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Avon Sabre Spirit 78

CA-27 Sabre of Indonesian Airforec display team

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Steve Houghton18/01/2020 16:59:05
586 forum posts
438 photos

Chris, thanks for the reply.

A quick update from today's progress, although nothing that hasn't been covered elsewhere.

Give me your support

The tubes for the closed loop rudder wires are supported quite high up by the addition of a filler into F8, to keep the runs as straight as possible:

2001_1801_f8 tube support.jpg

The remaining supports won't be fitted until after joining the fuselage, as they will be accessible from the wing seat and I'll be able to see better where they need to be. I like to connect the wires to the servo via a 180degree belllcrank so that the wires can be tightened without straining the servo bearings. Mounting this will need better visibility of the equipment bay layout later on. The wing bolt mounting plate has been fitted to one side, using a dry assembly of the two halves to ensure it was aligned:

2001_1802_tube and bolt plate.jpg

The battery box was glued into one side, using a couple of scrap balsa supports to hold it still:

2001_1803_battery box.jpg

Join me now

Finally, the grand fuselage joining ceremony, with support from the faithful Irwin clamps and some scrap balsa blocks, tapered to accommodate the fuselage taper:

2001_1804_fus tail join.jpg

Ssssteam Heat

Dry assembly revealed that both halves had banana'd slightly outwards during the planking phase, especially at the nose. Before joining, I therefore steamed the sides a little to allow them to bend in before clamping:

2001_1805_fus nose join.jpg

That'll be left to dry overnight to ensure the glue can hold the tension.

Phil Cooke18/01/2020 19:21:37
2650 forum posts
1851 photos

Very neat work Steve - your planking looks the business! Excellent stuff!! thumbs up

Chris Barlow19/01/2020 03:14:00
1904 forum posts
1308 photos

Good to see progress on the Sabre builds again Steve. It's a landmark step when you get the joined halves out of the clamps and have a full fuselage to work with. yes

Steve Houghton20/01/2020 22:37:01
586 forum posts
438 photos

Thanks, Phil and Chris. I'm following both your builds with interest to compare notes.

A Bender

I don't know about others, but my pet hate in any build is bending wire, so I wasn't looking forward to the tailplane joiners. That's probably because a small bench vice is my only bending facility, and it's a struggle with anything thicker than 12g wire, because the whole table tends to move or lift when I put my weight behind it:

2001_2001 bending vice.jpg


Hence, I went through several rejected attempts before I achieved a successful set of front 8g and rear 10g joiners complete with embedded tube AND the correct angles. I usually managed to bend the central part, so that it wouldn't rotate in the tube, or I flattened the tube itself. The final best results came from using the smallest possible wooden lever (see above), and much brute force (Anyone know the best treatment for pressure blisters on fingers?):

2001_2002 bent wires.jpg

How have the rest of you expert benders accomplished this daunting task?

I was intending to fit brass tubes into the tailplane halves, to make them removable, but I saw that some builders are planning to glue them in place. My worry with removable halves is that the wire joiners can slip sideways and the bends can bind on the central tubes, preventing rotation. Not sure how to prevent this yet.

Martin Gay21/01/2020 10:25:30
410 forum posts
255 photos


I would advise against gluing the tailplanes on. The prototype model has flown in 12mph winds all the way up to 45+mph without any issues with the tailplanes moving sideways.

If you have any worries then an application of a tiny bit of "Pritt-Stick" glue to the joiner will ensure that the tailplanes stay on.

Being able to remove them also helps with storing the model!


Steve Houghton21/01/2020 13:30:39
586 forum posts
438 photos

Thanks, Martin.

I am definitely aiming for removable halves. I'm just aware that if the wires drift sideways, even when pushing the halves onto the wires, then the bends in the wires could bind in the central tubes. Time will tell whether this ever becomes an issue.

The pritt-stick sounds useful - I'd heard that before but never tried it. Thanks.

Steve Houghton22/01/2020 23:07:20
586 forum posts
438 photos

Out with the bush

I've been looking at the size of the SLEC 834 tailplane control horn tonight and don't think there's enough plastic around the rear hole to drill it out to fit a 10g wire plus brass tube bush. The plan shows a bush on both the front and rear wires, but I'm thinking the rear wire doesn't need to pivot freely and probably doesn't need a bush.

