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Old 04-09-2013, 04:36 AM   #1
neddy191
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Default help with power system for 25% Cub

I'm building a 1/4 scale full wing (104") cub from a Sig kit. I was initially going to use a gas engine but I've now decided to go electric instead. I'm new to electric and need some help figuring out what motor, esc, battery size I'll need.

I figure the plane will weight 15-16lbs once complete.

Any help or recommendations are appreciated.
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Old 04-09-2013, 04:54 AM   #2
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you're looking at 6-10s lipo and a big low kv motor. hobbyking has some good choices for motors I was looking at one of the ntm motors but after pricing everything out im thinking gas will be the better deal
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Old 04-09-2013, 05:10 AM   #3
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I know that price will be more than gas. I already have a gas engine that I was going to put in it - I'm going to eventually sell it to fund going electric. This build has been stalled for 4 months and probably won't ever get done if I go gas. Getting the gas tank and throttle servo installed in the nose has been a PITA and if I were to get it all installed if something happened I'd end up having to rip off the covering and open the nose. I've already got a good charging set-up from some heli's I fly so I can parallel charge big 6s batteries without problems so I think electric will be way less headache.
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Old 04-09-2013, 06:28 AM   #4
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Originally Posted by neddy191 View Post
I'm building a 1/4 scale full wing (104") cub from a Sig kit. I was initially going to use a gas engine but I've now decided to go electric instead. I'm new to electric and need some help figuring out what motor, esc, battery size I'll need.

I figure the plane will weight 15-16lbs once complete.

Any help or recommendations are appreciated.
Ah Ha
Been there, done that. I've electrified a Top Flight Cessna 182 last year. Wingspan is 82 inches, area is 900 sq in, weight is 15.5 pounds. The power plant is a Hacker A60-5S motor, with a 10S2P 4600 mah A123 battery pack.

This powerplant turns a 19X12 APC-E wide blade prop at 5900 RPM, and hauls the model off the ground in a very unscale like 30 feet or so.

The A123 pack would be similar to an 8S 4500 Mah LiPo.

Also have a Giant Scale Big Stick model with 78 inch wingspan, 1500 sq in area, 16 pounds weight. Power is a Hacker A60-16M with the same 19X12 APC-E wide blade prop that turns over at 6700 RPM on the ground, using a 12S2P A123 battery pack. The 12S2P A123 pack would compare to a 10S LiPo battery. The A123's weight about 30% more than the LiPos, but A123's have zero fire hazard, and can be recharged as fast as your charger will go. My Cellpro Powerlab 8 charger will charge the 12S2P battery in 16 minutes.

Both models use the Castle Creations ICE HV ESC with an 80 Amp rating.

One big concern with the Piper Cub is the landing gear. Make danged certain you have ground clearance with a 19 inch diameter prop. I had to extend the LG by two inches on the Cessna 182 model.

IMHO, for models of this size, its not a good idea to skimp on the electric power system, especially with the motor. Motor weight and motor efficiency get real important real fast when running 2500 or 3000 watts power. The Hacker A60 series of motors are running about 90% efficiency at their rated power, a pretty good value. The Hacker A60 series of motors have a threaded shaft for the prop, just like the glow/gasser engines. The A60's do not use a propeller adapter. I've got 8 Hacker motors ranging from an A30, two A40's, three A50's and the two A60's. All of them can be run at their rated power levels without issue.

Check out www.motocalc.com for a computer program to help with your power selection, what ever it may be.

