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Oct 16, 2010, 01:59 AM
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Mr. UD's Avatar
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Ducting for EPP SUKHOI SU-39 (~SU-25 Frogfoot)

Hello scratchbuilders,

been starting to build a SU-39 made of EPP (massive). The Ducts came out quite smooth (for EPP) - so I'm not sure wether I should cover the inlet with plastc-sheet or not

-smooth surface

-my plastic-sheet is not long enough - so I would have a step if I made it out of two sheets
-sheets plus glue=weight
-too smooth is not good too

Whats your opinion?
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Oct 16, 2010, 05:04 AM
don't think you need plastc-sheet but you could paint inside. all so i whould run 4000ma 4s lots more thrust same wt. nice job you should kit
Oct 16, 2010, 12:32 PM
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Ed Waldrep's Avatar
Smoother would probably be better, especially behind the fan in the exhaust.

You could use lightweight paper and water based glue. Perhaps erasable typing paper (thin and lighter than normal copier paper), or perhaps tissue like some use to cover free-flight models.

Nice build!
Oct 16, 2010, 04:49 PM
jumpy's Avatar
I agree, the extra power from smoothing out the intakes and exhaust would outweigh the extra weight. Great job on the build, nice subject.
Oct 17, 2010, 03:08 AM
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Mr. UD's Avatar
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Thanks for the replies!
I planed to cover the nozzle with acetate sheet anyway (I only worried about the intakes - they are about 350mm (14") long - the acetate sheet is only 290mm)
I will weight the acetate sheet compared to different kind of paper - lets see how much is the difference...

I'm also thinking about reworking the intake lips - they are made of EPP and quite sharp (but soft). Maybe I will cut away 10mm from the front and replace it by a 5mm, well rounded, balsa-lip (?)

@space 1:
I'm using the 53mm 5000 kv from hk, they pull 50A each with 3s - users of this EDF told about exploding ones when they used 4s - so I guess 3s have to be enough - or I have to use another EDF
Last edited by Mr. UD; Oct 17, 2010 at 03:17 AM.
Dec 20, 2010, 03:45 PM
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LSSS's Avatar
How about an update?
Oct 15, 2011, 11:46 AM
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Mr. UD's Avatar
Thread OP
... after finishing my Nemesis Air Racer and my Henschel HS-129 B3 I decided to finish my SU-39 too - I will start with it tomorrow after a break of almost one year!

(I will post the further progress at the main threat: L-39 Build log)
Last edited by Mr. UD; Oct 15, 2011 at 12:22 PM.
Oct 15, 2011, 12:15 PM
jumpy's Avatar
I was wondering what happened to this project. Good luck, look forward to seeing it finished.

Oct 15, 2011, 12:26 PM
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Mr. UD's Avatar
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...thanks - she was standing at the end of my workbench, smiling at me for a year now - but I wanted to build (and fly!!) some propellor driven aircraft which are easier to fly for me before finishing that EDF-project

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