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Apr 27, 2014, 07:26 PM
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Great Planes Extra 300s 60 size

Been fiddling around with this project for a few weeks now, and its now at the framed up stage. This is the Great Planes Extra 300s 60 size, being converted to use an Emax 4030 400 kV motor on a 6s 5000 mAh pack. This is the first big electric conversion I've done, but I've run all the numbers on Motocalc, and it looks like I should get pretty decent sport plane performance, although not all-out 3d level.

Currently, as seen in the pictures, it weighs about 40 oz. I'm hoping for a ready to fly weight of around 7 1/2 lbs. With a 16/10 prop, Motocalc says I should get about 1000 watts, so the power loading should be reasonable.
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Apr 30, 2014, 05:38 AM
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I've considered building this kit with this very motor a few times...interested to see how you like this when you're done.

Looks like you did a really nice job on the frame-up. I see the stand-offs and plate for mounting the the rest of the motor-box stock or did you have to do anything else? Is that opening behind the firewall a hatch you cut for battery access?

I put the numbers into eCalc and at 7.5lbs AUW on 6S it looks like you would have more than enough for sport flying...according to eCalc you'd have like a 1.8:1 thrust to weight ratio (but that does seem a bit optimistic when you look at the data on the HURC site). eCalc also gave a temp. warning with that prop but I'm fairly certain it's because they have the motor can length entered incorrectly. After I changed the can length to something more like what is shown on the HURC site it was fine.

I'll be following this to see what your impressions are of how this flies and how the motor does.
Last edited by ChrisRD; Apr 30, 2014 at 05:47 AM.
Apr 30, 2014, 09:46 PM
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Chris, If you do decide to try this kit, you'll find the wing and tail goes together very easily, but the fuselage is a real pain. It's mostly that die-crunched, brittle, cheap lite ply that so many manufacturers are using now. It works, but it can be a bit tedious.

I kind of took a shot in the dark with the Emax motor. I'm going off the prop data the Heads Up Hobby has on its website. I'm guessing either a 15/10 or 16/10 should work well. I'm going to try and keep the current at about 45 A to begin with. I'm also using a Hifei 80A controller.

I didn't modify things too much. The motor box is stock, except for a few lightening holes. I just found that I need to add about another 1/2" standoffs to get the motor aligned right.

Yes, the opening aft of the firewall is the battery hatch. I'm using a pair of 3s 5000 mAh packs from ValueHobby.

May 03, 2014, 10:19 AM
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Thanks for the reply looks good...interested to hear your impressions when it flies.

I have the smaller Emax 4020 motor from HURC that I'm running on 4S in an old (formerly 4-stroke powered) .40 size trainer that I had plans to use for FPV...seems to be a good motor.
May 25, 2014, 08:30 PM
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Installed the motor, hinged all the control surfaces, and fitted the cowl and landing gear. Not sure if I really like the way the landing gear attaches- it's screwed in place with a pair of wood screws. I think it might be more secure if I replaced the wood screws with blind nuts and some hex bolts.
It's a bit heavier than I had hoped. As shown, it's 73 oz. I can still shave some weight off that with some sanding and more trimming on the plastic parts.
Good news is that there's plenty of clearance for a 15 or 16" prop, possibly even a 17".
Another mod I'm doing is using 2 elevator servos (hitec 225mg's) and mounting them in the tail. I'm also using a pull-pull for the rudder.
Nov 29, 2014, 02:14 PM
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Almost done!

Got a bit sidetracked and didn't get a chance to post any updates, but the Extra's almost ready to go.
Spent some time today doing some motor tests, and didn't quite get the results I expected. I think this motor's kV is probably closer to 320-330, as opposed to the 400 its advertised as. Using an APC 16/10, it pulled 32 A on a 6s 5000 mAh pack (60C). Prop tached at about 6500 rpm. Plenty of sport flying power, but I'm going to try a 16/12 sometime, possibly even a 17/12, prop clearance allowing.

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