6
$\begingroup$

I'm currently learning about Rotary Winged Aircraft, and I have a question regarding lift and fluid flow.

Given two wings of different material but same shape, will there be a difference in the amount of lift, and the amount of air that is pushed down? Is the lift created related to the material choice in any way?

$\endgroup$
  • 4
    $\begingroup$ In theory no effect at all if the blade shape and surface finish are the same. But bear in mind if the material and/or construction affect the blade flex and twist, there may be differences in the lift. (I gather twist of the retreating blade is important in helicopter design too by the way. Maybe someone will address this.) $\endgroup$ – Andy Mar 17 '16 at 11:45
  • 1
    $\begingroup$ You may want to use different materials specifically for their surface finish, but unless you have some very special materials, the effect wouldn't be too big. $\endgroup$ – Piskvor Mar 17 '16 at 13:36
  • 1
    $\begingroup$ Also, can you be more specific regarding whether you are talking about an ideal rotor blade or an actual one? In particular, blades of different material will react differently to vibration, "droop" (on startup/shutdown), and inertia (in autorotations), and generate differently amounts of lift. In an ideal blade, I don't think material is, well, material. $\endgroup$ – rbp Mar 17 '16 at 13:47
  • $\begingroup$ @rbp There would be no difference of lift generated by a fabric covered blade, compared to an aluminum one, further compared to carbon fiber? I'm not sure I agree that material is not relevant. $\endgroup$ – CGCampbell Mar 17 '16 at 14:13
  • $\begingroup$ yes, that's exactly my point: if its an ACTUAL blade or an IDEAL one. The ACTUAL blade cares, the IDEAL one doesn't $\endgroup$ – rbp Mar 17 '16 at 14:17
6
$\begingroup$

Yes.

Some materials are easier to shape (think composites versus metal) or stay in shape better over time or under stress (think metal versus wood). This difference between the intended and the actual shape will have the biggest material-related impact on lift.

If you slightly change the question and ask for useful lift (lift minus weight of the structure), the stiffness and relative strength of the specific material must be added to the comparison. Useful parameters are the ultimate strength relative to density (breaking length) or stiffness relative to density (strain length). A stiff structure deforms less under load, so its shape will change less. Ideally, the structure is shaped such that only under load it assumes the aerodynamically most advantageous shape while its elasticity helps it to avoid being overloaded (aeroelastic tailoring).

The surface finish is also material-related, but is more affected by the manufacturing method. A rough surface is better at very low flow speeds while a smooth surface is better at moderate to high flow speeds.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.