Electric equivalent to a Cox 049

[bert baker]

I am thinking of replacing a Cox 049 with a electric motor,Whilst I do fly electric I have only purchased planes that are already built and fitted out,So have no idea when it comes to motor, prop, speed controller and battery,

Given the vast array of equipment avalible is there a basic rule of thumb to selecting gear

[John Emms 1]

I did tests. A Speed 400 on 8 cells runs a 6x4 1000 revs faster than a Black Widow. The Speed 400 would be running at around 12A. We also did a comparison by putting a 400 size Mega 16/15/7 in a 400 glider with a 7.5x4 on 3S. The Mega way outperformed the 400 on only 8A (around 80W or so), and would have been comparable to the 400 on a 6x4.

To be on the safe side, I would run around 70 to 80W with a decent motor.

Hope that helps,

John

[Andy G.]

A Cox Bee type motor outputs around 40 watts .

[bert baker]

Many thanks gives me a starting point

[Kevan Gillings 2]

Hi, have a look at Component Shop site, they give the power output of there brushed motors under "more information"

Its surprising how little power the brushed motors produced.

[PatMc]

I designed & built a small motor glider for a Cox 049 20+ years ago. I flew it quite a lot with that power & as a slope soarer but to be honest faffing around with the engine was a pain so the majority of times it was used as a light wind sloper.
After a couple of years I converted it to replace the Cox with a Speed 400 & 7 x AA size nicads driving a Graupner 6x3 folder [also tried a Master 6x4 fixed prop which produced similar power] current consumption was around 9 Amps - about 60 - 70W at 10000rpm. Despite the increase in weight performance was a little better & power duration longer that with the Cox.The model was featured as a free plan in the now defunct Silent Flight mag.

Later I replaced the Speed 400 with an 1020 KV outrunner & early Etec 3s 2p 2500 lipo battery that could only manage 7C output. At 57g the outrunner was 16g lighter than the 400, the lipo weighed virtually the same as the nicads. This time current was 10A, for about 100W, the prop was a Graupner 9x5 folder running at 8500rpm. Performance was improved by a quantum leap. I usually had a number of flights with this model totaling at least an hour without the need to change or recharged the battery during a normal flying session.

Bottom line is my replacement for the Cox 049 was a 57g, 1020kv outrunner on 3s driving a 9x5 prop.

[Piers Bowlan]

A neat and characterful design Pat. It is funny but I was only looking at your plan a couple of days ago (spooky!). Just think of the performance with a modern 1300Ah LiPo. There have been a lot of old designs republished in RCM&E recently, have you thought of submitting it to David for publication? I am sure it will create a lot of interest amongst those of a gliding persuasion.

[Piers Bowlan]

'Henry' Silent Flight, 1998

63in span, Gottingen 796 wing section.

[bert baker]

Bottom line is my replacement for the Cox 049 was a 57g, 1020kv outrunner on 3s driving a 9x5 prop.

Many thanks for info,I will have a look about

[Tom Major]

Have a look at EMAX CF2812 motor, pair it with 18A ESC and 6x4 TGS sport prop and you'll have much more than Cox is able to give you. Had Sharkface powered by Golden Bee and another by said motor, the electric one was mental! I used it with 1300mAh lipo as far as I remember.

Edited By Tom Major on 29/11/2017 23:07:44

[PatMc]

Posted by Piers Bowlan on 28/11/2017 11:07:50:

A neat and characterful design Pat. It is funny but I was only looking at your plan a couple of days ago (spooky!). Just think of the performance with a modern 1300Ah LiPo. There have been a lot of old designs republished in RCM&E recently, have you thought of submitting it to David for publication? I am sure it will create a lot of interest amongst those of a gliding persuasion.

TBH the wings I built for "Henry" were a bit over-engineered & it had more dihedral than necessary. There were quite popular at one of the clubs I'm in, about 6 or 7 were built. Most had simplified [lightened] the wings. 2 or 3 had reduced dihedral which looked a lot better & didn't have any adverse effect on rudder effectiveness.

I have consider a redesign with ailerons, better battery access & off course lipo/brushless power but it's something that so far has lacked a round tuit.