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Old Oct 11, 2012, 07:18 PM
Extreme CNC Alloy EDF
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Analogies and hypothesis aside the CS10 performs almost as well in the air from my experience. I removed a wemotec from my F16 that was running just over 800w/1.5kg thrust and replaced it with an Alloy CS10 running at 890W 1.52kg thrust, the plane flies the same, speed is so close it would have to be measured to discern any difference.
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Old Oct 11, 2012, 07:19 PM
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Well that theory/maths seems right.....
But all I SEE is that (clearly on prop aircraft) more CFM, thus more thrust (measured statically to test) does not equal more speed.
So what that seems to really mean is that maybe YES thrust is efflux related... but the end result in a plane's SPEED is not. Sort of 'thrust is not thrust'.... but more depends on HOW that was created.
eg two fan design of equal thrust will not fly the plane the same - like the props, one type's THRUST is torque based, and the others is airspeed based.

So I can see and go along with that view on it....

It still means you need more power for a CS10... IF you want equal SPEED.

You aren't going to SEE that. It is not a chalk and cheese change. What is 5% out of 100kph??? 5kph. Try to SEE that in flight! LOL
Though I think it is more towards a 10% speed difference (from equal power).. Even that would be hard to SEE.... you need proper measurements, and even those are hard (as mentioned) as there are so many other variables per flight (wind, battery etc)... so you certainly could never tell much by SIGHT.
Though over a longer term average on my Meteor, I have worked out that it is slower with the CS10. (close to exact same power in static tests). But even that has tolerance range, because you HAD to use a different motor for the CS10... adding another variable of a slight unknown change.
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Old Oct 11, 2012, 07:32 PM
EDF rules... :)
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Joined Nov 1999
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Quote:
Originally Posted by Odysis View Post
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...
+1, the exhaust area is the ultimate area measurment in fan calculaton if you use an exhaust tube, if you dont use an exhaust tube the 100% Fan Swept Area is = 62mm outlet size for CS70mm.

Cheers,
Eric B.
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Old Oct 11, 2012, 07:36 PM
EDF rules... :)
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Joined Nov 1999
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Quote:
Originally Posted by PeterVRC View Post
Well that theory/maths seems right.....
But all I SEE is that (clearly on prop aircraft) more CFM, thus more thrust (measured statically to test) does not equal more speed.
So what that seems to really mean is that maybe YES thrust is efflux related... but the end result in a plane's SPEED is not. Sort of 'thrust is not thrust'.... but more depends on HOW that was created.
eg two fan design of equal thrust will not fly the plane the same - like the props, one type's THRUST is torque based, and the others is airspeed based.

So I can see and go along with that view on it....

It still means you need more power for a CS10... IF you want equal SPEED.

You aren't going to SEE that. It is not a chalk and cheese change. What is 5% out of 100kph??? 5kph. Try to SEE that in flight! LOL
Though I think it is more towards a 10% speed difference (from equal power).. Even that would be hard to SEE.... you need proper measurements, and even those are hard (as mentioned) as there are so many other variables per flight (wind, battery etc)... so you certainly could never tell much by SIGHT.
Though over a longer term average on my Meteor, I have worked out that it is slower with the CS10. (close to exact same power in static tests). But even that has tolerance range, because you HAD to use a different motor for the CS10... adding another variable of a slight unknown change.
Peter,

Do tell us from your engineering background what is the proper way to calcuate the fan thrust?
So far you have only touched on what you feel, let us know how you calculate thrust?

Eric B.
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Old Oct 11, 2012, 07:53 PM
Extreme CNC Alloy EDF
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Old Oct 11, 2012, 08:05 PM
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I don't think THRUST is the key here.
More important is Efllux Speed and CFM. And what that pair drive your plane too.
Thrust must come from the volume and how fast it moves.
The volume is not set JUST by the area, because air is made up of molecules that can have their density (of them) altered. So more dense means more 'weight' to their force.

How does someone come up with the idea that CFM by Velocity must always be equal end result 'thrust'??? Because DENSITY of that volume can change.
In a non-compressable liquid the resultant is fixed... but not in a gas.

