Hi @paul_oz, thanks for the clarification. yes left and right is the idea. I see the openppg thrust figures are listed as:
Thrust: 150lbs (22×10 props), 165 lbs (22×14)
Which makes me wonder why the same length KDE carbon props are only 21.5" X 7.3.
I don’t know how to apply pitch to a thrust calculation so I just ran some numbers based on total prop area. Looks like to replace four 22" props we’d need two 30" props. Which is way too big. KDE states that the triple props improve thrust by >70%. So going by that (and ignoring their pitch numbers) looks like two 24" triple props could provide the same thrust as the four 22s.
Two 24" triple props is about the most I’d want on my back. Something more compact would be better. Like those two 15.5" triple props that I originally linked to. By my area calc looks like to achieve the same thrust with those the motor sizes would have to be increased by 1.5x. Probably less battery life though.
you can not just increase pitch of the propellors, as the motor that are spinning the props, also need higher torque (more force).
In general, you can say that less RPM (rotations per minute) with higher torque of the motor and higher pitch of the prop is more effective than faster/more RPM with less pitch and less torque.
Now I’m wondering if a single-cage coaxial contra-rotating setup would be a simpler solution. as per
According to the performance data on this KDE motor, it can spin up a 30.5x9.7 triple prop to 48lbs of thrust at 3800W (12S).
Two of them nested together in contra should provide ~100lbs/45kg of thrust and no torque, right?
The Razeebuss Razmott produces 45kg of thrust with 130cm prop, apparently this is sufficient to get up to the thermals.
To simplify construction, a small 31"cage and frame could be 3d printed in one piece with carbon fiber polycarbonate composite. The whole setup with cage, motors and props might only weigh ~5kg.
The E glider looks very interesting. Personally I love the idea of thermalling and “gliding” as apposed to 100% powered flight. I wonder if we can get a similar idea together that focuses on these goals?
What would you like to see different? Something more like an XC paragliding harness? Because if you’ve got a universal wing, like the Dudek Universal, you can trim between flying styles.
I wrote KDE asking if they build coaxial motors and if they had performance data available. They replied that they will build a test rig and gather performance data.
Referring to a previous build, the KDE engineer said “the thrust capability increased >180% from a single motor – with 100% thrust-capability being recognized on the upper coax edition, and approximately 80% thrust-capability being generated on the lower-coax edition (losses due to pre-accelerated airflow of the upper plane). Overall, the losses in thrust versus two-independent motor ranged from 10% up to 14%, depending on the throttle position and air-conditions (weather conditions).”
So it sounds like a 14S coax 10218 with their 30.5" triple props could supply at least 100lbs of thrust which would make for a good compact no-torque e-ppg sufficient for reaching thermals.
Wondering if 2-6" larger props with greater pitch could push that value much higher while keeping efficient g/W performance. Looking forward to seeing their data.
I also contacted e-glider to see if they could design contra-rotating folding props, they’re thinking on the solution.
Perhaps no servos are even needed if a simple spring mechanism holds props folded together. Upon providing power, the thrust would open the props into flying position.
I really like the two prop side by side design but have a major safety concern. One motor failure during flight or even take off could cause pilot/paramotor twist consequently causing riser twist and of course loss of glider wing control. The speed (rpm) of each propeller must always remain equal to each other even during failure of one of them. If accomplished mechanically, the motors could be pulled closer together with propellers even operating in the same air space, allowing use of larger props for increased thrust.
Hi @Boyntonstu Though I got a pretty good thrust with my proof of concept build using stock 50cc Hobby King motors I suspect the motors that PDWhite et al have sourced will be a far more efficient solution. Looking back over this thread I notice a comment on how to replace 4x 22’ props you’d need 2x 30’ and that would be “too big”. I just overlapped mine… then it wasn’t too big.
Has anyone used minimum batteries to keep wieght down and what kind of wing would be required for minimum sink just to get up in the sky not for low flying but fly up kill power and glide around some figures based on most efficient wing pilot wieght would be good I know wind speeds also a factor but some guidance on this would really be appreciated.
I started out flying with only 2 Bonka batteries but they get hot fast which is not good on them (over 60 Celsius). 4 batteries stay under the recommended limit of 60 Celsius but even that wears them faster. I’ve been flying with 6 batteries lately and they barely feel warm at all (just under 40 Celsius).
Thinking 6 Bonkas is the magic number between battery cycle life and weight. What’s the run time on 6? Would you get 30 minutes? That would be about 15kms range over the ground given light to no wind.