Hai-Lee
Old and Bold RC PILOT
I have like most FB builders had a model or two that have folded their wings in flight. In my case thankfully they were older builds and often destined to be salvaged soon anyway.
After examining the points of failure I noticed that most were due to wing joint failure, (this was most prevalent on wings joined using Hotmelt - I live in a hot climate). The failures were generally just the glue letting go of the foam and not an actual foam board failure.
Initially I added extra bracing including wooden dihedral bracing and the like but this brought another aspect of the failure into focus. I started to get wings that would still break along the central glue line and change their incidence angle in flight.
The fitting of dual spars, (still my preferred method of construction), solved this side issue but the eventual failure of the wing joint was still a nagging problem, (and an added maintenance issue).
I hate weak structures and so I undertook a quick investigation of the stresses in the wing joint itself and I found something interesting. The FB wing has all the same structural failings of a shaped tube of FB. The spars themselves help a great deal with the maintenance of the wing shape and really cannot handle much stress and provide little resistance to folding when the central glue joint fails!
In order for the wing to fold the tube structure must fail, and for this to happen one of the wing joints needs to fail/break! Normally the lower seam/joint which has the greatest forces pulling it apart in level flight and in high positive "G" maneuvers! Rather than just adding large and heavy amounts of CF/Wood/Aluminium or the like I wanted a simple and very light method of securing the joint against the forces involved.
It just so happened I had a roll of very high strength tape, (I think it has woven fibres and a strong adhesive). I cannot rip the tape and I must use a sharp knife because even a blunt knife has problems cutting it. I now fit the tape across ALL wing joints on the inside of the wing before I fold the wing and glue!
Since using the tape across the wing joints on the inside I have not folded a single wing, (including my Explorer which lasted long enough to be gifted away). I use only lengths of around 150mm and one at the LE, one at the TE and one either side of the wing spar, (top and bottom panels).
I am sure that simple packing tape would suffice for most FB builds which I intend to start doing soon to all but my largest builds which will still get the strongest of tapes.
I still wrap the wing joint on the outside of the wing in a strong tape but now that is mostly aesthetic rather than a necessity!
My current rebuild of an Ugly Stick will show such tape being applied to the wing in the next few days, (it is not a really rushed build).
Just something that has improved the life and strengths of my builds, (and help keep the weight down).
Have fun!
After examining the points of failure I noticed that most were due to wing joint failure, (this was most prevalent on wings joined using Hotmelt - I live in a hot climate). The failures were generally just the glue letting go of the foam and not an actual foam board failure.
Initially I added extra bracing including wooden dihedral bracing and the like but this brought another aspect of the failure into focus. I started to get wings that would still break along the central glue line and change their incidence angle in flight.
The fitting of dual spars, (still my preferred method of construction), solved this side issue but the eventual failure of the wing joint was still a nagging problem, (and an added maintenance issue).
I hate weak structures and so I undertook a quick investigation of the stresses in the wing joint itself and I found something interesting. The FB wing has all the same structural failings of a shaped tube of FB. The spars themselves help a great deal with the maintenance of the wing shape and really cannot handle much stress and provide little resistance to folding when the central glue joint fails!
In order for the wing to fold the tube structure must fail, and for this to happen one of the wing joints needs to fail/break! Normally the lower seam/joint which has the greatest forces pulling it apart in level flight and in high positive "G" maneuvers! Rather than just adding large and heavy amounts of CF/Wood/Aluminium or the like I wanted a simple and very light method of securing the joint against the forces involved.
It just so happened I had a roll of very high strength tape, (I think it has woven fibres and a strong adhesive). I cannot rip the tape and I must use a sharp knife because even a blunt knife has problems cutting it. I now fit the tape across ALL wing joints on the inside of the wing before I fold the wing and glue!
Since using the tape across the wing joints on the inside I have not folded a single wing, (including my Explorer which lasted long enough to be gifted away). I use only lengths of around 150mm and one at the LE, one at the TE and one either side of the wing spar, (top and bottom panels).
I am sure that simple packing tape would suffice for most FB builds which I intend to start doing soon to all but my largest builds which will still get the strongest of tapes.
I still wrap the wing joint on the outside of the wing in a strong tape but now that is mostly aesthetic rather than a necessity!
My current rebuild of an Ugly Stick will show such tape being applied to the wing in the next few days, (it is not a really rushed build).
Just something that has improved the life and strengths of my builds, (and help keep the weight down).
Have fun!