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Alsema Sagitta 1:4 scale

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B Sharp
Posts: 704
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: Alsema Sagitta 1:4 scale

Post by B Sharp »

The problems with the former slots continue to get worse and worse the further I proceed. Aft of the wing I have started drawing lines on the edges of formers using a straight edge between the furthest forward and furthest back formers then cutting new slots. This allows the longerons to sit in a straight line forward to aft. I will have to fill in the gaps at a later date. :(

In the centre of the fuselage things are a bit more serious. The longerons that form the edge of the cockpit were sitting well proud of two of the main formers. As these longerons are critically positioned to seat the sliding canopy they have to be precise. Consequently I have had to add extensions to the top of each former and will have to adjust the sides when it comes to adding the skin of the fuselage at that point. :(

I am now regretting not redrawing the fuselage plans and using “Devcad” to draw the formers. I’m sure I could have made a better job than the old hand drawn plans. :cry: :cry: :cry:

Brian.
Attachments
Re-possitioned slots for longerons aft of wing.
Re-possitioned slots for longerons aft of wing.
More problems with the centre section.
More problems with the centre section.
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B Sharp
Posts: 704
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: Alsema Sagitta 1:4 scale

Post by B Sharp »

While I wait for more ¼ square spruce to arrive so that I can complete the longerons I have started to fill in the front of the fuselage.

Now normally I would have planked the whole of the fuselage with 1/8 balsa, however this plan specifies a different method. The plan requires me to infill between each of the longerons and formers with ¼ balsa cut and tapered to shape. This seems a very odd way of doing things and I am not all that happy with the results so far. Once the fuselage is covered in this manner back to the rear of the wings it can all be carved and sanded. The final instruction is to coat it in filler and sand back to the required final shape.

Has anyone tried this before and does it make a good job?

Brian. :shock: :shock: :shock:
Attachments
In-filling between the longerons.
In-filling between the longerons.
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Cliff Evans
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Joined: 29 Dec 2019, 15:13
Location: Bristol
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Re: Alsema Sagitta 1:4 scale

Post by Cliff Evans »

Vic Steel used this method on most of his models. I personaly don't like this method.
https://lasercutsailplanes.co.uk
https://patteaklegliders.co.uk
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B Sharp
Posts: 704
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: Alsema Sagitta 1:4 scale

Post by B Sharp »

This is the first time I have built one of Vic's designs so was totally unaware of his methods. I have seen a number of his aircraft flying and they looked just fine. However I supose I will just have to continue and see how I get on.
Brian. :?
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B Sharp
Posts: 704
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: Alsema Sagitta 1:4 scale

Post by B Sharp »

As my fresh timber has not yet arrived I did a little more of the infilling of the front end of the fuselage. In doing so I blocked out the front cockpit coaming as well. When all the glue had set I rough carved with a David Plane and then sanded back with 80 grit paper. After I had done a bit of filling with wood filler and then sanded that back as well, the nose of the fuselage was looking better than I had expected.
I still don’t like this form of construction but I now think I will be able to get a half decent finish after all.
Brian. :)
Attachments
Nose blocked out and ready to carve.
Nose blocked out and ready to carve.
Filled and sanded - not too bad.
Filled and sanded - not too bad.
Jilles
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Joined: 22 Mar 2015, 10:27
Location: Australia
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Re: Alsema Sagitta 1:4 scale

Post by Jilles »

glassing with a layer of 25gr/m2 cloth will make it even better and prevent dents in the softer balsa during handling
I did the same on my 1:3 ka8
the way to go on strong compound curves when the finish will be a paint job
You need weight in the nose anyway just as well make it useful.
Attachments
IMG_20200520_093604.jpg
IMG_20200520_093610.jpg
IMG_20200520_100838.jpg
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B Sharp
Posts: 704
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: Alsema Sagitta 1:4 scale

Post by B Sharp »

Jilles, thanks for the encouragement to continue with this form of “sheeting” on the fuselage. It is helpful to see that other builder successfully uses this method as well.
The infill between the longerons/formers continues to the rear of the wing. Aft of that the fuselage is covered in 1/64 (0.4mm) birch ply which will be wrapped round the structure.
It was my intension to cover the whole fuselage and fin in 50gm/m2 glass cloth & epoxy as I have done so often in the past. I would then skim with Upol where needed and sand back to a suitable finish before painting.
My timber has just arrived so I will concentrate today on finishing the application of the longerons before continuing the sheeting of the front end.
Brian. :)
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B Sharp
Posts: 704
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: Alsema Sagitta 1:4 scale

Post by B Sharp »

It’s been a couple of weeks since my last post and the Sagitta has progressed a little. Most of the front fuselage planking/sheeting is now complete. I will complete the underside once the airframe is removed from the jig. By the way, I still don’t like this form of construction! :?

I realised that I can’t sheet the rear of the fuselage until I had the fin assembly built. Having built the fin I found I required the rudder to check everything fitted properly so that was built as well.

I now find that it would be a good time to built the tailplane so that it’s a bit easier to get all that aligned without being fixed to the fuselage. So that’s next on the board.

Brian. :)
Front of fuselage pretty much built.
Front of fuselage pretty much built.
Fin and rudder.
Fin and rudder.
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B Sharp
Posts: 704
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: Alsema Sagitta 1:4 scale

Post by B Sharp »

I have had the whole day to myself in the workshop today and have started on the tailplane construction. Once again the ribs as shown on plan don’t match up with the tailplane plan view and I have had to re-draw about half of them. However the tailplane halves went together quite well and the joiner tubes (carbon, it was what I had of the correct size) matched up perfectly. I consider that to be quite a result.

The top sheeting is now in place and I have started making provision for the elevator servos. The servos I have chosen are small but are alleged to put out 1.75kg of torque at 6.0 volts. I have estimated that this will be more than enough for the designed elevator size provided that I can make the hinges as free moving as is possible.

Brian. :)
Basic tailplane structure.
Basic tailplane structure.
Top sheeted and servos possitioned.
Top sheeted and servos possitioned.
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B Sharp
Posts: 704
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: Alsema Sagitta 1:4 scale

Post by B Sharp »

I finished sheeting the tailplanes today by adding the undersides and servo hatches. I then set about installing the joiner tubes in the fin. I have used the same 6mm carbon tubes that I used in the tailplane halves.
I spent an absolute age setting the front tube to ensure that It was mounted square in every direction before locking it in place with cyano. After that setting up the rear tube was a piece of cake using the tailplane halves as a jig.
The only downside of using carbon is that when you sand it you get black dust everywhere and it stains the timber sheeting. However that will eventually disappear after a glass/epoxy/paint finish.
Brian. :)
Completed tailplane halves.
Completed tailplane halves.
Carbon tubes mounted in the fin.
Carbon tubes mounted in the fin.
the almost complete tail assembly.
the almost complete tail assembly.
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