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Rans S-9 Chaos. Peter Miller's new design blog

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Well, after searching for a long time I finally found the perfect design for my type of model.

THis is the RansS-9 Chaos.A microlight powered by a Rotax engine but one like you have never heard of before.

The aircraft is fully aerobatic and is stressed to +9 and -6 G. It is built like a model and features huge control surfaces (It would even make a good control line stunter!!)

The canopy is huge but is made up from curved flat sheets of plastic.

Although few seem to have heard of it there are masses of them out there with a wonderful choice of colour schemes from solid red to really gaudy multi coloured ones.

There are a lot of variations too.Different undercarriage arrangements,Variations on the rear turtle deck and stringered or rolled sheet decks.

One unusal feature is a built in parachute. There is even a video of a Chaos which lost a wing and floated down safely

Just go on Google and search for Rans S-9 Chaos images.

Also check out the videos



Here is a 3 view of the plane/


Edited By Peter Miller on 17/06/2020 12:21:23

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Right! Buildng is under way.I started with the wings because Iwas waiting for some other materials.

The sequence is my standard method.

One wing is built flat on the board with just the lower sheeting, spares,ribs,webs and leading edge. I also reme,bered to installthe paper tube for the servo lead.

I ave learned to have the leading edge overhanging the building board soI can pin the lower leading edge sheet to it easily.

The second wing is built to the sames stage but also has the leading edge sheet added and the trailing edge capstrip. Lots of clamps at the spar and map pins along the leading edge.

chaos 001.jpg

With one wing completed so it can be lifted off the board without any twists or warps getting in. I can propit up against the other one and join them. This ensures the coreect dihedral and no warps creeping in

chaos 005.jpg

The dihedral braces can be fitted.IT this case they are simply made from1/4" sq.spruce.

chaos 006.jpg

Now the secong wing can have allits topleading edge glued on. Once that has dried the complete wing can be lifted from the board and all the rest ofthe work can be done.

On this aircraft there is nodihedral onthe top surface of the wing

chaos 007.jpg

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The canopy is going to be very scale!!! Three pieces of flat sheet over the frame members. The frame members are 6laminations of 1/32"ply about 1/8" wide over a former.

chaos 004.jpg

I started cuttingthemout of 1/8"ply and realised that they would be rather weak and then I realised that the  inside waste would make a perfect former for the laminations.

Edited By Peter Miller on 21/06/2020 12:27:33

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Quite a lot more done now.

The wings have now had the centre section sheet done.The sheet matches the full size aircraft fuel tanks. The tips and cap strips to be done and the servo mounts made.


The basic fuselage has been built. Pulling sides in at the nose does call for a 6"G clamp and one could narrow F-2 down by 1/4" to make life a little easier but that would not be as scale. The battery platform, undercarriage mounting and the plate for the wing bolt are shown ready to fit


Rear view of the assembled basic fuselage


Close upof the nose showing the battery bay and battery platform supports


The battery platform fitted and 1/4"square edges to the battery access opening. Note I apply epoxy to the battery platform and press down a piece of acetate sheet to get a perfect surface. This can then be peeled off and self adhesive Velcro stuck down. It never moves again!!!


The undercarriage mounting.I have yet to have an undercarriage come loose with this method.


THis is the plate that takes the wing hold down bolt. It is 1/8" ply underneath and 3/8" balsa on top to give extra gluing surfaces. I will use one 1/4" UNC socket head nylon bolt for this.The socket head uses a 1/4" allen key which stops it slipping off (Model fixings stocks all this)




Edited By Peter Miller on 25/06/2020 12:30:19

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What I've done in the past where a tight curve is needed at the nose is to pre-bend the sides when attaching the doublers, that works well when using something like the old Thixofix which allows some movement. A packing piece under the bulkhead position and a big weight at F2. It will spring back a bit when released but takes much of the tension (!) out of clamping the bulkhead in place.

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Managed to get quite lot more done.

The wings are now complete and ready for covering apart from the cockpit area. Those ailerons are made from 3/16" sheet

chaos 008a.jpg

The servo mounts are quite so=imply mae from 1/16" and 1/4" ply

chaos 011.jpg

The fuselage has had the top nose sheeting done. The little bit at the front only needed a bit of fiddling and trimming to allow for the bend in the sides right at the front.

chaos 3 (7).jpg

Detail of the nose section with the battery hatch in place

chaos 3 (3).jpgThe underside of the battery hatch.The catch at the front will also (hopefully) hold the cowl in place as wellchaos 3 (2).jpg The rear of the fuselage. This varies a lot on the full size aircraft. Some have the stringered area covered with solid sheet, some have much taller hump backed stringered arrangement. The area covered with sheet on my modexls is sometimes cut awayto leave a big open area behind the pilot.

chaos 3 (4).jpg

The tail components are very light and scale. Note the hard points for the rigging which is meant to be functional.

chaos 3 (5).jpg

This model is going together much faster than I expected. However some of the colour schemes that I am looking at will make up for that!!!

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A lot more has been done

The cowl was built up with laminated 3/8" sheet on the 1/16" ply cowl former


And then shaped to match the aircraft beuing modelled. Most Chaos colws are like this but a few are more like flat 4 cowls with two air intakes.


The cowl is fitted using keyhole slots and four screws on F-1



The canopy is big and made from flat sheet. This means it will have tpo be screwed down so I have fitted edges of 1/8" liteply onto the wing. There will be hoops of laminated ply fpor the frame.


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Covering the model.Well most of it is pretty standard but the fin is a little tricky. The fin fairs into the fuselage which is the same for many fabric covered aircraft such as the Piper Cub etc so you might find my methos useful for other aircraft.

I looks messy at first but it works.

This is the basic framework.


Now apply the covering to the tailplane root and theyop member of the fuselage side.


Now stick it down to the top of the fuselage and round the edge of the fin. Don't try and pull it tight or smooth at this stage. Cover both side now. Don't try and take it far up the fuselage.


Now use a heat gun CAREFULLY. becareful because the last think that you want to do is shrink the covering away from the edges. And bingo!! you should get a smooth flowing covering from fuselage and up the fin.


Here is another view of the faired in fin.


And looking from the rear


Finally tidy up any tiny wrinkles and continue covering the fuselage


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  • 2 weeks later...

Yes, The full size has a hole behind the spinner but I felt that it might not be enough to cool the ESC and battery. So I simply took a 1" hole saw and cut the lower hole through the cowling.

I am glad that I did because when I took the battery out after the last flight it was pretty warm. MInd you,7 minutexs all at full power throwing themodel round thye sky was not giving it much rest!!.

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What I particularly like is it is so unobtrusive and preserves the scale shape of the cowl.

On my Ballerina build I have altered the cowl shape for an air scoop. It looks like I could have built as per plan then done as you have.

I like a neat solution especially when it was an afterthought. Almost like doing the right thing by accident smiley

Keep the lessons coming please, it's all very interesting.



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I contacted the owner of the fullsize aircraft to get some more photos of the colour scheme.

I have now sent him pictures of the model and I will be interested in his comments. Especially as I have pointed out the non scale intake. 

Edited By Peter Miller on 20/07/2020 09:30:24

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