So I would want to be seeing maths that includes air density...not just ambient air pressure, but pressure AFTER the 'pump'.
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Old Oct 11, 2012, 08:07 PM
chuck
santa barbara, CA
Joined May 2009
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Quote:
Originally Posted by Extreme_RC View Post
Analogies and hypothesis aside the CS10 performs almost as well in the air from my experience. I removed a wemotec from my F16 that was running just over 800w/1.5kg thrust and replaced it with an Alloy CS10 running at 890W 1.52kg thrust, the plane flies the same, speed is so close it would have to be measured to discern any difference.
well this is great news i am sold .

i am no expert, but........ i think u can match the cfm/efflux. in a given setup w/ nothing changing but the rotor , at some rpm it will create the same cfm and hence the same efflux speed. not the same watts or rpm but same cfm.

as far as the motor goes, although it sounds like the fan is capable of 1+kw, in my applications i wont have the battery to support more than ~800 watts on 4s so i hope the rotor still works well at those levels (rpm) , sounds like it from the quote above. so i have had good luck at or below 800watts w/motors in the 100-110gram range, at least in burst. again ,i wont have the battery to run constant 800watts anyway.


thanks to all who responded to my question , its good reading and from w/ i am hearing it sounds doable to me , but brings up 1 more question and it may have been answered, is it important to use the sc housing? i am guessing so due to length and hi stator count?

chuck.
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Old Oct 11, 2012, 08:09 PM
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Until now I hadn't thought about it a lot....
I did bench test, in-plane tests, of THRUST.. And just took it as that was the 'master' of results. Though I did recognise there was some cause of speed difference.... likely to be efflux speed.
But I did note the 2-blade/4-vlade propeller results I was seeing. And assigned reasons to that result. But still not to EDF's, as I didn't even think much about it.
Though I did SEE (result or tests) that CS10's ate a bit more power, and gave less speed, so that did make me ponder just a bit.
Just not to the time/level of like now.....
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Old Oct 11, 2012, 08:14 PM
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I hear people say EDF's are not a 'Compressor'... but just a pump.
How can something that speeds up air flow, and feeds that into stationary air, NOT get back pressure... and thus increase pressure... like a Compressor?
It must.

It may not be DESIGNED to mimic what a jet engine compressor compresses air down to... but it still does compress it.
And this air compression... density.... must come into play in the output... the maths... of it all...

CFM doesn't state what density the fluid had. It tends to just be a measure of "you moved this much of that item" and assumes the item was the same.
But denser air is not the same as less dense air....
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Old Oct 11, 2012, 08:50 PM
You are a "go" for reentry
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High Orbit.....
Joined Jun 2009
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I'm an Engineer. I can Fly!

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Pete this is in no way directed at you. Just keeping it light for all the Engineers.
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Old Oct 11, 2012, 09:08 PM
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Lmfao
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Old Oct 11, 2012, 09:09 PM
chuck
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Originally Posted by Maxthrottle View Post
I'm an Engineer. I can Fly!

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Pete this is in no way directed at you. Just keeping it light for all the Engineers.
yep........... flies like its on RAILS
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Old Oct 11, 2012, 09:14 PM
EDF rules... :)
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Joined Nov 1999
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Quote:
Originally Posted by PeterVRC View Post
I don't think THRUST is the key here.
More important is Efllux Speed and CFM. And what that pair drive your plane too.
Thrust must come from the volume and how fast it moves.
The volume is not set JUST by the area, because air is made up of molecules that can have their density (of them) altered. So more dense means more 'weight' to their force.

How does someone come up with the idea that CFM by Velocity must always be equal end result 'thrust'??? Because DENSITY of that volume can change.
In a non-compressable liquid the resultant is fixed... but not in a gas.

So I would want to be seeing maths that includes air density...not just ambient air pressure, but pressure AFTER the 'pump'.

Your an engineer arent you? There are others smarter than you and I that have defined all physics and math behind thrust force and power needed to make that happen, we arent breaking new ground. If you look up the right books fluid dynamics is right at your fingertips.
Websters defines thrust: to push or drive with force.

What changes a gas density? Temperature and altitude, since both are constant at the time of a test or the instance that the math models then they are taken a constant number in this instance.

Mass is in this instance a defined ammount of moving fluid (air) = density * velocity * area = mass flow rate or Mdot for William. The equation then becomes (density * area * velocity^2 = force) and (density * area * velocity^3 = power).

Peter are you trying to change accepted math/physics applied to fluid flow?

Eric B.
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Old Oct 11, 2012, 09:43 PM
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Joined Jul 2011
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Ok before you open up another can of worms, go grab some popcorn instead and watch this video.

parkzone habu 2 4s 10 blade fan (5 min 14 sec)


Here I am using the CS fan for the first time with my H2 and a 4s 3300 30C.
The landing was butt ugly and was entirely caused by my lack of concentration... Just some jitters.
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Old Oct 11, 2012, 09:45 PM
RAVI KOTHARI
Joined Nov 2005
259 Posts
Just mounted a Leopard 2850 2670KV in a dynam meteor, replaced my venerable HET 2w25 , the thrust seems significantly stronger in hand.

Flew Noticeably faster, running a 3700 25C compact pack from HK. PAcks were mildly warm, ran much cooler than my 2w25. Guess the longer Can is much better for dissipation.

Is my new reference motor on 4S for this fan. Great motors these leopards are, Temp on motor was barely warm, Had a heat sink mounted with Thermal Paste.

Cheers
Ravi
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