lmalone

Can someone tell me what would be the equal in brushless setup for a Goldberg Electra sailplane. I read a lot about brushless motors but nothing about what equals what. Is there a comparson chart someware out there that can help me? Also is a 7.4 volt lithim pack the same as a 7.4 nicad pack? Thank you.
lmalone

Matt Kirsch

My Feedback: (21)

If you're going to go with brushless, you don't want "equal." You want "better." Equal would mean you spent a whole bunch of extra money so the plane would perform exactly the same as it did with the cheap can motor and NiCds.

Truthfully, just going to brushless on the same input power, the same battery, as the stock system, your plane will see a marked performance increase. This is because the stock can motor is roughly 50% efficient while a brushless is around 80%. More of the input power is making it to the propeller, either in the form of more RPMs, or a larger propeller.

There are literally hundreds of motor/prop/gearbox combinations that will do that for you. How do you narrow it down? Well, you've got to look beyond that vague quantity known as "performance." This isn't like two glow engines of the same displacement, where one will turn X prop several hundred RPMs faster than the other due to porting, carburetion, or any of a host of variables. Motors are just magnets and wire. Two completely different motors will turn X prop at roughly the same RPM when given the same input power, provided they're run within their specified limits... You need to look at quality, service, price, what your peers are using to narrow your search.

Myself, I'd probably swap out the power system with a 10-cell NiCd or 3S (11.1V) LiPoly, an AXi 2820/10 motor, and a 12x8 folding prop. This combo would draw around 40 Amps on 11.1V versus 25-30 Amps on 7.2 or 8.4 Volts that the stock system uses. The additional voltage, higher current, and increased efficiency of both the larger prop and brushless motor equate to a TREMENDOUS increase in performance.

To answer your second question, Volts are Volts. Of course, there's more to it than just comparing the nominal voltages. You knew that after reading everything above, didn't you?

Generally speaking, a 2S LiPoly, which has a nominal voltage of 7.4V, is roughly equivalent in performance to a 7-cell NiMH, which has a nominal voltage of 8.4V.

lmalone

Thank you for the information, as i gather all this info and put a package together i will thank all of you for the help.
lmalone

ELTIGRE

inputs here make sense . but as he stated volts are volts . I dont see any "advantage" to going brushless in a otherwise stock beginers glider that flies well enough unless you are going into competition or want to set some endurance records. brushless is somewhere around 85% , cobalt 75-80 %. efficiency. cobalt will give a big performance boost as will the gear drive for reasonable costs. putting in 10 cells you will get a weight penalty over 7 cells. Im flying one now with 7 cells 1700 Mah & its really more weight than it should have . 1200-1500 Mah is plenty.

rahtware

Oh that hurts, in two ways... First, after 25 years in RC my favorite glider is still the Gentle Lady/Electra. I have to admit that I haven't been patient enough to advance beyond less temperamental to fly "beginners" planes.

2nd, "flies well enough" is true, but I sure would like to get my Electra off the ground without having to run, toss level and fight for every inch of altitude until the big "E" builds up enough airspeed to reach it's semi-pathetic climb-out. I should point out that I usually fly it from a field, not a hillside.

I to would be interested in upgrading the power system to something lighter and with enough power to give a decent climb-out so I can spend more time working on my thermal hunting and less on watching the grass grow as my Electra struggles to altitude...

OK, so I tend to exaggerate a bit..

Tall Paul

The nicest thing you can do to an Electra is go to 8 cells.
And then gild that lily with a Speed 600, 3.5:1 gear box, and a 13x10 prop.
Altitude is waiting right in your hand...

rahtware

Thanks Paul for the input.

I like your low-tech approach to the subject, but having just had great success with a LiPo conversion of another plane I am leaning towards a 3Cell LiPo instead of either of the Ni__ batteries.

Thanks again

Tall Paul

I got lots of Nicads, only 2 Lipos...