🚀 go-pugleaf

henry@zoo.toronto.edu (Henry Spencer) writes:

>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.
  
 This must be solvable.  First, there is no reason why all of the blades
have to be attached to the hub at the same level (one could be above another)
This allows you to overlap blades and retain full control over blade angle.
Second, even if they were overlapping in the same plane, if you feather all
the blades at once, and in the same direction, they shouldn't interfere with
each other.  (like a venetian blind.) I admit it sounds risky (what if blades
catch?) but its no worse than any overlapping blades scheme.
 Another advantage of having 90 degree change is that it allows you to precess
the axis of the sail easily.  If you get the blades rotating with twice the
period of the heliogyro, so they are all horizantal on one side of the disk
and vertical on the other, this produce a constant torque with no additional
control inputs.  The only problem I see with this is a possible resonance
in the blades - oscillations could build up with each revolution.
  Are there any other ways to precess the axis?  The problem is that it is
very difficult to tilt the entire blade at once on a useful time scale.  By
the time the blade is doing what you want, it has rotated around to the other
side of the craft. (and is likely oscillating).
			Dave Patterson, guest on this account