Take a look:
Giant Scale electric motors vs Gasoline Engines
http://www.wattflyer.com/forums/showthread.php?t=58035

Harbor Freight Gasoline/Alternator Setup
http://www.wattflyer.com/forums/showthread.php?t=66066,

Great Planes Giant Big Stick Electric Conversion (I put over 160 flights on this model last year. It became my favorite model to fly. The motor hauls that model straight up out of sight.)
http://www.wattflyer.com/forums/showthread.php?t=65052

Giant Scale Cessna Model
http://www.wattflyer.com/forums/showthread.php?t=66414

And, IMHO, these giant scale models should have dual battery supplies:
Giant Scale Power System:
Battery Backup System, note the input voltage limit on the Castle Creations 10 Amp uBEC.
http://www.wattflyer.com/forums/showthread.php?t=63794

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Old 04-09-2013, 07:18 AM   #5
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IIRC... the 1/4 scale Sig Cub calls for a pretty small engine... .60 2-stroke glow I think...

You can easily power that with a single 6S and an Axi 4120/18 or E-Flite Power 60 if that is correct. (easy to get the specs on those motors)

More power isn't really a bad thing... but you have lots of options from there up to the big E-Flite Power 160 to swing a scale prop. (there's always the throttle stick... you don't HAVE TO run it wide open)

You have a pretty large aircraft that can fly in many configurations... It really depends on how heavy you build it and how you want it to fly as to which power system to stick in.

As you add scale features you'll add weight and need more power... and potentially need to beef up some of the structure a little (For example, applying CF "TOW" to the main spars as spar caps.... light and very good at increasing wing strength)
As you add more power you'll add more weight and almost certainly want to pay attention to structural issues.... adding more weight...

*************

I had a Sig Kadet Sr with a .61 glow in it (with reinforced structure) and it could lift off at 18 lbs... and still flew like a slow trainer.

Smaller wing than that Cub... 15 lbs is a reasonable target for your plane.
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Old 04-09-2013, 05:18 PM   #6
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Originally Posted by neddy191 View Post
I'm building a 1/4 scale full wing (104") cub from a Sig kit. I was initially going to use a gas engine but I've now decided to go electric instead. I'm new to electric and need some help figuring out what motor, esc, battery size I'll need.

I figure the plane will weight 15-16lbs once complete.

Any help or recommendations are appreciated.
What size gas engine had you thought of using?

FYI, that Hacker A60-16M is comparable to a 35cc gasoline engine, and the Hacker A50 series motors are comparable to a 20cc gasoline engine.
One reason I went to the A60 series motors on my giant scale models is the very robust threaded 8 mm propeller shaft these motors use. (8mm is very close to 5/16 inch diameter)

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Old 04-10-2013, 04:37 AM   #7
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I was going to use a 30cc gas engine, I know alot of this model are flown with 20cc engines. I'm looking at Hacker A60-16M or A60-7s now. The 7s is back mounted which might make it easier to fit my cowl, just need to get or make the right length stand-offs to reach back to the firewall. The A60-16M from what I understand needs both front and rear support with the special Hacker mounting bracket, and I still might need standoffs so I'm not sure I want to mount everything like that. I'm leaning toward the 7s.
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Old 04-10-2013, 06:01 AM   #8
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Originally Posted by neddy191 View Post
I was going to use a 30cc gas engine, I know alot of this model are flown with 20cc engines. I'm looking at Hacker A60-16M or A60-7s now. The 7s is back mounted which might make it easier to fit my cowl, just need to get or make the right length stand-offs to reach back to the firewall. The A60-16M from what I understand needs both front and rear support with the special Hacker mounting bracket, and I still might need standoffs so I'm not sure I want to mount everything like that. I'm leaning toward the 7s.
Yeah, IMHO, the A60-7S motor would be a good choice. The A60-16M motor does have a bit more horsepower however. The A60-16M motor requires mounting to a flat plate directly behind the propeller. The backside of the A60-16M motor includes a fan, so the back side can not be used for mounting.

As far as stand-offs are concerned, take a look at your local Ace Hardware for an assortment of both aluminum and nylon stand-offs. The stand-offs with #10 screw holes would work fine.

I didn't do that with my Cessna, that was built up with a plywood firewall that was extended forward of the original firewall.

The attached photo shows how it was done. That is a 19X12 APC-E Wide blade prop on the motor.


