🚀 go-pugleaf

In article <ida.726473333@atomic> ida@atomic (David Goldschmidt) writes:
>>The stability produced by that spin is actively undesirable if you have
>>a maneuverability requirement...
>
>Heliogyros would actually be quite good at this.  You wouldn't have to
>turn the plane of rotation; you could just "feather" the blades 
>when moving towards the sun.

Thrust modulation schemes are indeed an alternative to turning the sail.
(You should have seen the first Canadian Solar Sail Project design...
thrust modulation up the wazoo.  It would also have had the most moving
parts ever launched in a single spacecraft, and deployment would have been
a mechanical nightmare.  That's where pushing for maneuverability leads...)

Unfortunately, in the case of the heliogyro, there is a design constraint:
having to feather the blades adds awkward complications at the hub, since
now the hub ends of the blades must remain clear of each other through
a 90-degree pitch change.  If you limit required pitch changes, the
packaging problems at the hub are simplified, because you can stack the
blades in multiple layers.  Since you want a large number of wide blades
to compensate for the heliogyro's fundamental scaling disadvantage (area
scales linearly, rather than quadratically, with diameter), packaging
is a real problem at a modest-sized hub.  With 90-degree pitch changes,
layers have to be separated by a full blade width.
-- 
"God willing... we shall return."       | Henry Spencer @ U of Toronto Zoology
       -Gene Cernan, the Moon, Dec 1972 |  henry@zoo.toronto.edu  utzoo!henry