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Old Oct 11, 2012, 01:10 PM View Post
munce31
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Old Oct 11, 2012, 01:18 PM
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Quote:
Originally Posted by chas650r View Post
guys, i need some opinions on this question;

is it viable to think that i could run this fan in the 800 watt range and expect to get similar performance to a 5 or 6 blade fan running in the 600watt range?
Yes! In fact you will get similar performance to that of a 5 or 6 blade fan in the 800w range give or take 50. You need to select the motor carefully though. The 5-6blade fan motors won't do for this one.

Quote:
Originally Posted by chas650r View Post
i am looking for sound improvement and noise reduction at similar thrust and eflux speeds and trying to judge about how many watts it costs.

thanks , chuck.
Noise reduction for sure. Sound improvement will depend on the airframe. I can't comment on eflux so I will leave it to others who have measured it.
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Old Oct 11, 2012, 01:27 PM
chuck
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thanks for the quick response! yes a kv change is in order, my first thought is a 100 gram motor at 3000 kv on 4's ?
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Old Oct 11, 2012, 01:55 PM
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Quote:
Originally Posted by chas650r View Post
thanks for the quick response! yes a kv change is in order, my first thought is a 100 gram motor at 3000 kv on 4's ?
3000kv is on the high side. 2700-2800kv is a better choice.
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Old Oct 11, 2012, 01:57 PM
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What kind of timing and PWM should be set on the Turnigy L2855-2300?

It's barley rotating now when I give it power.
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Old Oct 11, 2012, 04:46 PM
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For testing you need to set up a THRUST meter....LOL
A stand with scales.
This part you will have to make yourself... but luckily it is quite simple to even make one out of wood - which most people can at least work with viably.
I think you are better off making a VERTICAL based stand, because horizsontal based is pretty well impossible to remove all friction loss from (it needs to have rollers or something).

You can make it is 30mins.... hehe. And 45mins if you PLAN and THINK of how to make it in a fully usefual way so it can take ANY fan type or size.
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Old Oct 11, 2012, 04:48 PM
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For the L2855-2300, on 4S or 5S, I would go for high timing. PWM whatever you want, but I use 8khz.

I am thinking you damaged the motor (screws as mentioned).
If you have some other motor, run that up on that ESC to see what it does. It should at least run like a motor does, even if settings are amiss and not optimal.
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Old Oct 11, 2012, 04:57 PM
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From what I can see of the CS10 results, it seems to me that it 'costs' just a bit more to run it. A little bit more Watts used per thrust output.
Not 800w instead of 600W, but probably more like Anlucas said... 50W out of 800W area (5% area).

But another aspect that seems different is the thrust itself. It seems to me that it is a 'torque' thrust instead of a 'high speed efflux' thrust. Of course RPM can increase the efflux speed, but it will also raise the 'torque' of it.
'Torque' because it seems to have high lifting ability... and I think that is because the total fan blade area is almost the full FSA - hardly a gap between blades. But low blade count fans have fairly large gaps.

This is very much like comparing a 2 blade propeller to a 4 or 5 blade propeller. You can have a 2 blade 10x6 and a 5 blade 10x6, so the 'screw' effect through the air is equal - they have equal forwards motion per RPM - but the 5 blade obviously has massively more BITE into the air. It displaces a lot more VOLUME of air, but at the same air speed as the 2 blade.

This extra load of achieving this means the CS10 would either need more power to drive the larger volume OR it will run at a lower RPM.... than a low blade count fan.
So it is a bit of a 'diesel' power system, than a 'petrol' one (for a combustion engine analogy)..... (diesel more torque, petrol more BHP)

But that balance of torque to efflux speed is not something like two to one.... it is more like.... umm, a guess..... 20% more torque than low blade count fans, and thus 20% less efflux speed. Some sort of balance like that.
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Old Oct 11, 2012, 05:20 PM
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Yes Peter I can agree with that analogy. I would like to hear more about building a thrust meter in 45 mins. I got lots of wood and a few scales kicking around...
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Old Oct 11, 2012, 05:27 PM
chuck
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ok so thats why i am asking if i add the extra watts do i get back to the 6 blade efflux speed ? so maybe better put, i want the same cfm and efflux as w/ the 6 blade, and am willing to pay watt wise. if it turns out to be 15% , thats great, i just cant give up much efflux as these applications aren't any to fast to begin with.

thanks, chuck.
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Old Oct 11, 2012, 05:59 PM
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Before you worry too much about efflux velocity, volumetric flow (cfm) and all that 'fancy soundin' stuff, have a read of the 'how to compare fans' thread that was recently brought up.

