I would like to know how people in this group are getting their fixed wing systems airborne. In a recent blog at work I discussed our own experience with catapults, bungees and hand launches. Basically, we found that the hand launch was prone to crashes while the catapult was expensive. Our bungee cord offered a happy medium with a short setup time and affordability. If anybody is trying to build their own bungee cord I have a design layout with dimensions at 1:30 of this how-to video here, I hope this can help a few people out there who might be thinking of going with the bungee cord method.
Have you noticed temperature sensitivity in the bungee? I use a catapult system, that has proved to be reliable - I always use the same measured tension. It was reliable, until I tried launching in temperatures ~50 deg F cooler than usual. The launches (three attempts) all failed. My analysis showed that the latex bungee has significantly more internal damping at lower temperatures. Despite the same initial acceleration, the bungee contracted more slowly, yielding a significantly lower launch speed. I think that your bungee launch method (which I have been considering) would also be sensitive to these temperature dependent viscoelastic properties of latex.
I suggest you join the Catapult & Bungee Launch Group and post this question there, as there is over 40 people with experience, but from my experience of using all the methods, I found the Bungee is risky as the screw can come out and wing back at high speed towards the operator, plus you cannot use a bungee in standing crops! I've also seen many videos online of failed bungee launches, so its not perfect.
The catapult requires effort to transport it, time to set it up and its not so good if the wind is coming over the field boundary, so you need to be 50m away from the field boundary, in the crop, again this is not possible in standing crops.
I use a SkyWalker2013, because its easy to hand launch. Like Michael Leasure says, its better to design your plane to be hand launched for agricultural applications, rather than use a Catapult or Bungee Launcher.
Best of luck.