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Ultrasport 40 "Plum Crazy" Electric Conversion

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Ultrasport 40 "Plum Crazy" Electric Conversion

Old 01-19-2023, 07:06 AM
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Default Ultrasport 40 "Plum Crazy" Electric Conversion

Purchased this glow Ultrasport 40 from a club member with the intention of converting it to electric.
It appears to be constructed correctly, and the price of $60 wasn't too bad. Currently it weights 3.6 lb.
I don't think the wing will need any modification.
Most of the work will be on the fuselage. Right now, I am thinking of cutting off the nose back to the firewall, and
making a motor extension box out of 1/4" plywood. Probably cut a hatch in the bottom for battery access.
I see Fiberglass Specialty's makes a cowl, but I am not willing to spend the money on that option right now.
I am going to have to find some Plum Monokote. It appears to be discontinued.






Last edited by Moon Pie; 01-19-2023 at 07:25 AM.
Old 01-23-2023, 06:49 AM
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Default The dirty deed is done !

The deed is done. Sawed off the epoxy-soaked front end and sanded it smooth.
Cut a battery hatch in the bottom. I would have preferred to load the battery.
from the top, but that didn't seem to be an option.
he point here is just to make the plane fly. I will worry about looks later.



Old 01-26-2023, 06:31 AM
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Default Motor extension / weight box

Motor extension / weight box ready for the arrival of the motor.


Old 02-23-2023, 07:27 AM
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In an effort to reuse the original nose from the airplane I had to redesign the motor mount.
The motor box was SOLID, but it was too big to fit into the original cowling that I had sawed off.
I made this new mount using 3/8" aluminum rod and duralumin plate.
Now I am gluing a plywood former to the back of what remains of the front cowling.
and will soon be flushing out (with balsa) where the nitro engine used to stick out.
I hung the lead weight discs with 3/8" "P" clamps from the hardware store.




Old 02-28-2023, 06:46 AM
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I had cut the original front end off of this bird with the intention of buying a plastic or fiberglass cowl.
Being cheap by nature, I decided to rebuild the original front end. I was able to peal all of the epoxy off
the inside of the cowl, and I cut out the bad wood and white glued replacement wood in place.
I traced a 1/16" plywood former using the front end of the fuselage, and put new wood in place where the engine
cutout had been made.
I would take hours sanding this by hand, but only minuets with my belt sander!!
Almost ready to cover the cowl.





Old 03-09-2023, 07:17 AM
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Here is the final (for now) result of the fuel to electric conversion of my Ultra Sport 40. I think the cowl turned out very nice.
With the combined weight of the cowl, and the spinner I was able to remove the lead from the nose.
Thats a vintage 1980's Tru-Turn spinner I had saved from the 80's.
I did fly the model with the wood motor box, and it had plenty of power, but was nose heavy.
FYI, it is powered with a cheap 4250-800kv motor from China, 60-amp ESC, running on 4s 3300mah using a 12 X 8" prop.
With a full charge, the system is showing around 750 watts.
Looking forward to the next flight.




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