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« on: February 04, 2018, 12:42:42 PM »
Aravind298
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Greetings!

Has anyone tried CFD for the propeller air flow in a quad or something like that?
If so, I'd be eager to collect the results. Please PM me.
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« Reply #1 on: February 04, 2018, 11:44:29 PM »
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Whats that CFD???
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« Reply #2 on: February 04, 2018, 11:49:08 PM »
Aravind298
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Whats that CFD???

'Computational Fluid Dynamics'. Used to analyze the wind flow pattern. Similar to using a virtual wind tunnel.
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« Reply #3 on: February 04, 2018, 11:55:53 PM »
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Okey why you need that one!!!
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« Reply #4 on: February 04, 2018, 11:57:19 PM »
Aravind298
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Well, to study and make better props. We're in serious deficiency of efficient props. Well, we sure can do research in it, that's why.
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« Reply #5 on: February 05, 2018, 12:27:35 PM »
saikat
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and how are you stating that the available props are ineffecient ?
compared to what ?
do you have any data regarding the efficiency , or the lack thereof  ?
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« Reply #6 on: February 05, 2018, 02:53:38 PM »
Aravind298
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I didn't exactly mean inefficient; my bad. But for sure, we can work towards to decrease the prop noise. I'll post a few pics shortly.
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« Reply #7 on: February 05, 2018, 03:17:17 PM »
Aravind298
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Also, I wanted to know the how much thrust is produced in certain area of the prop, and find a way to link it with the torque produced.
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« Reply #8 on: February 05, 2018, 10:50:16 PM »
Aravind298
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Here's one of the sources: http://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node86.html

Here, in the efficiency part, P(in) and P(out) is pretty far apart, in the case of a fixed pitch propeller.
What I believe is, if we find a way, in which the propeller changes it's shape with increase in RPM, so as to remain in the most efficient region, we can get pretty much more flight time. Which will contribute to overall increase in lifecycles of almost every part in the plane/multirotor.

My comparison, which I'm yet to do, would be b/w a fixed pitch and variable pitch propeller. And combining them into a hybrid would be the aim.

Hope I've made it clear to Saikat.
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« Reply #9 on: February 05, 2018, 10:51:21 PM »
Aravind298
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Even this was helpful: http://www.nar-associates.com/technical-flying/propeller/cruise_propeller_efficiency_screen.pdf

And a basic idea on how propeller works from here: https://www.youtube.com/watch?time_continue=1&v=0bP2MH3LqvI
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« Reply #10 on: February 06, 2018, 04:39:10 AM »
K K Iyer
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@aravind298,
Sir,
In our typical electric powered model airplane applications, thrust (gms) / input power (watts) is a useful indicator of prop efficiency.
(I presume such props are what you are talking about, and not full size, ducted fans, contra rotating etc)

What is the range of gms/watt static thrust that you are experiencing with different makes and sizes?
(In sizes from say 5x3 to 12x7)
And what is the approximate improvement you are considering?

Regards
Iyer
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« Reply #11 on: February 06, 2018, 06:55:42 AM »
Aravind298
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Hi Iyer Sir!

Yes. We do measure the efficiency in g/w. And it's severely low at 5x3 (high RPM motors) to 12x7(low RPM motors) where the efficiency is significantly higher.
But that's motor specific too. A lower RPM motor tends to be much more efficient that one which rotates at higher RPMs.

I feel we can induce the efficiency of a larger prop to a smaller prop. And the larger ones even higher.

I'm not sure of how much I'll be able to make improvements, since I'm much limited by the data.
I'd start collecting the data with the thrust produced per unit area of the prop (and that's why I wanted the CFD models), both in CFD and practically measuring it.

I've a good feeling towards the variable pitch props. So, if we can find a way to change the angle of attack at certain parts of the prop at different RPMs(instead of manually doing it by FC), the efficiency would go significantly higher.
Honestly, I've no idea of how to do this, but I would try my best.


No, I'm not taking into account the full size, ducted fans or contra rotating props.

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« Reply #12 on: February 06, 2018, 06:57:55 AM »
Aravind298
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In short, the propeller should be smart enough to change itself, in order to remain at peak efficiency at all times.
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« Reply #13 on: February 06, 2018, 09:21:52 AM »
saikat
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you can use a heli main rotor head for vari - pitch

people have already made multirotors with vari pitch props (stingray 500)
the reason it is not mainstream is due to the mechanical complexity and cost.

plus crash resistance is poor.

In short, the propeller should be smart enough to change itself, in order to remain at peak efficiency at all times.

this is exactly how modern fullscale aircraft and helis operate.

on the other hand most full size ultralights and ab initio trainers use fixed pitch (inefficient ?) props beacuse it is an acceptable compromise between simplicity , cost and performance.

a single rotor heli ccpm configuration is alway more efficient than a multirotor layout

in multirotor - if you want to increase prop efficiency - explore using supercritical cross section and blade profile.
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« Reply #14 on: February 06, 2018, 09:30:24 AM »
Aravind298
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Quote
in multirotor - if you want to increase prop efficiency - explore using supercritical cross section and blade profile.

Exactly. That's what I'm after.

We can surely bring down the cost, once we understand how things work, and manufacturing stuffs ourselves  Smiley
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