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Old Jun 11, 2012, 02:31 PM
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skyracer068's Avatar
Singapore, Singapore
Joined Jan 2006
329 Posts
Just a thought their Bro!!! The Phase 3 F-16's that most of us have modified with a 70mm fan had cheater holes for the fan. When you had the "berries" poured on then, brought the throttle back to idle, the 16 would climb like a bandit from the inlet air escaping out of the cheater holes. I don't know where exactly your cheater holes are. If there behind the CG, it might have a opposite effect.
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Old Jun 11, 2012, 02:33 PM
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Looks awesome!!!
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Old Jun 11, 2012, 02:38 PM
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United States, FL, North Port
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just in case you didn't get it the first couple of times... I think a wall between the fans will help
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Old Jun 11, 2012, 02:50 PM
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Austin, Texas
Joined Dec 2005
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Quote:
Originally Posted by falcon5 View Post
Well here is what the fans sit in. Stu Maxwell did say that he would like to see my inlets a little less sharp were the air first enters the fuselage. :o
Stu is correct, every edge needs a radius, from the inlet all the way back to the exhaust tips. Eliminate any lips/edges where possible.

I can not see real clear in the image, but it looks like there is still a sizable lip right where the foam ends and the Stu's begin. It looks like an 1/8th inch or so. that needs to be cleaned up... Absolutely flush is best. You could be losing quite a bit from just that small lip, could be as much as 10% loss between the two fans. This is also a contributor to the fans robbing from each other, dirty flow down one fan allows other fan to pull more... This allows a back and forth pulsing or if one fan has just a slight advantage, then you get a differential to one side.

Divorcing the ducts will help reduce the fans robbing from each other, but there will still be a few % to gain from cleaning the flow at the fan.

Moving forward. :o)

Peace, Wolf
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Old Jun 11, 2012, 03:04 PM
Now in TN!
J Morgan's Avatar
Chapel Hill, TN USA
Joined Apr 2001
24,162 Posts
Man, great info here. I'm enjoying it and I don't do EDF!

J
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Old Jun 11, 2012, 05:12 PM
deltas are cool
AIR SALLY's Avatar
Tehachapi ,CA.
Joined Apr 2006
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Originally Posted by AIR SALLY View Post
do you have a wall between the inlets of the fans ? could be you need a bit of a wall to seperate them .seems to have a lot of rolling drag too
your welcome Falcon ,also remember the full scale takes 4000-5000 ft to take off in this heat ,so make sure you get a longer run ans you do have berings on your wheels right? the fan wall and the cheaters should help alot.
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Old Jun 11, 2012, 05:26 PM
Capt. Z
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Tonopah, Nevada
Joined Dec 2004
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Originally Posted by AIR SALLY View Post
your welcome Falcon ,also remember the full scale takes 4000-5000 ft to take off in this heat ,so make sure you get a longer run ans you do have berings on your wheels right? the fan wall and the cheaters should help alot.
Yeah thanks Rodger in fact you were telling me to put the wall in from the start..don't know how that fell through the cracks..you da man!!!

Just put the "V" wall in and separated the fans air supply That did it!! just ran em' up, both fans run equal now single or both at the same time makes no differance. Seems to be a big differance in thrust as well I feel quite a bit of differance from before in the force it takes to hold it back.

I think I should go to 11S also. I fully charged the packs and did a test run just now and I am right at 4000 Watts 107 amps, Fan 2 runs about 300 watts less for some reason at 3700 Watts 94 amps. My ESC's are rated to 120 amps contunious 180 burst so looks like i have room to grow a little.

Question..general rule of thumb what kind of gain in power could one expect in a situation like this by going one more cell?

Thanks again guys for all the help and advice...
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Old Jun 11, 2012, 05:41 PM
Capt. Z
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Tonopah, Nevada
Joined Dec 2004
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Running the fans just to get the batts back down to around 3.8v per cell and WOW!!! what a differance from before from wall compared to no wall. Those fans must have been just starving for air from turbulance from the two fans fighting each other..I really have to hold it back now at full throttle, before it just didn't seem to push against my hand all that hard.

