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Old Dec 22, 2006, 09:58 AM
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MattinAZ's Avatar
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Het 6904 Fan Test w Het 2W20

Hope this helps anyone that is interested.

Expected to have more fan tests completed by this time just been too busy with work and family.

Matt
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Old Dec 22, 2006, 11:26 AM
Look out! The lever!
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United States, AZ, Peoria
Joined Feb 2005
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Very good, Matt. Maybe I'm dumb or uninformed, but what is the "throttle" listing?

Thanks,

bob
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Old Dec 22, 2006, 12:37 PM
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How was the fan mounted? Inlet shroud, etc.?
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Old Dec 22, 2006, 12:56 PM
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great info. Thanks.
How about more details like
Inlet, thrust tube % FSA, ESC timing...
That would be nice.
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Old Dec 22, 2006, 07:22 PM
deltas are cool
AIR SALLY's Avatar
Tehachapi ,CA.
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Thanks great info ...but im confused i just got a HET 6904 fan and HET 2w-15 motor on 3s and with a cheap 4000 10c batt i was seeing 37,000 rpms...how can this be ? i was using my pc ,w/ a usb cord it allows you to run it of your pc and gives a rpm read out...i thought the 2w-20 would do more since it is 700 watts (you only got 647) on 4s .mine is rated at 450 watts i would think yours would have made 40,000 ish rpm's
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Old Dec 22, 2006, 10:14 PM
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Air Sally - From my experience I do not have a lot of faith in the RPM sensors as they are very touchy and everything has to be just right to get an RPM reading from it. I have no way to compare the rpm sensor, but if I calculate 2900kv x 15 volts you get 43,000 RPM which is probably closer. My main concern was how much thrust, amps, airspeed as a measure of performance. I will look into why my RPM sensor is registering low.

Bobthe nuke, 0-100, 0 being throttle off, 100 full throttle.

FlyingDwarf,

No intake ring/Het fan does not come with one, and exh duct dia = 92% FSA, timing was auto on the Jeti Opto 77.



Matt
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Old Dec 23, 2006, 12:33 AM
deltas are cool
AIR SALLY's Avatar
Tehachapi ,CA.
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Yea that make more sence...if you could get the rpm reading right i could guess-ta-mate my thrust,based on rpm's. i'm getting a watt meter for christmas so i'll be able to do the volts and watts ,and we have a scale we can run the plane on and get a lookat installed thrust...my tail pipe is 80% of the outside dia. of fan,it's 2.2 "..do you think thats to small?thanks again for all your work...how do you think the 6904 fan compares to the wemotec 480?
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Old Dec 23, 2006, 04:37 AM
ost
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You can compare a Wemo MF, a 6904 and a DS30 together when not using a inlet ring.
But the results without this ring is not right.
The watts are not right, and its possible to crash the fan because you can "read" only the wrong datas. One guy in germany crashed his fan and I think this was because he measured only the watts (830) while the fan runs over 50000 U/min or so.
Without the ring the airflow is very bad and there can be a stall at the rotortips.
No power, more rmps....bang.
Hard to explain for me.
Merry Chrsitmas to all!
Peace
Oliver
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Old Dec 23, 2006, 06:49 AM
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ost,

I dont quite understand your post. except for - Yes, airflow is better through the fan with an intake ring and thrust will increase.

I wanted to know a baseline of performance, thrust, airspeed out of exhaust, and amps, With or without a intake ring in the test stand their is no practical way to test how it will operate mounted in an airframe with its own intake lenght, shape and inlet. If you were using the fan in a pod like a airliner you could get very close because the inlet would be exactly like it will be mounted on the airframe. (Does this make sense?)

Through my testing is seems that the effect of the inlet ring is nearly 0 at full throttle and higher fan speeds. I could be wrong but there is a post somewhere from the Wemo Tec person that also states this. I did find that the intake ring did increase thrust significantly at lower settings, but then again it would have to mounted in the airframe to complete an accurate test. Which right now is not practical for me.

AIR SALLY, I really like the Het fan for a few reasons - it takes less than a minute to assemble with motor from opening the box to a complete assembly. Het fan comes pre balanced, has a one piece design where spinner and fan are 1. Makes life much easier. Does it give better performance? I cant say that it does, both fans seem to perform about the same. Better durability? Yet to be seen, but the Het fan is so easy to assemble and looks to be a great design.

