In the past months I worked on a torque neutral dual prop version based of the first SP-140 frame.
It is using the base frame of the SP-140 v1.1 but would work with the V2 as well.
Regarding powertrain it is using two MAD M20 with 32in x 9.6in Fluxer props and two 200A AMPX ESCs.
To supply both motors I cut an older SP-140 4kwh battery in half. One battery for each motor, or just one battery for both, when just doing short test flights.
My climb rate was quite weak. I expected it to be less powerful then the SP-140 but I was still surprised. Not sure if different props could help. I couldn`t pull more then 3.5kw per motor
In this cage setup, there’s one issue I noticed. When there’s no wind, it’s nearly impossible to launch the paraglider forward unless special line keepers are installed on the cage (like a trike).
I think you should try a heavier props with a higher blade angle.
I Understand the allure of not dealing with torque. I haven’t flown my Batch 3 X4 in a couple years now but I sure enjoyed not dealing with either torque or fuel when I was a new paramotor pilot. I now fly an Atom80 powered machine but still have the X4. Hoping for some huge battery tech breakthrough to happen.
Forgoing the netting is a bad idea as you discovered. And that width! Yeah it really would require some new launch technique. Maybe some guides to bring the lines over and between those prop guards? Or maybe mount them a tad lower and closer together? Dunno just spitballing here.
What about going co-axial? Mount one motor and propeller directly behind the other. This will require some serious propeller selection/engineering and will always be LOUD and not as efficient as a single large propeller either. But you’ll have that torque cancel and much smaller propeller area as benefits. If done right that might be worth the extra noise for some.
A few things to keep in mind, and I am sure you have thought about much of this:
-2x 32" propellers have the same sweep area as a single 45.25" propeller and only 67.7% the sweep area of a 140cm prop. Off sweep area alone, this will lead to about a 24% reduction in static thrust for a given power output. Also note that smaller propellers, motors, and ESCs all tend to be less efficient than larger ones.
-To find climb rate, you need to subtract cruise power from the equation. The SP140 takes roughly 4.5kw to maintain altitude. At 20kw motor power, this gives 15.5kw twards climbing. Your system will take closer to 6kw to maintain altitude according to my quick math. So at 7kw total peak motor power, you are probably getting only about 1kw going twards climbing.
Like you mentioned, double check your props and make sure your voltage is correct. You should be able to pull double your current power from those motors.
I showed some stats in my video here. Your estimation is pretty accurate. 7kw gave me just enough for a slight climb, whereas on my SP-140 the same climb rate would need around 5.5kw.
A higher pitch prop might help getting a wider climb range?
