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Alsema Sagitta 1:4 scale

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B Sharp
Posts: 700
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: Alsema Sagitta 1:4 scale

Post by B Sharp »

The construction of the tail feathers is now complete. The tailplanes are finish sanded and are drilled for Robart pin hinges. The elevators are also finish sanded and similarly hinged. The slots for the epoxyboard control horns have also been cut. I was very tempted to continue by covering the tailplanes and elevators with Diacov1000 but I decided to err on the side of caution. So many things have gone wrong on this build that waiting till the fuselage and wings are completed seemed a sensible option.

The fuselage has been removed from the jig and the front underside blocked in with 6mm balsa. The 3mm alloy undercarriage mount has been securely glued and bolted to the 6mm ply fuselage crutch. I have also now created a floor for the cockpit and installed a servo and receiver mounting tray.

My last job this afternoon was to go over all the seams and blocking on the forward fuselage filling the gaps (of which there were many) with Ronseal lightweight timber filler. The image below shows why I still don’t like this method of construction!

Brian.
Servo/Rx mount and cockpit floor.
Servo/Rx mount and cockpit floor.
Undercarriage mount.
Undercarriage mount.
This is why I dont like this construction method!
This is why I dont like this construction method!
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RobbieB
Posts: 530
Joined: 07 Mar 2015, 22:22
Location: North West

Re: Alsema Sagitta 1:4 scale

Post by RobbieB »

Hope that Ronseal filler is good stuff Brian - just ordered some. My last tub of Red Devil wouldn't go off.

Definitely not a nice form of construction that Sagitta - not sure how much strength it adds to the structure either.
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B Sharp
Posts: 700
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: Alsema Sagitta 1:4 scale

Post by B Sharp »

Robbie, Yes you are right . If I had thought things through before starting I would have reduced all the formers by 1/8 inch all round and then planked the fuselage as I normally do.
The Ronseal filler is fine, I have used it for all wood filling for years now. It goes on easily, dries to a crisp finish, is easily sanded and tastes of strawberries. (just joking about the last bit) The only problem I have found is that if you open the tin and then set it aside for a couple of months it can go hard.

Today I sanded off the filler on the forward fuselage and it looks a little better. I prepared the rear fuselage for sheeting. I spent an hour or so making a template for each side of the fuselage then marking the 1/62 ply sheet before cutting. I have now marked up the inner sides of the 1/64 sheets with the former and longeron positions ready to apply PVC glue prior to ironing into place.

Brian. :)
1/64 ply skins almost ready to attach.
1/64 ply skins almost ready to attach.
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Peter Balcombe
Posts: 1336
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: Alsema Sagitta 1:4 scale

Post by Peter Balcombe »

B Sharp wrote: 10 Feb 2022, 14:59 I have now marked up the inner sides of the 1/64 sheets with the former and longeron positions ready to apply PVC glue prior to ironing into place.
Brian,
If you apply PVA to the fuselage contact areas & then temporarily place the skin piece, it will transfer glue to the skins where it was on the fuselage side. Remove the skin & the glue imprint should be there. Let the glue dry & refit to iron on.
Makes things much easier when you have long D box skins & the like. (But I’m sure you knew all this anyway ;) )
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B Sharp
Posts: 700
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: Alsema Sagitta 1:4 scale

Post by B Sharp »

I have done quite a bit on the Sagitta in the last few days.
I cut up half disks of church roof and attached it each side of the nose cone. This will be covered with filler when I skim coat the whole front end.
The rear fuselage skins went into place with very little trouble at all. However I am disappointed that the 1/64 ply is so thin that the underlying structure shows through. If I had used 1/32 ply for the skinning it would have held the profile rather better but would have been twice as heavy. However I can’t do anything about it now. :?
The fin was fixed in place after much fettling and checking and appears to be perpendicular to the fuselage and the tailplane is in line with the datum line. Result! :D
The elevator servo cable (with plugs and sockets fitted) running to the receiver has been installed and attached to the framework to keep it in firmly place. I am using a PTFE tube and bowden cable for the rudder and that has also been installed. :)
Finally the very rear of the fuselage has all been blocked in and sanded to profile. :)
Brian. :)
Lots of church roof!
Lots of church roof!
Skinning added.
Skinning added.
Fin in place and fuz blocked in.
Fin in place and fuz blocked in.
Starting to look like a fuselage!
Starting to look like a fuselage!
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B Sharp
Posts: 700
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: Alsema Sagitta 1:4 scale

Post by B Sharp »

More compromises!

