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Avon Sabre Spirit 78


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Pitchy Binders

I encountered a problem with mounting the tailplane halves, due to me having them removable. While assembling the tailplanes onto the rods I found that the front rod slid sideways in its bearing tube, and the bend in the rod would then bind into the end of the bearing tube, causing the servo to stall. Without disconnecting the pushrod each time the tailplanes are slid into place, it was impossible to tell if they were free to move or jammed until the servo complained!

 

Here's my solution to stop this happening and causing a crash due to a binding linkage:

 

I carefully sawed a 3mm 'washer' off each side of the bearing tube, smoothed the cut edges with a small file and then glued the washers onto the rod with JB Weld epoxy leaving approx 1mm gap between the washers and bearing. Now it's impossible for the rod to slide sideways. Even if the glue does not hold, the bend in the rod will now bind into a movable washer instead of the fixed tube, and there should be no linkage binding.

 

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The washers were carefully spaced so as not to lie outside the edges of the tail fairings. This has made it much easier to slide everything together, and should prevent that feared binding:

large.42186412_2103_7302FrontBushMod.JPG.15c23fa37345a597b693d8cbb3985bc0.JPG

 

The inner bearing tube will be glued into the slots in F15, as per plan, but the washers must be free to rotate with the rod.

 

 

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Hi Danny,

It's pure friction holding them on. I'm told a wipe of Pritt Stik on the rods is also an added insurance for those of a worrying nature, as recommended by Martin and Gordon.

I can certainly confirm that mine are tight, due to a slight misalignment of the rods (woops!), so that the rods on one side need spreading slightly to line up with the tubes, thus putting the other side under tension against their tubes.

Time will tell, but I'm assured it will be fine.

 

Thanks for your comment.

 

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  • 3 weeks later...

Roll Your Own

Following a similar principle to my Jet Provost tailpipe, and a few ideas borrowed from Chris McG, I made the tailpipe by rolling a ring of 1/32" ply around the best sized former I could find (other body cleaning products are available), and then added a few layers of 1/16" balsa to thicken it up. This was all wetted with water and left to dry:

 

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After overnight drying it was all laminated with aliphatic glue, the top flattened off, and a location tab added to the top to fit between the tailplane fairings. This allowed dry-fitting to the fuselage and rough shaping:

165499285_2103_1402Tailpipe_Tab.thumb.JPG.894ba457a54621b814a9313835019e6f.JPG

 

Put Another Ring On It

I wanted the ply ring to be as near to the fuselage skin as possible. However, my fuselage was not an accurate round shape and with the initial ring size it would have been too high up the fuselage to allow enough meat for carving the streamlined duct shape. Hence I added two more inner rings of 1/16" balsa and another 1/32" ply ring. This seemed to be adequate to carve a nice shape, albeit giving much thicker side walls than I wanted:

large.2103_2101_TailpipeShaping.JPG.f7790f5bad1f9912e56658ca050768de.JPG

 

With the duct still dry fitted I could remove it to carve the initial shape onto the tailplane fairings:

large.2103_2104_TailpipeShaping.JPG.6686355b2c7d64a6d2627945689e21e3.JPG

 

Mistaken Identity

Further study of the Avon Sabre's duct showed that it needed a different shape to that which I originally carved, which was based on other F86 marks. After gluing it all together, with a top ply plate as used by other builders and a further 1/32" ply liner inside the top of the duct, I ended up with this:

large.2103_2804_TailpipeFinish.JPG.9a1497d1a5281a332bace3419831dbbe.JPG

 

The taper on the tailplane fairings extends further forwards and higher up:

large.2103_2805_TailpipeFinish.JPG.cad8cd86fed7527eff6fc8d52b31e34d.JPG

 

Here's One We Made Earlier

It should have ended up with something like this, from a different Avon Sabre, but the shape is the same for mine:

large.1384008752_A94-935Tailpipe.jpg.ce2b8bb36b00a8f61ac7f23dcf1caf8a.jpg

 

... and this is how it turned out - final shaping and sanding still needed:

large.2103_2802_TailpipeFinish.JPG.57350be1585a25d72f153aca802a3302.JPG

 

The inner lining will be smoothed down in due course. The side walls of the duct can be thinned a little, but I can't get them down to the thickness of one layer of metal. It will definitely be 'stand well off' scale. However, I'm fairly pleased with the overall effect.

 

 

 

 

Edited by Steve Houghton
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Thanks Gents,

Chris, I did draw inspiration from your roll. It all helps us to develop new ideas and techniques. I am seriously contemplating my first glassfibre covering for this build, so may be coming back for advice on the Sauce. I've read your's and Phil's blogs on the matter, so I think I understand the principles and ingredients.

 

I'm still hoping to meet the September deadline, but progress needs to be significantly faster than last year!

 

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Hi Steve & thanks for the kind words.

 

Regarding the glassing, please remember to use as less resin as possible.  Ideally the weight of the resin should equal the glass cloth weight but that is close to impossible to achieve. Even if you're left with some pin holes in the unfilled wave, don't worry the Sauce will take care of them. Possibly two thin coats of Sauce if needed.

 

As for the Sauce recipe - from my Ballerina build in 2016 - I posted a 'reminder' recently as the old blog wasn't easy to find.

