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Avon Sabre Spirit 78


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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.

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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)!

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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?
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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

Cheers

Chris

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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)

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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

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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.

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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.

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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?

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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?

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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.

Rob

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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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Radio Bay

I wanted to install the radio before any more work on the tail horn. In order to keep the weight forward I decided to tuck the RX away on top of the battery box on a tray mounted on sliding rails. This would have been easier to install before joining the fuselage sides, but ... hey ho .. hindsight is wonderful!

The rails were made from 1/8" sq spruce, mounted on 1/16" ply sides, held together at the far end (the nose end) by a cross piece of 1/8 spruce, acting as both a spacer and to hold the rails 1/8" above the battery box.

2002_0802_rx rails.jpg

The sliding tray is simply 1/16" ply with two runners from 1/4" wide strips of ply. These also space the tray above the battery box to allow the velcro strap to wrap underneath:

2002_0804_rx tray.jpg

The velcro strap holds the RX in place, with a spare pair of slots in case I feel the need for two straps:

2002_0805_rx tray.jpg

Imagine looking down on the battery box from the top of the fuselage; the side ply strips of the rails will now be glued to the sides of the battery box, so that the tray is free to slide over the battery box:

2002_0807_rx assembly.jpg

Glue it all together, using a temporary 1/8" balsa spacer, avoiding glueing the spacer into the rails, and the end result is thus. Note that I cut away approx 5mm of former F4 to allow the RX to pass through:

2002_0902_railsonbox.jpg

My usual sliding ply strip will retain both the battery in the box, and the end of the RX tray:

2002_0903_retainerslide.jpg

Slide the tray into the rails, having cut a locking slot in the end of the tray:

2002_0906_trayclip.jpg

...and there we have a RX tray out of harm's way, securely locked into place.

2002_0908_rx_overview.jpg

Next, on with the servo mountings.

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Hi folks,

Phil: Pinch away - I'm sure the idea isn't new, although I'm quite pleased at how well the retro-fitting was accomplished!

Martin: That thought did cross my mind, but I wanted to keep the aerials out of harms way, and mine are perpendicular. I'm never sure whether they will achieve the same reception if I straighten either of them up. Bear in mind that my radio is 'old' DSM2 technology, so not as much frequency hopping as some. I toyed with buying a new carbon friendly RX with longer aerials, but I'm too tight and not sure if all the DSMX RXs necessarily operate DSM2.

I'm still in mourning at the passing of JR! So much so that I've just bought some dinky JR DS396 mini digital servos from Hobbyplastic - being sold off at half price at the moment (similar size/power to the HS-65MG).

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  • 1 month later...

It's bin a while!

No progress for 4 weeks due to other commitments, but crawling along again now.

Thanks for your comments, Dirk.

Two halves make a whole

There have been so many useful postings about the wing build from talented builders that it seems there's not much left to say, so excuse any repeats. I took the 'build in two halves' approach, having only a narrow building board. I used the same jig components for port and starboard wings, totally glue-less, and found that the port jig needed stretching a little, and the starboard, shown here, needed a little compression to fit the plan. This was accomplished with strategically placed pins. The excellent fit of the parts ensured it gripped tightly without glue.

2003_2201_jig_pins.jpg

And squeeze....

Pins placed mainly outside the jig sections, to squeeze it into place.

2003_2202_jig_pins_tip.jpg

The root ribs had to be checked for verticality. Since both R1A jigs were used, this meant a 1/8" gap between the squares and R1:

2003_2203_root_squares.jpg

You raise me up..!

As noted by other builders, I packed up the R1A jig pieces with 1/16" balsa glued to the base of each one, to level them with the other rib supports. Packing just visible below:

Gotcha

I fell for the gotcha of buying 1/4 x 1/8 spruce spars instead of 1/4 x 3/16, so just laminated the spars with a layer of 1/16 balsa on top, before glueing into the ribs. This has a useful benefit of being easier to sand in line with the tops of the ribs:

2003_2204_r1a_packing.jpg

Spar webs applied to both sides of the spars:

2003_2205_unused_jig.jpg

2003_2206_spar_webs.jpg

Tip of the day

Here's the tip jig, showing the 'compression' pins holding the jig, and the laminated spars (sounds grander than 'messed up'!):

2003_2207_tip_packing.jpg

The completed halves. Great job with the jig production, Martin and Gordon. It made the assembly very quick and painless, although I'm glad I bought the pre-cut parts rather than cutting them all myself!

2003_2209_two_wings.jpg

Now I need to decide whether to go for inboard or outboard servos - still deliberating.

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  • 3 weeks later...

Torque of the Town

I'm using a hybrid wing servo solution, with in-wing mounted aileron servos and torque rods for flaps. Noting Phil's advice on another thread about possible damage to flaps on a low-winger, I thought that thin torque rods would provide a little 'give' in the event of the flaps catching on landing. Hence, Radio Active 14swg rods from Blackburn Models - 7.5inches long.

2004_1001 torquerods.jpg

Slimmers World

I'm using slim wing servos, at 10mm thick. Hitec HS-125MGs for ailerons and KST DS135MGs for flaps. I've always wanted to try KSTs, and am hoping the slightly stonger gear train than the Hitec will provide more resilience against flaps getting caught on landing and damaging the gears:

2004_1002 ail&flapservos.jpg

Mountings are cut from 5mm ply:

2004_1004 flapservomounted.jpg

The tabs on the top of the aileron mount below (one marked 'L' are actually spacers to keep it the correct distance from the spar, and parallel to the trailing edge of the wing. Here the servo is resting on the top of the mount, but will be fixed below it in the wing, for bottom driven aileron horns:

2004_1006ailservomounted.jpg

A few recesses cut into the wing for the aileron servo, which will hang under the mount:

2004_1007 ailservorecess.jpg

A few recesses more for the flap servo, which will sit atop the mount:

2004_1008 flapservorecess.jpg

Drop the mounts into place and thankfully everything fits nicely:

2004_1009 servosinwing.jpg

The shot below shows the spacer tabs on front of the mount, ensuring that the pushrod exits perpendicular to the trailing edge. I'm not a great lover of angled rods - they never run smoothly for me! I've mounted it one rib bay nearer to the root than shown on the plan, so that the wire reaches the root cavity without needing a buried extension plug, and also keeping the weight further forwards:

2004_1011 hs-125_seated.jpg

I've not yet mounted the circular access panels, but am hoping to use a 3-screw retention:

2004_1013 ailservoaccess2.jpg

The KST flap servo is also parallel to the trailing edge, for a straight pushrod. It's mounted as far forward as possible without bringing the torque rod ends too close to the centre of the wing. As other builders have noted, the wing bolt plate will need some recesses to be cut to clear the torque rods, and the servo plus mount must all be flush inside R3, so as not to foul the F14 fuselage keels:

2004_1015flapservoaccess2.jpg

Mounting Pressure

Now, I just need a way to mount those aileron servo access hatches......

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