we would like never combine with oxygen and do not get burned in the chamber, but get excited by the heat of combustion and mate up further town stream about where your EGT probe is installed. Many other problems can be traced right to this same problem. No starts due to low cranking speed is one. No heat of compression equals no excitement and no combining and no start.
You can see Mazda working to reduce this problem by getting the engine to warm quickly, and thus reduce the fleet HC output and be allowed to sell them in California. First you see that god awful stock thermostat, with its two plungers and plugs. When cold the lower hole is open and the upper hole is closed. So as the engine starts up cold, water can circulate inside the engine only. So, the engine warms uniformly and when at full operating temperature the upper hole opens to the cooling system and the lower hole is closed off.
That is the water trick. The oil trick is the balls and springs in the crank. If the engine is started and left to idle, the balls remain seated and no oil sprays into the rotors to cool them off. From a cold start they want the rotors to heat up ASAP to reduce the HC. So if you drive away, you are heating the rotors with the combustion process, and the balls unseating from RPM changes makes little difference. If left to idle for long periods, only bearing spill will enter the rotors to cool them, but that is plenty.
There have been and are other schemes involved as well but the ideas are the same. Rapid heating of the chamber on startup.
So limiting cooling during warmup is to reduce HC and improved mileage due to the lower viscosity and less drag of warmed oil. Simple.
To meter the amount of oil there is a specific sized hole in a bolt head that holds the springs and balls in the gallery in the crank. The down side of removing the balls and springs is that the rather small oil pump cannot maintain enough oil pressure to keep the idiot light out at hot idle. The missing balls produce 2 big oil leaks in the crank. Not a thing to worry about, because the bearings are huge for the loads involved, but it worries people to see the light on, or the gage below 20 pounds on a hot day.
Racers increase the oil pressure in order to move heated oil off of the bearings quickly to prevent melting the soft grey stuff on the bearings. Ay higher revs the stock pump has enough output to do this. The higher oil pressure (say 100 pounds instead of the stock 71 pounds) then causes the two cooling jets in the crank to put out a bit too much oil to the rotors. This results in plenty of cooling of course, but it also adds to the foaming of the oil that then drops back into the sump through that hole in the center iron. Foamed oil has trapped air mixed up in it, and air is an insulator, so the effect is that oil coolers start to act smaller than they are. So if you have jacked up the oil pressure on an early engine, then you probably need to add the Weber air correction jet to replace the ball and spring. The amount of oil supplied is reduced with RPM when you scream the engine because of the centrifugal load of the oil column being pushed into the crank. So the FD or twin turbo engines used 115 pounds of oil pressure. So at modest speeds you are putting a bunch of oil through the rotors.
I suspect, but do not know if the later engines have smaller jets to account for the higher oil pressure. Typical jets are.220MM for turbo engines or .200 MM for NA engines. (Racing Beat). I use .180MM and 100 pounds of pressure but I have very good oil cooling. Oil temps above 160 degrees cost HP according to Daryl Drummond who built our first race engines. Also all of the star Mazda and Formula Mazda series engines.
At airplane RPM there is just no problem with rotor cooling that can be attributed to the balls and springs or lack thereof. Oil cooling is a function of cooler size and airflow. Some improvement might be seen if a straight weight oil is used over a multi grade to avoid some of the foaming. Or if a racing oil is used that has anti foaming agents and additional anti scuffing agents. Mistral found that to be the case as they used airplane oil at first, and kept overheating the oil. It was an airplane after all.
Although it reduces power, the hotter rotor would produce better mileage due to better fuel burn. So if you lean it way out anyway, it is off of full power, so it might be worth some investigation, since there is much whining about fuel consumption in rotaries.
Lynn E. Hanover
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