Currently there is a great deal of research and development work going on into flying wing and blended wing body concepts in aviation (for example, the Boeing X-48). These ideas are centered around the goal of getting more passengers into each individual plane, and therefore increasing efficiencies and reducing costs - not to mention lessening runway congestion.
At the same time, emissions from air travel are a big bone of contention and there is no simple way to make air travel carbon-free. There is simply no viable alternative to aviation fuel.
However, there may be a way to increase aircraft efficiency still further, utilising the flying wing concept.
Imagine a flying wing with a capacity for 480 passengers on two floors, 20 rows deep, 12 seats across. This doesn't use most of the large capacity of the wing. Instead, the wings are filled with helium bags. The helium makes the plane lighter so that it can take off on a shorter runway and gain cruising altitude using less fuel. However, it doesn't have the air resistance of a blimp, and can reach the high speeds of conventional airliners.
Obviously, I'm no aircraft designer. But if planes augmented by helium lift to make them lighter are more efficient, then perhaps the idea deserves looking into. Certainly, a comparison between the relative merits of extra seats and filling the space with helium instead should be made. The balance point in benefits may be zero helium, or it may be 25% or more helium, but I'd like to see a study.
There are some hybrid blimp-plane concepts:
But they are more agile blimps than light airplanes.
I am, of course, not the first blogger to look into these matters.