Helicopter stringing allows conductor to be installed across terrain, spans and environmental constraints that make ground-based stringing slow or impractical. It also changes the dynamics of the stringing system: conductor is paid out at several times conventional speed while mechanically connected to an aircraft in flight.
Legend Hire operates the first OMAC T30.H Helicopter Tensioner and High-Speed Stand in Australia, a system engineered around that duty rather than adapted to it. This case study sets out the engineering differences between a conventional puller-tensioner and a purpose-built helicopter tensioner, and why equipment selection functions as a safety control on aerial stringing projects.
Project details
Project: On-site operator training, OMAC T30.H Helicopter Tensioner and High-Speed Stand
Sector: Transmission line construction / utility infrastructure
Services Provided: Equipment supply, OEM-backed operator training, technical and engineering support
Equipment Used: OMAC T30.H Helicopter Tensioner, OMAC High-Speed Stand
What Is Helicopter Stringing?
Helicopter stringing is a transmission line construction method in which a helicopter pulls a pilot rope or conductor between towers, with conductor paid out from a ground-based tensioner at speeds of up to 25 km/h. It is used where terrain, span length, vegetation or environmental constraints make conventional ground-based stringing slow, high-risk or impractical.
The method can significantly improve access and installation productivity across difficult terrain, long spans and environmentally constrained corridors. But it also changes the operating dynamics of the stringing system.
Traditional puller-tensioners and tensioners are engineered around controlled, ground-based stringing. Their operating speed, hydraulic response and braking systems are matched to that duty. Helicopter stringing requires conductor payout at several times the speed of conventional operations, while the conductor is directly connected to an aircraft in flight.
The Engineering Mismatch: Conventional vs Helicopter Equipment
A conventional hydraulic puller-tensioner is highly capable when used for the application it was designed for. The issue is not whether it can physically pay conductor out. The issue is whether its full operating philosophy is appropriate for helicopter stringing.
Negative braking systems
Conventional stringing machines commonly use negative — or fail-safe — braking systems. In simplified terms, braking is the safe state: hydraulic pressure or a control input releases the brake, and loss of that input causes the brake to apply. For conventional ground stringing, this is an important and deliberate safety principle.
In helicopter stringing, an unexpected braking event at high payout speed can introduce a rapid increase in conductor tension. Because the conductor links the machine and the aircraft, that force can be transmitted toward the helicopter while also increasing stored-energy and equipment-movement hazards around the ground crew.
A key principle A fail-safe philosophy suitable for one operating environment can introduce a different hazard when the application changes.
Braking Philosophy and Why It Changes the Risk Profile
During normal helicopter payout, the aircraft is moving forward while the ground system allows conductor to pass through the tensioner. The conductor forms the mechanical link between the aircraft and the ground machine. Any significant resistance introduced at the machine can therefore influence tension across that system.
GROUND MACHINE > CONDUCTOR > HELICOPTER
If braking is applied unexpectedly, tension can increase quickly across this connection. For the helicopter crew, that can mean an unwanted load on the aircraft. For the ground crew, it can mean a rapid increase in stored energy, conductor reaction and machine loading.
This is the reason the T30.H is built around an open braking philosophy rather than a negative braking philosophy. It does not mean the machine lacks braking protection, the T30.H retains independent braking systems for genuine emergency and shutdown conditions. The distinction is when braking is the default state. On a conventional machine, brake-applied is the resting condition. On the T30.H, free payout is the normal operating condition, and braking is a controlled, deliberate action rather than an automatic response to a lost input.
Speed Is a System Requirement, Not a Spec
The difference between conventional and helicopter stringing is often first noticed in the speed rating. But speed affects the complete system, not just the hydraulic drive.
| Design factor | Conventional puller/tensioner | OMAC T30.H helicopter system |
| Typical maximum speed | Approx. 4–6 km/h | 20 km/h continuous; 25 km/h maximum |
| Primary duty | Controlled ground stringing | High-speed helicopter conductor payout |
| Braking philosophy | Commonly negative/fail-safe braking | Purpose-designed open braking system |
| Dynamic demand | Lower-speed, controlled pull/tension cycle | Rapid payout demand linked to aircraft movement |
| System design focus | Ground equipment and conductor control | Aircraft interface, ground crew safety and high-speed payout |
| Reel handling | Conventional reel stand duty | Purpose-designed High-Speed Stand integration |
At 20–25 km/h, reel rotation, conductor payout, hydraulic response, braking behaviour and operator reaction all occur in a much faster dynamic environment. A high-speed helicopter operation therefore requires a high-speed system, not a single faster component fitted to conventional equipment.
