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Electric Gentle Lady

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Old 09-17-2016, 01:45 PM
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Baysidejim
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Hi All. I'm new to this so I hope my questions aren't too lame. I've learned to fly my Radian and I am addicted! I like to build planes as well and have a Gentle Lady almost complete. I want to set it up with an electric motor and am looking for advise. Can I do something as simple as buy a Radian and transfer the guts (motor, esc., etc.) into the G.L.? Is there a better option? Thanks!
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Old 09-17-2016, 04:07 PM
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I have done a little research on the Electra, Sig's version of what you are asking about and found it had the glide ratio of a brick if set up with the old school electronics it came with.
BMatthews put a post in my thread that may shed some light on what you're wanting to do. Due to this, I've cut and pasted the relevant information from his post below:
The overall weight for an Electra or Gentle Lady is best kept to 30 oz give or take a couple. It truly is a model where "lighter is righter" due to the choice of airfoil section. It's definetly not what you'd call a windy weather penetration model by any stretch.

At 32 oz or two lbs it means that you can achieve a "nice" but not rocket like climb with as little as 50 to 60 watts per lb. Or 100 to 120 watts total. On a 3S Lipo pack at 11.1 volts that's a mere 120/11.1= 11 amps. At this power setting the model would climb at or just a bit faster than it's normal gliding speed with an angle of climb of around 40 to 50 degrees.

Let's look at a more moderate setup for this model. For the heck of it lets "overkill" a little and go for a system that'll run at 70 watts/lb or a total of 140 watts running. From the Electrafly Rimfire series the Rimfire 400 looks pretty good with a continuous power rating of 160 watts and a burst at 220 watts. So with any sort of airflow around the motor it'll run cool at 140 watts. Now 140 watts on a 3S pack will pull around 12.5 amps. A 1250 mah pack will thus provide 1/10 of an hour of run time or 6 minutes. At the sort of climb you'll get with this setup at 140 watts this will easily give you 3 to 4 climbs up to around 400 to 500 feet and leave lots of power for running the radio gear. The good news? A setup of this sort will weigh in at 1.9 oz + 4.5oz = 6.4 oz total.

In other designs carrying an extra 3 oz would not hurt so much. In fact it would help in windy conditions and hurt only a little in calmer times. But the Electra isn't such a model. The free flight like design with the free flight inspired airfoil it has thrives on a lighter wing loading.

By the way, if you're building the Electra from scratch or from a kit with lighter wood or don't mind replacing some of the heavier wood it's very possible to build an Electra with that Rimfire 400 and a 3s 900 to 1000 pack and have it come in at around the 25oz mark. At this weight you'd have a really delightful summer evening floater. And given that you could prop the motor for back around the 120 watt range you'd still get a good 3 to 4 climbs to thermal country per pack along with lots of radio power in reserve.

At least this is my side of the story......
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Old 09-17-2016, 04:51 PM
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Wow, that was much more that I expected. Thank you! I don't know what a lot of that is, but now I have something to research and a direction to head in. Thanks!
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Old 09-23-2016, 11:50 AM
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Jim, electric motor specs can be confusing to new folks. But there are two key factors to shop for. One is Maximum power in continuous watts and the other is the Kv value. Kv is short for RPM per volt. Don't ask now they get "Kv" from that! ! ! !

You want a Kv value for a sailplane/glider that allows you to turn a larger folding prop. A bigger and slower turning prop on a glider makes for a more efficient climb. And the folding aspect aids with a cleaner front end for less drag while gliding and less abuse on the motor's shaft during less than ideal landings. Generally a lower Kv value that will let you work with a 10 to 12 inch diameter prop on your Gentle Lady is going to be around 1000 to 1100 or so. But look at what the motor's instructions call for. Or if shopping from Hobby King look at what the user reviews suggest. Then buy a folding prop of around that size range.

Post pictures so we can all see how it's going.
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