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Setting up a power system for AP for nature photography

Old 09-23-2011, 08:23 PM
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hucker
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Default Setting up a power system for AP for nature photography

I'm building a plane for an AP project. It is using easy glider wings on a custom fuselage designed for packability. The model is going to weigh about 36 ounces. I would like it to be as quiet as possible. It doesn't need to be silent by any means but if I can avoid much of the high pitch whine that would be great.

I think I need about a 250W motor and I'd like to use a 3 bladed prop as I think that will be quieter. As I said it is more of a glider so the flight speed will be on the slow side.

When I go to the various calculators i find online there are so many options for motors and batteries it is tough to be grounded. How do I get started on picking my motor/prop?
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Old 09-23-2011, 10:25 PM
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CNY_Dave
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I think you want to go with the largest prop you can fit with the highest pitch you can find then work backwards.

Slow-turning prop with no gearbox will be the quietest, this means you want a low-kva motor.

dave
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Old 09-23-2011, 10:44 PM
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pmullen503
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Backpackable AP plane...Sounds cool!

Start with the prop diameter. A larger, slower turning 2 blade prop will be quieter.

At 250W I'd go with 3s lipo.

Now that you have the voltage, wattage, and the prop size you should be able to easily narrow your choices using a calculator. This one http://www.drivecalc.de/ allows you to enter prop size and battery and have it match those parameters.
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Old 09-24-2011, 01:26 AM
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hucker
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Did you mean 3 blade would be quieter? I'm under the impression that a 3 blade prop will be quieter since the tip speed should be slower for a given thrust. I realize I will loose a little efficiency and add a little weight but reducing annoyance is a big deal.

I see that master air screw has 2 props that will fit - 3 blades 8x6 and a 9x7. The 8x6 should fit no problems while the 9 might be a little tight.

So how do I design this? I can see the sizes used on similar models (easy glider = 3100kv/275W/37A ESC but it uses an 11x8 with a gearbox) but I don't understand how to know if I need a gear box, what the efficiencies when using a 3 bladed prop etc.

This is all clear as mud!
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Old 09-24-2011, 10:46 PM
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CNY_Dave
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That fine a point I think would only be figured out through testing.
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Old 09-24-2011, 11:36 PM
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mclarkson
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If you are turning, say, a 9" 3-bladed prop at the same RPM as a 9" 2-bladed prop, then the tip speed would be the same as they are both traveling 27.25" every time around.

A tractor arrangement will be much quieter than a pusher, so if you want quiet, that's the most important consideration.

I would start somewhere around, say, the Radian. That runs a 4oz 480size 960Kv motor with a folding prop. No gearbox. I think this is in the ballpark for what you want: a 3oz - 4oz motor turning at 1000Kv or a little less.

You'll want a 10" - 11" propeller on there.

A good option is always to contact Jeff at Headsuprc.com and ask him for recommendations. Here's one of his motors that might work for you.
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