Equipment Used: OMAC T30.H and High-Speed Stand
The OMAC T30.H is purpose-designed for helicopter stringing. It is not a conventional tensioner operated at a higher speed. Its operating philosophy is built around the specific dynamics and hazards of high-speed conductor payout with an aircraft in flight.
Purpose-built capability 20 km/h continuous payout • 25 km/h maximum payout • open braking philosophy • high-speed conductor handling • integration with the OMAC High-Speed Stand
Open braking philosophy
The key engineering difference is the T30.H open braking system, together with additional safety features developed around helicopter operations. The objective is to reduce the risk of the ground machine introducing an unintended braking force that could be transferred through the conductor toward the helicopter.
High-speed system design
The T30.H and High-Speed Stand are intended to operate as a coordinated system. At helicopter payout speeds, stable conductor supply from the reel is critical. Reel behaviour, rotational speed, conductor handling and tensioner response must work together so that conductor is paid out smoothly and predictably.
Legend Hire brought the first OMAC T30.H helicopter tensioner in Australia into the national fleet, alongside a wider range of stringing and winching equipment supporting transmission, distribution and rail electrification projects.
Engineering Considerations for Equipment Selection
Machine selection should not be based only on conductor diameter, rated pull, rated tension, or whether a machine is already available on site. For helicopter stringing, the engineering review should also consider:
- Required continuous and maximum payout speed
- Braking system philosophy and brake response
- Machine behaviour if hydraulic pressure or control is lost
- Dynamic response to rapid changes in payout demand
- High-speed reel and conductor handling capability
- Potential forces that could be transferred through the conductor to the aircraft
- Consequences for ground personnel if the system does not respond as expected
From Equipment Selection to Crew Competence
Legend Hire was engaged to attend site and deliver hands-on training on the OMAC T30.H Helicopter Tensioner and High-Speed Stand for transmission line personnel. The training focused not only on machine controls, but on the engineering reasons the helicopter system differs from conventional stringing equipment.
Key training topics included:
- Differences between conventional and helicopter stringing operating principles
- Machine speed and high-speed hydraulic response
- Negative braking compared with the T30.H braking philosophy
- High-speed conductor payout and conductor handling
- OMAC High-Speed Stand setup and operation
- Integrated machine safety systems and expected machine behaviour
- Ground crew operating procedures and communication with helicopter crews
- Abnormal operating conditions and appropriate responses
This sits alongside Legend Hire’s broader OEM-backed VOC training on stringing machines, delivered Australia-wide.
Familiar Controls, Different Safety Philosophy
Experienced transmission line crews may already have extensive knowledge of conventional puller-tensioners. That experience remains valuable, but helicopter stringing requires a different operating mindset. Controls may appear familiar while the safety philosophy and expected machine behaviour are fundamentally different.
Training outcome By understanding not only how the T30.H operates, but why it has been engineered differently, ground and helicopter crews can work with a shared understanding of the system and the hazards being controlled.
The Technical Takeaway
The difference between a conventional puller-tensioner and the OMAC T30.H cannot be reduced to 6 km/h versus 25 km/h. The more important difference is the engineering philosophy behind the machines.
One is designed to safely control and stop a conventional ground-stringing operation. The other is designed to support high-speed payout while a helicopter is mechanically connected to the system through the conductor.
That distinction affects the hydraulics, braking philosophy, operating speed, reel handling, safety systems and operating procedures. When the ground machine and aircraft are connected by the conductor, equipment selection becomes part of the safety system.
Don’t select a machine that can do the job. Select the machine engineered for it.
OMAC T30.H Helicopter Tensioner & High-Speed Stand | Swift. Smart. Specialist.
Frequently Asked Questions
Helicopter stringing is a transmission line construction method in which a helicopter pulls a pilot rope or conductor between towers, with conductor paid out from a ground-based tensioner. It is used where terrain, span length or environmental constraints make conventional ground-based stringing slow or impractical.
A conventional puller-tensioner can physically pay conductor out, but it is generally not engineered for the speed, braking philosophy and dynamic response helicopter stringing demands. Conventional machines typically operate at 4–6 km/h and use negative braking, where brake-applied is the default state. At helicopter payout speeds, an unexpected braking event can transmit a rapid tension increase through the conductor toward the aircraft.
The OMAC T30.H Helicopter Tensioner pays out conductor at 20 km/h continuous and 25 km/h maximum, roughly four to five times the speed of a conventional puller-tensioner.