Will Ducting Your RC Props Increase Thrust?
HTML-код
- Опубликовано: 26 авг 2024
- Edit: after learning more about ducted fans, having airflow over the entire lip of the duct would provide the possible increase in inflight thrust, but not static thrust. In this video, I found that the static thrust does not increase. Simply ducting normal propellers will not increase thrust in most scenarios, and marginal gains will be small or insignificant for added features.
Original Description:
I noticed that my thrust seemed to be reduced when I made a homemade duct for an experimental plane, so I decided to investigate further... Interesting results.
Intro song credit: Denver Simmons
Outro song credit: The Lemon Twigs - I Wanna Prove To You
Since you 3D printed the duct, you could also print a 6-blade propeller that matches the duct perfectly.
I actually made a crude EDF when I was a kid. It was part of a grade school mechanical engineering class. It was very weak, powered by a little 9v Radio Shack hobby motor, a crude homemade 2" wooden prop (modified ice cream cup paddle) and used a tin can and a Solo cup for a shroud. Very little thrust, but did move the hobby car it was attached to at a snail's pace.
What would be an interesting experiment is to build an electric motor with the duct housing the stator. The rotor magnets (or a squirrel cage for an asynchronous motor) would be a ring around the propeller blades, attached to this rotor housing ring. The only gap would be between the rotor and stator - this needs to be about 1/2 mm anyway. So the rotor assembly, including the propeller blades, spins as a unit. In other words, you don’t have to worry about the duct/propeller gap. The only gaps are between the rotor and stator, which can be miniscule.
Aren’t the 3 duct beams pitched the wrong way ? I mean, with that duct I would choose a CCW propeller not a CW like yours. So they would be parallel with the airflow, as the air behind the prop is flowing around the axis, CW in your case.
Indeed. Now they fight the rotating air coming from the propeller. And yet oddly they increased thrust compared to the straight beams. Something seems fishy there. The thrust should still increase if the beams were oriented properly. Also the duct surfaces are so coarse here that they will compromise thrust at least a little.
One of the variables that cant be seen on this test stand setup is the ram air effect. In theory The slightly wider mouth helps shove more air through the fan when at speed. I've been getting ready to test this just as you have by putting another fan in front of the duct on the stand and also the naked blade. I'm running a 4 blade and normal stand setup has netted me equal thrust already. In my case I'm just looking for equality anyway as I'm using a longer tube and thrust vectoring to replace rudder and elevator
I removed the front cover of a usb fan thinking that would increase thrust but it didn't. The grilles on the front cover aren't just that, they're actually guide vanes. Without it the fan air is slower.
You have an obvious gap between the blade tip and the inside diameter of the duct. This is mitigating one of the primary ways a duct helps to improve thrust and efficiency.
Very good experiment. I wonder what will happen if you build the duct as part of the blades (the duct rotates along with the blade)?
****BINGO*** this is what needs to be done.
Tty to narrow the duct from inside same as turbofan jet engines. Meaning, decrease the gap between the center of the prob and the duct inner side. Just keep the air flow through that narrow area by installing a spinner (nose) on the center of the prop and see the difference. I have never tested it but I am sure it will generate higher thrust
I just bought an airpix which is a super tiny drone, and it has like zero flight time, i wonder if cutting off the ducts on it would actually increase flight time.
interesting but you should have started with a factory made EDF, tested that, then removed the duct and tested again, that would be a good test
LOL, I just wrote that in the comment, then saw your comment from 10 months ago. I think that the pointy tips of the blades he's using aren't tight enough to prevent vertex losses. So the duct just produces resistance, but doesn't prevent losses.
Exactly! For accurate results, a working model is needed as a base level comparison. An unproven design will not give useful results. Many variables still to consider, including prop design, prop edge to duct gap, duct surface aerodynamics and motor KV. The motor, props and ducts are matched. All are present in a working model.
A ducted fan gains efficiency over a prop when designed and used as a lift fan...where it used for hovering. In this configuration the blades of the fan are quite different than a propeller blade. Just think about the lift fan in the F35 fighter..It is meant for hovering and landing, not for forward propulsion. In forward flight a propeller is more efficient.
