Sbach3D 65 size - Design and Construction

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Sbach3D 65 size - Design and Construction

PostPosted: Mon Jan 04, 2010 6:21 am

Time for a larger version of the Sbach. Everyone says bigger is better so we will see how it works out. Not a lot of 65 size slabs out there, Mojo65 and the OMP 67” Fusion and 65” Yak. Do not know why, perhaps anyone considering a bird this big would just as soon go up to the quarter scale fatties. This is going to be my winter works project so progress will be slow compared to my previous builds, also I am going to be a lot more detailed in this build.

Design

I scaled the 45 up to 65 size then increased the span and aspect ratio and thinned the wing to keep it from getting too floaty. Larger airplanes are inherently more stable so I have made the wing span longer than the fuse total length. While the span to length ratio is more the tail moment arm is the same, by doing this I am hoping to get the smoothness of the 55 and the tumbleness of the 45 in one package.

I am expecting to have the total all up weight to come out at less than 8 lbs. At least that will be my goal.

Specs:

Wing Span ----- 65.0 in
Wing area ----- 1250 sq in or 8.7 sq ft
Length -------- 63.5 in
Flying weight – 7½ - 8 lbs
Wing loading -- 14 – 15 oz sq ft
Last edited by TriFlyer3D on Fri Sep 16, 2011 11:12 am, edited 1 time in total.
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PostPosted: Mon Jan 04, 2010 6:22 am

Power

Now we have to decide how to power this beast. Glow is easy, an OS 120AX would be ideal for the 2 stroke fans and any of the .120 to .140 size 4 strokes would also work well.

Epower has turned out to be a bit more difficult, at first I had decided to go with an F3A equivalent system on 10S, this would be super broverpower but after checking out the total weight of such a system I am not quite sure if that is the right thing to do. The F3A outrunner is a whopping 27.6 oz, we will need a 100 Amp controller at 4.5 oz. And at least 2 5S 3300Mah batteries at 31.6 oz. This comes to a total of 63.7 oz. (almost 4 lbs!) and we still need the mounting hardware. Hanging that much weight on the nose of the plane is probably not going to work very well either.

A smaller system on 8S should still be more than enough power and quite a bit lighter. The OS 120AX weighs 31 oz + 3 oz for tank and lines + 10 oz for fuel + 3 oz for servo and linkage = 47 oz.
8S size outrunner is 17.5 oz + 4.5 oz for controller + 26 oz for 2 4S 3300 = 48 oz.

A 1512 series Neumotor would work and be a bit lighter as well.

Anyways I think I will wait until I get it framed up and see how much weight it is going to take to get it to balance before I make a decision.
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PostPosted: Mon Jan 04, 2010 6:23 am

Construction

I am going to stick with the wing joiner block system, despite the earlier problems with the Sb45. Now that we have everything worked out I am sure this way is better than the wing tube method. Transferring the fuse load to the wing directly at the wing spars has to be better than transferring it through a tube and 2 or 3 plywood ribs.

I have decided to go with a fuse width of 5/8”. A 5/8” tube is almost the same strength as 2 1/2” tubes and lighter as well, and a 3/4” tube would be way more than is needed for a 65 size plane.

I am constantly surprised at how few scratch builders there are here especially since our planes have such a high mortality rate. One would think that with the high cost of kits and arfs in the larger sizes that many would do it for the cost savings alone. I ordered more than enough wood from Clay at The Balsa Store to build two Sb65’s and the cost was only about $80.00.

