Hello fella's, a friend of me consider to electrify a sig somethin extra.
I don't have a lot of experience with electric flight, so please give us some tips.

as it been done already ?
what structural mods did u do to lighten the airframe?
what engine?

thanks a lot


Phil

It's certainly been done before. You ought to be able to find at least one discussion on this plane in the thread archives.

The standard tips for building light also apply. You can replace lite ply with balsa of the same thickness, aircraft ply with lite ply, slab surfaces with stick-built "truss" structures. On a solid plane like the Sig SE, you can probably save several ounces just in the stucture; it's overbuilt even for glow power.

At my club, one of the members has a Something Extra that was built stock for glow then converted. He's running a geared astro 25 on 14-16 cells. Heavy, but flies well.

John

I converted this plane to electric a few year ago and still find it to be one of my favorite to fly. Built stock it comes out pretty light but you can take and extra 1/2 pound out if you replace some wood and use micro equipment.

http://www.rccraze.com/something.html

Well after the great success I (finally) had converting my Wonder, I'm now mapping out the power system for my Somethin' Extra. It's already built, I originally was planning on putting a Saito .91 in it, but that was a bit much, and, well, I'm tired of messing with nitro engines

On to the details/goals:
AUW (less power system) 63oz - includes radio system but no Rx batt - planning on either BEC or UBEC
Looking for, let's say Aerobatic+ performance, I built it for 3D stuff, but I'm just out to have fun, so I'm not planning on takeoff-to-land 3D flights.
My goal is at least 100W/lb, you can never have too much power.
Hoping for >1 thrust-to-weight

So, with that in mind, I'm aiming for 500-700W to power the thing. So here's what I've mapped out so far:

4S Lipo will give me the desired power if I draw 30-45A. From looking at specs and playing in Motocalc a bit, it looks like an AXI 4120/14 is what I'm looking for, capable of 45A bursts, and according to Motocalc, with a 14x8 will give me 45A and ~91oz of thrust.

So far so good (feel free to critique if I've made a flaw in my plan so far ).

So now on to the questions.

ESC:
I'm looking at topping out at 45A, so I was thinking a Phoenix 45 would fit the ESC bill. Normally I prefer headroom, but this system is going to be expensive, so I'd like to save money where possible. Will a Phoenix-45 work, or maybe I should say, is the headroom of the Phoenix-60 necessary? Considering, most of the flight will be pulling <45A, I'm thinking the 60 would not be necessary.

Batteries:
This is the trickier part, since there are a number of options:
1) Kokam 3200HD 4s - 64A capable, more than enough, actually one of the lighter options - AUW would be ~88oz.
2) PolyQuest 2600 4s2p (these are the 10c) - 52A capable pack - about 2.5 oz heavier than the Kokams, but a little cheaper
3) PolyQuest 2600N 4s2p (these are 12c) - 62A - about 4 oz heavier than the Kokams
4) PolyQuest 3100N 4s (these are 12c) - 37A cont, but they're rated to ~50A burst - but 3oz lighter than the Kokams and much cheaper

So, considering the "fagility" (for lack of a better term) of lipos, I'm inclined to go with Kokams. If I got that 4s from 2x 2s packs, there would be the added benefit that I could use the Kokams in (2s) my Wonder also. And with the 64A rating, I could also use the 4s pack in the A-26 I'll be building . Oh, and I'm figuring on an Astro 109.

I guess this is mostly a sanity check, any comments would be appreciated, thanks

Hi stanger89,

Let me how your conversion goes...I was looking at this kit today and wanted to convert it to electric power...have an Axi 2820/12...specs says it's good up to 5.5 pounds...believe the sig kit comes in at between 4.5 and 5 pounds.

Would also be using a ubec and 2 kokam 3S 2000mah 15C lipo in parallel...I can get about 400watts out of it...if I lighten up the kit...I should be able to get the weight down a bit...I do from what I read online...the kit is over built even for glow and judging from the weight of the boxed kit I believe it.

Cheers,

Gord.

Moving at a snails pace here.

I've actually got everything for it. I've got a couple comments, just my personal thoughts. I don't think that 2820/12 will be enough power. I looked at those but decided that they just weren't capable of the power i wanted. As you said, 5.5 pounds is a reasonable expectation for AUW, and for good performance, that's 550W, the 2820/12 tops out at about 500W, and that's pushing it's limits, at least spec wise.

That's why I chose the 4120/14 for my Somethin'. You can get 700W out of one of those, with plenty of torque to spin really large propellers for a lot of thrust.

I will say that I built the kit for glow, (was going to but a Saito .91 in it, but that turned out to be too much ) so my kit wasn't lightened at all. I don't remember the AUW but I'd go for a 4s pack over the 3s. I've got 2 Kokam 2s 3200 packs in series for mine. I ran it with a 13x8 and pulled a bit over 500W. I'm planning on running either a 14x8 or more likely a 3-blade 13x8 (ground clearance). I ran a 14x8 which pulled a lot harder than the 13, but I didn't measure that one. I would say that based on my somewhat foggy memory, that the 4120 is pulling similarly to the Saito

Hasn't flown yet, mainly becuase I'm lazy and haven't figured out a satisfactory way to mount the batteries.

My problem is solved...my friend bought back the 2820/12...he needed it for a project...guess in retrospect it was better to build a plane around a motor than trying to fit a motor around a plane.

Cheers,

Gord.

I am presently flying a Sig 4 star 40 w/ the AXI 4120/14 and 14 GP 3300 NImh cells and am pulling 45 amps for a power loading of 106 w/lb, and this set up will be going in my Sig something Extra. However I may try the new Poly Quest Lipo 4 cell 4000 mah pack [$149.00] from Hobby-lobby. I will be saving about 1 1/4 lbs with this change I think you would be happy with this setup in the Somethig Extra

RCPunk,

What prop are you using?

Tweet, I am using an APC 13x 6.5

Hi,
Just wondering what will be the cost for the setup minus the plane?