Let’s talk about props

Getting way to complicated for this Cowboy!

How do you define “optimal pitch”? To maximize thrust you would want to set your pitch for the greatest possible thrust within the limits of the motor/esc combo (or 80-90% to be conservative). This will correspond to different pitches for static compared to flying at 22mph (for a hang glider speed would be 30mph). Alternatively is “optimal pitch” the most efficient setting i.e. highest grams / watt?

If you “optimized” pitch at 22mph to most efficient and / or max thrust and pushed the ESC/Motor combo to its max rating you may overload the motor at 0 airspeed trying to take off. However if you mountain launch and just want power once airborne this would likely work. The pitch needs to be a balance for both scenarios, tuned for just flight, or variable pitch.

Pitches of 6 and 8 maybe good for takeoff but are way too low once you get to speed. 10 is good for takeoff (static) however a little low at airspeed optimal for flying is around 16-24.

For the previous chart i don’t have amp and voltage data as that chart is based on an equation not actual data. I have static data for 21x12 and 22x12 props, however it’s a 30v setup with different motors and ESC combo than Open PPG. Below is static data I have for my CF folding 18.5 x 10 prop setup, I didn’t test that setup yet on a car at speed.

The new test stand is based on a 50v system with motors rated at 4,400 Watts so i think it is more comparable to open PPG. I’ll post the test data when i have it.

I’m outside of Philadelphia in case anyone is local and wants to help.

Charles

Thanks so much for your input! I agree with almost everything you said. I am very data driven and have collected tons of data on my Open PPG and it conflicts with only a couple of points that you have made. I would love to see more data with different prop sizes

Most of us on here are not looking for more thrust. We are looking for maximum efficiency so that we get longer flights. So when we talk about optimal pitch that’s what we mean. The OpenPPG has plenty of power for climbing as is.

With the current setup I pull the same amps at full throttle in a static state as I do during flight at full throttle. Therefore I am not convinced that our airspeed has that big of an impact… I think 22 mph is pretty slow and therefore the effect is close to static. I do understand the physics of what’s going on here… at speed the RPMs are probably higher than at static resulting in the same amp draw. Because of what I know about this from my own testing I don’t think you will burn up your system at static if you optimize it for 22 mph level flight. I actually think the opposite… optimized for efficiency at level flight would likely give us less thrust to climb and less thrust at static and draw fewer amps overall.

I also don’t think anyone will find some magic combination to add more than a couple minutes to a 25 minute flight. Any change we make will be small (like a small pitch change) and the results will be even smaller. In other words… we are probably pretty close to optimal efficiency making little room for improvement but I would love to benefit from being wrong here.

Thanks again for your input and your data. I would love to see more data… as well as collect more data.

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Very impressive test setup @cwallen93117 ! Nice! Attaching it to the car was a brilliant move!

There will likely be some improvement, as @GliderPilot suggests, on the order of a few minutes from optimization. We’re not talking 2x flight time, but it could be as high as 20% depending on our current efficiency.

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Hey everyone! Long time RC aeromodeler & drone flyer/builder here. I also have background in elec engineering. And now a new Paramotor pilot. :metal:t3::grin: Just wanted to chime in with my 2 cents on this OpenPPG project. IMO airplane style props are not the correct style for this application. Drone props may not be the best for this application either but IMO they are closer to what this project needs to have nice trust plus good efficiency. Remember, drones don’t just hover. They can pitch fwd and move along at a decent rate of speed too. IMO a done prop with a low pitch (around 4-5), and a wider blade towards the hub / narrower towards the tip would provide the right combination of good trust and efficiency. I feel airplane props are not good for this application because their design was intended to where, after takeoff, where the prop is pushing or pulling the weight of the plane fwd to a good rate of speed, the prop is said to start to “unload”. At that speed the propeller just needs to provide some trust to keep the plane moving fwd without crating a ton of aerodynamic drag. On a Paramotor we do not travel fast enough fwd to have this unloading effect happen. So similar to a drone, the props are mostly always nicely loaded.

IMO the setup on this Paramotor is way too inefficient. The whole power system is drawing way too much current for it to be worth switching over from a gas motor Paramotor. But… there is a light at the end of the tunnel. IMO, bigger motors (same diameter stator but taller stator, almost double (MAD M17) @ same Kv rating) coupled with a drone style prop would provide (I’m guessing) around a 30-40% increase in flight time with similar trust of the stock power system. And who knows, maybe even more… Another thing that needs to change is the prop mounting method. The drone “T” style prop mounting (which the MAD motors are capable of) would benefit this project greatly. The “T” style (2 small bolt) retaining design lessens the rotational mass of the motor/prop combo and also provides waaaay better security of a prop becoming undone in flight. All of the motors are using right hand threaded locknuts, and that’s fine for 2 motors in this setup. But the other 2 motors which spin against the threading rotation of the prop locknut risk the possibility of undoing the nut in flight. Especially at takeoff which is when the props are spinning at their peak RPM of a normal flight. An acro pilot would prob put even more stress on this situation as they rev the engine high/low/high/low more often.

Let me know what u guys think.
Manny

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That would be so awesome if what you are predicting is true!

Here’s a link to the thread about that motor (For those who may not have seen it):

The thing I liked most about the Mad props is they look like what you described:
http://madcomponents.co/index.php/fluxer_propellers/

We seem to all agree that a larger prop is more efficient. We don’t want larger props though but the best way to imitate a larger prop is to have a large taper.