Sand the duct as smooth as possible!
Now let me give example of real principles that work. If u double the size of prop keeping load on motor same (make sure motor runs WARM ) ie gear it down by 8 times, efficiency will increase 2 times.
eg 8520 motor produce 30g thrust on direct drive. i gear it down 4.5 timeS applying 1.5 times bigger prop & I get 45 g thrust
If you did the same but used it instead of an edf inside of a edf jet would it work.
Very good! tank you for the information
I am under the impression ( i could be wrong ) that as air speed increases a ducted fan produces more thrust
It's the opposite. Static is the most thrust.
ruclips.net/video/0bP2MH3LqvI/видео.html
Maybe theres some unkown variable that you are not controlling for
impressive scenery, where was this?
Thank you for your investigation. I was wondering about ducts... And why they are uncommon which is counter intuitive to what some people say on the internet. This seems to answer the question. So much to say about a good practical experiment vs a guy talking bs in front of a whiteboard.
Mate isn't it possible to instead of making the duct and the propeller as separate pieces, what if they were made a single piece?
riiiight ... so the motor has to move more mass ... that makes total sense
What you would rather need is a Q-Tip propeller, you can look at the video from RC Model reviews about them.
Moving more mass is not a problem, once it is moving, it tends to stay moving. Ignore commenters who lack basic science knowledge.
I was looking at wind turbines, which use an arrangement that was counter-intuitive to me. Instead of placing a converging cone in front of the fan (prop), these turbines place a diverging cone behind the fan. This forces air to spin and expand behind the fan, creating low pressure, and therefore sucking much more air through the fan. Have you tried that? I will experiment with this.
Any luck?
Thank you for your well conducted tests and conclusions.. I would also like to add that there is the added drag of the duct when moving forward.
i think the low pressure due to the bernoulli is just not sustainable with these props. When you just have 3 rotors i imagine, they cant really hold the pressure and the effect kind of cancels... and in the end you just have more vortexes due to the structure.... duct fans i saw hat a different rotor design and i think higher rpm... but thats kind of my guess after watching the 101 video you referenced.
Maybe you could test your plane with the 3d printed duct. Matbe the lip starts helping when moving through the air mass... what about putting the whole test rig in a home made wind tunnel?
What happens if i increase the no. Of rotating blades. will the thrust increase?
Can you retest this to determine whether or not the ducting diminished or exacerbated the ground resonance?
Nice test!
well... many things that is obviously wrong here... if i only mention that you even tried measuring the trust with your first duct with thick wooden beams right in the airflow, that kind of tells the whole story, you also got the angle of the beams the wrong way in the 3d printed one.
Hi, nice vid, why don't you try this with an 8 bladed prop. Might be better suited for a duct. And like the comment here below try to pitch the duct beams the other way. looks like they obstruct the airflow. Regards
How did you made that airplane
Putting a duct around a propeller designed for open operation is unlikely to give good results. The pitch distribution of the propeller has to change to work with the duct.
this video actually answered my question precisely. thank you for the content!
The orientation of your propeller experiments did not take into account the air pressure needed to travel above and below the blades ' but rather through a fixed duct ' where air pressure was same all over blade ' how about horizontal setup that is moving forward or Q tip propeller with no duct
Quite usefull, cheers!
whilst its a good video of an experiment, the conclusion doesnt really conclude anything. its simply not tight enough and the duct isnt long enough.
I think your uses the wrong propeller and angles just my opion
Try removing the top half of the duct. It won’t increase thrust, but it’ll increase the lift. It’s called a channel wing if you want to research what I mean
It's not worth the time, effort and weight penalty (which negates whatever real world potential increases in performance.) The only thing it's good for is as prop guards.