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Name:	Hacker A60-16M with Giant Big Stick.jpg
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Old 04-10-2013, 01:49 PM   #9
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Guys it is a cub! Relax a bit on the power.

I used to fly the 1/4 scale Sig Cub a great deal. Used a 1.20 Saito and it was MORE than abundant power.

I would think that you could use 6s on the low end of power and 8s should be abundant for nice scale Cub flying. I would look for a motor in the 300kV range you will need nose weight anyway so a 110 type would be good with 6-8s LiPo battery.

Cheap route you could look at something like this...

http://www.hobbypartz.com/96m607-big...325-295kv.html
About $53 for the motor...

Two of these 4s packs in series:
http://www.hobbypartz.com/98p-25c-4000-4s1p.html
About $110 bucks

And an ESC that will work on 8s. Shoot for about 1400 watts for very spirited Cub performance.

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Old 04-10-2013, 11:00 PM   #10
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I agree that an A60 hacker sounds like a lot of motor for a cub, I know it will be overpowered on it but I will have a throttle stick that I don't have to push all the way forward. I think I'm still going to go with it - at least initally. I'm wanting to move to all electric eventually and part of getting an A60 is for the wife to approve the purchase of a big motor. Down the road I can tell her its too much and change to a smaller more appropriate motor which then leaves me with a nice powerful motor that will need a new plane to live in. I've already convinced her that the move and expense of moving to electric is worth it in terms of safety - I won't be cranking big gassers by hand and getting my hand near spinning props to tune the motor.
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Old 04-11-2013, 01:19 AM   #11
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Originally Posted by neddy191 View Post
I agree that an A60 hacker sounds like a lot of motor for a cub, I know it will be overpowered on it but I will have a throttle stick that I don't have to push all the way forward. I think I'm still going to go with it - at least initally. I'm wanting to move to all electric eventually and part of getting an A60 is for the wife to approve the purchase of a big motor. Down the road I can tell her its too much and change to a smaller more appropriate motor which then leaves me with a nice powerful motor that will need a new plane to live in. I've already convinced her that the move and expense of moving to electric is worth it in terms of safety - I won't be cranking big gassers by hand and getting my hand near spinning props to tune the motor.
That's not even considering the high vibration levels of those gasser engines on your model, and what it could do to your radio system. I've personally measured vibration levels over 25 G's at the aileron servo location on a club members giant scale model with a 120 cc Twin cylinder engine up front.

I've got an 65 inch wingspan scratch built electric model that's working on its third electric power system. It was built in 2003, and still looks like brand new, even with over 1000 flights in its on board flight recorder. This model started out with a geared 40 Astroflight brush type motor with 22 Nicad cells for power. Second power system was a geared Astroflight geared 40 brushless system.

It's now running with a Hacker A50-12S motor, 15X10 prop, and 6S2P A123 battery pack. That A123 battery pack has over 350 flights on it, and still performs as it did when brand new.

As for spinning props, IMHO, it's mandatory on these big electrics to have a positive battery disconnect for that motor. I'd not want to be anywhere near the propeller of a Hacker A60 class motor that suddenly started by an accidental movement of the transmitter throttle.

If you're running a Spektrum DX8 transmitter, mixing in a throttle kill switch is easy to do. It's a bit more work on the original Spektrum DX7. I've done it, if you'd like more info on the DX7, let me know.

As far as the big Hackers go, check out the Hacker A80, A100 and A200 series. For these giant monsters, you almost need to own the LiPo battery factory to run them.

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Old 04-11-2013, 03:24 AM   #12
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The couple electric models I have now I've programmed the Futaba 10c I use for them to have a throttle kill switch. I'm very accustomed now to making sure the throttle hold is on when near an armed model since I started learning to fly heli's. Now I just want to figure out how to program in both a throttle kill and a switch that keeps a low idle when the throttle stick is all the way down.
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