View Full Version : Carl D

04-05-2006, 06:09 PM
I have a Goldberg-Gentle Lady and I want to install a motor. I have 2 motors, a 500 and a 400 that I got from Tower Hobbies a few years ago. I also have a 30A esc. Has anyone converted this 2m sailplane to electric? I think the weight of the motor will really change the cg unless I cut off the nose.
I would appreciate some advice on this because I really enjoy flying this plane.


Sky Sharkster
04-06-2006, 01:59 PM
Hi Carl, welcome to Wattflyer"! For 2 meter gliders like the "Gentle Lady" the usual size brushed motor is the SP600. A 400 will really struggle with a plane this large unless it's geared. Sp500 is a little under-sized also.
Sp600's run about $20.00, will put out close to 200 watts and turn an 8" x 4" or 8" x 5" prop (CAM folding prop) close to 10,000 RPM on 8 cell (9.6V) NiCad or NiMh batteries. Your 30A ESC will work with this set-up, the Sp600's pull between 15A-25A. This is with direct drive.
The motor will change the C.G. but not as much as you might think. Typically a 2 meter glider requires several ounces of noseweight to balance; The 600 weighs 8 ounces, so I would tape or rubber-band the motor to the nose and move it back until you obtain the correct C.G. Now check and make sure the battery pack will fit right under the C.G. (centered under the C.G). With a little juggling of these components you can establish the best nose length and battery location. Once you've got it located, chop off the nose and front-mount the motor! In other words, cut the nose off at the location of the front of the motor. Make up a circular plywood nose bulkhead (firewall or motor mount) with a hole in the center for the prop shaft and 2 smaller holes for the front mounting bolts. The motor mounts behind this bulkhead. Hobby-Lobby.com has the motors, props, metric screws and lots of handy info.
Good Luck!

04-06-2006, 07:30 PM
Thanks alot Ron, I'll let you know how this turns out.

Jeremy Z
04-06-2006, 08:17 PM
To add to what Ron said, if the plane is typically powered by a 600 class motor, a speed 400 will probably not even fly it; even geared.

For reference, my EasyGlider Electric (1.8m foam sailplane) weighs about 31 oz. It is a slow climber with a 3:1 geared speed 400 and a 9.5x6 folding prop. I believe the Gentle Lady is a good bit heavier than this. On mine, the speed 400 is adequate for a thermal sailplane, but it takes some patience to get to a decent altitude. ;)

04-11-2006, 01:54 AM
CD, I am converting a 2 meter Aspire to electric as we speak. It is very similar to the GL but a bit lighter than some in this class since the wings are not fully LE sheeted. I originally tried a Speed 400 geared 4:1 and a 12" or so prop. It was meant to be an experiment to see how little power I could get away with to keep it as light as it was when I flew it off a histart.

Too bad I couldn't stand to try to climb out with it for more than a few flights! I guess I found my answer to THAT experiment!

A Phasor 3 BL motor (direct for now) is on the nose and I know it will haul the mail since I have used them in other 2M gliders! A 2:1 beltdrive is available for it that will spin an even larger prop (the key to getting up there FAST!)

A metal planetary redrive I had previous used was too heavy for my taste but incredibly strong and served me well for several yrs till I centerpunched a tennis court at terminal velocity when I shed the wings trying to escape a killer thermal! WHAP!!

The Phasor 3 measures 170 watts with a 12/6 prop and a 6 cell 1900ma nicad at 28 amps. Even tho this is less than a Speed 600 CONSUMES, far more gets to the prop since it is far more efficient than the 50% efficiency (COLD- drops off quickly as the motor heats up) of a brushed ferrite motor- so keep it cool! A Speed 500 will do but MUST use a redrive to make it even useable in a plane of this size.

Most E gliders of this class come with a Speed 600 direct, as my first glider, a Windstar, then a CGM Electra was also. Unless you use a reduction drive you will be very frustrated with the poor climb. I added one after my first frustrating season and was floored by the difference in climb! Suddenly I zipped to altitude and got to enjoy the flight instead of grinding away for the entire battery charge just to get up ONCE! In addition there was plenty of battery left to climb up AGAIN!

The catch? Hobby Lobby wants about $55 for a Speed 600 with an integral redrive (the one I originally chose and changed everything for the better). That will get you a long way towards a much lighter, more powerful and far more efficient brushless than the ol boat anchor of a S600! I would expect the S500 to be marginal. But since you already have the motor- add a redrive and see what it can do- the difference is incredible- and its the cheapest improvement you can make!

Be sure you get some advice on what prop to use with your battery and the particular redrive ratio you get. Get it right and have a ball! Its a whole new airplane and the flying is very good with a minimum of money.

Best of luck- and good soaring!


Jeremy Z
04-11-2006, 02:03 PM
TW: Great post. I espcially like the phrasing of "...center-punched a tennis court..." LMAO :D

04-16-2006, 10:45 AM
I have a Goldberg-Gentle Lady and I want to install a motor. I have 2 motors, a 500 and a 400 that I got from Tower Hobbies a few years ago. I also have a 30A esc. Has anyone converted this 2m sailplane to electric? I think the weight of the motor will really change the cg unless I cut off the nose.
I would appreciate some advice on this because I really enjoy flying this plane.


Carl. Goldberg themselves electrified the lady. I built a Gentle Lady for a easy going slope glider in 86 and it was excellent. Later I bought a electrified lady (forget what they called it then) from Goldberg in 97-98. It was the same plane except the cowling was plastic to house the motor vs a balsa nosecone. It had a mabuchi 550 and I used a 7 cell nicad. It flew but was very marginal in the power department. Having one I would never go brushed 550 or lower. S600 or brushless. Goldberg now makes the "Electra Glider Kit" 78.3" span. Says they came with 600's but will come with goldberg turbo 550's now. Hermit

04-16-2006, 08:00 PM
I have always enjoyed the quality and design of Carl Goldberg models and built more than a dozen over the years- but when it comes to electric ARFs there is a problem with them all in this 2 meter category. The CG E-ARF they made was the Electra, a nice flying plane but poor as configured with the cheapo motor.

The 550s and 600s are barely useable in this size machine and do not represent what the sport is about since if you can't get high, you can't soar. As configured, they are not a good buy.

JEREMY- Thanks, friend! Glad ya liked it! It sure left an impression me- and center court also! If we cannot inform we must at least entertain.... :D

UPDATE: the Aspire now has a 14/7 CAM prop on the Phasor3 and climbs fantastically. Max amps is 35 with fully charged 6 cell nicad on a 30 amp ESC. Watts are a bit over 200. The thrust is equal to the weight of the fuse minus the wing!

A few seconds of run and its under 30 amps. This is pushing it but the runs are short and the glides in between are long and I've allowed for plenty of cooling air. I had to throttle back to keep it from zooming straight up- do not underestimate a healthy dose of downthrust built in to the thrustline!

Note: Carl, I misspoke when I suggested adding a redrive to the 550. It is a waste of money that will not fix the problem. Haven't seen one in years and forgot how poorly they are matched to a plane of this size. A 600 CAN be geared successfully I know from personal experience and if cost is the main deal then I would recommend that. Otherwise go brushless and prepare to be STUNNED and SMILIN! Get comfy- you could be up all afternoon with such a system!

All the best,