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F-86A Sabre Montana Air National Guard

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Harry Twist19/11/2019 23:29:35
333 forum posts
246 photos

Hi Steve, one servo - sat at the centre, it will only make one movement per flight, pulling two lightweight piano wires around 5mm (one wire per wing). Not decided on the servo yet, but it will be a light one! Pushrod geometry, nothing complex hopefully, 90 degree bends taking the pushrod up to the servo. Each pushrod end then located into opposite ends of a servo arm. There's more detail in the John H A4 build - thanks Martin for the link.

Edited By Harry Twist on 19/11/2019 23:34:24

Harry Twist23/11/2019 23:36:43
333 forum posts
246 photos

Hi All, I've moved the fuselage on a little, well one half of it anyway!

I cut the spines from sheet and decided to cut them slightly oversize at 8mm x 3mm. This was to ensure that the very top of the formers sat on the spine and not slightly below it. I used the straight top spine as the starting point, pinning it to the plan and ensuring all the touching formers sat in location and square. I then pinned, clamped, glued and weighted the combined nose unit / central crutch / top spine and the tail unit. Once dry I added the curving bottom keel as one piece, curved and pinned. Again, once all dry I added the F3 F5 formers and the longitudinal stringers. So for me, the fuselage framework ended up as a three stage assembly process.

I did have an issue with the lower stringer, which at full length along the curve just about sat on F1 and F10, but not enough for me to be happy that it was secure front and back, so I scarf jointed a piece in, with the joint sat on the double former F4/F4a. The other two stringers were fine.

Now onto the planking, prior to planking I sanded gently to ensure all the stringers sat flush with the formers. I've cut my planks 7mm wide, parallel full length and have so far added 4 planks. I'm taking my time over this - trying to align the planks carefully and trying to visualise how it will look.

It's great to see and read all the ideas, guidance and sharing of information that's going on in the Sabre build blogs.

Happy building!

 

Bare framework completed - one half only

img_20191121_111536000_hdr.jpg

 

Short scarf joint at F4/F4A- the dark lines at the former /keel joints are not gaps they're blue pen ink lines delineating the locating/gluing boundary!

img_20191121_112109190_hdr.jpg

Long view - curving keel, one piece of 8mm x 3mm.

img_20191121_112124910_hdr.jpg

 

First planks - plank width here is 7mm, planks parallel nose to tail.

img_20191123_221034752_hdr.jpg

 

 

Edited By Harry Twist on 23/11/2019 23:43:32

John A H24/11/2019 04:16:32
126 forum posts
154 photos
Posted by Steve McLaren on 19/11/2019 21:11:53:

What size servo do you plan to use? and does 1 servo do both tanks? I'm trying to visualise the geometry of pushrods meeting the servo.

I used a Hitech HS65mg servo for the drop tanks on the A4 Skyhawk. I located the servo in one wing (so you don't have to cut into R1). Bend the pushrod (or pullrod !) diagonally up to exit the wing skin with one side going to the "front" and other side going to the "back" of the servo horn. I initially fit the wire before putting in ribs R1 and the ones outboard of the mounting - means you can slide it in and out of position while messing about trying to get the "line" and bend.

Hopefully the pictures make sense of above comments - holes in ribs reinforced with 1/32 ply.

a4-11.jpga4-21.jpg

McG 696924/11/2019 09:27:00
avatar
2729 forum posts
1024 photos

Great progress already, Harry. smiley

Thank goodness, I don't have any external fuel tanks installed to my 'Dog' version, but then I do have enough pondering with the fuselage mods...

Looking at the background of one of your pics, I noticed that you have been 'lightening' your battery box as well, héhé... wink

Cheers

Chris

Harry Twist29/11/2019 23:22:00
333 forum posts
246 photos

Hi All, I've moved the fuselage on a little more. I have been worried about the major "glue up" required to join two part planked fuselage halves in one go. This involves, applying glue along all the major joint lines of the top and bottom spines, and along all the former joint lines, gluing and fitting the wing bolt plate, then aligning and clamping, all  in one gluing "event". I did'nt trust myself to get this all square and had visions of glue everywhere and an out of line fuselage!

So I tried an alternative. I part finished one fuselage half to the point of adding 10 planks (7mm wide). I then built the second half, section by section, onto the part planked first half. I starting by adding the straight top keel, then worked front to back, adding each sub structure in turn and allowing drying between each stage. At the end I added the stringers and the small part bulkheads of F3 and F5.

Photos hopefully show all!

Nose and battery box added, after top keel

img_20191126_200506433_hdr.jpg

Central crutch and wing bolt plate, I adjusted the plate to move it back approx 5mm to sit against F7

img_20191127_114225654_hdr.jpg

 

Tail unit, clamps and more clamps

img_20191127_232103343_hdr.jpg

 

Last addition- lower curved spine

img_20191128_182251603_hdr.jpg

 

End product

img_20191129_185622427_hdr.jpg

Edited By Harry Twist on 29/11/2019 23:23:23

Mark Kettle 130/11/2019 10:01:25
avatar
2471 forum posts
1492 photos

Exciting Harry, seeing the parts gradually assembled then the great fuselage shapes emerging.

McG 696930/11/2019 17:31:14
avatar
2729 forum posts
1024 photos

That's indeed a very different approach, Harry.

I'm not having your 'visions' yet, but I might follow your route for joining up the fuse halves.

Does your 10 planking bits gave the half fuse enough stiffness to go on with?

Great progress, young man.

Cheers

Chris

Harry Twist30/11/2019 19:03:14
333 forum posts
246 photos

Hi Chris & Mark, thanks for your comments.

Ref the planking - I added 10 planks on the first half before adding the second half in sections. Each plank is 7mm wide, they were all butted together, but distributed above and below the fuselage centreline. ( I started on the centreline and worked down by 5 planks, then back to the centreline and worked up 5 planks).

I reckoned that the combination of planking and stringers, plus adding the top spine (which doubles the spine thickness) would minimise any warp risk. I think its further helped by adding the substructures of the second half, one by one, allowing drying in between. Anyway - I don't think its warped yet!

I'll carefully plank the non planked side, then do alternate side planking until I'm done.

Edited By Harry Twist on 30/11/2019 19:17:43

Phil Cooke01/12/2019 16:59:47
avatar
2286 forum posts
1555 photos

great stuff Harry, coming on really well! I like the idea of assembling the second side onto the mostly completed first side, to guarrantee former to former alignment etc - still not started here quite just yet, but I think I will follow your lead. Good going! thumbs up

Harry Twist02/12/2019 19:36:26
333 forum posts
246 photos

Thanks Phil, hope you get your Sabre on the go soon.

General question to Sabre builders out there, has anyone tried any fuselage sheeting or part sheeting? or is everyone planking all round? I think there may be some part sheeting opportunities in a couple of places such as the rear underside or forward of the canopy. I'm not there yet but may look at it. Any comments appreciated!

McG 696902/12/2019 21:06:10
avatar
2729 forum posts
1024 photos

I'm subscribed to your thread, Harry...

... but I can't really be of any help here. blush

Hopefully someone will be jumping in with more knowledge.

Cheers

Chris

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