I thought I gave a fairly good step by step, including some of the reasoning behind statements like "any two fans with the same exhaust diameter, producing the same thrust, will have the same efflux velocity".
That is completely independent of number of blades, RPM, power, even fan diameter.
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Old Oct 11, 2012, 05:59 PM
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hehe, I don't think you can match the CFM/Efflux. If one fan is designed a certain way - blade count, pitch, area covered - then it has certain total properties. And then another fan will have its own different ones.
You could match off ONE of those values.... CFM or Efflux Speed.... but you can't alter their ratio in that given fan.

For a rough guide, as mentioned, throw another 5% power at it.

I have not tested - and it would be hard to quantify accurately really - but from what I see, it seems if you get Thrust X from a CS10, and had that same thrust (benched) from another low blade count fan, the CS10 installed in a plane will have a lower top speed.
Again, probably because thrust measured on a bench can come from efflux or CFM, but throw that into a plane and top speed is set by efflux mainly (as long as the CFM is still adequate for the load it propels)..
The CS10 powered plane will sustain climb better.... more 'torque'. Which always can get grey when testing, because a faster entry speed will visually look like a faster plane "climbed" as well anyway. But if you had all the measuring abilities, you should see the CS10 is like a 'diesel pulling a load up a hill' = less speed loss, as it was slower but with more torque all the way.

This means to get the same fast top speed, you had to throw more power at the CS10 and whether you wanted it or not you also got more torque - which is where that 'wasted' extra power that they 'need' (versus low blade count) went. So you still are getting something for that power, whether you wanted it or not (torque).
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Old Oct 11, 2012, 06:02 PM
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The relationship between CFM (volumetric flow) and efflux velocity is, wait for it, exhaust area.

Why?

Volumetric flow = velocity * area. Units of volume / time. We use m3/s, yanks use CFM.
So, efflux velocity * exhaust area = ..... ta da!

Has anyone here read Stu's threads on fan design? They're easily accessible, and explain a lot...
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Old Oct 11, 2012, 06:07 PM
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Chuck,

To fill in how this kind of impulse engine works to preface my explanation, the thrust wont be there if the velocity is not there.
Air has density, the fan adds momentum to the air forced thru the fan shroud, the math is (fan area(feet^2)*density(lb/feet^3)*velocity(feet/second))*velocity(feet/second)= force(lb/foot). You can see there velocity is tied to the force, without velocity there is no force.

Now since the fan is so highly pitched it requires a lot of torque to move the air mass described earlier. Depending on what you want to attain in force the velocity will be there same as the 6 blade fan as number of blades have no effect on the force or velocity of the airstream only the rotor blade pitch. 3000 kv motors as Anlucas stated are a little high kv to be efficient unlet the motor length is long, how long depends on the motor mass needed to handle the heat load. Remember short motors 100-150 grams will only handle 600 to 1000 watts for 3minutes WFO flying. The 3000kv motor will generate ~1300 watts so asses the motor you want to use.
The best motor for this fan for high power use is the Eflight 2150kv motor for thier 80mm fan. It is large enough to take the load and abuse of higher power 5s-6s setups, it will need an aluminum fan shroud/motor holder that will act as a heat sink to best contain the waste heat that will be generated.

Cheers,
Eric B.
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Old Oct 11, 2012, 06:09 PM
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Odysis, that can't be right.
As mentioned via propeller analogy, that definitely does not occur.
Propellers are even better for demonstrating it, because they cover a very small total swept area. eg Two thin blades out of a huge swept area.
Then throw in the 4 or 5 blades and you don't gain speed, but you can pull a stump out of the ground when climbing!! LOL

That shows the THRUST of the higher blade count was far more than the 2 blade.... but with the same 10x6 resultant airspeed. Thus 'efflux' and its speed, which a propeller basically still has, did NOT add up to the same total thrust.

An EDF with a WEENY profile 2 blade fan would need to run at massive airflow speed, to produce the same thrust as a fan that covers a large amount of swept area. So its efflux speed would be way higher.

It would be interesting to see what 'balances' they came out with to explain why they say what they did.....
Half of mine is theory (and will be possibly lacking some base factors here or there).... half of mine is what I see my planes do (which backs it up).
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