02-27-2014, 02:50 PM
Join Date: Aug 2005
Location: NY, USA
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Club: Long Island Silent Flyers
2 Meter Glider Conversion to Electric - Sample Package
CONVERTING A PURE GLIDER TO ELECTRIC LAUNCH
I often see questions about converting a pure glider to electric launch. Often it is an older 2 to 3M woody that has been neglected because the pilots no longer wants to bother with a hi-start or a winch. So I thought I would draft something as a starting point for pilots looking for advice on such a conversion.
Have you done a conversion like this? We would love to hear your feedback and for you to add your set-up for other people. Please also add any tips or advice.
What glider did you convert?
What did you use?
What would you do differently if you did it over?
Here are some sample components that would work in many cases. These are certainly not your only options and these are not necessarily the best options for your individual glider, but they give you a feeling for what is needed and you can branch out from here. How much power you need will depend on the weight of the glider, after the conversion, and what kind of climb you want to achieve. My power to weight ratio recommendation would be to shoot for 75 watts/pound for about a 45 degree climb for sport flying. For electric contest flying, like ALES or F5J, I would suggest about 130 watts per pound to hit 200 meters in 30 seconds or less. More than that and you are building a helicopter, but some people feel that way too much power is just about right.
This particular combination of components was based on the conversion of a Spectra 2M to brushless power. The Spectra was built for electric power but used an old heavy brushed motor. This set-up will run about 250 to 300 watts and the estimated finished weight of that glider was about 3 pounds, 48 ounces. Depending on what prop was chosen this would provide a power to weight ratio of about 80 to 100 watts per pound.
I have limited experience with HK motors but many people like them so I have used one as an example here. If you prefer some other brand you can use the specs of these components to help you find the parts you want from another maker.
Most pure gliders have fairly thin noses with tight interior space, so I have selected a 2836 mm outrunner motor with the assumption you are going to put the motor inside. The outside of the motor itself is 28 mm and the length of the internal motor is 36 mm thought the overall motor is actually longer than that. You can see the actual dimensions on the page at the link for the motor. Remember that you need to leave space for the spinning can and have to safely route the wires.
You don’t have to put the motor inside fuselage. Some pilots just cut off the nose block and mount the motor on the outside, later adding a cowl over it. If you do that then you are less constrained in motor size, but again a 28 MM wide motor will work well in most situations. Also having the motor further forward can work well for balance in SOME gliders.
If you are converting an old electric glider, like a spectra, that was based on a brushed motor, be sure to take into account that the brushless motor may be lighter than the old motor. For example a Speed 700 motor is almost 8 ounces while the 2836 motor suggested below is about 5.5 ounces. That means that you will have to add lead to the nose or reposition components forward in order to get the glider to balance properly. Take that into account. An electric conversion can often be an opportunity to move things around to achieve the best weight distribution possible and avoid adding a lot of lead.
I am using a 2836 motor as the example. Max power is 330 watts. However the actual power level will be based on what prop you use. I would guestimate about 250 to 300 with one of the props I recommend. So this could be a good fit or a 30 ounce glider at 130 watts per pound for ALES contests or a 48 ounce glider at 75 watts per pound for casual sport soaring.
HobbyKing doesn't provide a prop recommendation for this 28X36 motor but, from the posts by users, a 10X6 or 10X7 should do. Maybe an 11X6. Be sure to test with a watt meter.
If you have a lighter glider you can consider a 2830 for lighter weight at a lower amp draw, about 180 watts. This would work for a 20 to 36 ounce glider depending on the power to weight ratio you want. Be sure to use a proper prop size, probably a 9X6, and a proper ESC, around 20 amps. Always look for a manufacturer’s recommendation and look at recommendations by users. Always check it with a watt meter.
ESC – For the 2836 motor this needs to be at least 30 amps. Whatever ESC you use, confirm it has a brake before you buy or the prop will keep spinning and KILL the glide. Most ESC don’t need any kind of special programming card but some do offer them and they can make set-up simpler. I have my gliders set to brake on. If I have an option I set for a soft start and a soft brake to reduce the load on the motor. For gliders those settings are usually fine.
Not sure if this spinner will be wide enough for the folded blades to clear the fuse of your glider with an internal motor mount. This is just a sample that would work with the 2836 motor. If you are mounting the motor externally than it is less of an issue as you will design the cowl to match to the spinner.
These blades are where I would start with for the 2836 Motor. I would get a 10X6, 10X7 and maybe an 11X6 to test. They are cheap enough. Here is where a wattmeter comes in very handy to insure you know what power draw you are creating with each prop so you don't under or over load the motor.
I would recommend a 3S lipo for the 2836 motor in the 1800 to 2200 mah 20C+ range for fit and weight. Figure 20 to 40 second climbs at about 25 amps. Expect about 3-4 minutes full throttle run time from the 1800. That should give you about 4-6 good climbs with some reserve.
Something like this will probably work. Measure the space for the battery. And be prepared to solder connectors to match the battery and the ESC.
Feel free to ask questions. If this all seems confusing because you don't understand electric power systems you might find this book useful. Read the above, then look at the chapters of the book, then read the above again and it will start to make sense.
EVERYTHING YOU WANTED TO KNOW ABOUT ELECTRIC POWERED FLIGHT