[Spaceships] [Alternate GURPS] Building a Hovercraft . . .

[vicky_molokh]

Originally Posted by Ashtagon

Yes, there is. If they are used for vertical lift (not horizontal thrust; the book uses the two terms distinctly) and the vehicle has a ground-effect curtain or wall, the lift from those rotors has a multiplier while the vehicle is in close proximity to the ground.

Relevant section is page 9, hovercraft sub-assemblies, page 33 (ducted fans, the conventional hovercraft lift engine), and page 136 (hovercraft performance).

Okay, so I see that thrust is multiplied by 2 to 5 depending on subassemblies. Let's assume a skirt (×5), but reduce the modifier to ×4 to account to possible losses from converting a helicopter rotor into a ducted hover fan (after all, some mass spent on the duct/skirt is not spent on the drivetrain). That seems to indicate that a hovercraft lift system can be reduced to a one-SM-smaller system, unlike usual helicopter rotors. Seems neat, actually, since presumably those 2/3rds of mass can be dedicated to more forward propulsion. I guess an SS-based streamlined hovercraft could theoretically be faster than a helicopter. Interesting.