I had intended to have an opening canopy on the Sagitta. On the prototype there is a front wrap-around windscreen with the rear canopy sliding back on rails. Now, all of this is shown on the plan, and I intended to set it up as per instructions. I spent some time making up the sliding rails and it was only when I tried to incorporate them onto the cockpit opening that I realised that there was a major problem. The fuselage sides are not parallel but taper towards the rear. The front windscreen will fit without a problem but the rear canopy section will never slide as the distance between the rails narrows all the way back.

I went back and checked the plans and they show the fuselage being parallel between F4 and F5 and then tapering back through F6 and beyond. The rails as shown are straight all the way back as far as F6 (how does that work?). When I checked the drawn formers on the plan F5 was narrower than F4 and F 6 was narrower than F5. Since I used the drawn formers in my fuselage build, it was always going to be tapered!
I left the workshop in disgust!

Having calmed down I decided to make the rear cockpit canopy totally removable. The rear canopy frame has been cut and will now be held in place with button magnets at the rear and piano wire pegs at the front. I am not happy but it is the best compromise I can make. I have to say that this project is within a whisker of getting thrown in a corner and allowed to rot!

Brian.
The tidied up cockpit area.
The tidied up cockpit area.
Plan View showing tapering fuselage sides.
Plan View showing tapering fuselage sides.
Barry_Cole

Re: Alsema Sagitta 1:4 scale

Post by Barry_Cole »

Stay with it Brian....

8-) 8-) 8-) 8-)

BC
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Trevor
Posts: 136
Joined: 19 Jul 2016, 16:29
Location: Hampshire
Contact:

Re: Alsema Sagitta 1:4 scale

Post by Trevor »

Yes, I'm sure there must be an ancient Chinese saying along the lines of 'The light shines brightest at the end of the darkest tunnel' !
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Philkiteflyer
Posts: 93
Joined: 17 Mar 2015, 21:53
Location: Invercargill, NZ

Re: Alsema Sagitta 1:4 scale

Post by Philkiteflyer »

Trevor wrote: 17 Feb 2022, 07:58 Yes, I'm sure there must be an ancient Chinese saying along the lines of 'The light shines brightest at the end of the darkest tunnel' !
Whooo . . That's deep man . . ;)

I did a bit of web surfing and may have the answer. I found some pics of canopies open and I 'think' (just my quess :? ) the canopy slides on the front two and a central rear slide of some sort.
I have attached the photos to show why I think this.
Maybe I'm clutching at straws . . . maybe someone can get access to the full size to clarify this puzzle.

Good luck
Phillip C
New Zealand.
Attachments
This one shows a gap behind the front slider - marked with red line. You can clearly see daylight under the frame behind that.
This one shows a gap behind the front slider - marked with red line. You can clearly see daylight under the frame behind that.
This one shows the central rear 'something' and the line shows what I think is the total travel length of the front sliders.
This one shows the central rear 'something' and the line shows what I think is the total travel length of the front sliders.
This canopy is open and you can see some sort of strut - possibly telescopic.
This canopy is open and you can see some sort of strut - possibly telescopic.
Sagitta Canopy-Rear.JPG (8.49 KiB) Viewed 1149 times
"Keep it simple stupid"
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B Sharp
Posts: 700
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: Alsema Sagitta 1:4 scale

Post by B Sharp »

Thanks for the images Phillip. This is exactly what I had envisaged building when I started this project. It is also what is shown on part of the plan and in the magazine write up which accompanied the publication of the plan.

However it was only once I had constructed the side rails from the plan and did a trial fit that I realised that they would not work. At that point I had even produced the sliding tube mechanism for the rear of the canopy.

As I said in my last post, the sides of the fuselage taper inwards from F4 (the break in the front/rear canopy) aft. If I were to place the rails on the fuselage sides as directed the canopy would be crushed inwards as it was slid rearwards. Because of the canopy frame being rigid the canopy would not slide rearwards as it would quickly become jammed in the side frames.

The problem comes from me trusting that the formers as shown on the plan were correctly drawn to allow the sides at the cockpit to be built parallel. In actual fact they are inaccurately drawn and produce a tapered opening. By the time I have reached the present juncture it is too late to alter the structure as that would require me to tear the whole centre of the fuselage to bits in order to insert two new formers.

It all comes down to trusting someone else’s hand drawn plans. I should not have been lazy and drawn my own plans in the first place.
Every Day Is A Learning Day!! :?

Brian. :? :? :?
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