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Old Mar 17, 2012, 12:58 PM
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Well the fewer bends in the intake, the better

My L-39 tends to be tail heavy, I think it's that heavy Neu 1515 motor ...

I can only imagine the CG problems wit the CS fan, which is twice as heavy as the WeMoTec fan.

Also, you can't move the fan back because of where the fan mount is located (unless you rip out the thing and entirely redo the mount).

Trial CG adjustments indicate my batteries have to move all the way forward near the nosegar. The 120A HV ESC will be right behind the batts in the nose compartment, for CG reasons.

The receiver battery also will go as far forward as I can get it to go, again for CG reasons.

With all that weight moved as forward as it will go I think I should get the CG right w/o lead weights
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Old Mar 17, 2012, 06:35 PM
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I did weigh the whole thing today ...

Mine with an 8S 3000 setup weighs 8.85 lb (4.02 kg) with 2 oz (60g) of lead weight in the nose.

It was still tailheavy with the receiver pack moved all the way forward next to the batteries, the extra lead was necessary.

Maybe I'll just use a bigger receiver pack .
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Old Mar 18, 2012, 07:40 PM
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United States, CA, Millbrae
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Quote:
Originally Posted by Herb View Post
I did weigh the whole thing today ...

Mine with an 8S 3000 setup weighs 8.85 lb (4.02 kg) with 2 oz (60g) of lead weight in the nose.

It was still tailheavy with the receiver pack moved all the way forward next to the batteries, the extra lead was necessary.

Maybe I'll just use a bigger receiver pack .
i will be using 8s 4000s maybe that will help with tailheavy
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Old Mar 18, 2012, 07:51 PM
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Yes it should, better to keep it light for the maiden though.
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Old Mar 19, 2012, 10:22 AM
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United States, CA, Millbrae
Joined Apr 2011
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just saw another post, he has CG at 55mm from LE
and the plane AUW was 8LB
but in the video i looked and flys great
i think you was going to run it at 90mm?
i will try to find the post again!
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Old Mar 19, 2012, 10:27 AM
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http://www.youtube.com/watch?feature...&v=jSFC_bRJGgc
here it is.
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Old Mar 19, 2012, 10:28 AM
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sorry it was 9.3 lb
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Old Mar 19, 2012, 02:15 PM
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55mm CG is way noseheavy ... The root chord is 31cm, and the wing has hardly any sweep !

Landings will take up several runways - and it will be prone to tipstall.

I am going to use ca. 70-80mm on mine.

http://www.rcgroups.com/forums/showp...3&postcount=23

Same CG as Savex 90mm composite edf, which is almost exactly same size (120cm ws), and has been flying fine for many years at that CG.

Both turbine and edf, no need to reinvent the wheel :

http://www.rcuniverse.com/forum/m_13..._1/key_/tm.htm (165 pages !)

The CMP factory CG is clearly a bit too far back (and awfully close to the mains).
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Old Mar 20, 2012, 07:31 PM
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looks good,i will go with your setup of 70-80mm
found some springs that fit the retracts and feels good with my fatass built of 9lbs
been very busy! slow built, but enjoy all the input from you and others.
also looking at your cmp hawk built too, have one in the box for this summer.
going to put a stumax in it on 10s
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Old Mar 22, 2012, 07:51 PM
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Herb have you Maiden??
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Old Mar 24, 2012, 12:20 PM
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Not yet ... just busy with work.

Also I am planning the maiden at the field with a nice long runway, as I don't trust the new landing gear on grass - yet.
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Old Mar 25, 2012, 05:26 PM
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white lake michigan
Joined Oct 2004
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Nice build Herb. Have a few questions. Is the duct tape your usiing the aluminum tape for heater ducts or the grey stuff everyone calls 100mph tape. Also wondering I also need to move my esc in a jet Im building and does it hurt to add all that wire from motor to esc. And one last thing where can I find the little fan to cool the esc. Good luck on the Maiden and Thanks Dave
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Old Mar 26, 2012, 12:32 PM
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Hi Dave, Thanks

The tape I use is regular duct tape, mine is called colored "Duck Tape" and is from Lowe's. I think Home Depot carries similar stuff, it is the flexible filamented type. It does not tear easily and sticks well. I suppose any quality duct tape should work.

The problem with thin hvac aluminum tape (usually on the same shelf at home improvement stores) is that it sticks well but tears easily, so it's unsuitable here.

The motor wires have to be extended so that you (a) follow the manufacturer's recommendation on keeping the battery wires short, (b) don't clog up the thrust tube with a cluncky (and heavy) esc, and (c) allow for easy servicing of the esc (ie exchange).

There is basically no limit on how long the motor wires can be (their inductance is negligible), but usually batt wires need to be < 20cm or so, otherwise it puts a strain on the esc capacitors.

The motor wire gauge should be same as the pre-soldered motor wire gauge on the esc, which is often a slight bit lower (ie thinner wire) than the red/black batt wire gauge. You can save some weight by soldering the wires directly, instead of using a connector. But I usually prefer the latter.

The esc fans I use nowadays are all from HK, they run fine on the rec. batt voltage (4-5v), there are several sizes :

http://www.hobbyking.com/hobbyking/s...idProduct=9131

http://www.hobbyking.com/hobbyking/s...1_10_Car_.html

A small graphics card fan will work too, if you can find one ...


.
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Old Mar 27, 2012, 01:54 PM
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I just received this new 120A HV esc,

http://www.hobbyking.com/hobbyking/s...ler_OPTO_.html

which looks almost like an exact copy of a YGE at 1/4-th the price ...

http://www.yge.de/artikel.php?search=yge120hv

I wonder if they have a manufacturing agreement, or just copied the hardware and microcode. Even the programming card looks identical.

It is a bit of a brick at 168g, but nevertheless can handle 14S, with built-in antispark.

Too heavy maybe for the L-39 but perhaps for something else

Edit: It seems this ESC is made by Sunrise Model : http://www.sunrisemodel.com/showproduct.asp?id=519

See YGE's opinion here (in German) : http://www.yge.de/kundeninfopop.php

.
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Last edited by Herb; Apr 05, 2012 at 12:29 AM.
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Old Mar 28, 2012, 12:22 AM
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white lake michigan
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Thanks Herb very good info and the links too. I like the esc, I will have to get one for my next setup. I can't wait till HK gets more of the stuff over in the states, that we use in are edf jets.
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