OpenPPG 30" props MOD

I never really liked the small props on the openPPG, but I know they help make it foldable and are simple, but efficiency is of course less than a larger prop.

I ended up buying 2 30" props and 9235 motors for another project, but then I thought, why not make an electric paramotor out of them, and bought 2 more. The design process is still in its infancy, but it ls looking good. It may end up being a whole new design, but first I am going to try to modify the OpenPPG frame to accept my power system…

of course to fit 4 30" props they have to be overlapping.

Some more info here Eppg1 design at primalflight paramotorforum, but I will also post stuff here.
(link is to a brand new forum that I created…not trying to take people away from here, just a place to put stuff)

These are the motors OpenPPG uses for Batch4


Max 94 Amp / 4500 Watt! Your current motors (max 57A / 2800 Watt lack the torque to power 30x8 props! As well with your current Motors and props you will have around 90 lbs thrust with 4 motors at full throttle…

I like the idea with overlapping props and there are threads here, as well threads with props and power consumption…

You can use the KV150 motors and it will work, but maybe it is not the most efficient combination.

I am going of the manufacturers data on thrust and current using the 30" prop…i do plan to test them myself as well. But the props are rather low pitch, so i think it should turn them ok

I 'm just saying 4 x 11000 gram = 44 kg thrust!
OpenPPG%20263
For level flight it may work, but to climb you should go for 60 kg thrust…

BTW you can go for 20-30% overlap of the props (prop total length) with 5-10 % lost of efficiency,
but they will be real noisy thru the tip vortices…

Under 15% overlap there is no loss and no increase in noise…

good point…I will also be testing 4 blade props, and perhaps 14s. I wonder if 6 motors would fit…

What are the losses from 100% overlap (co-ax)? curious what it maxes out to.

4 blade props double the number of tips and therefore tip vortices. Their intended use is to get the needed area when a larger prop can’t be used. If you are going with larger props then you will have more area and therefore no need to increase the number of blades.

The pitch must be enough so the pitch speed is appropriate for the trim speed. If your a light weight on a large wing the trim speed is lower but probably not much. And the wind speed and turbulence will remain the same so your limiting your safe flying weather to calmer air.

With electric power systems on aircraft you’re balancing volts, amps, propeller pitch, propeller diameter, and motor KV and size, with the wing, and airframe, payload, and range.

I purchased the openPPG because it’s designers have worked out all that math into a slick, working package. Going to a different power system typically means re engineering everything.

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Works for me just as Paul and his brother designed it. With quite a few flights behind me, the only issue has been a split prop and sand blasted blades (the two lower ones). A get 20 to 30mn on 4 Bonka packs depending on the wing and never climb more than 600/700’. Crossing my fingers, but so far so good and a bunch of people are really excited about the machine and what’s to come :smiley:

What is the purpose of your mod in this picture?

No problem with lines at forward launch getting caught? I’m just curious…

Lines catching: no so far.
The purpose of the kit is to keep the hoop straight (viewed from the side) because the connectors for the hoop tubing pieces are not long enough to keep a smooth shape. The cage bends backward when the net is taught firmly. It gives the cage a funky angled look. The kit solved the problem. It takes a few more minutes to install and adds about 1 lbs. The velcro(s) seen on your snapshot are gone - the design evolved since that time. There is a possibility that a line could catch I guess, but 99% of my inflations are reversed and that totally eliminate the risk of a line getting caught anyway https://www.youtube.com/watch?v=ypuShbIP4cs and https://www.youtube.com/watch?v=L4RNneP5fG0
Phil

Makes sense to me… Thank you.

I always wondered how other ppg connect there cage frame…

Your solution will not twist for sure.

My solution was to make the mating 3D printed part a little longer. Works fine, doesn’t add weight or setup time, and doesn’t create a snag point. The hoop still distorts a little but it’s only cosmetic. The net actually pulls the hoop forward (not backwards) so it gives more clearance between the net and the props.

Standard PPG use a different system and have welded joints which in addition to the spars stiffens the cage sections. The cage on the OpenPPG is a bit weak even with the four stiffeners. If it hits the ground during a butt landing, it will deform more than with standard PPG cages such as the one on your photo. BTW, the net on your photo looks way too opened. The gap between the frame and the inner-cord is too wide. There have been many instances when something passed that gap (loose strap, piece of clothing, a line, even a cable throttle,… the pilot’s hand was inserted in the handle strap and when the cable wrapped itself around the prop after the cable bent because the pilot tried to reach something calling for his arm/hand to reach back ( should not have been the case), at full or near full RPM, his hand was pull and a prop strike ensued with serious consequences.
Nets and cages have always been lousy compromises against prop strikes. It is the best we have for now, and it is pretty lousy at best no matter what the brand claims. There is not in my view enough efforts made by manufacturers to come up with a better system. In the early PPG days, it was very common the see a double hoop with the propeller rotating inside that “cage”. The single hoop became fashionable a few years later. But that design also has issues when a cage hits the ground hard, it ovalized, thus reducing the distance between the blades tips and the hoop, then the wooden prop was turned into toothpicks. I know of one case when a piece of the prop perforated the pilot’s upper back after shattering.
It has been suggested to have an additional smaller hoop to the halfway point on the cage to reduce a potential strike.

Depends how you look at your machine;-) I pull on the modified cord/elastic system front the “front” (harness side) thus the top sections of the hoop comes closer to me (backward). Yes, I could fly without the kit but like it better with the reinforcements (psychological reinsurance perhaps !?) The flat/curved about 3mm thick ribs will also disperse the shock wave if the cage hits. The metal reinforcements are over 1’ long and have 3 steel pins inserted through them and the hoop pieces to keep the whole assembly pretty stiff, but not enough in the great scheme of things.

Here’s a better view of the reinforcements atop the hoops:

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I did some testing, and it matched the specs. 11kg at 46A on 12S. I also tried 4 blades, and predictably got more thrust and pulled more amps (over the motor specs).

The M10 at 16.5kg/94A or 1.76Kg/10A, The 9235 is 2.39Kg/10A …so even with 15% efficiency losses due to overlaps , they are still at 2.03Kg/10A.

I am planning on 6 of them now, the overlap is odd, and the hoop will be big, but it should work, and then I should have 56.1Kg (66Kg - 15%) of thrust and maybe more efficient overall.

I like your enthusiasm… But unfortunately you can throw the manufacturer numbers into the trash!

The M10 numbers are with 48 Volt and 27x8 prop’s. OpenPPG use totally different prop’s.
Your numbers are as well with constant 48 Volt - this is not real life!
Here your numbers with KV100 motor and 30x8 props /12S battery full:


After 5 minutes full throttle your voltage will sag and you have only 70% thrust at full throttle!
Why do you not buy 4 x MAD M10 KV100 with 16.5kg thrust?

not sure why…I like to design different stuff. same with the day job.

I am 90% sure I will need to up the voltage. 13s or 14s, I’m pretty sure the motors can handle that, but testing will prove that out.

I did not trust the factory numbers and did my own testing. http://www.primalflight.com/paramotorforum/viewtopic.php?f=29&t=11
I have video, but have not uploaded it…Getting hit by Dorian soon too, but might be able to work on it more during. (if the roof stays on the house that is).