Frogman1195

My Feedback: (2)

I have a Gentle Lady that I have been trying to get to fly for some time know. I just installed an ECS and new cobalt 400 motor into the girl and an 8.4 battery and 9x6 apc prop.

This is about my third interation at trying to get this thing up. She always seems to have no pull. I hand toss it into the wind and she loses forward momentum until she rolls off to one side or the other.

I have 2 standard S-148 servos. The Great planes ESC-30, 8.4 1800 mah AA battery pack, R-114 Futaba receiver, the Global Super Cobalt 400 motor and the 9x6 apc prop.

Have not tached it but it seems to have good thrust in my hands. I have used an 8x4 prop with the same results.

Help[&o]

Dave

craig

My Feedback: (1)

If you're not running a gear it's way too much prop. A speed 400 direct drive should swing a 5 inch prop. I would suggest getting a gear reduction unit, 3:1 ratio and run the same prop. I would also look at an eight cell battery pack.

Good luck,
Craig

Frogman1195

My Feedback: (2)

So Greg. The idea is to slow the prop down to say 4000 rpm? Why would this help? Also the ESC and motor won't have troubles with 9.6v?

Dave

NMPhi767

He's right, you'll need more torque to swing a prop that big on a 400 motor and the only way you'll get it is with a gear box. The prop will slow down but the air will be moved more efficiently with a gear box. A word of caution with the motor you are using though. I would be hesitant to run 9.6 volts through those global cobalt 400's. Most everyone I know (including me) has burned those motors up quickly just using 8.4 volts. I hate to be a downer, but those motors just suck up energy from the batteries and turn half of the energy into heat. I have heard they are only 50 percent efficient at best. Keep the volts down or that motor will burn up.

Frogman1195

My Feedback: (2)

OK Thanks. NM. Can you reccommend a good motor for the job or should I stay with this one and just but a gear reduction on it?

NMPhi767

Well, if you want to stay with this motor, break it in properly (I guess this doesn't matter since you're running it anyway) and do not go over 8.4 volts. I know they offer planetary gear boxes for them if you want to run the bigger prop. I ran it direct drive and I think my prop was a 7X4. Don't go any bigger than that with this motor on a direct drive. I think you can find the gearboxes at www. [link=http://www.hobbypeople.net]hobbypeople.net[/link]. These motors can be used but they are just touchy. My problem was that I used lithium batteries and I extended the flight time out to about 15 minutes. This motor probably needs to take a break every 6 or 7 minutes or so. Another problem with it is that it needs lots of amps to run. I had to use a tanic battery to get the 18 amps I needed not including the amps that it can be surged to. Coming from GWS motors that I never broke in, rarely maintained, and just threw li-poly's on, this super cobalt 400 was just a real pain. So you could be successful with it, but you will have to put up with its weird quirks.

How much does you plane weigh when it is ready to fly? Gentle ladies are sailplanes right? Tell me a little more about it and I think I could recommend a better motor.

Here is the link for that gear box. It is really exoensive though. [link=http://www.hobbypeople.net/gallery/131478.asp]http://www.hobbypeople.net/gallery/131478.asp[/link]

Frogman1195

My Feedback: (2)

Yes NM the Gentle Lady is an old sailplane I had laying around. I don't have a scale but I'd say it weighs around a pound with out the motor and battery. I am using a NiMH 7 cell 1200mah battery right now. Thinking of going to a Li-Po for the extra current and weight.

Thanks

Dave

Matt Kirsch

My Feedback: (21)

Yes, it's no wonder you were having problems.

1. A 9x6 prop direct drive is way to big for this motor. Makes it draw too much current, and is a good way to turn a decent motor into a smoking heap of ash.
2. AA batteries are not capable of producing anywhere near enough power for this motor, even if it's got a reasonably sized prop on it. Stay away from AA batteries in electric flight applications. They're meant for low-current applications like digital cameras and toys.

I'd say use the Electra for inspiration, because it's just a Gentle Lady with a motor on it, but that power system is far from ideal. You'll be much better off with the Cobalt motor, and maybe a gearbox. It'll keep the plane lighter, and run about the same amount of power.

The quickest fix is a 7-cell pack of KAN1800 cells and a 7x4 prop. My favorite vendor doesn't handle KAN1800s, so you're going to have to hunt down a pack for yourself.

Frogman1195

My Feedback: (2)

Great so I need a 3:1 gearbox and a KAN1800 battery. The only thing I'm wondering now is that you said to use a 7x4 prop. Earlier someone said to use the 9x6 prop with the gearbox. Which is it? Nevermind I'll try both after I get the gearbox and battery in. Thanks to all.

Dave

jonnyjetprop

My Feedback: (3)

I'd look into an Astroflight 05 cobalt geared with a 12-8 folding prop. There are great bargins out there as guys are dumping the old stuff for brushless. Check here or at www.ezonemag.com in the for sale thread.

John

NMPhi767

Use 7x4 with a direct drive. If you are going to use a gear box, then you can swing the 9x6. Thats the difference.