tailplane spars

[Tim Mackey]

I was wondering what were folks preferred method of fitting spars into foam wings.

Tailplane actually - on the B52. Each tailplane half spans approx 360mm, with the root glued onto the fuselage sides ( balsa faced ).

I plan to fit a front and rear 6mm OD C/F tube, passing right through the fus, and into each panel by around 125 mm or so. Now, do I cut a slot into the panel, sit the spars in there, and infill, or "drill" a hole into the panel. My thoughts are.

1) Slotting and infilling - maybe easier to get more accurate, (as any misalignment would affect incidence and symmetry) - but inferior strength perhaps ?

2) Drilling - always a bit dodgy in foam - hot wire rod of correct diameter allowing for melt, but need to be carefully jigged somehow to ensure the hole is parallel and identical on both tail halves etc. Perhaps drill the alignment holes in the fus sides first, fit the spar, and then glue on the panels ensuring alignment as glue sets.

Suggestions welcomed .

[Biggles' Elder Brother - Moderator]

Unless you can create some kind of jig Tim I'd be tempted to go with slotting them - its much more under your control. Drilling a 6mm diameter, 125mm deep, hole accurately is not going to be easy! I assume the tailplane is not going to be detactable? On that basis you could fix the spar into the slot very securely with a suitable adhedsive and even partially infill with something fairly strong like a ply strip.

 

BEB

[Myron Beaumont]

Timbo

Not a subject that I am able to offer my experience about but if it was me ,I think I would go for a hot wire running along two blocks on the worktop with a V cut in their tops ,the half tailplane held securely to the bench (Mc Claren "Glue" ?--Sorry-Had to throw that one in ).Maybe about 3/16" dia to get to your 125 mm .A bit at a time with the wire not blistering hot Then finish with an "interference fit ".

Sounds like a grandmother and eggs situation .I'm sure you can do it .

I'll get mi coat AGAIN

Myron

[Tim Mackey]

Thanks BEB - I thought that may be the case. I wont even have the saddles to keep the tailplanes level and even, as they are being routed out to shape, rather than cut with a bow.

I think if I cut a slot, and glue the spar in with PU glue, and a ply filler strip, that should surely be beefy enough. Nope, tail wont be detachable on this one.

[Myron Beaumont]

Timbo (3rd attempt at a reply)

I misunderstood your ref to a slot. I was thinking of one from root to tip direction about mid thickness of the section for125mm.but cut into the aerofoil section somehow .How wrong can I be today ? Anyway ,you have my indesputable support for your groovy method along with my mentor BEB ( Enough wind for you today ?)

Myron YO13 Time for bed dept

[Andy Green]

Timbo,

 

For accuracy I'd slot. If you've seen my build blogs you will see I'm a fan of spar slotters.

 

Andy

[Tim Mackey]

Ok, think thats settled it then slotting it is - thanks all.

[Andy Green]

So now you'll be needing some of these

 

Andy

[Tim Mackey]

Hmm, more bloomin expense. I do love my couple of perma grit files, but was hoping to get away with just a scalpel, some needle nose pliers, and a sandpaper stick !