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Sep 27, 2011, 02:05 AM
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Build Log

My First Scratch Build

So here we are finally at the beginning!!

To give you some background, I have built a number of arf's and a couple of balsa kits but now I wanted to move to the real thing

I have noticed that many of you guys here are so well versed in scratch building that when you are making your build logs you skip over a few points and beginners like me can't understand a bunch of stuff in them, because of this i'm going to do my best to log as much detail as possible in the hope that others can learn from it.

On that note when i'm making the log if I miss word or miss describe anything I would like one of you guys to jump in and correct me.

I also need you to jump in at any time and help me to figure out things and hopefully prevent mistakes!

Finally and most importantly.......

.............I really want to thank LuvEvolution7 his kind words help and encouragment are what made me go from thining about doing this for months to finally doing it, he taught me in 2 days more about scratch building than i learned in who knows how long of thank you!

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Sep 27, 2011, 08:12 AM
BOOM! I mean't to do that...
RCoomber's Avatar

This sounds fantastic! What plane are you thinking of building?

Sep 27, 2011, 02:27 PM
Registered User
So lets begin with materials,

Luvevolution7 directed me to the dollar tree for my depron, they call it poster board and it has paper on either side.

You have to soak the paper with a sprayer then it just peals right off, I was worried that it would take a long time but it doesn't, I brought a whole box of 50 sheets and it took me 1 hour 20 minutes to strip them all.

The box cost $50 and i figured that the same ammount of foam would usually be over $200 so its well worth the time.

when removing the paper if you make it to wet it will tear all the time if you don't make it wet enough it won't come off properly and you will get a little pitting in the depron.

see in the pricture when its right it comes of in a nice sheet.

secondly, plans......

I'm using this (thanks for the info luvevolution7)

I have printed out the 109% plans which I believe are for a 70mm and I have blown them up to 150% to make a large 90mm.
Sep 27, 2011, 02:44 PM
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Hey RCoomber I used to live in Bath before I moved to LA, hows the flying over there?
Sep 27, 2011, 02:47 PM
Registered User
Since i'm building a larger plane and the depron I have is only about 4mm i decided to glue pieces together to give me a thicker fuse!

Here is the glue i'm using, FYI it comes out like spray paint so make sure your work area is ready for it.

Make sure once you glue it you put the sheets on a nice flat surface to dry, you don't want warped panels

Sep 27, 2011, 03:46 PM
Registered User
LuvEvolution7's Avatar

if you are using the foamboard method, I forgot to mention can always leave the paper on a few key pieces, such as in the area around the fan. the paper will add a bit of weight, but will add considerable strength in that area. mix that with balsa, basswood, etc and it will make for a very strong section of the airplane. with my 757, most of my formers are foam only, but every so often, I have key bulkheads that I've left the paper on for the strength it gives the airframe. you will only be talking about a few ounces extra for the entire build, so it's something to think about. not saying you should keep the paper on some pieces, but rather suggesting that you think about the option in key structural areas of the build. by the way, you are welcome for the help. that's what we're here for.

Sep 27, 2011, 03:48 PM
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LuvEvolution7's Avatar
be careful about doubling up too many parts of the aircraft. believe it or not, the thickness of the single sheet is enough for a 90mm size plane. I can see in areas of the fuselage sides where you might want some roundness to it, rather than the flat sides of the plan, I would keep adding pieces till there's enough to sand to a rounded shape.
Sep 27, 2011, 04:09 PM
BOOM! I mean't to do that...
RCoomber's Avatar

Its great down in Westbury. We have the Westbury white horse which offers some of the best slope soaring ive ever come across. Up near Melksham is Keevil airfield which has a fantastic flying club which i will be joining. Its definitely better than the midlands where i use to live. That was far to flat
Sep 27, 2011, 04:12 PM
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LuvEvolution7's Avatar
tell me about it. I used to live in the West Midlands and we had to go to Shropshire to slope soar, or out to Malvern.
Sep 27, 2011, 07:28 PM
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Cool, I didn't go crazy with the glue so i can change out some parts and get the best of both worlds.

I removed all the paper already but I want to glass the insides as you suggested so it should be fine
Sep 27, 2011, 07:34 PM
Registered User
ok next step is to cut out the paper paterns and then cut them out of foam

I just taped my cut out templates onto the foam then cut around them with a sharp knife.

some of the pieces were larger than one sheet of foam so i just glued the foam together with overlapping edges!

I put lines on my foam so that i could tell which way up they are supposed to be, i later realized that i didn't need to do this for this item but its better safe than sorry!
Sep 27, 2011, 07:41 PM
Registered User
this is where i'm up to now!!

figured out my jigsaw puzzle and taped it all together ready for glueing later!
Sep 27, 2011, 07:45 PM
Registered User
ok time for some questions,

first I'm not sure if i have the canopy sill in the correct place? its the funny shaped piece I photographed.

