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Old Jun 22, 2012, 07:47 AM
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yeah I think your right I had my finger on the lock thread button and my finger was twitching....I counted to ten and re grouped..

I had no idea I also have terets..
LOL it comes and goes with me too........
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Old Jun 22, 2012, 10:33 AM
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Tonopah, Nevada
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The 38 is not on it's feet just yet. The new retracts are on the way. Also ordered fresh air line and some quick disconnects for the two wing and nose air line connections.

After talking it over with C/N we have a plan of attack on getting the most out the the T-38. Definitely taking Nut's advice on the exits and we talked over a few other little nip tuck things to do.

With those changes in mind I am going to employ that new on board GPS data logger and after each flight make small changes to stuff and see how it helps or hurts performance.

Also the new watt meter is on the way also so I hope to get some good numbers on the 12S setup when that arrives.

realisticly I hope to see 5000 watts per fan on 12S, I will be scratching for 5500 but not sure it will get quite that high. A grand total of 11,000 for both would be sweet but will be happy with 10,000, that would be a 2500 watt increase over what I had on the maiden.

On mail man watch for now
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Old Jun 22, 2012, 10:45 AM
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Originally Posted by corsair nut View Post
i suggested opening up the tail pipes more for two reasons...one is...these are super long pipes....closing them to normal sizes can really hurt performance. ive tried normal sized exits on long pipes and it causes too much back presure. also....with andys flight speeds beeing waaay lower than the eflux....more eflux isnt really what he needs. he needs more push. the two extra cells and bigger pipes will make a large differance in flight for sure.
+1

I've done this to two different jets and came out with way better take of and in flight speeds.

I then measure static thrust on one of the aircraft by standing the weight scale on it's edge and it was half the bench thrust numbers...for some reason exhaust ducting was choking down thrust but not upping amps...
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Old Jun 22, 2012, 10:48 AM
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Originally Posted by corsair nut View Post
i suggested opening up the tail pipes more for two reasons...one is...these are super long pipes....closing them to normal sizes can really hurt performance. ive tried normal sized exits on long pipes and it causes too much back presure. also....with andys flight speeds beeing waaay lower than the eflux....more eflux isnt really what he needs. he needs more push. the two extra cells and bigger pipes will make a large differance in flight for sure.
That's pretty interesting. It makes me question is some sort of mass flow per unit duct length can be identified for a limiting factor on larger EDF's. Simple solution being mounting the fan at the extreme aft end of available positions for a short exhaust duct. Assuming you could mount the batteries far enough forward to offset the fans and motors. Then the inlet to the fan might have to be stabilized a little just forward of the fan with a straight as an arrow lead in and center body as the long inlet duct is going to add airflow issues.
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Old Jun 22, 2012, 10:59 AM
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Originally Posted by falcon5 View Post

realisticly I hope to see 5000 watts per fan on 12S, I will be scratching for 5500 but not sure it will get quite that high. A grand total of 11,000 for both would be sweet but will be happy with 10,000, that would be a 2500 watt increase over what I had on the maiden.

On mail man watch for now
Those numbers seem very good to me. Thinking aloud... the maiden flight you were running 187 watts per pound with a lot of issues to yet be fine tuned, right? I've flown 25+ pound EDF models with 190 watts per pound and they were a more sprightly than the -38 maiden but they had the advantage of having all the ducting issues already worked out via much simpler ducting and a single 120mm fan vs. a twin with long ducts. With your updated figures at 250 watts per pound (for your conservative low end estimate)... and all the duct improvements... I think we will see a whole new airplane. It already flies very light on that scale wing (an accomplishment in itself) but now it should have some get up and go.
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Old Jun 22, 2012, 11:12 AM
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Simple solution being mounting the fan at the extreme aft end of available positions for a short exhaust duct. Assuming you could mount the batteries far enough forward to offset the fans and motors. .
Yea fan mounting position was a though call. I had to find a happy medium between thrust tube length and battery/motor wire length. If the fans were in the back battery wires would be almost 90" long and the ripple current issue came into focous.The motor/battery wire length topic is another discussion all together and many differant opinions on that as well. But I decided to split the difference and still have long battery wires of 44" and a thrust tube of 38"
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Old Jun 22, 2012, 11:20 AM
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I still think you made the best call. Long wires and balance are a reality. The exhaust ducting being anything more of a "slightly more losses" thing has been a surprise to me but I'm a layman as far as ducting goes - not being a monster garage HVAC guy I suppose most EDF's up to this point being this large, 144" long with fans in the middle and exhaust outlet being at the aft end of the tail, have been single motor high power fans so the relative ducting issues are more "relative" vs smaller fans in higher numbers running these long lengths.

Your steady problem solving and successes one by one are great to follow. Thanks for posting all of these discoveries for us to see.
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Old Jun 22, 2012, 08:14 PM
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This is an incredible opportunity to learn about large EDF's. I read each page thoroughly. Each page has a new lesson. It's stimulating to learn something you've never done before. Thanks, Andy.
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Old Jun 26, 2012, 07:50 AM
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Where did everybody go?
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Old Jun 26, 2012, 07:56 AM
Hey Guys, Watch This.......
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Where did everybody go?
Some are here.

http://www.rcgroups.com/forums/showthread.php?t=1672388

Mike
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Old Jun 26, 2012, 08:01 AM
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Thanks Mike I missed that thread.....
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Old Jun 26, 2012, 08:05 AM
Hey Guys, Watch This.......
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Yea, looks promising. With Falcon and some of the other guys involved it just might fly.
Mike
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Old Jun 26, 2012, 02:28 PM
Capt. Z
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Thanks Randy!!!

Yea Reco I in a hold waiting on some stuff to arrive in the mail. and am hanging out in the foamy section on an 81" T-38 that's being conceived.
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Old Jun 26, 2012, 07:38 PM
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Thanks Randy!!!

Yea Reco I in a hold waiting on some stuff to arrive in the mail. and am hanging out in the foamy section on an 81" T-38 that's being conceived.
Andy,,where's that one at,, I can't seem to find it. W.
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Old Jun 26, 2012, 08:02 PM
Hey Guys, Watch This.......
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Post 1885.
Mike
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