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Old Nov 10, 2007, 08:13 PM
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E-Flux

YES, I've searched the forums and Google for info about E-Flux.

I should lead off by saying what I think I know about eflux. From the reading I've done it is a measure of the airspeed after the Ducted Fan Housing. BUT...

My question: Is there a standard way of doing this measure? Is there a specific distance from the DF that the measurement is taken? Is it after the ducting that goes out the tail area of the ACFT? Is it in the ducting prior to exiting the ACFT? what types of meters are being used?

The only reason I'm asking is that I am new the the Foam Jets and very interested in the way things work and getting the maximum out of every aspect of the ACFT. I've read tons on different setups and E-Flux is used numerous times to estimate the approximate speed of the ACFT, but I'm curious if the E-Flux is being tested by different people the same way(Apples for Apples). I've seen pictures of little motors with fans hooked up to voltage readouts that approximate the speed via a crude table that was developed on the hood of a car . I've seen PPL use wind meters or pitot tubes.

So sorry for the long question, but can someone that knows give me the low-down on E-Flux and the correct, most standardized way to do it. Thanks in advanced!

SFL
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Old Nov 10, 2007, 08:25 PM
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IIRC within 1 inch of exit. outside is where it matters, measured inside and you're bypassing part of the ducting and will get erroneous readings.
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Old Nov 10, 2007, 08:32 PM
EDF rules... :)
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E-flux is the air mass that has been accelerated by the rotor. If your testing on a stand then a good distance is within 1inch and same for the outlet. Move the pitot tube arround in the airstream and you will notice near the center the velocity is lower and also near the shroud wall the velocity is a little lower so there is a sweet spot where the highest velocity can be measured. Antoher thing you will notice is further away from the fan the velocity is lower as the airstream spreads and slows, this makes it important to get close to the outlet either way.

Eric B.
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Old Nov 11, 2007, 02:12 AM
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Actually, putting a little fan on the front of a car would be fairly accurate... it's just, as you get up to 150kph that gets a little difficult. Although, I guess I'm OK... I could tape it to a plane and get speeds up to... hmm... about 300kph, I guess.

A pitot tube with the tip in the output plane would be the most correct way to measure, but I'm thinking anywhere within a couple of cm would do. An eagle tree logger with airspeed probe would do it.

By the way, it's 'efflux', if you want to search the net for more info it'll help to use the correct spelling.
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Old Nov 11, 2007, 10:38 AM
EDF rules... :)
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I would say that just putting it in front of the car might not give a reliable reading, the fan would need to be outside the boundary layer to get clean airflow wouldn't you think?

We all make mistakes...

Eric B.
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Old Nov 11, 2007, 02:35 PM
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I was thinking more about your question and you would be better off FIRST measuring the thrust output in ounces or grams rather than measuring efflux speed. Not many EDF people actually measure efflux speed. airspeed sensors are not common but weight scales are.
A far more practical means of deciding whether "W" fan will fly "X" plane' using "Y" motor and "Z" voltage. Is to simply put said setup on a cheap digital postage scale, nosedown if its in a plane or rig up a stand to hold the fanunit. Efflux speed isn't the only aspect to be considered. That actually has more to do with top speed, if you got a 50mm fan with an efflux speed of 150mph, it still won't fly a 70mm HET F-18.
A larger fan is needed and even though efflux may be only around 100mph it flys very well. A scale is a much more usable tool then an air speed sensor in EDF.
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Old Nov 11, 2007, 03:29 PM
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Quote:
Originally Posted by AirX
I would say that just putting it in front of the car might not give a reliable reading, the fan would need to be outside the boundary layer to get clean airflow wouldn't you think?

We all make mistakes...

Eric B.
Er, yes, I was assuming you'd put it on a pylon to get it away from the immediate boundary layer... I guess I could have said so
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Old Nov 11, 2007, 05:55 PM
EDF rules... :)
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No problem mate, there is always good knowledge to be shared and we all apreciate the contributions. I for one make enough wording mistakes...

Cheers,
Eric B.
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Last edited by AirX; Nov 11, 2007 at 05:58 PM. Reason: Spelling
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Old Jun 16, 2010, 12:55 PM
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hI;
rEGARDING EEFLUX;
Couldn't you just put an anemomiter behind the edf?
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Old Jun 16, 2010, 04:46 PM
Carbon fiber is our friend
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Sure you can, but it will only tell you pressure.

Steve C
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Old Jun 16, 2010, 06:05 PM
EDF rules... :)
AirX's Avatar
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I found this about the word anemometer

NOUN: An instrument for measuring wind force and velocity.

http://education.yahoo.com/reference...try/anemometer

I would think if you can get one that reads high enough you could use one. The ones we used for sailing and windsurfing would not read higher than 120mph.

Eric B.
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Old Jun 16, 2010, 06:13 PM
Carbon fiber is our friend
Steve C's Avatar
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I was just thinking the u tube kind that you can measure pressure with, but you're right. The word can mean more. Pressure isn't a bad thing to know if you're testing these things anyway.

Steve C
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Old Jun 16, 2010, 06:17 PM
EDF rules... :)
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OIC a manometer. I did not think of that being your meaning as that is used as a pressure measurement instrument.

NOUN: An instrument used for measuring the pressure of liquids and gases.

http://education.yahoo.com/reference...ntry/manometer

Eric B.
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Old Jun 16, 2010, 08:11 PM
Carbon fiber is our friend
Steve C's Avatar
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Ah, there we are. I suspected me of some sort of confusion!

I'm gonna blame the hydrocodone.

Steve C
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