Those UAVs were far heavier (wing loading) than the project mentioned by L Duck.
That makes a fair bit of difference in how they fly --
One of my long time friends, David Stuart ,flies these UAVs as part of his living . Dave and I have had many long conversations about these things .Some - not to flattering about the designs used.
It seems the original design requirements often do not match the later task requirements
That is however, SNAFU for many government designs .
Having designed a fair amount of industrial equipment -mostly for clothing manufacturers and later on a number of competition models -- the real problem is each case -- is really nailing down the task -FIRST.
One patented concept I developed for Levi Strauss -in the 60's was a case in point-
The competition was not willing to come up with a precision heat and control setup which was a must for the fabrics being processed - We were because the task showed nothing available could do the job..

Unless the task is thoroughly researched - all the rest is just wasted effort.
A classic case was the Ford EDSEL.
Ford asked select goups what they wanted in a car --they should have asked what they thought their neighbors wanted in a new car.
Really nailing down criteria -and sticking with it - can do much of the design work for you.