I will try and complete some additional testing, but all I really wanted and what most people probably want to know is how much thrust and eflux spped to expect based on Fan/motor/esc/battery combo. I think I would have a real hard time trying to figure out which fan gives the best performance becuase of all the variables and the accuracey of the test equipment. The test equipment is very good but I am not sure it can reliably detect the differences between two fans due to all the variability.

Matt

Matt
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Old Dec 23, 2006, 07:08 AM
ost
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Quote:
Originally Posted by MattinAZ
ost,

I dont quite understand your post. except for - Yes, airflow is better through the fan with an intake ring and thrust will increase.

Matt
Hmm, I think, that not only the thrust will increase, also amps and watts,
the voltage will drop down a littel bit, when the airflow is better.
You can hear the dif. between a run with or without a intake lip.
A intake duct has also an intake lip.
I donīt belive, that thereīs no difference on amps and watts.
This is also a testing and you can see- more watts.
With a wemo intake lip.
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Old Dec 23, 2006, 01:04 PM
EDF rules... :)
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Quote:
Originally Posted by MattinAZ
Air Sally - From my experience I do not have a lot of faith in the RPM sensors as they are very touchy and everything has to be just right to get an RPM reading from it. I have no way to compare the rpm sensor, but if I calculate 2900kv x 15 volts you get 43,000 RPM which is probably closer. My main concern was how much thrust, amps, airspeed as a measure of performance. I will look into why my RPM sensor is registering low.

Bobthe nuke, 0-100, 0 being throttle off, 100 full throttle.

FlyingDwarf,

No intake ring/Het fan does not come with one, and exh duct dia = 92% FSA, timing was auto on the Jeti Opto 77.



Matt
I dont know the pitch to see if anything is correct but the rpm numbers of the highlighted line in the pdf would be good simply as 14.355volts X 2900kv = 41629rpm which is not taking the motor efficiency into effect, 41629rpm / 33900rpm = 81%effciency at the motor.

Eric B.
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Old Dec 23, 2006, 01:28 PM
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Post removed in protest of RCG's pandering to left wing extremeists in the LTUP forum.
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Old Dec 23, 2006, 03:47 PM
ost
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Rob
your english is much better than mine
Oliver
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Old Dec 25, 2006, 08:49 PM
deltas are cool
AIR SALLY's Avatar
Tehachapi ,CA.
Joined Apr 2006
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6904 2w-15 on 3s 4000mah

I got a e-flite power meter,and with a 4000mha 10c batt i got readings of 480-512 watts it was pulling 47-51 amps at about 9.75 volts ...the numbers would go up after the batt got a little warm...then the batt seamed to struggle with holding the power. but with a 10c batt i would expect the batt to drop off ...it also got really warm ,but the motor and esc were fine.just warm. i change the timing to 20-30 degree,but the motor came to a abrut stop that scared me ...i thought it smoked the motor so i put it back to 10-20 degrees and it did the same thing so i was freaked out to think i smoked after a few mins of running i took it apart to see what was going on and all i could see was a small rubbing on the fan shroud...so i cleaned it all up. put it back together i tried the timing at 4-10 degrees and it ran fine it was a few thousand rpm down...so i put the timing back to 10-20 degreea and it ran up to 37,000 rpms and was again pulling up to 500watts . so the 2w-15 runs as advertized a solid 450+ watts at 47-51 amps...i just need a batt that is 20c no thrust readings as we don't have a scale set up and we were running in the air frame through the inlets in my 32" C/N skyray (see the foamy edf thread)and out the 2.2 tailpipe. so i'm pretty happy with the perfomance.i just need a batt that can handle the power i guess i need a 3700-4000 20 c or some thunderpower 2100 (2) wired in 2p. what do you guys think is this thing running ok?
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Old Dec 26, 2006, 11:19 AM
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Air Sally I'm using the Thunderpower 5000 extremes and love them, great power and they hardly break a sweat at 60 amps. Some of the smaller cells (4600 or 4000, other sizes) they have would be fine, but remember you'll likely see a power boost due to high voltage, don't know if that will push the limits with your motor.

Two of the 2070 Extreme packs would work with a parallel connector if you want to go that route, but a single larger pack is easier to charge.
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