Why the Bungee Cord!?

Over the past year, many of my clients have been asking me why we use a bungee cord to launch our fixed wing Hornet drone here at Agribotix.  Why not make a drone that can be hand launched? - they ask.  Some have even suggested that a catapult launcher might be more convenient for field operations.  I've had a lot of experience with catapults and even built my own; one of which can be viewed here. Catapults offer consistent, reliable launches but with a price: catapults are expensive because they condense several pounds of tension into about a four foot span that a bungee would normally spread over ±40 yards; catapults need to be well built to withstand the stresses they endure, and even then they often break down.  Hand launches on the other hand are unreliable and often result in crashes due to operator error.  I remember this well from my time in the Army where I saw a lot of this happening.

But assuming we are only working with drone professionals who know how do a hand launch properly (and also know better than to put the propeller on backwards) there is yet another reason not to go with the hand launch: doing so limits the range of your drone!  This is because in order for your drone to be hand launched, it needs to have a wingspan that can produce adequate lift for takeoff at slower (hand launching) speeds.  Once that same drone is in the air at cruising speed, its wingspan will produce excess drag, this is why manned aircraft have flaps.  Flaps produce the extra lift at takeoff and landing needed to maintain flight at lower speeds but retract once the plane is cruising in the air so as to reduce the drag of the wingspan.  Although these work well on larger airframes, they tend to complicate the design of sUAS systems to a point where they become more of a burden than an asset.

Bungee cord launches offer a happy medium between the heavy costs of catapults on the one hand, and the limiting range (and crash potential) for a hand-launched drone on the other.  No matter how much battery weight your hand-launched drone is currently carrying, it could carry more and go farther if it were bungee launched.  We now have a video here showing how to use our bungee cord and how it is put together (1:30) -to be sure, there is a short setup time of about 8-12 minutes, but we feel this is a small drawback when considering the alternatives discussed above.