Why Aspect Ratio doesn’t Matter

In the ever-present drive to improve the efficiency of aircraft, “higher aspect ratio wings” are frequently named as one of the reasons that new aircraft are more efficient than previous generations. Here are a couple of examples: “… carbon fiber allowed designers to produce a higher-aspect-ratio wing for lower drag…” (Aviation Week, May 2015) “… wings with high aspect ratio generate the lowest lift-induced drag…” (Flight International, April 2006) “A higher aspect ratio wing has a lower drag…” (NASA, May 2015) Indeed there seems to be a general consensus that higher aspect ratio wings are more efficient. This is however misleading, since Continue Reading

Why are Helicopters so Slow?

Helicopters are undeniably slow compared to aeroplanes. There is no pure helicopter that flies faster than 400km/h (250mph), yet aeroplanes have been going much faster for a long time, and even some trains and cars can go faster. The Short Skyvan, a propeller driven aircraft with fixed landing gear nicknamed “The Shed” by pilots, has about the same top speed as the world’s fastest pure helicopter. What do helicopters do differently? Helicopters have rotors instead of wings. This one difference leads to big changes because, unlike an aeroplane wing, a helicopter rotor has parts moving at different speeds even when it is hovering Continue Reading