I've therefore bent up a bushless rear 10g wire instead. I was also unable to keep the rear horn hole horizontal when drilling out, so I now need to order a replacement (or two)!

Peter Garsden23/01/2020 09:52:00
1739 forum posts
1306 photos

Reading this makes me worry Steve as I haven't got there yet to be honest.

  1. I thought the plan said that one ought to make the bend on one half over the template, then insert the wire into the tube, then bend the second half in situ because otherwise you won't be able to get the thing onto the tailplane support, or have I misunderstood?
  2. I agree that the rear wire doesn't need a bush.
  3. At what point, Martin, just to clarify, is one meant to do the bending of the wire?
McG 696923/01/2020 10:39:22
3369 forum posts
1287 photos

Hi Steve & Peter,

Hereunder is what Martin wrote in his 'Gamma' build blog (page 4 for some picture) :

- First bend on the pivot wire at 10deg

- Slide brass sleeve on

- Fit a suitable spacer to stop bellcrank moving sideways [optional]

- Fit bellcrank

- Fit second spacer [optional]

- Second bend [careful not to damage brass sleeve]

- Pivot wire must be free to move in brass sleeve

- Re-check bend angles using ply guide and then glue brass sleeve into F15

The rear (2mm) joiner is 'bush-less' on his example.

Hope this helps



Chris Barlow23/01/2020 10:56:26
1904 forum posts
1308 photos

If it's any help I drilled the holes for the forward (pivoting) wire oversize to allow the pre bent wire and bush to pass through over the bend. The wire and bend fits through the hole in the bell crank without the bush, and out through the other side, as the bush is pushed into the bell crank. The oversized hole also helps in getting the wire accurately perpendicular to the fuselage.

Once centralised and in position the bush was glued to the tail plane fairings with epoxy and micro balloons. Mine is slightly different in that I made my own bell crank and I have used a PTFE bush instead of a brass tube but I think the principle is still the same?

Once glassed I was going to glue the wire joiners into the tail plane halves with epoxy but I think I'll use a dab of Uhu instead as this will secure them in place but will allow easier removal in the event of any damage. (similar to the pritt-stick idea)

Steve Houghton23/01/2020 22:16:11
586 forum posts
438 photos

Peter: I agree with your points 1 and 2. This also answers 3 - the wire is bent before insertion into the horn.

Chris MgG: Yes, I have followed Martin's procedures, except that I have now removed the bush (sleeve) from the rear wire.

Chris B: I think my use of 'bush' was incorrect. I have fitted the brass sleeve to the front wire, but no bushes (either side of the sleeve). I have made a new rear wire with no sleeve.

Thanks for these.

Forlorn Horn

My problem with the rear wire is best illustrated thus:

2001_2301 crooked rear wire.jpg

It's difficult to enlarge a hole in a plastic horn without the drill snatching on the plastic and being pulled off line.That above would give significant trimming problems, so I am ordering more horns. You can't see above, but this is an Acute angle horn (SL833) instead of an Obtuse one (SL834). Must order the right ones this time!

Take a Seat

I puzzled over how to cut out the wing seat quickly and accuratey, and decided to adapt the 'plan pricking' idea. Take a piece of 16g wire approx 5" long, with both ends sharpened. Rest it across the two F14 keels and gently push it from side to side:

2001_2201 side spike.jpg

Gradually the light dawns:

2001_2202 spiked holes.jpg

Then simply join the dots with a marker:

2001_2203 join dots.jpg

A little knife work and the cut almost falls apart. Extend the lines front and back to extend the curves beyond the curved parts of F14, and the rough outline is done. Saw off the bottom of the former to the same level, and that'll do for now until I have a wing to do the final trimming:

2001_2204 cut seat.jpg



Edited By Steve Houghton on 23/01/2020 22:17:20

Phil Cooke23/01/2020 22:32:02
2650 forum posts
1851 photos

A clever solution for that tricky operation Steve - nice one! thumbs up

Your last photo shows clearly those who, like me, are adopting a central servo and pushrod/torque rod arrangement for the ailerons will have to remove the lower half of the former in the middle of the wing bay.

Steve Houghton23/01/2020 22:50:26
586 forum posts
438 photos

Phil, Yes, I'm planning the same central servo arrangement, although still pondering whether to fit flaps as well. I keep having flashbacks to Hanno Prettner's flaps on the Super Sicroly, I think, where he used an aileron torque rod within a brass tube that controlled snap flaps, all housed within a further brass tube bearing. I've not figured out the precise details yet, or whether it's worth bothering with flaps - I noted your comments on your blog.

dirk tinck23/01/2020 23:51:13
655 forum posts
922 photos

Hi Steve ,nice going !

