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Scratch
09-16-2005, 06:56 PM
I'm fairly new to electric rc and have lots to learn. The forums have been great, but I just need a little help in selecting the appropriate power system.

I have a 36" wingspan profile/3d (scratch built) type plane. Airframe weight is approx 25oz. Radio gear add another 5oz, so ready to add power and battery/esc weight of around 30oz let's say.

I'm looking at the Axi 2820/12 with 40a Jeti and TP2100 3 cell lipo. I figure that set up would weigh approx 12oz for an AUW of 42 oz.

Is that set up enough? Is it overkill? What prop you think? (I'm looking for 3d performance.)

Thanks a ton.

Scratch
09-19-2005, 02:17 AM
Ideas.... anyone.....???

Dr Kiwi
09-19-2005, 03:53 AM
I'm fairly new to electric rc and have lots to learn. The forums have been great, but I just need a little help in selecting the appropriate power system.

I have a 36" wingspan profile/3d (scratch built) type plane. Airframe weight is approx 25oz. Radio gear add another 5oz, so ready to add power and battery/esc weight of around 30oz let's say.

I'm looking at the Axi 2820/12 with 40a Jeti and TP2100 3 cell lipo. I figure that set up would weigh approx 12oz for an AUW of 42 oz.

Is that set up enough? Is it overkill? What prop you think? (I'm looking for 3d performance.)

Thanks a ton.


3D performance from a 42oz plane with only 36" span - whoa! That's a brick.

How did the bare airframe get to 25oz - for 36" span, 3D capable, I'd have been looking for an AUW [everything! airframe, servos, Rx, motor, batteries] of less than that.

Scratch
09-19-2005, 04:36 AM
Yeah, it's a brick, I know. This was my attempt to scratch build a 3D profile, which turned out heavier than I wanted. I tend to over-build stuff. Maybe I should just buy an ARF that has a million pages in a thread on motor set up. Thanks for your help. I now see the light.

Matt Kirsch
09-19-2005, 04:46 PM
Unfortunately, physics is a cruel mistress. A 42oz plane with a 36" wingspan is way too heavy for 3D. The plane would have to weigh about half that much, in the 22-28 ounce range, to make a reasonably good 3D ship.

At 42oz, you were pretty close on the power system, though a little shy in the battery department. The TP2100 is only capable of about 21 Amps... You'd need a second one in parallel to handle the current a 2820/12 would need to draw to effectively power a plane that heavy. That's another 6oz, for a total AUW of 48oz...

Don't get discouraged, though. Take a look at your first prototype, identify where it's overbuilt, and build your second prototype lighter. Electric planes don't need lots of 1/8" aircraft ply, large solid sheets of anything, or large amounts of epoxy. Build stick structures where you used sheets, or drill lightening holes. Replace aircraft ply with lite ply, or even balsa.

Did you use full-size radio equipment? 5oz is quite heavy for micro gear.

Scratch
09-19-2005, 06:52 PM
That's good to know, Matt, thanks. I had no idea about the amps with that battery set up. Like I said, I'm learning this electric stuff - a little frustrating I'll say, but I'm addicted to it.

I maidened it the other day with the world's worst set up possible I think (stuff I had lying around): brushed 600 geared 3.5:1 with an 8cell 2400 NiCd. The AUW 56oz. cement slab eventually left the ground, flew around for about 8 minutes and landed. It was honestly a great flying plane for just cruising, very little trim and it was flying good. For my first attempt at scratch building my own design, I was pleased it flew at all. Then like the idiot I am, I tried hand launching the second battery. Yep. Too heavy. At least now I have the opportunity to do it again - lighter.

I had a Hitec 555 receiver with HS-81 servos. Obviously too much for a plane of this nature. I'll have to cut back to lighter gear in the future as well.