Re: Boeing 747 - assisted Skyhook Launch System
The one you saw was probably unloaded with engines on idle, so it seemed really quiet. Below 10,000 feet the Boeing 747 can stand on its tail and climb at 3800 feet/min with maximum thrust while fully loaded with a quarter-million pounds of cargo. Of course such a trajectory is not the maximum rate of climb for minimum fuel consumption, so it is generally not done. But it could be done.
On a side note the same material that may be used for Skyhook tethers, Zylon, is also being considered as the first truely bulletproof fragment barrier for jet turbines.