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If the load is heavier than a single helicopter could lift, how possible is to use multiple helicopters for this task?

I have only seen this in some movies. The biggest doubts are

  • If we attach two ropes to the single point of the load in a V shaped way, a side force will be created pulling the helicopters together into collision.
  • Even without this, the flight of the two machines probably needs to be very coordinated.

In movies like "Pacific Rim" a whole swarm of helicopters lift a heavy robot. How realistic are these visions?

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Yes, this is possible, as demonstrated in this video from almost 2 years ago:

Video

  • Each helicopter probably does not weigh more than the woman being lifted.
  • The two helicopters are tilted such that the forces are in equilibrium with no collisions.
  • Both are coordinated as two pilots are flying these by Line-of-Sight.
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    $\begingroup$ These are remotely controlled drones, not helicopters. Still this probably shows that the V configuration is probably manageable. Seems that really long ropes were used, giving enough horizontal distance between drones to make collision avoidance actions manageable. $\endgroup$ – h22 Feb 7 '16 at 10:11
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    $\begingroup$ I beg to differ. "Drones" is not a correct label for a pair of vehicles that are being actively controlled by human operators. The vehicles have a minimal amount of feedback in the controls system, only to remain stable, not navigate. And by mechanical definition, these are helicopters: They use a fully actuated swash plate for collective pitch control and cyclic pitch and roll, there is nothing that separates these from full-scale helicopters in mechanical principle. There is no reason the same maneuver cannot be preformed with manned helicopters save it be pilot skill and courage. $\endgroup$ – Steve Feb 7 '16 at 22:40
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    $\begingroup$ @Steve: This still qualifies for "drone" category, or Remotely Piloted Aircraft System (RPAS) if you prefer. $\endgroup$ – mins Jun 16 '16 at 20:57
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This video on YouTube apparently shows that it has been done at least once. A rigid beam was used to counter the forces that would draw the two helicopters together.

Screen grab: Screen Grab

I also found this fascinating report (.PDF link) from Piasecki (now part of Boeing Defense, Space & Security) that studied the feasibility of attaching two CH-53D helicopters to each other, including interconnected powerplants and flight controls!

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  • $\begingroup$ This video youtube.com/watch?v=_7jENWKgMPY shows that it can go horribly wrong. $\endgroup$ – Anthony X Feb 7 '16 at 5:24
  • $\begingroup$ Aka: "Testing a blimp at Lakehurst – What could possibly go wrong?" $\endgroup$ – Jörg W Mittag Feb 9 '16 at 1:26
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The Soviets tested this for very outsize cargo - spacecraft components.

The developers considered using a couple of Mil Mi-26 helicopters to "bundle" lift the Buran, but test flights with a mock-up showed how risky and impractical that was.

This site (cited in the quote above) goes into a little more detail:

The newly developed MI-26 helicopter of the weight-lifting capacity of 26 tons was offered for delivery by helicopter. According to this project, bulky cargoes of high mass (airframe and rocket bays) tied with cables had to be carried by 2 or 3 helicopters, and such ‘bundle’ had to move along the route, at the best fit height and flying speed. As the basis for such version the example of helicopters application for ‘crane’ operations was brought, but there was still no experience of flights ‘in bundles’.

Test flights with mock-up cargo having the configuration of a tank section of the rocket were carried out at LII. The tests revealed a complexity and risk of such kind of delivery. During one of the flights at a suddenly arisen weak turbulence of atmosphere, a ‘pendulous’ swing of cargo on the cables started which caused a disturbance of the helicopters flight stability, owing to what the crews were compelled to dump the cargo.

The natural way to lift something like this would seem to be seperate slings at the two ends, which would counteract the side force problem but at the cost of having the two helicopters very close. Three would complicate it even more!

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