The only difference between a scratch built and a kit is a few parts to cut out, on all the Sbachs I have tried to keep the amount of cut parts to a minimum,

To cut out a kit all you really need is two power tools, a scroll saw and a small 8” drill press. They do not have to be anything special, you can probably get both of them on sale from Harbor Freight for about $120. With 65 size kits costing over $150 one could almost save enough on one scratch build to pay for the tools.
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PostPosted: Mon Jan 04, 2010 6:24 am

Full size printed plans on D size paper with patterns for all the parts are available, pm me for details.
Last edited by TriFlyer3D on Sat Feb 27, 2016 1:09 pm, edited 5 times in total.
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PostPosted: Mon Jan 04, 2010 6:25 am

Build

Cut the wing, aileron, fuse, rudder and stab layout drawings from the plans sheet. Allow enough room as needed around the layouts for taping to the build table. Cover them with wax paper or your favorite ‘keep the parts from sticking to the plans’ material.

Cut out the rib patterns from the parts sheet leaving about 1/8” all around for final cutting. Glue them to the 1/8 X 3 X 36” balsa sheet. If you lay them out carefully they will just fit on 3 sheets. Note that you will need to stack two sheets together for cutting to get two sets of ribs. I usually stack up 4 sheets for an extra set, it is no more effort to cut and it is always good to have an extra set. While cutting keep a piece of scrap wing spar material handy to check the fit in the rib cut out for the spar.
Attachments
Sb65-1.JPG
All the ribs on three 1/8 x 3 x 36” balsa sheets.
Sb65-2.JPG
Cutting out the rib outline 4 at a time.
Sb65-3.JPG
Checking the spar cutouts with a piece of wing spar.
Sb65-4.JPG
Cutting out the rib lightening holes.
Sb65-5.JPG
A complete set of cut ribs.
Last edited by TriFlyer3D on Mon Jan 04, 2010 6:50 am, edited 1 time in total.
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PostPosted: Mon Jan 04, 2010 6:26 am

Cut out the nose doubler, servo trays, root rib doubler from the plans sheet allowing about 1/8” all around for final cutting. Glue the patterns to the 1/8” plywood and cut out the parts.

Do the same for the wing spar shear webs and hatch from 3/32” plywood.

Cut the 5/16 X 3 X 24” balsa sheet in half and glue one on top of the other to make a 5/8” thick lamination. Glue the wing attach block and the top nose block patterns to it and cut them out.

Lay and cut out the tail parts from the 3/8” thick balsa sheet.

Remove the fuzzies from the edges and sand all the parts smooth.

Now we have ourselves a kit.
Attachments
Sb65-6.JPG
Wing attach block and top nose block patterns glued to the 5/8” thick material.
Sb65-7.JPG
Fuse nose pattern on the 3/8” balsa.
Sb65-8.JPG
All the cut parts for the wing joiner system.
Sb65-9.JPG
All the cut parts for the tail.
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PostPosted: Mon Jan 04, 2010 9:01 am

Looking good, Ron
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PostPosted: Mon Jan 04, 2010 9:27 am

Your a sick man Ron! :wink:


Keep up the good work! :D
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PostPosted: Tue Jan 05, 2010 7:24 am

Wings

The wing should be built first. The wing attach block and the root ribs are fitted together as an assembly and the wing built around it. This way when the wing attach block is glued in the fuse we will be sure the wing will fit to it properly.

The wing is built in two panels and both panels are built together, upside down over the wing plan layout which is drawn upside down, that is the right wing is on the left side on the plans.

Start by selecting the two root ribs, the 5/8” balsa wing attach block and the two 1/8” plywood rib doublers marked for the attach bolt and the wing locating dowel hole. As accurately as possible drill out a 3/32” pilot hole in each of the hole locations.

Lay one of the root ribs on the build table and using a couple of scrap pieces from the wing spars and the 1/16” plywood wing shear web or a scrap piece of 1/16” ply as a gauge, glue the 1/8” plywood rib doublers in place. Use a 3/32” drill bit in the pilot holes to line everything up. Do the same for the opposite rib. Be sure to make a right and left side.
Attachments
Sb65-10.JPG
Root ribs and wing joiner block lined up.
Sb65-11.JPG
Root ribs with ply doubler glued to them.
Sb65-12.JPG
Trial fitting the pocket for the wing joiner block assembly. How it looks from inside the wing.
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PostPosted: Tue Jan 05, 2010 10:30 am

Brutus do you have mine built yet?
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PostPosted: Tue Jan 05, 2010 1:41 pm

funflyr wrote:Brutus do you have mine built yet?


