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Helicopter rotor blades in newer helicopter designs are made from composite materials. This results in improved performance. Is this simply because they are lighter or is there another reason behind that?

For example, for the new CH-53K the blades are made from titanium fiberglass composite. The use composite rotor blades results in better "hot+high performance".

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How can that be? Isn't performance simply weight/lift ratio?

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  • $\begingroup$ @mins what do you mean? $\endgroup$ – mike Dec 15 '17 at 20:45
  • $\begingroup$ I was referring to your last sentence: "Isn't performance simply weight/lift ratio?". Without changing the weight, only the material, performance is affected due to different characteristics of the materials, which lead to different modes of vibration or deformation of the blade. $\endgroup$ – mins Dec 15 '17 at 20:51
  • $\begingroup$ Have you got a reference for the quote on better "hot+high performance"? $\endgroup$ – Koyovis Dec 18 '17 at 7:46
  • $\begingroup$ wikipedia has two references in the design section. Unfortunately, both are no longer valid. I also read it in a newspaper article about the helicopter but also without references. $\endgroup$ – mike Dec 18 '17 at 7:54
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The Hot and High conditions refer to the worst atmospherical conditions for the performance of an aero-engine in general. This is due to two phenomena:

  • HOT: When the outside temperature is high, on one hand, the pressure decreases (due to the decrease of density of the air) and thus the mass flow rate and thus the power decreases (the power is proportional to the mass flow rate). On the other hand, the ratio TIT/Ta (Turbine Inlet Temperature of the atmospheric temperature) will also decrease. This will lead to a reduction of P and to a reduction of the effective efficiency (the power and the effective efficiency are proportional to this ratio), the result is also an increase off the specific fuel consumption (SFC).

  • HIGH: At high altitude, the pressure decreases and thus the density and the mass flow rate. The power will then decrease (as above for the HIGH condition) and the SFC will increase.

What are your options then ? Well, you can put a more powerful engine to compensate for these conditions but you will most probably increase the weight and the fuel consumption a lot (and the cost for sure). You can use the same engine but at a higher regime, but again, you will consume a lot which is not ideal. But there is another solution: you can make your helicopter or aircraft lighter. This whey, you need less power. And that's what brings composites in general; an important gain of weight.

Hope it helps !

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