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Old Feb 26, 2003, 07:41 PM
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optimum power system for KA Models L-39


Would like your opinions on best power system for the L39 when measured by mph/cost.
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Old Feb 26, 2003, 08:39 PM
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You might want to look at the L-39 video to see what kind of speed & power you are aiming at...

Steve's L-39: http://aeneas.ps.uci.edu/edf/mirrors/l-39_k&a.wmv

and do a search under L-39:

https://www.rcgroups.com/forums/sear...der=descending

In general it's a low drag airframe which will fly fast on relatively low power. It's also a light fuse which won't tolerate a lot of batteries.

The Kyosho AP-29L in the MF480 costs $30 and gives 60 mph or so, so the ratio is about 2. If you go with a Hacker B40 S or Kontronic Fun 400 or Mega 15/16/2 the ratio becomes 80/200 = 0.4 or so (If you keep it hanging in the garage you get 0/0 which is indeterminate ).
Last edited by Herb; Feb 27, 2003 at 03:08 PM.
Old Feb 26, 2003, 10:29 PM
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I considered using a brushed motor in my L39 until I saw that the fan in glued into the ducting and the bottom of the fuselage is sealed up. Basically it would have been a big pain to open it all up to check/replace brushes IMO. I went with the fairly cheap brushless combo of a Mega 22-20-2, Jeti 40A BEC ESC and a HW609 fan. I get pretty good speed and about 4 minutes of flight on 10 FAUP cells. I agree with Herb it is a low drag airframe and I can fly just fine on half throttle.

Cheers

Dean
Old Feb 27, 2003, 08:39 AM
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What do you really want mph or cost? If you just divide raw mph by cost, I would guess you would end up with a kyosho fan or mf480 with apl29.

I wouldn't do this however. Because of the way the fan is mounted it is a pain to do any work on the motor, so I would go brushless as a minimum.

Not sure what Herb counts as lots cells, but I have 14 1250scr in mine and I think 16 would be no problem. If you want to step out onto the bleeding edge I think you could get acceptable performance on Li-poly and really long flights.
Old Feb 27, 2003, 10:27 AM
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Hi all,

just a general question:
normal or enlarged wings on your model ?

Is there a big diffrence in flight ?

Thank's

Olivier
Old Feb 27, 2003, 10:31 AM
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Quote:
Originally posted by Olivier
Hi all,

just a general question:
normal or enlarged wings on your model ?

Is there a big diffrence in flight ?

Thank's

Olivier
the scale wing flys very well. ............gregg
Old Feb 27, 2003, 03:07 PM
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Quote:
Originally posted by Olivier
Normal or enlarged wings on your model ? Olivier
To me the enlarged wing looks odd. Don't even understand the motivation behind it ... I would go with the scale wing, it flies just fine as gregg says. Just don't overload it with batteries, 10 CP 1700 would seem a sensible choice.
Old Feb 27, 2003, 03:11 PM
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Steve's very nice L-39:
Old Feb 27, 2003, 10:59 PM
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Gentlemen,
Thanks very much for your advice. I do have the enlarged wings, guess I was concerned with wing loading and figured I could but and build the scale wing later if I wanted.
Old Feb 27, 2003, 11:57 PM
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The sport wing is noticeably not scale, but flies fine.
Old Feb 28, 2003, 03:18 AM
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Thank's for your answers,
It looks like the scale wing is the choice

Olivier
Old Feb 28, 2003, 03:32 AM
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In the flight video Herb posted of my L-39, I was having trouble with the motor.

I was not at full throttle and you can see clearly how well it flies with the scale wing at slow speeds.

I think the large wing is for PSS.

You've made the only choice.

My AUW is 42 oz.

Good luck with it!


Steve
Old Mar 01, 2003, 11:40 AM
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What does everyone here think about this model in terms of high performance? Is this the closest someone can get to the El Bandido for sleekness and low drag in a fiberglass kit already in production? What other jet is this low drag? How does this compare with thier MIG kit in terms of drag. What would you choose as a performance jet scale or not?
Last edited by GregG; Mar 01, 2003 at 11:42 AM.
Old Mar 01, 2003, 12:20 PM
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Quote:
Originally posted by GregG
What does everyone here think about this model in terms of high performance? Is this the closest someone can get to the El Bandido for sleekness and low drag in a fiberglass kit already in production? What other jet is this low drag? How does this compare with thier MIG kit in terms of drag. What would you choose as a performance jet scale or not?
between the two kits, i'd expect equal performance with the same set up. i haven't seen an L39 with 600w, but it should go 100+ like the mig.

now the el bandito, that's a ferrari in terms of performance and kit quality. although at a much higher cost, around $1500 nicely equipped. about 30% larger too..................gregg
Old Mar 01, 2003, 12:20 PM
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I built one a couple of years ago with the scale wing. It flew very fast considering the relatively low power (about 360 watts). I am building number two now. I ordered it with the long wing but I cut it down to 38". With this I will get a little less taper to the wing and along with the longer span (scale wing is 35) more wing area. The scale wing has only about 220 sq/in of area and if your going to load up on batteries and power that wing loading is going to be very high (in the mid 30's). My modified wing will give me about 250sq/in. and I feel this enough of a difference to carry more battery weight.
The mig has about 300 sq's and so guys have able to load it up with a lot of cells, I think Steve used 16-20! The mig has a very efficient straight through intake but also has a thicker airfoil and I think more overall drag than the L-39
So my L-39 number two will have 600-700 watts pumping throught a minfan with the exhaust necked down to 54-55mm and I will post a report when I test it
here is a picture of my original L-39, unfortunately a locked up aileron servo sealed its fate


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