Disc loading

May 7, 2010 by Tim McAdams

Disc loading is defined as the ratio of a helicopter’s gross weight to its rotor system’s disc area. A large disc area allows the rotor system to work with more air creating a higher efficiency in a hover. A smaller rotor system compromises hover efficiency for speed and a compact rotor system.

An example of a production helicopter with low disc loading is the Robinson R22. This improves the R22’s hover performance using the relatively low power of its Lycoming piston engine. Taking the concept of low disc loading to an extreme is human-powered flight in a helicopter. The low power output of a human requires a very large rotor system. Students at California Polytechnic State University at San Luis Obispo designed a human powered helicopter that weighted 250 pounds including the pilot/power source. It had a rotor diameter of more than 100 feet and was only designed to hover. In December 1989 it flew for 7.1 seconds reaching a height of 20 cm. It was built to compete for the Sikorsky Prize offered in 1980 by the American Helicopter Society. The award is $250,000 to the team whose human-powered helicopter can stay airborne for 60 seconds and reach an altitude of 3 meters. To date, the prize is unclaimed.

In contrast, a helicopter with high-disc loading requires a lot of power to hover. For example, the Sikorsky CH-53E Sea Stallion uses three General Electric T64-GE-416/416A turboshaft engines producing 4,380 shp each. Its gross weight is 73,500 lbs and has a rotor diameter of 79 feet. The CH-53’s rotor downwash in a hover is so strong that standing near it is nearly impossible. In addition, high disc loaded helicopters have rapid descent rates making them more challenging to autorotate. Taking high disc loading even further is the V 22 Osprey tilt rotor. It has two 38 foot diameter rotors and a max gross weight of 60,500 lbs. In order to hover it uses two Rolls-Royce Allison T406/AE 1107C-Liberty turboshaft engines producing 6,150 hp each.

Tags:

2 Responses to “Disc loading”

  1. Brendan Fitzpatrick Says:

    Good refresher – got to stand under a CH53-E – like being in a hurricane even when still 20 feet in the air.

  2. Sean C Says:

    It seems axiomatic that all of the larger multi-engined helicopters will have a higher disc loading than their smaller and medium sized counterparts. To keep a similar ratio, their overall rotor blade diameter becomes impractically large, and operations outside the airport environment becomes problematical. The higher decent rates in autorotation are VERY noticable, the UH-60 for example comes down like a lead brick compared to the older UH-1.

Leave a Reply

*