(Jeremy Thomson) wrote in message om...
I'm not aware of any tip-jet helicopters that have made it into
production.
Please correct me if I'm wrong.

The french had one in the 60's called a Djin. I saw one flying in
South Africa where they were trying to adapt it for agricultural
flying in the Cape Province. It was never very popular nor successful.

At first the idea seems a no-brainer, no torque to counter, no
gearbox, should result in a lighter & thus more efficient aircraft.
I suppose the devil is in the details.
Is the problem with tip-jets the rotor hub?
Either you have to pass fuel or hot gas through the rotor hub to the
blades.
I guess sealing a rotating assembly with hot gases flowing through may
be a non-trivial problem?
But that shouldnt be a problem for jets-at-the-tips type designs, fuel
would not be hot enough to damage seals.
Perhaps there is a inherant flaw in the jets-at-the-tips style design?

I've seen videos of the Hughes heavy lift helicopter that directed the
output of a couple of turbojets(/fans ?) through the blades.
I thought that design was successful, it was more a matter of funding
that it wasnt put into production, am I wrong?

Jeremy Thomson