The Most Economic Method for sUAS Launch

Posted by Richard Burd on January 14, 2015 at 2:54pm

All,

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.

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Replies

  • Lockhart January 14, 2015 at 6:57pm

    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.

  • Keith Geary January 14, 2015 at 3:54pm

    Hi Richard,

    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.

    Keith,

  • Michael Leasure January 14, 2015 at 3:19pm
    The bungee has its place as well. My 47 pound ag heavy lift UAV takes off in 70 feet but that can be radically shortened by deploying the inboard flaps and a HD bungee.

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  • Michael Leasure January 14, 2015 at 3:07pm
    We have tried all of the above over the years, including a car top release scheme. I much prefer to design from the start for hand launch. A competent, experienced launcher is a real plus. Our students graduate and move on so it seems I am always training a new guy on the subtle and not so subtle act of arm acceleration. With systems becoming lighter and smaller, the market share continues to move to more and more UAS being hand launch candidates. I will say, a 21pound UAV, spanning 10 feet with electric propulsion can be hand launched successfully. We did it for 11 years over farm fields that had little to no clear space for takeoff. Landing was typically in the tops of the mint, corn, or soybeans. Our latest aircraft spans 6 feet, weighs 10 1/2 pounds carrying the new Headwall Nano hyperspec and hand launches easily. Landing is on any smooth spot nearby on conventional tricycle gear. Touch down and rollout are an abrupt 15-20 feet. I would not hesitate to drop this one on top of standing vegetation as well. It is rugged, and very slow on approach. It has a high angle of attack, without tip stalling that is approaching a deep stall descent. Actually fun to fly if it wasn't for that expensive, borrowed camera in the payload bay.

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