So who wants to be the guinea pig to test the m17 motor with the Mad Fluxer or similar propeller? I would make the investment if I was guaranteed to get even half of what you are predicting in return.

davek79 agree there will only be a 15-20% efficiency gain. However, the project I’ve been working on for last 5 years, which resulted in designing the test stand, is for an electric propulsion unit for a powered hand glider which would benefit from an extra 1-2 minutes flight time. The criteria of my project is below:

  • Generate enough thrust to climb at 100-200 ft per minute
  • Optimized for best glide of 30mph (if I go with a variable pitch prop then optimized through 65mph which is a little less than top speed of 70mph)
  • Flight time of 7-12 minutes (about 1 climb of 1,500ft or 5-8miles of level flight)
  • Total weight of about 10lbs (including batteries). Right now its at about 13lbs with some heavy hardware.
  • Does not need to provide enough thrust to take off

The design criteria is a bit different but very close to Open PPG in many respects. I’m also contemplating a single blade prop as it would be the most efficient and i could have it feather and fold into an airfoil shaped spar that holds the motor.

That’s what I had in mind while designing my paramotor. I used to be a RC flyer and learned a bit about propellers and I totally agree with you. The propellers I’m going to use are these:
https://express.google.com/u/0/product/7006686174783085415_7412456500414076452_100003215?utm_source=google_shopping&utm_medium=tu_prop&utm_content=eid-lsjeuxoeqt&gtim=CPWgs_zF6u2dZRDE2raalMLr7ocBGLDu9HIiA1VTRCjwxIbkBTCP29cv&utm_campaign=100003215&gclid=CjwKCAiAqt7jBRAcEiwAof2uK55LoP9t3A5O78GXba6aBq_9LQK8MFOgYR2YjxzsOufXyJskXa8quxoCITMQAvD_BwE
IMO, 22 inches are too small. 26 inches with 3 blades should provide more thrust with lower RPM and quieter as well.

That’s a Pricey Meatball!

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Totally worth it though.

T-Motor Carbon Fiber Prop (6pcs, 2 sets) - 26 x 8.5 – $240.99

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At those possible gains might be something that Pdwhite might want to "invest"igate for future batches - maybe as as an extra cost upgrade package. If the numbers pan out than maybe it could be just made a stock setup with a small price increase? Who would not want to spend, say 300-400$ more to get 30% more efficiency!
Cheers

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So it sounds like @cwallen93117 has an excellent test stand. Maybe we can pool together to get him a M17 and a number of props to test? Are you game for this @cwallen93117? What do you need to accelerate or expand your test matrix?

The test matrix needs to include the current M10 motor and current prop as a baseline

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CW
I live in Chalfont, Bucks Cty Pa and would be interested in trying different props on my OPPG.
John

Open to using my test stand to test the Open PPG motor and various props. However earliest would be May as its too cold now and I’m gone in April to fly comps in Florida. I would also need to design and mfg a new motor mount to work with the M10 motor, could start on this now if i had a motor in hand. My ESC is different brand but should be close enough as its a 12s 80amp.

John - Would be great if you could help, I’m in Radnor PA so about 20-30min away, could I use your motor to get dimensions to make it fit on test stand. I also need to find a straight and flat road with minimal to no traffic to test any ideas? I just moved to area so don’t have a good spot.

Charles

These props will do no good on the current OpenPPG setup. #1 the 26” diameter will prob not clear the cage ring. And if it does, it will be very close. #2, that prop will load down the motor so bad ur current draw would be crazy high, maybe even exceeding the ESCs burst rating. 3 blade props are good when a higher level of “bite” is needed. Or, when the motor is way over powering a 2 blade prop of a certain size and a larger diameter is not an option due to X reason. On a plane it may be that the larger diameter will put the prop tips too close to the ground, etc… And #3, the more blades u add to a prop, the more inefficient it becomes. When a propeller spins, each blade cutting through the air causes turbulence that the trailing blade somewhat has to deal with. This is called cavitation. At a faster speed moving fwd it is not as bad as the propeller is being force fed clean air. But at slower fwd speeds (like paramotors fly at) this becomes worse. The closer the blades are to each other, the less time/chance there is for the trailing blade to get clean air while it’s rotating. Actually, in theory, and in real life, a single blade propeller (with a counterbalance on the opposite end) is said to be the most efficient propeller design. Crazy, but true.

But never seen – why?

A single blade is too expensive to balance and maintain compared to a 2 or 3 blade. Also they were popular when engines were very weak and the added efficiency made a difference. When gas engines evolved and power wasn’t an issue it made more sense to use a simpler 2 bladed prop. The increase in engine power led to the use of 3-4 blade props to increase thrust for the same diameter. This makes a huge difference for aircraft like spitfires where prop ground clearance is an issue. Also a single bladed prop will need to be longer since it only has one blade making thrust. I don’t see any reason for Open PPG to use a single blade prop. For my application the single blade could be stopped such that it wouln’t get damaged on landing or setup.

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The only reason they are said to be more efficient is because the 1 blade only has to deal with turbulence it creates for itself. A standard 2 blade propeller generates more thrust. But here ya go, now u’ve seen a single bladed prop in action. Lol