Bell Trail Rotor convertiplane (stowed rotor)

[AeroFranz]

Going over an AHS paper I found some nice artist's impression of their trail rotor concept - sadly of poor quality and B&W.
The trail rotor concept is similar to the folding tilt rotor (Bell/Boeing FASTR program) but the rotor pylons tilt back.


for FASTR, see http://www.secretprojects.co.uk/forum/index.php/topic,14644.msg63621.html#msg63621

 

[Jemiba]

Similar to the type in the first picture and the T-Bird derivative, we had here, I think:
http://www.secretprojects.co.uk/forum/index.php/topic,8471.msg94103.html#msg94103
Any idea, how the rotor is powered ? The rotor nacelles don't seem to carry any engines.
Engine bleed air for tip driven rotors, or shafts ? For the latter solution, I see problems
due to the thin engine pylons.

 

[AeroFranz]

My understanding is that it used a 'convertible' engine. A turbofan in cruise flight, and a turboshaft in hover mode. IIRC, NASA tested a TF-34 which had some fan inlet vanes and an additional power take-off shaft that enabled it to switch from one mode to the other. And yeah, putting shafts in those pylons would be a challenge.

 

[yasotay]

DARPA hard?

(As in one of the likely contenders for new DARPA program)

 

[AeroFranz]

First trail rotor concepts emerged at Bell in the early sixties. It was later picked up by MD in the eighties (I think).
The problem of a dedicated convertible engine remains. It's not that I don't think it can be done. It probably requires less consecutive miracles than other DARPA programs I am familiar with, but the convertible engine should be a DARPA program on its own.