Converting a 12 foot sailplane to electric.
05-12-2004, 07:19 PM
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Converting a 12 foot sailplane to electric.
Because my local flying field is great for flying with good runway etc, it isn't suitable for bungee or winch usage. I have a ready built 'wildflecken' kitted by RCSAILPLANES which I believe was a UK company that no longer is trading. The all up weight is just over 4lbs, fibre glass fuselage and with its dihedral split wings is well built at the roots to increase the payload quite considerably.
When buying a new JR PCM9X radio outfit from an Australian supplier, on recommendation, I also bought an AXI 4120/14 brushless motor.
I am about to buy..speed controller..propeller..motor mount...battery..in order to commence the conversion rebuild.
The manual accompaning the motor raises some questions in the area of cooling etc
I already have some ideas about the mount and the propeller.
If there is any of you guys that is interested in helping me with this project to get me up and flying, please respond and I will raise the questions.
When buying a new JR PCM9X radio outfit from an Australian supplier, on recommendation, I also bought an AXI 4120/14 brushless motor.
I am about to buy..speed controller..propeller..motor mount...battery..in order to commence the conversion rebuild.
The manual accompaning the motor raises some questions in the area of cooling etc
I already have some ideas about the mount and the propeller.
If there is any of you guys that is interested in helping me with this project to get me up and flying, please respond and I will raise the questions.
05-12-2004, 10:14 PM
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RE: Converting a 12 foot sailplane to electric.
Don't be shy. Go ahead and fire away with the questions. That's what this forum is here for. 
Technically, this is a nothing-to-electric conversion, not a glow to electric, so it belongs right here.
Usually when you go to electrify a plane, you start out with the battery since it's the source of the plane's power. Motor's usually near the bottom of the list. The AXi 4120/14 just might do it, though you may need more oomph, a higher cell count, so a 4130/16 or 4130/20 might be in order. 4120/14s are limited to about 16 cells or 5S LiPoly, and 40A continuous. You'll have about 650-750 Watts to work with.
A few details about the plane would help. How much does it weigh now? At 50 Watts per pound, you can go up to about 14 pounds, maybe 15 pounds, or 7Kg, on a sailplane. That's total with battery and motor, so your plane will have to weigh somewhat less than that without electric gear.
How much performance are you looking for? 50 Watts per pound will give you nice sedate climbs. I assume you're not trying to fly a giant hotliner here.
Technically, this is a nothing-to-electric conversion, not a glow to electric, so it belongs right here.
Usually when you go to electrify a plane, you start out with the battery since it's the source of the plane's power. Motor's usually near the bottom of the list. The AXi 4120/14 just might do it, though you may need more oomph, a higher cell count, so a 4130/16 or 4130/20 might be in order. 4120/14s are limited to about 16 cells or 5S LiPoly, and 40A continuous. You'll have about 650-750 Watts to work with.
A few details about the plane would help. How much does it weigh now? At 50 Watts per pound, you can go up to about 14 pounds, maybe 15 pounds, or 7Kg, on a sailplane. That's total with battery and motor, so your plane will have to weigh somewhat less than that without electric gear.
How much performance are you looking for? 50 Watts per pound will give you nice sedate climbs. I assume you're not trying to fly a giant hotliner here.
05-13-2004, 08:41 PM
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RE: Converting a 12 foot sailplane to electric.
Hi Matt, Thanks very much for your responce which you sent so quickly!
I'll start with the model data, taken from the kit box (alas,no plans). Wildflecken 144"..12ft. Radio Sailplanes. Suitable for tow line,
Bungee or power assist, slope and thermal soaring. More about its strenghth of build later.
Wing Span 144" 3660mm. O/A lenght; 49.5" 1260mm. Wing Area 7.3 sq. ft. 67.0 sq dcm. Total surface area: 8.25 sq. ft.
78.0 sq.dms. Wing loading: 8.5-9 ozs sq.ft. Total surface area loading: 7.5 ozs sq.ft. 23g/sq.dms
All up weight ,ready to fly ..RC installed: 60-64oz. There is about 3 cu ins of lead in the nose, which I think has been added as an extra for c of g balancing, which I intend to discard when detaching the nose for fitment of the mount.