Be carefull sanding the wing seat and keep in mind the wing dihedral ! It goes from neg. in the front to positive towards the back .Don't ask me how i know !!embarrassed

I just did thesame task this evening....

Steve Houghton31/01/2020 21:17:17
586 forum posts
438 photos

Hi Dirk,

Thanks for the warning. I won't do much with the wing seat until I have built the wing. A rather slow week for building this week, although I'm moving on with the tailplanes, fin and rudder. Will post pictures when I have made progress.

Chris Barlow31/01/2020 22:51:33
1904 forum posts
1308 photos
Posted by Steve Houghton on 23/01/2020 22:50:26:

Phil, Yes, I'm planning the same central servo arrangement, although still pondering whether to fit flaps as well. I keep having flashbacks to Hanno Prettner's flaps on the Super Sicroly, I think, where he used an aileron torque rod within a brass tube that controlled snap flaps, all housed within a further brass tube bearing. I've not figured out the precise details yet, or whether it's worth bothering with flaps - I noted your comments on your blog.

That's a very clever and neat solution to the problem of flaps and ailerons with central servos! I might have to try that on something.

Steve Houghton02/02/2020 14:04:47
586 forum posts
438 photos

Flappy Bits

Chris, and anyone who's interested in centre mounted servos. Here's Hannos's solution, snapped from the Super Sicroly plan (courtesy of Outerzone).

super sicroly.jpg

Questions, Questions

I'm scratching my head about the tailplane block fairings. If anyone can cast light on these, it would be appreciated.

1) The plan's side elevation shows the block fairings fitted below the top of F15, but the A-A cross section shows them to be level with the top of F15. I realise I could set them lower down and then fill over the top with more block, but has anyone any advice on the best approach?

2) Are the tailplane block fairings parallel on the outside, or do they taper toward the tail? This will affect how the tubes are glued into the tailplane halves. If parallel, the tubes will be perpendicular to the root of the halves. If tapered, the tubes will be angle forwards slightly to accommodate the sweep back. I can see from Martin's build notes that he fitted the tubes by clamping them against the tail, but I don't have confidence that I can get them straight by that method and would like to do them flat on the bench. Any advice?

Gordon S02/02/2020 17:26:19
25 forum posts

Steve, hopefully this will help.

- Top of the fairings should be level with top of F15 or as near as you can get. Run a sanding block over F15 if they are a bit proud.They are going to be covered with triangular section to blend into fin anyway.

- the reason they may be a bit low is that the fairings do taper in towards the rear. On some scale drawings, this taper was only in the last third of the fairing, in others it shows the whole length. for simplicity I tapered the whole fairing on both the prototype and Gamma builds. Because the fairings are further apart at the front than back, mine did drop a fraction but that could have been my heavy sanding!?!?!?

Hope that helps?

robk02/02/2020 18:01:16
123 forum posts
168 photos

Hi Steve

I have similar problems with bending thick wire in my small bench vice. I think the ones I used were worse than your rejects! Anyway they are in now. Both wires are allowed to move in the bell crank as my plan was to secure them by gluing them into the stabilisers (as not recommended by Martin here. Oops - is the reason for not gluing them in so that they can be removed for repairs? Most stabilisers are fitted permanently to the fuselage so I didn't think it would be a problem but if it is... Chris's idea of a less strong glue (fitted into brass tubes?) might an alternative solution.


Steve Houghton02/02/2020 20:59:03
586 forum posts
438 photos

Gordon: Thanks, that helps greatly. I can set about the fairings now. I understand about the triangular section on top, but it's hard to visualise how 3D shapes like this will end up after carving!

Rob: Having checked your blog, it looks like you made a great job of the wire bending - it all seems to line up. After ruining three tail horns, I have just about succeeded with my fourth. The crank wobbles slightly on the front sleeve, but I'm hoping that will not matter once the sleeve is glued into the slot. I kept the rear wire as tight as possible as it should only need to rotate slightly when sliding on the tail halves. After that, I think it should be tight.

I'm sure the reason for removable tailplanes is to minimise transport damage in the car. The glue stick idea sounds perfect to allay fears.

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