I you visit the Dog's blog, my post of March 18 shows a link to the original thread.

Possibly helpful to refresh your memory...  ?

 

Cheers 

Chris

 

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Chris, Many thanks for the reminder of your link. I have already downloaded your orignal Ballerina posts about the sauce, to save as a reference document.

 

If anyone wants references to the glassing technique (after reading the excellent blogs on this forum, of course):

  • RCM&E Special Issue 2019, article by Danny Fenton.
  • RCM&E June 2018 Workshop Supplement, article by Tony Nijhuis.
  • I ordered some materials from Phil Clark at Fighteraces, and he also sent a helpful article of his own.

Skip, glad my struggles are helping. It will be great to see some photos on your Avon Sabre blog in due course - I hope the shoulder is clearing up to allow you to proceed. You have some useful photos, especially of the tail end, which I have only just spotted.

 

 

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Thanks Steve, the shoulder has turned the corner and is slooooooowly getting better. Lack of sleep has made it hard to get enthused about things, the blogs and particularly that of another Avon builder are great motivation though. About to get back into it.

I've posted a good Avon Sabre walk-around on my blog with a note at which point the tail is shown which you may find helpful.

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  • 6 months later...

They think its all over!!

It isn't now!

A 6 month deficit of spare time has set me back a little and I missed the main event, but I'm pressing on....

 

It was great to see that stunning array of 16 Sabres at the Great Orme in September - I'm sure there must still be a few in hiding, along with mine.

 

Closing the Loop

Here's a general shot of the radio bay progress. The elevator pushrod is disconnected to show the closed loop operating crank - I like to take any strain off the servo bearings if possible. The take-off points for the cables (not yet attached) are +/-16mm from the pivot, to match the spacing of the holes in the rudder horns. The cable guide tubes are still free to slide back into place when I'm ready but I aimed to set them to the same spacing as the attachments to the crank, which I managed fairly well.

2110_1101_ClosedLoop.thumb.JPG.bf9355cd910f1b4b648939506188b8e3.JPG

 

I couldn't get the required rudder throw from the standard Hitec servo arms, so I've used one of these Hitec adjustable arms for the first time - it works a treat, and allows very fine adjustments to the throw (I prefer mechanical to electronic adjustments - it doesn't matter if I lose the radio settings then!).

2110_1102_ExtendableHorn.thumb.JPG.774c56f48f8fbb7e43f31e5e1af05075.JPG

 

Blending In

I'm fairing the fin with 1/2" triangular stock along the base of the fin, and will use thinner stock along the strake.

2110_1104_FinFairings.thumb.JPG.d981ec948f089a701499deec323cc7d5.JPG

 

I chose to keep the fin fat while I add the fairings, and then trim the trailing edge later to blend in with the rudder. The reason being so that I didn't lose any width from the fairings - on my photos they seem to be the full width of the tailplane fairing and then taper off towards the front. I hope I can achieve the correct rudder blending shape with this method.

2110_1106_RudderFairings.thumb.JPG.efefcb09b2c719a3ba8196788193d9d0.JPG

 

For the strake at the front of the fin I used 1/4" balsa. This leaves quite a step in front of the leading edge of the 1/2" fin, even after shaping the LE. The triangular fairing has to bend downwards and sideways at this point, so I applied many saw cuts underneath, and a dampening of the top wood, to coax it into shape while the glue dried. Again, I tried to keep the closed loop tubes +/-16mm apart, and they'll eventually be trimmed flush with the wood.

2110_1107_StrakeBlending.thumb.JPG.0d3d9abcb63b0531602c705159f285ae.JPG

 

I glued the fin strake onto the top stringers rather than onto the planking because I wanted to leave the last pieces of top planking until the last minute in case I needed to see inside to re-thread the cable guide tubes through the fuz. Having satisfied myself of an adequate cable routing, I then butted the top planks against the fin sides:

2110_1109_FinSeatOnStringer.thumb.JPG.d4c276a3d00c2d4cd0d52e539d13e05b.JPG

 

 

 

 

Edited by Steve Houghton
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  • 2 months later...

Hi David, Thanks for your query. The fin fairings are now finished and shaped, but I didn't think they were significant enough to post pictures. I'll try to post some shortly.

 

Tailplane Incidence

I wondered if anyone can tell me what incidence the all moving tail should be set at relative to the wing? With my wing propped up at 0 degrees (parallel to my bench), I have -1mm at the leading edge of the tailplane. Alternatively, with the tailplane propped at 0 degrees I have +2.5mm at the wing leading edge. Does this sound about right?

 

Regards, Steve

 

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Hi Martin, Thanks for that.

The main restriction on up elevator on my model is the leading edge catching on the fuselage. However, I don't think it needs to move that far for the movements quoted on the plan. If I now remove the -1mm tailplane incidence in line with your recommendation, that will give me even more clearance at the LE and TE..

 

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Steve,

It sounds like you already have the maximum possible movement. Well done on that.

Be prepared to adjust elevator trim after the first launch to set the model to your preferred flying style. However, this model likes to be flown fast, but will slow down well for landing, especially if you are using flaps and CROW.

Martin.

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