Swept Wing Theory

[05pearcj]

Landmark1234,

Thank you for raising this topic. I have been doing some studying on this, understanding the basic principles post ATPL but wanted a firmer understanding of the topic. Many of the explanations i have found are lacking any substance or useful explanation.

For example regarding velocity vectors (Normal v Effective) on a swept wing and how they act in relation to the wings cord, "Ace the technical pilot interview" states : "in effect the wing is persuaded to believe it is flying slower than it is" . I find explanation like this particularly annoying and unhelpful.

I found a useful diagram that helped me to understand the difference in tickness:cord ratio between a straight and swept wing, the link is below.

Swept and unswept airfoils

The diagram simply shows what you assumed and John Farley stated in an earlier post. Sweeping the wing simply extends the cord length whilst maintaining the wings thickness thus thickness:cord ratio decreases. This is visible when a cross section is viewed parallel to the aircrafts longitudinal axis.

Don't forget as stated below there are other advantages of sweeping a wing than a greater Mcrit.

- Greater lateral stability (Just look at a hang glider)
- Higher wing loading, therefore less effected by turbulence
- Greater wing thickness for equivalent Mcrit allowing for stronger structures carrying more fuel and equipment.

These advantages come with many disadvantages that we all know, I.e. Poor low speed handling and wingtip stall tendency due to spanwise flow. I guess you win some you loose some. I look forward to reading some more explanations and enhancing my own knowledge.

Hope this helped in a small way.

J