Still experimental, but I'm surprised nobody thought of this first:
FROM THE
WEBSITE:
One of the most unusual aircraft ever to fly from Lakehurst was the Piasecki PA-97 Heli-stat.
The Heli-stat had been built under a 1980 U.S. Navy contract for the Forest Service to demonstrate economic & ecological potential of heavy vertical air lifters in harvesting timber & other natural resources in difficult-to-get-to terrain. The demonstration vehicle utilized a Navy ZPG-2W aerostat (with a 1-million cubic-foot envelope) and 4 surplus Sikorsky H-34J helicopters.
Inflating the aerostat envelope with helium to its length of 343 feet
made the Heli-Stat the largest aircraft in the world (longer than the span of the Hughes flying boat).
The first free hovering flight of the Piasecki PA-97 Heli-stat was made at Lakehurst on April 26, 1986.
On July 1, 1986 the Helistat had just completed a test flight successfully & landed at Lakehurst.
A power loss was noted on the #3 helicopter & the test was terminated & the mooring mast called for.
Prior to re-mooring a wind shift caused an uncommanded left turn which the pilot could not counteract with the flight controls.
With a tailwind, no wheel brakes or ground steering a takeoff was attempted.
The 4 main landing gear which had no shimmy dampers started to shimmy.
The 4 helicopters started to react to the shimmy with ground resonance.
As the Helistat finally lifted off, the 4 individual helicopters broke off & fell to the ground.
One pilot was killed, 3 received serious injuries, one received minor injuries. and the Helistat was destroyed.
The power loss on the #3 helicopter was traced to a missing throttle linkage correlation pin.