In terms of weight, which would you prefer to deal with..metric or imperial??
The tech spec of the Axi 4120/14, which I checked before buying, shows it can handle (as you say) 12 to 16 cells. Model weight:
2000 to 3500 gms. I figured that the current all up weight of 1.82kgs would be increased by under 50% when including 12 cells,
the motor, mount and speed controller. This would fall under the next jump to 14 cells at 2.75kgs. 3.5kgs taking 16 cells.
Propeller: The manual with the motor suggests 12 cells 13"x11". 14 cells 13"x8" and 16 cells 12"x 8".. I'm planning the 13"x11"
folding prop by Aeronaut the German company. Am I correct in believing that this prop would give higher torque at lower revs??
I am thinking Sanyo 12 cell, 6 cells dual in line Lithium in respect of cost and the way I feel re experience of their product. Ease of supply and fitment behind a newly fitted double bulhead ( remembering the radio and servos may well have to be ahead of batts)
as a form of bombay area around the C of G.
Anyhow Matt, I hope this enough to chew for the mo..getting v.late here.
More to throw in the pot about the Mount..Speed Controller/strenght of build of the existing model.. and finally, cooling.
Thanks for your interest so far fella. Regards, Derek Horder.
I'll start with the model data, taken from the kit box (alas,no plans). Wildflecken 144"..12ft. Radio Sailplanes. Suitable for tow line,
Bungee or power assist, slope and thermal soaring. More about its strenghth of build later.
Wing Span 144" 3660mm. O/A lenght; 49.5" 1260mm. Wing Area 7.3 sq. ft. 67.0 sq dcm. Total surface area: 8.25 sq. ft.
78.0 sq.dms. Wing loading: 8.5-9 ozs sq.ft. Total surface area loading: 7.5 ozs sq.ft. 23g/sq.dms
All up weight ,ready to fly ..RC installed: 60-64oz. There is about 3 cu ins of lead in the nose, which I think has been added as an extra for c of g balancing, which I intend to discard when detaching the nose for fitment of the mount.
In terms of weight, which would you prefer to deal with..metric or imperial??
The tech spec of the Axi 4120/14, which I checked before buying, shows it can handle (as you say) 12 to 16 cells. Model weight:
2000 to 3500 gms. I figured that the current all up weight of 1.82kgs would be increased by under 50% when including 12 cells,
the motor, mount and speed controller. This would fall under the next jump to 14 cells at 2.75kgs. 3.5kgs taking 16 cells.
Propeller: The manual with the motor suggests 12 cells 13"x11". 14 cells 13"x8" and 16 cells 12"x 8".. I'm planning the 13"x11"
folding prop by Aeronaut the German company. Am I correct in believing that this prop would give higher torque at lower revs??
I am thinking Sanyo 12 cell, 6 cells dual in line Lithium in respect of cost and the way I feel re experience of their product. Ease of supply and fitment behind a newly fitted double bulhead ( remembering the radio and servos may well have to be ahead of batts)
as a form of bombay area around the C of G.
Anyhow Matt, I hope this enough to chew for the mo..getting v.late here.
More to throw in the pot about the Mount..Speed Controller/strenght of build of the existing model.. and finally, cooling.
Thanks for your interest so far fella. Regards, Derek Horder.
05-14-2004, 06:53 AM
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RE: Converting a 12 foot sailplane to electric.
Correction on the batteries... I think the standard layout for 12 cells is 3 cells dual in line, double tier. Layout is important in respect of fitting to existing, underneath the control linkages. Cheers...Derek.
05-14-2004, 08:22 AM
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RE: Converting a 12 foot sailplane to electric.
I was expecting the plane to be signifigantly heavier. Only 4 pounds RTF stock. Not bad, well within the capabilities of the 4120/14.
You're on the right track near as I can tell. For a slow glider, a bigger prop at a lower RPM will give you a better fit, and that's right where you're at.
You're on the right track near as I can tell. For a slow glider, a bigger prop at a lower RPM will give you a better fit, and that's right where you're at.
