Helicoptor whifs

[Weaver]

Evidently the Skyhook project is still going forward:
http://en.wikipedia.org/wiki/SkyHook_JHL-40

... and of course there is the Cyclocrane which is neither fish-nor-fowl:
http://www.uh.edu/engines/epi311.htm

http://www.youtube.com/watch?v=cWLhH3wsxUo

I've never understood the logic behind the cyclocrane: rotating the whole envelope and having the wings at the widest points forces you to suspend the cabin way below it, with all the resultant ground handling problems graphically demonstrated in that video (which was very interesting BTW - cheers!  ).

The helistat makes a hell of a lot more sense. One thing strikes me though: why only have enough helium lift for the craft's own weight? Why not have a bit more? Regular blimps use ballonets inside the envelope to regulate buoyancy with out dumping ballast or helium. These are inflated with atmospheric air by small compressors, and as they expand, they reduce the volume of the helium, increasing it's density and thereby reducing it's buoyancy. By having separate fore and aft ballonets, they can also provide trim.

To my mind, the helistat should have excess helium lift up to the limit that can be trimmed out using a practical ballonet system. When you pick up a load, you deflate the ballonets first to get as much static lift as possible, and only then start to apply dynamic lift with the rotors.

[jcf]

The helistat makes a hell of a lot more sense. One thing strikes me though: why only have enough helium lift for the craft's own weight? Why not have a bit more? Regular blimps use ballonets inside the envelope to regulate buoyancy with out dumping ballast or helium. These are inflated with atmospheric air by small compressors, and as they expand, they reduce the volume of the helium, increasing it's density and thereby reducing it's buoyancy. By having separate fore and aft ballonets, they can also provide trim.

To my mind, the helistat should have excess helium lift up to the limit that can be trimmed out using a practical ballonet system. When you pick up a load, you deflate the ballonets first to get as much static lift as possible, and only then start to apply dynamic lift with the rotors.

Theoretically you have more control if the machine is neutrally buoyant, think scuba and submarines rather than flying machines.
A ballonet system is fine for trimming but the reaction time is far too slow to work as a control system for a flying crane.
For heli-logging in particular you would not want your lifter to be positively buoyant, that could be disastrous.

Of course the biggest problem is that airships of any sort are far more sensitive to the vagaries and changes in motion of the fluid
in which they operate than are scuba divers, submarines or heavier-than-air machines. The age old Achilles heel of LTA.

[Weaver]

The helistat makes a hell of a lot more sense. One thing strikes me though: why only have enough helium lift for the craft's own weight? Why not have a bit more? Regular blimps use ballonets inside the envelope to regulate buoyancy with out dumping ballast or helium. These are inflated with atmospheric air by small compressors, and as they expand, they reduce the volume of the helium, increasing it's density and thereby reducing it's buoyancy. By having separate fore and aft ballonets, they can also provide trim.

To my mind, the helistat should have excess helium lift up to the limit that can be trimmed out using a practical ballonet system. When you pick up a load, you deflate the ballonets first to get as much static lift as possible, and only then start to apply dynamic lift with the rotors.

Theoretically you have more control if the machine is neutrally buoyant, think scuba and submarines rather than flying machines.
A ballonet system is fine for trimming but the reaction time is far too slow to work as a control system for a flying crane.
For heli-logging in particular you would not want your lifter to be positively buoyant, that could be disastrous.

Fair comment, but I think the problem could be overcome by a refinement of the concept:

1. The helistat has enough static lift to make it neutrally buoyant, enough dynamic lift to lift the load when neutrally buoyant, and an optional excess of static lift that can be "switched on/off" by using the ballonets.

2. You approach the pickup point in neutral buoyancy and pick up the load using ONLY dynamic lift, with all the fine & fast control that implies.

3. Once clear of the pickup and in the cruise, you deflate the ballonets to increase static lift. This can be traded off in one of two ways:

   a. Reduced throttle setting to reduce fuel consumption/increase range,

   or

   b. Increased cyclic pitch setting for increased speed.

4. At the drop point, you go into a high hover and then inflate the ballonets (reducing static lift) while increasing throttle, until you're back in the condition where the craft itself is neutrally buoyant and the load is entirely supported by dynamic lift again.

5. You then drop the load using all the fine & fast control offered by neutral buoyancy and dynamic load-lift.

Admittedly, whether this would show a cost-effective advantage or not would depend on how long the cruise phase was, which might make it more applicable to cargo transport than heli-logging.