View Full Version : Cub Help Needed

10-15-2006, 08:56 PM
I finally finished my Cub. I got stuck trying to swap out the small brushed motor for a small brushless motor (even though people said the stocker was plenty good). So I ended up chopping the stick mount back and intended to try to use the remaining part as the base for a firewall of some sort. But I went from a Park 450 to an Esskay 400XT along the way and thought my mount was out the window. I cut the stick too short for the 400XT. But ultimately, it dawned on me that I could still use the same design simply by using some spacers to get the smaller motor lined up forward enough. I am happy with how it came out. I tried to cut the stick square to itself so I could keep whatever down and side offset the stick had in it already.

Anyway, it is ready to go. I got a suggestion for a 47mm CoG from someone in here. I am actually a little nose heavy at that spot. I guess (as accurately as my fingers will let me be) that I am balanced at about 42mm. Can I get some feedback on this? I have no idea if 47mm was suggested as a maiden CoG, or if that was more sporty. I like to fly with tame controls. I always fly in low rates at about 60% or so of suggested full rates.

Incidentally, this is a Green RC cub with a 47" span. My AUW is 19.6 oz. I hesitated to mention the make because I am very unhappy with the support I got from the manufacturer. I had to spend a lot of money out of pocket to finally get a useable fuse. This model cost me about twice what it should have.

One other thing I am looking for help on is the motor/prop. I went with the 400XT obviously, but my prop choice was not so easy. Intuitively, I wanted something like the 10x3.8 SF so I could get a big slow prop on it. I figured it would fly this thing more like a Cub if I used this prop over the 8x6 SF that I use on a lot of my one pound warbirds. But this prop draws about 12.49 amps and made 127.6 watts. A little too hot for my motor (amp wise). I'm sure I probably wouldn't burn the motor up the way I fly, but it still seems like a "hot" selection.

So I went down to a 9x4.7SF and the amp draw fell to a comfortable 9.57, but the watts fell to 100.3 as well. I am worried that this will be too weak for the nearly 20 oz plane. The only other choice is the 8x6 SF. It draws 10.46 amps and makes 109 watts. Still a reasonable amp draw, and a few extra watts of output. But this is going to be the fastest of the props (not the type of flight I was hoping for).

I am inclinded to go with the compromise (9x4.7SF) to keep the speed down, but I am worried that 89 watts per pound is going to be underpowered. It's hard for me to figure this one out because I've only flown warbirds on the smaller, faster pitch props. I don't have any basis for this decision.

Can anyone help me out with this??

Thanks for the help!! Andy

10-30-2006, 06:58 PM
The 400XT flies my 28 oz scale Berkeley Stinson Reliant conversion in a scale like manner, 1100mah 3S lipo, duration about 8 minutes cruising flight. I use a GWS Direct Drive 9x5 drilled out to fit the prop adapter shaft. I found that GWS 9x4.7 Slow Flyer props pulled too many amps, voltage drops and LVC cuts in. A 2200mah 3S pack would be better for your Cub, 15-20 minute flights. I'm also using the 400XT in my MM Switchback 3D, 9x5 DD prop and 1100 3S Lipo, very aerobatic but not a lot of vertical. :)

10-30-2006, 07:07 PM
Hey, thanks for the ideas!

I actually flew this baby already. It did extremely well on the APC 9x4.7 SF. You are correct too about the 400XT. It had PLENTY of power for this 20 ounce'r!

I was toying with the idea of some different wheels for the grass. The tiny ones in the kit didn't stand a chance. I found some bicycle type wheels that people were using on parkflyers and figured I would get those. I have some 2.5" and 3" Dubros, but they are heavy in comparision. But I think I am going to use them anyway. I will be adding about 8 grams per side, so only a little over .5 oz. Knowing that you are flying a 28 ounce plane with the 400XT is comforting.

With the battery, I can get about 10-12 minutes on the 1350 mah. It also "fits" in terms of size and balance, so I gave up on trying to throw anything bigger in there. All in all, it is a very nicely balanced flyer!