# Performance of PPG concept with 2 Counter-rotating propellers each side

Hi, It’s my first post. I am working on a e-PPG concept with 2 counter-rotating propellers on each side of the frame (in fact , 4 propellers of 32’ diameters). Something very close to the concept of Rogerthat, but with high diameters:

My goal is to significantly increase flight duration compared to one propeller e-ppg (49’ diameter like exomo ppg, http://www.exomo.com), to pass from 45 minutes to 100 minutes of flight.
In my design, I increase wing loading by +70% (= 4*32^2/49^2), and hope better efficiency also because of no obstruction on rear/front propellers, even if counter-rotating concept reduces efficiency by -10%
Is it realistic?
I am trying to make a first demonstration with the same wing load ration (+70%) on rc ppg models at ground, to see at same thrust the electric power consumption, in both cases.

sorry for my bad English, it’s contra-rotating, and not counter-rotating…

in order to be able to fly efficiently with paramotor you need a cylindrical air stream as a thrust column. Ideal for paragliders and people with 60 to 120 kilograms is an air column diameter of about 130 cm. then the pitch velocity of the air mass in the ideal case can be around 1.4 - 1.6 times the airspeed at full throttle. That’s around 55 km / h. when you fly around the level with about 40%, the efficiency is perfect. the propeller “pulls you with very little loss through the crowded air mass” if you have a smaller area with small propellers can only reach the thrust with higher pitchspeed. the efficiency is lost very much. additional noise arises. if you want to increase efficiencies, that can only be done by designing the tail of the concept. your tail must look like a boat. actually like a good competition pod harness. the difference between the average paramotor 1.5 m / sec and the pod eppg 1.1 - 1.2 lies at factor 0.3 -0.4. this is very much only by the design of the tail. and by the way: there are very few in the world who can prove how long the flight time is. believe no catalog or texts in the internet during the flight time if these are not proven.

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I suggest you carefully read that entire thread since this concept has already been discussed in great detail in that thread and there are a lot of concerns with that design. If your goal is to significantly increase flight time you would be better off looking into a single prop design.

If you’re going to have two contra rotating props, one covering the other, why not just have two and not two sets of two? I’m thinking that it would look somewhat like a regular paramotor but without the torque issues…

Paul

Paul , 2 contra-rotating propellers behind pilot, keeping the same propeller diameter, could be a option because you would increase by 2 the surface swept by propellers, increasing a lot the propulsion efficiency. Nevertheless, tow drawbacks, which are:
-No gain due to “no air flow obstruction in front”, as in case propellers placed on each side
-Complexity of the mechanism to have a coaxial double shafts (one inside the other). This problem would be avoided, in my concept, because, you have just arms where are mounted on each side two brushless motors.

I made a calculations, on your proprosal, and find a passage from 45 to 75 minutes of flight.
In my concept, in fact, I have to values:
-pessimistic estimation (hyp: no gain due to no obstruction in front): passage from 45 to 70 minutes of flight
-optimistic estimation (hyp: significant gain due to non obstruction in front) : passage from 45 to 100 minutes of flight

For engine/propeller/esc for a prototype, all is available on the T-motor website: 4 x 400 €= 1600 €.

A picture is worth a thousand words