Still waiting for Ron to post plans... :wink:
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PostPosted: Tue Jan 05, 2010 3:01 pm

So I am curious why you went with the 45 verson tabs rather than the tube verson that is on the 55?
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PostPosted: Tue Jan 05, 2010 3:11 pm

:popcorn: 8) :popcorn:
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PostPosted: Tue Jan 05, 2010 10:37 pm

Zamfir wrote:So I am curious why you went with the 45 verson tabs rather than the tube verson that is on the 55?


The thing about the 55 is that the second rib takes all the transferred load from the fuse to the wings. This plywood rib transfers the load from the tube to the wing spars. With more Bros wanting to put the batteries in the wings it would mean cutting this critical rib. One could make the tube longer and make the third or fourth rib plywood but this adds a lot of weight without any gain in strength.

The wing joiner block system transfers the load directly from the fuse to the wing spars, which I think is the way it should be. It is lighter and easier to build than the tube system, and if you cut out the leading edge ribs to make room for the bats it will not affect the wing structure.

I know some are leary about the joiner block system after Rookies failure, but I think it was a blessing in disquise, it showed a possible weakness in the build which has been rectified. There was a reason I sent one of the prototypes to Rookie, I knew if anyone could break it he could, and he did. Thanks Rookie, sorry about the receiver tho.

All of the Sbachs are prototypes, they are new designs and an experiment in new ideas, one cannot try something new without having some risk.

Maybe it is a bad idea and it will not work, I dunno, but I want to try it. I have not been able to break mine and I have tried to.

I am seriously considering building another 55 with the joiner block system, a lighter build for electric power only and room in the wings for the batteries.
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PostPosted: Tue Jan 05, 2010 10:46 pm

I've at least got the wings for the .45 on the board,... Progress is slow,... I"m a bit burnt lately, but it'll live again as an R-wing,... I'll be doing everything I can to make sure this wing doesn't fail,...

EXCEPT for the way I'm gonna fly it! :twisted: I'm gonna tear it off again if it is possible.

Don't worry about the RX,... it was bound to happen sooner or later that I'd have a plane tear a RX in half on impact. :shrug2: With the way I fly I'm really surprised that was my first! :twisted:
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PostPosted: Wed Jan 06, 2010 12:13 am

Gotcha. I think the tab method can work well. I was just wondering the reasoning and that makes purfect sense. Thanks!
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PostPosted: Wed Jan 06, 2010 6:53 am

Clamp the ribs to the wing attach block using the 3/32” drill bit in the holes to line everything up. When you are satisfied that all is straight and lined up, drill through the ribs and block with a 7/64” drill bit for the 8-32 wing bolt, then drill through 3/8” at the back of the rib for the 3/8” wing locating dowel. Take the right side rib (the one opposite the wing hatch and drill it out for the 8-32 T nut. Fit the whole assembly together with the bolt and 3/8” dowel. Put some wax paper between the wing attach block and the root ribs to keep from accidentally gluing the wing to it.
Attachments
Sb65-13.JPG
Ribs and wing joiner block lined up.
Sb65-14.JPG
Drilling out for the 3/8” wing locating dowel.
Sb65-15.JPG
Root ribs and wing joiner block assembled.
Last edited by TriFlyer3D on Wed Feb 10, 2010 4:34 pm, edited 1 time in total.
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PostPosted: Wed Jan 06, 2010 8:02 am

I think I might need one of these. Subscribed,
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PostPosted: Wed Jan 06, 2010 10:49 am

Will I get to fly one in South Kansas City? Please!!!!!!!!
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PostPosted: Wed Jan 06, 2010 12:29 pm

Very nice!! :popcorn:
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