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carbon/wood spar considerations

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Rienk

Well-Known Member
Joined
Oct 11, 2008
Messages
1,366
Location
Santa Maria, CA (SMX)
I second Topaz - nice classic design, almost a bit line-wise like an older Blanik.

Hey Orion, I have a couple of questions about making spars for such a design as we've been discussing in this thread.
I intend to waterjet out all the various parts, including the wing ribs and spar web - using CF pultrusions for the caps.

Let's see if I can explain this clearly...
Right now, I have the design so that spar web has a step tapered pattern cut into it, to allow for the lengths of the required pultrusions. This allows the top and bottom of the spar to be straight, so that they align with the each of the ribs perfectly.

The spar web also has rectangular holes cut into it for which the ribs have tabs that fit into - laid out in such a way that only certain ribs can go into certain BL locations (don't want builders gluing in the wrong ribs and messing up the wing kit).

First question:
I've been thinking about finishing off the top surface of the spar with a strip of wood, to which thin plywood would be glued to on each side, glued also to the central spar web geodesic design, essentially creating a thin box spar. The main idea behind this is to better encapsulate the CF, and hopefully help prevent delamination due to buckling, etc.
IS THIS A GOOD IDEA?

Second question:
The other thought I had was this: rather than mounting the CF pultrusions to the top of the plywood spar web, having them mount to the side face of the plywood web instead, and then having the ribs properly notched to allow for the varying thickness of the different numbers of rods used.
By doing this, the various CF rods are being stressed in their largest dimension, not relying as much on the bond joint between rods to keep from buckling (yet still captured between plywood spar cap and ribs).
IS THIS A BETTER IDEA?

Third question:
What is the simplest/best way to have automatic control surface connections/engagement on a light wing?
I've seen how various gliders do it, but most of these are not simple to fabricate. I thought about a basic torque tube for flaps and/or speed brakes, and push-pull cables for the ailerons (I know this will add some friction, but I'm not sure that is a bad thing on such a light plane).
maybe even UT's proportional actuators?


Feedback from yourself and others would be greatly appreciated.
Once I have come to terms with these options, I may likely build a POC wing and see how it does.


Bonus question:
With the precision and ease of waterjetting out ribs and spars, I'm very intrigued with the idea of building a complex wing, using both leading edge slats and drop hinged flaps (true fowler seems a bit overkill).
We can easily frame up these components with ply ribs, spars and skins - and it would be a fun exercise in high lift systems for very light aircraft (like the Suitcase Airplane I have).
  • DO YOU HAVE ANY ADVICE FOR HOW TO DO THIS? WHAT AIRFOILS TO USE, ETC? (or specific reasons why not to do this, beside being more parts and more complicated?)
  • CAN THE SPRING LOADED SLATS BE ON JUST THE INBOARD HALF OF THE WING, OR DO THEY NEED TO GO ALL THE WAY ACROSS? IF ACROSS, DOES IT NEED TO BE ONE PIECE/SYSTEM?
  • WHAT SHOULD THE SLAT PROFILE LOOK LIKE?
 
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