I haven't tried to draw air through a spinner yet (haven't had the need to), but I have used scoops/baffles to direct the air. It has worked very well for me.
Some motors (mainly heli motors) have fans to draw air through the motor. In a heli application there is almost no airflow.
Neodymium magnets are safe up to about 100C (212 deg F). The case and copper wire can handle much higher temperatures. If you take a temperature reading try to get a reading directly off the magnets.
This is a general statement, because different magnets (ferrite or cobalt) can handle higher temperatures. Go by the manufacturers specifications to be safe (or at least see what they reccomend).
Hi Mike,
Thanks for your post. I was hoping you had already experimented with this. (using the extra 5 min. per week you have left over in your busy schedule. ;-) The reason I asked about the "cooling holes in the spinner" is that our outrunner elec. motors need most of their cooling inside, which is totally blocked by our spinners. With our IC engines the spinner actually helped us by directing some of the airflow into the cylinder cooling fins. As you, more than most, know, many of the "old ways" of doing things with our airplanes no longer apply to elec. power! The standard spinner is sure one of them.
I envision the perfect Elec. CL (and elec. R/C) spinner to have large openings with some form of scops in the spinner and or in the backplate that forces air through the motor for the best possible cooling. We are already part way there with the excellent Tru Turn Electric spinners that have most of the backplate cut out, and they are light weight. If someone could just make the backplate do double duty as an impeller it might be the answer? ...... With our very small customer base it may take awhile before we have a real "cooling spinner", made for us. We may get help from the R/C elec. world, ........ their customer base is probably ours to the fourth power +? ;-)
I realize that we can cool our motors with good baffles, 2X+ air exhaust ports, and good cowl designs, etc. but I was just hoping someone had experimented successfully with an elegant spinner solution. ..... Bob Hunt has tried using small holes, but he said this did not work out. I'm sure someone will come up with one someday, I just hoped it would be sooner than later. ;-)
MOTOR TEMPS: Here are some good comments from the tech dept. at MEGA motors:
QUESTION: "What is the maximum temperature a Mega Motors can reach?
ANSWER: MEGA Motor recommends that your motor not exceed 140 degrees F. As a rule of thumb, you should be able to hold your finger on the motor after operation. If the motor burns your finger or is uncomfortable to hold, it is too hot. Motors that are continuously operated at high temperatures will suffer from demagnetization of the permanent magnets and lose power. Models such as airplanes should be designed with air flow around and through the motor. For helicopters an impeller or fan blade can be added to the motor shaft to create cooling and increase air flow. Heat sinks added to the case are also a good option for cooling. Cool motors such as MEGA Motors run better and last longer......" Tech Dept.
I have talked to several experts about our motors and they all seem to agree on this 140 degree F as a safe top limit. The possible motor failure temp, and/or very short life span, seems to start around 165 to 175 F, and like you said total failure somewhere above 200 F. They all agreed that we should shoot for < 125 F to get good performance and longer life.
The research also says that our motors want to run as cool as possible, (I'm not sure about below freezing? ;-) to get MAX power, but our batteries want to run warm (90 to 110) for max power. This is why I was looking to maximize our motor cooling, not just to stay under the too hot limit, but to get closer to the MAX power lower temps. IMHO we should be working harder to get our motors cooler than we are running them now. There is some free power being missed, and as pilots often say: "you can never have too much power!"
Alan mentioned this "cooler motor is better" fact, and I agree with him that a cooling fan forcing air through our motors is a good start. In R/C elec. we seldom run very long at full power, and we often have a power off downhill line to cool the motor back down after the full power up line. In CL we are full power for 6+ min., with NO cooling period.
In the future we may end up using the shaft that sticks out the back of our motors to drive a small ducted-fan unit that doubles as a cooling fan sucking air through the back of the motor AND providing some extra thrust. ...... So many projects, So little time! ;-)
Alan, thank you for your informative post. I would like to make one suggestion re: the exhaust of the motor's hot air. We need to be careful directing this heated air over the battery, or the controller. If possible it should exit the plane through it's own exhaust system. The batt and controller, etc., should have their own "fresh" air and exhaust system. If I could post photos to this forum I could show you how I accomplished this on my elec. Vector. After more than 30 years as a commercial pilot, I have been fortuneate to have had the opportunity to see the many methods that have been used to move air in and around airplanes. The engineering used for intake and cooling systems, and jet fan systems, is amazing. I have always been impressed with the genius of engineers who thought through and solved the many problems in order to make air flow exactly where it was needed to get the job done. ............ We can learn from full scale A/C and hopefully be able to improve our much less sophisticated, but still challenging aircraft systems. ;-)
I feel that, like props, cooling is an area where we can make some easy (almost cost free, and weight free) improvements to our electric CL systems. Our systems are very good now, but there is still room for improvement. ....... I'm sure innovators like Mike, Dean, Bob, Will, etc. will continue to improve our systems and make our elec. CL planes even better than they are today. My hats off to them for their past and future help!
Regards,