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Removable CF spar wings (Simple?)

Hai-Lee

Old and Bold RC PILOT
#1
Maybe it is my Scottish ancestory shining through but I was not happy with the idea of gluing in CF spars in my FB models and then having to cut them out and clean them up if I wanted to reuse them in another model.

Also I wanted a model that I could remove the wings individually for easy storage and transport. Whilst there were other posts showing "Back Pack" versions of various models the wing fitting procedure seemed rather too involved and complex to make in the first place. Extra pieces, Wood, screws, Velcro, and the like just seemed to add weight.

I have had a Bixler or a Bixler clone for over a year but about a month ago I purchased a RochHobby MXS - 3D and suddenly the penny dropped.

Here is my wing fitting and joining procedure, made out of FB and CF only, that I am trying out on my latest experimental build. The build was simple in that you replace the original FB spar with 2 FB spars spaced sufficiently to just allow the CF tube to slide between them. Above and below the CF spar there is a layer of FB top and bottom to reach the desired wing thickness and allow the CF tube to fit snuggly. In addition I fitted a couple of stopper blocks at the travel limit of the CF tube in each wing.

The unfinished wings with the CF spar tube and the unfinished fuselage.
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The CF tube fitted to the travel stop in one wing.
SUNP0012.JPG

The first wing keyed into the fuselage with the CF spar protruding through the fuselage
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Remaining wing on the CF spar about to be pushed home into the keyway.
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Both wings in position and properly "keyed" into the fuselage.
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As viewed from the fuselage nose
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Just for your perusal

it works for me!

Have fun!
 

jpot1

Elite member
#2
Details please. What is keeping the wings attached to the fuse? I know you said they are “keyed” but what are you using as the key? BBQ skewer or some type of screw/nut?
 

Hai-Lee

Old and Bold RC PILOT
#3
Friction is holding the wings on place as the hole in the spar tube is actually 6x5 and the spar is 6mm diameter. That makes it a very tight fit.

I do have the option of fitting tongues of wood, (Popsicle sticks) into the fuselage end of each wing and fitting a screw through them if the spar ever seems too loose, (currently a very tight fit).

The fuselage sides have a FB doublers around the wing root and so I cut a wing profile opening in the side of the fuselage, (outer FB layer only). When the wing is inserted it cannot move or twist because it is held in place perfectly buy the wing profile hole in the fuselage side.

Between the fuselage doublers internally I made up a box to fit snugly between the fuselage sides. This box transfers sideways forces from one side of the fuselage to the other. The box also gives me a place to mount my Rx and any extra wing holding mechanism I might require in the future.

Servo leads from wing servos are just passed into a hole through the sides, doublers and the box directly into the box and from there to the Rx. Additionally any servos for tail surfaces can be mounted on/in the box if required. Currently this means that the entire remainder of the fuselage is free and open for ESC and Battery location or Options like bombs Etc.

The spar tube I am using is just a uniform box, (made in the standard FB fold and glue methods), but should I require to add a little dihedral I can make the hole in the spar tube angled to suit and either trim the wing root to suit or adjust the box geometry to support the required dihedral. :) No more messy glued in dihedral braces for my planes, (under 1500mm Wing Span), from now on.:applause:

Just what works for me!

Have fun!
 
Last edited:

rockyboy

Skill Collector
Mentor
#4
If I had only seen this post about 3 days ago, I'd have gone in a very different direction on my FW-42 mini build.

Oh well, there's sure to be another one coming :)
 

Hai-Lee

Old and Bold RC PILOT
#5
There is always another build!

Just a little side note! When under flight loads the wings actually increase the friction on the CF tube and so lock everything together even tighter!

have fun!