Even with a pv-solar situation where you only realize 50 watts/m^2 the
blimp would still go 17 mph which allows for a lot of options not
possible with a balloon.

Yeah - but travel by balloon is pretty rare.

This thread was never about commercial aviation but scenic tours. Hot
air balloon tours are quite popular. One got tangled in a high voltage
power line near Phoenix just last year.

Blimp tours with their greater range, flexibility and safety should be
even more popular.

If you have a blimp that
can do 17 mph, you're facing a lot of days where you can only fly
downwind.

What's the point of quiet propulsion on windy days?

The only other alternative for silent flight is to have something like
a hybrid electric vehicle drive train with a good sized battery.

Or a really good muffler on a regular, internal combustion engine. Can
you tell if a Lexus is running from 200 feet away?

Some might want to get closer to a charismatic animal than 200 feet. I
was thinking of flight where you could only hear your own breathing.

The other thing
you need is a large, slow moving prop.

A large slow moving prop is quiet.

Have you ever seen the props on ballistic subs? They are a unique
design that is supposed to be ultra quiet, but I've never seen them on
trolling motors. DoD takes forever to declassify technology.

Anyway we need the compressible flow equivalent. In fact, the quietest
low rpm large diameter air prop is probably has pretty much the same
size and shape as a ballistic sub prop.

A LOT of the noise from an
airplane is from the prop.

Heavier than air aircraft generally require higher speed propulsion
which is inherently noisy.

Most of the work that's made helicopters
quieter has been with the tail rotor.

Still way too loud. Hikers complain about choppers in the Grand
Canyon.

Maybe get a police dept to replace a helicopter with an electric hybrid
electric blimp. Not only does the noise wake everyone up but it alerts
the criminals.

But they want something that can fly faster than a criminal can
run/drive.

Give those meth heads a real workout!


Bret Cahill