I think the problem of  uncertainties and robustness in UAV path planning has not been researched much. Also unknown or partially unknown environments  may be interested.

for more suggestion you can read this survey :

'A Survey of Motion Planning Algorithms

from the Perspective of Autonomous UAV Guidance'

Here are two ideas for research topics that I know are of interest to the UAV user community:

1.  Micro-UAV path planning and flight control.  Unlike larger UAVs, micro-UAVs are significantly disturbed by uncertain wind and gusty conditions.

2. Micro-UAV path planning in confined spaces, such as building interiors, holes, caves and tunnels, ventilator shafts, and so forth.

It is very important to consider these problems in the case of unknown/uncertain environments as well as environments that may be subject to variable uncertainty such as the presence of dust, fog, or smoke that degrades sensor data.  You should also consider these problems exclusive of the availability of GPS.

Good luck!

I think you can also formulate the UAV path planning problems as the control problems or optimization problems. On one hand, so many control/optimization algorithms can be used for your applications; on the other hand, you can develop new techniques and algorithms for nonlinear control, efficient numerical computations that related to UAVs.

there are lots of interesting problems related to UAV path planning: off-line/on-line path planning, multi-UAV path coordination, path planning under uncertainties, path following, moving target tracking. You can pick any one you prefer to do some work.

Can you say how far your work is done.

Can you say me why you have choose only the Path planning in UAV instead of other issues.

Even i am also doing the same work   which is related to UAV path planning. i have also refereed many algorithms for path planning but i too found some difficult to understand. but i hope much work is left to do in this topic.