Can it float, and can it get anywhere afterwards?
Land it on water
Flotation is trivial and it is not the problem. A simulator that integrates the real seakeeping, and the finding that a sealed pneumatic float is stiffer than the water it replaces.
Land it on water
Flotation is trivial and it is not the problem. The load resting on the water is the STATIC HEAVINESS, not the weight: trimmed 800 kg heavy this vehicle displaces 0.8 m³ under a 31,657 m³ envelope. It is a cork with a 115 m sail on it, and every consequence is the opposite of boat intuition.
Relieving at 0.35 kPa gauge through 0.35 m² of vent. It cannot push harder than that times its 56 m² of contact, times the 2.5 overshoot the XC-8A actually measured, because a relief valve does not dump air instantly.
Hull speed is 5.2 m/s and the porpoising limit is 11.6 m/s. The hull carries so little weight that it walks through the wave-making hump and runs into dynamic instability instead.
It does not slam. It gets picked up.
A floatplane is limited to about 0.3 m of wave because it is heavy: several tonnes have to be stopped in a hull length and the deceleration breaks things. This vehicle puts 800 kg on the water. It is far too light to slam.
What happens instead is that a crest tries to LIFT it. The envelope above is fixed in altitude by 30 tonnes of buoyancy and an enormous added mass, so the whole relative motion goes into the suspension. A rigid hull is a hydrostatic spring with no ceiling: in a 0.3 m sea it feeds 124 kN up the cables against a 50 kN flight design load.
| Sea state | Hs | Rigid hull | Sealed bag | Vented bag |
|---|---|---|---|---|
| 1 calm rippled | 0.05 m | 92% | 602% | 92% |
| 2 smooth | 0.3 m | 248% | 3494% | 100% * |
| 3 slight | 0.875 m | 614% | 10127% | 100% * |
| 4 moderate | 1.875 m | 1171% | 21590% | 100% * |
| 5 rough | 3.25 m | 1948% | 37351% | 100% * |
| 6 very rough | 5 m | 2949% | 57420% | 100% * |
Suspension load as a fraction of its flight design load, with the dynamic amplification from the 59,184 kg effective heave inertia included: the wave has to accelerate the ship AND the air it drags with it. A rigid hull is limited to sea state 1. A SEALED bag reaches sea state none at all, because it is a gas spring at absolute pressure and nearly sixty times stiffer than the water. Only the VENTED bag, relieving at 0.35 kPa through 0.35 m² of vent, reaches sea state 6. An asterisk marks where it is venting rather than transmitting.
Motoring to windward
The question that decides whether marine mode is an escape or a trap. The hull could be towed at hull speed by a rowing boat; what has to be pushed through the air is the entire envelope.
| Wind | Speed made good | Of the drag, air is | |
|---|---|---|---|
| 0 m/s | 11.36 m/s | 50% | |
| 3 m/s | 9.46 m/s | 60% | |
| 5 m/s | 8.11 m/s | 66% | |
| 8 m/s | 6.22 m/s | 78% | |
| 10 m/s | 5.23 m/s | 90% | |
| 12 m/s | 3.80 m/s | 97% | |
| 15 m/s | 1.06 m/s | 100% | |
| 18 m/s | 0.00 m/s | 100% | blown backwards |
| 20 m/s | 0.00 m/s | 100% | blown backwards |
Above 16 m/s the vehicle goes wherever the wind goes. That is not a failure of the propulsion, it is the ratio of a 31,657 m³ envelope to 7.1 kN of thrust, and the answer to it is the bow drogue rather than more power.