After a good long full throttle run the back of the motor reads 107 degrees with the laser temp gauge.
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Old Jun 11, 2012, 05:43 PM
Fly it like you STOL it!
Endlesslag's Avatar
USA, VA, Spotsylvania
Joined Jan 2011
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Quote:
Originally Posted by falcon5 View Post
Running the fans just to get the batts back down to around 3.8v per cell and WOW!!! what a differance from before from wall compared to no wall. Those fans must have been just starving for air from turbulance from the two fans fighting each other..I really have to hold it back now at full throttle, before it just didn't seem to push against my hand all that hard.

After a good long full throttle run the back of the motor reads 107 degrees with the laser temp gauge.
that's great! More testing tomorrow?
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Old Jun 11, 2012, 06:12 PM
Capt. Z
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Tonopah, Nevada
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Originally Posted by Endlesslag View Post
that's great! More testing tomorrow?
Back to work tomorrow Next weekend I will be out on the lake bed though..
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Old Jun 11, 2012, 06:16 PM
Lee Liddle
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Carrollton, Tx
Joined Dec 2006
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[QUOTE=falcon5;21869070]Yeah thanks Rodger in fact you were telling me to put the wall in from the start..don't know how that fell through the cracks..you da man!!!

Just put the "V" wall in and separated the fans air supply That did it!! just ran em' up, both fans run equal now single or both at the same time makes no differance. Seems to be a big differance in thrust as well I feel quite a bit of differance from before in the force it takes to hold it back.

I think I should go to 11S also. I fully charged the packs and did a test run just now and I am right at 4000 Watts 107 amps, Fan 2 runs about 300 watts less for some reason at 3700 Watts 94 amps. My ESC's are rated to 120 amps contunious 180 burst so looks like i have room to grow a little.

Question..general rule of thumb what kind of gain in power could one expect in a situation like this by going one more cell?[/QUOTE ]

Without a chart on the specific fan or at least some data points, it's hard to say about the increase in power from one more cell. But with a fairly well loaded fan like the SM, you could see another 20-25a, so,let's say 122a and say 40V,that would give you another 800 to 900w per fan. Total additional power is going to be somewhere between 1.5kw and 2kw. That's a rough guesstimate, but I'd bet burger and a beer on it.

Also on the difference in power between the two fans, check all of the bullet connections for loose fitting or dirty surfaces.
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Old Jun 11, 2012, 06:52 PM
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Common sense tells me that 7.5Kwatt is nowhere good enough to fly 40 pound EDF model, 12Kwatts or good 13-14kg thrust is minimum you need, it does not take scientist to work that out, Joe.
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Old Jun 11, 2012, 07:22 PM
Another one on the way...
ysolomon's Avatar
Plano, Texas
Joined Feb 2009
2,346 Posts
jofro or anyone, how do you translate KW into lb of thrust? Is there a general rule of thumb? What other factors are you taking into consideration?

I was not aware that this model is 40lb... I'm a bit concerned too... At the same time, I will be flying an 18lb F-18 on a 4000W Dynamax fan, so my ratio is only slightly better.
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Old Jun 11, 2012, 07:23 PM
DELTAS RULE
corsair nut's Avatar
tehachapi, CA
Joined Jan 2006
21,762 Posts
i think youll be pleasantly suprised how wrong you will be a model this size is a whole differnt ball game, especially at this weight. you get 40 lbs going 130-140 mph, it will go upstairs juuuust fine. will it have killer power ratio, with tons of vertical? no, it wont. but the real T-38 doesnt either. in fact, the real one is a dog as far as thrust goes, but its a fast airframe, the real one going past mach 1 on hardly any thrust by todays standards. with 240+ mph eflux, the model might even reach 150mph.....imo thats doing damned good. i think now that andy has the thrust issues worked out, its going to fly right off that lakebed no problems.

andy, going 11s is a great idea. i say just go for 12, and only use it for takeoff and vertical manuvers. im not even sure you can buy a 1s 8000...but you should be able to get a 2s 8000...




Quote:
Originally Posted by jofro View Post
Common sense tells me that 7.5Kwatt is nowhere good enough to fly 40 pound EDF model, 12Kwatts or good 13-14kg thrust is minimum you need, it does not take scientist to work that out, Joe.
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Old Jun 11, 2012, 07:24 PM
Fly it like you STOL it!
Endlesslag's Avatar
USA, VA, Spotsylvania
Joined Jan 2011
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Originally Posted by falcon5 View Post
Back to work tomorrow Next weekend I will be out on the lake bed though..
Alright, can't wait! In the meantime I'll entertain myself trying to fix leaking retracts
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