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Fitting incidence tubes in wing

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StephenB
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Joined: 26 Dec 2018, 08:45
Location: Hungary

Fitting incidence tubes in wing

Post by StephenB »

I'm at the stage where I need to fit the brass incidence tube in my Spatz wing, but unsure of the best way to proceed.

It needs to be parallel with the main wing joiner blade and at right angles to the root rib in the horizontal plane, easily done by the use of a square:
IMG_0392.jpeg

But I assume it also needs to be parallel with the joiner blade in the vertical plane which is not so easily done. This assumes that the incidence peg/rod runs through the fuselage and in to the other wing.

Or alternatively do I make the rod two separate pegs and fit the tube square in both planes which (I think) would make the setting up of wing incidence much easier.

All advice welcomed!

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Peter Balcombe
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Re: Fitting incidence tubes in wing

Post by Peter Balcombe »

Stephen, unless the positioning of the tubes is very well controlled in a CNC cut wings & fuselage build, I usually don’t fix the rear incidence tubes in the wings until I can dry assemble the wings to fuselage with the main joiner, then set up the wing TE correctly.
As you have already mentioned, the angles need to be correct, but also the spacing between main joiner & incidence pins/wire. If you fit everything together to install the incidence tubes, then it should go together again correctly later.
If I have a single straight-through joiner system, then I usually fit a tube across the fuselage & a single incidence wire, engaging in both wings - if only to have less joiner bits to have to remember to take to the flying site!
Peter

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RobbieB
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Re: Fitting incidence tubes in wing

Post by RobbieB »

Stephen,
It isn't necessary to carry the incidence pin across the fuselage to the other wing at all - the torsional loads on the wing at the TE are not monumental (under most sane flying conditions) so a short, unconnected pin in each wing is quite adequate; and as you say, simplifies the installation a lot.
As Peter points out, a dry fit which ever method you choose is an absolute must. A system I have used is to make the tube holes in the ribs a little over size to give you some leeway when setting the incidence but have snug fitting round or square ply plates fitted to the tube both sides of the rib which you can then epoxy to the rib and tube when you are happy with the incidence and the fit.
Another thing, make sure both stub tubes are secured to a small ply former if there isn't one there already - doesn't have to be a full fuselage depth former but should key with at least one longeron on each side.

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RobbieB
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Re: Fitting incidence tubes in wing

Post by RobbieB »

Peter Balcombe wrote:
04 Aug 2020, 10:33
'..............................& a single incidence wire, engaging in both wings - if only to have less joiner bits to have to remember to take to the flying site!'
Peter
Not that any of us forget to take those things when we go flying do we....................... :oops:

StephenB
Posts: 176
Joined: 26 Dec 2018, 08:45
Location: Hungary

Re: Fitting incidence tubes in wing

Post by StephenB »

Peter and Robbie, thanks for the input.

At this point nothing is bonded in to the fuselage and only the main wing box is epoxied between the spars so all options are, theoretically, open. Whichever option I choose it appears I will have to leave the final bit of wing sheeting around the root rib until the incidence tube is secure.

If I went for the potentially easier option of separate pins (I once had this on an electric model where the pins were bonded in to the wing root and so nothing to lose) Robbie suggests I need to reinforce around the tube(s) in the fuselage? That may be tricky as the fuselage is sheeted and so access all but impossible. A straight through tube would be supported by the 3mm liteply/0.8mm fus sides in this area as well as car body filler etc. that will form the fairing around the root.

I'm wondering if I can set the one wing up that I have and finish that completely before starting on the other wing. Or is it more sensible to jig up both wings together? None of this is easy when working with large wings and having to secure the fuselage to stop it rotating!


Edit to add:

Re-reading Peters post I think I need to build both wings and get them rigged to properly set this up. I think in that case a straight through pin is the way to go. The tidy part of me likes to completely finish something before moving on to the next bit. I'll have to dampen down the OCD :lol:

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Peter Balcombe
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Re: Fitting incidence tubes in wing

Post by Peter Balcombe »

Stephen,
The down side of the straight through tube, is needing both wings when you assemble the fuselage incidence tube as you need to be able to make sure that the fuselage tube is exactly parallel to the main joiner, otherwise the fuselage exit for the 2nd wing may not be in the right place when you get to fit that wing.

The up side of the split approach is that you have a bit more room for manoeuvre as long as the wings aren’t assembled twisted. However, as Robbie says, you need to support the fuselage tubes a bit more (and put some kind of stopper on the tube to stop a pin going in too far - unless the pin is fixed in the wing. Presumably, you cannot get at the fuselage rear tube positions from the cockpit area in order to do what is needed?
If this is the case then you are probably limited to the single tube.

With the single tube, just take it step by step.
As Robbie says, try a dry fit of everything, then secure the fuselage tube (even if only a tack glue to start with, followed up be fully securing).
Once the fuselage tube is fully in place, you can sort each wing separately.
Peter

StephenB
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Location: Hungary

Re: Fitting incidence tubes in wing

Post by StephenB »

Thanks again Peter!

One other thought, I assume the rectangular brass box is left unglued in the fuselage so as to allow the wing to rotate around it in order to adjust the incidence?

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Peter Balcombe
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Re: Fitting incidence tubes in wing

Post by Peter Balcombe »

Stephen,
Yes, but I suggest that you dry assemble the wings & at least tack glue the fuselage main joiner tube before the others unless you can realistically do the fuselage rear incidence tube at the same time.
I find that it is easier to do one at a time, then if any problems you only have one to undo.
It basically means that you need to find a way of supporting both wings plus fuselage to get everything aligned before glueing the main fuselage tubes. Then it’s just a matter of moving through fuselage incidence tube, then wing tubes in sequence.
I would lightly oil the joiner bars before assembly to reduce likelihood of Inadvertently glueing them into the tubes ;)
Peter

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chris williams
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Location: Blandford Dorset

Re: Fitting incidence tubes in wing

Post by chris williams »

Stephen, I am usually a proponent of short incidence pegs that live in the wing: a small bend in the rod will ensure that they don't fall out (usually!) yet leave them removable if necessary. I can't remember: do you have all the build pics for this model?
Attachments
07220011.JPG

StephenB
Posts: 176
Joined: 26 Dec 2018, 08:45
Location: Hungary

Re: Fitting incidence tubes in wing

Post by StephenB »

Thanks Peter, all this has clarified how I need to go about it. Complete both wings, get the airframe out of the workshop and rig the whole thing.

Chris, yes I do have all the pictures thank you but I assumed from these and the drawing that it was a single incidence pin.

Whilst I've got your attention Chris, the plan shows 0.8mm ply gussets on ribs 3 - 7 at the TE but your pictures seem to show that you simply capped the ribs all the way to the TE. I ask as the gussets would butt up to the caps but be a different depth (0.8mm >1.5mm) also leaving an anomaly where they butt the balsa TE compared to where the cap strips meet it on the remaining ribs.

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