The Early Rotor Blades
Early helicopters like the famous Bell 47 came with main rotor blades made of wood. The inherent characteristic of wood being strong and flexible provided the perfect material for early rotor blade designs.
There were problems however as wood can easily be damaged by woodpeckers, dust and stones, and even rain causing the blade to swell leading to severe vibrations from an out of balance rotor system.
As the realization of the versatility of the helicopter become more popular, the design and evolution of the airframe and the rotor blades began to move forward.
A rotor blade needs to be strong but also very flexible. You have probably seen that when a helicopter is parked the main rotor blades droop down, but in flight centrifugal force keeps them flat. Not only that, but the blades also flex in flight, especially when affected by turbulence and they need to be able to withstand these loads as well as keeping the helicopter in the air.
To be able to withstand these stresses placed on the blades they need to be designed to be strong in certain areas, but yet flexible in others. Although wood is great at doing this they are limited to the weight they can lift and the speed at which the tips can rotate. This is where new materials were needed.
One of the first advances into rotor blade design was the skinning of the blade’s leading edge with corrosion-resistant steel to aid in erosion control, especially towards the tips of the rotor blade where it is moving the fastest.
The Hiller UH -12B was one of these aircraft to adopt such a design on its blades during the 1950’s.
As testing and development into metals really began to take stride it became inevitable that rotor blades would find themselves made of them.
As metals solved some of the problems presented in wooden blades, they presented their own. Constant flexing of certain metals over time can cause it to break. Think of what happens to a paperclip when you twist it back and forth. The other problem with metal is that a crack can rapidly spread causing catastrophic failure – Which is not generally welcomed by pilots!
This was one of the first reasons that rotor blades started to have a time limit on their use. Until this point, wooden blades were considered to last indefinitely!
The addition of honeycomb technology into rotor blades really helped to improve the design and lifespan of a rotor blade. Used in conjunction with other metals, rotor blades can be produced strong, flexible, light, and cheaper than their advanced composite younger brothers.
To ensure the long-term safe operation of the FRP membrane housing, please observe the following regulations and recommendations:
1. The shrinkage expansion rate of the FRP membrane housing is relatively small. Please observe the rated design pressure index during use. Operate it within the allowable pressure range.Long time overpressure operaton is strictly forbidden!
2. The service temperature of FRP membrane housing is generally from 7 to 49 . It is strictly forbidden to work under the condition beyond this temperature range.
3. The back pressure of the two-end permeate water outlet shall not exceed 125 PSI.
4. Strictly abide by the pressure level of each medium, such as clean water, sewage, seawater, etc. If you use water with special media, please contact our company in advance to avoid accidents.
5. When the RO system is working or there is pressure in the frp membrane housing, it is strictly prohibited to knock, disassemble or move the membrane housings. The surrounding vibration source environment must be strictly controlled.
6. It is strictly forbiden to apply pressure or gravity to the upper part of the membrane shell, or to its corresponding accessories.
7. In order to ensure the inner surface of the fiberglass membrane housing clean, manufacturer use a neutral cleaning solution to clean. It is strictly forbidden to use concentrated hydrochloric acid, concentrated sulfuric acid, etc. as cleaning fluid.
The above is all the content that the editor introduces to everyone, we need to maintain and clean the FRP membrane housings regularly during use.