i have two of these, one is on stock muffs (very loud) and one has MTW re3 pipes (mo better). i am starting this thread to discuss any aspects of this motor. to begin, i will be posting some telemetry data of these two engines and i will also mention the props used. the telemetry data can be confusing, and i want to clarify this from the get go. the rpm data is from an onboard optical sensor, just like the ones on tachometers, except, it is on the airplane and connected to the radio system. it is not magnetic or infrared. it is not associated with the firing of the Cdi either. the data on RPM, that most people are accustomed to seeing is based on running the engine on the ground, and using a tachometer. for years, people have posted numbers on RPM based on this technique. now, i will say, that my telemetry sensor is as accurate as a hand held tachometer. this i have validated by running the engine on the ground, looking at My tx and at same time, looking at the hand held tach, and comparing the two. they are both within 100 rpm. interesting observations made are that the high rpm values seen on telemetry are higher than when the airplane is on the ground. i suspect, from reading and hearing guys mention "unloading" that this concept is well known and accepted. therefore, just be aware that high rpm is obtained during flight, when the engine is not under a load, possibly flying level with a tailwind, at full throttle.
For the temperature, this gets even more complicated and interesting. for years, people measure their engine temps by using a infra-red thermometer of sorts. or at least, this is how i assume people make these measurements. they have then reported these temps, and after some while, people get an idea of what "normal" range should be.
when using the infrared thermometer guns, you must keep in mind that if you point it to the front of the engine, while the propeller is spinning, the temperature that is read is of the surface of the front of the motor. be it the cylinder or the crankcase or whatever you point it at. this type of info, lets say, you get the temp of the engine soon after cranking it on, or, you check it upon landing, or if you run it on the ground, and check the temp there, whatever, you first will need to appreciate the cooling of the engine and how the engine dissipates heat.
i told you this would get complicated. After having had performed many experiments, i have concluded that the temperature in the front of the engine, when the engine is running, and there is a propeller connected forcing air onto the engine, the cylinder temperature in the front of the cylinder is way cooler than the temperature in the back of the cylinder (sometimes difference is greater than 100 degrees F). the temperature in the top of the cylinder (closest to spark plug) gets hotter than the temperature of the cylinder closer to the crankcase. the crankcase temperature is way lower than the cylinder temps (can be over 100 degrees cooler). the hottest area on the engine is the area directly behind the cylinder and the highest area (fins) area as well. if you put a sensor at this spot, you will get the "hottest temp". interesting, if you have a muffler in this location that is very close to the back and top of the cylinder, this can alter the reading due to making it a false reading. that is, the heat of the muffler may be adding to the actual temp of the cylinder. this seems to not be a problem on twin cylinder engines, due to the mufflers or headers usually pointing down.
More interesting observations: the temperature peaks during flight occur during up-lines, knife edge flight, hovering and flat spins, etc.. really make it hotter!!!! usually temperatures are not sustained, but peaks due to whatever flight maneuver you are doing that increases the load on the engine. Also interesting is that cooler days can lower the temperature down significantly more than the actual ambient temperature compared to another day. for instance, i was flying in 95 degrees temp, and the engines peaks temps were in 320's, then another day, temps were in 85 and high engine temps did not get over 280, all other variables were unchanged (altitude, prop diameter/pitch, needle settings, gas oil mixture, gasoline octane rating).
i will attach a diagram depicting the position of the temp sensor.
8918=3182-sensor position for da 70.jpg
For the temperature, this gets even more complicated and interesting. for years, people measure their engine temps by using a infra-red thermometer of sorts. or at least, this is how i assume people make these measurements. they have then reported these temps, and after some while, people get an idea of what "normal" range should be.
when using the infrared thermometer guns, you must keep in mind that if you point it to the front of the engine, while the propeller is spinning, the temperature that is read is of the surface of the front of the motor. be it the cylinder or the crankcase or whatever you point it at. this type of info, lets say, you get the temp of the engine soon after cranking it on, or, you check it upon landing, or if you run it on the ground, and check the temp there, whatever, you first will need to appreciate the cooling of the engine and how the engine dissipates heat.
i told you this would get complicated. After having had performed many experiments, i have concluded that the temperature in the front of the engine, when the engine is running, and there is a propeller connected forcing air onto the engine, the cylinder temperature in the front of the cylinder is way cooler than the temperature in the back of the cylinder (sometimes difference is greater than 100 degrees F). the temperature in the top of the cylinder (closest to spark plug) gets hotter than the temperature of the cylinder closer to the crankcase. the crankcase temperature is way lower than the cylinder temps (can be over 100 degrees cooler). the hottest area on the engine is the area directly behind the cylinder and the highest area (fins) area as well. if you put a sensor at this spot, you will get the "hottest temp". interesting, if you have a muffler in this location that is very close to the back and top of the cylinder, this can alter the reading due to making it a false reading. that is, the heat of the muffler may be adding to the actual temp of the cylinder. this seems to not be a problem on twin cylinder engines, due to the mufflers or headers usually pointing down.
More interesting observations: the temperature peaks during flight occur during up-lines, knife edge flight, hovering and flat spins, etc.. really make it hotter!!!! usually temperatures are not sustained, but peaks due to whatever flight maneuver you are doing that increases the load on the engine. Also interesting is that cooler days can lower the temperature down significantly more than the actual ambient temperature compared to another day. for instance, i was flying in 95 degrees temp, and the engines peaks temps were in 320's, then another day, temps were in 85 and high engine temps did not get over 280, all other variables were unchanged (altitude, prop diameter/pitch, needle settings, gas oil mixture, gasoline octane rating).
i will attach a diagram depicting the position of the temp sensor.
8918=3182-sensor position for da 70.jpg
