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Old 03-06-2011, 02:49 AM   #2
kyleservicetech
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Originally Posted by constantmotion View Post
I have a 1/4 Scale Clipped Wing Piper Cub that I have just obtained. I am in the process of making some minor repairs and completely recovering it. It has an 86" wingspan. RTF it'll weigh bout 13lbs (close guestimation). I plan on running a pair 4S 3000mAh in series for an 8S configuration. Not sure if this'll be enough...just throwing that out there. What Turnigy brushless motor would be suitable for the bird? I am kind of dumb on the large sized brushless motors. I am used to the tiny park flyer outrunners. I have read that I will need to spin a large prop at a low rpm and need something that'll push around 1200W. What size prop would work? I am planning on running an 80 or 90 amp ESC.

I flew a very similar full scale model of this Piper Cub back in the late 1990's. Power was an Astroflight geared 90 brush type motor running on 38 2400 Milliampere Hour Sanyo Nicad cells. It was pulling about 950 watts, turning a 20X10 standard wood propeller at about 5900 RPM.

With all those Nicads, weight was about 16 pounds. The take off run off of very short grass was on the order of about 40 feet or so. The model flew very scale like. It would not "hover" but no full size Piper Cub plane ever did.

That model had a LOT of flights on it with that power system. Finally sold it some 6 years after building it from a kit.

At 13 pounds, any motor that can turn a 20X10 prop at around 6000 RPM will do very well. I'm a person that only flys Hacker motors. Expensive, but reliable. They will do what their specifications say they will.

This model will fly around 50 MPH or so, so you don't want a high pitch small diameter prop on it.

To help you in your motor selection and battery selection, check out one of those computer spreadsheets, such as www.motocalc.com for help. Free for 30 days, then $39.00, IMHO worth every penny.

I'd think a battery on the order of 8 Lipos, and 5000 Milliampere Hours would work on this model. Or, 10S2P 2300 Mah A123 cells. And you'd use motocalc to find a good motor.

I've got a Hacker A60-16M motor running on 12S2P A123 cells that turns a 19X12 APC-E prop at 6800 RPM, pulling around 2400 watts. That motor will match a good 30 cc gasoline engine for power. This motor would be way to much power for your Cub.

If you've flown models larger than a park flyer, you'll have no problem flying this Cub. IMHO, models this size are far more stable in flight than a park flier. If not, might be a good idea to find someone to help you on the first flights. Just a warning on these Cubs, and many similar type models. When turning them, you bank with ailerons. Due to adverse yaw on those big wings, banking left will result in a noticeable turn of the nose of the model to the right. You need both rudder and ailerons to turn these things to make it look right.

Keep the wattflyer readers posted on your progress!
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