Cheers
Is it possible that the airspeed is faster?
great video. every tiny bit of area of the homemade duct makes drag on the inside, and when flying, on the outside, also to front edge make a drag and a some separate drag at the back of it. yeah obvious the the stator blades, or mount struts whatever you want to call them, can play a big role too. I guess there are different designs for for those, and you could make them farther from the prop though that would increase weight and vibration., or maybe they could be angled (form a cone) idk is all new to me those esoteric details. all fun stuff though. So much detail in this tech that matters. Plus the leakage looks extreme in you homemade one. It may help a lot to have the end of the prop more square and radiused to match the radius of the prop/duct interior. i think maybe the prop tip clearance/fit thing may be the post important of all, idk, and it still looks like you have no good fit there. But you should be able to mod you prob if you start with a slight larger diameter prop (yeah that takes a lot of careful work and balancing and you really add prop tip back if you take off too much.
The ducts and propellers used are crap, hence the poor results.
Your outlet is way to wide - you need to do the bernoulli maths if you want to get ~ 20% performance increase from a duct - the prop causes inlet pressure to be low, and outlet to be high, so the duct needs a larger-than-the-prop inlet, and a smaller-than-the-prop outlet (otherwise, as you found out, the duct is robbing the power from the prop to try and fit the changing-speed air into your constant-diameter shroud... oops!). You can see how much loss you're suffering without a duct simply by observing the airflow around your prop - like I did here: ruclips.net/video/fbOXXLtaOVg/видео.html / chrisdrake.com/Airfoil_Tools/g0061296.jpg - it goes "backwards" at the tips, and "inwards" behind them... by a lot
You attach some bullshit to the prop and wonder why it does work worse?
Your blade tips are too sharp. It's almost as if you're not using the duct, since the business part of the blade is too far from the duct, separated by those pointy tips. I think a better test would be to get yourself a proper ducted fan, measure the thrust, then remove the duct and measure again. Or at least get blades with flat (or slightly round) tips, so they fit better to the duct.
This is true, although I think in general a properly sized duct should improve the static thrust of any propeller, if only marginally. That's why I was surprised he didn't get better results with the 3d printed duct. It may be that he didn't have the prop positioned deep enough in the duct.
He would have only seen a slight improvement anyway and that would be more than offset by the additional weight and drag of the duct when he flew the model, as he was experiencing.
Using a larger dia prop with tips cut flat to fit close to the duct would have given better static results although performance would still be reduced in flight. Properly designed, a ducted prop should give upwards of 2x efficiency increase, but only in static thrust.
almost there, one more test, - cone shaped duct-smaller end of duct where air exits- ( DUCT LONGER WHERE AIR EXITS) -SMALLER CURL WHERE AIR ENTER DUCT
You are using the wrong propeller lol
TOTALLY the wrong prop for ducted use. Check out the "sabre" style curved blades (and MORE of them) in a ducted application. In essence you are creating compressor.
Best blades are those that have the largest surface area thats next to the duct wall. (DAL 5045T) This will create a tiny gap of around 1 mm and prevent prop-losses due to vortices.
@@4DCResinSmoker Agreed. Also sloping the sides of the duct in VERY SLIGHTLY after the trailing edge of the prop will significantly decrease the "backpressure" as the air gets a kick of velocity. Likewise, broader blades with higher pitch towards the centre ensure even exit velocity and less turbulence also as the angular velocity (I think I'm right here) of the centre of the prop is lower and thus produces less thrust leading to the thrust from the outer edge being "sucked" towards the centre (lower pressure) creating eddy flows and "dead" thrust areas.
What you ideally want is a constant speed prop with variable geometry to get the best efficiency. Hard to make at this size 😞
I've found that an inward slope / angle of 3% is ideal but the big problem comes from the length of the Diffuser making the duct too heavy. This is why multi-rotors don't often use them and why they're only practical for prop sizes under 4". Even then, most ducts used for Tiny-Whoops perform poorly. I've designed several 5 and 6" ducts and have seen limited success with them. Here are some of my posted designs: www.thingiverse.com/1Smug_Bastard/designs
Here is a flight i did with my Son about a year back: ruclips.net/video/M8KeK9aeGXI/видео.html
Then you should send boeing your video so they can stop putting ducts. Wow man your observations are so uuugggh. C for effort, halfway you give up. Find out first WHY it works! what principles does it use and then apply them. Don't half-ass it and then say it doesn't work.
Looking forward too part 2