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Old Oct 16, 2010, 01:59 AM
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Mr. UD's Avatar
Deutschland, BY
Joined Oct 2007
169 Posts
Question
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

pro's:
-smooth surface

con's:
-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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Old Oct 16, 2010, 05:04 AM
Registered User
USA
Joined Apr 2007
2,391 Posts
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
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Old Oct 16, 2010, 12:32 PM
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Ed Waldrep's Avatar
Las Vegas, NV
Joined Dec 1996
7,929 Posts
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!
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Old Oct 16, 2010, 04:49 PM
smithy
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Cornwall, UK
Joined Dec 2004
524 Posts
I agree, the extra power from smoothing out the intakes and exhaust would outweigh the extra weight. Great job on the build, nice subject.
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Old Oct 17, 2010, 03:08 AM
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Mr. UD's Avatar
Deutschland, BY
Joined Oct 2007
169 Posts
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
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Old Dec 20, 2010, 02:45 PM
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LSSS's Avatar
Ontario, California
Joined Apr 2007
64 Posts
How about an update?
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Old Oct 15, 2011, 11:46 AM
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Mr. UD's Avatar
Deutschland, BY
Joined Oct 2007
169 Posts
... 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)
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Last edited by Mr. UD; Oct 15, 2011 at 12:22 PM.
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Old Oct 15, 2011, 12:15 PM
smithy
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Cornwall, UK
Joined Dec 2004
524 Posts
I was wondering what happened to this project. Good luck, look forward to seeing it finished.

Phil
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Old Oct 15, 2011, 12:26 PM
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Mr. UD's Avatar
Deutschland, BY
Joined Oct 2007
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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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