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Old Nov 16, 2014, 09:02 PM
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Build Log
LFI-S21 Russian 70mm Build

Well here is my 70mm build thread of the Russian LFI-S21. I had already built a 55mm version and it flies so well I just had to build it bigger. I decided to do the hot wire sectionals as Frank40 has done so often. Thanks Frank40 for giving me the inspiration to give this hot wiring a try. First off, here is the build thread from the 55mm version for those who care. http://www.rcgroups.com/forums/showthread.php?t=1642427

Okay, here we go. I have been working on this for some time now, so here is where I am. I have all the fuselage sectional parts hot wired and started gluing them together.


Specs:
Wing Span: 32" inches
Wing Area: 396 sq. in.
Length: 47" inches
Weight (no Battery) 1107 grams
Fan: 70mm 10 Blade Change Sun
Motor: Cyclone 3300kv
ESC: 120amp with external BEC
Battery: Nano Tech 4400mah 4S 65-130C rating
Battery weight: 525 grams
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Last edited by VIDEOPRO; May 11, 2016 at 09:05 PM. Reason: added specs
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Old Nov 16, 2014, 10:46 PM
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Very nice work!
What glue do you use to laminate the foam with? How do you finish the surface? There is company in Russia making similar kits called Bukvorez and I will build one in the same fashion as yours (when I summon the courage).
Thanks Eric
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Old Nov 17, 2014, 03:32 PM
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Originally Posted by 4stripes View Post
Very nice work!
What glue do you use to laminate the foam with? How do you finish the surface? There is company in Russia making similar kits called Bukvorez and I will build one in the same fashion as yours (when I summon the courage).
Thanks Eric
I am using Gorilla Glue to glue the sectionals together. The yellow expanding glue. I apply the glue drops into the 1/8" deep holes that are also about 1/8" to 3/16" in width. I only apply the glue to one side. Then get my finger wet and run over the holes spreading the glue down into the holes and rubbing any excessive amount along the flat surfaces. The water causes the glue to foam up and expand. I also will mention that the hot wire will also cut through the Gorilla Glue after drying. This allowed me to cut out my battery hatch and EDF fan housing access panel.

The surface will be sanded down and I use Ace Hardware's super light spackling to fill in any voids. Then sand re-apply and sand. Then I will paint the surface with interior flat latex paint mixed down 50/50 with clear glass cleaning fluid. Depending on what color scheme I use will determine if I apply water base Polycrylic over the paint.
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Last edited by VIDEOPRO; Nov 17, 2014 at 03:46 PM.
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Old Nov 17, 2014, 05:17 PM
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Very nice! subbed
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Old Nov 18, 2014, 04:21 PM
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More completed. Nose added. will need some more shaping to get it correct. EDF screw mounts installed. Wing, vertical stabs and elevator profiles cut out onto mat board and getting ready to cut wings etc..
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Old Nov 20, 2014, 03:17 PM
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Can you give us some details of your hotwire setup?
Thanks Eric
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Old Nov 20, 2014, 04:38 PM
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Doug:
I don't do much 70mm stuff anymore but this is really nice work and I might just have to put a few of my 70mm units back to work. As mentioned in a previous post by 4stripes, how about a little info on your hotwire setup. Also what foam are you using and where did you get it?

Ed
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Old Nov 21, 2014, 07:26 PM
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Quote:
Originally Posted by 4stripes View Post
Can you give us some details of your hotwire setup?
Thanks Eric
Sure thing Eric.

This is my hot wire setup. I had looked into building my own power supply from reading instructions right here on RCGroups. I actually purchased the 12/24 volt transformer, dimmer switch and fuse etc... from Jacobs online. Great info there about hot wire setups etc.. I just did not feel safe putting it together so I just bought a power supply that would work. I bought the Volteq GPS-1850 20v 5amp supply. Here is a link to the website. http://www.mastechpowersupply.com/dc...a/prod_65.html

As for the wire I use the smallest steel guitar string available. I made my own jig board and bows. I made three different size bows. Long, medium and a small handheld for sculpting if needed. For straight 90 degree cuts I use the jig table.

The foam I use is from Lowe's Hardware. Not all the Lowe's carry it. I have to go to the Bigger Lowe's Hardware store further down the road from me to find all three thickness' The closest store only carries the thinner sizes. The green board insulation. They sell it here in Maryland in three different thickness' First size of 1/2" thickness with a variance of up to 9/16". Second a 1" thickness with a variance of up to 1 1/8" thickness and a 2" thickness with a variance of up to 2 1/8" thickness. It is pretty darn strong stuff. I will show you some pictures later with weights on a piece hanging over the edge of the table.
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Old Nov 21, 2014, 07:38 PM
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Wings, elevators and the vertical stabs are all cut. Starting to look like a jet. Now it's time to think about my color scheme choices.
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Old Nov 21, 2014, 07:44 PM
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Color Scheme? Thinking about it. I will have to get on my Real Flight sim and fly all the color schemes I made up to see what I like flying the best.
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Old Nov 21, 2014, 08:42 PM
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Thanks for the detailed description of the hotwire system! It certainly opens up a lot of possibilities.
As you finish your plane can you post the products used as finishing foam can sometimes present compatability issues (melting the foam for example).
Thanks again Eric
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Old Nov 21, 2014, 09:02 PM
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I used the pivot method when I cut the cores for my Scorpion build.. Excellent results-- only way to cut near perfect cores!

BTW- Real nice set-up.
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Old Nov 21, 2014, 09:53 PM
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Quote:
Originally Posted by 4stripes View Post
Thanks for the detailed description of the hotwire system! It certainly opens up a lot of possibilities.
As you finish your plane can you post the products used as finishing foam can sometimes present compatability issues (melting the foam for example).
Thanks again Eric
Will do Eric. By the way, nice edf fleet you have there. Love the detail in your cockpits.
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Old Nov 21, 2014, 09:56 PM
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Quote:
Originally Posted by CoolerByTheLake View Post
I used the pivot method when I cut the cores for my Scorpion build.. Excellent results-- only way to cut near perfect cores!

BTW- Real nice set-up.
Yes, great results. My first try at it didn't go to well. Wire temp was a little to low and it stuttered throughout the cut. Key is have the temp just right.

I have seen your builds and some day I hope to get there myself.
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