Second is about the wings, should i have hollow or foam wings, what type and how should i create my aerofoil?

do i need to worry about aerofoil for the horizontal stab or just make it smooth?

same with vertical stab?

where should i get my fiberglass from? i'm in LA is there anywhere close to here?

what type of epoxy resin should I use, just regular automotive stuff watered down?

what should I water it down with?

do you guys glass then spackle or the other way around?

are you just using home spackle or automotive filler?

I want to make the inlets %85 fsa, I have an Fsa calculator on my computer, do i use the bifuricated calculations?

thanks everyone

Sep 27, 2011, 11:13 PM
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LuvEvolution7's Avatar
ok, I'll go through this in point by point form.

the canopy looks ok to me. it just needs to be placed and shaped properly

if you are doing a built up fuselage, it's a good idea to also do built up wings. you can make a jig to make sure you build straight, or try another method. I'm sure you remember us talking about using a symmetrical airfoil so I'll assume you are going with that method. the easiest way to build a wing straight, is to cut out all your airfoils first. make sure you draw a line through the center of your foil from front to back. also, choose a spot along the entire span of each wing, so you can put a spar through there, from root to tip. you'll also want a leading spar and a trailing edge spar, so make cuts into your foam so everything fits. remember that you will also be skinning the wing, so your LE and TE spar, should come up above the foil surface, so your skin can sit flush with it. then you assemble all this on a flat surface, but assemble it only as an upper half. once this is built and you know it's straight, simply glue on the other halves of te foils to the under side of the wing. add your LE and TE spars to the bottom and then you are ready for sheeting/skinning. it would be prudent to make root and tip jigs here, so you can get some washout into the tips. 2 degrees max should be enough. so, using the center point of the foil, draw a line that is roughly 2mm higher at the TE and roughly 2mm lower at the LE of the foil. make sure everything is square and cut out that piece. what you are essentially doing, is creating a cradle for the root and tip to sit in, so that you can skin the upper surface with the correct amount of washout. the skin will allow you to build the washout right into the wing, by setting it in place once it's glued. I think it's also proper to point out that your root incidence should be zero and be inline with your thrust line. so, make your root cradle at zero incidence and your tip cradle at about 2mm (up) at the TE and 2mm (down) at the LE. make sense? if not, we can go further into the wing assembly, once you get to that point.

for the vertical and horizontal stabs, simply round off the leading edges. for the trailing edges, I glue a thin strip of balsa to the mid point of the surface. then I choose a spot an inch or so from the TE and sand from there to sharpen the TE to the balsa strip.

you can get fiberglass from any automotive or marine supplier. I'm not sure if you'll be able to get glass light enough though. most auto and marine applications start around 2oz or so. you'll need about 1oz or less if you can get it. you may need to go to a hobby shop for this, or order it online.

be careful how you water down epoxy. you weaken the epoxy by doing this. if you are going to, be careful about going any more than 25%. to water it down, use denatured alcohol that's available at pretty much any pharmacy.

for epoxy, agood finishing resin is probably your best bet, although I've used 30 minute epoxy with good results.

once your structure is finished, this is when you spackle. remember that FG will take on the characteristics of what's underneath, so imperfection will show through. spackle only as much as you need to get straight, then FG. regular spackle is fine. I use LePage's instant stuff with good results. once you've glassed the fuse, you can use spot putty, thinned, then use a credit card to wipe it all over the fuse. sand it, then prime, sand, prime, sand as much as you need to. remember the more of this stage, the heavier you'll be. then paint. only spray as much paint as it takes to cover and no more. the less weight, the better off you'll be.

for inlets, you need to know the FSA of the fan. generally, full FSA is about 4965mm squared for a typical 90mm fan. 85% of this is 4220mm. half of that is 2110, so that's how big your inlets need to be on each side, give or take a few. remember to use a nice rounded lip and count half the lip as part of the total area, not just the throat of the inlet. so, if you use 6mm thick foam for example, count 3mm all around as part of the total area, not just the inside of the inlet.

hope that all helps for now.

Sep 28, 2011, 02:28 AM
Registered User
Hey Rich

Yeah it does make sense i think, so your saying that the LE is effectively 4mm lower than the TE and the tip while the root remains straight with the thrust line (parallel with the center of the fuse line) right.

I remember the talk of symetrical aerofoils and i'm deffinatly going with it so that it handles better, I also remember you saying that thinner is faster while thicker has more lift!

And I believe your saying that I should make ribs, Right? do i just make them however thick I wish slowly reducing the size towards the tip or is there some method to making them correctly?



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